Circulatory responses to a meal in patients with a newly transplanted heart

Abstract

It is well established that consumption of a meal releases a gradually developing and quite marked increase in blood flow to the gastrointestinal organs and a similar and simultaneous increase in cardiac output (CO). It is not known through which mechanism the pumping of the heart adjusts so accurately to the gastrointestinal flow increase. We have approached this problem by serving a standardized, mixed meal to five patients with recently transplanted and thus denervated hearts and to five sex- and age-matched controls. Pre- and postprandial levels of CO and blood flow in the superior mesenteric artery (SMA) were recorded with Doppler ultrasound technique. The patients with transplanted hearts had significantly higher preprandial levels of heart rate (HR) and CO than the controls. With a timing similar to that seen in the controls did all five patients develop considerable and synchronous postprandial increases in superior mesenteric arterial flow and in CO. Increases in superior mesenteric arterial flow were significantly greater than the controls. Also, COs, high even before meals were given, increased further and to the same relative extent as in the control persons. The marked postprandial increase in CO, probably secondary to the increase in intestinal blood flow, could hardly come about through any sort of nervous reflex to the recently transplanted and denervated hearts. It appears more likely that a humoral connection of some sort exists between the two circulatory events.

Mechanisms behind the postprandial increase in cardiac output: a clue obtained from transplanted hearts

“…Normal innervated hearts exhibit marked HR Xuctuations in synchrony with respiratory movements, provided that the vagal cardiac innervation is intact (Toska and Eriksen 1993). Such Xuctuations were completely absent in all Wve patients when they were tested for the Wrst time (Waaler et al 2002). The new measurements showed that three of the patients still exhibited steady, nonXuctuating HR levels at rest.…”

“…The Doppler sample volume was again directed to just above the aortic oriWce. The cross-sectional area of the rigid aortic ring, which was necessary for the calculation of CO, had been determined in the previous tests (Waaler et al 2002). The ring diameter and cross-sectional area were again measured and calculated and were consistently found to be unchanged from the earlier measurements.…”

“…Measurements CO was measured with pulsed ultrasound Doppler at 2 MHz, using the same recording techniques as previously described (Eriksen and Walløe 1990) and exactly as applied in the tests 18 months earlier (Waaler et al 2002). The Doppler sample volume was again directed to just above the aortic oriWce.…”

“…Flow into the superior mesenteric artery (SMA) was arrived at by recording velocity and vessel diameter in the artery just distal to its departure from the aorta, using Doppler techniques as described in detail for the tests on the same patients 18 months earlier (Waaler et al 2002).…”

“…However, it is not known what mechanism lies behind the postprandial increase in cardiac performance, or whether or not it is reXex in nature. In order to gain information on possible regulatory connections between the digestive processes and the postprandial increase in CO, we have previously recorded circulatory responses to a meal in Wve patients with newly transplanted and thus fully denervated hearts (Waaler et al 2002). Their splanchnic blood Xow and CO increased, following a time course indistinguishable from that seen in Wve matched normal controls.…”