Acute effects of low aortic pressure on cardiac performance

Aortic pressure has dual effects on the heart: One as the afterload pressure for the left heart and the other as a determinant of coronary perfusion pressure. As aortic pressure becomes subphysiological, these two effects may come to an imbalance. In dogs in which aortic pressure, aortic flow and heart rate were controlled at constant levels, a critical level of low aortic pressure (CAP) was studied below which an acute and progressive rise of left atrial pressure was observed. In normal heart, an elevation of CAP was observed from 15 to 36 mm Hg, as aortic flow was increased from 30 to 180 ml/min/kg. The elevation was less marked in response to the increase of heart rate from 100 to 250 beats/min. Coronary ligation or administration of a large amount of propranolol (1 to 2 mg/kg) caused a significant elevation of CAP. The results obtained from the present study is suggestive of the role of low aortic pressure in the development of cardiac deterioration during shock.