Effects of heat and cold stress on central vascular pressure relationships during orthostasis in humans.

Central venous pressure (CVP) provides information regarding right ventricular filling pressure, but is often assumed to reflect left ventricular filling pressure. It remains unknown whether this assumption is correct during thermal challenges when CVP is elevated during skin-surface cooling or reduced during whole-body heating. The primary objective of this study was to test the hypothesis that changes in CVP reflect those in left ventricular filling pressure, as expressed by pulmonary capillary wedge pressure (PCWP), during lower-body negative pressure (LBNP) while subjects are normothermic, during skin-surface cooling, and during whole-body heating. In 11 subjects, skin-surface cooling was imposed by perfusing 16 degrees C water through a water-perfused suit worn by each subject, while heat stress was imposed by perfusing 47 degrees C water through the suit sufficient to increase internal temperature 0.95 +/- 0.07 degrees C (mean +/- s.e.m.). While normothermic, CVP was 6.3 +/- 0.2 mmHg and PCWP was 9.5 +/- 0.3 mmHg. These pressures increased during skin-surface cooling (7.8 +/- 0.2 and 11.1 +/- 0.3 mmHg, respectively; P < 0.05) and decreased during whole-body heating (3.6 +/- 0.1 and 6.5 +/- 0.2 mmHg, respectively; P < 0.05). The decrease in CVP with LBNP was correlated with the reduction in PCWP during normothermia (r = 0.93), skin-surface cooling (r = 0.91), and whole-body heating (r = 0.81; all P < 0.001). When these three thermal conditions were combined, the overall r value between CVP and PCWP was 0.92. These data suggest that in the assessed thermal conditions, CVP appropriately tracks left ventricular filling pressure as indexed by PCWP. The correlation between these values provides confidence for the use of CVP in studies assessing ventricular preload during thermal and combined thermal and orthostatic perturbations.