Background: Trimethylamine N-oxide (TMAO), the gut microbiota-dependent metabolite, is a potential biomarker in several cardiovascular diseases. However, no study has investigated its value in pulmonary hypertension (PH). Therefore, this study aimed to explore the association between plasma TMAO levels and prognosis in patients with PH.Methods: Inpatients with idiopathic/heritable pulmonary arterial hypertension (IPAH/HPAH), PAH associated with congenital heart disease (CHD-PAH), and chronic thromboembolic pulmonary hypertension (CTEPH) at Fuwai Hospital were enrolled after excluding those with relative comorbidities. The endpoint was defined as a composite outcome including death, rehospitalisation due to heart failure, and at least 15% decreased 6-min walk distance from the baseline. Fasting blood samples were collected to measure plasma levels of TMAO and other clinical indicators. The associations between TMAO levels with disease severity and patients’ prognosis were investigated.Results: In total, 163 patients with PH were included, with a mean follow-up duration of 1.3 years. After adjusting for confounding factors, elevated TMAO levels were still associated with severe disease conditions. TMAO levels dynamically decreased in stable and improved patients after treatment [ΔTMAO = − 0.2 (− 1.6, 0.7) μmol/L,P = 0.006]. Moreover, high plasma TMAO levels predicted a poor prognosis in the PH cohort (P < 0.001), and the association remained significant after adjusting the confounders, including treatment, risk stratification, and PH subtypes.Conclusion: Elevated plasma TMAO levels were associated with severe disease conditions and poor prognosis in patients with PH, indicating its potential biomarker role in PH.

Objective: Obstructive sleep apnoea (OSA) is one cause of pulmonary hypertension (PH) and can also emerge along with PH. The clinical diagnosis and treatment of OSA in patients with PH are still controversial. The purpose of this clinical observation study was to observe and summarize the incidence and clinical characteristics of OSA in patients with PH and to explore possible predictors of PH combined with OSA. Methods: Patients with PH diagnosed by right heart catheterization who underwent overnight cardiorespiratory monitoring from December 2018 to December 2020 were enrolled. OSA was defined as an apnoea–hypopnoea index of ≥ 5/h with ≥ 50% of apnoeic events being obstructive. Baseline clinical characteristics and parameters were collected to compare PH patients with and without OSA. Logistic regression analysis was run to determine the risk factors for OSA in PH patients. Results: A total of 35 (25%) of 140 patients had OSA. OSA is relatively frequent in patients with PH, especially in patients with chronic thromboembolic pulmonary hypertension and patients with lung disease– or hypoxia-associated PH. The patients who had OSA were mostly male and had a higher age and a lower daytime arterial oxygen pressure. Logistic regression analysis found that older age, male sex, and lower daytime arterial blood oxygen pressure correlated with OSA in PH patients. Conclusion: OSA is common in patients with PH. Lower daytime arterial oxygen pressure is a risk factor for OSA in older male patients with PH.