Cardiac responses to the Valsalva manoeuvre in different body positions.

A standardized Valsalva manoeuvre (VM) with a 15-s straining period was repeated in each of four postures by six male subjects. The postures were supine (SUP), sitting leaning back (LB), sitting leaning forward (LF) and standing (ST). During straining, the increase in heart rate (fc) was different between LB and LF (+50% and +23%, respectively P less than 0.05). The decrease in stroke volume (SV), which was monitored by means of impedance cardiography, was different (63%, 68%, 39%, and 72%, P less than 0.001) as well as the decrease in cardiac output (CO) (55%, 53%, 26%, and 61%, P less than 0.001) in SUP, LB, LF, and ST, respectively. Accordingly, after pressure release the smallest changes of SV, fc and CO were found in LF. In conclusion, cardiovascular stability during straining was increased during LF. Consequently, this posture would appear to be superior to other postures during unavoidable VM (weight lifting and defaecation). To perform tests on autonomic function LB would appear to be superior to the other postures because of the large autonomic responses, combined with minimum risk for the subject. The impedance method provided simple and reproducible determinations of SV changes during VM.