RATE OF CORONARY FLOW ADAPTATION IN RESPONSE TO CHANGES IN HEART-RATEBEFORE AND DURING ANESTHESIA FOR CORONARY-ARTERY SURGERY

Background: The rate of adaptation of coronary blood now in response t o stepwise changes in heart rate (HR) has been extensively studied in dogs and goats to improve our understanding of the dynamics of coronar y regulation processes and their pathophysiology and to obtain time co nstants for mathematical modeling of the coronary regulation. However, little is known about the dynamic characteristics of coronary now ada ptation in humans, In patients undergoing coronary artery surgery, we investigated the rate of coronary adaptation in response to stepwise c hanges in HR, in the awake and anesthetized states. Methods: In 11 pat ients with stable coronary artery disease, arterial blood pressure, ri ght atrial pressure, and coronary sinus blood now, measured by continu ous thermodilution, were calculated per beat. The ratio of beat-averag ed arterial blood pressure minus right atrial pressure and coronary si nus blood flow was calculated to obtain an index of coronary resistanc e, The rate of change of coronary resistance index was quantified by t (50), defined as the time required to establish 50% of the total chang e in coronary resistance index. Responses of coronary resistance index after HR changes, before and after induction of anesthesia, were comp ared, The anesthesia technique consisted of 100 mu g . kg(-1) fentanyl and 0.1 mg . kg(-1) pancuronium bromide in combination with oxygen in air ventilation (FIO2 = 0.5). Results: In the awake situation, t(50) values of the dilating and constricting responses, induced by an incre ase and a decrease in HR were 5.0 +/- 2.1 (SD) s (range 2.6-9.0 s) and 5.7 +/- 1.2 s (range 4.1-7.8 s), respectively. During fentanyl/pancur onium anesthesia, the rate of coronary now adaptation was significantl y slower, with t(50) values of 10.2 +/- 2.1 s (range 7.7-13.1 s) after an HR step-up and 9.8 +/- 2.1 s (range 6.6-13.2 s) after an HR step-d own. Compared to the awake situation, arterial blood pressure was sign ificantly reduced during anesthesia, but coronary vascular resistance remained unchanged, This implies that the steady-state static regulati on of coronary blood flow had not changed. Conclusions: These prelimin ary data suggest that, in patients with coronary artery disease, the r ate of change in coronary vascular resistance in response to pacing-in duced changes in HR is mitigated by fentanyl/pancuronium anesthesia du ring positive pressure ventilation, A further qualification of our fin dings in a larger number of patients is warranted.