Study objectives: Obesity has many detrimental effects
on the respiratory function and may lead to chronic hypoventilation in
some patients, an association known as the obesity-hypoventilation
syndrome (OHS). In many cases, patients with OHS also have sleep
apneas. Hereafter, we describe several features of a cohort (n = 34)
of patients with OHS and show the comparisons with a large cohort
(n = 220) of patients with obstructive sleep apnea syndrome (OSAS).
We compare also OHS patients with a group of patients with the
association of OSAS and COPD, also known as “overlap”
Design: Descriptive analysis of
prospectively collected clinical data.
Respiratory care unit and sleep laboratory of university hospital.
Results: In OHS patients, OSAS was present in most of the
cases (23 of 26 patients). However, in three patients, OHS was not
associated with OSAS, showing that obesity per se may
lead to chronic hypoventilation. As expected by definition, OHS
patients had, on average the worst diurnal arterial blood gas
measurements, compared to the other groups. For the OHS patients, the
mean diurnal Pao2 was 59 ± 7 mm Hg, which
was significantly different from the Pao2 of
the OSAS patients (75 ± 10 mm Hg; p = 0,001) but also from the
overlap patients (66 ± 10 mm Hg; p = 0.015). Pulmonary
hypertension (ie, mean pulmonary artery pressure > 20
mm Hg) was more frequent in OHS patients than in “pure” OSAS
patients (58% vs 9%; p = 0.001).
Patients with OSAS and chronic respiratory insufficiency had in most
cases an associated OHS or COPD. Patients with OHS were older than
patients with pure OSAS. They had mild-to-moderate degrees of
restrictive ventilatory pattern due to obesity. Severe gas exchange
impairment and pulmonary hypertension were quite frequent. The
association of OHS and OSAS was the rule. However, in three patients,
OHS was not associated with OSAS, suggesting that OHS is an autonomous