Cardiovascular responses at the onset of static exercise in
patients with dual-chamber pacemakers.
Williamson, J. W., A. C. L. N[acute]obrega, J. A. Garcia, D. B.
Friedman, and J. H. Mitchell.
Harry S. Moss Heart Center, U.T. Southwestern Medical Center,
Dallas, Texas 75235-9034
APStracts 2:0324A, 1995.
Cardiac output responses to exercise can be altered by ventricular
pacing in pacemaker-dependent patients. The relative contributions of
cardiac output (CO) and peripheral vascular resistance (PVR) towards
the initial increase in blood pressure with the initiation of static
exercise were investigated in eight otherwise healthy pacemaker-
dependent subjects (age = 24 +/-2 yr (range 17 - 37)). Beat-by-beat
measures of heart rate (HR, electrocardiography), mean arterial
pressure (MAP; Finapres) and cardiac output (CO) derived from stroke
volume (SV) (CO = HR x SV; 2-D echocardiography) were determined
during the first 20 s of a one-legged static knee extension performed
at 20% MVC using three pacing modalities: dual pacing and sensing
mode (DDD- "normal physiological HR response"), fixed at
resting heart rate (DOO-R) and fixed at peak exercise heart rate
(DOO-E) as previously achieved during five minutes of sustained
contraction in the DDD mode. There were no differences in MAP, CO, or
peripheral vascular resistance (PVR = MAP x CO-1) between modes at
rest (P > 0.05). With DOO-E pacing, SV was lower at rest as
compared to the other modes and increased with exercise (P <
0.05). While there were no significant increases in MAP or CO during
DOO-R pacing, both variables were elevated by leg contraction during
DDD and DOO-E pacing (P < 0.05), with no significant change in
PVR. Additionally, the CO and MAP increases were significantly
greater with DOO-E pacing (P < 0.05). Thus, the magnitude of the
initial increase in arterial pressure at the onset of mild one-legged
static exercise was dictated by the changes in cardiac output as
peripheral vascular resistance remained unchanged.
Received 18 August 1994; accepted in final form 27 June 1995.
APS Manuscript Number A875-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.