Visceral blood flow distribution during exercise to exhaustion in conscious dogs

We measured changes in organ blood flow (OBF) distribution and systemic hemodynamics in 9 dogs running 5-13 km/h during steady-state (SS) and exhaustive (EE) exercise on a treadmill at 8-15% grade for an average of 35 min. SS was defined when a heart rate (HR) of 80% maximum was attained and when HR was constant for 5-8 min. EE was defined as when the dog collapsed, unable to run longer. We measured heart rate, mean aortic pressure, cardiac output, and stroke volume via implanted probes and catheters. All hemodynamic parameters rose significantly (P less than 0.05) with exercise. Stroke volume and aortic pressure did not rise above SS levels during EE. OBF, determined with microspheres, to the liver, stomach, and intestines declined during SS and returned to control levels during EE. OBF to the kidneys and pancreas was not significantly changed by either SS or EE. OBF to the spleen declined progressively with SS and EE. We concluded that 1) the effect of exercise on OBF depends on the severity of exercise, emphasizing the need to quantify work loads in exercise studies, and 2) the splanchnic organs do not respond homogeneously to exercise and that this response is not adequately described by % of CO assessments.