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 (+G_z) has applicability to daily life and pathophysiology. Increased +G_z and reduced CO affect the lung, resulting in reduced oxygen transport. A variety of studies have examined tolerance to high +G_z. Methods: The present study examines the effect of +1 to +3 G_z on steady-state cardiopulmonary variables at rest and while exercising at +2 G_z and +3 G_z. This study also looks at the deterioration of steady-state cardiopulmonary variables with sustained increased +G_z and after de-training in eight male centrifuge trained subjects. Results: CO (-1.53 L · min⁻¹/+G_z), stroke volume (−30 ml/+G_z, SV), and pulmonary diffusing capacity (−3.42 ml · mmHg⁻¹/+G_z, DL_CO) decreased linearly with increased +G_z at rest while heart rate (23 bpm/+G_z, HR), total peripheral resistance (0.0095 TPRU/G_z, TPR), mean arterial pressure (13.2 mmHg/+G_z, MAP), and ventilation (4.13 L · min⁻¹/+G_z, V_E) increased linearly. During graded exercise, CO and SV increased less at +2 G_z and +3 G_z while MAP and V_E increased more. Failure to endure increased +G_z and the effects of de-training were primarily due to the inability to regulate MAP. Discussion: The incremental increase in increased +G_z 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 +G_z and reduced CO compromised lung function and oxygen transport (−18–30%), thus compromising exercise capacity. The failure to regulate MAP at lower increased +G_z levels resulted in intolerance to higher increased +G_z.