Effects of passive tilting on capillary filtration in the lower leg in idiopathic dilated cardiomyopathy and after heart transplantation for the samecondition

Abnormal reflex control of the peripheral microvasculature during orthostas is in congestive heart failure (CHF) and after heart transplantation (HT) m ay cause failure of microvascular homeostasis and peripheral edema. We expl ored the effect of passive head-vp tilt on lower leg capillary filtration m easured by strain-gauge plethysmography in 24 patients with CHF, in 20 pati ents after HT (12 patients with preserved native right atrium, 8 patients w ithout native right atrium), and in 18 controls. We hypothesized that an im paired peripheral microvascular reflex during orthostasis in CHF and Hi mig ht allow increased arterial hydrostatic pressure to increase pressure at th e capillary level. To identify an impact of changes in arterial hydrostatic pressure, capillary fluid filtration was expressed per mm Hg arterial hydr ostatic pressure (capillary filtration coefficient(arterial pressure) [CFCA P]) and was measured (1) during elevated venous pressure alone (50 mm Hg ve nous stasis in supine position), and (2) during elevated hydrostatic pressu re at both the venous and arterial side of the vascular tree (head-up tilt with a vertical distance from the right atrium to the strain-gauge of 68 cm of water [50 mmHg]). Elevated venous pressure alone resulted in the highes t CFCAP in controls (0.79 +/- 0.28 ml/min 100 ml mm Hg . 10(-3) +/- SD) ver sus those with CHF (0.44 +/- 0.23, p <0.0001) and those after HT (0.54 +/- 0.22, p <0.01). However, during head-vp tilt, CFCAP was similar in all 3 gr oups, because CFCAP decreased in controls (to 0.49 +/- 0.22, p <0.0001), in contrast to unchanged CFCAP in those with CHF (0.43 +/- 0.24) and in those with HT (0.50 +/- 0.21). HT patients with complete removal of the native r ight atrium had higher CFCAP (0.62 +/- 0.17) during head-up tilt than patie nts with preserved native right atrium (0.36 +/- 0.16, p <0.005). In conclu sion, patients with CHF and those after HT have increased capillary filtrat ion to a lesser degree than controls during elevated venous pressure alone. However, during orthostasis this apparent edema-protective mechanism vanis hes, probably because of compromised microvascular reflex control. During d aily upright activities, this may be one important factor in the edema path ogenesis. The phenomenon is particularly distinct in HT patients without pr eserved native right atrium. (C) 1999 by Excerpta Medica, Inc.