Chest
Volume 103, Issue 5, May 1993, Pages 1325-1329
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Clinical Investigations
Pulmonary Function and Respiratory Chemosensitivity in Moderately Obese Patients with Sleep Apnea

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To determine whether moderately obese, normocapnic, sleep apnea patients are distinguished from normal obese individuals by differences in waking pulmonary function and respiratory chemosensitivity, we compared the waking pulmonary function, hypercapnic, and hypoxic ventilatory responses of 35 nonhypercapnic sleep apnea patients (32 men and 3 women) with those of 17 age-, sex-, weight-, and obesity-matched nonapneic control subjects (16 men and 1 woman). The waking ventilatory response to hypercapnia was lower among sleep apnea patients (mean ± SD, 2.05 ± 1.29 L/min/mm Hg) than control subjects (3.02 ± 2.05 L/min/mm Hg, p<0.05). Patients with sleep apnea demonstrated a higher waking PaCO2 (40.4 ± 2.9 vs 37.0 ± 2.7 mm Hg, p<0.001), and a lower waking PaO2 (81.4 ± 11.7 vs 89.7 ± 10.4 mm Hg, p<0.03). The waking hypoxic ventilatory response, however, was not significantly different between the groups. Moreover, control subjects had a higher total lung capacity than sleep apnea patients (6.99 ± 1.12 L and 6.27 ± 1.09 L, respectively, p<0.05). The lower hypercapnic ventilatory response, higher waking PaCO2, and lower total lung capacity in the sleep apnea patients resemble the pattern observed in patients with pickwickian syndrome. This suggests that disturbances in pulmonary function and ventilatory control in moderately obese sleep apnea patients are intermediate along a continuum from normal obesity to the pickwickian syndrome.

Section snippets

METHODS

The study was designed to compare the waking pulmonary function and ventilatory responses to progressive hypercapnia and hypoxia of moderately obese, normocapnic sleep apnea patients with those of a matched control group. Thirty-five patients with sleep apnea underwent full-night sleep studies and testing of waking pulmonary function and hypoxic and hypercapnic ventilatory responses. None of the patients was following a prescribed diet at the time of the evaluation.

The control group was

RESULTS

The sleep apnea patients were 51 ± 11 (mean ± SD) years of age, 172.3 ± 7.5 cm in height, and were moderately obese, weighing 103.6 ± 17.7 kg with a body mass idex of 34 ± 5. Thirty-two patients were male, and three were female. Their sleep parameters (Table 1) indicate moderate to severe sleep apnea with marked daytime somnolence. Thirty-two patients had predominantly obstructive and mixed apnea and three had predominantly central apnea. The control population (16 men and 1 woman) was matched

DISCUSSION

The major findings of this study were that compared with matched control subjects, normocapnic, moderately obese sleep apnea patients have a reduced slope of their waking ventilatory response to hypercapnia and an elevated PaCO2. No significant difference was demonstrated between groups in the waking hypoxic ventilatory response. The patients with sleep apnea and control subjects, however, did not differ regarding obesity, intrathoracic or extrathoracic airflow obstruction, or ability to

ACKNOWLEDGMENTS

The authors thank Lorena Clary for her secretarial assistance and Dr. Morris Gold for his help with the statistical analysis.

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  • Cited by (0)

    Supported by NIH R01 HL37379-01, NIH P01AG04402-01AG, and Maryland Chapter of American Lung Association

    Dr. Schwartz is a recipient of NIH Clinical Investigator Award HL02031-01A1

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