AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 2 160-R165, Copyright © 1983 by American Physiological Society
Effects of training on cardiorespiratory function in the horse
D. P. Thomas, G. F. Fregin, N. H. Gerber and N. B. Ailes
The effects of 5- and 10-wk treadmill exercise training on
cardiorespiratory function were evaluated in the horse. Cardiac output (Q),
heart rate (HR), and stroke volume (SV), as well as left ventricular (LVP),
aortic (AoP), and mean right atrial (RAP) pressures and the peak first time
derivative of LVP (LV dP/dtmax), were measured at rest and at five
different levels of exercise up to 90% of initial predicted maximal HR
(HRmax). Oxygen uptake (VO2) and respiratory exchange ratio (R) were also
obtained under the same conditions. At rest, although HR was no different
after training, LV dP/dtmax was lower at 10 wk (2,369 +/- 502 vs. 1,615 +/-
302 mmHg/s). At the different measured work loads during exercise, Q and
VO2 remained unchanged with training, whereas there were consistent trends
toward lower LVP, AoP, and LV dP/dtmax and significant reductions in HR and
R (both P less than 0.05). In contrast, SV and mean RAP were elevated (P
less than 0.05) during exercise after the 10-wk training program. Although
the observed changes in cardiorespiratory function in response to a
training program in the horse are generally similar to those reported for
other species, our data also suggest a training-induced increase in venous
pressures during exercise as measured by elevated mean RAP values.
