Abstract
We investigated the differences in the responses of the circulatory system between the sitting and supine positions for defecation in the setting of effective intrathoracic （IT） pressure. Ten healthy volunteers （age 34.1±11.2 years） consented to participate in this study. They raised their IT pressures to 10, 20 and 30 mmHg in the supine and sitting positions for 15 sec each. From the beginning to the end of the experiment, the heart rate （HR）, blood pressure （BP）, stroke volume （SV） assessed by chest impedance, IT pressure and intra-rectal （IR） pressure were sampled. In addition, the BP, HR, SV corresponding to the IT pressure with an IR pressure of 10 mmHg or higher, defined by us as sufficient for defecation, were measured again every second by using the spline function.
The IT pressure in the sitting position was significantly higher as compared to that in the supine position （P ＝0.036）.
After rising at the beginning starting of the IT pressure rise, the BP fell, to rise once again 9 seconds later ； it increased after falling just after the release of the breath. The HR increased and remained high from the beginning of the IT pressure overload to the end of the experiment. The rate of change of the SV decreased during the IT pressure strain as compared with that at rest, and increased again after the strain was released. No significant differences of any of the parameters depending on the posture were observed. For the same IR pressure for defecation, there were no significant differences in the circulatory indices between the two different postures. These findings suggest that defecation in the seated position might be indicated even from an early stage if the patient can maintain the sitting posture.
