Teaching principles of cardiovascular function in a medical student laboratory

Abstract

We describe an animal laboratory using anesthetized swine to demonstrate the regulation of arterial blood pressure to second-year medical students at Saint Louis University School of Medicine (St. Louis, MO). The laboratory is designed to illustrate basic pharmacological and physiological concepts learned in the classroom. The specific learning objectives covered in this lab include maintenance of anesthesia, basic surgical technique including cannulation of blood vessels, understanding the measurement and significance of basic physiological parameters, premortem examination of in situ heart and lungs, direct cardiac massage and induction of ventricular fibrillation, understanding the fundamentals of the baroreceptor reflex, and cardiovascular responses to various pharmacological agents. Pharmacologic agents used include epinephrine, norepinephrine, isoproterenol, atropine, prazosin, propranolol, acetylcholine, nitroprusside, and angiotensin II. The laboratory demonstration has proven effective in reinforcing the fundamental principles of cardiovascular physiology and autonomic pharmacology. By the completion of this experiment, students are expected to be able to: 1) describe the basics of maintenance of anesthesia in a live animal; 2) describe basic surgical technique; 3) observe the procedure for proper cannulation of blood vessels; 4) describe the proper method of controlling hemorrhage from a bleeding source; 5) describe the measurement and recording of four physiological parameters: mean arterial pressure from a pressure transducer, heart rate from an ECG, hindquarters resistance from Doppler measurement of femoral arterial blood flow, and cardiac contractility by calculating dP/d t from left ventricular pressure measured with a Millar transducer; 6) perform a premortem exam of the heart and lungs and appreciate the in situ cardiothoracic anatomy of the living animal; 7) assist in the induction of ventricular fibrillation and perform direct cardiac massage; 8) characterize the autonomic responses activated by the baroreceptor reflex; 9) describe the effects of the adrenergic agonists epinephrine, norepinephrine, and isoproterenol on cardiovascular parameters and construct a dose response curve for each agent; 10) describe the effects of the adrenergic antagonists propranolol and prazosin on cardiovascular parameters and explain how they affect cardiovascular responses to adrenergic agonists; 11) describe the difference between endothelium-dependent and endothelium-independent vasodilation using acetylcholine, nitroprusside, and atropine; 12) observe the pressor response of angiotensin II and describe why this response is not blocked by pretreatment with prazosin; and 13) participate in the collection and analysis of experimental data and the presentation of results.