Central venous pressure in space

Gravity affects cardiac filling pressure and intravascular fluid distribution significantly. A major central fluid shift occurs when all hydrostatic gradients are abolished on entry into microgravity (μG). Understanding the dynamics of this shift requires continuous monitoring of cardiac filling pressure; central venous pressure (CVP) measurement is the only feasible means of accomplishing this. We directly measured CVP in three subjects: one aboard the Spacelab Life Sciences-1 space shuttle flight and two aboard the Spacelab Life Sciences-2 space shuttle flight. Continuous CVP measurements, with a 4-Fr catheter, began 4 h before launch and continued into μG. Mean CVP was 8.4 cmH₂O seated before flight, 15.0 cmH₂O in the supine legs-elevated posture in the shuttle, and 2.5 cmH₂O after 10 min in μG. Although CVP decreased, the left ventricular end-diastolic dimension measured by echocardiography increased from a mean of 4.60 cm supine preflight to 4.97 cm within 48 h in μG. These data are consistent with increased cardiac filling early in μG despite a fall in CVP, suggesting that the relationship between CVP and actual transmural left ventricular filling pressure is altered in μG.