Underdiagnosis of Obstructive Sleep Apnoea in Peripheral Arterial Disease

Relationship Between Peripheral Arterial Diseases and Obstructive Sleep Apnea: A Systematic Review

Although the effects of obstructive sleep apnea (OSA) on the cardiovascular outcomes of coronary artery disease (CAD) have been well-established, its significance on the occurrence of peripheral arterial disease (PAD) remains debatable. Prompt diagnosis and treatment of OSA would help reduce cardiovascular comorbidities. Our study aimed to assess the relationship between OSA and PAD and report any statistical association between the two conditions. Here, we investigated the prevalence and association of OSA in PAD based on related articles from PubMed, Embase, and the Cochrane Library. All databases were systematically searched from January 2000 to December 2020. A total of 238 articles deemed relevant were assessed for eligibility, of which seven articles were selected for the systematic review. Seven prospective cohorts were qualified for inclusion, which included 26,881 male and 34,403 female patients (N = 61,284). The retrieved articles described OSA severity based on the apnea-hypopnea index and reported increased OSA prevalence in PAD patients. The Epworth sleepiness scale showed no association between OSA severity, poor ankle-brachial index values, and increased daytime sleepiness. The prevalence of OSA increased in patients with PAD. Further research and prospective clinical trials are required to establish strong associations between OSA and PAD to make appropriate changes in patient management algorithms and improve their outcomes.

Dietary Risk Factors and Eating Behaviors in Peripheral Arterial Disease (PAD)

Dietary risk factors play a fundamental role in the prevention and progression of atherosclerosis and PAD (Peripheral Arterial Disease). The impact of nutrition, however, defined as the process of taking in food and using it for growth, metabolism and repair, remains undefined with regard to PAD. This article describes the interplay between nutrition and the development/progression of PAD. We reviewed 688 articles, including key articles, narrative and systematic reviews, meta-analyses and clinical studies. We analyzed the interaction between nutrition and PAD predictors, and subsequently created four descriptive tables to summarize the relationship between PAD, dietary risk factors and outcomes. We comprehensively reviewed the role of well-studied diets (Mediterranean, vegetarian/vegan, low-carbohydrate ketogenic and intermittent fasting diet) and prevalent eating behaviors (emotional and binge eating, night eating and sleeping disorders, anorexia, bulimia, skipping meals, home cooking and fast/ultra-processed food consumption) on the traditional risk factors of PAD. Moreover, we analyzed the interplay between PAD and nutritional status, nutrients, dietary patterns and eating habits. Dietary patterns and eating disorders affect the development and progression of PAD, as well as its disabling complications including major adverse cardiovascular events (MACE) and major adverse limb events (MALE). Nutrition and dietary risk factor modification are important targets to reduce the risk of PAD as well as the subsequent development of MACE and MALE.

Association between apnea-hypopnea index and coronary artery calcification: a systematic review and meta-analysis

BACKGROUND

The present study aimed to evaluate the association between presence and severity of obstructive sleep apnoea (OSA) and the presence of subclinical coronary artery disease (CAD) as assessed by coronary calcium score.

METHODS

Medline, Cochrane, and Google Scholar databases were searched. The presence of coronary artery calcification (CAC) and CAC score were assessed.

RESULTS

Irrespective of the cut-off value of apnoea-hypopnea index (AHI) (5 or 15 events/h), patients in the OSA group had higher rate of CAC presence and mean CAC score than those in the control group. Subgroup analyses of patients monitored with home sleep apnoea testing (HSAT) or in-hospital/laboratory polysomnography showed that the OSA group had higher rate of CAC presence and mean CAC score than the control group, except in the comparison of mean CAC score between AHI ≥5 vs. <5 events/h for patients using HSAT, which was not significant. Pair-wise comparison showed that CAC score may increase with increased OSA severity.

CONCLUSIONS

In participants without symptomatic coronary disease, the presence of OSA was associated with the presence and extent of CAC. However, potential confounders such as age, gender, and BMI and the diversity of CAC scores may affect the association.

Association of sleep apnea with outcomes in peripheral artery disease: Insights from the PORTRAIT study

BACKGROUND

Sleep apnea is a predictor of adverse cardiovascular outcome in many cardiovascular diseases but whether it is associated with worse health status outcomes or mortality in peripheral artery disease (PAD) is unknown.

METHODS

PORTRAIT is an international (US, Netherlands, Australia) prospective PAD registry that consecutively enrolled patients who presented with new-onset or recent exacerbations of PAD symptoms to any of 16 vascular specialty clinics. Health status was assessed upon presentation and at 12 months with the disease-specific Peripheral Artery Questionnaire (PAQ). Higher PAQ scores indicate better health status. A sequentially-adjusted hierarchical linear regression model examined the association between sleep apnea and 1-year PAQ symptoms, quality of life, and summary scores. Five-year survival curves by comorbid sleep apnea status for US patients were compared using the log-rank test.

RESULTS

The mean age of the 1204 PORTRAIT participants was 67.6 ± 9.4 years with 37.5% women and 8.3% (n = 100) having sleep apnea. Patients with sleep apnea were more likely to be from the US, more sedentary, and to have diabetes, obesity, coronary disease, more depressive symptoms and a history of prior peripheral interventions. Paradoxically, they also had higher ankle-brachial indices, but lower PAQ Summary scores at presentation and 12 months (41.2 ± 22.0 vs. 49. 9± 21.6 and 58.6 ± 27.9 vs. 71.3 ± 24.9, respectively, p = <0.05). The association between sleep apnea and 1-year health status persisted after multivariable adjustment, but there were no differences in all-cause mortality over 5 years (28.0% vs. 23.4%, p = 0.76).

CONCLUSION

In patients presenting with PAD, comorbid sleep apnea is independently associated with worse health status over time. Future studies should test whether better treatment of sleep apnea can improve the health status of patients with PAD.

CLINICAL TRIAL REGISTRATION

NCT01419080.

Cardiovascular Disease in Patients with Chronic Obstructive Pulmonary Disease, Obstructive Sleep Apnoea Syndrome and Overlap Syndrome

Chronic obstructive pulmonary disease (COPD) and obstructive sleep apnoea syndrome (OSAS) are among the most prevalent chronic respiratory disorders. Accumulating data suggest that there is a significant burden of cardiovascular disease (CVD) in patients with COPD and OSAS, affecting negatively patients' quality of life and survival. Overlap syndrome (OS), i.e. the co-existence of both COPD and OSAS in the same patient, has an additional impact on the cardiovascular system multiplying the risk of morbidity and mortality. The underlying mechanisms for the development of CVD in patients with either OSAS or COPD and OS are not entirely elucidated. Several mechanisms, in addition to smoking and obesity, may be implicated, including systemic inflammation, increased sympathetic activity, oxidative stress and endothelial dysfunction. Early diagnosis and proper management of these patients might reduce cardiovascular risk and improve patients' survival. In this review, we summarize the current knowledge regarding epidemiological aspects, pathophysiological mechanisms and present point-to-point specific associations between COPD, OSAS, OS and components of CVD, namely, pulmonary hypertension, coronary artery disease, peripheral arterial disease and stroke.

An Update on Obstructive Sleep Apnea for Atherosclerosis: Mechanism, Diagnosis, and Treatment

The occurrence and development of atherosclerosis could be influenced by intermittent hypoxia. Obstructive sleep apnea (OSA), characterized by intermittent hypoxia, is world-wide prevalence with increasing morbidity and mortality rates. Researches remain focused on the study of its mechanism and improvement of diagnosis and treatment. However, the underlying mechanism is complex, and the best practice for OSA diagnosis and treatment considering atherosclerosis and related cardiovascular diseases is still debatable. In this review, we provided an update on research in OSA in the last 5 years with regard to atherosclerosis. The processes of inflammation, oxidative stress, autonomic nervous system activation, vascular dysfunction, platelet activation, metabolite dysfunction, small molecule RNA regulation, and the cardioprotective occurrence was discussed. Additionally, improved diagnosis such as, the utilized of portable device, and treatment especially with inconsistent results in continuous positive airway pressure and mandibular advancement devices were illustrated in detail. Therefore, further fundamental and clinical research should be carried out for a better understanding the deep interaction between OSA and atherosclerosis, as well as the suggestion of newer diagnostic and treatment options.

Atherosclerotic Burden and Arterial Stiffness are Not Increased in Patients with Milder Forms of Primary Aldosteronism Compared to Patients with Essential Hypertension

Patients with primary aldosteronism (PA) are at increased cardiovascular risk, compared to patients with essential hypertension (EH). Cardiovascular damage could depend on PA phenotype, potentially being lower in milder forms of PA. Our aim was to assess atherosclerotic burden and arterial stiffness in 88 prospectively recruited patients, including 44 patients with mild PA and EH respectively. All patients underwent a structured study program, including measurements of ankle-brachial index, oscillometric measurement of central pulse wave velocity (cPWV) and vascular ultrasound examination of the supraaortic arteries, the abdominal aorta, and the femoropopliteal arteries. A plaque score was calculated to estimate atherosclerotic burden for each patient. This is a prospective case-control study set at a tertiary care hospital. Patients with PA and EH matched well for age, gender, blood pressure, BMI, and cardiovascular risk factors such as diabetes mellitus and smoking status. Common carotid intima-media thickness (0.77 vs. 0.75 mm; p=0.997) and cPWV (7.2 vs. 7.1 m/s; p=0.372) were comparable between patients with PA and EH. The atherosclerotic burden, as expressed by the plaque score, did not differ between the two groups (p=0.159). However, after initiation of treatment cPWV was significantly decreased in patients with PA (p=0.017). This study shows that subclinical atherosclerotic burden and arterial stiffness in patients with milder forms of PA is comparable to patients with EH. Nevertheless, specific treatment for PA significantly improved cPWV, which argues for a more liberal use of mineralocorticoid receptor antagonists in patients with arterial hypertension.

Obstructive sleep apnea and peripheral vascular disease: a systematic review based on current literature

Introduction

Obstructive sleep apnea (OSA) is an established risk factor for poor cardiovascular outcomes and coronary artery disease, but its influence on the development of peripheral artery disease (PAD) is not well established. The aim of our study was to understand the mutual prevalence of OSA and PAD and any reported statistical association between the two conditions.

Methods

PubMed, Ovid Embase, Web of Science, Cochrane library and clinicaltrials.gov databases were systematically searched up to 29 November 2018. A total of 844 articles were identified and 744 articles were screened for relevance.

Results and Conclusion

Eleven prospective cohorts qualified for inclusion with N = 63,642 (M = 28,062, F = 35,494). All studies evaluated OSA severity primarily with apnea–hypopnea index (AHI) values. The overall prevalence of PAD was 20.5% (N = 13,068). Except for two studies, all studies reported an increased prevalence of OSA in patients with PAD. OSA severity was not found to have an association with poor ankle brachial index values or increasing daytime sleepiness as measured by Epworth sleepiness scale. Further prospective clinical trials are required to further delineate this finding.

Sleep-Disordered Breathing and Peripheral Arterial Disease: Current Evidence

INTRODUCTION

Sleep-disordered breathing (SDB) is associated with atherosclerosis. Peripheral arterial disease (PAD) is a manifestation of atherosclerosis in lower extremity arteries. No systematic review addressing the relationship between PAD and SDB was found. We performed this study aimed to summarize the relationship between SDB and PAD described in current clinical studies.

MATERIAL AND METHODS

PubMed and Embase electronic databases were searched for clinical articles (published before 3 April, 2019) describing studies that evaluated the association between SDB and PAD. We showed the results involved in the association in clinical studies.

RESULTS

In total, 8 clinical studies have been included, and most of them were cross-sectional studies. Six articles demonstrated the coexistence of SDB and PAD, evidenced by high prevalence of SDB in patients with PAD and vice versa. Meanwhile, the included studies exhibited independent positive associations between SDB or sleep parameters and PAD after adjusting for multiple confounders.

CONCLUSION

From present clinical prospective, positive association between SDB and PAD was shown. More prospective, randomized controlled studies are needed to establish the cause-effect relationships involved.

Obstructive sleep apnea, sleep symptoms, and their association with cardiovascular disease

OBJECTIVES

To determine the frequency of obstructive sleep apnea (OSA), insomnia, restless legs, and other sleep symptoms in patients with cardiovascular disease and the association of these sleep disorders with quantitative cardiovascular measures.

METHODS

Study design was a cross-sectional survey and retrospective chart review. A questionnaire containing validated sleep symptoms was distributed to 202 patients with cardiovascular disease at a tertiary referral cardiology clinic. Following a focused review of these patients' medical charts, their questionnaire responses were examined for associations with clinical cardiovascular parameters.

RESULTS

Twenty-one percent of patients reported a prior diagnosis of OSA. A total of 115 patients (60%) had at least one additional sleep symptom. Clinically significant insomnia was significantly associated with heart disease (relative risk [RR] = 1.5, confidence interval [CI] = 1.1 to 2.1), prior myocardial infarction or cerebrovascular accident (RR = 2.1, CI = 1.2 to 3.6), and heart failure (RR = 2.2, CI = 1.3 to 3.8). Left ventricular ejection fraction was significantly associated with insomnia by Insomnia Severity Index (β = -0.52, CI = -0.89 to -0.13).

CONCLUSION

The frequency of OSA in patients in this tertiary cardiology clinic was higher than the general population in the United States, with the majority of patients experiencing at least one sleep symptom. Insomnia symptoms were shown to be associated with multiple cardiovascular measures, including left ventricular ejection fraction. These findings imply an interwoven relationship between cardiovascular and sleep symptoms as captured by validated sleep questionnaires.

LEVEL OF EVIDENCE

IV Laryngoscope, 130:1595-1602, 2020.

CHADS₂, CHA₂DS₂ASc, and New ABCD Scores Predict the Risk of Peripheral Arterial Disease in Patients with Sleep Apnea

The association between sleep apnea (SA) and peripheral artery disease (PAD) remains debatable, and there is no clinical tool to predict incident PAD in SA patients. The CHADS₂ score has been found useful in predicting PAD risk. This study was designed to investigate the association between these diseases and the usefulness of CHADS₂ and CHA₂DS₂ASc scores in predicting subsequent PAD in SA patients. From a population-based database of one-million representative subjects, adult patients with SA diagnosis were enrolled as the suspected SA group, and those having SA diagnosis after polysomnography were further extracted as the probable SA group. Twenty sex- and age-matched control subjects were randomly selected for each SA patients. The occurrence of PAD after SA was taken as the primary endpoint. Totally, 10,702 and 4242 patients were enrolled in the suspected and probable SA groups, respectively. The cumulative incidence of PAD was similar between SA patients and the corresponding control groups. Multivariable Cox regression analyses showed that SA was not an independent risk factor for subsequent PAD. Sensitivity analyses using propensity score-matched cohorts showed consistent results. Furthermore, in stratifying the SA patients by CHADS₂, CHA₂DS₂ASc, or a newly-proposed ABCD (composed of Age, high Blood pressure, Cerebral vascular disease, and Diabetes mellitus) score, patients with higher scores predicted higher risks of subsequent PAD, while the ABCD score appeared to be the most robust. Aggressive risk modification is suggested to reduce the subsequent PAD risk in SA patients with a higher CHADS₂, CHA₂DS₂ASc, or ABCD score.

Alterations in heart rate variability in patients with peripheral arterial disease requiring surgical revascularization have limited association with postoperative major adverse cardiovascular and cerebrovascular events

Objective

Obstructive sleep apnea (OSA) is common in peripheral arterial disease (PAD) and associates with high mortality after surgery. Since abnormal heart rate variability (HRV) is predictive of postoperative complications, we investigated the relations of HRV with PAD, OSA and major adverse cardiovascular and cerebrovascular events (MACCE).

Materials and methods

Seventy-five patients (67±9 years) scheduled for sub-inguinal revascularization and 15 controls (63±6 years) underwent polysomnography and HRV analyses. OSA with an apnea-hypopnea index (AHI) ≥20/hour was considered significant. HRV was measured during wakefulness, S2, S3-4 and rapid eye movement (REM) sleep with time and frequency domain methods including beat-to-beat variability, low frequency (LF) and high frequency (HF) power, and detrended fluctuation analysis (DFA). MACCE was defined as cardiac death, myocardial infarction, coronary revascularization, hospitalized angina pectoris and stroke.

Results

Thirty-six patients (48%) had AHI≥20/hour. During follow-up (median 52 months), 22 patients (29%) suffered a MACCE. Compared to controls, fractal correlation of HRV (scaling exponent alpha 1 measured with DFA) was weaker during S2 and evening wakefulness in all subgroups (+/-AHI≥20/hour, +/-MACCE) but only in patients with AHI≥20/hour during morning wakefulness. The LF/HF ratio was lower in all subgroups during S2 but only in patients with AHI ≥20/hour during evening or morning wake. In the covariance analysis adjusted for age, body mass index, coronary artery disease and PAD duration, the alpha 1 during morning wakefulness remained significantly lower in patients with AHI≥20/hour than in those without (1.12 vs. 1.45; p = 0.03). Decreased HF during REM (p = 0.04) and S3-4 sleep (p = 0.03) were predictive of MACCE. In analyses with all sleep stages combined, mean heart rate as well as very low frequency, LF, HF and total power were associated with OSA of mild-to-moderate severity (AHI 10-20/hour).

Conclusions

HRV is altered in patients with PAD. These alterations have a limited association with OSA and MACCE.

Carotid strain measurement in patients with pseudoxanthoma elasticum - Hint for a different pathomechanism?

Pseudoxanthoma Elasticum (PXE), caused by autosomal-recessive mutations in the ATP-binding cassette transporter (ABCC6) gene, is known for high prevalence of atherosclerosis. A novel method investigating elastic properties of arteries in atherosclerotic patients is vascular strain analysis. We compared 44 PXE patients with peripheral artery disease (PXE+PAD group) with 50 control patients, each 25 without (control group) and with PAD (PAD group). All participants underwent an angiological examination including ankle-brachial index (ABI) and were examined with speckle-tracking based vascular strain analysis of common carotid arteries, measuring radial displacement (r.Dis), radial velocity (r.Vel), radial strain (r.Str), circumferential strain (c.Str), radial strainrate (r.SR) and circumferential strainrate (c.SR). We found significant lower ABI in patients with PXE compared to all other groups (each p < 0.01). The vascular strain analysis resulted in significantly decreased values in the PAD group compared to PXE with PAD (each p ≤ 0.01) and controls without PAD (each p ≤ 0.05), whereas no significant difference could be found between PXE+PAD and controls without PAD. We found significant negative correlations between low strain values and a higher prevalence of PAD in non-PXE patients (r.Str r = -0.34; c.Str r = -0.35; r.SR: r = -0.51; c.SR: r = -0.53). In conclusion, PXE patients had similar values for arterial stiffness compared to controls without PAD in vascular strain analysis. In this group, arterial stiffness parameters were significantly higher compared to non-PXE PAD patients. It is worth to discuss whether PAD-like manifestations in PXE are a different kind of disease and might need another strategy in diagnostics and therapy.

Recognition of Sleep Apnea Is Increasing. Analysis of Trends in Two Large, Representative Databases of Outpatient Practice

RATIONALE

Little is known about recent trends in physician reporting of sleep apnea during outpatient practice visits.

OBJECTIVES

To assess trends in the frequency of adult outpatient visits for sleep apnea in the United States, the clinicians who provided those visits, and the characteristics of patients reported to have sleep apnea; and to assess whether the reporting of a diagnosis of sleep apnea varies across regions of the country as a function of body weight and insurance status.

METHODS

We reviewed annual stratified samples of patients identified as having sleep apnea during physician office visits in the U.S. National Ambulatory Medical Care Survey database, and during visits to hospital outpatient practices in the U.S. National Hospital Ambulatory Medical Care Survey database, between 1993 and 2010. The aggregate data set included records of 838,000 ambulatory practice visits.

MEASUREMENTS AND MAIN RESULTS

During this 17-year period, survey reports of a diagnosis of sleep apnea increased 14.6- fold, from 420,000 to 6.37 million per year (P = 0.0002). Thirty-three percent were reported by primary care providers, 17% by pulmonologists, and 10% by otolaryngologists. Over the period of observation, reports of a diagnosis of sleep apnea by "other groups" increased considerably (P < 0.001). The per capita rate of sleep apnea diagnoses per 1,000 persons per year differed across regions of the United States (P < 0.0001). Regions that reported a higher rate of sleep apnea appeared to be influenced by obesity (P < 0.001) and health insurance status (P < 0.005).

CONCLUSIONS

Diagnoses of sleep apnea during outpatient visits to hospital-based and non-hospital-based practices in the United States were much more frequent in 2010 than in 1993, as reported by outpatient practice clinicians participating in national surveys. Although the majority of diagnoses of sleep apnea were reported by primary care providers, pulmonologists, and otolaryngologists (60%), there was a substantial increase in reports of sleep apnea by clinicians practicing other specialties during the study period. Reporting of a diagnosis of sleep apnea varied by obesity prevalence and health insurance status across U.S. geographic regions.

Peripheral Arterial Disease

Peripheral arterial disease (PAD) affects 15% of the Australian population and is a powerful and serious predictor of cardiovascular mortality yet continues to be under-recognised and undertreated. Diagnosis is simple and management is centred upon symptom relief and risk minimisation. While novel and specialised therapies play a role, the bulk of management is approachable and feasible. In this review, we cover the epidemiology, risk factors, associated conditions, classification, and natural history of PAD. We then discuss current diagnostic and therapeutic options as well as emerging therapies for this common condition.

Sleep apnoea is common in severe peripheral arterial disease

Background

Atherosclerotic conditions have been demonstrated to be associated with sleep- disordered breathing (SDB). Peripheral arterial disease (PAD) represents severe atherosclerosis with a high mortality. In early stages of PAD a substantial prevalence of sleep apnoea has already been shown. Here, we sought to determine the frequency of undiagnosed sleep apnoea in a homogeneous group of advanced PAD patients undergoing percutaneous revascularization.

Methods

59 consecutive patients (mean age: 71.1 ± 9.8 years, 67.8% males) with PAD in Fontaine stages IIb-IV that underwent percutaneous transluminal angioplasty at our department were enrolled for pre-procedural polygraphy.

Results

Patients appertained to Fontaine clinical stage IIb, III and IV in 54.2%, 23.8% and 22.% of cases, respectively, and were principally intervened for femoropopliteal occlusive disease (71.2% of total study population). Polygraphy revealed sleep apnoea in 48 out of 59 patients (81.4%), of whom 60.4% offered a primarily obstructive-driven genesis. Among those patients with polygraphically confirmed sleep apnoea, mean apnoea hypopnoea index (AHI) and mean oxygen desaturation index (ODI) averaged 28.2 ± 19.5/h and 26.7 ± 18.8/h, respectively. 18 patients even offered an AHI ≥30/h that is indicative of severe sleep apnoea. For obstructive-driven apnoeic events, AHI correlated significantly with PAD severity stages (p = 0.042).

Conclusions

In our PAD collective, sleep apnoea was frequent and obstructive sleep apnoea´s severity correlated with PAD severity stages. Long-term results regarding the vasoprotective impact of CPAP treatment on PAD course remains to be determined.

Association of diabetic vascular complications with poor sleep complaints

BACKGROUND

Literatures reported that poor sleep complaints were associated with a great deal of health outcomes. However, there are few studies on the association of poor sleep complaints with diabetic vascular complications.

METHODS

Aiming on the association, a cross-sectional survey was conducted among 1220 diabetic patients in this study. Poor sleep complaints were composed of difficulty falling asleep, early final awakening, short sleep and long sleep. The diabetic vascular complications involved in the study were diagnosed according to the Standards of Medical Care in Diabetes (ADA 2016).

RESULTS

Our findings indicated that short sleep remained independently associated with diabetic kidney disease (DKD) (OR > 1, P < 0.05) after the adjustments; long sleep independently associated with diabetic retinopathy (DR) (OR > 1, P < 0.05); early final awakening and short sleep independently associated with cardiovascular disease (OR > 1, P < 0.05); short sleep independently associated with peripheral arterial disease (OR > 1, P < 0.05); there was no association between poor sleep complaints and neuropathy (P > 0.05).

CONCLUSIONS

The study suggests that the poor sleep complaints were distinguishably associated with diabetic vascular complications. Clinicians should take poor sleep complaints into account in diabetes treatment.

Work of Breathing in Fixed and Pressure Relief Continuous Positive Airway Pressure (C-Flex™): A post hoc Analysis

BACKGROUND

Expiratory pressure relief continuous positive airway pressure (pressure relief CPAP; C-Flex™) causes increases in inspiratory duty cycle and shortening of expiratory time. It has been suggested that these changes are caused by an increase in work of breathing.

OBJECTIVES

We studied the effects of C-Flex on work of breathing and intrinsic positive end-expiratory pressure as compared to fixed CPAP.

METHODS

Work of breathing was analyzed in 24 patients with obstructive sleep apnea during treatment with fixed CPAP and C-Flex with 3 different pressure relief settings in a randomized order during rapid-eye-movement (REM) and non-REM sleep. Work of breathing was assessed on a breath-by-breath basis using a piezoelectric esophageal pressure catheter and a pneumotachograph for measuring airflow.

RESULTS

We found there was no increase in inspiratory work of breathing observed using C-Flex compared to fixed CPAP. Instead, we found a linear decrease in inspiratory work of breathing with increasing pressure relief, with a mean difference of 1.22 J/min between CPAP and maximum pressure release (C-Flex 3; 90% of the value with nasal CPAP); however, the decrease was not statistically significant. The decrease in inspiratory work of breathing associated with C-Flex has a significant inverse correlation with BMI.

CONCLUSIONS

The C-Flex technology does not change work of breathing but shows a tendency towards a reduction of inspiratory work of breathing in patients with a lower BMI using higher C-Flex. The effect is probably caused by diminishing airway resistance generated by the positive end-expiratory pressure. Our findings may lead to additional fields of application of the C-Flex technology, such as chronic obstructive pulmonary disease or muscular dystrophy.