Diurnal PaCO2 tension in obese women: relationship with sleep disordered breathing

Obesity-hypoventilation syndrome and associated factors

BACKGROUND AND OBJECTIVES

Obesity causes important alterations in the respiratory physiology like sleep obstructive apnoea (SOA) and obesity-hypoventilation syndrome (OHS), both associated with high morbidity and mortality. Also, these entities are clearly infradiagnosed and in the case of OHS the prevalence is unknown in the general obese population. To determine the prevalence of OHS in the population of patients with morbid obesity and to know the comorbidity related with OHS, the associated respiratory symptoms and the pulse oximetry alterations.

PATIENTS AND METHOD

Descriptive study. Selection of 136 adult patients with morbid obesity (BMI >40). Collected were, anthropometric data, toxic habits, concomitant disease, symptom data, analytic data, dyspnoea grade, sleepiness scale (Epworth Test), electrocardiogram, chest X-ray, spirometry, nocturne ambulatory pulse oximetry and arterial gasometry.

RESULTS

136 were studied, mean age 60 years old (SD 12.9 years), 73% (98) were women; 6.6% of patients presented diurnal hypercapnia indicative of OHS; 72% presented high blood pressure, 44% dyslipidaemia, 18% presented cardiovascular disease, 83% snored and 46% had apnoea; 30% presented stageII dyspnoea and 10% stageIII. The desaturation/hour index was above 3% ≥30 of occasions in 28.6% of patients and the percentage of patients with saturations <90% more than 30% of the time was 23.5%. The results were worse in patients with OHS.

CONCLUSIONS

The prevalence of OHS was lower than expected. Noteworthy was the high comorbidity of cardiovascular disease and the high frequency of respiratory symptoms associated with important alterations of pulse oximetry.

Big breathing: the complex interaction of obesity, hypoventilation, weight loss, and respiratory function

Obesity places a significant load on the respiratory system, affecting lung volumes, respiratory muscle function, work of breathing, and ventilatory control. Despite this, most morbidly obese individuals maintain eucapnia. However, a subgroup of morbidly obese individuals will develop chronic daytime hypercapnia, described as the obesity hypoventilation syndrome (OHS). While obesity is obviously a crucial component of this syndrome, the relationship between excess fat accumulation and the development of awake hypercapnia is complex and extends beyond simply impairments of pulmonary mechanics and lung volumes as a consequence of obesity. Various compensatory mechanisms operate to maintain eucapnia even in the presence of extreme obesity. However, if compensation is impaired, hypoventilation will ensue. While obesity alone does not account for the development of hypoventilation, weight loss will produce significant improvements in lung function and awake gas exchange. Such improvements have the potential to substantially reduce morbidity and mortality in these individuals. Nevertheless, many individuals remain overweight despite substantial weight loss, with persistence of upper airway obstruction. Attention to this residual abnormality is important given the high incidence of cardiovascular abnormalities, including pulmonary hypertension, in individuals with OHS.

Gender, age and menopause effects on the prevalence and the characteristics of obstructive sleep apnea in obesity

BACKGROUND

In the 1970s and 80s it was believed that obstructive sleep apnea (OSA) was primarily a disease of men. The present study was addressed to evaluate the effect of gender and menopause on the prevalence and the characteristics of OSA and on anthropometric, clinical, respiratory and polysomnographic data in a population of obese individuals.

PATIENTS AND METHODS

A total of 230 obese subjects (BMI >/= 30 kg m-2), 148 women and 82 men, aged 16-75 years, were recruited and evaluated for general and anthropometric parameters, respiratory function, sleep-related symptoms and sleep disorders of breathing.

RESULTS

Respiratory disturbance index (RDI) and the prevalence of OSA were lower in women than in men (P < 0.001 and P < 0.001, respectively). Among subjects < 55 years, neck circumference, percentage of predicted normal neck circumference (PPNC), waist-to-hip ratio (WHR), PaCO2, RDI and the prevalence of OSA were lower in female subjects (P = 0.05, P < 0.05, P < 0.001, P < 0.01 and P < 0.01, respectively). BMI, neck circumference, PPNC, WHR, RDI and the prevalence of OSA were higher in postmenopausal compared with premenopausal women (P < 0.01, P < 0.01, P < 0.01, P < 0.01 and P < 0.01, respectively).

CONCLUSIONS

Our study demonstrates that (i) the male dominance regarding the prevalence and the severity of OSA disappears in men older than 55 years, and (ii) menopause seems to play a pivotal role in modulating both the presence and the degree of sleep disorder.