The effect of meal size on postprandial increase in cardiac output

Heart rate, stroke volume, cardiac output and mean arterial blood pressure were followed from the resting pre-meal situation and for 2 hours after intake of standardized meals in four healthy individuals. Continuous records of stroke volume and cardiac output were achieved with an improved method of Doppler ultrasonography. A smallish meal and one 2 1/2 times larger were both given twice and in random order to each of the four test persons. The consumption of a meal invariably resulted in a cardiac output increase, which developed gradually to reach a maximum level 30 to 60 min after end of the meal. The postprandial cardiac output increase resulted from significant increases in both heart rate and stroke volume. There were distinct and significant differences between the circulatory responses to small and large meals. The increase in cardiac output after a large meal was considerably larger and lasted for longer than the increase after a small meal. Two hours after a small meal cardiac output was nearly or fully back to pre-meal values, while cardiac output was still markedly elevated 2 hours after a large meal. Consequently, the total 'extra' amount of blood delivered by the heart over 2 post-meal hours was significantly--about 100%--larger after the large meal than after the small one. Mean arterial blood pressure either fell or remained almost unchanged in the hour after a meal, so that total peripheral resistance was consistently and significantly reduced in the postprandial period--and considerably more so after a large meal than after a small one.