Redistribution of cardiac output in response to heat exposure in the pony.
Radioactive microspheres were used to measure cardiac output and blood flow to most major tissues in 4 ponies at rest in thermoneutral (16 degrees C/60% RH) and mildly hot (41 degrees C/34% RH) environments. In response to heat stress there were increases in cardiac output (2-fold), respiratory frequency (5-fold), blood flow to the skin of the body (3-fold), and limbs (50%), respiratory muscles (2-fold) and the upper respiratory tract (3-fold). Ponies were able to maintain body temperature in the hot environment by increasing blood flow to the tissues involved in heat dissipation, while blood flow to all other tissues remained stable. This was achieved by increasing the cardiac output without need for reduction of blood flow to other tissues.
McConaghy
F F
FF
Equine Performance Laboratory, University of Sydney, NSW, Australia.
Hodgson
D R
DR
Rose
R J
RJ
Hales
J R
JR
D000818:Animals; D002302:Cardiac Output; D006339:Heart Rate; D006734:Horse Diseases / Q000209:etiology / Q000503:physiopathology*; D006736:Horses / Q000502:physiology*; D006358:Hot Temperature / Q000009:adverse effects*; D008297:Male; D008863:Microspheres; D009297:Nasal Mucosa / Q000098:blood supply; D010101:Oxygen Consumption; D012039:Regional Blood Flow; D012132:Respiratory Muscles / Q000098:blood supply; D012867:Skin / Q000098:blood supply; D012881:Skin Temperature; D013312:Stress, Physiological / Q000209:etiology / Q000503:physiopathology / Q000662:veterinary*; D013318:Stroke Volume; D014420:Turbinates / Q000098:blood supply