The effects of +Gz on the coronary circulation: a review

The exposure of the human body to +Gz acceleration produces dramatic effects on the cardiovascular system. For example, during +Gz stress, heart rate has been reported to increase in excess of 200 b . min-1 and left ventricular pressure has been estimated to reach 300 mm Hg. Several reviews have dealt with the overall effects of +Gz stress on the cardiovascular system. However, none of these reviews has dealt specifically with the effects of +Gz on the coronary circulation and on the ability of the coronary circulation to maintain adequate perfusion of the heart. A common misconception exists within the aeromedical community that coronary blood flow must be compromised during +Gz due to the high heart rates and stress levels encountered during +Gz exposures. The purpose of this review is to deal with this issue by reviewing available information about basic coronary physiology, acceleration physiology, and their interaction. The current state of our understanding of basic coronary function will first be summarized. Serious students of coronary physiology are referred to other reviews for more detailed discussion. The current understanding of normal coronary function will then be integrated with the available information about the effects of +Gz on the heart and coronary circulation. Finally, potential chronic effects of +Gz and its interrelationships with cardiac and cardiovascular pathology in relation to the coronary circulation will be briefly considered.