OBJECTIVE: To understand the change of the cardiovascular function and to evaluate the usefulness of sphygmography and heart rate variability (HRV) spectrum techniques on estimating cardiovascular function during HUP + LBNP. METHOD: Blood pressure, ECG, cerebral oxygen saturation and sphygmogram of 16 subjects were studied during 75 degrees head up tilt plus lower body negative pressure (HUP + LBNP). RESULT: (1) During HUP + LBNP, heart rate, blood pressure, normalized low frequency component (LFn), LFn/HFn increased significantly, the cerebral blood oxygen saturation, T wave (ECG), HFn decreased significantly; (2) Blood pressure, heart rate and cerebral blood oxygen saturation decreased significantly in presyncopal state; (3) The heart rate in low tolerance group was higher than that in high tolerance group during the initial stage of HUT + LBNP; (4) The shape of pulse wave changed enormously during HUP + LBNP, so that no analysis could be made. CONCLUSION: HUP + LBNP was an effective approach to examine the regulatory function of cardiovascular system, and the sphygmogram could not be used in studying the regulatory function of cardiovascular system during HUP + LBNP.