Hemodynamic Changes in Trained Dogs During Experimental Renal Hypertension

The hemodynamic events, during onset of experimental renal hypertension, and during its progression to the chronic state, were recorded in 19 trained quiet dogs for 20 to 30 minutes daily for four to forty-two days. This was made possible by implanting a flow probe around the root of the aorta, and a catheter in the aortic arch for connection to an external pressure gauge. Continuous graphic recordings of blood pressure, cardiac output, stroke volume, heart rate, and peripheral resistance were made daily during a period of training to obtain control values, and after hypertension was initiated by partial occlusion of a renal artery and unilateral nephrectomy. The average mean arterial pressure in 34 unanesthetized dogs in this study was 85 mm Hg (range, 68 to 116 mm Hg). This is about 30% below values previously reported by others in unanesthetized dogs. These low pressures were ascribed to lack of restraint, to training, and to the natural posture of the dogs. At onset of hypertension a sharp rise in arterial pressure was accompanied by a decrease of cardiac output and heart rate, and by a large abrupt increase of peripheral resistance. After one to four days, the continued rise of arterial pressure was associated with return of cardiac output and heart rate toward normal. Peripheral resistance eventually stabilized at a level above that of the initial large rise. A chronic state of hypertension was reached by ten to twenty days after the initial rise of pressure. At this time cardiac output and heart rate were restored to normal, while peripheral resistance remained elevated. Studies lasting for as long as forty-two days did not show further changes. If the renal arterial constriction was severe, a third, "malignant" phase ensued with extreme elevation of diastolic pressure, reduction of cardiac output, and greatly increased peripheral resistance. This terminated in uremic death after a few days.