Cardiovascular and Pulmonary Responses to Increased Acceleration Forces During Rest and Exercise
Pendergast DR, Olszowka A, Farhi LE. Cardiovascular and pulmonary responses to increased acceleration forces during rest and exercise. Aviat Space Environ Med 2012; 83:488–95.Background: The reduced cardiac output (CO) secondary to increased acceleration
forces (+Gz) has applicability to daily life and pathophysiology. Increased +Gz and reduced CO affect the lung, resulting in reduced oxygen transport. A variety of studies have examined tolerance to high +Gz. Methods: The present study examines
the effect of +1 to +3 Gz on steady-state cardiopulmonary variables at rest and while exercising at +2 Gz and +3 Gz. This study also looks at the deterioration of steady-state cardiopulmonary variables with sustained increased +Gz and after de-training
in eight male centrifuge trained subjects. Results: CO (-1.53 L · min−1/+Gz), stroke volume (−30 ml/+Gz, SV), and pulmonary diffusing capacity (−3.42 ml · mmHg−1/+Gz, DLCO)
decreased linearly with increased +Gz at rest while heart rate (23 bpm/+Gz, HR), total peripheral resistance (0.0095 TPRU/Gz, TPR), mean arterial pressure (13.2 mmHg/+Gz, MAP), and ventilation (4.13 L · min−1/+Gz,
VE) increased linearly. During graded exercise, CO and SV increased less at +2 Gz and +3 Gz while MAP and VE increased more. Failure to endure increased +Gz and the effects of de-training were primarily due to the inability to regulate
MAP. Discussion: The incremental increase in increased +Gz from 1 to 3 resulted in increased MAP, which was accomplished by increasing TPR sufficiently so as to offset the reduced CO. The effects of increased +Gz and reduced CO compromised lung function
and oxygen transport (−18–30%), thus compromising exercise capacity. The failure to regulate MAP at lower increased +Gz levels resulted in intolerance to higher increased +Gz.
