Respiratory Determinants of Diurnal Hypercapnia in Obesity Hypoventilation Syndrome. What Does Weight Have to Do with It?

Targeting Hypercapnia in Chronic Lung Disease and Obesity Hypoventilation: Benefits and Challenges

Hypoventilation is a complication that is not uncommon in chronic obstructive pulmonary disease and calls for both medical treatment of the underlying disease and, frequently, noninvasive ventilation either during exacerbations requiring hospitalization or in a chronic state in the patient at home. Obesity hypoventilation syndrome by definition is associated with ventilatory failure and hypercapnia. It may or may not be accompanied by obstructive sleep apnea, which when detected becomes an additional target for positive airway pressure treatment. Intensive research has not completely resolved the best choice of treatment, and the simplest modality, continuous positive airway pressure, may still be entertained.

Factors Associated with the Efficiency of Home Non-Invasive Ventilation in Patients with Obesity-Hypoventilation Syndrome in Martinique

Obesity-hypoventilation syndrome (OHS) is a respiratory complication of obesity characterized by chronic hypercapnic respiratory failure. It is often associated with several comorbidities and is treated by positive airway pressure (PAP) therapy. This study aimed to identify factors associated with persistent hypercapnia in patients receiving home non-invasive ventilation (NIV). We performed a retrospective study including patients with documented OHS. In total, 143 patients were included (79.7% women, age 67 ± 15.5 years, body mass index 41.6 ± 8.3 kg/m²). After 4.6 ± 4.0 years of follow-up, 72 patients (50.3%) remained hypercapnic. In bivariable analysis, clinical data showed no difference in follow-up duration, number of comorbidities, comorbidities, or circumstance of discovery. Patients with persistent hypercapnia on NIV were generally older, with lower BMI and more comorbidities. (5.5 ± 1.8 versus 4.4 ± 2.1, p = 0.001), female sex (87.5% versus 71.8%), was treated by NIV (100% versus 90.1%, p < 0.01), had lower FVC (56.7 ± 17.2 versus 63.6 ± 18% of theoretical value, p = 0.04), lower TLC (69.1 ± 15.3 versus 74.5 ± 14.6% of theoretical value, p = 0.07), lower RV (88.4 ± 27.1 versus 102.5 ± 29.4% of theoretical value, p = 0.02), higher pCO2 at diagnosis (59.7 ± 11.7 versus 54.6 ± 10.1 mmHg, p = 0.01) and lower pH (7.38 ± 0.03 versus 7.40 ± 0.04, p = 0.007), higher pressure support (12.6 ± 2.6 versus 11.5 ± 2.4 cmH₂O, p = 0.04) and lower EPAP (8.2 ± 1.9 versus 9 ± 2.0 cmH₂O, p = 0.06). There was no difference in non-intentional leaks and daily use between patients between both groups. By multivariable analysis, sex, BMI, pCO2 at diagnosis, and TLC were independent risk factors for persistent hypercapnia on home NIV. In individuals with OHS, persistent hypercapnia on home NIV therapy is frequent. Sex, BMI, pCO2 at diagnosis, and TLC were all associated with an increased risk of persistent hypercapnia in persons treated with home NIV.

OSA and Chronic Respiratory Disease: Mechanisms and Epidemiology

Obstructive sleep apnea (OSA) is a highly prevalent disorder that has profound implications on the outcomes of patients with chronic lung disease. The hallmark of OSA is a collapse of the oropharynx resulting in a transient reduction in airflow, large intrathoracic pressure swings, and intermittent hypoxia and hypercapnia. The subsequent cytokine-mediated inflammatory cascade, coupled with tractional lung injury, damages the lungs and may worsen several conditions, including chronic obstructive pulmonary disease, asthma, interstitial lung disease, and pulmonary hypertension. Further complicating this is the sleep fragmentation and deterioration of sleep quality that occurs because of OSA, which can compound the fatigue and physical exhaustion often experienced by patients due to their chronic lung disease. For patients with many pulmonary disorders, the available evidence suggests that the prompt recognition and treatment of sleep-disordered breathing improves their quality of life and may also alter the course of their illness. However, more robust studies are needed to truly understand this relationship and the impacts of confounding comorbidities such as obesity and gastroesophageal reflux disease. Clinicians taking care of patients with chronic pulmonary disease should screen and treat patients for OSA, given the complex bidirectional relationship OSA has with chronic lung disease.

Severity stages of obesity-related breathing disorders - a cross-sectional cohort study

INTRODUCTION

There is a general underappreciation of the spectrum of obesity-related breathing disorders and their consequences. We therefore compared characteristics of obese patients with eucapnic obstructive sleep apnea (OSA), OSA with obesity-related sleep hypoventilation (ORSH) or obesity hypoventilation syndrome (OHS) to identify the major determinants of hypoventilation.

PATIENTS AND METHODS

In this prospective, diagnostic study (NCT04570540), obese patients with OSA, ORSH or OHS were characterized applying polysomnography with transcutaneous capnometry, blood gas analyses, bodyplethysmography and measurement of hypercapnic ventilatory response (HCVR). Pathophysiological variables known to contribute to hypoventilation and differing significantly between the groups were specified as potential independent variables in a multivariable logistic regression to identify major determinants of hypoventilation.

RESULTS

Twenty, 43 and 19 patients were in the OSA, ORSH and OHS group, respectively. BMI was significantly lower in OSA as compared to OHS. The extent of SRBD was significantly higher in OHS as compared to OSA or ORSH. Patients with ORSH or OHS showed a significantly decreased forced expiratory volume in 1 s and forced vital capacity compared to OSA. HCVR was significantly lower in OHS and identified as the major determinant of hypoventilation in a multivariable logistic regression (Nagelkerke R² = 0.346, p = 0.050, odds ratio (95%-confidence interval) 0.129 (0.017-1.004)).

CONCLUSION

Although there were differences in BMI, respiratory mechanics and severity of upper airway obstruction between groups, our data support HCVR as the major determinant of obesity-associated hypoventilation.

Risk factors associated with pulmonary hypertension in obesity hypoventilation syndrome

STUDY OBJECTIVES

Pulmonary hypertension (PH) is prevalent in obesity hypoventilation syndrome (OHS). However, there is a paucity of data assessing pathogenic factors associated with PH. Our objective is to assess risk factors that may be involved in the pathogenesis of PH in untreated OHS.

METHODS

In a post-hoc analysis of the Pickwick trial, we performed a bivariate analysis of baseline characteristics between patients with and without PH. Variables with a p value ≤0.10 were defined as potential risk factors and were grouped by theoretical pathogenic mechanisms in several adjusted models. Similar analysis was carried out for the two OHS phenotypes, with and without severe concomitant obstructive sleep apnea (OSA).

RESULTS

Of 246 patients with OHS, 122 (50%) had echocardiographic evidence of PH defined as systolic pulmonary artery pressure ≥40 mmHg. Lower levels of awake PaO₂ and higher body mass index (BMI) were independent risk factors in the multivariate model, with a negative and positive adjusted linear association, respectively (adjusted odds ratio 0.96; 95% CI 0.93 to 0.98; p = 0.003 for PaO₂, and 1.07; 95% CI 1.03 to 1.12; p = 0.001 for BMI). In separate analyses, BMI and PaO₂ were independent risk factors in the severe OSA phenotype, whereas BMI and peak in-flow velocity in early (E)/late diastole (A) ratio were independent risk factors in the non-severe OSA phenotype.

CONCLUSIONS

This study identifies obesity per se as a major independent risk factor for PH, regardless of OHS phenotype. Therapeutic interventions targeting weight loss may play a critical role in improving PH in this patient population.

CLINICAL TRIALS REGISTRATION

Registry: Clinicaltrial.gov; Identifier: NCT01405976.

Effect of ventilation therapy on mortality rate among obesity hypoventilation syndrome and obstructive sleep apnoea patients

Introduction

The prevalence of obesity is continually increasing worldwide, which increases the incidence of obesity hypoventilation syndrome (OHS) and its consequent mortality.

Methods

We reviewed the therapy mode, comorbidity and mortality of all OHS patients treated at our hospital between 2005 and 2016. The control group consisted of randomly selected patients with obstructive sleep apnoea (OSA) treated during the same period.

Results

We studied 206 OHS patients and 236 OSA patients. The OHS patients were older (56.3 versus 52.3 years, p<0.001) and heavier (body mass index 46.1 versus 32.2 kg·m^-2, p<0.001), and the percentage of women was higher (41.2% versus 24.2%, p<0.001), respectively. The OHS patients had more hypertension (83% versus 61%, p<0.001) and diabetes (62% versus 31%, p<0.001) than the OSA patients, but no higher stroke (4% versus 8%, p=0.058) or ischaemic heart disease (14% versus 15%, p=0.437) incidence. The 5- and 10-year, unadjusted survival rates were lower among the OHS patients than among the OSA patients (83% versus 96% and 74% versus 91%, respectively; p<0.001). Differences in mortality rates were not related to age, sex or body mass index; covariates such as Charlson Comorbidity Index and ventilation therapy predicted survival. The mortality rate decreased significantly (p<0.001) both in OHS and OSA patients even after adjusting for covariates.

Conclusions

The mortality rate in OHS was significantly higher than that in OSA patients even after adjusting for covariates. Ventilation therapy by continuous positive airway pressure or noninvasive ventilation have reduced mortality significantly in all patients.

More than Heart Failure: Central Sleep Apnea and Sleep-Related Hypoventilation

Central sleep apnea (CSA) comprises a variety of breathing patterns and clinical entities. They can be classified into 2 categories based on the partial pressure of carbon dioxide in the arterial blood. Nonhypercapnic CSA is usually characterized by a periodic breathing pattern, while hypercapnic CSA is based on hypoventilation. The latter CSA form is associated with central nervous, neuromuscular, and rib cage disorders as well as obesity and certain medication or substance intake. In contrast, nonhypercapnic CSA is typically accompanied by an overshoot of the ventilation and often associated with heart failure, cerebrovascular diseases, and stay in high altitude. CSA and hypoventilation syndromes are often considered separately, but pathophysiological aspects frequently overlap. An integrative approach helps to recognize underlying pathophysiological mechanisms and to choose adequate therapeutic strategies. Research in the last decades improved our insights; nevertheless, diagnostic tools are not always appropriately chosen to perform comprehensive sleep studies. This supports misinterpretation and misclassification of sleep disordered breathing. The purpose of this article is to highlight unresolved problems, raise awareness for different pathophysiological components and to discuss the evidence for targeted therapeutic strategies.

Supine awake oximetry as a screening tool for daytime hypercapnia in super-obese patients

BACKGROUND

Evidence-based screening tools are required for detection of daytime hypercapnia in high-risk patient populations.

AIMS

To determine the validity of supine awake oximetry as a test for daytime hypercapnia and severe sleep disordered breathing (SDB) in super-obese patients.

METHODS

This was a cross-sectional diagnostic test evaluation of super-obese adults (body mass index >50 kg/m² ) presenting to Liverpool Hospital, Australia, between 2009 and 2015 for diagnostic polysomnography (PSG) and arterial blood gas measurement. Supine awake oxygen saturation (SpO₂ ) was determined using oximetry measurements from the first three awake epochs of raw PSG data. Sensitivity and specificity of SpO₂ for detecting patients with daytime hypercapnia (PaCO₂ >45 mmHg) and severe SDB (respiratory disturbance index (RDI) >30 events/h) were assessed at various cut-off points and displayed using a receiver operating characteristic (ROC) curve. Area under the ROC curve and positive and negative predictive values (PPV and NPV) in the present patient population were derived.

RESULTS

Of 52 patients, 23 (44%) had daytime hypercapnia. SpO₂ measured awake in the supine position was associated with the presence of daytime hypercapnia but not with the presence of severe SDB. Overall, awake supine SpO₂ <91.2% had 34.8% sensitivity, 96.6% specificity and 88.8% PPV, and SpO₂ <96.7% had 87.0% sensitivity, 20.7% specificity and 66.7% NPV for the presence of daytime hypercapnia.

CONCLUSION

Awake supine oximetry is an easily performed test that may have novel use in identifying patients at high risk of respiratory failure. Future studies are required to evaluate prospectively its role in screening patients at risk of daytime hypercapnia.

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.

Obesity Hypoventilation Syndrome: Choosing the Appropriate Treatment of a Heterogeneous Disorder

The obesity hypoventilation syndrome (OHS) is associated with significant morbidity and increased mortality compared with simple obesity and eucapnic obstructive sleep apnea. Accurate diagnosis and commencement of early and appropriate management is fundamental in reducing the significant personal and societal burdens this disorder poses. Sleep disordered breathing is a major contributor to the developmental of sleep and awake hypercapnia, which characterizes OHS, and is effectively addressed through the use of positive airway pressure (PAP) therapy. This article reviews the current evidence supporting different modes of PAP currently used in managing these individuals.

Definition, discrimination, diagnosis and treatment of central breathing disturbances during sleep

The complexity of central breathing disturbances during sleep has become increasingly obvious. They present as central sleep apnoeas (CSAs) and hypopnoeas, periodic breathing with apnoeas, or irregular breathing in patients with cardiovascular, other internal or neurological disorders, and can emerge under positive airway pressure treatment or opioid use, or at high altitude. As yet, there is insufficient knowledge on the clinical features, pathophysiological background and consecutive algorithms for stepped-care treatment. Most recently, it has been discussed intensively if CSA in heart failure is a “marker” of disease severity or a “mediator” of disease progression, and if and which type of positive airway pressure therapy is indicated. In addition, disturbances of respiratory drive or the translation of central impulses may result in hypoventilation, associated with cerebral or neuromuscular diseases, or severe diseases of lung or thorax. These statements report the results of an European Respiratory Society Task Force addressing actual diagnostic and therapeutic standards. The statements are based on a systematic review of the literature and a systematic two-step decision process. Although the Task Force does not make recommendations, it describes its current practice of treatment of CSA in heart failure and hypoventilation.

Short-term modulation of the ventilatory response to exercise is preserved in obstructive sleep apnea

BACKGROUND

The ventilatory response to exercise can be transiently adjusted in response to environmentally (e.g., breathing apparatus) or physiologically altered conditions (e.g., respiratory disease), maintaining constant relative arterial P_CO2 regulation from rest to exercise (Mitchell and Babb, 2006); this augmentation is called short-term modulation (STM) of the exercise ventilatory response. Obesity and/or obstructive sleep apnea could affect the exercise ventilatory response and the capacity for STM due to chronically increased mechanical and/or ventilatory loads on the respiratory system, and/or recurrent (chronic) intermittent hypoxia experienced during sleep. We hypothesized that: (1) the exercise ventilatory response is augmented in obese OSA patients compared with obese non-OSA adults, and (2) the capacity for STM with added dead space is diminished in obese OSA patients.

METHODS

Nine obese adults with OSA (age: 39±6 yr, BMI: 40±5kg/m², AHI: 25±24 events/h [range 6-73], mean±SD) and 8 obese adults without OSA (age: 38±10 yr, BMI: 37±6kg/m², AHI: 1±2) completed three, 20-min bouts of constant-load submaximal cycling exercise (8min rest, 6min at 10 and 30W) with or without added external dead space (200 or 400mL; 20min rest between bouts). Steady-state measurements were made of ventilation (V˙_E)_, oxygen consumption V˙_O2), carbon dioxide production (V˙_CO2), and end-tidal P_CO2 (PET_CO2). The exercise ventilatory response was defined as the slope of the V˙E-V˙_CO2 relationship (ΔV˙E/ΔV˙_CO2).

RESULTS

In control (i.e. no added dead space), the exercise ventilatory response was not significantly different between non-OSA and OSA groups (ΔV˙E/ΔV˙_CO2 slope: 30.5±4.2 vs 30.5±3.8, p>0.05); PET_CO2 regulation from rest to exercise did not differ between groups (p>0.05). In trials with added external dead space, ΔV˙E/ΔV˙_CO2 increased with increased dead space (p < 0.05) and the PET_CO2 change from rest to exercise remained small (<2mmHg) in both groups, demonstrating STM. There were no significant differences between groups.

CONCLUSIONS

Contrary to our hypotheses: (1) the exercise ventilatory response is not increased in obese OSA patients compared with obese non-OSA adults, and (2) the capacity for STM with added dead space is preserved in obese OSA and non-OSA adults.

Determinants of Wake Pco2 and Increases in Wake Pco2 over Time in Patients with Obstructive Sleep Apnea

RATIONALE

The progression from obesity and obstructive sleep apnea to obesity with hypoventilation and daytime hypercapnia may relate to features of sleep-disordered breathing events that affect loading and unloading of carbon dioxide.

OBJECTIVES

To determine whether the wake Pco2 increases over time in untreated obstructive sleep apnea, and whether that increase is explained by changes in sleep-disordered breathing event duration, interevent duration, or postevent ventilation amplitude.

METHODS

We selected 14 adults who had two polysomnographic studies more than 1 year apart because of untreated or suboptimally treated moderate to severe obstructive sleep apnea. Demographic and polysomnographic data were reviewed for both sets of studies, including the evening wake end-tidal CO2, the ratio of mean event to mean interevent duration (subsuming apneas and hypopneas), and the ratio of mean post- to preevent breath amplitude.

MEASUREMENT AND MAIN RESULTS

The mean (SD) wake end-tidal Pco2 increased between studies from 35.9 (4.2) to 39.5 (3.9) mm Hg (P < 0.005). The wake end-tidal CO2 correlated inversely with the post- to pre-event breath amplitude and positively with the ratio of mean event to mean interevent duration and with body mass index. However, those three variables were not significantly changed between the two studies. The wake end-tidal CO2 did not correlate with the apnea-hypopnea index or age. There was a significant increase in bicarbonate level between studies (median, 24.0-26.5 mmol/L; P = 0.01).

CONCLUSIONS

In our study cohort, wake end-tidal CO2 correlated with body mass index and features of sleep apnea that influence the balance of loading and unloading of CO2. However, those features remained fixed over time, even as the wake Pco2 and bicarbonate levels increased with untreated sleep apnea.

The clinical characteristics and hospital and post-hospital survival of patients with the obesity hypoventilation syndrome: analysis of a large cohort

OBJECTIVE

The worldwide prevalence of obesity has reached epidemic proportions. Obesity hypoventilation syndrome (OHS) is a common yet largely undiagnosed and mistreated condition that likely carries a high mortality. The aim of this study was to determine the clinical characteristics, hospital outcome, outcome following hospital discharge and predictors of death in a large cohort of patients hospitalized with OHS. OHS is an important condition as many patients with this syndrome are misdiagnosed and receive inappropriate treatment.

METHODS

We reviewed the electronic medical records of patients with unequivocal OHS admitted to a 525-bed tertiary-care teaching hospital over a 5-year period. Demographic and clinical data as well as hospital disposition were recorded. In order to determine the patients' post-discharge status, we linked our database to the database of death certificates of the State Registrar of Vital Records.

RESULTS

We identified 600 patients who met the inclusion criteria for this study. The patients' mean age was 58 ± 15 years with a mean body mass index of 48.2 ± 8.3 kg m-2; 64% were women. Thirty-seven percent had a history of diabetes and 43% had been misdiagnosed as having chronic obstructive pulmonary disease, while none had been previously diagnosed with OHS. The most common admission diagnoses were respiratory failure, heart failure and sepsis. Ninety (15%) patients died during the index hospitalization. The patients' age, S-creatinine, respiratory failure, sepsis and admission to the ICU were independent predictors of hospital mortality. The hospital survivors were followed for a mean of 1,174 ± 501 d (3.2 ± 1.3 years) from the index hospitalization. On follow-up, 98 of the 510 (19%) hospital survivors died, with an overall cumulative mortality of 31.3%. The patients' age, S-creatinine and admission to the ICU were independent predictors of post-hospital mortality.

CONCLUSION

Obesity hypoventilation syndrome is a common disease that is frequently misdiagnosed and mistreated and carries a 3-year morality, which is significantly worse than that for most cancers combined. Considering the high mortality of this disease, all patients with a body mass index > 35 kg m-2 should be screened for OHS; those patients with both early and established OHS should be referred to a pulmonary and/or sleep specialist for evaluation for non-invasive positive pressure ventilation, to a dietician for dietary counseling and lifestyle modification and to a bariatric surgeon for evaluation for bariatric surgery.

Obesity Hypoventilation Syndrome: Weighing in on Therapy Options

Obesity hypoventilation syndrome is becoming an increasingly encountered condition both in respiratory outpatient clinics and in hospitalized patients. The health consequences and social disadvantages of obesity hypoventilation syndrome are significant. Unfortunately, the diagnosis and institution of appropriate therapy is commonly delayed when the syndrome is not recognized or misdiagnosed. Positive airway pressure therapy remains the mainstay of treatment and is effective in controlling sleep-disordered breathing and improving awake blood gases in the majority of individuals. Evidence supporting one mode of therapy over another is limited. Both continuous and bilevel therapy modes can successfully improve daytime gas exchange, with adherence to therapy an important modifiable factor in the response to treatment. Despite adherence to therapy, these individuals continue to experience excess mortality primarily due to cardiovascular events compared with those with eucapnic sleep apnea using CPAP. This difference likely arises from ongoing systemic inflammation secondary to the morbidly obese state. The need for a comprehensive approach to managing nutrition, weight, and physical activity in addition to reversal of sleep-disordered breathing is now widely recognized. Future studies need to evaluate the impact of a more aggressive and comprehensive treatment plan beyond managing sleep-disordered breathing. The impact of early identification and treatment of sleep-disordered breathing on the development and reversal of cardiometabolic dysfunction also requires further attention.