A species comparison of the effects of changing perfusion pressure on blood flow and metabolic heat production in the myocardium.

1. A heated thermocouple technique (internal calorimetry) has been used to investigate blood flow and heat production responses in the myocardium to changing blood pressure in monkeys, dogs, rabbits, guinea-pigs and rats. 2. Perfusion experiments (isolated guinea-pig and dog hearts) showed linear relations between conductivity increment and coronary blood flow up to 1 x 5 ml. g(-1) min(-1) (dog heart perfused with blood) and 5 ml. g(-1) min(-1) (guinea-pig heart perfused with saline). This relation was the same in the beating and non-beating heart. 3. In rabbits, guinea-pigs and rats the relation between flow (conductivity increment) and blood pressure was linear. In contrast, in monkeys and dogs, over the range 100-40 mm Hg, little change in blood flow occurred. After the injection of procaine around the stellate ganglion, the relation between pressure and flow in both species was linear. It is suggested that the constancy of blood flow displayed in the monkey and dog over this blood pressure range was due to the activity of adrenergic rasodilator fibres. 4. Evidence is adduced to show an increased myocardial heat production when systemic arterial pressure fell below about 60 mm Hg. This was not affected by cardiac denervation. The possible significance of this effect is discussed.