Local carbachol application induces oral microvascular recruitment and improves gastric tissue oxygenation during hemorrhagic shock in dogs

Introduction

Hemorrhagic shock is characterized by derangements of the gastrointestinal microcirculation. Topical therapy with nitroglycerine or iloprost improves gastric tissue oxygenation but not regional perfusion, probably due to precapillary adrenergic innervation. Therefore, this study was designed to investigate the local effect of the parasympathomimetic carbachol alone and in combination with either nitroglycerine or iloprost on gastric and oral microcirculation during hemorrhagic shock.

Methods

In a cross-over design five female foxhounds were repeatedly randomized into six experimental groups. Carbachol, or carbachol in combination with either nitroglycerine or iloprost were applied topically to the oral and gastric mucosa. Saline, nitroglycerine, or iloprost application alone served as control groups. Then, a fixed-volume hemorrhage was induced by arterial blood withdrawal followed by blood retransfusion after 1h of shock. Gastric and oral microcirculation was determined using reflectance spectrophotometry and laser Doppler flowmetry. Oral microcirculation was visualized with videomicroscopy. Statistics: 2-way-ANOVA for repeated measurements and Bonferroni post-hoc analysis (mean ± SEM; p < 0.05).

Results

The induction of hemorrhage led to a decrease of gastric and oral tissue oxygenation, that was ameliorated by local carbachol and nitroglycerine application at the gastric mucosa. The sole use of local iloprost did not improve gastric tissue oxygenation but could be supplemented by local carbachol treatment. Adding carbachol to nitroglycerine did not further increase gastric tissue oxygenation. Gastric microvascular blood flow remained unchanged in all experimental groups. Oral microvascular blood flow, microvascular flow index and total vessel density decreased during shock. Local carbachol supply improved oral vessel density during shock and oral microvascular flow index in the late course of hemorrhage.

Conclusion

The specific effect of shifting the autonomous balance by local carbachol treatment on microcirculatory variables varies between parts of the gastrointestinal tract. Contrary to our expectations, the improvement of gastric tissue oxygenation by local carbachol or nitroglycerine application was not related to increased microvascular perfusion. When carbachol is used in combination with local vasodilators, the additional effect on gastric tissue oxygenation depends on the specific drug combination. Therefore, modulation of tissue oxygen consumption, mitochondrial function or alterations in regional blood flow distribution should be investigated.

Regional tissue oxygenation in asymptomatic neonates at high risk for neonatal abstinence syndrome and impact of non-pharmacologic interventions: A case report

BACKGROUND

Improving neonatal abstinence syndrome (NAS) management is an important concern, and objective measures of its physiologic impact remain elusive. We sought to determine whether near-infrared spectroscopy (NIRS)-derived tissue oxygenation (rSO2) and fractional tissue oxygen extraction (FTOE) demonstrated physiologically plausible changes correlating with standard NAS scoring.

METHODS

Thirty subjects (mean 39 weeks' GA and 3 127 g BW) underwent cerebral and peripheral muscle NIRS monitoring on Days of Life (DOL) Three, Five, and Seven. We examined correlations between NAS scores and FTOE and assessed the impact of non-pharmacologic swaddling and cuddling.

RESULTS

No statistically significant correlations between NAS scores and FTOE were observed; however, plausible trends were demonstrated between NAS scores and cerebral measurements. Buprenorphine-exposed babies (57%) showed significantly lower FTOE when swaddled (DOL7).

CONCLUSIONS

Tissue oxygenation monitoring demonstrates potential to provide objective, clinically relevant physiologic information on infants at risk for NAS. Further study is required to determine whether NIRS-derived measures could assist in individualizing NAS care.

Development of a Tissue Oxygenation Flow-Based Index Toward Discerning the Healing Status in Diabetic Foot Ulcers

Objective: The objective of this study is to characterize breath-hold (BH)-induced oxygenation changes in diabetic foot ulcers (DFUs) and develop an oxygenation flow index (OFI) to discern nonhealing from healing DFUs. Approach: The imaging approach utilizes an innovative BH stimulus that induces vasoconstriction and measures for altering oxygenation flow in and around the tissues of DFUs and controls. The modified Beer-Lambert law was utilized to calculate hemoglobin-based spatiotemporal oxygenation maps in terms of oxygen saturation. Results: We found controls had synchronous BH-induced oxygenation changes across the dorsal (OFI: 29.0%) and plantar (OFI: 57.6%) aspects of the foot. Nonhealing DFUs, however, had less synchronous BH-induced oxygenation changes (OFI <28%). In addition, two complicated healing DFU cases, or cases with underlying issues or poor long-term healing outcomes, were observed to have OFIs <28%. Innovation: An OFI was developed to differentiate nonhealing DFUs from healing DFUs using a single, noncontact, near-infrared optical scanner for spatiotemporal oxygenation monitoring. The OFI has potential to provide immediate feedback on the microcirculation in DFUs, through hemoglobin-based oxygenation parameters. Conclusion: A preliminary threshold (OFI <28%) could differentiate nonhealing and complicated DFUs from healing DFUs. The overall oxygenation flow pattern was less synchronous (or the OFI value reduced) in the nonwound areas of the feet that were nonhealing. In other words, the reduced OFI value (<28%) in the entire foot, excluding the wound region is a possible indicator that the wound may not heal.

Switchable LED-based laparoscopic multispectral system for rapid high-resolution perfusion imaging

Significance

Multispectral imaging (MSI) is an approach for real-time, quantitative, and non-invasive tissue perfusion measurements. Current laparoscopic systems based on mosaic sensors or filter wheels lack high spatial resolution or acceptable frame rates.

Aim

To develop a laparoscopic system for MSI-based color video and tissue perfusion imaging during gastrointestinal surgery without compromising spatial or temporal resolution.

Approach

The system was built with 14 switchable light-emitting diodes in the visible and near-infrared spectral range, a 4K image sensor, and a 10 mm laparoscope. Illumination patterns were created for tissue oxygenation and hemoglobin content monitoring. The system was calibrated to a clinically approved laparoscopic hyperspectral system using linear regression models and evaluated in an occlusion study with 36 volunteers.

Results

The root mean squared errors between the MSI and reference system were 0.073 for hemoglobin content, 0.039 for oxygenation in deeper tissue layers, and 0.093 for superficial oxygenation. The spatial resolution at a working distance of 45 mm was 156    μ m . The effective frame rate was 20 fps.

Conclusions

High-resolution perfusion monitoring was successfully achieved. Hardware optimizations will increase the frame rate. Parameter optimizations through alternative illumination patterns, regression, or assumed tissue models are planned. Intraoperative measurements must confirm the suitability during surgery.

Dobutamine and Goal-Directed Fluid Therapy for Improving Tissue Oxygenation in Deep Inferior Epigastric Perforator (DIEP) Flap Breast Reconstruction Surgery: Protocol for a Randomized Controlled Trial

BACKGROUND

Breast reconstruction is an integral part of breast cancer care. There are 2 main types of breast reconstruction: alloplastic (using implants) and autologous (using the patient's own tissue). The latter creates a more natural breast mound and avoids the long-term need for surgical revision-more often associated with implant-based surgery. The deep inferior epigastric perforator (DIEP) flap is considered the gold standard approach in autologous breast reconstruction. However, complications do occur with DIEP flap surgery and can stem from poor flap tissue perfusion/oxygenation. Hence, the development of strategies to enhance flap perfusion (eg, goal-directed perioperative fluid therapy) is essential. Current perioperative fluid therapy is traditionally guided by subjective criteria, which leads to wide variations in clinical practice.

OBJECTIVE

The main objective of this trial is to determine whether the use of minimally invasive cardiac output (CO) monitoring for guiding intravenous fluid administration, combined with low-dose dobutamine infusion (via a treatment algorithm), will increase tissue oxygenation in patients undergoing DIEP flap surgery.

METHODS

With appropriate institutional ethics board and Health Canada approval, patients undergoing DIEP flap surgery are randomly assigned to receive CO monitoring for the guidance of intraoperative fluid therapy in addition to a low-dose dobutamine infusion (which potentially improves flap oxygenation) versus the current standard of care. The primary outcome is tissue oxygenation measured via near-infrared spectroscopy at the perfusion zone furthest from the perforator vessels 45 minutes after vascular reanastomosis of the DIEP flap. Low dose (2.5 μg/kg/hr) dobutamine infusion continues for up to 4 hours postoperatively, provided there are no associated complications (ie, persistent tachycardia). Flap oxygenation, hemodynamic parameters, and any medication-associated side effects/complications are monitored for up to 48 hours postoperatively. Complications, rehospitalizations, and patient satisfaction are also collected until 30 days postoperatively.

RESULTS

Funding and regulatory approvals were obtained in 2019, but the study recruitment was interrupted by the COVID-19 pandemic. As of October 4, 2023, 34 participants have been recruited. Because of the significant delays associated with the pandemic, the expected completion date was extended. We expect the study to be completed and ready for potential news release (as appropriate) and publication by July 2024. No patients have suffered any adverse effects/complications from participating in this study, and none have been lost to follow-up.

CONCLUSIONS

CO-directed fluid therapy in combination with a low-dose dobutamine infusion via a treatment algorithm has the potential to improve DIEP flap tissue oxygenation and reduce complications following DIEP flap breast reconstruction surgery. However, given that the investigators remain blinded to group randomization, no comment can be made regarding the efficacy of this intervention for improving tissue oxygenation at this time. Nevertheless, no patients have been withdrawn for safety concerns thus far, and compliance remains high.

TRIAL REGISTRATION

Clinicaltrials.gov NCT04020172; https://clinicaltrials.gov/study/NCT04020172.

The Molecular Size of Bioengineered Oxygen Carriers Determines Tissue Oxygenation in a Hypercholesterolemia Guinea Pig Model of Hemorrhagic Shock and Resuscitation

Polymerized human hemoglobin (PolyhHb) has shown promise in preclinical hemorrhagic shock settings. Different synthetic and purification schemes can control the size of PolyhHbs, yet research is lacking on the impact of polymerized hemoglobin size on tissue oxygenation following hemorrhage and resuscitation in specialized animal models that challenge their resuscitative capabilities. Pre-existing conditions that compromise the vasculature and end organs, such as the liver, may limit the effectiveness of resuscitation and exacerbate the toxicity of these molecules, which is an important but minimally explored therapeutic dimension. In this study, we compared the effective oxygen delivery of intermediate molecular weight PolyhHb (PolyhHb-B3; 500-750 kDa) to high molecular weight PolyhHb (PolyhHb-B4; 750 kDa-0.2 μm) for resuscitative effectiveness in guinea pig models subjected to hemorrhagic shock. We evaluated how the size of PolyhHb impacts hemodynamics and tissue oxygenation in normal guinea pigs and guinea pigs on an atherogenic diet. We observed that while PolyhHb-B3 and -B4 equivalently restore hemodynamic parameters of normal-dieted guinea pigs, high-fat-dieted guinea pigs resuscitated with PolyhHb-B4 have lower mean arterial pressures, impaired tissue oxygenation, and higher plasma lactate levels than those receiving PolyhHb-B3. We characterized the plasma of these animals following resuscitation and found that despite similar oxygen delivery kinetics, circulating PolyhHb-B3 and -B4 demonstrated a size-dependent increase in the plasma viscosity, consistent with impaired perfusion in the PolyhHb-B4 transfusion group. We conclude that intermediate-sized PolyhHbs (such as -B3) are ideal for further research given the effective resuscitation of hemorrhagic shock based on tissue oxygenation in hypercholesterolemic guinea pigs.

Photoacoustic Imaging for Non-Invasive Assessment of Physiological Biomarkers of Intestinal Injury in Experimental Necrotizing Enterocolitis

Background

Necrotizing enterocolitis (NEC) is an often-lethal disease of the premature infants' intestinal tract that is exacerbated by significant difficulties in early and accurate diagnosis. In NEC disease, the intestine often exhibits hypoperfusion and dysmotility, which contributes to advanced disease pathogenesis. However, these physiological features cannot be accurately and quantitively assessed within the current constraints of imaging modalities frequently used in the clinic (plain film X-ray and ultrasound). We have previously demonstrated the ability of photoacoustic imaging (PAI) to non-invasively and quantitively assess intestinal tissue oxygenation and motility in a healthy neonatal rat model. As a first-in-disease application, we evaluated NEC pathogenesis using PAI to assess intestinal health biomarkers in a preclinical neonatal rat experimental model of NEC.

Methods

NEC was induced in neonatal rat pups from birth to 4 days old via hypertonic formula feeding, full-body hypoxic stress, and lipopolysaccharide administration to mimic bacterial colonization. Healthy breastfed (BF) controls and NEC rat pups were imaged at 2- and 4-days old. Intestinal tissue oxygen saturation was measured with PAI imaging for oxy- and deoxyhemoglobin levels. To measure intestinal motility, ultrasound and co-registered PAI cine recordings were used to capture intestinal peristalsis motion and contrast agent (indocyanine green) transit within the intestinal lumen. Additionally, both midplane two-dimensional and volumetric three-dimensional imaging acquisitions were assessed for oxygenation and motility.

Results

NEC pups showed a significant decrease of intestinal tissue oxygenation as compared to healthy BF controls at both ages (2-days old: 55.90% +/- 3.77% vs 44.12% +/- 7.18%; 4-days old: 56.13% +/- 3.52% vs 38.86% +/- 8.33%). Intestinal motility, assessed using a computational intestinal deformation analysis, demonstrated a significant reduction in the intestinal motility index in both early (2-day) and established (4-day) NEC. Extensive NEC damage was confirmed with histology and dysmotility was confirmed by small intestinal transit assay.

Conclusions

This study presents PAI as a successful emerging diagnostic imaging modality for both intestinal tissue oxygenation and intestinal motility disease hallmarks in a rat NEC model. PAI presents enormous significance and potential for fundamentally changing current clinical paradigms for detecting and monitoring intestinal pathologies in the premature infant.

Determination of tissue oxygen saturation by diffuse reflectance spectroscopy

Significance

Tissue oxygenation is a parameter that allows for determining the health status of human beings. In diabetic patients, it is particularly important to evaluate this parameter as an indicator of microcirculatory problems in the extremities.

Aim

We aim to obtain tissue oxygen saturation from diffuse reflectance measurements.

Approach

A computational algorithm to automate the methodology was implemented with the aim of establishing a medical diagnosis technique that is non-invasive and easy to apply and requires a short evaluation time. Tissue oxygen saturation measurements were performed on a group of volunteers to whom a vascular occlusion was applied. It was observed that, by increasing the applied pressure to the arm of each volunteer, the tissue oxygen saturation progressively decreased.

Results

The results indicate that the developed technique is an effective method for monitoring changes in blood hemodynamics in patients with some type of pathology in which tissue oxygenation is compromised. In addition, the expected behavior of tissue oxygen saturation during a vascular occlusion was obtained.

Conclusions

A methodology to obtain tissue oxygen saturation from diffuse reflectance measurements was successfully developed. It meets the necessary characteristics to be considered a technique for obtaining StO 2 because it can be applied in vivo and non-invasively and does not require a high computational cost; thus it is fast and capable of providing an objective and quantifiable evaluation.

Comparison of the SenSmart™ and the INVOS™ neonatal cerebral near-infrared spectrometry devices

Objectives

To determine the correlation and agreement between the SenSmart™ and the INVOS™ devices of neonatal cerebral regional oxygen saturation (CrSO2) measurements using neonatal sensors. The secondary objective was to develop a regression model that predicts CrSO2-INVOS values using CrSO2-SenSmart indices and determine whether the values between the devices are interchangeable.

Methods

A prospective, cross-sectional study was conducted in infants during the first 4 weeks of life. Simultaneous, bilateral CrSO2 was measured using the SenSmart™X100 (CrSO2-SenSmart) or INVOS™ 5100C (CrSO2-INVOS) device in each frontoparietal area for 2 h. Five-minute CrSO2 values were extracted for analysis.

Results

Thirty infants were recruited with 720 pairwise measurements and 26 (84%) were evaluated in the first week of life. Mean gestational age of the preterm and term infants was [30.9 ± 2.8 (n = 14) and 38.8 ± 1.1 (n = 16)] weeks, respectively. Overall CrSO2- was 77.08 ± 9.70% and 71.45 ± 12.74% for the SenSmart and INVOS, respectively (p < 0.001). The correlation coefficient (r) between the CrSO2-SenSmart and INVOS was 0.20 (p < 0.001). The mean difference between the CrSO2-SenSmart and INVOS was 5.63 ± 13.87% with -21.6% to 32.8% limits of agreement. The r and mean difference was 0.39 (p < 0.001) and 8.87 ± 12.58% in preterm infants, and 0.06 (p = 0.27) and 2.79 ± 14.34 in term infants.

Conclusion

The CrSO2-SenSmart tended to read higher than the CrSO2-INVOS device. There was no correlation between the CrSO2-SenSmart and the CrSO2-INVOS in term infants and it was weak in preterms. Due to imprecise agreement, the CrSO2-SenSmart values are not interchangeable with those of the CrSO2-INVOS.

Calculation of Tissue Oxygenation via an Inverse Boundary Problem for Transcutaneous Oxygenation Wearable Applications

In this article, we present a toolset to fully leverage a previously developed transcutaneous oxygenation monitor (TCOM) wearable technology to accurately measure skin oxygenation values. We describe numerical models and experimental characterization techniques that allow for the extraction of precise tissue oxygenation measurements. The numerical model is based on an inverse boundary problem of the parabolic equation with Dirichlet boundary conditions. To validate this model and characterize the diffusion of oxygen through the oxygen sensing materials, we designed a series of control/calibration experiments modeled after the device's clinical application using oxygenation values in the physiological range expected for healthy tissue. Our results demonstrate that it is possible to obtain accurate tissue pO2 measurements without the need for long equilibration times with a small wearable device.

Venous Minus Arterial Carbon Dioxide Gradients in the Monitoring of Tissue Perfusion and Oxygenation: A Narrative Review

According to Fick's principle, the total uptake of (or release of) a substance by tissues is the product of blood flow and the difference between the arterial and the venous concentration of the substance. Therefore, the mixed or central venous minus arterial CO₂ content difference depends on cardiac output (CO). Assuming a linear relationship between CO₂ content and partial pressure, central or mixed venous minus arterial PCO₂ differences (P_cv-aCO₂ and P_mv-aCO₂) are directly related to CO. Nevertheless, this relationship is affected by alterations in the CO₂Hb dissociation curve induced by metabolic acidosis, hemodilution, the Haldane effect, and changes in CO₂ production (VCO₂). In addition, P_cv-aCO₂ and P_mv-aCO₂ are not interchangeable. Despite these confounders, CO is a main determinant of P_cv-aCO₂. Since in a study performed in septic shock patients, P_mv-aCO₂ was correlated with changes in sublingual microcirculation but not with those in CO, it has been proposed as a monitor for microcirculation. The respiratory quotient (RQ)-RQ = VCO₂/O₂ consumption-sharply increases in anaerobic situations induced by exercise or critical reductions in O₂ transport. This results from anaerobic VCO₂ secondary to bicarbonate buffering of anaerobically generated protons. The measurement of RQ requires expired gas analysis by a metabolic cart, which is not usually available. Thus, some studies have suggested that the ratio of P_cv-aCO₂ to arterial minus central venous O₂ content (P_cv-aCO₂/C_a-cvO₂) might be a surrogate for RQ and tissue oxygenation. In this review, we analyze the physiologic determinants of P_cv-aCO₂ and P_cv-aCO₂/C_a-cvO₂ and their potential usefulness and limitations for the monitoring of critically ill patients. We discuss compelling evidence showing that they are misleading surrogates for tissue perfusion and oxygenation, mainly because they are systemic variables that fail to track regional changes. In addition, they are strongly dependent on changes in the CO₂Hb dissociation curve, regardless of changes in systemic and microvascular perfusion and oxygenation.

Concurrent Optical- and Magnetic-Stimulation-Induced Changes on Wound Healing Parameters, Analyzed by Hyperspectral Imaging: An Exploratory Case Series

The effects of concurrent optical and magnetic stimulation (COMS) therapy on wound-healing-related parameters, such as tissue oxygenation and water index, were analyzed by hyperspectral imaging: an exploratory case series. Background: Oedema and inadequate perfusion have been identified as key factors in delayed wound healing and have been linked to reduced mitochondrial respiration. Targeting mitochondrial dysfunction is a promising approach in the treatment of therapy refractory wounds. This sub-study aimed to investigate the effects of concurrent optical and magnetic stimulation (COMS) on oedema and perfusion through measuring tissue oxygenation and water index, using hyperspectral imaging. Patients and methods: In a multi-center, prospective, comparative clinical trial, eleven patients with chronic leg and foot ulcers were treated with COMS additively to Standard of Care (SOC). Hyperspectral images were collected during patient visits before and after treatment to assess short- and long-term hemodynamic and immunomodulatory effects through changes in tissue oxygenation and water index. Results: The average time for wound onset in the eleven patients analyzed was 183 days, with 64% of them being considered unresponsive to SOC. At week 12, the rate of near-complete and complete wound closure was 64% and 45%, respectively. COMS therapy with SOC resulted in an increased short-term tissue oxygenation over the 8-week treatment phase, with oxygen levels decreasing in-between patient visits. The study further found a decrease in tissue water content after the therapy, with a general accumulation of water levels in-between patient visits. This study's long-term analysis was hindered by the lack of absolute values in hyperspectral imaging and the dynamic nature of patient parameters during visits, resulting in high interpatient and intervisit variability. Conclusions: This study showed that COMS therapy as an adjunct to SOC had a positive short-term effect on inflammation and tissue oxygenation in chronic wounds of various etiologies. These results further supported the body of evidence for safety and effectiveness of COMS therapy as a treatment option, especially for stagnant wounds that tended to stay in the inflammatory phase and required efficient phase transition towards healing.

Hydrogen Sulfide and Oxygen Homeostasis in Atherosclerosis: A Systematic Review from Molecular Biology to Therapeutic Perspectives

Atherosclerosis is a complex pathological condition marked by the accumulation of lipids in the arterial wall, leading to the development of plaques that can eventually rupture and cause thrombotic events. In recent years, hydrogen sulfide (H₂S) has emerged as a key mediator of cardiovascular homeostasis, with potential therapeutic applications in atherosclerosis. This systematic review highlights the importance of understanding the complex interplay between H₂S, oxygen homeostasis, and atherosclerosis and suggests that targeting H₂S signaling pathways may offer new avenues for treating and preventing this condition. Oxygen homeostasis is a critical aspect of cardiovascular health, and disruption of this balance can contribute to the development and progression of atherosclerosis. Recent studies have demonstrated that H₂S plays an important role in maintaining oxygen homeostasis by regulating the function of oxygen-sensing enzymes and transcription factors in vascular cells. H₂S has been shown to modulate endothelial nitric oxide synthase (eNOS) activity, which plays a key role in regulating vascular tone and oxygen delivery to tissues. The comprehensive analysis of the current understanding of H₂S in atherosclerosis can pave the way for future research and the development of new therapeutic strategies for this debilitating condition. PROSPERO ID: 417150.

The relationship between cytochrome c oxidase, CBF and CMRO2 in mouse cortex: A NIRS-MRI study

Quantifying relationships between cerebral blood flow (CBF), mitochondrial function (cytochrome c oxidase oxidation state), and metabolic rate of oxygen (CMRO₂) could provide useful insight into normal neurovascular coupling, as well as regulation of oxidative metabolism in neurological disorders. This paper uses a multimodal NIRS-MRI method to quantify these parameters in rodent brain and, in so doing, provides novel information on the regulation of oxygen metabolism by stimulating with hypercapnia or variations in oxygenation. Under hypercapnia, although oxygenation, oxidation state, and CBF increased, there was no increase in CMRO₂. Also, there was no correlation between CBF and CCO oxidation state. Conversely, changing oxygenation resulted in a strong correlation between the oxidation of CCO and CBF. This proves that the association between CBF and the redox state of CCO is not fixed and depends on the type of perturbation. Having a means to measure CBF and CCO oxidation state simultaneously will help understanding their contribution to intact neurovascular coupling and detecting abnormal cellular oxygen metabolism in many neurological disorders.

Magnetic resonance imaging of hypoxia in acute stroke compared with fluorine-18 fluoromisonidazole-positron emission tomography: A cross-validation study?

Acute ischemic stroke results in an ischemic core surrounded by a tissue at risk, named the penumbra, which is potentially salvageable. One way to differentiate the tissues is to measure the hypoxia status. The purpose of the current study is to correlate the abnormal brain tissue volume derived from magnetic resonance-based imaging of brain oxygen saturation (S_t O₂ -MRI) to the fluorine-18 fluoromisonidazole ([¹⁸ F]FMISO) positron emission tomography (PET) volume for hypoxia imaging validation, and to analyze the ability of S_t O₂ -MRI to depict the different hypoxic tissue types in the acute phase of stroke. In a pertinent model of stroke in the rat, the volume of tissue with decreased S_t O₂ -MRI signal and that with increased uptake of [¹⁸ F]FMISO were equivalent and correlated (r = 0.706; p = 0.015). The values of S_t O₂ in the tissue at risk were significantly greater than those quantified in the core of the lesion, and were less than those for healthy tissue (52.3% ± 2.0%; 43.3% ± 1.9%, and 67.9 ± 1.4%, respectively). A threshold value for S_t O₂ of ≈60% as the cut-off for the identification of the tissue at risk was calculated. Tissue volumes with reduced S_t O₂ -MRI correlated with the final lesion (r = 0.964, p < 0.0001). The findings show that the S_t O₂ -MRI approach is sensitive for the detection of hypoxia and for the prediction of the final lesion after stroke. Once validated in acute clinical settings, this approach might be used to enhance the stratification of patients for potential therapeutic interventions.

There is no evidence that carbon dioxide-enriched oxygen before apnea affects the time to arterial desaturation, but it might improve cerebral oxygenation in anesthetized obese patients: a single-blinded randomized crossover trial

PURPOSE

Carbon dioxide (CO₂) increases cerebral perfusion. The effect of CO₂ on apnea tolerance, such as after anesthesia induction, is unknown. This study aimed to assess if cerebral apnea tolerance can be improved in obese patients under general anesthesia when comparing O₂/Air (95%O₂) to O₂/CO₂ (95%O₂/5%CO₂).

METHODS

In this single-center, single-blinded, randomized crossover trial, 30 patients 18-65 years, with body mass index > 35 kg/m², requiring general anesthesia for bariatric surgery, underwent two apneas that were preceded by ventilation with either O₂/Air or O₂/CO₂ in random order. After anesthesia induction, intubation, and ventilation with O₂/Air or O₂/CO₂ for 10 min, apnea was performed until the cerebral tissue oxygenation index (TOI) dropped by a relative 20% from baseline (primary endpoint) or oxygen saturation (SpO₂) reached 80% (safety abortion criterion). The intervention was then repeated with the second substance.

RESULTS

The safety criterion was reached in all patients before cerebral TOI decreased by 20%. The time until SpO₂ dropped to 80% was similar in the two groups (+ 6 s with O₂/CO₂, 95%CI -7 to 19 s, p = 0.37). Cerebral TOI and PaO₂ were higher after O₂/CO₂ (+ 1.5%; 95%CI: from 0.3 to 2.6; p = 0.02 and + 0.6 kPa; 95%CI: 0.1 to 1.1; p = 0.02).

CONCLUSION

O₂/CO₂ improves cerebral TOI and PaO₂ in anesthetized bariatric patients. Better apnea tolerance could not be confirmed.

Five Days of Tart Cherry Supplementation Improves Exercise Performance in Normobaric Hypoxia

Previous studies have shown tart cherry (TC) to improve exercise performance in normoxia. The effect of TC on hypoxic exercise performance is unknown. This study investigated the effects of 5 days of tart cherry (TC) or placebo (PL) supplementation on hypoxic exercise performance. Thirteen healthy participants completed an incremental cycle exercise test to exhaustion (TTE) under two conditions: (i) hypoxia (13% O2) with PL and (ii) hypoxia with TC (200 mg anthocyanin per day for 4 days and 100 mg on day 5). Pulmonary gas exchange variables, peripheral arterial oxygen saturation (SpO2), deoxygenated hemoglobin (HHb), and tissue oxygen saturation (StO2) assessed by near-infrared spectroscopy in the vastus lateralis muscle were measured at rest and during exercise. Urinary 8-hydro-2′ deoxyguanosine (8-OHdG) excretion was evaluated pre-exercise and 1 and 5 h post-exercise. The TTE after TC (940 ± 84 s, mean ± standard deviation) was longer than after PL (912 ± 63 s, p < 0.05). During submaximal hypoxic exercise, HHb was lower and StO2 and SpO2 were higher after TC than PL. Moreover, a significant interaction (supplements × time) in urinary 8-OHdG excretion was found (p < 0.05), whereby 1 h post-exercise increases in urinary 8-OHdG excretion tended to be attenuated after TC. These findings indicate that short-term dietary TC supplementation improved hypoxic exercise tolerance, perhaps due to lower HHb and higher StO2 in the working muscles during submaximal exercise.

Cerebral tissue oxygenation response to brain irradiation measured during clinical radiotherapy

SIGNIFICANCE

Cancer therapy treatments produce extensive changes in the physiological and morphological properties of tissues, which are also individual dependent. Currently, a key challenge involves developing more tailored cancer therapy, and consequently, individual biological response measurement during therapy, such as tumor hypoxia, is of high interest. This is the first time human cerebral haemodynamics and cerebral tissue oxygenation index (TOI) changes were measured during the irradiation in clinical radiotherapy and functional near-infrared spectroscopy (fNIRS) technique was demonstrated as a feasible technique for clinical use in radiotherapy, based on 34 online patient measurements.

AIM

Our aim is to develop predictive biomarkers and noninvasive real-time methods to establish the effect of radiotherapy during treatment as well as to optimize radiotherapy dose planning for individual patients. In particular, fNIRS-based technique could offer an effective and clinically feasible online technique for continuous monitoring of brain tissue hypoxia and responses to chemo- and radiotherapy, which involves modulating tumor oxygenation to increase or decrease tumor hypoxia. We aim to show that fNIRS is feasible for repeatability measuring in patient radiotherapy, the temporal alterations of tissue oxygenation induced by radiation.

APPROACH

Fiber optics setup using multiwavelength fNIRS was built and combined with a medical linear accelerator to measure cerebral tissue oxygenation changes during the whole-brain radiotherapy treatment, where the radiation dose is given in whole brain area only preventing dosage to eyes. Correlation of temporal alterations in cerebral haemodynamics and TOI response to brain irradiation was quantified.

RESULTS

Online fNIRS patient measurement of cerebral haemodynamics during clinical brain radiotherapy is feasible in clinical environment, and results based on 34 patient measurements show strong temporal alterations in cerebral haemodynamics and decrease in TOI during brain irradiation and confirmed the repeatability. Our proof-of-concept study shows evidently that irradiation causes characteristic immediate changes in brain tissue oxygenation.

CONCLUSIONS

In particular, TOI seems to be a sensitive parameter to observe the tissue effects of radiotherapy. Monitoring the real-time interactions between the subjected radiation dose and corresponding haemodynamic effects may provide important tool for the researchers and clinicians in the field of radiotherapy. Eventually, presented fNIRS technique could be used for improving dose planning and safety control for individual patients.

Home-Based Electrical Stimulation to Accelerate Wound Healing-A Double-Blinded Randomized Control Trial

BACKGROUND

Electrical stimulation (E-Stim) may offer a unique adjunctive treatment to heal complicated diabetic foot ulcers (DFU). Our primary goal is to examine the effectiveness of daily home-based E-Stim therapy to speed-up wound healing.

METHODS

Patients with chronic DFUs and mild to severe peripheral arterial disease (PAD) were recruited and randomized to either control (CG) or intervention (IG) groups. The IG received 1-hour home-based E-Stim therapy on daily basis for 4 weeks (4W). E-Stim was delivered through electrical pads placed above the ankle joint using a bio-electric stimulation technology (BEST^®) platform (Tennant Biomodulator^® PRO). The CG was provided with an identical but non-functional device for the same period. The primary outcome included wound area reduction at 4W from baseline (BL).

RESULTS

Thirty-eight patients were recruited and 5 were removed due to non-compliance or infection, leaving 33 participants (IG, n = 16; CG, n =17). At 4W, the IG showed a significant wound area reduction of 22% (BL: 7.4 ± 8.5 cm² vs 4W: 5.8 ± 8.0 cm², P = 0.002). Average of wound area was unchanged in the CG (P = 0.982). The self-report adherence to daily home-therapy was 93.9%.

CONCLUSIONS

Daily home-based E-Stim provides early results on the feasibility, acceptability, and effectiveness of E-Stim as an adjunctive therapy to speed up wound healings in patients with chronic DFU and mild to severe PAD.

Phosphorescent Microneedle Array for the Measurement of Oxygen Partial Pressure in Tissue

The knowledge of the exact oxygen partial pressure in tissue is crucial for patient care and in the treatment of ischemic medical conditions. However, current methods to assess oxygen partial pressure in tissue suffer from a variety of disadvantages, including complex equipment and procedures that necessitate trained personnel. Additionally, the barrier function of the stratum corneum reduces oxygen exchange and can consequently hamper surface measurements of rapidly changing oxygen partial pressure in tissue. To overcome these challenges, a novel, easy-to-use technique to monitor the oxygen partial pressure in tissue using microneedle arrays (MNAs) has been developed. The MNAs can be made from poly(ethyl methacrylate) and poly(propyl methacrylate) and overcome the skin's barrier function to measure oxygen in the capillary bed and interstitial fluid of the skin. The MNAs' tips are embedded with an oxygen-sensitive phosphorescent metalloporphyrin, where the oxygen partial pressure inversely correlates to changes in both emission intensity and phosphorescence lifetime of the in-house developed red emitting Pt-core porphyrin. It was demonstrated that the oxygen-sensing MNAs are sufficiently robust to puncture human skin via rupture of the stratum corneum, and that the MNAs can detect changes in oxygen partial pressure in skin within the physiologically relevant range (0-160 mmHg). Additionally, the MNAs can be combined with a wearable wireless optical readout system, making these oxygen-sensing MNAs a novel wearable and portable method for user-friendly monitoring of oxygen partial pressure in skin.

Quantification of the Tissue Oxygenation Delay Induced by Breath-Holding in Patients with Carotid Atherosclerosis

Carotid artery stenosis (CAS) is a common vascular disease with long-term consequences for the brain. Although CAS is strongly associated with impaired cerebral hemodynamics and neurodegeneration, the mechanisms underlying hemodynamic impairment in the microvasculature remain unknown. In this work, we employed functional near-infrared spectroscopy (fNIRS) to introduce a methodological approach for quantifying the temporal delay of the evoked hemodynamic response. The method was validated during a vasodilatory task (breath-holding) in 50 CAS patients and 20 controls. Our results suggest that the hemodynamic response to breath-holding can be delayed by up to 6 s in the most severe patients, a significant increase from the median 4 s measured for the control group (p = 0.01). In addition, the fraction of brain regions that responded to the task decreased as the CAS severity increased, from a median of 90% in controls to 73% in the most severe CAS group (p = 0.04). The presence of collateral circulation increases the response to breath-holding and decreases the average time delays across the brain, although the number of communicating arteries alone cannot predict these fNIRS-based hemodynamic variables (p > 0.09). Overall, this work proposes a method to quantitatively assess impaired cerebral hemodynamics in CAS patients.

Investigation of Different Methods of Intraoperative Graft Perfusion Assessment during Kidney Transplantation for the Prediction of Delayed Graft Function: A Prospective Pilot Trial

Delayed graft function (DGF) after renal transplantation is a relevant clinical problem affecting long-term organ function. The early detection of patients at risk is crucial for postoperative monitoring and treatment algorithms. In this prospective cohort study, allograft perfusion was evaluated intraoperatively in 26 kidney recipients by visual and formal perfusion assessment, duplex sonography, and quantitative microperfusion assessment using O2C spectrometry and ICG fluorescence angiography. The O2C tissue spectrometry device provides a quantitative method of microperfusion assessment that can be employed during kidney transplantation as an easy-to-use and highly sensitive alternative to ICG fluorescence angiography. Intraoperative microvascular flow and velocity in the allograft cortex after reperfusion predicted DGF with a sensitivity of 100% and a specificity of 82%. Threshold values of 57 A.U. for microvascular flow and 13 A.U. for microvascular velocity were identified by an ROC analysis. This study, therefore, confirmed that impairment of microperfusion of the allograft cortex directly after reperfusion was a key indicator for the occurrence of DGF after kidney transplantation. Our results support the combined use of intraoperative duplex sonography, for macrovascular quality control, and quantitative microperfusion assessment, such as O2C spectrometry, for individual risk stratification to guide subsequent postoperative management.

Optical Monitoring of Breathing Patterns and Tissue Oxygenation: A Potential Application in COVID-19 Screening and Monitoring

The worldwide outbreak of the novel Coronavirus (COVID-19) has highlighted the need for a screening and monitoring system for infectious respiratory diseases in the acute and chronic phase. The purpose of this study was to examine the feasibility of using a wearable near-infrared spectroscopy (NIRS) sensor to collect respiratory signals and distinguish between normal and simulated pathological breathing. Twenty-one healthy adults participated in an experiment that examined five separate breathing conditions. Respiratory signals were collected with a continuous-wave NIRS sensor (PortaLite, Artinis Medical Systems) affixed over the sternal manubrium. Following a three-minute baseline, participants began five minutes of imposed difficult breathing using a respiratory trainer. After a five minute recovery period, participants began five minutes of imposed rapid and shallow breathing. The study concluded with five additional minutes of regular breathing. NIRS signals were analyzed using a machine learning model to distinguish between normal and simulated pathological breathing. Three features: breathing interval, breathing depth, and O₂Hb signal amplitude were extracted from the NIRS data and, when used together, resulted in a weighted average accuracy of 0.87. This study demonstrated that a wearable NIRS sensor can monitor respiratory patterns continuously and non-invasively and we identified three respiratory features that can distinguish between normal and simulated pathological breathing.

The potential therapeutic benefits of low frequency haemodynamic oscillations

Haemodynamic oscillations occurring at frequencies below the rate of respiration have been observed experimentally for more than a century. Much of the research regarding these oscillations, observed in arterial pressure and blood flow, has focused on mechanisms of generation and methods of quantification. However, examination of the physiological role of these oscillations has been limited. Multiple studies have demonstrated that oscillations in arterial pressure and blood flow are associated with the protection in tissue oxygenation or functional capillary density during conditions of reduced tissue perfusion. There is also evidence that oscillatory blood flow can improve clearance of interstitial fluid, with a growing number of studies demonstrating a role for oscillatory blood flow to aid in clearance of debris from the brain. The therapeutic potential of these haemodynamic oscillations is an important new area of research which may have beneficial impact in treating conditions such as stroke, cardiac arrest, blood loss injuries, sepsis, or even Alzheimer's disease and vascular dementia.

The local physiological effects of a single-use topical negative pressure device in healthy volunteers: the PICO-1 study

OBJECTIVE

This study aimed to investigate the effects of a single-use negative pressure wound therapy (sNPWT) device on tissue perfusion, oxygenation and pressure in the intact skin of healthy volunteers.

METHOD

Healthy volunteers wore a PICO sNPWT device (Smith+Nephew, UK) on their right medial calf for one week. Perfusion, tissue oxygenation and tissue pressure were recorded in superficial and deep tissues over a period of seven days. At the baseline visit, measurements were recorded before and after dressing application without activation. Macrovascular flow and transduced needle pressure measures were recorded at 0 minutes, 30 minutes and 60 minutes after device activation. Superficial tissue perfusion and both oxygenation measures were recorded continuously over the hour following activation. All outcome measures were repeated at 24 hours and again after seven days, both with the dressing and following dressing removal.

RESULTS

The device was associated with a measurable increase in perfusion of the limb in 12 healthy volunteers. Superficial tissue oxygenation adjacent to the dressing was reduced during wear, while deeper tissue demonstrated an increase in oxygenation levels. Superficial skin perfusion was observed to differ between skin overlying muscle and that overlying bone. Pressure in tissue underneath the dressing pad was increased throughout dressing wear and returned to baseline levels on dressing removal.

CONCLUSION

sNPWT produced measurable changes in local physiology in healthy volunteers with intact skin, despite the absence of a wound. Effects may differ according to anatomical site and the composition of underlying tissues. Other factors that promote healing were not explored in this study.

DECLARATION OF INTEREST

This study was funded by Smith+Nephew investigator-initiated grant IIS 684. The funder had no input into study design, conduct, analysis, manuscript preparation or dissemination. The authors have no conflicts of interest to declare.

Detection of hypoxia by near-infrared spectroscopy and pulse oximetry: a comparative study

SIGNIFICANCE

Pulse oximetry is widely used in clinical practice to monitor changes in arterial oxygen saturation (SpO2). However, decreases in SpO2 can be delayed relative to the actual clinical event, and near-infrared spectroscopy (NIRS) may detect alterations in oxygenation earlier than pulse oximetry, as shown in previous cerebral oxygenation monitoring studies.

AIM

We aim to compare the response of transcutaneous muscle NIRS measures of the tissue saturation index with pulse oximetry SpO2 during hypoxia.

APPROACH

Episodes of acute hypoxia were induced in nine anesthetized Yucatan miniature pigs. A standard pulse oximeter was attached to the ear of the animal, and a transcutaneous NIRS sensor was placed on the hind limb muscle. Hypoxia was induced by detaching the ventilator from the animal and reattaching it once the pulse oximeter reported 70% SpO2.

RESULTS

Twenty-four episodes of acute hypoxia were analyzed. Upon the start of hypoxia, the transcutaneous NIRS measures changed in 5.3 ± 0.4 s, whereas the pulse oximetry measures changed in 14.9 ± 1.0 s (p < 0.0001).

CONCLUSIONS

Transcutaneous muscle NIRS can detect the effects of hypoxia significantly sooner than pulse oximetry in the Yucatan miniature pig. A transcutaneous NIRS sensor may be used as an earlier detector of oxygen saturation changes in the clinical setting than the standard pulse oximeter.

Tissue Oxygenation Measurements to Aid Scalpel Debridement Removal in Patients With Diabetes

BACKGROUND

Callus formation in the diabetic foot increases the risk of ulcer onset. It is standard procedure to remove these dead tissue layers to reduce rising pressures. In a surgical procedure known as scalpel debridement, or chiropody the callus tissue is removed up to the epidermal layer. Factors may influence the outcome of this surgical process such as clinician inexperience. In an effort to standardize the debridement process, tissue oxygenation (TO) measurements are obtained before and after to study the effect of debridement on callus tissue.

METHODS

Fifteen debridement cases were analyzed using near infrared (NIR) imaging to study changes in TO. The NIR-based device used in this study estimates effective changes in TO in terms of oxy-, deoxy-, total hemoglobin, and oxygen saturation. Weber contrasts between callus tissue and the surrounding normal tissue were compared following debridement for all TO parameters. In a secondary analysis, callus tissue was segmented into quadrants and a percent of significance (in terms of total TO change) was calculated using a t-test.

RESULTS

Results show majority of cases displayed greater than 80% as the significant change in TO following debridement, except in cases with the presence of blood clot (a common precursor for ulceration). In cases where incomplete debridement was suspected, a significant change in TO was still observed.

CONCLUSIONS

With extensive systematic studies in the future, NIR imaging technique to measure changes in TO may be implemented as a low-cost hand-held imaging device useful for objectively assessing the effectiveness of the scalpel debridement process.

Near-Infrared Spectroscopy (NIRS) versus Hyperspectral Imaging (HSI) to Detect Flap Failure in Reconstructive Surgery: A Systematic Review

Rapid identification of possible vascular compromise in free flap reconstruction to minimize time to reoperation improves achieving free flap salvage. Subjective clinical assessment, often complemented with handheld Doppler, is the golden standard for flap monitoring; but this lacks consistency and may be variable. Non-invasive optical methods such as near-infrared spectroscopy (NIRS) and hyperspectral imaging (HSI) could facilitate objective flap monitoring. A systematic review was conducted to compare NIRS with HSI in detecting vascular compromise in reconstructive flap surgery as compared to standard monitoring. A literature search was performed using PubMed and Embase scientific database in August 2021. Studies were selected by two independent reviewers. Sixteen NIRS and five HSI studies were included. In total, 3662 flap procedures were carried out in 1970 patients using NIRS. Simultaneously; 90 flaps were performed in 90 patients using HSI. HSI and NIRS flap survival were 92.5% (95% CI: 83.3–96.8) and 99.2% (95% CI: 97.8–99.7). Statistically significant differences were observed in flap survival (p = 0.02); flaps returned to OR (p = 0.04); salvage rate (p < 0.01) and partial flap loss rate (p < 0.01). However, no statistically significant difference was observed concerning flaps with vascular crisis (p = 0.39). NIRS and HSI have proven to be reliable; accurate and user-friendly monitoring methods. However, based on the currently available literature, no firm conclusions can be drawn concerning non-invasive monitoring technique superiority

Non-invasively Measured Venous Oxygen Saturation as Early Marker of Impaired Oxygen Delivery in Preterm Neonates

INTRODUCTION

Adequate oxygen supply for preterm neonates may be defined through non-invasive measurement of venous oxygen saturation (SvO₂) and fractional oxygen extraction using near-infrared spectroscopy (NIRS). We investigated whether there was a difference in peripheral muscle SvO₂ (pSvO₂) and peripheral fractional oxygen extraction (pFOE) in preterm neonates with early inflammation/infection compared to healthy subjects during the first 72 h after birth.

MATERIALS AND METHODS

We retrospectively analyzed secondary outcome parameters of prospective observational studies, including preterm neonates at risk of infection in whom peripheral NIRS measurements were performed in combination with venous occlusions. Early neonatal inflammation/infection was diagnosed by clinical signs and laboratory parameters. Peripheral muscle tissue oxygenation index (pTOI) was measured using either NIRO 300 or NIRO 200-NX (both Hamamatsu Photonics, Japan) on the patients' lower legs. Using 20-s venous occlusions, pSvO₂ and pFOE were calculated incorporating simultaneous measurements of arterial oxygen saturation (SpO₂).

RESULTS

We analyzed measurements from 226 preterm neonates (median gestational age 33.9 weeks), 64 (28.3%) of whom were diagnosed with early neonatal inflammation/infection. During the first 24 h after birth, pSvO₂ (66.9% [62.6-69.2] vs. 69.4% [64.6-72.0]; p = 0.04) and pTOI (68.6% [65.3-71.9] vs. 71.7% [67.3-75.1]; p = 0.02) were lower in those neonates with inflammation/infection, while there was no such difference for measurements between 24-48 and 48-72 h.

DISCUSSION

NIRS measurement of pSvO₂ and pFOE is feasible and may be utilized for early detection of impaired peripheral oxygen delivery. As pTOI was also significantly lower, this parameter may serve as substitute for diminished regional oxygen supply.

MEDEX 2015: Prophylactic Effects of Positive Expiratory Pressure in Trekkers at Very High Altitude

Purpose: Positive expiratory pressure (PEP) breathing has been shown to increase arterial oxygenation during acute hypoxic exposure but the underlying mechanisms and consequences on symptoms during prolonged high-altitude exposure remain to be elucidated. Methods: Twenty-four males (41 ± 16 years) were investigated, at sea level and at 5,085 m after 18 days of trekking from 570 m. Participants breathed through a face-mask with PEP = 0 cmH₂O (PEP₀, 0-45^th min) and with PEP = 10 cmH₂O (PEP₁₀, 46-90^th min). Arterial (SpO₂), quadriceps and prefrontal (near infrared spectroscopy) oxygenation was measured continuously. Middle cerebral artery blood velocity (MCAv, transcranial Doppler), cardiac function (2D-echocardiography), extravascular lung water accumulation (UsLC, thoracic ultrasound lung comets) and acute mountain sickness (Lake Louise score, LLS) were assessed during PEP₀ and PEP₁₀. Results: At 5,085 m with PEP₀, SpO₂ was 78 ± 4%, UsLC was 8 ± 5 (a.u.) and the LLS was 2.3 ± 1.7 (all P < 0.05 versus sea level). At 5,085 m, PEP₁₀ increased significantly SpO₂ (+9 ± 5%), quadriceps (+2 ± 2%) and prefrontal cortex (+2 ± 2%) oxygenation (P < 0.05), and decreased significantly MCAv (-16 ± 14 cm.s^-1) and cardiac output (-0.7 ± 1.2 L.min^-1) together with a reduced stroke volume (-9 ± 15 mL, all P < 0.05) and no systemic hypotension. PEP₁₀ decreased slightly the number of UsLC (-1.4 ± 2.7, P = 0.04) while the incidence of acute mountain sickness (LLS ≥ 3) fell from 42% with PEP₀ to 25% after PEP₁₀ (P = 0.043). Conclusion: PEP₁₀ breathing improved arterial and tissue oxygenation and symptoms of acute mountain sickness after trekking to very high altitude, despite reduced cerebral perfusion and cardiac output. Further studies are required to establish whether PEP-breathing prophylactic mechanisms also occur in participants with more severe acute mountain sickness.

Effect of an ionic antineoplastic agent Cytoreg on blood chemistry in a Wistar rat model

Cytoreg is an ionic therapeutic agent comprising a mixture of hydrochloric, sulfuric, phosphoric, hydrofluoric, oxalic, and citric acids. In diluted form, it has demonstrated efficacy against human cancers in vitro and in vivo. Although Cytoreg is well tolerated in mice, rats, rabbits, and dogs by oral and intravenous administration, its mechanism of action is not documented. The acidic nature of Cytoreg could potentially disrupt the pH and levels of ions and dissolved gases in the blood. Here, we report the effects of the intravenous administration of Cytoreg on the arterial pH, oxygen and carbon dioxide pressures, and bicarbonate, sodium, potassium, and chloride concentrations. Our results demonstrate that Cytoreg does not disturb the normal blood pH, ion levels, or carbon dioxide content, but increases oxygen levels in rats. These data are consistent with the excellent tolerability of intravenous Cytoreg observed in rabbits, and dogs. The study was approved by the Bioethics Committee of the University of the Andes, Venezuela (CEBIOULA) (approval No. 125) on November 3, 2019.

Effect of ventilator modes on neonatal cerebral and peripheral oxygenation using near-infrared spectroscopy

AIM

The effect of ventilator modes on regional tissue oxygenation in premature neonates with respiratory distress syndrome (RDS) has yet to be delineated. Previous studies have looked at global oxygen delivery and have not assessed the effects on regional tissue oxygenation. Our aim in this study was to assess such tissue oxygenation in premature babies with RDS in relation to differing modes of ventilation using near-infrared spectroscopy (NIRS).

METHODS

In 24 stable preterm infants with RDS, undergoing elective wean in ventilator mode, cerebral and muscle tissue oxygenation were assessed using NIRS. Infants were weaned from high-frequency oscillator or jet ventilator to conventional invasive ventilation (CV) or extubated from CV to non-invasive mechanical ventilation. Data at 30 minutes prior and at one hour after change in ventilator mode were compared (paired t test).

RESULTS

In babies changed from high-frequency oscillation to CV, jet to CV and CV to non-invasive ventilation, the differences in cerebral NIRS (mean ± SD) were 1.7 ± 9.9%, 2.3 ± 5.7% and 2.1 ± 8.4%, respectively. The concomitant changes in muscle NIRS were -2.9 ± 8.5%, 8.1 ± 9.7% and 3.6 ± 22.4%, respectively. No changes were statistically significant.

CONCLUSION

Our data suggest that there is no alteration in regional tissue oxygenation related to ventilator mode in stable preterm infants with improving RDS.

Stem Cell Therapy for Microvascular Injury Associated with Ischemic Nephropathy

Ischemic nephropathy reflects progressive loss of kidney function due to large vessel atherosclerotic occlusive disease. Recent studies indicate that this process is characterized by microvascular rarefaction, increased tissue hypoxia and activation of inflammatory processes of tissue injury. This review summarizes the rationale and application of functional MR imaging to evaluate tissue oxygenation in human subjects that defines the limits of renal adaptation to reduction in blood flow, development of increasingly severe tissue hypoxia and recruitment of inflammatory injury pathways in ischemic nephropathy. Human mesenchymal stromal/stem cells (MSC) are capable of modifying angiogenic pathways and immune responses, but the potency of these effects vary between individuals and various clinical characteristics including age and chronic kidney disease and levels of hypoxia. We summarize recently completed first-in-human studies applying intrarenal infusion of autologous adipose-derived MSC in human subjects with ischemic nephropathy that demonstrate a rise in blood flow and reduction in tissue hypoxia consistent with partial repair of microvascular injury, even without restoring main renal arterial blood flow. Inflammatory biomarkers in the renal vein of post-stenotic kidneys fell after MSC infusion. These changes were associated with modest but significant dose-related increments in kidney function. These data provide support a role for autologous MSC in repair of microvascular injury associated with tissue hypoxia.

Effect of low vs high haemoglobin transfusion trigger on cardiac output in patients undergoing elective vascular surgery: Post-hoc analysis of a randomized trial

BACKGROUND

During vascular surgery, restricted red-cell transfusion reduces frontal lobe oxygen (ScO₂ ) saturation as determined by near-infrared spectroscopy. We evaluated whether inadequate increase in cardiac output (CO) following haemodilution explains reduction in ScO₂ .

METHODS

This is a post-hoc analysis of data from the Transfusion in Vascular surgery (TV) Trial where patients were randomized on haemoglobin drop below 9.7 g/dL to red-cell transfusion at haemoglobin below 8.0 (low-trigger) vs 9.7 g/dL (high-trigger). Fluid administration was guided by optimizing stroke volume. We compared mean intraoperative levels of CO, haemoglobin, oxygen delivery, and CO at nadir ScO₂ with linear regression adjusted for age, operation type and baseline. Data for 46 patients randomized before end of surgery were included for analysis.

RESULTS

The low-trigger resulted in a 7.1% lower mean intraoperative haemoglobin level (mean difference, -0.74 g/dL; P < .001) and reduced volume of red-cell transfused (median [inter-quartile range], 0 [0-300] vs 450 mL [300-675]; P < .001) compared with the high-trigger group. Mean CO during surgery was numerically 7.3% higher in the low-trigger compared with the high-trigger group (mean difference, 0.36 L/min; 95% confidence interval (CI.95), -0.05 to 0.78; P = .092; n = 42). At the nadir ScO₂ -level, CO was 11.9% higher in the low-trigger group (mean difference, 0.58 L/min; CI.95, 0.10-1.07; P = .024). No difference in oxygen delivery was detected between trial groups (MD, 1.39 dL_O2 /min; CI.95, -6.16 to 8.93; P = .721).

CONCLUSION

Vascular surgical patients exposed to restrictive RBC transfusion elicit the expected increase in CO making it unlikely that their potentially limited cardiac capacity explains the associated ScO₂ decrease.

Portable Oxygen-Sensing Device for the Improved Assessment of Compartment Syndrome and other Hypoxia-Related Conditions

Measurement of intramuscular oxygen could play a key role in the early diagnosis of acute compartment syndrome, a common condition occurring after severe trauma leading to ischemia and long-term consequences including rhabdomyolysis, limb loss, and death. However, to date, there is no existing oxygen sensor approved for such a purpose. To address the need to improve the assessment of compartment syndrome, a portable fiber-optic device for intramuscular oxygen measurements was developed. The device is based on phosphorescence quenching, where the tip of an optical fiber was coated with a poly(propyl methacrylate) (PPMA) matrix containing a brightly emitting Pt(II)-core porphyrin. The optoelectronic circuit is highly portable and is based on a microspectrometer and a microcontroller readout with a smartphone. Results from an in vivo tourniquet porcine model show that the sensor is sensitive across the physiological oxygen partial pressure range of 0-80 mmHg and exhibits an appropriate and reproducible response to changes in intramuscular oxygen. A commercial laboratory oxygen sensor based on a lifetime measurement did not respond as expected.

Evaluation of the human placenta optical scattering properties using continuous wave and frequency-domain diffuse reflectance spectroscopy

SIGNIFICANCE

Placenta is an essential organ for fetal development and successful reproduction. Placental insufficiency can lead to fetal hypoxia and, in extreme cases anoxia, leading to fetal death. Of the 145 million deliveries per year worldwide, ∼15 million neonates are small for gestational age and, therefore, at risk for antepartum and intrapartum hypoxia. Clinical methods to assess placental function largely rely on the assessment of fetal heart rate changes but do not assess placental oxygenation. Near-infrared spectroscopy (NIRS) allows non-invasive, real-time assessment of tissue oxygenation in intact organs, which can be used to assess placental oxygenation. However, tissue optical properties can affect the accuracy of methods to measure tissue oxygenation.

AIM

This study was performed to estimate the scattering coefficient of the human placenta. We have computed the scattering coefficients of the human placenta for the range of 659 to 840 nm using two methods of diffuse reflectance spectroscopy (DRS).

APPROACH

Measurements were performed using an in-house DRS device and a well-established frequency-domain diffuse optical spectroscopic system (DOSI). Measurements were performed in eight placentas obtained after cesarean deliveries. Placentas were perfused with normal saline to minimize the effects of absorption due to blood. Three sites per placenta were measured. Absorption and scattering coefficients were then calculated from the measured reflectance using the random walk theory for DRS and frequency-domain algorithm for DOSI.

RESULTS

Average reduced scattering coefficient (μs  '  ) was 0.943  ±  0.015  mm  -  1 at 760 nm and 0.831  ±  0.009  mm  -  1 at 840 nm, and a power function μs  '    =  1.6619 (λ/500  nm)  -  1.426 was derived for the human placental scattering coefficient.

CONCLUSION

We report for the first time the scattering coefficient of the human placenta. This information can be used to assess baseline scattering and improve measurements of placental oxygen saturation with NIRS.

Association between Regional Tissue Oxygenation and Body Temperature in Term and Preterm Infants Born by Caesarean Section

Body temperature (BT) management remains a challenge in neonatal intensive care, especially during resuscitation after birth. Our aim is to analyze whether there is an association between the BT and cerebral and peripheral tissue oxygen saturation (crSO₂/cTOI and prSO₂), arterial oxygen saturation (SpO₂), and heart rate (HR). The secondary outcome parameters of five prospective observational studies are analyzed. We include preterm and term neonates born by Caesarean section who received continuous pulse oximetry and near-infrared spectroscopy monitoring during the first 15 min, and a rectal BT measurement once in minute 15 after birth. Four-hundred seventeen term and 169 preterm neonates are included. The BT did not correlate with crSO₂/cTOI and SpO₂. The BT correlated with the HR in all neonates (ρ = 0.210, p < 0.001) and with prSO₂ only in preterm neonates (ρ = −0.285, p = 0.020). The BT was lower in preterm compared to term infants (36.7 [36.4–37.0] vs. 36.8 [36.6–37.0], p = 0.001) and prevalence of hypothermia was higher in preterm neonates (29.5% vs. 12.0%, p < 0.001). To conclude, the BT did not correlate with SpO₂ and crSO₂/cTOI, however, there was a weak positive correlation between the BT and the HR in the whole cohort and a weak correlation between the BT and prSO₂ only in preterm infants. Preterm neonates had a statistically lower BT and suffered significantly more often from hypothermia during postnatal transition.

Noninvasive Cellular Oxygenation Measurement During Graded Hypoxia Using Visible-Near-Infrared Spectroscopy

In critically ill patients, direct knowledge of intracellular pO₂ would allow for identification of cellular hypoxia, which when prolonged leads to organ failure. We have developed a visible-near-infrared optical system that noninvasively measures myoglobin saturation, which is directly related to intracellular pO₂, from the surface of the skin. We used an animal model of graded hypoxia from low levels of inspired oxygen (n = 5) and verified that low intracellular pO₂ is correlated with high steady-state serum lactate values. In addition, the pO₂ gradient between arterial blood and inside muscle cells was 83 mm Hg at 21% O₂, but fell to 24 mm Hg at 8% O₂. Continuous myoglobin saturation measurement in skeletal muscle displayed the same trends as cerebral oxygenation with no lag in changes over time, demonstrating its relevance as a measure of systemic oxygenation.

Multicenter International Survey on Cardiopulmonary Bypass Perfusion Practices in Adult Cardiac Surgery

OBJECTIVES

To assess current practice in adult cardiac surgery during cardiopulmonary bypass (CPB) across European and non-European countries.

DESIGN

International, multicenter, web-based survey including 28 multiple choice questions addressing hemodynamic and tissue oxygenation parameters, organ protection measures, and the monitoring and usage of anesthetic drugs as part of the anesthetic and perfusion practice during CPB.

SETTING

Online survey endorsed by the European Association of Cardiothoracic Anesthesiologists.

PARTICIPANTS

Representatives of anesthesiology departments in European and non-European adult cardiac surgical centers.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The survey was distributed via e-mail to European Association of Cardiothoracic Anesthesiologists members (n = 797) and kept open for 1 month. The response rate was 34% (n = 271). After exclusion of responses from the same centers and of incomplete answers, data from 202 cardiac centers in 56 countries, of which 67% of centers were university hospitals, were analyzed. Optimization of pump flows and tissue oxygenation parameters during CPB were applied by the majority of centers, with target flow rates of >2.2 L/min/m² in 93% (n = 187) of centers and mean arterial blood pressures between 51 and 90 mmHg in 85% (n = 172). Hemoglobin transfusion triggers were either individualized or between 7 and 8 g/dL in 92% (n = 186) of centers. Mixed venous oxyhemoglobin saturations were assessed routinely in 59% (n = 120) and lactate in 88% (n = 178) of cardiac surgery units. Noninvasive cerebral saturation monitoring was used in a subgroup of patients or routinely in 84% (n = 169) of sites, and depth-of-anesthesia monitoring was used routinely in 53% (n = 106). Transesophageal echocardiography and pulmonary artery catheters were used routinely or in subgroups of patients in 97% (n = 195) and 71% (n = 153) of centers, respectively. The preferred site for temperature monitoring was the nasopharynx in 66% (n = 134) of centers. Anesthetic techniques were variable, with 26% of centers (n = 52) using low-tidal-volume ventilation and 28% (n = 57) using continuous positive airway pressure during CPB. Volatile agents were used routinely as the only agent during CPB in 36% sites (n = 73) and propofol in 47% (n = 95). Other drugs routinely administered included magnesium in 45% (n = 91), steroids in 18% (n = 37), tranexamic acid in 88% (n = 177), and aprotinin in 15% (n = 30) of the centers.

CONCLUSION

This international CPB survey revealed that techniques for optimization of pump flow and oxygenation during CPB usually were applied. Furthermore, cerebral and hemodynamic monitoring devices were frequently used during CPB. However, most CPB-related anesthetic techniques and medications were more variable. More high-quality randomized controlled trials are needed to assess anesthetic techniques and organ protection.

Quantitative Results of Perfusion Utilising Hyperspectral Imaging on Non-diabetics and Diabetics: A Pilot Study

There is a paucity of quantitative measures of microvascular perfusion values in the skin. Newly developed, handheld hyperspectral imaging devices identify unique spectral fingerprints of oxygenated and deoxygenated haemoglobin in the superficial microvasculature. Establishing value ranges for healthy patients without vascular complications will subsequently help standardise assessments for perfusion defects. In particular, diabetics who are prone to vascular calcifications and lower extremity wounds may benefit. A total of 73 subjects were enrolled in the study and split in two cohorts: 36 'non-diabetic' non-vascularly compromised patients and 37 'diabetic' patients with a formal diagnosis of diabetes but without history of pedal ulceration. Values of oxygenated haemoglobin (HT-Oxy) and deoxygenated haemoglobin (HT-DeOxy) from both devices are analysed.

Cerebral and peripheral tissue oxygenation in stable neonates: Absent influence of cardiac function

Aim

Cardiac function is a major factor for tissue perfusion and therefore may affect the tissue oxygen saturation. Aim was to analyse possible associations between cardiac function parameters and cerebral and peripheral tissue oxygenation in neonates on the first day after birth.

Methods

For the present study, we analysed secondary outcome parameters of a previously performed prospective single centre observational study. The prospective study was conducted at the Medical University of Graz, Austria between September 2011 and June 2013. We included preterm and term neonates who were admitted to the neonatal intensive care unit and in whom simultaneous near‐infrared spectroscopy measurements and echocardiography were obtained on the first day after birth. Cardiac function parameters were correlated to cerebral and peripheral tissue oxygen saturation and cerebral and peripheral fractional tissue oxygen extraction at the time of echocardiography.

Results

A total of 60 neonates of whom 47 were preterm and 13 were term (median gestational age: 34; IQR 33‐35 weeks, mean birth weight: 2276 ± 774 grams) were included. There were no statistically significant correlations between cardiac function parameters and regional tissue oxygenation parameters.

Conclusion

In the present study, we found no correlation between regional tissue oxygenation and parameters of cardiac function in cardio‐circulatory stable neonates on the first day after birth.

Regular Use of FlowAid FA100 SCCD Reduces Pain While Increasing Perfusion and Tissue Oxygenation in Contralateral Limbs of Amputees With Diabetic Neuropathy and Peripheral Arterial Disease: Results of an Open, Pre-Post Intervention, Single-Center Study

Patients with diabetic neuropathy and peripheral arterial disease often suffer pain, develop foot wounds, and go on to lose limbs leaving them with a painful limb. Electrical stimulation is one possibility open to physicians. In this study, the effects of the FlowAid FA100 SCCD, a sequential contraction compression device, were tested. The FA100 device is noninvasive; it uses 4 electrodes to sequentially stimulate the calf muscles in a modified intermittent pneumatic compression manner. A total of 14 patients with diabetic neuropathy, peripheral arterial disease, unilateral amputation, and a painful limb were treated with FlowAid FA100 (FlowAid Medical Technologies Corporation, New York, NY) with prior ethical approval. The study design was open, pre-post intervention comparison, and nonrandomized. Pain perceived was measured using Visual Analogue Scale (VAS) scores. Assessments of ankle brachial index (ABI), ultrasound color Duplex, and tissue oxygen using the transcutaneous oxygen technique were done at baseline and 2 successive follow-ups 4 weeks apart. Three out of 14 patients dropped out on account of distances involved in traveling to the clinic. Eleven out of 14 patients experienced statistically significant reduction in pain mean VAS scores (7.5 ± 0.93 to 5.8 ± 1.47, P = .002) associated with increase in ABI (0.64 ± 0.06 to 0.69 ± 0.04, P < .001) and transcutaneous oxygen tension measured on the dorsum (29.4 ± 4.03 to 33.2 ± 5.26 in mm Hg, P = .005). When pain scores were regressed against ABI and transcutaneous oxygen tension values, there was a significant association between these (r = 0.8, P = .002). The reduction in pain following regular use of FlowAid was accompanied by beneficial and statistically significant increases in perfusion and oxygenation.

Examination of a new mobile intermittent pneumatic compression device in healthy adults

OBJECTIVE

Intermittent pneumatic compression (IPC) is an alternative method of compression treatment designed to compress the leg and mimic ambulatory pump action to actively promote venous return. This study explores the efficacy of a new portable IPC device on tissue oxygenation (StO₂) in two sitting positions.

METHOD

In this quantitative, healthy single cohort study, participants were screened and recruited using Physical Activity Readiness Questionnaire (PAR-Q, Canada). Participants attended two separate one-hour sessions to evaluate StO₂ in an upright chair-sitting position and in a long-sitting position. StO₂ was recorded for 20 minutes before, during and after a 20-minute intervention of the IPC device (Venapro, DJO Global, US).

RESULTS

A total of 29 healthy volunteers took part in the study. A significant difference was seen between the two seating positions (p=0.003) with long-sitting showing a 12% higher StO₂ level than chair-sitting post-intervention. A similar effect was seen in both sitting positions when analysing data over three timepoints (p=0.000). Post-hoc pairwise comparisons showed that significant improvements in StO₂ (p≤0.000) were seen from baseline, throughout the intervention, continuing up to 15 minutes post-intervention, indicating a continued effect of the device after a short intervention.

CONCLUSION

Increasing StO₂ through short intervention sessions with this portable device has potential for use within various health and sports-based practices, improving tissue health, potentially reducing postoperative deep vein thrombosis (DVT) risk or inflammation. Such devices lend themselves to wide self-management implementation.

A prospective trial of intraoperative tissue oxygenation measurement and its association with anastomotic leak rate after Ivor Lewis esophagectomy

Background

Anastomotic leak following Ivor Lewis esophagectomy is associated with increased morbidity/mortality and decreased survival. Tissue oxygenation at the anastomotic site may influence anastomotic leak. Methods for establishing tissue oxygenation at the anastomotic site are lacking.

Methods

Over a 2-year study period, 185 Ivor Lewis esophagectomies were performed. Study participants underwent measurement of gastric conduit tissue oxygenation at the planned anastomotic site using the wireless pulse oximetry device. Associations between anastomotic leaks or strictures and tissue oxygenation levels were analyzed using Wilcoxon rank sum test or Fisher’s exact test.

Results

Among study participants (n=114), median gastric conduit tissue oxygenation level was 92% (range, 62–100%). There were 8 (7.0%) anastomotic leaks and 3 (2.6%) strictures. Analysis of tissue oxygenation as a continuous variable showed no difference in median tissue oxygenation in patients with and without leaks (98% and 92%; P=0.2) and stricture formation (89% and 92%; P=0.6). Analysis of tissue oxygenation as a dichotomous variable found no difference in anastomotic leak rates [7.5% (n=93) in >80% vs. 0% (n=20) in ≤80%; P=0.3]. There were no significant differences in leak rates in concurrent study nonparticipants.

Conclusions

No significant association was observed between intraoperative tissue oxygenation at the anastomotic site and subsequent anastomotic leak or stricture formation among patients undergoing Ivor Lewis esophagectomy.

Frontal cerebral oxygenation asymmetry: intersubject variability and dependence on systemic physiology, season, and time of day

Significance: Our study reveals that frontal cerebral oxygenation asymmetry (FCOA), i.e. a difference in the oxygenation between the right and left prefrontal cortex (PFC), is a real phenomenon in healthy human subjects at rest. Aim: To investigate FCOA, we performed a study with 134 healthy right-handed subjects with the systemic physiology augmented functional near infrared spectroscopy (SPA-fNIRS) approach. Approach: Subjects were measured 2 to 4 times on different days resulting in an unprecedented number of 518 single measurements of the absolute values of tissue oxygen saturation (StO 2 ) and total hemoglobin concentration ([tHb]) of the right and left PFC. Measurements were performed with frequency-domain functional near-infrared spectroscopy. In addition, the cardiorespiratory parameters were measured simultaneously. Results: We found that (i) subjects showed an FCOA (higherStO 2 on the right PFC), but not for tHb; (ii) intrasubject variability was excellent for bothStO 2 and tHb, and fair for FCOA; (iii) StO 2 correlated significantly with bloodCO 2 concentration, [tHb] with heart rate, respiration rate (RR), and the pulse-respiration quotient (PRQ), and FCOA with RR and PRQ; (iv) FCOA andStO 2 were dependent on season and time of day, respectively; (v) FCOA was negatively correlated with the room temperature; and (vi) StO 2 and tHb were not correlated with the subjects mood but with their chronotype, whereas FCOA was not dependent on the chronotype. Conclusion: Our study demonstrates that FCOA is real, and it provides unique insights into this remarkable phenomenon.

Findings From Somatic and Cerebral Near-Infrared Spectroscopy and Echocardiographic Monitoring During Ductus Arteriosus Ligation: Description of Two Cases and Review of Literature

Background: Preterm infants with hemodynamically significant patent ductus arteriosus (HsPDA) are exposed to low cerebral tissue oxygen saturation (rScO₂) values. Additionally, infants requiring surgical ligation are at risk of further changes in cerebral oxygenation and postligation cardiac syndrome (PLCS). Previous studies have assessed the effect of PDA ligation on rScO₂ with variable results. Cases description: In this report we analyse near-infrared spectroscopy (NIRS) and echocardiographic findings of two patients who underwent ligation of PDA and presented low cardiac output. Literature on regional tissue oxygenation saturation (rSO2) before and after PDA ligation was briefly reviewed. Discussion: Cerebral oxygenation values before and after PDA ligation may be influenced by gestational age, vasopressor use, ductal shunt volume, time of exposure HsPDA, chronological age and the presence of cerebral autoregulation. PLCS complicates 28-45% of all PDA ligations and is associated with higher mortality. Cerebral and somatic NIRS monitoring in the postoperative period may enhance the identification of PLCS at early stages. Conclusion: Cerebral oxygenation in the perioperative period of PDA ligation may be influenced by numerous clinical factors. Early detection of PLCS using multisite NIRS after ligation could prevent further alterations in cerebral hemodynamics and improve outcomes. A decrease in somatic-cerebral difference and/or a significant drop in somatic NIRS values may precede clinical signs of hypoperfusion. NIRS values should be interpreted as trends along with echocardiographic findings to guide goal directed interventions.

Renal Tissue Oxygenation Monitoring-An Opportunity to Improve Kidney Outcomes in the Vulnerable Neonatal Population

Adequate oxygenation of the kidney is of critical importance in the neonate. Non-invasive monitoring of renal tissue oxygenation using near-infrared spectroscopy (NIRS) is a promising bedside strategy for early detection of circulatory impairment as well as recognition of specific renal injury. As a diagnostic tool, renal NIRS monitoring may allow for earlier interventions to prevent or reduce injury in various clinical scenarios in the neonatal intensive care unit. Multiple studies utilizing NIRS monitoring in preterm and term infants have provided renal tissue oxygenation values at different time points during neonatal hospitalization, and have correlated measures with ultrasound and Doppler flow data. With the establishment of normal values, studies have utilized renal tissue oxygenation monitoring in preterm neonates to predict a hemodynamically significant patent ductus arteriosus, to assess response to potentially nephrotoxic medications, to identify infants with sepsis, and to describe changes after red blood cell transfusions. Other neonatal populations being investigated with renal NIRS monitoring include growth restricted infants, those requiring delivery room resuscitation, infants with congenital heart disease, and neonates undergoing extracorporeal membrane oxygenation. Furthermore, as the recognition of acute kidney injury (AKI) and its associated morbidity and mortality in neonates has increased over the last decade, alternative methods are being investigated to diagnose AKI before changes in serum creatinine or urine output occur. Studies have utilized renal NIRS monitoring to diagnose AKI in specific populations, including neonates with hypoxic ischemic encephalopathy after birth asphyxia and in infants after cardiac bypass surgery. The use of renal tissue oxygenation monitoring to improve renal outcomes has yet to be established, but results of studies published to date suggest that it holds significant promise to function as a real time, early indicator of poor renal perfusion that may help with development of specific treatment protocols to prevent or decrease the severity of AKI.

Magnetic resonance imaging of oxygen microbubbles

Oxygen loaded microbubbles are being investigated as a means of reducing tumour hypoxia in order to improve response to cancer therapy. To optimise this approach, it is desirable to be able to measure changes in tissue oxygenation in real-time during treatment. In this study, the feasibility of using magnetic resonance imaging (MRI) for this purpose was investigated. Longitudinal relaxation time (T1) measurements were made in simple hydrogel phantoms containing two different concentrations of oxygen microbubbles. T1 was found to be unaffected by the presence of oxygen microbubbles at either concentration. Upon application of ultrasound to destroy the microbubbles, however, a statistically significant reduction in T1 was seen for the higher microbubble concentration. Further work is needed to assess the influence of physiological conditions upon the measurements, but these preliminary results suggest that MRI could provide a method for quantifying the changes in tissue oxygenation produced by microbubbles during therapy.

Positive expiratory pressure improves arterial and cerebral oxygenation in acute normobaric and hypobaric hypoxia

Positive expiratory pressure (PEP) has been shown to limit hypoxia-induced reduction in arterial oxygen saturation, but its effectiveness on systemic and cerebral adaptations, depending on the type of hypoxic exposure [normobaric (NH) versus hypobaric (HH)], remains unknown. Thirteen healthy volunteers completed three randomized sessions consisting of 24-h exposure to either normobaric normoxia (NN), NH (inspiratory oxygen fraction, FiO2 = 13.6%; barometric pressure, BP = 716 mmHg; inspired oxygen partial pressure, PiO2 = 90.9 ± 1.0 mmHg), or HH (3,450 m, FiO2 = 20.9%, BP = 482 mmHg, PiO2 = 91.0 ± 0.6 mmHg). After the 6th and the 22nd hours, participants breathed quietly through a facemask with a 10-cmH₂O PEP for 2 × 5 min interspaced with 5 min of free breathing. Arterial (SpO2, pulse oximetry), quadriceps, and cerebral (near-infrared spectroscopy) oxygenation, middle cerebral artery blood velocity (MCAv; transcranial Doppler), ventilation, and cardiovascular responses were recorded continuously. SpO2without PEP was significantly lower in HH (87 ± 4% on average for both time points, P < 0.001) compared with NH (91 ± 3%) and NN (97 ± 1%). PEP breathing did not change SpO2 in NN but increased it similarly in NH and HH (+4.3 ± 2.5 and +4.7 ± 4.1% after 6h; +3.5 ± 2.2 and +4.1 ± 2.9% after 22h, both P < 0.001). Although MCAv was reduced by PEP (in all sessions and at all time points, -6.0 ± 4.2 cm/s on average, P < 0.001), the cerebral oxygenation was significantly improved (P < 0.05) with PEP in both NH and HH, with no difference between conditions. These data indicate that PEP could be an attractive nonpharmacological means to improve arterial and cerebral oxygenation under both normobaric and hypobaric mild hypoxic conditions in healthy participants.