Quantifying the Impact of Sustained Acceleration on Critical Care Transport Medical Equipment

Military and commercial stakeholders are investing to explore the use of hypersonic aircraft and orbital spacecraft to transport cargo, medical supplies, passengers, and casualties. These vehicle platforms require periods of sustained acceleration, but to date, these dynamic forces have not been comprehensively considered in the environment of critical care patient movement because injured patients and advanced aeromedical evacuation (AE) equipment are rarely subjected to these conditions. While military AE equipment does undergo crash hazard acceleration testing, equipment functionality during or after sustained acceleration remains to be evaluated. This study was performed to fill that knowledge gap.

AE equipment currently used by the U.S. Air Force and Critical Care Air Transport Teams (ZOLL EMV+ 731 ventilator and ZOLL Propaq MD cardiac monitor) was subjected to low (2.5 g), moderate (4.5 g), and variable acceleration (1.5-4.5 g) for 3-minute periods at the KBR Brooks Centrifuge. AE equipment was tested for functionality in 3 different orientations (gX, gY, and gZ). Predetermined variations were made in equipment input settings to ensure each equipment item would function across mission-relevant conditions (differing ventilator tidal volumes, differing cardiac monitor arterial pressure inputs, etc.). AE was evaluated for accuracy compared to controlled inputs, alarm conditions, and equipment failure.

The EMV+ 731 ventilator and Propaq MD cardiac monitor had no equipment failures during testing. The ventilator had clinically negligible variations in tidal volume, peak pressure, and fraction of inspired oxygen during acceleration. At the highest tidal volume tested (480 mL), the ventilator had elevated peak pressure results. However, we believe this was due to limitations in test-lung resistance and was not related to a ventilator fault. Mild effects of sensor orientation were recorded in the Propaq MD blood pressure results; for example, gX and gY differed by 5.9 ± 1.21 mmHg at 75 mmHg input (P < .01) and 6.45 ± 1.229 mmHg with 150 mmHg input (P < .001).

The EMV+ 731 ventilator and Propaq MD cardiac monitor had reliable clinical performance despite sustained acceleration. This knowledge will facilitate immediate follow-on experimentation with advanced models of combat injury during simulated medical evacuation in sustained acceleration environments.