Abstract
Background: Nocturnal hypoxemia is important in precapillary pulmonary hypertension (pPH) as it worsens pulmonary hemodynamics. Whether daytime oxygen saturation (Sp<smlcap>o</smlcap><sub>2</sub>) predicts nocturnal hypoxemia in pPH patients has not been conclusively studied. Objectives: To investigate the prevalence of nocturnal hypoxemia in comparison to daytime Sp<smlcap>o</smlcap><sub>2</sub> and disease severity in ambulatory patients with pulmonary hypertension. Methods: Consecutive patients diagnosed with pPH classified as either pulmonary arterial (PAH) or chronic thromboembolic pPH (CTEPH) had daytime resting and exercise Sp<smlcap>o</smlcap><sub>2</sub> (at the end of a 6-min walk test); thereafter, they underwent overnight pulse oximetry at home. Functional class, pro-brain natriuretic peptide (pro-BNP) and the tricuspid pressure gradient were assessed. Results: Sixty-three patients [median (quartiles) age 62 (53; 71), 43 females] with PAH (n = 44) and CTEPH (n = 19) were included. The resting Sp<smlcap>o</smlcap><sub>2</sub>, exercise Sp<smlcap>o</smlcap><sub>2</sub>, and mean nocturnal Sp<smlcap>o</smlcap><sub>2</sub> were 95% (92; 96), 88% (81; 95), and 89% (85; 92), respectively. Forty-nine patients (77%) spent >10% of the night with Sp<smlcap>o</smlcap><sub>2</sub> <90% (desaturators), and 33 (52%) spent >50% of the night with Sp<smlcap>o</smlcap><sub>2</sub> <90% (sustained desaturators). The positive predictive values of daytime Sp<smlcap>o</smlcap><sub>2</sub> >90% for being a nocturnal nondesaturator or sustained nondesaturator were 25 and 53%, respectively. Nocturnal Sp<smlcap>o</smlcap><sub>2</sub> was negatively correlated with the tricuspid pressure gradient, but not with functional class, 6-min walk test, or pro-BNP. Conclusions: Nocturnal hypoxemia is very common in PAH and CTEPH despite often normal daytime Sp<smlcap>o</smlcap><sub>2</sub> and reflects disease severity. Nocturnal pulse oximetry should be considered in the routine evaluation of pPH patients and research should be directed toward the treatment of nocturnal desaturation in pPH.
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