Hypercapnic Pulmonary Vasoconstriction as a Mechanism for Regional Perfusion Redistribution in Asthma

Prevalence of pulmonary hypertension on echocardiogram in children with severe obstructive sleep apnea

STUDY OBJECTIVES

Pulmonary hypertension (PH) is a rare yet serious complication of obstructive sleep apnea (OSA). Echocardiographic screening for PH is recommended in children with severe OSA, but the health care burden of universal screening is high. We sought to determine the prevalence of PH on echocardiogram among children with severe OSA and identify variables associated with a positive PH screen.

METHODS

Retrospective study of 318 children with severe OSA (obstructive apnea-hypopnea index ≥ 10 events/h) and echocardiogram within 1 year of polysomnogram. PH-positive echocardiogram was defined by peak tricuspid regurgitation velocity ≥ 2.5 m/s and/or 2 or more right-heart abnormalities suggestive of elevated pulmonary artery pressure. Patient characteristics and polysomnogram data were compared to identify factors associated with PH.

RESULTS

Twenty-six children (8.2%; 95% confidence interval [CI] 5.4-11.8%) had echocardiographic evidence of PH. There was no difference in age, sex, body mass index, obstructive apnea-hypopnea index, or oxygenation indices between patients with and without PH. Sleep-related hypoventilation (end-tidal CO₂ > 50 mmHg for > 25% of total sleep time) was present in 25% of children with PH compared with 6.3% of children without PH (adjusted prevalence ratio = 2.73; 95% CI 1.18-6.35). Forty-six percent of children (12/26) with PH had Down syndrome vs 14% (41/292) without PH (adjusted prevalence ratio = 3.11; 95% CI 1.46-6.65).

CONCLUSIONS

There was a relatively high prevalence of PH on echocardiogram in our cohort of children with severe OSA. The findings of increased PH prevalence among children with sleep-related hypoventilation or Down syndrome may help inform the development of targeted screening recommendations for specific pediatric OSA populations.

CITATION

Maloney MA, Davidson Ward SL, Su JA, et al. Prevalence of pulmonary hypertension on echocardiogram in children with severe obstructive sleep apnea. J Clin Sleep Med. 2022;18(6):1629-1637.

Borderline pulmonary hypertension associated with chronic hypercapnia in chronic pulmonary disease

Pulmonary hypertension (PH) due to lung diseases is classified as group 3 by the Dana Point classification. Given the basic pathophysiological conditions of group 3 lung diseases and the previously well-known concept of hypercapnic pulmonary vasoconstriction, chronic hypercapnia besides alveolar hypoxia might be another causative factor to increase mean pulmonary arterial pressure (PAm). Two hundred twenty-five subjects with chronic pulmonary diseases were assessed by a right heart catheterization and blood gas parameters. The subjects were classified into the following 4 groups: Hypercapnic Hypoxia (HCHX), Hypercapnic Normoxia (HCnx), Normocapnic Hypoxia (ncHX), and Normocapnic Normoxia (ncnx). Compared with ncnx, the HCHX, HCnx and ncHX groups all showed significantly higher PAm and met the criteria of borderline PH. Multiple regression analysis showed that PaCO₂, as well as SaO₂, was an independent variable for PAm. Given the poor prognosis with borderline PH, the elimination of excess pulmonary carbon dioxide in hypercapnia could be a considerable treatment strategy in chronic pulmonary disease.