Effect of different degrees of tilt on cardiac output, heart rate, and blood pressure in normal man.

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Abstract
The effects of different angles of head-up tilting on cardiac output, heart rate, and arterial blood pressure have been studied. The results show that when normal subjects are placed at head-up tilt positions of either 10[degree], 20[degree], 30[degree], 40[degree], 55[degree], or 60[degree], the major change of cardiac output occurs between 10[degree] and 20[degree] and there is little change on further tilting to 60[degree]. On return to recumbency, there is a delay of at least 11 to 25 min. before the cardiac output reaches the level recorded before tilting. The changes in heart rate and systemic blood pressure do not correlate with the magnitude of the decrease in cardiac output. Although the cardiac output does not fall further when the subject is tilted beyond 20[degree], the stroke output continues to fall up to 60[degree].