Cardiovascular changes during and following 1-min exposure to +Gz stress

Magnitude and duration of cardiovascular responses following anesthetized dogs. During lower G forces (+1 to +3GZ), responses were variable. In most dogs during higher G forces (+4 or +5GZ), aortic pressure, cardiac output, left ventricular pressure, and dp/dt were dramatically compromised. These changes were observed whether the onset of the gravitational inertial force was slow (0.1 G/s) or rapid (1.0 G/s). Cardiovascular changes after acceleration were consistent. Left atrial pressure and arterial pressure rose and a transient rise in dp/dt was often observed. Cardiac output rose briefly, then fell; hence, peripheral resistance increased. Magitude and duration of these changes were directly related to G forces during acceleration. Our results confirm that +GZ stress produces major cardiovascular changes. Our experiments also demonstrate that responses following +GZ stress may be dramatic and prolonged. Increased peripheral resistance elevates perfusion pressure and, concurrently, the increased preload may cause acute cardiopulmonary congestion.