Slow deep breathing reduces muscle sympathetic nerve activity and improves breathing efficiency in pulmonary hypertension

<title>Extract</title> Excessive muscle sympathetic nervous activity (MSNA) in pulmonary arterial hypertension (PAH) has been associated with impaired exercise capacity and risk of clinical deterioration [1]. In animal models of PAH and chronic thromboembolic pulmonary hypertension (CTEPH), SNA promotes deleterious pulmonary vascular and right ventricular remodelling [2, 3]. Despite this, no therapies target sympatho-excitation in pulmonary hypertension. MSNA cycles with respiration such that it is suppressed by high lung volumes [4]. Slow deep breathing, by enhancing within-breath suppression of MSNA, could reduce sympatho-excitation. Small uncontrolled trials of home device-guided slow deep breathing in pulmonary hypertension (PAH and CTEPH) for 2–3 months have shown improvements in WHO functional class, health-related quality of life, and NT-proBNP [5, 6]. However these two studies have not assessed the physiologic implications (acute or longer term) of this therapy. We hypothesised that slow deep breathing would acutely reduce MSNA in pulmonary hypertension.