The haemodynamic effects of head-up tilt (HUT) at different tilt angles were investigated non-invasively in eight normal male subjects. Mean arterial pressure (MAP; by Ohmeda Finapres 2300), stroke volume (SV) and heart rate (HR; by BoMed NCCOM3-R7S) were continuously recorded whilst performing a series of HUTs (55 degrees, 10 degrees, 20 degrees, 30 degrees and 55 degrees) lasting 3 min each. The response to HUT was proportional to the sinc of the tilt angle. The magnitude of the response varied between subjects. HUT to 55 degrees resulted in mean (95% confidence limits) increases in MAP by 16 (+/-16)% and HR by 11 (+/-24)% and a decrease in SV by -25 (+/-22)%. These results were repeatable after 30 min. At small tilt angles, i.e. < or = 20 degrees, MAP did not change and HR decreased by -3 (+/-4)%. A detailed analysis revealed immediate dynamic (0-30 s), late dynamic (30-90 s) and plateau (after 90 s) phases in the response to HUT. In conclusion, HUT produces reproducible haemodynamic effects, although differences exist among subjects. A detailed analysis of these effects can be successfully performed using non-invasive methods.
Adult Blood Pressure