Effects of Variable Infusion Rates of Propofol on Arterial Baroreflex Sensitivity / 대한마취과학회지

BACKGROUND: Induction of anesthesia with propofol caused a decrease in arterial blood pressure and systemic vascular resistance. This effects of propofol on the circulation can be more clarified by studying cardiovascular control mechanism such as baroreflex sensitivity during variable rate infusion of propofol. METHODS: The effects of three infusion rates of propofol (3, 6, 12 mg/kg/hr) to supplement 66% nitrous oxide in oxygen anesthesia on baroreflex sensitivity were studied and compared with awake value in 80 ASA I or II patients (20-55 years old, n=20 in each group). Baroreflex control of heat rate was studied by pertubing the patients' arterial pressure with 100 microgram of phenylephrine in each three infusion rates of propofol which was maintained at least 30 min without any surgical stimulation. RESULTS: Baroreflex slope representing baroreflex sensitivity among three infusion rates of propofol did not show any significant differences. The slope of each infusion rate was 8.4+/-0.7 at awake, 8.9+/- 1.7 at 3 mg/kg/hr, 8.0+/-1.3 at 6 mg/kg/hr, 7.2+/-1.0 at 12 mg/kg/hr, respectively. But, resetting of the reflex occured at low heart rates. CONCLUSIONS: Usual propofol-nitrous oxide-oxygen anesthesia was not associated with impairment of baroreflex sensitivity, but showed reflex resetting at low heart rates.

Age-related Difference of the Vagal Reflex and Baroreceptor Reflex under General Anesthesia with Enflurane / 대한마취과학회지

BACKGROUND: Baroreceptor reflex responds to the decrease in blood pressure caused by drug, dehydration, or severe bleeding. Vagal reflex caused by direct pressure on vagus nerve, the traction, or lung inflation develops bradycardia and severe arrhythmia. Lung inflation elicits a vasodepressor reflex, resulting in stimulation of the vagus nerve which causes a decrease in sympathetic outflow. METHODS: 75 patients who had elective surgery were divided into 3 groups according to the age, such as group I: or = 65 years of age. Lung inflation test has been performed at 20 cmH2O for 20 seconds. Baroreceptor was stimulated by lowering blood pressure with intravenous infusions of nitroglycerin. Baroreceptor sensitivity was assessed by measuring the decrease in blood pressure. Vagal reflex sensitivity was calculated by the subtraction of G2 (baroreceptor reflex sensitivity after introglycerin infusion) from G1 (heart rate response to lung inflation). RESULTS: Baroreceptor reflex induced by hypotension and vagal reflex originated from lung influe-nced the heart rate inversely when lung inflated. Baroreceptor reflex sensitivity was highest in younger patients and lowest in older patients when nitroglycerin infused. Vagal reflex sensitivity was highest in older patients and lowest in younger patients. CONCLUSIONS: Baroreceptor reflex was most sensitive in younger patients, but vagal reflex was moresensitive in older patients.