Abstract

Objectives: To determine, in patients with pulmonary arterial hypertension (PAH), whether there is a relationship: (1) between sympathetic nerve firing rate and spectral indices of sympathetic neural heart rate modulation; and (2) between heart rate variability (HRV) and right atrial pressure, a stimulus to sinoatrial node stretch.

Design: Characterisation of patients and healthy controls.

Setting: Teaching hospital-based study.

Patients: 9 PAH patients without elevated pulmonary capillary wedge pressure and nine age-matched control subjects.

Interventions: Heart rate (HR) and muscle sympathetic nerve activity (MSNA) were recorded during 10 min of supine rest in both PAH patients studied after right heart catheterisation, and healthy volunteers. Coarse-graining spectral analysis determined HR spectral power.

Main outcome measures: (1) Low-frequency (P_L) spectral component of HRV; (2) MSNA burst frequency; and in PAH patients: (3) right atrial pressure.

Results: MSNA burst frequency was higher in PAH patients (48 (24) and 29 (11) bursts/min, respectively; mean (SD); p = 0.05), whereas total power (p = 0.01), its fractal (p<0.01) and harmonic (p = 0.04) components, and P_L (p = 0.01) were all reduced. P_L related inversely to both MSNA burst frequency (r = −0.86, p = 0.005) and right atrial systolic pressure (r = −0.77, p = 0.04).

Conclusions: Thus, in PAH (as in patients with left ventricular systolic dysfunction) loss of P_L relates inversely to gain in MSNA burst frequency. Diminished sympathetic neural heart rate modulation and increased right atrial stretch may combine to attenuate HRV, an adverse prognostic marker.