Near infrared monitoring of human skeletal muscle oxygenation during forearm ischemia

Using high-resolution imaging to study the impact of the Kalogon wheelchair cushion on blood flow in the gluteal area

AIM OF THE STUDY

This study investigated how the air-bladder offloading mode of the Orbiter by Kalogon wheelchair cushion (Orbiter) affected blood flow in the gluteal region of non-disabled subjects. The hypothesis was that the cushion's offloading mode would improve blood flow, resulting in reduced reactive hyperemia when compared to the static setting, or Loaded Control (LC). Furthermore, the study proposed a technique using a high-resolution image laser speckle contrast system to measure blood flow in the gluteal area.

METHODS

Two procedures were carried out, one with the participant sitting on a cushion in LC, and the second, the cushion was set to offloading mode. Blood flow was measured through data imaging after each procedure. Three trials were performed, starting and ending in different cushion bladders. Customized algorithms were used to select regions of interest on the images for calculations. The Wilcoxon Signed-Rank Test was conducted to compare the offloads and loaded control values of each region of interest. Results were considered significant at α = 0.05.

RESULTS

Ten healthy, non-disabled adults participated in the study, seven females and three males. There were no significant differences among the participants. However, results showed that seven subjects tended to decrease reactive hyperemia in the offload sequence of trial when the last two bladders offloaded were the sacrum followed by the right ischial tuberosity.

CONCLUSIONS

The high-resolution imager showed that the Orbiter Offloads helped reduce reactive hyperemia in seven subjects, potentially improving blood flow. More research is necessary to comprehend the mechanisms of these effects fully.

Respiratory and locomotor muscle blood flow measurements using near-infrared spectroscopy and indocyanine green dye in health and disease

Measuring respiratory and locomotor muscle blood flow during exercise is pivotal for understanding the factors limiting exercise tolerance in health and disease. Traditional methods to measure muscle blood flow present limitations for exercise testing. This article reviews a method utilising near-infrared spectroscopy (NIRS) in combination with the light-absorbing tracer indocyanine green dye (ICG) to simultaneously assess respiratory and locomotor muscle blood flow during exercise in health and disease. NIRS provides high spatiotemporal resolution and can detect chromophore concentrations. Intravenously administered ICG binds to albumin and undergoes rapid metabolism, making it suitable for repeated measurements. NIRS-ICG allows calculation of local muscle blood flow based on the rate of ICG accumulation in the muscle over time. Studies presented in this review provide evidence of the technical and clinical validity of the NIRS-ICG method in quantifying respiratory and locomotor muscle blood flow. Over the past decade, use of this method during exercise has provided insights into respiratory and locomotor muscle blood flow competition theory and the effect of ergogenic aids and pharmacological agents on local muscle blood flow distribution in COPD. Originally, arterial blood sampling was required via a photodensitometer, though the method has subsequently been adapted to provide a local muscle blood flow index using venous cannulation. In summary, the significance of the NIRS-ICG method is that it provides a minimally invasive tool to simultaneously assess respiratory and locomotor muscle blood flow at rest and during exercise in health and disease to better appreciate the impact of ergogenic aids or pharmacological treatments.

Evaluation of the Influence of Short Tourniquet Ischemia on Tissue Oxygen Saturation and Skin Temperature Using Two Portable Imaging Modalities

BACKGROUND

The exact influence of tourniquet ischemia on a treated extremity remains unclear.

METHODS

Twenty patients received an operation on one hand under tourniquet ischemia. Twenty healthy volunteers received 10 min of tourniquet ischemia on one of their arms. Measurements of tissue oxygen saturation using near-infrared reflectance-based imaging and skin temperature of the dorsum of the hand were performed at five different timepoints (t0 was performed just before the application of the tourniquet ischemia, t1 directly after the application of the tourniquet ischemia, t2 before the release of the ischemia, t3 directly after the release of the ischemia, and t4 on the following day).

RESULTS

In both groups, tissue oxygen saturation dropped after the application of the tourniquet ischemia compared to t0 and increased after the release of the tourniquet ischemia. In the patient group, tissue oxygen saturation at t4 was higher compared to t0; in contrast, the level of tissue oxygen saturation in the participant group dropped slightly at t4 compared to t0. The measured skin temperature in the patient group showed an increase during the observation period, while it continuously decreased in the group of healthy participants.

CONCLUSIONS

Short-term ischemia did not appear to permanently restrict perfusion in this study design. The non-invasive imaging modalities used were easy to handle and allowed repetitive measurement.

Intra- and Inter-Day Reliability of the NIRS Portamon Device after Three Induced Muscle Ischemias

(1) Background: Near-infrared spectroscopy (NIRS) is an innovative and non-invasive technology used to investigate muscular oxygenation. The aim of this study is to assess the within- and between-session reliability of the NIRS Portamon (Artinis, Elst, Netherlands) device following three sets of induced muscle ischemia. (2) Methods: Depending on the experimental group (G1, G2 or G3), a cuff was inflated three times on the left upper arm to 50 mmHg (G1), systolic blood pressure (SBP) + 50 mmHg (G2) or 250 mmHg (G3). Maximum, minimum and reoxygenation rate values were assessed after each occlusion phase, using a Portamon device placed on the left brachioradialis. Reliability was assessed with intraclass correlation coefficient (ICC) value and ICC 95% confidence interval (CI-95%), coefficient of variation (CV) and standard error of measurement (SEM) (3) Results: Our results showed a good to excellent reliability for maximums and minimums within-session. However, the reoxygenation rate within sessions as well as measurements between sessions cannot predominantly show good reliability. (4) Conclusions: Multiple measurements of maximums and minimums within a single session appeared to be reliable which shows that only one measurement is necessary to assess these parameters. However, it is necessary to be cautious with a comparison of maximum, minimum and reoxygenation rate values between sessions.

The association of elevated blood pressure during ischaemic exercise with sport performance in Master athletes with and without morbidity

Background

An exaggerated exercise blood pressure (BP) is associated with a reduced exercise capacity. However, its connection to physical performance during competition is unknown.

Aim

To examine BP responses to ischaemic handgrip exercise in Master athletes (MA) with and without underlying morbidities and to assess their association with athletic performance during the World Master Track Cycling Championships 2019.

Methods

Forty-eight Master cyclists [age 59 ± 13yrs; weekly training volume 10.4 ± 4.1 h/week; handgrip maximum voluntary contraction (MVC) 46.3 ± 11.5 kg] divided into 2 matched groups (24 healthy MA and 24 MA with morbidity) and 10 healthy middle-aged non-athlete controls (age 48.3 ± 8.3 years; MVC 40.4 ± 14.8 kg) performed 5 min of forearm occlusion including 1 min handgrip isometric contraction (40%MVC) followed by 5 min recovery. Continuous beat-by-beat BP was recorded using finger plethysmography. Age-graded performance (AGP) was calculated to compare race performances among MA. Healthy Master cyclists were further grouped into middle-age (age 46.2 ± 6.4 years; N:12) and old-age (age 65.0 ± 7.7 years; N:12) for comparison with middle-aged non-athlete controls.

Results

Healthy and morbidity MA groups showed similar BP responses during forearm occlusion and AGP (90.1 ± 4.3% and 91.0 ± 5.3%, p > 0.05, respectively). Healthy and morbidity MA showed modest correlation between the BP rising slope for 40%MVC ischaemic exercise and AGP (r = 0.5, p < 0.05). MA showed accelerated SBP recovery after cessation of ischaemic handgrip exercise compared to healthy non-athlete controls.

Conclusion

Our findings associate long-term athletic training with improved BP recovery following ischaemic exercise regardless of age or reported morbidity. Exaggerated BP in Master cyclists during ischaemic exercise was associated with lower AGP during the World Master Cycling Championships.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04828-9.

Effects of Acceleration-Induced Reductions in Retinal and Cerebral Oxygenation on Human Performance

BACKGROUND: Ischemic hypoxia induced by suprathreshold G-force loading can adversely affect vision, cognition, and lead to loss of consciousness (LOC). The purpose of this study was to determine whether reductions in cerebral oxygenation, caused by subthreshold G-forces (up to 4 G_z and of limited durations that do not lead to LOC), would affect visual perception and working memory performance.METHODS: Sixteen subjects performed visual perception and working memory tasks both before and during G_z exposures (1, 2.2, 3, 4 with leg pressurization, 4 with leg and abdomen pressurization) within a human-use centrifuge.RESULTS: As measured using near-infrared spectroscopy, blood oxygenation over medial prefrontal cortex was similar in the 1 and 2.2 G_z conditions, but was reduced to a similar extent in the 3 and 4 G_z conditions. In parallel, visual perception accuracy was reduced in the 3 and 4 G_z conditions, with no difference between the 3 and 4 G_z conditions. No change in reaction time was seen. Conversely, neither accuracy nor reaction time changes were observed for the visual working memory task.DISCUSSION: These results indicate that although visual working memory is not affected, the ability to visually discriminate between stimuli is reduced at G-forces as low as 3 and 4 G_z. This may have important ramifications for pilots who are routinely subjected to such forces.Croft RJ, Klegrd R, Tribukait A, Taylor NAS, Eiken O. Effects of acceleration-induced reductions in retinal and cerebral oxygenation on human performance. Aerosp Med Hum Perform. 2021; 92(2):7582.

Venous occlusion during blood collection decreases plasma nitrite but not nitrate concentration in humans

BACKGROUND

To maintain vascular tone and blood flow when tissue oxygenation is reduced, nitrite anions are reduced to nitric oxide (NO). From a practical perspective, it is unclear how the application of a tourniquet during blood collection might influence measurement of NO metabolites. Accordingly, this study evaluated the effect of venous occlusion on plasma nitrite and nitrate during venous blood collection.

METHODS

Fifteen healthy participants completed two trials that were preceded by the ingestion of nitrate-rich beetroot juice (BRJ; total of ~8.4 mmol nitrate) or no supplementation (control). In both trials, blood was collected using a venepuncture needle while a tourniquet was applied to the upper arm and using an indwelling intravenous cannula, from the opposing arm. The venepuncture samples were collected at 35 s post occlusion. Changes in the oxygenation of forearm flexor muscles were assessed using near-infrared spectroscopy. Plasma nitrite and nitrate were analysed using gas-phase chemiluminescence.

RESULTS

In the control trial, plasma nitrite was significantly elevated when collected via the cannula (179 ± 67 nM) compared to venepuncture (112 ± 51 nM, P = 0.03). The ingestion of BRJ increased plasma nitrite and values remained higher when sampled from the cannula (473 ± 164 nM) compared to venepuncture (387 ± 136 nM, P < 0.001). Plasma nitrate did not differ between collection methods in either trial (all P > 0.05). The delta changes in total-, deoxy-, and oxy-haemoglobin were all significantly greater during venepuncture sample compared to the cannula sample at the point of blood collection (all P < 0.05).

CONCLUSIONS

Venous occlusion during venepuncture blood collection lowers plasma nitrite concentration, potentially due to localised changes in haemoglobin concentration and/or a suppression of endogenous NO synthesis. Accordingly, the method of blood collection to enable measurements of NO metabolites should be carefully considered and consistently reported by researchers.

The Effect of Static Stretching Duration on Muscle Blood Volume and Oxygenation

Matsuo, H, Kubota, M, Shimada, S, Kitade, I, Matsumura, M, Nonoyama, T, Koie, Y, Naruse, H, Takahashi, A, Oki, H, Kokubo, Y, and Matsumine, A. The effect of static stretching duration on muscle blood volume and oxygenation. J Strength Cond Res XX(X): 000-000, 2020-Muscle blood volume increases due to stretching; however, the minimum duration of stretching to sustainably increase the muscle blood volume after stretching has not yet been elucidated. This study examined whether the duration of static stretching influenced the muscle blood volume and oxygenation. Ten healthy male subjects participated in this controlled laboratory study. Static stretching of the gastrocnemius muscle was performed for 5 durations (20 seconds, and 1, 2, 5, and 10 minutes). Changes in both the total-Hb (ΔtHb), as an index of blood volume, and tissue oxygenation index (ΔTOI) from baseline were determined using near-infrared spectroscopy. Both the ΔtHb and ΔTOI decreased during stretching and increased after stretching. The minimum value of ΔtHb during stretching did not differ in each of the 5 durations, but minimum ΔTOI progressively decreased with longer durations of stretching. The peak value of ΔtHb after stretching increased with longer durations of stretching. The value of ΔtHb at 5 minutes after the end of stretching increased with more than 2 minutes of stretching compared with 20 seconds of stretching, although the value of ΔtHb did not significantly differ between the 2, 5, and 10 minutes' durations. These findings suggest that a longer duration of stretching elicits a decrease in muscle oxygenation during stretching, and an increase in both the muscle blood volume and oxygenation after stretching. The results indicated that the minimum duration of stretching to sustain an increase in the muscle blood volume after stretching is 2 minutes.

Flexible graphene photodetectors for wearable fitness monitoring

Wearable health and wellness trackers based on optical detection are promising candidates for public health uses due to their noninvasive tracking of vital health signs. However, so far, the use of rigid technologies hindered the ultimate performance and form factor of the wearable. Here, we demonstrate a new class of flexible and transparent wearables based on graphene sensitized with semiconducting quantum dots (GQD). We show several prototype wearable devices that are able to monitor vital health signs noninvasively, including heart rate, arterial oxygen saturation (SpO2), and respiratory rate. Operation with ambient light is demonstrated, offering low-power consumption. Moreover, using heterogeneous integration of a flexible ultraviolet (UV)-sensitive photodetector with a near-field communication circuit board allows wireless communication and power transfer between the photodetectors and a smartphone, offering battery-free operation. This technology paves the way toward seamlessly integrated wearables, and empowers the user through wireless probing of the UV index.

Thigh Ischemia-Reperfusion Model Does Not Accelerate Pulmonary VO 2 Kinetics at High Intensity Cycling Exercise

Background: We aimed to investigate the effect of a priming ischemia-reperfusion (IR) model on the kinetics of pulmonary oxygen uptake (VO₂) and cardiopulmonary parameters after high-intensity exercise. Our primary outcome was the overall VO₂ kinetics and secondary outcomes were heart rate (HR) and O₂ pulse kinetics. We hypothesized that the IR model would accelerate VO₂ and cardiopulmonary kinetics during the exercise.

Methods: 10 recreationally active men (25.7 ± 4.7 years; 79.3 ± 10.8 kg; 177 ± 5 cm; 44.5 ± 6.2 mL kg⁻¹ min⁻¹) performed a maximal incremental ramp test and four constant load sessions at the midpoint between ventilatory threshold and VO₂ max on separate days: two without IR (CON) and two with IR (IR). The IR model consisted of a thigh bi-lateral occlusion for 15 min at a pressure of 250 mmHg, followed by 3 min off, before high-intensity exercise bouts.

Results: There were no significant differences for any VO₂ kinetics parameters (VO₂ base 1.08 ± 0.08 vs. 1.12 ± 0.06 L min⁻¹; P = 0.30; τ = 50.1 ± 7.0 vs. 47.9 ± 6.4 s; P = 0.47), as well as for HR (MRT_180s 67.3 ± 6.0 vs. 71.3 ± 6.1 s; P = 0.54) and O₂ pulse kinetics (MRT_180s 40.9 ± 3.9 vs. 48.2 ± 5.6 s; P = 0.31) between IR and CON conditions, respectively.

Conclusion: We concluded that the priming IR model used in this study had no influence on VO₂, HR, and O₂ pulse kinetics during high-intensity cycling exercise.

Wearable, Luminescent Oxygen Sensor for Transcutaneous Oxygen Monitoring

We present a new concept for a wearable oxygen (O₂) sensor for transcutaneous O₂ pressure (tcpO₂) monitoring by combining the technologies of luminescent gas sensing and wearable devices. O₂ monitoring has been exhaustively studied given its central role in diagnosing various diseases. The ability to quantify the physiological distribution and real-time dynamics of O₂ from the subcellular to the macroscopic level is required to fully understand mechanisms associated with both normal physiological and pathological conditions. Despite its profound biological and clinical importance, few effective methods exist for noninvasively quantifying O₂ in a physiological setting. The wearable sensor developed here consists of three components: a luminescent sensing film attached onto skin by a carbon tape, an organic light-emitting diode (OLED) as a light source, and an organic photodiode (OPD) as a light detector. All the components are solution-processable and integrated on a plane in a bandage-like configuration. To verify the performance, tcpO₂ variations by pressure-induced occlusion were measured in the lower arm and a thumb by the wearable sensor, and the results were comparable to those measured by a commercial instrument. In addition to its flexibility, other features of this sensor render it a potential low-cost solution for the simultaneous monitoring of tcpO₂ in any part of a body.

Sensing, monitoring, and release of therapeutics: the translational journey of next generation bandages

This article aims to be a progress report on the Sensing, Monitoring And Release of Therapeutics (SMART) bandage-one of the three technologies that received the inaugural SPIE Photonics West Translational Research Symposium Award in 2015. Invented and developed by Dr. Conor L. Evans and his research team at the Wellman Center for Photomedicine, Massachusetts General Hospital, the SMART bandage is a tool aiming to provide measurements of physiological parameters in the skin alongside the administration of therapeutics on-demand. Since the project began in 2012, the chemists, physicists, and biomedical engineers in the team have worked closely with partners from academia and industry to develop oxygen-sensing SMART bandage prototypes that are now in first-in-human clinical studies. This report gives perspectives on the genesis and translational journey of the technology with an emphasis on the challenges encountered, and the solutions innovated at each stage of development.

A flexible organic reflectance oximeter array

The optical method to determine oxygen saturation in blood is limited to only tissues that can be transilluminated. The status quo provides a single-point measurement and lacks 2D oxygenation mapping capability. We use organic printed optoelectronics in a flexible array configuration that senses reflected light from tissue. Our reflectance oximeter is used beyond conventional sensing locations and accurately measures oxygen saturation on the forehead. In a full system implementation, coupled with a mathematical model, we create 2D oxygenation maps of adult forearms under pressure-cuff–induced ischemia. Our skin-like flexible sensor system has the potential to transform oxygenation monitoring of tissues, wounds, skin grafts, and transplanted organs.

Transmission-mode pulse oximetry, the optical method for determining oxygen saturation in blood, is limited to only tissues that can be transilluminated, such as the earlobes and the fingers. The existing sensor configuration provides only single-point measurements, lacking 2D oxygenation mapping capability. Here, we demonstrate a flexible and printed sensor array composed of organic light-emitting diodes and organic photodiodes, which senses reflected light from tissue to determine the oxygen saturation. We use the reflectance oximeter array beyond the conventional sensing locations. The sensor is implemented to measure oxygen saturation on the forehead with 1.1% mean error and to create 2D oxygenation maps of adult forearms under pressure-cuff–induced ischemia. In addition, we present mathematical models to determine oxygenation in the presence and absence of a pulsatile arterial blood signal. The mechanical flexibility, 2D oxygenation mapping capability, and the ability to place the sensor in various locations make the reflectance oximeter array promising for medical sensing applications such as monitoring of real-time chronic medical conditions as well as postsurgery recovery management of tissues, organs, and wounds.

Physiological and psychological determinants of whole-body endurance exercise following short-term sustained operations with partial sleep deprivation

Purpose

The study examined the effects of short-term field-based military training with partial sleep deprivation on whole-body endurance performance in well-trained individuals.

Methods

Before and after a 2-day sustained operations (SUSOPS), 14 cadets performed a 15-min constant-load cycling at 65% of peak power output (PPO; CLT₆₅), followed by an exhaustive constant-load trial at 85% of PPO (CLT₈₅). Physiological [oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot {V}$$\end{document}V˙O₂), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO), and regional oxygenation (TOI) in the frontal cerebral cortex and vastus lateralis muscle] and psychological [effort perception (RPE), affective valence (FS), and perceived activation (FAS)] variables were monitored during exercise.

Results

SUSOPS reduced time to exhaustion in CLT₈₅ by 29.1% (p = 0.01). During the CLT₆₅ trial, SUSOPS potentiated the exercise-induced elevations in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot {V}$$\end{document}V˙O₂ and HR (p < 0.05), and blunted MAP (p = 0.001). CO did not differ between trials. Yet, towards the end of both CLT₈₅ trials, CO tended to decline (p ≤ 0.08); a response that occurred at an earlier stage in the SUSOPS trial. During CLT₆₅, SUSOPS altered neither cerebral nor muscle TOI. The SUSOPS CLT₈₅ trial, however, was terminated at similar leg-muscle deoxygenation (p > 0.05) and lower prefrontal cortex deoxygenation (p < 0.01). SUSOPS increased RPE at submaximal intensities (p = 0.05), and suppressed FAS and FS throughout (p < 0.01).

Conclusions

The present findings indicate, therefore, that a brief period of military sustained operations with partial sleep deprivation augment cardiorespiratory and psychological strain, limiting high-intensity endurance capacity.

Tissue oxygenation index reflects changes in forearm blood flow after brief ischemia

Whether the near-infrared spectroscopy (NIRS) technology correctly detects the changes in oxygenation related to ischemia and reperfusion of organs and tissues other than brain remains unclear. The present study examined how different tissue oxygenation parameters derived from NIRS reflect the changes in the forearm blood flow (FBF) according to the brief ischemia and the subsequent reperfusion, and whether values of these parameters move in parallel with the medial and lateral sides of FBF. Thirteen volunteers underwent the prospective observational study. The tissue oxygenation index (TOI), regional saturation of oxygen (rSO₂), skin tissue oxygenation (StO₂), and FBF values were evaluated in the forearm. Medial rSO₂ values at 1 to 3 minutes after the termination of brief ischemia were higher than lateral rSO₂ and respective TOI values. FBF and StO₂ values quickly increased according to the cessation of brief ischemia, whereas the medial and lateral values did not differ during and after the brief ischemia. TOI and StO₂, but not rSO₂, reflected changes in FBF of both medial and lateral sides simultaneously in response to the reperfusion after brief ischemia. The muscle tissue oxygenation during reperfusion favors the use of TOI and StO₂, but not rSO₂, as the surrogate parameter. J. Med. Invest. 64: 228-232, August, 2017.

Intraocular pressure and cerebral oxygenation during prolonged headward acceleration

PURPOSE

Supra-tolerance head-to-foot directed gravitoinertial load (+Gz) typically induces a sequence of symptoms/signs, including loss of: peripheral vision-central vision-consciousness. The risk of unconsciousness is greater when anti-G-garment failure occurs after prolonged rather than brief exposures, presumably because, in the former condition, mental signs are not consistently preceded by impaired vision. The aims were to investigate if prolonged exposure to moderately elevated +Gz reduces intraocular pressure (IOP; i.e., improves provisions for retinal perfusion), or the cerebral anoxia reserve.

METHODS

Subjects were exposed to 4-min +Gz plateaux either at 2 and 3 G (n = 10), or at 4 and 5 G (n = 12). Measurements included eye-level mean arterial pressure (MAP), oxygenation of the cerebral frontal cortex, and at 2 and 3 G, IOP.

RESULTS

IOP was similar at 1 (14.1 ± 1.6 mmHg), 2 (14.0 ± 1.6 mmHg), and 3 G (14.0 ± 1.6 mmHg). During the G exposures, MAP exhibited an initial prompt drop followed by a partial recovery, end-exposure values being reduced by ≤30 mmHg. Cerebral oxygenation showed a similar initial drop, but without recovery, and was followed by either a plateau or a further slight decrement to a minimum of about -14 μM.

CONCLUSION

Gz loading did not affect IOP. That cerebral oxygenation remained suppressed throughout these G exposures, despite a concomitant partial recovery of MAP, suggests that the increased risk of unconsciousness upon G-garment failure after prolonged +Gz exposure is due to reduced cerebral anoxia reserve.

PlanHab: hypoxia exaggerates the bed-rest-induced reduction in peak oxygen uptake during upright cycle ergometry

The study examined the effects of hypoxia and horizontal bed rest, separately and in combination, on peak oxygen uptake (V̇o2 peak) during upright cycle ergometry. Ten male lowlanders underwent three 21-day confinement periods in a counterbalanced order: 1) normoxic bed rest [NBR; partial pressure of inspired O2 (PiO2 ) = 133.1 ± 0.3 mmHg]; 2) hypoxic bed rest (HBR; PiO2 = 90.0 ± 0.4 mmHg), and 3) hypoxic ambulation (HAMB; PiO2 = 90.0 ± 0.4 mmHg). Before and after each confinement, subjects performed two incremental-load trials to exhaustion, while inspiring either room air (AIR), or a hypoxic gas (HYPO; PiO2 = 90.0 ± 0.4 mmHg). Changes in regional oxygenation of the vastus lateralis muscle and the frontal cerebral cortex were monitored with near-infrared spectroscopy. Cardiac output (CO) was recorded using a bioimpedance method. The AIR V̇o2 peak was decreased by both HBR (∼13.5%; P ≤ 0.001) and NBR (∼8.6%; P ≤ 0.001), with greater drop after HBR (P = 0.01). The HYPO V̇o2 peak was also reduced by HBR (-9.7%; P ≤ 0.001) and NBR (-6.1%; P ≤ 0.001). Peak CO was lower after both bed-rest interventions, and especially after HBR (HBR: ∼13%, NBR: ∼7%; P ≤ 0.05). Exercise-induced alterations in muscle and cerebral oxygenation were blunted in a similar manner after both bed-rest confinements. No changes were observed in HAMB. Hence, the bed-rest-induced decrease in V̇o2 peak was exaggerated by hypoxia, most likely due to a reduction in convective O2 transport, as indicated by the lower peak values of CO.

Shoulder skin and muscle hemodynamics during backpack carriage

The purpose of this study was to quantify the effects of loaded backpacks on shoulder muscle oxygenation, skin blood flow, and pain. We hypothesized that backpack load carriage is associated with lower shoulder muscle oxygenation and skin microvascular flow. Near-infrared spectroscopy quantified shoulder tissue oxygenation and laser Doppler flow measured skin microvascular flow. Eight adult volunteers donned a standard backpack without added load, 5 kg load, and 10 kg load for 5 min while standing. An 8 min rest period before each backpack donning condition ensured that all measured parameters returned to baseline. Data were analyzed using a repeated measures ANOVA and significance set at p < 0.05. Donning a 10 kg backpack significantly reduced shoulder muscle oxygenation by 22 ± 23% as compared to the empty backpack control condition (p = 0.023). In addition, a 10 kg backpack load reduced skin microvascular flow by 82 ± 22%, as compared to the empty backpack control condition (p = 0.024). Perceived pain was significantly higher when wearing the 10 kg backpack (level 4 on a 10-maximal pain scale) as compared to the empty backpack (0, 0-no pain) (p < 0.05). In conclusion, backpack loads of 10 kg decrease shoulder muscle oxygenation and skin microvascular flow.

Reflectance Photoplethysmography as Noninvasive Monitoring of Tissue Blood Perfusion

In the last decades, photoplethysmography (PPG) has been used as a noninvasive technique for monitoring arterial oxygen saturation by pulse oximetry (PO), whereas near-infrared spectroscopy (NIRS) has been employed for monitoring tissue blood perfusion. While NIRS offers more parameters to evaluate oxygen delivery and consumption in deep tissues, PO only assesses the state of oxygen delivery. For a broader assessment of blood perfusion, this paper explores the utilization of dual-wavelength PPG by using the pulsatile (ac) and continuous (dc) PPG for the estimation of arterial oxygen saturation (SpO2) by conventional PO. Additionally, the Beer-Lambert law is applied to the dc components only for the estimation of changes in deoxyhemoglobin (HHb), oxyhemoglobin (HbO2), and total hemoglobin (tHb) as in NIRS. The system was evaluated on the forearm of 21 healthy volunteers during induction of venous occlusion (VO) and total occlusion (TO). A reflectance PPG probe and NIRS sensor were applied above the brachioradialis, PO sensors were applied on the fingers, and all the signals were acquired simultaneously. While NIRS and forearm SpO2 indicated VO, SpO2 from the finger did not exhibit any significant drop from baseline. During TO, all the indexes indicated the change in blood perfusion. HHb, HbO2, and tHb changes estimated by PPG presented high correlation with the same parameters obtained by NIRS during VO (r(2) = 0.960, r(2) = 0.821, and r(2) = 0.974, respectively) and during TO (r(2) = 0.988, r(2) = 0.940, and r(2) = 0.938, respectively). The system demonstrated the ability to extract valuable information from PPG signals for a broader assessment of tissue blood perfusion.

Peripheral circulation evaluation with near-infrared spectroscopy in skeletal muscle during cardiopulmonary bypass

Background:

We designed a non-invasive, observational, real-time study, using near-infrared spectroscopy (NIRS) to assess the in vivo effects of cardiopulmonary bypass (CPB) on patients’ skeletal muscle as well as the effects of hemodilution and hypothermia on tissue oxygen delivery during CPB.

Methods:

The study included 20 consecutive adult patients undergoing open-heart surgery with CPB. Evaluation parameters for peripheral circulation were measured using the NIRO-200NX and recorded every 30 seconds. To assess how hemodilution influences peripheral circulation parameters, we compared data between a group of patients with hematocrit (Hct) values >22% (high Hct group) and those with Hct values ⩽22% (low Hct group).

Results:

Changes in the concentration of oxygenated hemoglobin (ΔO2Hb, μmol/L), which flows into the skeletal muscle, was an important factor for deciding the tissue oxygenation index (TOI%), showing the tissue oxygen saturation. The low Hct group showed a significant increase in the normalized tissue hemoglobin index (nTHI), showing the percentage change in the amount of initial hemoglobin and TOI compared to the high Hct group. Changes in the concentration of oxygenated hemoglobin (ΔO2Hb, μmol/L) and deoxygenated hemoglobin (ΔHHb, μmol/L) were significantly less in the low Hct group than in the high Hct group, thus, showing good peripheral circulation despite the low hematocrit levels.

Conclusion:

Our study indicated the presence of a compensatory mechanism in which increased blood flow of the microcirculation is in compensation for the lack of oxyhemoglobin delivery caused by hemodilution.

Assessment of in vivo skeletal muscle mitochondrial respiratory capacity in humans by near-infrared spectroscopy: a comparison with in situ measurements

The present study aimed to compare in vivo measurements of skeletal muscle mitochondrial respiratory capacity made using near-infrared spectroscopy (NIRS) with the current gold standard, namely in situ measurements of high-resolution respirometry performed in permeabilized muscle fibres prepared from muscle biopsies. Mitochondrial respiratory capacity was determined in 21 healthy adults in vivo using NIRS to measure the recovery kinetics of muscle oxygen consumption following a ∼15 s isometric contraction of the vastus lateralis muscle. Maximal ADP-stimulated (State 3) respiration was measured in permeabilized muscle fibres using high-resolution respirometry with sequential titrations of saturating concentrations of metabolic substrates. Overall, the in vivo and in situ measurements were strongly correlated (Pearson's r = 0.61-0.74, all P < 0.01). Bland-Altman plots also showed good agreement with no indication of bias. The results indicate that in vivo NIRS corresponds well with the current gold standard, in situ high-resolution respirometry, for assessing mitochondrial respiratory capacity.

Reliability of the Vascular Claudication Reporting in Diabetic Patients With Peripheral Arterial Disease

We evaluated whether altered reporting of ischemic symptoms occurs in diabetic patients with peripheral arterial disease (PAD) and stable claudication. Patients (n = 152) with claudication were enrolled (120 males; mean age: 71.0 ± 8.6 years): 74 with diabetes (DM-PAD) and 78 without (DMfree-PAD). The degree of muscle oxygenation at symptom onset and maximal speed (Smax) during an incremental treadmill test was recorded at the gastrocnemius by near-infrared spectroscopy (NIRS) and quantified by area under the curve of oxygenated hemoglobin (AUC-Hbo2) and area under the curve of differential hemoglobin (AUC-dHb). The DM-PAD and DMfree-PAD showed similar exercise capacities inversely correlated with the degree of muscle oxygenation but significantly lower values of AUC-Hbo2 and AUC-dHb for DM-PAD at symptom onset and Smax (−356 vs −122 and −1200 vs −359, P < .0001). During a NIRS-assisted test, the report of claudication in the presence of diabetes was delayed, occurring at a lower degree of oxygenation than in patients with PAD only, with potential implications for testing, functional staging, and balance disorders.

Culture media from hypoxia conditioned endothelial cells protect human intestinal cells from hypoxia/reoxygenation injury

Remote ischemic preconditioning (RIPC) is a phenomenon, whereby short episodes of non-lethal ischemia to an organ or tissue exert protection against ischemia/reperfusion injury in a distant organ. However, there is still an apparent lack of knowledge concerning the RIPC-mediated mechanisms within the target organ and the released factors. Here we established a human cell culture model to investigate cellular and molecular effects of RIPC and to identify factors responsible for RIPC-mediated intestinal protection. Human umbilical vein cells (HUVEC) were exposed to repeated episodes of hypoxia (3 × 15 min) and conditioned culture media (CM) were collected after 24h. Human intestinal cells (CaCo-2) were cultured with or without CM and subjected to 90 min of hypoxia/reoxygenation injury. Reverse transcription-polymerase chain reaction, Western blotting, gelatin zymography, hydrogen peroxide measurements and lactate dehydrogenase (LDH) assays were performed. In HUVEC cultures hypoxic conditioning did not influence the profile of secreted proteins but led to an increased gelatinase activity (P<0.05) in CM. In CaCo-2 cultures 90 min of hypoxia/reoxygenation resulted in morphological signs of cell damage, increased LDH levels (P<0.001) and elevated levels of hydrogen peroxide (P<0.01). Incubation of CaCo-2 cells with CM reduced the hypoxia-induced signs of cell damage and LDH release (P<0.01) and abrogated the hypoxia-induced increase of hydrogen peroxide. These events were associated with an enhanced phosphorylation status of the prosurvival kinase Erk1/2 (P<0.05) but not Akt and STAT-5. Taken together, CM of hypoxia conditioned endothelial cells protect human intestinal cells from hypoxia/reoxygenation injury. The established culture model may help to unravel RIPC-mediated cellular events and to identify molecules released by RIPC.

Simultaneous measurement of deep tissue blood flow and oxygenation using noncontact diffuse correlation spectroscopy flow-oximeter

We report a novel noncontact diffuse correlation spectroscopy flow-oximeter for simultaneous quantification of relative changes in tissue blood flow (rBF) and oxygenation (Δ[oxygenation]). The noncontact probe was compared against a contact probe in tissue-like phantoms and forearm muscles (n = 10), and the dynamic trends in both rBF and Δ[oxygenation] were found to be highly correlated. However, the magnitudes of Δ[oxygenation] measured by the two probes were significantly different. Monte Carlo simulations and phantom experiments revealed that the arm curvature resulted in a significant underestimation (~−20%) for the noncontact measurements in Δ[oxygenation], but not in rBF. Other factors that may cause the residual discrepancies between the contact and noncontact measurements were discussed, and further comparisons with other established technologies are needed to identify/quantify these factors. Our research paves the way for noncontact and simultaneous monitoring of blood flow and oxygenation in soft and vulnerable tissues without distorting tissue hemodynamics.

Peak oxygen uptake and regional oxygenation in response to a 10-day confinement to normobaric hypoxia

We investigated the effect of hypoxic acclimatization per se, without any concomitant influence of strenuous physical activity on muscle and cerebral oxygenation. Eight healthy male subjects participated in a crossover-designed study. In random order, they conducted a 10-day normoxic (CON) and a 10-day hypoxic (EXP) confinement. Pre and post both CON and EXP confinements, subjects conducted two incremental-load cycling exercises to exhaustion; one under normoxic, and the other under hypoxic (F(I)O(2)  = 0.154) conditions. Oxygen uptake (V˙O(2)), ventilation (V˙(E)), and relative changes in regional hemoglobin oxygenation (Δ([HbO(2)]) in the cerebral cortex and in the serratus anterior (SA) and vastus lateralis (VL) muscles were measured. No changes were observed in the CON confinement. Peak work rate and V˙O(2peak) were similar pre and post in the EXP confinement, whereas V˙(E) increased in the EXP post normoxic and hypoxic trials (P < 0.05). The exercise-induced drop in VL Δ[HbO(2)] was less in the post- than pre-EXP trial by 4.0 ± 0.4 and 4.2 ± 0.6 μM during normoxic and hypoxic exercise, respectively. No major changes were observed in cerebral or SA oxygenation. These results demonstrate that a 10-day hypoxic exposure without any concomitant physical activity had no effect on normoxic or hypoxic V˙O(2peak), despite the enhanced VL oxygenation.

Comparison of two different generations of "NIRS" devices and transducers in healthy volunteers and ICU patients

The purpose of this study is to compare Near Infrared Spectroscopy (NIRS) thenar eminence parameters obtained with 2 different devices from the same manufacturer (InSpectra Models 325 and 650, Hutchinson Tech, Min USA), and 2 different probes (15 vs. 25 mm spacing), in healthy volunteers (HV) and ICU patients. Prospective, observational study in ICU setting. Simultaneous, cross over NIRS inter-device comparison and comparison between different probes (25 vs. 15 mm spacing) were done at baseline and during vascular occlusion tests (VOTs). Forty patients (19 septic shock, 21 trauma), and 29 HV were included. NIRS inter-device comparison showed similar baseline StO(2) values in HV and patients. The VOT result were significantly different for minimal StO(2) value reached during VOT (StO(2min)) (intraclass concordance coefficient (ICC) = 0.18), the occlusion slope (ICC = 0.16) and the reperfusion slope (StO(2reperf)) (ICC = 0.26). The probe comparison was also significantly different for VOT parameters (StO(2min) (ICC = 0.43), occlusion (ICC = 0.50) and StO(2reperf) (ICC = 0.48). The low concordance, poor agreement and large bias (ICC and Bland & Altman) observed, were related both to the device used and the probe spacing. StO(2) data obtained with NIRS model 650 and 15 mm probe differ from values obtained with the previous device (325 and probe spacing 25 or 15 mm). This difference is not related to the population tested, but to the device and probe spacing. As a consequence, despite similar trends for variations between HV and patients during VOT, threshold and predictive values for outcome should be revisited with the new device before the acceptance for routine clinical use.

Increased muscle size and strength from slow-movement, low-intensity resistance exercise and tonic force generation

The authors investigated the effects of low-intensity resistance training on muscle size and strength in older men and women. Thirty-five participants (age 59-76 yr) were randomly assigned to 2 groups and performed low-intensity (50% of 1-repetition maximum) knee-extension and -flexion exercises with either slow movement and tonic force generation (LST; 3-s eccentric, 3-s concentric, and 1-s isometric actions with no rest between repetitions) or normal speed (LN; 1-s concentric and 1-s eccentric actions with 1-s rests between repetitions) twice a week for 12 wk (2-wk preparation and 10-wk intervention). The LST significantly increased thigh-muscle thickness, as well as isometric knee-extension and -flexion strength. The LN significantly improved strength, but its hypertrophic effect was limited. These results indicate that even for older individuals, the LST can be an effective method for gaining muscle mass and strength.

Noninvasive optical quantification of absolute blood flow, blood oxygenation, and oxygen consumption rate in exercising skeletal muscle

This study investigates a method using novel hybrid diffuse optical spectroscopies [near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS)] to obtain continuous, noninvasive measurement of absolute blood flow (BF), blood oxygenation, and oxygen consumption rate (V̇O(2)) in exercising skeletal muscle. Healthy subjects (n=9) performed a handgrip exercise to increase BF and V̇O(2) in forearm flexor muscles, while a hybrid optical probe on the skin surface directly monitored oxy-, deoxy-, and total hemoglobin concentrations ([HbO(2)], [Hb], and THC), tissue oxygen saturation (S(t)O(2)), relative BF (rBF), and relative oxygen consumption rate (rV̇O(2)). The rBF and rV̇O(2) signals were calibrated with absolute baseline BF and V̇O(2) obtained through venous and arterial occlusions, respectively. Known problems with muscle-fiber motion artifacts in optical measurements during exercise were mitigated using a novel gating algorithm that determined muscle contraction status based on control signals from a dynamometer. Results were consistent with previous findings in the literature. This study supports the application of NIRS/DCS technology to quantitatively evaluate hemodynamic and metabolic parameters in exercising skeletal muscle and holds promise for improving diagnosis and treatment evaluation for patients suffering from diseases affecting skeletal muscle and advancing fundamental understanding of muscle and exercise physiology.

Changes in calf muscle deoxygenation after foam sclerotherapy in patients with superficial venous insufficiency

OBJECTIVE

This study assessed changes in the calf muscle deoxygenated hemoglobin (HHb) level during light-intensity exercise after ultrasound-guided foam sclerotherapy (UGFS) for superficial venous insufficiency.

METHODS

UGFS with 1% or 3% polidocanol foam (POL-F) was used to treat unilateral great saphenous vein reflux in 84 patients. Near-infrared spectroscopy (NIRS) was used to measure calf muscle HHb levels before and 3 months after UGFS. The calf venous HHb blood-filling index was calculated on standing, the calf venous HHb ejection index was obtained after one tiptoe movement, and the venous HHb retention index was obtained after 10 tiptoe movements. The primary end point was an evident improvement in calf muscle deoxygenation after UGFS. The secondary end point was obliteration of the great saphenous vein.

RESULTS

Treatment consisted of 1% POL-F in 48 limbs and 3% POL-F in the remaining 36. Ultrasound imaging at the 3-month follow-up demonstrated complete occlusion in 56.3% of the patients who received injections of 1% POL-F and in 66.7% of those who received injections of 3% POL-F. The difference in treatment outcome between the groups was not significant (P=.333). Reflux was absent in 39 limbs (81.3%) treated with 1% POL-F and in 34 limbs (94.4%) treated with 3% POL-F, and no significant difference was observed between the two groups (P=.076). Postsclerotherapy NIRS demonstrated significant reductions in the levels of the HHb filling index in both treatment groups (P=.039, P=.0001, respectively) and significant reductions in the levels of the HHb retention index (P<.0001, P=.008, respectively). However, the differences in the levels of the HHb ejection index before and after UGFS were not significant (P=.250, P=.084, respectively).

CONCLUSIONS

Our present findings suggest that changes in the values of these parameters may be of potential use for assessing the effects of foam sclerotherapy in patients with superficial venous insufficiency.

Effect of exercise intensity on oxygen consumption kinetics in non-exercising muscle during exercise

This study examined the effect of exercise intensity on the kinetics of muscle oxygen consumption in non-exercising forearm flexor muscles (VO(2mf)) during exercise. Seven healthy male subjects performed cycling exercise for 60 min at 30% of maximal oxygen consumption (%VO(2max)) and 30 min at 50% VO(2max) on separate days. The VO(2mf) values at rest and during exercise were measured by near-infrared spectroscopy. The VO(2mf) at 30% VO(2max) significantly increased to 1·2 ± 0·1-fold over resting value at 20 min after the beginning of exercise (P<0·05) and remained constant within 1·2- to 1·3-fold over resting value until 60 min during exercise. The VO(2mf) at 50% VO(2max) significantly increased to 1·2 ± 0·1-fold over resting value at 15 min after the beginning of exercise (P<0·05). Subsequently, the VO(2mf) at 50% VO(2max) increased with time to 1·3 ± 0·1-fold over resting value at 20 min after the beginning of exercise and to 1·5 ± 0·2-fold over resting value at 30 min. The VO(2mf) 15-30 min of exercise at 50% VO(2max) was significantly higher than that at 30% VO(2max) (P<0·05). These data suggest that the increase in VO(2mf) has a time lag from the beginning of exercise, and the kinetics of VO(2mf) during exercise differs with exercise intensity. Therefore, we conclude that the kinetics of VO(2mf) during exercise is dependent on exercise intensity.

Tourniquets in orthopedic surgery

Tourniquets are commonly used in limb surgeries, be it orthopedic or plastic surgeries. But the inflation pressures, the duration, and release guidelines are still not clear. According to a survey, majority of orthopedic surgeons inflate the tourniquet to fixed pressures for the upper and the lower limbs without considering the baseline blood pressure of the patient on whom the tourniquets are being applied. This review was designed to recall and review the safe use of tourniquets and the various techniques that can be employed to minimize the complications of tourniquet use. Google, science direct, and pubmed were searched for appropriate literature and relevant articles were identified.

Physiological influence of basic perturbations assessed by non-invasive optical techniques in humans

New non-invasive techniques enabling frequent or continuous assessments of various pathophysiological conditions might be used to improve in-hospital outcome by enabling earlier and more reliable bedside detection of medical deterioration. In this preclinical study, three modern non-invasive optical techniques, laser Doppler imaging (LDI), near-infrared spectroscopy (NIRS), and tissue viability imaging (TVI), were all evaluated with respect to the influence of basic physiological perturbations (including local changes in arm positioning, skin temperature, and regional blood flow conditions) on quasi simultaneously obtained values of skin perfusion, muscle tissue oxygenation (StO2), and skin blood volume, recorded in eighteen healthy volunteers. Skin perfusion measured by LDI responded prominently to changes in positioning of the arm, whereas muscle StO2 measured by NIRS did not change significantly. Total haemoglobin count (HbT) measured by NIRS and blood volume estimated by TVI both increased significantly on lowering of the limb. On local cooling, the perfusion and blood volume were both found to increase considerably, while StO2 and HbT did not change. Local heating induced a more than 10-fold increase in skin perfusion and a small increase in blood volume. On progressive venoarterial occlusion, the perfusion, StO2, HbT, and blood volume values decreased, after transient increases in HbT and blood volume before full arterial occlusion occurred, and all values approached the baseline level on release of the occlusion with a slight overshoot of the StO2. The results obtained have potential bearing on future utilization of these non-invasive techniques in the management of severely injured and (or) critically ill patients.

Reproducibility and sensitivity of muscle reoxygenation and oxygen uptake recovery kinetics following running exercise in the field

The purpose of this study was to assess the reliability of postexercise near-infrared spectroscopy (NIRS)-derived measurements and their sensitivity to different exercise intensities in the field. Seventeen athletes (24·1 ± 5·6 year) repeated, on three occasions, two 2-min submaximal shuttle-runs at 40% and 60% of V(IFT) (final speed of the 30-15 intermittent fitness test) and a 50-m shuttle-run sprint (Sprint), with (OCC) or without (CON) repeated transient arterial occlusions of the medial gastrocnemius during the postexercise period. NIRS variables (i.e. oxyhaemoglobin [HbO(2)], deoxyhaemoglobin [HHb] and their difference [Hb(diff)]) were measured continuously for 3 min after each exercise. Half-recovery (½Rec) and mean response (MRT; monoexponential curve fitting) times of muscle reoxygenation and muscle oxygen uptake (mVO(2)) recovery were calculated. Reliability was assessed using the typical error of measurement, expressed as a coefficient of variation (CV). Postexercise recovery of muscle reoxygenation revealed CVs ranging from 16·8% to 37·3%; CV for mVO(2) recovery ranged from 6·2% to 20·9%, with no substantial differences shown between NIRS variables and exercise intensities. While running, intensity did not affect MRT or ½Rec for muscle reoxygenation, and differences were found for mVO(2) recovery (e.g. [Hb(diff)]-mVO(2) MRT = 28·7 ± 5·2, 34·2 ± 5·1 and 37·3 ± 6·2 s for 40%, 60% and Sprint, respectively, P<0·01). To conclude, the kinetics of postexercise NIRS measurements showed CV values ranging from 6% to 37%, with no substantial differences between exercise intensities or NIRS-derived variables. However, exercise intensity did influence mVO(2) recovery kinetics, but not that of muscle reoxygenation in an occlusion-free condition.

Postoperative quantitative assessment of reconstructive tissue status in a cutaneous flap model using spatial frequency domain imaging

BACKGROUND

The purpose of this study was to investigate the capabilities of a novel optical wide-field imaging technology known as spatial frequency domain imaging to quantitatively assess reconstructive tissue status.

METHODS

Twenty-two cutaneous pedicle flaps were created on 11 rats based on the inferior epigastric vessels. After baseline measurement, all flaps underwent vascular ischemia, induced by clamping the supporting vessels for 2 hours (either arteriovenous or selective venous occlusions); normal saline was injected into the control flap and hypertonic-hyperoncotic saline solution was injected into the experimental flap. Flaps were monitored for 2 hours after reperfusion. The spatial frequency domain imaging system was used for quantitative assessment of flap status over the duration of the experiment.

RESULTS

All flaps demonstrated a significant decline in oxyhemoglobin and tissue oxygen saturation in response to occlusion. Total hemoglobin and deoxyhemoglobin were increased markedly in the selective venous occlusion group. After reperfusion and the administration of solutions, oxyhemoglobin and tissue oxygen saturation in those flaps that survived gradually returned to baseline levels. However, flaps for which oxyhemoglobin and tissue oxygen saturation did not show any signs of recovery appeared to be compromised and eventually became necrotic within 24 to 48 hours in both occlusion groups.

CONCLUSIONS

Spatial frequency domain imaging technology provides a quantitative, objective method of assessing tissue status. This study demonstrates the potential of this optical technology to assess tissue perfusion in a very precise and quantitative way, enabling wide-field visualization of physiologic parameters. The results of this study suggest that spatial frequency domain imaging may provide a means for prospectively identifying dysfunctional flaps well in advance of failure.

Prolonged ischaemia impairs muscle blood flow and oxygen uptake dynamics during subsequent heavy exercise

Muscle oxygen uptake ( ˙VO₂,mus) dynamics at the onset of exercise can be affected by prior heavy exercise.We tested the hypothesis that elevated forearm blood flow (FBF) following prior circulatory occlusion would also be associated with accelerated ˙VO₂,mus dynamics during subsequent heavy hand-grip exercise. Ten trained young men performed 5 min of heavy hand-grip exercise at 30% MVC as a control (CON), and four additional heavy bouts after brief recovery from: (1) prior heavy exercise (Heavy A), (2) heavy exercise followed by 2 min occlusion (Heavy B), (3) 15 min occlusion (Heavy C), and (4) 5 min occlusion with 1 min of moderate exercise during occlusion (Heavy D). FBF was measured by ultrasound and arterial venous oxygen content difference was calculated from venous blood samples to estimate ˙VO₂,mus. FBF and ˙VO₂,mus dynamics were quantified from the rise time. All priming conditions elevated FBF immediately before the start of subsequent heavy bout (Heavy A: 207.4 ±92.8, B: 207.8±75.8, C: 135.8±59.2, D: 199.5±59.0 vs. CON: 57.4±16.6mlmin−1, P <0.01). Unexpectedly, prior occlusion reduced FBF and O2 extraction at the onset of subsequent heavy exercise and consequently slowed ˙VO₂,mus dynamics (Heavy C: rise time=95.9±28.9 vs. CON: 58.6±14.3 s, P <0.01). FBF and ˙VO₂,mus dynamics were faster in Heavy A, B and D compared to CON (P <0.05). Overall, there was a positive correlation between the rise times for ˙VO₂,mus and FBF (r² =0.75) indicating that ˙VO₂,mus dynamics during heavy forearm exercise are linked to O₂ delivery in trained young men. To investigate a possible mechanism for slower adaptation of ˙VO₂,mus following ischaemia, the prior occlusion condition was repeated after ingesting a high dose of ibuprofen. This resulted in restoration of the FBF and ˙VO₂,mus to control levels suggesting that a prostaglandin-mediated mechanism after occlusion retarded the adaptation of blood flow and oxygen consumption at the onset of subsequent heavy exercise.

Early detection of complete vascular occlusion in a pedicle flap model using quantitative [corrected] spectral imaging

BACKGROUND

Vascular occlusion after tissue transfer is a devastating complication that can lead to complete flap loss. Spatial frequency domain imaging is a new, noncontact, noninvasive, wide-field imaging technology capable of quantifying oxygenated and deoxygenated hemoglobin levels, total hemoglobin, and tissue saturation.

METHODS

Pedicled fasciocutaneous flaps on Wistar rats (400 to 500 g) were created and underwent continuous imaging using spatial frequency domain imaging before and after selective vascular occlusion. Three flap groups (control, selective arterial occlusion, and selective venous occlusion) and a fourth group composed of native skin between the flaps were measured.

RESULTS

There were no statistically significant differences between the control flap group and the experimental flap groups before selective vascular occlusion: oxyhemoglobin (p=0.2017), deoxyhemoglobin (p=0.3145), total hemoglobin (p=0.2718), and tissue saturation, (p=0.0777). In the selective arterial occlusion flap group, percentage change in total hemoglobin was statistically different from that of the control flap group (p=0.0218). The remaining parameters were not statistically different from those of the control flap: percentage change in oxyhemoglobin (p=0.0888), percentage change in deoxyhemoglobin (p=0.5198), and percentage change in tissue saturation (p=0.4220). The selective venous occlusion flap group demonstrated changes statistically different compared with the control flap group: percentage change in oxyhemoglobin (p=0.0029) and deoxyhemoglobin, total hemoglobin, and tissue saturation (p<0.0001).

CONCLUSIONS

Spatial frequency domain imaging provides two-dimensional, spatially resolved maps of tissue oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and tissue saturation. Results presented here indicate that this can be used to quantify and detect physiologic changes that occur after arterial and venous occlusion in a rodent tissue transfer flap model. This portable, noncontact, noninvasive device may have a high clinical applicability in monitoring postoperative patients.

Muscle oxygenation of vastus lateralis and medialis muscles during alternating and pulsed current electrical stimulation

This study compared between alternating and pulsed current electrical muscle stimulation (EMS) for muscle oxygenation and blood volume during isometric contractions. Nine healthy men (23-48 years) received alternating current EMS (2500 Hz) modulated at 75 Hz on the knee extensors of one leg, and pulsed current EMS (75 Hz) for the other leg separated by 2 weeks in a randomised, counter-balanced order. Pulse duration (400 μs), on-off ratio (5-15 s) and other stimulation parameters were matched between conditions and 30 isometric contractions were induced at the knee joint angle of 100° (0° full extension). Changes in tissue oxygenation index (∆TOI) and total hemoglobin volume (∆tHb) of vastus lateralis and medialis muscles over 30 contractions were assessed by a near-infrared spectroscopy, and were compared between conditions by a two-way repeated measures ANOVA. Peak torque produced during EMS increased over 30 contractions in response to the increase in the stimulation intensity for pulsed current, but not for the alternating current EMS. The torque during each isometric contraction was less stable in alternating than pulsed current EMS. The changes in ∆TOI amplitude during relaxation phases and ∆tHb amplitude were not significantly different between conditions. However, the decreases in ∆TOI amplitude during contraction phases from baseline were significantly (P < 0.05) greater for the pulsed current than alternating current from the 18th contraction (-15.6 ± 2.3 vs. -8.9 ± 1.8%) to 30th contraction (-10.7 ± 1.8 vs. -4.8 ± 1.5%). These results suggest that the muscles were less activated in the alternating current EMS when compared with the pulsed current EMS.

Spectral and spatial dependence of diffuse optical signals in response to peripheral nerve stimulation

Using non-invasive, near-infrared spectroscopy we have previously reported optical signals measured at or around peripheral nerves in response to their stimulation. Such optical signals featured amplitudes on the order of 0.1% and peaked about 100 ms after peripheral nerve stimulation in human subjects. Here, we report a study of the spatial and spectral dependence of the optical signals induced by stimulation of the human median and sural nerves, and observe that these optical signals are: (1) unlikely due to either dilation or constriction of blood vessels, (2) not associated with capillary bed hemoglobin, (3) likely due to blood vessel(s) displacement, and (4) unlikely due to fiber-skin optical coupling effects. We conclude that the most probable origin of the optical response to peripheral nerve stimulation is from displacement of blood vessels within the optically probed volume, as a result of muscle twitch in adjacent areas.

Tissue hemoglobin index: a non-invasive optical measure of total tissue hemoglobin

INTRODUCTION

The tissue hemoglobin index (THI) is a hemoglobin signal strength metric provided on the InSpectra StO2 Tissue Oxygenation Monitor, Model 650. There is growing interest regarding the physiologic meaning of THI and whether a clinically useful correlation between THI and blood hemoglobin concentration exists. A series of in vitro and in vivo experiments was performed to evaluate whether THI has potential utility beyond its primary purpose of helping InSpectra device users optimally position a StO2 sensor over muscle tissue.

METHODS

The THI and tissue hemoglobin oxygen saturation (StO2) were measured using the InSpectra StO2 Tissue Oxygenation Monitor, Model 650, with a 15 mm optical sensor. A THI normal reference range was established in the thenar eminence (hand) for 434 nonhospitalized human volunteers. In 30 subjects, the thenar THI was also evaluated during 5-minute arterial and venous blood flow occlusions, and with blood volume exsanguination in the hand induced with an Esmarch bandage. In addition, correlation of the THI to blood total hemoglobin concentration (Hbt) was studied in five pigs whose Hbt was isovolumetrically diluted from 13 to 4 g/dl systemically and 0.5 g/dl locally in the hind limb. The sensitivity and specificity of the THI to measure tissue hemoglobin concentration (THC) were characterized in vitro using isolated blood tissue phantoms.

RESULTS

In human thenar tissue, the average THI was 14.1 +/- 1.6 (mean +/- standard deviation). The THI extrapolated to 100% blood volume exsanguination was 3.7 +/- 2.0 units presumably from myoglobin. On average, the THI increased 1.5 +/- 1.0 units with venous occlusion and decreased 4.0 +/- 2.0 units with arterial occlusion. In porcine hind limbs, the THI weakly correlated with Hbt (r2 = 0.26) while DeltaTHI during venous occlusion had a stronger correlation (r2 = 0.62). In vitro tests indicated that THI strongly correlated (r2 > 0.99) to phantom THC and was insensitive to StO2 changes.

CONCLUSIONS

Steady-state THI values do not reliably indicate Hbt. The THI is a reproducible quantitative index for THC, and THI trends can discriminate between arterial or venous blood flow occlusions. The THI magnitude permits the estimation of myoglobin's contribution to StO2.

Cardiac troponin and skeletal muscle oxygenation in severe post-partum haemorrhage

INTRODUCTION

Cardiac troponin has been shown to be elevated in one-half of the parturients admitted for post-partum haemorrhage. The purpose of the study was to assess whether increased cardiac troponin was associated with a simultaneous alteration in haemoglobin tissue oxygen saturation in peripheral muscles in post-partum haemorrhage.

METHODS

Tissue haemoglobin oxygen saturation of thenar eminence muscle (StO2) was measured via near-infrared spectroscopy technology. Two sets of StO2 parameters (both isolated baseline and during forearm ischaemia-reperfusion tests) were collected at two time points: upon intensive care unit admission and prior to intensive care unit discharge. Comparisons were performed using Wilcoxon paired tests, and univariate associations were assessed using logistic regression model and Wald tests.

RESULTS

The 42 studied parturients, admitted for post-partum haemorrhage, had clinical and biological signs of severe blood loss. Initial cardiac troponin I was increased in 24/42 parturients (0.43 +/- 0.60 microrg/l). All measured parameters of muscular haemoglobin oxygen saturation, including Srecovery, were also altered at admission and improved together with improved haemodynamics, when bleeding was controlled. Multivariate analysis showed that muscular Srecovery <3%/second at admission was strongly associated with increased cardiac troponin.

CONCLUSIONS

Our study confirmed the high incidence of increased cardiac troponin, and demonstrated the simultaneous impairment in the reserve of oxygen delivery to peripheral muscles in parturients admitted for severe post-partum haemorrhage.

Monitoring muscle oxygenation after eccentric exercise-induced muscle damage using near-infrared spectroscopy

Eccentric exercise (EE), a common type of muscular activity whereby muscles lengthen and contract simultaneously, is associated with higher levels of force but may also evoke muscle damage. We investigated the hypothesis that unaccustomed EE might impair muscle oxygenation and muscle blood flow in healthy adults. Ten healthy males performed a bout of 70 maximal eccentric contractions of the elbow flexors. Before and after EE on day 1 and over the next 6 days, maximum voluntary isometric torque (MVT), serum creatine kinase (CK), and the changes in muscle oxygen saturation, blood flow, and oxygen uptake (using near-infrared spectroscopy) within the biceps brachii were assessed. MVT decreased, whereas muscle soreness and CK increased after EE (p < 0.05). Mean resting oxygen saturation increased by 22% after acute EE, and remained elevated by 5%–9% for the following 6 days. During isometric contractions, significant decreases were observed in oxygen desaturation and re-saturation kinetics after EE and these declines were also significantly prevalent over the following 6 days. Both muscle blood flow and oxygen uptake increased significantly after acute EE, but recovered on the next day. This study revealed some prolonged alterations in muscle oxygenation at rest and during exercise after EE, which might be due to a decrease in muscle oxygen consumption, an increase in oxygen delivery, and (or) a combination of both. However, both oxygen consumption and blood flow recovered within 24 h after the eccentric exercise session, and therefore, the reason(s) for the changes in tissue oxygen saturation remain unknown.