Topic Areas: Health Effects of Air Pollution
A new method for determining carbon monoxide (CO) in minute quantities (100-200 WI) was developed. This is probably the most accurate procedure available at the present time. Elimination rates of CO in anesthetize spontaneously breathing dogs was found to be biphasic. The initial distribution curve was exponential, followed by an elimination curve which was linear. Prediction equations for elimination of CO from blood were developed. A method was developed for accurately adjusting a subject's blood carboxyhemoglobin (HBCO) level and then maintaining this level during rest or exercise. The effects of low concentrations of HBCO on exercise performance (submaximal levels) were determined. No substantial decrements were observed. Cardiovascular responses, particularly coronary blood flow, of the dog to various levels of HBCO (6.2 to 35.6%) were determined. When ('O was given as a bolus (within 2-3 minutes) coronary blood flow increased progressively as HBCO levels increased. This increase was accompanied by decreased arterial and Coronary sinus oxygen tensions and decreased myocardial oxygen extraction. Animals exposed for I hour to a constant level of HBCO had the anticipated increase in coronary blood flow maintained for the duration of the exposure. Animals exposed to 100 ppm CO for four hours each day, five days a week for six weeks (HBCO levels approximately 10%) showed no evidence of adaptation. Their responses to an acute exposure to 10% HBCO did not differ from those observed in animals with no prior exposure to ambient carbon monoxide. A most suggestive study was conducted on animals in whom a complete atrioventricular (AV) block was produced. These animals were maintained by cardiac pacemakers. Following exposure to 6-7% HBCO in contrast to normal control animals, coronary blood flow failed to increase as anticipated. These data are suggestive of the potential danger of low levels of HBCO to Cardiac disabled individuals.
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