The effects of carbon monoxide and methylene chloride on the canine heart

Abstract

The effects of separate and combined exposures to carbon monoxide (CO) and methylene chloride (CHâ‚‚CIâ‚‚) on the heart and cardiovascular system were studied. Inhalation studies were conducted on two groups of ten conscious dogs with chronic cardiac instrumentation to evaluate coronary hemodynamics, left ventricular function, myocardial metabolism and the effects on the blood. In the first group of dogs, breathing a 1,500 ppm CO-air mixture through a tracheostomy for 30 min., the carboxyhemoglobin (COHb) increased slightly less than 1%/min. At 4% COHb above control, there were significant increases in left circumflex coronary artery blood flow (13%), heart rate (4%), and coronary flow per beat (6%). At 20% COHb the coronary flow increased linearly to 54% above control, while heart rate and coronary flow per beat increased 20% and 34%, respectively. During the CO exposure there were significant decreases in the arteriovenous difference in oxygen content in the heart and in myocardial oxygen consumption. Arterial oxygen content decreased, while the coronary sinus oxygen content increased. Arterial and coronary sinus P[subscript Oâ‚‚] remained constant. Left atrial pressure decreased slightly, but there was no significant change in left ventricular pressure or maximum left ventricular dP/dt. The increase in coronary blood flow was not adequate to fully compensate for the increased energy expenditure of the myocardium. The decrease in oxygen consumption suggests metabolic inhibition; however, neurogenic components were evidenced by the rise in heart rate. ...