Central hemodynamics in a baboon model during microgravity induced by parabolic flight.

We developed a chronically instrumented nonhuman primate model (baboon) to evaluate the central cardiovascular responses to transient microgravity induced by parabolic flight. Instrumentation provided simultaneous recording of high fidelity (Ao) and pulmonary artery (PA) pressures, right and left ventricular and atrial pressures, Ao and PA blood flow velocities and vessel dimensions, ECG and pleural pressures. Four daily flights in 1991 and five in 1992 were flown with forty parabola per flight. Animals flown in 1991 were not controlled for volume status. Animals flown in 1992 were studied in one of three conditions: 1) volume depleted by furosemide (DH), 2) volume expanded by saline infusion (VE), and 3) euvolemic (EU, no intervention, used for echo only). Mean right atrial pressures (RAP) during 1991 flights had a variable early microgravity response: increases in n=3 and decrease in n=3 (supine) and increases in n=5, decreases in n=2 (upright). In 1992 flights, DH, upright and supine, changed -10 +/- 4.1 mmHg, -3.2 +/- 2.2 mmHg, respectively (p < .05) compared to the pull-up phase. In contrast, VE changed (from pull-up to microgravity) +13 +/- 1.5 mmHg and +4.25 +/- 2.9 mmHg (upright and supine, respectively, p < .05). EU increased with microgravity +6.9 +/- .9 mmHg (upright only). LAP responses were similar, but more variable. Finally, heart chamber areas paralleled pressure changes. Thus, right and left heart filling pressure changes with sudden entry into microgravity conditions were dependent on initial circulatory volume status and somewhat modified by position (supine vs upright).