Chest
Volume 120, Issue 2, August 2001, Pages 369-376
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Clinical Investigations
Obesity And Hypoventilation
The Obesity-Hypoventilation Syndrome Revisited: A Prospective Study of 34 Consecutive Cases

https://doi.org/10.1378/chest.120.2.369Get rights and content

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” patients.

Design

Descriptive analysis of prospectively collected clinical data.

Setting

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).

Conclusion

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 disease.

Section snippets

Materials and Methods

We included in this study 34 patients who were consecutively admitted to our department between 1991 and 1997. These patients met the criteria for obesity-hypoventilation: (1) hypoventilation defined by a Pao2 < 70 mm Hg and a Paco2 > 45 mm Hg by diurnal blood gas analysis at rest, and (2) obesity with a body mass index (BMI)> 30 kg/m2.

Patients were excluded if the impairment of gas exchange could be explained by any other cause. Therefore, we excluded patients with COPD when they showed an

Results

Among the 34 patients with OHS, mean age was 61 ± 11 years; 9 patients were women. The average BMI was 40 ± 8 kg/m2, indicating severe obesity. Seventeen of 34 patients were smokers. While 13 patients were ex-smokers, 4 patients still continued smoking. Smoking duration was, on average, 35 ± 25 pack-years. Seven patients complained of chronic bronchitis. Half of the patients had been hospitalized for one or more times in an ICU before definitive diagnosis was made, and eight patients had been

Discussion

Our study highlights the impairment of gas exchange, which occurs in some patients with OSAS and an associated OHS or COPD. The deleterious effects on gas exchange of these associations can be observed even when the ventilatory defect is of mild-to-moderate degree, and would not induce per se respiratory insufficiency.

In a study published previously by our group,4 we examined patients with the association of OSAS plus COPD, and we showed that these patients had more gas exchange abnormalities

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