Transcutaneous oximetry values in chronic ulcer patients during Hyperbaric treatment at 1.4 ATA compared to 2 ATA

Chronic wounds have a significant impact on a patient's quality of life. Different pathologies, such as poor blood supply and tissue breakdown, may lead to inadequate oxygenation of the wound. Hyperbaric oxygen (HBO2) is a widely used treatment for an increasing number of medical practices. A new so-called "hyperbaric treatment" trend has emerged. The use of low-pressure, soft-sided, or inflatable chambers represents a growing trend in hyperbaric medicine. Used in professional settings as well as directly marketed to individuals for home use, they are promoted as equivalent to clinical hyperbaric treatments provided in medical centers. However, these chambers are pressurized to 1.3 atmospheres absolute (ATA) on either air or with an oxygen concentrator, both generate oxygen partial pressures well below those used in approved hyperbaric centers for UHMS-approved indications. A total of 130 consecutive patients with chronic ulcers where tested. TcPO2 was measured near the ulcer area while the patient was breathing 100% O2 at 1.4 ATA for five and 10 minutes. The average TcPO2 at 1.4 ATA after 10 minutes of O2 breathing was 161 mmHg (1-601 mmHg, standard deviation 137.91), compared to 333 mmHg in 2 ATA (1-914±232.56), p < 0.001. Each electrode tested was also statistically significant, both after five minutes of O2 breathing and after 10 minutes. We have not found evidence supporting the claim that 1.4 ATA treatment can benefit a chronic ulcer patient. The field of HBO2 is constantly evolving. We have discovered new ways to treat previously incurable ailments. Nevertheless, it is important to note that new horizons must be examined scientifically, supported by evidence-based data. The actual effect of 1.4 ATA on many ailments is yet to be determined.

The Precision Between Transcutaneous Carbon Dioxide Versus PaCO2 in Infants Undergoing Therapeutic Hypothermia

BACKGROUND

Infants with hypoxic-ischemic encephalopathy are often treated with therapeutic hypothermia and high-frequency ventilation. Fluctuations in PaCO2 during therapeutic hypothermia are associated with poor neurodevelopmental outcomes. Transcutaneous CO2 monitors offer a noninvasive estimate of PaCO2 represented by transcutaneously measured partial pressure of carbon dioxide (PtcCO2 ). We aimed to assess the precision between PtcCO2 and PaCO2 values in neonates undergoing therapeutic hypothermia.

METHODS

This was a retrospective chart review of 10 neonates who underwent therapeutic hypothermia requiring respiratory support over 2 y. A range of 2-27 simultaneous PtcCO2 and PaCO2 pairs of measurements per neonate were analyzed via linear mixed models and a Bland-Altman plot for multiple observations per neonate.

RESULTS

A linear mixed-effect model demonstrated that PtcCO2 and PaCO2 (controlling for sex) were similar. The 95% CI of the mean difference ranged from -2.3 to 5.7 mm Hg (P = .41). However, precision was poor as the PtcCO2 ranged from > 18 mm Hg to < 13 mm Hg than PaCO2 values for 95% of observations.

CONCLUSIONS

The neonates' PtcCO2 was as much as 18 mm Hg higher to 13 mm Hg lower than the PaCO2 95% of the time. Transcutaneous CO2 monitoring may not be a good trending tool, nor is it appropriate for estimating PaCO2 in patients undergoing therapeutic hypothermia.

Test-retest Reliability and Minimal Detectable Change in Exercise Oximetry in Claudicants

BACKGROUND

Exercise transcutaneous oxygen pressure measurement (Exercise-TcPO2) can be used to diagnose Lower Extremity Artery Disease (LEAD) and allows the quantification of limb ischemia during exercise on treadmill. Exercise-TcPO2 test-retest reliability in patients with LEAD and severe walking impairment is unknown. The aim of this study was to evaluate the test-retest reliability, standard error of measurement (SEM), and Minimal Detectable Change (MDC) of exercise-TcPO2 in patients with claudication.

METHODS

Data were collected from patients that performed 2 treadmill tests within a 1-month interval. Delta from Rest of Oxygen Pressure (DROP) values were measured at both buttocks (proximal) and both calves (distal). Test-retest reproducibility was assessed by recording transcutaneous oximetry measurements twice and expressed as SEM and intra-class correlation coefficients. MDC was calculated using the formula MDC = SEM x 1.96 x √ 2.

RESULTS

Twenty eight LEAD patients (61 ± 9 years old) were included. Intra-class correlation coefficients were 0.66 [0.50, 0.79] and 0.65 [0.49, 0.79] for the proximal and distal levels, respectively. The SEM of DROP at the proximal and distal levels were 7 [6, 9] mm Hg and 9 [8, 11] mm Hg, respectively. The SEM for all (proximal and distal) DROP values was 8 [7, 10] mm Hg and the MDC of DROP was 23 mm Hg.

CONCLUSIONS

Exercise-TcPO2 with measurement of DROP values has a moderate test-retest reliability in LEAD patients with a maximal walking distance ≤ 300m. For an individual, an improvement or deterioration in DROP of ≥ 23 mm Hg after an intervention would be required to be 95% confident that the change is significant. It should be considered in evaluating the impact of treatment in patients with claudication.

Sleep disordered breathing assessment in patient with slowly progressive neuromuscular disease

BACKGROUND

Sleep-disordered breathing (SDB) is common in patients with neuromuscular diseases (NMD). Focusing on hypercapnia may lead to the neglect of other SDB such as obstructive and/or central sleep apnea syndrome (SAS). Our objectives were to assess the risk of inappropriate SDB management according to different screening strategies and to evaluate the prevalence and determinants of isolated and overlapping sleep apnea in patients with slowly progressive NMD.

METHODS

This monocentric, cross-sectional, retrospective study analyzed medical records of adult NMD patients referred to a sleep department. Diagnostic strategies, including respiratory polygraphy (RP), nocturnal transcutaneous capnography (tcCO2), and blood gases (BG), were assessed for their performance in diagnosing SDB. Demographics and pulmonary function test results were compared between patients with or without SDB to identify predictors.

RESULTS

Among the 149 patients who underwent a full diagnostic panel (RP + tcCO2 + BG), 109 were diagnosed with SDB. Of these, 33% had isolated SAS, and central apneas were predominant. Using single diagnostic strategies would lead to inappropriate SDB management in two thirds of patients. A combination of 2 diagnostic tools resulted respectively in 21.1, 22.9 and 42.2 % of inappropriate SDB management for RP + tcCO2, RP + BG and tcCO2 + BG.

CONCLUSION

The significant prevalence of sleep apnea syndrome in patients with slowly progressive NMD highlights the need for increased awareness among clinicians. Improved diagnostics involve a systematic approach addressing both sleep apnea and diurnal and nocturnal alveolar hypoventilation to avoid inappropriate management and limit the consequences of SDB.

Use of consecutive transcutaneous oxygen measurement when assessing the need for revascularization and association with the outcomes of ischemic diabetic ulcers

This study compared the ankle-brachial index (ABI) with transcutaneous oxygen pressure (TcPO2 ) in assessing peripheral vascular disease (PVD) prevalence in 100 diabetic foot ulcer (DFU) patients. Patients were categorized into vascular or nonvascular reconstruction groups and underwent both ABI and TcPO2 measurements four times over 6 months. Predictive validity for PVD diagnosis was analysed using the area under the receiver-operating characteristic curve (AUC). The study found TcPO2 to be a superior predictor of PVD than ABI. Among the DFU patients, 51 with abnormal TcPO2 values underwent vascular reconstruction. Only TcPO2 values showed significant pretreatment differences between the groups and increased post-reconstruction. These values declined over a 6-month follow-up, whereas ABI values rose. For those with end-stage renal disease (ESRD), TcPO2 values saw a sharp decrease within 3 months. Pre-reconstruction TcPO2 was notably lower in amputation patients versus limb salvage surgery patients. In conclusion, TcPO2 is more effective than ABI for evaluating ischemic limb perfusion and revascularization necessity. It should be prioritized as the primary follow-up tool, especially for ESRD patients.

TcPO2 Value Can Predict Wound Healing Time in Clinical Practice of CLTI Patients

BACKGROUND

Transcutaneous oxygen pressure (TcPO2) is a noninvasive, nonradiological test to measure local oxygen released from capillaries through the skin. Since it reflects the metabolic state of the lower limb, it can predict wound healing in patients with critical limb threatening ischemia (CLTI). The purpose of this study was to determine the effectiveness of TcPO2 test in evaluating wound healing potential of patients with CLTI.

METHODS

This was a retrospective, single-center, nonrandomized, and observational study. A prospectively registered database of patients who visited Vascular Surgery Department of St. Mary's Hospital for CLTI and underwent TcPO2 tests from October 1, 2015 to July 1, 2021 was reviewed. Patients were divided into 2 groups: (1) those who had amputation only; and (2) those who underwent revascularization procedures. Patients whose wound healing status could not be determined were excluded. The clinical characteristics of patients, patient characteristics related to lower TcPO2 value, treatment success rate, and time for the wound to be healed were analyzed.

RESULTS

A total of 84 patients were included in this study. There was no difference in background patient characteristics between the 2 groups despite better survival within 12 months and shorter healing time in the revascularization group. A total of 76 patients survived 12 months after surgery, and 63 patients were healed. Higher HbA1c, higher serum creatinine, history of stroke, and history of coronary artery disease were related to lower TcPO2 value on multiple linear regression. The cutoff value of TcPO2 was determined to be 40 mm Hg for predicting wound healing. This value was similar to those of previous studies. In addition, there was a negative correlation between TcPO2 and wound healing time. Correlations among the anklebrachial index (ABI), toe-brachial index (TBI), and TcPO2 were not determined because ABI and TBI for some patients could not be obtained due to wound condition.

CONCLUSIONS

The TcPO2 value can predict the wound healing process of ischemic lower extremity injury.

Effect of Different Oxygen Delivery Methods on Transcutaneous Oxygen Pressure and Fraction of Inspired Oxygen During Noninvasive Positive Pressure Ventilation

OBJECTIVE

The aim of this study was to investigate the effects of different oxygen delivery methods during noninvasive positive-pressure ventilation (NPPV) on transcutaneous oxygen pressure (PtcO2), transcutaneous carbon dioxide pressure (PtcCO2) and fraction of inspired oxygen (FiO2) in order to find more effective oxygen delivery methods.

METHODS

A total of 20 healthy volunteers participated in this study, all of whom received NPPV. All volunteers received oxygen through a nasal cannula (NC) located in a mask or through a mask alone (OSTM) (oxygen flow rate was 3L/min and 5L/min), PtcO2 and PtcCO2 were measured, and the effects of the 2 methods of oxygen concentration on PtcO2 and PtcCO2 levels were evaluated during noninvasive ventilation. Then, the additional oxygen concentration was stopped, oxygen was delivered through the ventilator, and the oxygen concentration was adjusted so that the PtcO2 reached the same oxygen concentration level as noted through the NC or OSTM. This concentration of oxygen indirectly reflects FiO2 in different oxygen delivery methods.

RESULTS

When NPPV was used under the same pressure, FiO2 increased from 44.4% to 65.3% when oxygen was delivered through an NC compared with oxygen supplied by OSTM alone. PtcO2 was also significantly increased from 18.9% to 24.9%; the difference was significant (P < .05), while there was no significant change in PtcCO2 (P > .05).

CONCLUSION

When NPPV is used, an NC can obviously improve FiO2 and PtcO2 without increasing PtcCO2. It can save oxygen and is more suitable for NPPV during an emergency and for home use.

Capillary hemodynamics and contracting skeletal muscle oxygen pressures in male rats with heart failure: Impact of soluble guanylyl cyclase activator

In heart failure with reduced ejection fraction (HFrEF), nitric oxide-soluble guanylyl cyclase (sGC) pathway dysfunction impairs skeletal muscle arteriolar vasodilation and thus capillary hemodynamics, contributing to impaired oxygen uptake (V̇O2) kinetics. Targeting this pathway with sGC activators offers a new treatment approach to HFrEF. We tested the hypotheses that sGC activator administration would increase the O2 delivery (Q̇O2)-to-V̇O2 ratio in the skeletal muscle interstitial space (PO2is) of HFrEF rats during twitch contractions due, in part, to increases in red blood cell (RBC) flux (fRBC), velocity (VRBC), and capillary hematocrit (Hctcap). HFrEF was induced in male Sprague-Dawley rats via myocardial infarction. After 3 weeks, rats were treated with 0.3 mg/kg of the sGC activator BAY 60-2770 (HFrEF + BAY; n = 11) or solvent (HFrEF; n = 9) via gavage b.i.d for 5 days prior to phosphorescence quenching (PO2is, in contracting muscle) and intravital microscopy (resting) measurements in the spinotrapezius muscle. Intravital microscopy revealed higher fRBC (70 ± 9 vs 25 ± 8 RBC/s), VRBC (490 ± 43 vs 226 ± 35 μm/s), Hctcap (16 ± 1 vs 10 ± 1%) and a greater number of capillaries supporting flow (91 ± 3 vs 82 ± 3%) in HFrEF + BAY vs HFrEF (all P < 0.05). Additionally, PO2is was especially higher during 12-34s of contractions in HFrEF + BAY vs HFrEF (P < 0.05). Our findings suggest that sGC activators improved resting Q̇O2 via increased fRBC, VRBC, and Hctcap allowing for better Q̇O2-to-V̇O2 matching during the rest-contraction transient, supporting sGC activators as a potential therapeutic to target skeletal muscle vasomotor dysfunction in HFrEF.

Carbon Dioxide Sensing-Biomedical Applications to Human Subjects

Carbon dioxide (CO2) monitoring in human subjects is of crucial importance in medical practice. Transcutaneous monitors based on the Stow-Severinghaus electrode make a good alternative to the painful and risky arterial "blood gases" sampling. Yet, such monitors are not only expensive, but also bulky and continuously drifting, requiring frequent recalibrations by trained medical staff. Aiming at finding alternatives, the full panel of CO2 measurement techniques is thoroughly reviewed. The physicochemical working principle of each sensing technique is given, as well as some typical merit criteria, advantages, and drawbacks. An overview of the main CO2 monitoring methods and sites routinely used in clinical practice is also provided, revealing their constraints and specificities. The reviewed CO2 sensing techniques are then evaluated in view of the latter clinical constraints and transcutaneous sensing coupled to a dye-based fluorescence CO2 sensing seems to offer the best potential for the development of a future non-invasive clinical CO2 monitor.

An Infra-Red-Based Prototype for a Miniaturized Transcutaneous Carbon Dioxide Monitor

New types of miniaturized biomedical devices transform contemporary diagnostic and therapeutic techniques in medicine. This evolution has demonstrated exceptional promise in providing infrastructures for enabling precision health by creating diverse sensing modalities. To this end, this paper presents a prototype for transcutaneous carbon dioxide monitoring to diversify the measurable critical parameters for human health. Transcutaneous carbon dioxide monitoring is a noninvasive, surrogate method of assessing the partial pressure of carbon dioxide in the blood. The partial pressure of carbon dioxide is a vital index that can help understand momentarily changing ventilation trends. Therefore, it needs to be reported continuously to monitor the ventilatory status of critically ill patients. The proposed prototype employs an infrared LED as the excitation source. The infrared emission, which decreases in response to an increasing carbon dioxide concentration, is applied to a thermopile sensor that can detect the infrared intensity variations precisely. We have measured the changes in the partial pressure of carbon dioxide in the range of 0-120 mmHg, which covers humans' typical values, 35-45 mmHg. The prototype occupies an area of 25 cm² (50 mm × 50 mm) and consumes 85 mW power.

Agreement Between Transcutaneous Monitoring and Arterial Blood Gases During COPD Exacerbation

BACKGROUND

Transcutaneous measurements of CO₂ and O₂ ([Formula: see text], [Formula: see text]) are noninvasive and allow for continuous monitoring in adults with exacerbation of COPD, but substantial accuracy issues may exist. We investigated agreement between results of arterial blood gas analysis and transcutaneous measurements of CO₂ and O₂ in patients with COPD.

METHODS

Adult subjects were monitored after acute admission to a respiratory intermediate care unit or ICU due to exacerbation of COPD and with ongoing noninvasive ventilation or immediately following extubation. Monitored variables were continuous transcutaneous measurement and simultaneous routine arterial blood gas analysis. Agreement between measurements was assessed by calculating bias with 95% limits of agreement for single-point estimates of [Formula: see text] versus [Formula: see text] and versus [Formula: see text], and for changes in transcutaneous measurements between 2 time points ([Formula: see text] and [Formula: see text]). We considered limits of agreement within ± 7.5 mm Hg to be acceptable.

RESULTS

A total of 57 transcutaneous measurements were made in 20 subjects for comparison with concurrent arterial blood gas analysis at 36 time points. The bias (limits of agreement) for [Formula: see text] and [Formula: see text] was 2.5 mm Hg (-10.6 to 15.6 mm Hg) and 11.2 mm Hg (-28.2 to 50.6 mm Hg), respectively. The bias for [Formula: see text] and [Formula: see text] was 2.3 mm Hg (-3.8 to 8.3 mm Hg) and -5.3 mm Hg (-37.5 to 27 mm Hg), respectively.

CONCLUSIONS

[Formula: see text] and [Formula: see text] did not accurately reflect results from arterial blood gas analyses in this study of mostly hypercapnic subjects. Agreement between changes in CO₂ during the monitoring period was acceptable, however, and transcutaneous monitoring may be used for continuous monitoring of [Formula: see text] in conjunction with arterial blood gas analysis for reference.

Recent Insights into the Measurement of Carbon Dioxide Concentrations for Clinical Practice in Respiratory Medicine

In the field of respiratory clinical practice, the importance of measuring carbon dioxide (CO2) concentrations cannot be overemphasized. Within the body, assessment of the arterial partial pressure of CO2 (PaCO2) has been the gold standard for many decades. Non-invasive assessments are usually predicated on the measurement of CO2 concentrations in the air, usually using an infrared analyzer, and these data are clearly important regarding climate changes as well as regulations of air quality in buildings to ascertain adequate ventilation. Measurements of CO2 production with oxygen consumption yield important indices such as the respiratory quotient and estimates of energy expenditure, which may be used for further investigation in the various fields of metabolism, obesity, sleep disorders, and lifestyle-related issues. Measures of PaCO2 are nowadays performed using the Severinghaus electrode in arterial blood or in arterialized capillary blood, while the same electrode system has been modified to enable relatively accurate non-invasive monitoring of the transcutaneous partial pressure of CO2 (PtcCO2). PtcCO2 monitoring during sleep can be helpful for evaluating sleep apnea syndrome, particularly in children. End-tidal PCO2 is inferior to PtcCO2 as far as accuracy, but it provides breath-by-breath estimates of respiratory gas exchange, while PtcCO2 reflects temporal trends in alveolar ventilation. The frequency of monitoring end-tidal PCO2 has markedly increased in light of its multiple applications (e.g., verify endotracheal intubation, anesthesia or mechanical ventilation, exercise testing, respiratory patterning during sleep, etc.).

Measuring hemoglobin spectra: searching for carbamino-hemoglobin

SIGNIFICANCE

The arterial carbon dioxide (CO2) partial pressure PaCO2 is a clinically relevant variable. However, its measurement requires arterial blood sampling or bulky and expensive transcutaneous PtcCO2 meters. While the spectrophotometric determination of hemoglobin species-such as oxy-hemoglobin (O2Hb) and deoxy-hemoglobin (HHb)-allowed for the development of pulse oximetry, the measurement of CO2 blood content with minimal discomfort has not been addressed yet.

AIM

Characterizing human carbamino-hemoglobin (CO2Hb) absorption spectrum, which is missing from the literature. Providing the theoretical background that will allow for transcutaneous, noninvasive PaCO2 measurements.

APPROACH

A tonometry-based approach was used to obtain gas-equilibrated, lysed, diluted human blood. Equilibration was performed with both CO2, dinitrogen (N2), and ambient air. Spectrophotometric measurements were carried out on the 235- to 1000-nm range. A theoretical background was also derived from that of pulse oximetry.

RESULTS

The absorption spectra of both CO2Hb and HHb were extremely close and comparable with that of state-of-the-art HHb. The above-mentioned theoretical background led to an estimated relative error above 30% on the measured amount of CO2Hb in a subject's blood. Auxiliary measurements revealed that the use of ethylene diamine tetraacetic acid did not interfere with spectrophotometric measurements, whereas sodium metabisulfite did.

CONCLUSIONS

CO2Hb absorption spectrum was measured for the first time. Such spectrum being close to that of HHb, the use of a theoretical background based on pulse oximetry theory for noninvasive PaCO2 measurement seems extremely challenging.

Artificial intelligence mobile health platform for early detection of COVID-19 in quarantine subjects using a wearable biosensor: protocol for a randomised controlled trial

INTRODUCTION

There is an outbreak of COVID-19 worldwide. As there is no effective therapy or vaccine yet, rigorous implementation of traditional public health measures such as isolation and quarantine remains the most effective tool to control the outbreak. When an asymptomatic individual with COVID-19 exposure is being quarantined, it is necessary to perform temperature and symptom surveillance. As such surveillance is intermittent in nature and highly dependent on self-discipline, it has limited effectiveness. Advances in biosensor technologies made it possible to continuously monitor physiological parameters using wearable biosensors with a variety of form factors.

OBJECTIVE

To explore the potential of using wearable biosensors to continuously monitor multidimensional physiological parameters for early detection of COVID-19 clinical progression.

METHOD

This randomised controlled open-labelled trial will involve 200-1000 asymptomatic subjects with close COVID-19 contact under mandatory quarantine at designated facilities in Hong Kong. Subjects will be randomised to receive a remote monitoring strategy (intervention group) or standard strategy (control group) in a 1:1 ratio during the 14 day-quarantine period. In addition to fever and symptom surveillance in the control group, subjects in the intervention group will wear wearable biosensors on their arms to continuously monitor skin temperature, respiratory rate, blood pressure, pulse rate, blood oxygen saturation and daily activities. These physiological parameters will be transferred in real time to a smartphone application called Biovitals Sentinel. These data will then be processed using a cloud-based multivariate physiology analytics engine called Biovitals to detect subtle physiological changes. The results will be displayed on a web-based dashboard for clinicians' review. The primary outcome is the time to diagnosis of COVID-19.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from institutional review boards at the study sites. Results will be published in peer-reviewed journals.

A Simple Scale for Screening Lower-Extremity Arterial Disease as a Possible Cause of Low Back Pain: a Cross-sectional Study Among 542 Subjects

BACKGROUND

Epidemiological, imaging, and anatomical studies suggest an association between proximal arterial atherosclerosis and development of low back pain (LBP).

OBJECTIVES

We aimed to define (1) the frequency and (2) factors associated with exercise-induced proximal ischemia (EIPI) in individuals with LBP and (3) develop a clinical screening scale.

DESIGN

Monocentric cross-sectional study.

PARTICIPANTS

All patients with history of ongoing LBP referred to our exercise investigation laboratory for exercise transcutaneous oximetry (ex-tcPO₂) between January 2011 and December 2017 (n = 542; mean age, 65.4 ± 10.9; 83.9% men).

MAIN MEASURES

EIPI was defined as a decrease from rest of oxygen pressure (DROP) below - 15 mmHg on the lumbar and/or buttock probes. Ex-tcPO₂ is a reliable validated tool for diagnosing EIPI in comparison with arteriography and computed tomography angiography. Ex-tcPO₂ was performed on a treadmill until symptom manifestation or exhaustion. Clinical data were collected using interview questionnaires, medical file review, and clinical examination.

KEY RESULTS

EIPI was diagnosed in 282 patients (52%). Age ≤ 70 years (OR, 2.22; 95% CI, 1.35-3.57; p = 0.002), a history of proximal revascularization (OR, 2.64; 95% CI, 1.50-4.65; p = 0.001), use of antiplatelet medication (OR, 1.71; 95% CI, 0.96-3.06; p = 0.069), a relationship between exercise and LBP (OR, 2.61; 95% CI, 1.49-4.57; p = 0.001), and an abnormal ankle to brachial index (OR, 2.87; 95% CI, 1.77-4.66; p < 0.0001) were identified as EIPI predictors. Using these items, we developed a screening scale that showed an area under the receiver operating characteristics curve of .756. At a score of ≥ 3, the sensitivity, specificity, and accuracy for EIPI were 84%, 55%, and 71%, respectively.

CONCLUSIONS

EIPI was common among our patients with LBP undergoing ex-TcPO₂. Our screening scale could help better select the patients who require angiography.

First Evaluation of a Transcutaneous Carbon Dioxide Monitoring Wristband Device during a Cardiopulmonary Exercise Test

We introduce an innovative wristband wireless device based on a dual wavelength NDIR optical measurement and an optimized thermo-fluidic channel to improve the extraction of the carbon dioxide gas from the blood within the heated skin region. We describe a signal processing model combining an innovative linear quadratic model of the optical measurement and a fluidic model. The evaluation is achieved using a cardiopulmonary exercise test (CPET). We compare carbon dioxide tension measurement at the forearm level using our device, with an electrochemical measurement at the forearm level, and an optical measurement of the end-tidal exhaled breath. These curves demonstrate a significant reduction of the variability of carbon dioxide pressure measurement with respect to the pressure dynamic range during the test.

The effect of 50% oxygen on PtCO2 in patients with stable COPD, bronchiectasis, and neuromuscular disease or kyphoscoliosis: randomised cross-over trials

BACKGROUND

High-concentration oxygen therapy causes increased arterial partial pressure of carbon dioxide (PaCO2) in patients with COPD, asthma, pneumonia, obesity and acute lung injury. The objective of these studies was to investigate whether this physiological response to oxygen therapy occurs in stable patients with neuromuscular disease or kyphoscoliosis, and bronchiectasis.

METHODS

Three randomised cross-over trials recruited stable patients with neuromuscular disease or kyphoscoliosis (n = 20), bronchiectasis (n = 24), and COPD (n = 24). Participants were randomised to receive 50% oxygen and 21% oxygen (air), each for 30 min, in randomly assigned order. The primary outcome was transcutaneous partial pressure of carbon dioxide (PtCO2) at 30 min. The primary analysis was a mixed linear model.

RESULTS

Sixty six of the 68 participants had baseline PtCO2 values < 45 mmHg. The intervention baseline adjusted PtCO2 difference (95% CI) between oxygen and room air after 30 min was 0.2 mmHg (- 0.4 to 0.9), P = 0.40; 0.5 mmHg (- 0.2 to 1.2), P = 0.18; and 1.3 mmHg (0.7 to 1.8), P < 0.001, in the neuromuscular/kyphoscoliosis, bronchiectasis and COPD participants respectively.

CONCLUSIONS

The small increase in PtCO2 in the stable COPD patients with high-concentration oxygen therapy contrasts with the marked increases in PaCO2 seen in the setting of acute exacerbations of COPD. This suggests that the model of studying the effects of high-concentration oxygen therapy in patients with stable respiratory disease is not generalisable to the use of oxygen therapy in the acute clinical setting. Appropriate studies of high-concentration compared to titrated oxygen in acute clinical settings are needed to determine if there is a risk of oxygen-induced hypercapnia in patients with neuromuscular disease, kyphoscoliosis or bronchiectasis.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12615000970549 Registered 16/9/15, ACTRN12615000971538 Registered 16/9/15 and ACTRN12615001056583 Registered 7/10/15.

Transcutaneous carbon dioxide monitoring as a predictive tool for all-cause 6-month mortality after acute pulmonary embolism

BACKGROUND

Pulmonary embolism (PE) frequently remains undiagnosed. The partial pressure of carbon dioxide (Pa_CO2)_, a surrogate of dead-space ventilation, is useful in the evaluation of the degree of pulmonary artery occlusion. At present, there is no knowledge about the prognostic role of Pa_CΟ2 variations during the first hours of an acute PE. Transcutaneous measurement of CO₂ (Ptc_CO2) is a simple, non-invasive method that correlates well with Pa_CO2 levels, evaluated in this study for the first time in patients with PE.

PURPOSE

To assess the correlation between Ptc_CO2 and Pa_CO2 levels in the acute phase of PE and the role of Ptc_CO2 in predicting 6-months mortality.

METHODS

This was a pilot study including 53 patients with acute PE who hospitalized in Respiratory Medicine Department at University Hospital of Larissa in central Greece during 15 months. Ptc_CO2 was constantly monitored for four hours after PE diagnosis with the TCM40 monitoring system (SmartCal). Simultaneous arterial blood gas measurements were performed. Each patient was prospectively recorded for six months via standard telephone calls.

RESULTS

Pa_CO2 and Ptc_CO2 values were well-correlated in the acute phase of PE. Decreased Ptc_CO2 levels in the first monitoring hour were associated with a higher risk of mortality. In the PE subgroup who died, the lower Ptc_CO2 level in the first hour of PE was a predictor of shorter survival time independently of gender, age, comorbidities, and smoking status.

CONCLUSION

Ptc_CO2 measurement, especially in the first hour after PE, seemed to be a valid tool in predicting all-cause 6-month mortality.

Influence of Peripheral Neuropathy and Microangiopathy on Skin Hydration in the Feet of Patients With Diabetes Mellitus

INTRODUCTION

Maintaining adequate skin hydration is crucial in the feet of patients with diabetes because xerotic skin may crack and develop fissures, thereby increasing vulnerability to ulceration and infection. The nervous system is considered the powerhouse for maintaining adequate skin hydration; however, no clinical study has assessed the effect of the nervous system on skin hydration. In addition, it is hypothesized that microcirculation may play an important role in maintaining adequate hydration in patients with diabetes.

OBJECTIVE

This study aims to evaluate the influence of peripheral nerve function and microvascularity on skin hydration in the feet of patients with diabetes mellitus and compare the effects of these 2 functions on skin hydration.

MATERIALS AND METHODS

This study included 266 patients with diabetic foot disease. Skin hydration was evaluated using corneometry and microvascularity by measuring the transcutaneous oximetry (TcpO₂) of the foot. The Semmes-Weinstein 5.07/10-g monofilament test, electromyography, and nerve conduction velocity test were conducted to evaluate peripheral neuropathy. Patient data were divided into 3 subgroups according to test values, and statistical comparisons were performed using the linear-by-linear association trend and Pearson's chi-square tests.

RESULTS

There was a significant correlation between skin hydration and TcpO₂. However, there was no significant correlation between skin hydration and peripheral nerve function (P = .338).

CONCLUSIONS

The results of this study demonstrated that skin hydration in the feet of patients with diabetes mellitus mainly is influenced by microcirculation rather than peripheral nerve function.

Exercise testing criteria to diagnose lower extremity peripheral artery disease assessed by computed-tomography angiography

BACKGROUND

The sensitivity and specificity of exercise testing have never been studied simultaneously against an objective quantification of arterial stenosis. Aims were to define the sensitivity and specificity of several exercise tests to detect peripheral artery disease (PAD), and to assess whether or not defined criteria defined in patients suspected of having a PAD show a difference dependent on the resting ABI.

METHODS

In this prospective study, consecutive patients with exertional limb pain referred to our vascular center were included. All patients had an ABI, a treadmill exercise-oximetry test, a second treadmill test (both 10% slope; 3.2km/h speed) with post-exercise pressures, and a computed-tomography-angiography (CTA). The receiver-operating-characteristic curve was used to define a cut-off point corresponding to the best area under the curve (AUC; [CI95%]) to detect arterial stenosis ≥50% as determined by the CTA.

RESULTS

Sixty-three patients (61+/-11 years-old) were included. Similar AUCs from 0.72[0.63-0.79] to 0.83[0.75-0.89] were found for the different tests in the overall population. To detect arterial stenosis ≥50%, cut-off values of ABI, post-exercise ABI, post-exercise ABI decrease, post-exercise ankle pressure decrease, and distal delta from rest oxygen pressure (DROP) index were ≤0.91, ≤0.52, ≥43%, ≥20mmHg and ≤-15mmHg, respectively (p<0.01). In the subset of patients with an ABI >0.91, cut-off values of post-exercise ABI decrease (AUC = 0.67[0.53-0.78]), and DROP (AUC = 0.67[0.53-0.78]) were ≥18.5%, and ≤-15mmHg respectively (p<0.05).

CONCLUSION

Resting ABI is as accurate as exercise testing in patients with exertional limb pain. Specific exercise testing cut-off values should be used in patients with normal ABI to diagnose PAD.

Agreement of clinical tests for the diagnosis of peripheral arterial disease

AIM

The aim of this study was to compare different screening modalities in the detection of PAD in a primary care setting.

METHODS

Fifty participants living with Type 2 diabetes were recruited. Pulse palpation, waveform analysis, ankle brachial pressure index, absolute toe pressure, toe brachial pressure index and transcutaneous oxygen pressure were compared in the detection of peripheral arterial disease. One hundred limbs were included for analysis.

RESULTS

This study showed different results in peripheral arterial disease screening tests in the same group of participants. The highest percentage of participants who had PAD was for the Doppler Waveform (93.0%). This was followed by TBPI (72.0%), ABPI (57.0%), ATP (35.0%), TCPO (30.0%) and pulse palpation (23.0%). The difference between these percentages is significant (p<0.0005). The magnitude of the effect size is medium/moderate (Cramer's V=0.498).

CONCLUSION

This study demonstrates that inconsistencies exist between the agreement of the 6 different modalities used to detect PAD. These findings should create an awareness amongst clinicians when interpreting results of these tests. The authors advocate for urgent, more robust studies utilizing a gold standard modality for the diagnosis of PAD in order to provide evidence regarding which screening modalities would yield the most valid results.

The association of diabetic microvascular and macrovascular disease with cutaneous circulation in patients with type 2 diabetes mellitus

AIMS

To study the impact of diabetic neuropathy, both peripheral sensorimotor (DPN) and cardiac autonomic neuropathy (CAN), on transcutaneous oxygen tension (TcPO₂) in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 163 participants were recruited; 100 with T2DM and 63 healthy individuals. Peripheral arterial disease (PAD) was defined as ankle-brachial index (ABI) values ≤0.90. Diagnosis of DPN was based on neuropathy symptom score and neuropathy disability score (NDS), while diagnosis of CAN on the battery of the cardiovascular autonomic function tests. TcPO₂ was measured using a TCM30 system.

RESULTS

Patients with T2DM had lower TcPO₂ levels when compared with healthy individuals. Among the diabetic cohort, those who had either PAD, DPN or CAN had significantly lower TcPO₂ values than participants without these complications. Multivariate linear regression analysis, after controlling for diabetes duration, diastolic blood pressure, HbA1c, albumin to creatinine ratio and CAN score, demonstrated that TcPO₂ levels were significantly and independently associated with current smoking (p = 0.013), ABI (p = 0.003), and NDS (p = 0.013).

CONCLUSION

Presence of DPN is independently associated with impaired cutaneous perfusion. Low TcPO₂ in subjects with DPN may contribute to delay in healing of diabetic foot ulcers, irrespectively of PAD.

Transmucosal oxygen tension of the clitoris: a new parameter for future investigations of the sexual, metabolic, and cardiovascular health of women

BACKGROUND

Several studies suggested that abnormalities in tissue perfusion of external genitalia and vagina can lead to female sexual dysfunctions (FSDs) and can be associated to metabolic and cardiovascular risk factors. However, there are some technical difficulties in assessing these abnormalities. The measurement of oxygen partial pressure is a noninvasive method to measure oxygen partial pressure (pO₂) at the skin surface to assess tissue perfusion. The aim of this study was to evaluate whether transmucosal oxygen tension (TmPO₂) can be measured at the mucosal surface of clitoris and whether the measurements are reliable.

METHODS

TmPO₂ was measured in six young healthy women by using a device to measure transcutaneous pO₂ on the skin and by choosing a small sensor, usually used for newborns. The identical procedure for the detection of pO₂ at the skin surface was used.

RESULTS

The mean value of TmPO₂ was 42.3 mmHg (range: 24.1-53.4 mmHg). All the trend curves of the TmPO₂ showed the same behavior: after a stabilization time, there was a stable pO₂ (plateau phase) that corresponds to the TmPO₂ of the clitoris. These curves had a similar trend to those recorded at the skin surface.

CONCLUSIONS

TmPO₂ can be easily measured at the mucosal surface of clitoris. Large epidemiological studies in healthy and unhealthy women and in women with FSD are needed to establish both the normal range of TmPO₂ and the meaning that different values of TmPO₂ can have on sexual and general health of the women.

Oxygen versus air-driven nebulisers for exacerbations of chronic obstructive pulmonary disease: a randomised controlled trial

BACKGROUND

In exacerbations of chronic obstructive pulmonary disease, administration of high concentrations of oxygen may cause hypercapnia and increase mortality compared with oxygen titrated, if required, to achieve an oxygen saturation of 88-92%. Optimally titrated oxygen regimens require two components: titrated supplemental oxygen to achieve the target oxygen saturation and, if required, bronchodilators delivered by air-driven nebulisation. The effect of repeated air vs oxygen-driven bronchodilator nebulisation in acute exacerbations of chronic obstructive pulmonary disease is unknown. We aimed to compare the effects of air versus oxygen-driven bronchodilator nebulisation on arterial carbon dioxide tension in exacerbations of chronic obstructive pulmonary disease.

METHODS

A parallel group double-blind randomised controlled trial in 90 hospital in-patients with an acute exacerbation of COPD. Participants were randomised to receive two 2.5 mg salbutamol nebulisers, both driven by air or oxygen at 8 L/min, each delivered over 15 min with a 5 min interval in-between. The primary outcome measure was the transcutaneous partial pressure of carbon dioxide at the end of the second nebulisation (35 min). The primary analysis used a mixed linear model with fixed effects of the baseline PtCO2, time, the randomised intervention, and a time by intervention interaction term; to estimate the difference between randomised treatments at 35 min. Analysis was by intention-to-treat.

RESULTS

Oxygen-driven nebulisation was terminated in one participant after 27 min when the PtCO2 rose by > 10 mmHg, a predefined safety criterion. The mean (standard deviation) change in PtCO2 at 35 min was 3.4 (1.9) mmHg and 0.1 (1.4) mmHg in the oxygen and air groups respectively, difference (95% confidence interval) 3.3 mmHg (2.7 to 3.9), p < 0.001. The proportion of patients with a PtCO2 change ≥4 mmHg during the intervention was 18/45 (40%) and 0/44 (0%) for oxygen and air groups respectively.

CONCLUSIONS

Oxygen-driven nebulisation leads to an increase in PtCO2 in exacerbations of COPD. We propose that air-driven bronchodilator nebulisation is preferable to oxygen-driven nebulisation in exacerbations of COPD.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry number ACTRN12615000389505 . Registration confirmed on 28/4/15.