Pathophysiology of hypertension following coronary artery bypass surgery: An experimental dog model for postoperative hypertension

Immediate postoperative hypertension has been reported to occur during the first 3-6 h in 30%-75% of patients who have undergone aortocoronary bypass operations. Although some causes and potential predisposing factors of this type of hypertension have been cited, the mechanisms involved still remain unclear. Some studies have implicated the involvement of nerve reflexes originating from the heart, great vessels, and coronary arteries, but they do not explain the exact role of such impulses. The paucity of data in humans is, needless to say, due primarily to the invasive nature of the experimental procedure. To further our knowledge on the involvement of nerve reflexes as a factor in initiating immediate postoperative hypertension, we used a dog model and devised a modified form of surgery by inserting a soft catheter into the left coronary artery to form a stenosis; we measured several factors usually involved in hypertension. We succeeded in performing this modified form of surgery in 10 of 81 dogs. Our model showed that the mean aortic pressure significantly increased from 81 +/- 5.5 to 102 +/- 7.0 mmHg (P less than 0.05), systemic vascular resistance from 7604 +/- 833 to 9648 +/- 1101 dyn.s.cm-5 (P less than 0.05), and plasma noradrenaline levels from 0.45 +/- 0.092 to 0.51 +/- 0.087 ng/ml (P less than 0.01) immediately after restoration of blood flow to the distal area behind the stenosis. These dynamic and humoral characteristics are similar to ones documented in current clinical reports. To our knowledge, this is the first experimental animal model of hypertension after coronary artery bypass graft surgery.