Chest
Volume 109, Issue 2, February 1996, Pages 380-386
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Clinical Investigations: Sleep/Airways
Pulmonary Hemodynamics in the Obstructive Sleep Apnea Syndrome: Results in 220 Consecutive Patients

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We have investigated pulmonary hemodynamics in a large series of consecutive, unselected patients with obstructive sleep apnea syndrome (OSAS). The aims of this study were to evaluate the frequency of pulmonary artery hypertension (PH) in OSAS and to analyze, as far as possible, its mechanisms. Two hundred twenty patients were included on the basis of a polysomnographic diagnosis of OSAS (apnea+hypopnea index>20). PH, defined by a resting mean pulmonary artery mean pressure (PAP) of at least 20 mm Hg, was observed in 37 of 220 patients (17%). Patients with PH differed from the others with regard to pulmonary volumes (vital capacity [VC], FEV1) and the FEV1/VC ratio that were significantly lower (p<0.001); PaO2 (64.4±9.3 vs 74.7±10.1 mm Hg; p<0.001), PaCO2 (43.8±5.4 vs 37.6±3.9 mm Hg; p<0.001), apnea+ hypopnea index (100±33 vs 74±32; p<0.001), and mean nocturnal arterial oxygen saturation (SaO2) (88±6% vs 94±2%; p<0.001). Patients with PH were also more overweight (p<0.001). Multiple regression analysis showed that 50% of the variance of PAP could be predicted by an equation including PaCO2 (accounting for 32% of the variance), FEV1 (12%), airway resistance (4%), and mean nocturnal SaO2 (2%). In conclusion, PH is observed, in agreement with previous studies, in less than 20% of OSAS patients. PH is strongly linked to the presence of an obstructive (rather than restrictive) ventilatory pattern, hypoxemia, and hypercapnia, and is generally accounted for by an associated obstructive airways disease. In this regard, the severity of OSAS plays only a minor role.

Section snippets

METHODS

The study included consecutive, unselected patients who had been referred to the sleep laboratory for symptoms evocative of OSAS. All the patients had an established diagnosis of OSAS on the basis of polysomnographic criteria of more than 20 apneas and (or) hypopneas per hour of sleep, of which more than 80% were of the obstructive type. All the patients underwent conventional spirography and arterial blood gas measurements. All the patients included in the present study gave an informed

RESULTS

Patients were subdivided into two groups according to the results of pulmonary hemodynamic investigations. Group 1 included 37 patients with PH defined by a resting PAP of 20 mm Hg or greater. Group 2 included the remaining 183 patients without PH. It can be seen from Table 1 that the proportion of female patients was low (<10%) in both groups and that age was similar in patients with and without PH. The body mass index (BMI) was higher in PH patients (p<0.0l). Obesity defined by a BMI greater

DISCUSSION

The present study shows that 17% of OSAS patients exhibit permanent (daytime) PH, defined by a PAP of 20 mm Hg or more. Thus, resting PH is not a common finding and this figure (17%) is in good agreement with data obtained in earlier studies from our laboratory,4, 5 where the numbers of patients were smaller, 9 of 46 (20%)4 and 19 of 100 (19%),5 but also with the results of Podszus et al13 who noticed that 13 of 65 patients (20%) had PH. Higher figures of PH have been observed in earlier reports

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