The relationship between pressure and flow in the systemic circulation of the dog.

Cardiac output was determined in dogs over a wide range of pressures before and after preclusion of compensatory reflex mechanisms. When the moderator reflexes are functional, total peripheral resistance increases markedly with moderate reductions in arterial pressure. When reflex alterations of vasomotor tone are obviated, pressure and flow usually vary proportionately as arterial pressure is altered. In the average experiment, total peripheral resistance remains relatively constant although appreciable deviations may be observed in individual cases.