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

Extract 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.