Unveiling orthostatic hypotension in precapillary pulmonary hypertension

In addition to critical alterations in the pulmonary arterial network, pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) may exhibit cardiovascular abnormalities that impair systemic arterial pressure regulation during gravitational challenges. Therefore, we investigated the prevalence, subtypes, and hemodynamic mechanisms of orthostatic hypotension (OH) in PAH or CTEPH. OH was assessed using a 10-min active standing manoeuvre from supine baseline, with heart rate (HR; electrocardiogram) and arterial pressure (volume clamp finger photoplethysmography) measured beat-by-beat. Stroke volume (SV) was estimated from the arterial pressure waveform, while cardiac output (CO) and total peripheral resistance (TPR) were calculated. Among 60 patients, 31 (52%) had OH. Patients with and without OH did not differ in clinical characteristics and OH related symptoms (all p>0.050). HR, SV, CO, and TPR responses (% change from supine baseline) were not different between groups with and without initial OH (p>0.05). However, SV decrease was greater in the group with than without delayed arterial pressure recovery (−31±21 versus −19±14%; p=0.033). Additionally, a compensatory increase in TPR was blunted in the group with classic/delayed OH than without OH (−6±21 versus 7±15%; p=0.023). In sum, OH is common in patients with PAH or CTEPH but is not associated with specific clinical characteristics. Initial OH lacks a clear hemodynamic cause, whereas delayed recovery and classic/delayed OH are linked to impaired SV and TPR responses to standing, respectively.