Head-up tilt and passive leg raising in healthy volunteers as a preclinical model for preload-induced stroke volume modification

Introduction

In clinical practice, fluid responsiveness is tested by inducing changes in the stroke volume (SV), as measured with invasive monitoring techniques in often time-consuming procedures. To be able to investigate the effects of changes in SV on other hemodynamic parameters, there is the need for a preclinical model that can be translated to clinical practice. For this purpose we studied the effect of the head-up tilt (HUT) test and passive leg raising (PLR) test on SV in five healthy volunteers.

Methods

The tilt table test consisted of 3 minutes of supine rest followed by a HUT of 70° on a manually operated tilt table and ending with 3 minutes of supine rest. The PLR test consisted of 3 minutes of rest in a semirecumbent position of 30°, followed by 3 minutes PLR (lower limbs elevated at 30° and trunk in supine position) and ending with 3 minutes of rest in a semirecumbent position. Three HUTs and two PLR tests were performed. The SV was measured continuously and noninvasively using a NICOM (Cheetah Medical, Tel Aviv, Israel), based on chest bioreactance, and a Finometer (TNO Biomedical Instrumentation, Amsterdam, the Netherlands), based on the Modelflow method. The Finometer also measured the mean arterial pressure.

Results

Both HUT and PLR induced significant changes in SV (Figure 1). In addition the cardiac output changed significantly, but not during HUT when measured with the Finometer. Although both devices showed a similar response to the postural changes, the baseline values and magnitude of these responses were not identical. The mean arterial pressure remained constant during these manoeuvres. The heart rate significantly increased during HUT but not during PLR.

Figure 1

abstract P210

Conclusion

The combination of noninvasive monitoring techniques with preload-induced SV modifications in healthy volunteers provides an excellent preclinical model for the study of fluid responsiveness. Although these hemodynamic monitors might provide different results, this model should be very suitable to assess the effect of SV variations on, for instance, parameters of peripheral perfusion.