Can stroke volume and cardiac output be determined reliably in a tilt-table test using the pulse contour method?

The applicability of the finger pressure-derived pulse contour (PC) techniq ue was evaluated in the measurement of stroke volume (SV), cardiac output ( CO) and their changes in different phases of the tilt-table test. The refer ence method was whole-body impedance cardiography (ICG). A total number of 40 physically active patients, aged 41 +/- 19 years, were randomly chosen f rom a pool of 230. Specifically speaking, 20 of the patients experienced (p re)syncope (tilt+ patients) during the head-up tilt (HUT), and 20 did not ( tilt-). A total number of three measurement periods, 30-60 s each, were ana lysed: supine position, 5 min after the commencement of HUT, and 1 min befo re set down. SV and CO values measured by PC underestimated significantly t hose measured by ICG (biases +/- SD 19 +/- 14 ml and 1.55 +/- 1.14 l min(-1 ), respectively) in agreement with earlier reports. The bias between the me thods was almost the same in the different phases of the test. However, the SD of the bias was bigger for tilt+ (P < 0.05). When the bias between the methods was eliminated by scaling the first measurement to 100%, the agreem ent between the methods in the second and third measurements was clearly be tter than without scaling. Both methods showed a physiological drop in SV a fter the commencement of HUT. These results indicate that PC suffices in tr acking the changes in CO and SV, but for absolute values it is not reliable .