Abstract 19395: Increased Multiple Firing of Single Muscle Vasoconstrictor Neurons during Lower Body Positive Pressure in Human Heart Failure
Introduction: Functionally specific efferent renal sympathetic nerves fire selectively in response to distinct hemodynamic afferent inputs. Using norepinephrine spillover, our group detected a heart failure (HF)-specific cardio-cardiac sympathoexcitatory reflex stimulated by high atrial pressure. Efferent discharge directed at other vascular beds similarly activated by atrial stretch might not be detected by multi-unit sympathetic recordings.
Hypothesis: In contrast to healthy controls (CON), in HF some muscle sympathetic fibers respond paradoxically (i.e. increase firing) to increases in filling pressure.
Methods: Single-unit muscle sympathetic nerve activity (sMSNA; microneurography) and peripheral venous pressure (PVP; forearm catheter) were recorded from 11 CON and 10 treated HF (LVEF 27±6%) patients at baseline and during non-hypotensive lower body negative pressure (LBNP; -10mmHg) and non-hypertensive lower body positive pressure (LBPP; +10mmHg). sMSNA firing frequency and incidence, and the percentage of multiple within-burst firing was calculated for each condition.
Results: PVP was reduced with LBNP (p<0.05) and increased with LBPP (p<0.05) in both groups, with PVP greater in HF across each condition (p<0.05). Blood pressure and heart rate were unchanged by LBNP or LBPP in both groups (p>0.05). We identified 26 and 22 single-units in CON and HF patients, respectively. sMSNA firing frequency was similar (p>0.05) in CON and HF at baseline (30±18 vs. 35±15 spikes/min) and during LBNP (45±24 vs. 42±23 spikes/min) but higher in HF during LBPP (28±17 vs. 40±22 spikes/min, p=0.05). sMSNA firing incidence was similar (p>0.05) in both groups across each condition. The percentage of within-burst multiple spike firing was similar (p>0.05) in CON and HF during baseline (24±9% vs. 24±7%) and LBNP (25±11% vs. 28±14%) but higher in HF during LBPP (17±8% vs. 34±16%, p<0.001).
Conclusions: In HF, increases in PVP with non-hypertensive LBPP cause a paradoxical increase in muscle sympathetic single-unit firing frequency and multiple within-burst firing, compared to CON. This provides evidence of a sympathoexcitatory cardiac-skeletal muscle vasoconstrictor reflex in human HF that may be attenuated by normalizing filling pressures.
- © 2012 by American Heart Association, Inc.