Single‐unit muscle sympathetic recordings identify in human heart failure unique fibers discharging in response to both unloading and loading of cardiopulmonary receptors (LB735)

Abstract

In healthy men, multi‐unit muscle sympathetic nerve activity (MSNA) has been shown to integrate two populations of single‐units exhibiting directionally opposite discharge to acute selective perturbations in atrial pressure. The behaviour of these single‐units was consistent during application of lower body negative and positive pressure (LBNP and LBPP). The aim of the present study was to compare single‐unit discharge characteristics of patients with and without heart failure (HF). We measured central venous pressure and single‐unit MSNA in 6 HF patients (LVEF: 24±6%; 54±13 years [mean±SD]) and 9 healthy controls (56±8 years) before and during 7 minutes of LBNP and LBPP (±10mmHg). These interventions had no effect on stroke volume, heart rate or systemic blood pressure (All P>0.05). Twelve HF and 22 control single‐units were identified. In controls, single‐unit responses to LBNP and LBPP exhibited either ‘anticipated’ (increased with LBNP and decreased with LBPP) or ‘paradoxical’ (decreased with LBNP and increased with LBPP) firing behavior. In HF, the majority (8/12; 67%) of single‐units exhibited a unique U‐shaped discharge pattern, with ‘anticipated’ responses to LBNP but ‘paradoxical’ responses to LBPP. This novel observation provides evidence for the emergence in HF of a population of cardiopulmonary mechanoreceptors exerting consistently sympathoexcitatory efferent firing characteristics.Grant Funding Source: Supported by the Canadian Institutes of Health Research (PJM) and Canadian Research Chairs program (JSF)