Effect of cardiac pacing on forearm vascular responses and nitric oxide function.
We examined the hypothesis that changes in heart rate at rest influence bioactivity of nitric oxide (NO) in humans by examining forearm blood flow responses during cardiac pacing in six subjects. Peak forearm and mean forearm blood flows across the cardiac cycle were continuously recorded at baseline and during pacing, with the use of high-resolution brachial artery ultrasound and Doppler flow velocity measurement. The brachial artery was cannulated to allow continuous infusion of saline or N(G)-monomethyl-L-arginine (L-NMMA). As heart rate increased, no changes in pulse pressure and mean or peak blood flow were evident. L-NMMA had no effect on brachial artery diameter, velocity, or flows compared with saline infusion. These results contrast with our recent findings that exercise involving the lower body, associated with increases in heart rate and pulse pressure, also increased forearm blood flow, the latter response being diminished by L-NMMA. These data suggest that changes in blood pressure, rather than pulse frequency, may be the stimulus for shear stress-mediated NO release in vivo.
Green
Daniel
D
Department of Human Movement and Exercise Science, The University of Western Australia, Nedlands 6907, Western Australia 6000.
Cheetham
Craig
C
Henderson
Chelsea
C
Weerasooriya
Rukshen
R
O'Driscoll
Gerard
G
D001794:Blood Pressure / Q000502:physiology; D001916:Brachial Artery / Q000502:physiology; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D015444:Exercise / Q000502:physiology; D005542:Forearm / Q000098:blood supply*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D017078:Laser-Doppler Flowmetry; D008875:Middle Aged; D009569:Nitric Oxide / Q000502:physiology*; D010138:Pacemaker, Artificial; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D013314:Stress, Mechanical; D019323:omega-N-Methylarginine / Q000008:administration & dosage
D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D009569:Nitric Oxide