Physiologic effects of simulated + Gx orbital reentry in primate models of hemorrhagic shock.

INTRODUCTION: While the physiologic effects of space travel are documented in healthy individuals, little is known about its impact on medically ill or injured persons. In this study, hemorrhagic shock in primates was used to model a potentially common pathophysiologic condition during exposure to gravitational forces simulating return from Earth orbit. This experiment did not model the effects of cardiovascular deconditioning that normally occur during spaceflight. METHODS: Using invasive hemodynamic monitoring, serial cardiovascular and laboratory parameters in baboons (Papio papio) were studied. Subjects were centrifuged at either a low +Gx (3.3 G maximum) or high +Gx (7.8 G maximum) acceleration reentry profile before and after being subjected to either class II (20% volume loss) or class IV (40% volume loss) hemorrhagic shock. RESULTS: Significant alterations in cardiovascular and laboratory parameters occurred during shock and exposure to high and low +Gx acceleration. Shock classification was the primary determinant of change in cardiovascular function. During the experimental protocol, 31 of 32 animals survived (97% survival). After a 1-wk post-protocol observation period, 28 of 32 subjects survived (88% survival). CONCLUSIONS: This preliminary study presents data that suggest that the emergent return of a medically compromised individual without resuscitation may be potentially survivable. However, medical stabilization with volume resuscitation, supplemental oxygen, and noninvasive monitoring would likely optimize clinical outcomes in the event of significant hemorrhagic shock states necessitating emergent deorbit.

Cardiopulmonary resuscitation in microgravity: efficacy in the swine during parabolic flight.

INTRODUCTION: The International Space Station will need to be as capable as possible in providing Advanced Cardiac Life Support (ACLS) and cardiopulmonary resuscitation (CPR). Previous studies with manikins in parabolic microgravity (0 G) have shown that delivering CPR in microgravity is difficult. End tidal carbon dioxide (PetCO2) has been previously shown to be an effective non-invasive tool for estimating cardiac output during cardiopulmonary resuscitation. Animal models have shown that this diagnostic adjunct can be used as a predictor of survival when PetCO2 values are maintained above 25% of pre-arrest values. METHODS: Eleven anesthetized Yorkshire swine were flown in microgravity during parabolic flight. Physiologic parameters, including PetCO2, were monitored. Standard ACLS protocols were used to resuscitate these models after chemical induction of cardiac arrest. Chest compressions were administered using conventional body positioning with waist restraint and unconventional vertical-inverted body positioning. RESULTS: PetCO2 values were maintained above 25% of both 1-G and O-G pre-arrest values in the microgravity environment (33% +/- 3 and 41 +/- 3). No significant difference between 1-G CPR and O-G CPR was found in these animal models. Effective CPR was delivered in both body positions although conventional body positioning was found to be quickly fatiguing as compared with the vertical-inverted. CONCLUSIONS: Cardiopulmonary resuscitation can be effectively administered in microgravity (0 G). Validation of this model has demonstrated that PetCO2 levels were maintained above a level previously reported to be predictive of survival. The unconventional vertical-inverted position provided effective CPR and was less fatiguing as compared with the conventional body position with waist restraints.