Hemodynamic effects of eating and prolonged supine position in healthy subjects studied under clinical-pharmacological test conditions.

The influences of both being in a supine position for a prolonged period and food intake on cardiovascular variables were studied under clinical-pharmacological test conditions. In a randomized crossover design study without drug or placebo administration, 6 healthy male volunteers received a light standard meal before and during test A and fasted in test B. In both tests, while they were continuously supine for more than 8 h, a synchronous recording of cardiovascular variables was done at 24, 26 and 28 min after starting the supine position (first recordings) and 25 times from 2 to 480 min after the first recordings. Using a multifactorial statistical analysis, each parameter was evaluated regarding the factors eating and time of supine recording. Eating led to a significant decrease in diastolic and mean blood pressure, PQ time and QS₂ time, a downward trend in systemic vascular resistance and an upward trend in systolic blood pressure and cardiac output. When the subjects remained in a supine position for prolonged periods, significant increases in systolic, diastolic, mean blood pressure and systemic vascular resistance were noted as well as significant decreases in cardiac output and QS₂ time. Thus, eating and remaining in a supine position for prolonged periods should be considered as sources of bias in clinical-pharmacological studies on cardiovascular drug effects and accompanying placebo controls.