THE EFFECT OF PASSIVE TILTING ON MICROVASCULAR PARAMETERS IN THE HUMAN CALF - A STRAIN-GAUGE PLETHYSMOGRAPHY STUDY

1. Cumulative small steps in venous congestion pressure were used to s tudy the effect of passive tilt on vascular parameters in dependent ti ssues. Using this protocol we have non-invasively assessed venous pres sure (P-v,P-est), isovolumetric cuff pressure (P-v,P-i), which is the congestion cuff pressure (P-cuff) that has to be exceeded to induce fl uid filtration. We have also assessed microvascular filtration capacit y (K-f), which is the linear relationship between filtration rate (J(v )) and P-cuff, when P-cuff > P-v,P-i, and is the product of the availa ble exchange vessel surface area and wall conductance. 2. The pre-tilt value of K-f did not change after the imposition of the passive tilt, the values being 3.2 +/- 0.4 x 10(-3) and 3.6 +/- 0.4 x 10(-3) ml min (-1) (100 ml(-1)) mmHg(-1), respectively, (n = 13). 3. The pre-tilt va lue of K-f did not change after the imposition of the passive tilt, th e values being 3.2 +/- 0.4 x 10(-3) and 3.6 +/- 0.4 x 10(-3) ml min(-1 ) (100 ml(-1)) mmHg(-1), respectively, (n = 13). 4. These results supp ort the notion that passive postural change alters the pre-capillary r esistance, thereby altering the pressure and flow characteristics with in the exchange vessels, but does not alter the surface area available for fluid exchange in the calf contrary to previous findings in the d ependent human foot using a single-step venous occlusion protocol.