Obesity is associated with a lower resting oxygen saturation in the ambulatory elderly: results from the cardiovascular health study

Impact of nocturnal hypoxia on glycaemic control, appetite, gut microbiota and inflammation in adults with type 2 diabetes mellitus: A single-blind cross-over trial

High altitude residents have a lower incidence of type 2 diabetes mellitus (T2DM). Therefore, we examined the effect of repeated overnight normobaric hypoxic exposure on glycaemic control, appetite, gut microbiota and inflammation in adults with T2DM. Thirteen adults with T2DM [glycated haemoglobin (HbA1c): 61.1 ± 14.1 mmol mol-1; aged 64.2 ± 9.4 years; four female] completed a single-blind, randomised, sham-controlled, cross-over study for 10 nights, sleeping when exposed to hypoxia (fractional inspired O2 [F I O 2 ${{F}_{{\mathrm{I}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$ ] = 0.155; ∼2500 m simulated altitude) or normoxic conditions (F I O 2 ${{F}_{{\mathrm{I}}{{{\mathrm{O}}}_{\mathrm{2}}}}}$  = 0.209) in a randomised order. Outcome measures included: fasted plasma [glucose]; [hypoxia inducible factor-1α]; [interleukin-6]; [tumour necrosis factor-α]; [interleukin-10]; [heat shock protein 70]; [butyric acid]; peak plasma [glucose] and insulin sensitivity following a 2 h oral glucose tolerance test; body composition; appetite indices ([leptin], [acyl ghrelin], [peptide YY], [glucagon-like peptide-1]); and gut microbiota diversity and abundance [16S rRNA amplicon sequencing]. During intervention periods, accelerometers measured physical activity, sleep duration and efficiency, whereas continuous glucose monitors were used to assess estimated HbA1c and glucose management indicator and time in target range. Overnight hypoxia was not associated with changes in any outcome measure (P > 0.05 with small effect sizes) except fasting insulin sensitivity and gut microbiota alpha diversity, which exhibited trends (P = 0.10; P = 0.08 respectively) for a medium beneficial effect (d = 0.49; d = 0.59 respectively). Ten nights of overnight moderate hypoxic exposure did not significantly affect glycaemic control, gut microbiome, appetite, or inflammation in adults with T2DM. However, the intervention was well tolerated and a medium effect-size for improved insulin sensitivity and reduced alpha diversity warrants further investigation. KEY POINTS: Living at altitude lowers the incidence of type 2 diabetes mellitus (T2DM). Animal studies suggest that exposure to hypoxia may lead to weight loss and suppressed appetite. In a single-blind, randomised sham-controlled, cross-over trial, we assessed the effects of 10 nights of hypoxia (fractional inspired O2 ∼0.155) on glucose homeostasis, appetite, gut microbiota, inflammatory stress ([interleukin-6]; [tumour necrosis factor-α]; [interleukin-10]) and hypoxic stress ([hypoxia inducible factor 1α]; heat shock protein 70]) in 13 adults with T2DM. Appetite and inflammatory markers were unchanged following hypoxic exposure, but an increased insulin sensitivity and reduced gut microbiota alpha diversity were associated with a medium effect-size and statistical trends, which warrant further investigation using a definitive large randomised controlled trial. Hypoxic exposure may represent a viable therapeutic intervention in people with T2DM and particularly those unable or unwilling to exercise because barriers to uptake and adherence may be lower than for other lifestyle interventions (e.g. diet and exercise).

Home Oxygen After Hospitalization for COVID-19: Results From the Multi-Center OXFORD Study

BACKGROUND

In the first months of the pandemic, prior to the introduction of proven-effective treatments, 15-37% of patients hospitalized with COVID-19 were discharged on home oxygen. After proven-effective treatments for acute COVID-19 were established by evidence-based guidelines, little remains known about home oxygen requirements following hospitalization for COVID-19.

METHODS

This was a retrospective, multi-center cohort study of subjects hospitalized for COVID-19 between October 2020-September 2021 at 3 academic health centers. Information was abstracted from electronic health records at the index hospitalization and for 60 d after discharge. The World Health Organization COVID-19 Clinical Progression Scale score was used to identify patients with severe COVID-19.

RESULTS

Of 517 subjects (mean age 58 y, 47% female, 42% Black, 36% Hispanic, 22% with severe COVID-19), 81% were treated with systemic corticosteroids, 61% with remdesivir, and 2.5% with tocilizumab. About one quarter of subjects were discharged on home oxygen (26% [95% CI 22-29]). Older age (adjusted odds ratio [aOR] 1.02 per 5 y [95% CI 1.02-1.02]), higher body mass index (aOR 1.02 per kg/m2 [1.00-1.04]), diabetes (yes vs no, aOR 1.73 [1.46-2.02]), severe COVID-19 (vs moderate, aOR 3.19 [2.19-4.64]), and treatment with systemic corticosteroids (yes vs no, aOR 30.63 [4.51-208.17]) were associated with an increased odds of discharge on home oxygen. Comorbid hypertension (yes vs no, aOR 0.71 [0.66-0.77) was associated with a decreased odds of home oxygen. Within 60 d of hospital discharge, 50% had documentation of pulse oximetry; in this group, home oxygen was discontinued in 46%.

CONCLUSIONS

About one in 4 subjects were prescribed home oxygen after hospitalization for COVID-19, even after guidelines established proven-effective treatments for acute illness. Evidence-based strategies to reduce the requirement for home oxygen in patients hospitalized for COVID-19 are needed.

Pulse oximetry values from 33,080 participants in the Apple Heart & Movement Study

Wearable devices that include pulse oximetry (SpO₂) sensing afford the opportunity to capture oxygen saturation measurements from large cohorts under naturalistic conditions. We report here a cross-sectional analysis of 72 million SpO₂ values collected from 33,080 individual participants in the Apple Heart and Movement Study, stratified by age, sex, body mass index (BMI), home altitude, and other demographic variables. Measurements aggregated by hour of day into 24-h SpO₂ profiles exhibit similar circadian patterns for all demographic groups, being approximately sinusoidal with nadir near midnight local time, zenith near noon local time, and mean 0.8% lower saturation during overnight hours. Using SpO₂ measurements averaged for each subject into mean nocturnal and daytime SpO₂ values, we employ multivariate ordinary least squares regression to quantify population-level trends according to demographic factors. For the full cohort, regression coefficients obtained from models fit to daytime SpO₂ are in close quantitative agreement with the corresponding values from published reference models for awake arterial oxygen saturation measured under controlled laboratory conditions. Regression models stratified by sex reveal significantly different age- and BMI-dependent SpO₂ trends for females compared with males, although constant terms and regression coefficients for altitude do not differ between sexes. Incorporating categorical variables encoding self-reported race/ethnicity into the full-cohort regression models identifies small but statistically significant differences in daytime SpO₂ (largest coefficient corresponding to 0.13% lower SpO₂, for Hispanic study participants compared to White participants), but no significant differences between groups for nocturnal SpO₂. Additional stratified analysis comparing regression models fit independently to subjects in each race/ethnicity group is suggestive of small differences in age- and sex-dependent trends, but indicates no significant difference in constant terms between any race/ethnicity groups for either daytime or nocturnal SpO₂. The large diverse study population and study design employing automated background SpO₂ measurements spanning the full 24-h circadian cycle enables the establishment of healthy population reference trends outside of clinical settings.

Effect of different levels of acute hypoxia on subsequent oral glucose tolerance in males with overweight: A balanced cross-over pilot feasibility study

Previous research has shown that ≤60 min hypoxic exposure improves subsequent glycaemic control, but the optimal level of hypoxia is unknown and data are lacking from individuals with overweight. We undertook a cross-over pilot feasibility study investigating the effect of 60-min prior resting exposure to different inspired oxygen fractions (CON F_I O₂  = 0.209; HIGH F_I O₂  = 0.155; VHIGH F_I O₂  = 0.125) on glycaemic control, insulin sensitivity, and oxidative stress during a subsequent oral glucose tolerance test (OGTT) in males with overweight (mean (SD) BMI = 27.6 (1.3) kg/m² ; n = 12). Feasibility was defined by exceeding predefined withdrawal criteria for peripheral blood oxygen saturation (SpO₂ ), partial pressure of end-tidal oxygen or carbon dioxide and acute mountain sickness (AMS), and dyspnoea symptomology. Hypoxia reduced SpO₂ in a stepwise manner (CON = 97(1)%; HIGH = 91(1)%; VHIGH = 81(3)%, p < 0.001), but did not affect peak plasma glucose concentration (CON = 7.5(1.8) mmol∙L^-1 ; HIGH = 7.7(1.1) mmol∙L^-1 ; VHIGH = 7.7(1.1) mmol∙L^-1 ; p = 0.777; η²  = 0.013), plasma glucose area under the curve, insulin sensitivity, or metabolic clearance rate of glucose (p > 0.05). We observed no between-conditions differences in oxidative stress (p > 0.05), but dyspnoea and AMS symptoms increased in VHIGH (p < 0.05), with one participant meeting the withdrawal criteria. Acute HIGH or VHIGH exposure prior to an OGTT does not influence glucose homeostasis in males with overweight, but VHIGH is associated with adverse symptomology and reduced feasibility.

Diet-induced obesity leads to sleep fragmentation independently of the severity of sleep-disordered breathing

Obesity is associated with sleep-disordered breathing (SDB) and unrefreshing sleep. Residual daytime sleepiness and sleep impairments often persist after SDB treatment in patients with obesity, which suggests an independent effect of obesity on breathing and sleep. However, examining the relationship between sleep architecture and SDB in patients with obesity is complex and can be confounded by multiple factors. The main goal of this study was to examine the relationship between obesity-related changes in sleep architecture and SDB. Sleep recordings were performed in 15 lean C57BL/6J and 17 diet-induced obesity (DIO) mice of the same genetic background. Arousals from sleep and apneas were manually scored. Respiratory arousals were classified as events associated with ≥30% drops in minute ventilation (VE) from baseline. We applied Poincaré analysis of VE during sleep to estimate breathing variability. Obesity augmented the frequency of arousals by 45% and this increase was independent of apneas. Respiratory arousals comprised only 15% of the arousals in both groups of mice. Breathing variability during non-rapid-eye-movment (NREM) sleep was significantly higher in DIO mice, but it was not associated with arousal frequency. Our results suggest that obesity induces sleep fragmentation independently of SDB severity.NEW & NOTEWORTHY Our diet-induced obesity (DIO) model reproduces sleep features of human obesity, including sleep fragmentation, increased apnea frequency, and larger breathing variability. DIO induces sleep fragmentation independently of apnea severity. Sleep fragmentation in DIO mice is mainly attributed to non-respiratory arousals. Increased breathing variability during sleep did not account for the higher arousal frequency in DIO. Our results provide a rationale to examine sleep in patients with obesity even when they are adequately treated for sleep-disordered breathing.

Accuracy of Oxygen Saturation Measurements in Patients with Obesity Undergoing Bariatric Surgery

BACKGROUND

We aimed to determine the magnitude, direction, and influencing factors of the concordance between arterial oxygen saturation (SaO₂) and peripheral capillary oxygen saturation (SpO₂) in patients with obesity undergoing bariatric surgery, supporting the measurement of SaO₂ and SpO₂ in key populations.

METHODS

Patients with obesity undergoing bariatric surgery from 2017 to 2020 were included. Preoperative SpO₂ and SaO₂ were collected. Linear correlation and multiple linear regression analyses were performed to characterize the relationships between body mass index (BMI), age, and sex with pulse oximetry and arterial blood gas (ABG) parameters. Bland-Altman analysis was applied to determine the concordance between SpO₂ and SaO₂ and the limits of this concordance.

RESULTS

A total of 134 patients with obesity undergoing bariatric surgery were enrolled. SaO₂ was negatively associated with BMI (p < 0.0001) and age (p = 0.006), and SpO₂ was negatively associated with BMI (p = 0.021) but not with age. SpO₂ overestimated SaO₂ in 91% of patients with a bias of 2.05%. This bias increased by 203% in hypoxemic patients compared with nonhypoxemic patients (p < 0.0001). The bias was 1.3-fold higher (p = 0.023) in patients with a high obesity surgery mortality risk score (OS-MRS) than in those with low or intermediate scores.

CONCLUSION

Compared with SpO₂, preoperative SaO₂ can more accurately reflect the real oxygen saturation in patients with obesity undergoing bariatric surgery, especially for those with BMI ≥ 40 kg/m², age ≥ 40 years, and high OS-MRS. ABG analysis can provide a more reliable basis for accurate and timely monitoring, ensuring the perioperative safety of susceptible patients.

Abdominal obesity phenotype is associated with COVID-19 chest X-ray severity score better than BMI-based obesity

PURPOSE

Chest X-ray (CXR) severity score and BMI-based obesity are predictive risk factors for COVID-19 hospital admission. However, the relationship between abdominal obesity and CXR severity score has not yet been fully explored.

METHODS

This retrospective cohort study analyzed the association of different adiposity indexes, including waist circumference and body mass index (BMI), with CXR severity score in 215 hospitalized patients with COVID-19.

RESULTS

Patients with abdominal obesity showed significantly higher CXR severity scores and had higher rates of CXR severity scores ≥ 8 compared to those without abdominal obesity (P < 0.001; P = 0.001, respectively). By contrast, patients with normal weight, with overweight and those with BMI-based obesity showed no significant differences in either CXR severity scores or in the rates of CXR severity scores ≥ 8 (P = 0.104; P = 0.271, respectively). Waist circumference and waist-to-height ratio (WHtR) correlated more closely with CXR severity scores than BMI (r = 0.43, P < 0.001; r = 0.41, P < 0.001; r = 0.17, P = 0.012, respectively). The area under the curves (AUCs) for waist circumference and WHtR were significantly higher than that for BMI in identifying a high CXR severity score (≥ 8) (0.68 [0.60-0.75] and 0.67 [0.60-0.74] vs 0.58 [0.51-0.66], P = 0.001). A multivariate analysis indicated abdominal obesity (risk ratio: 1.75, 95% CI: 1.25-2.45, P < 0.001), bronchial asthma (risk ratio: 1.73, 95% CI: 1.07-2.81, P = 0.026) and oxygen saturation at admission (risk ratio: 0.96, 95% CI: 0.94-0.97, P < 0.001) as the only independent factors associated with high CXR severity scores.

CONCLUSION

Abdominal obesity phenotype is associated with a high CXR severity score better than BMI-based obesity in hospitalized patients with COVID-19. Therefore, when visiting the patient in a hospital setting, waist circumference should be measured, and patients with abdominal obesity should be monitored closely. Level of evidence Cross-sectional descriptive study, Level V.

Sources of Inaccuracy in Photoplethysmography for Continuous Cardiovascular Monitoring

Photoplethysmography (PPG) is a low-cost, noninvasive optical technique that uses change in light transmission with changes in blood volume within tissue to provide information for cardiovascular health and fitness. As remote health and wearable medical devices become more prevalent, PPG devices are being developed as part of wearable systems to monitor parameters such as heart rate (HR) that do not require complex analysis of the PPG waveform. However, complex analyses of the PPG waveform yield valuable clinical information, such as: blood pressure, respiratory information, sympathetic nervous system activity, and heart rate variability. Systems aiming to derive such complex parameters do not always account for realistic sources of noise, as testing is performed within controlled parameter spaces. A wearable monitoring tool to be used beyond fitness and heart rate must account for noise sources originating from individual patient variations (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to the skin). Here, we present a comprehensive review of the literature that aims to summarize these noise sources for future PPG device development for use in health monitoring.