Daytime Pulmonary Hypertension in Patients with Obstructive Sleep Apnea Syndrome

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Abstract
The frequency of daytime pulmonary hypertension (PH) in patients with obstructive sleep apnea syndrome (OSAS) has been well established and its mechanisms are sill under debate. We have thus performed right heart catheterization, in addition to standard spirography and arterial blood gas measurements, in a series of 46 consecutive patients in whom OSAS was firmly diagnosed by whole-night polysomnography. Only 9 of the 46 patients (20%) had PH defined by a mean resting pulmonary arterial pressure (P.hivin.p.hivin.a) .gtoreq. 20 mm Hg. Among the patients without resting PH, 14 had exercising PH (defined by a P.hivin.p.hivin.a > 30 mm Hg during 40-watt, steady-state exercise). Patients with resting PH differed from the others by a lower daytime PaO2 (60.8 .+-. 7.6 versus 76.2 .+-. 9.4 mm Hg; p < 0.001), a higher daytime PaCO2 (44.6 .+-. 4.2 versus 38.0 .+-. 4.0 mm Hg; p < 0.001), and lower VC and FEV1 (p < 0.001). There was no difference between the 2 groups with regard to apnea index (62 .+-. 34 versus 65 .+-. 40) or the lowest sleep SaO2 (59 .+-. 21 versus 66 .+-. 18%) or the time spent in apnea. For the group as a whole, there was a good correlation between P.hivin.p.hivin.a and daytime PaO2 (r = -0.61; p < 0.001), PaCO2 (r = 0.55; p < 0.001), and FEV1 (r = -0.52; p < 0.001), but there was no significant correlation between P.hivin.p.hivin.a and the apnea index, the lowest sleep Sa02, or the time spent in apnea. Of the 9 patients with PH, 5 had a permanent chronic airway obstruction (CAO) of mild to moderate degree and 2 had severe obesity. These results suggest that (1) daytime PH is far from being the rule in patients with OSAS, (2) PH is not correlated with the severity of OSAS but with the presence of daytime hypoxemia, (3) an associated CAO is present in some patients with PH but is not an obligatory factor, and (4) in the absence of CAO, daytime hypoxemia could be due to severe obesity and/or to a diminished chemosensitivity.