Intracardiac hemodynamics in man during short periods of head-down and head-up tilt.

The intracardiac hemodynamic responses to short periods of 70 o l head-down and head-up tilts were studied in 12 normal male subjects, ages 19-24 years. Echo-Doppler techniques were used to measure the transmitral and transaortic flow velocities as well as cardiac index, and to evaluate the peripheral impedance. Head-down tilt (HDT) rapidly induced an increase (9.7%, p<0.05) in the early passive filling of the left ventricle (Me peak of the transmitral flow velocity curve) and in transaortic flow velocity (8%, p<0.05), as well as in cardiac output (6%, p<0.05)