Simulations of exercise and brain effects of acute exposure to carbon monoxide in normal and vascular-diseased persons

Abstract

At some level, carboxyhemoglobin (COHb) due to inhalation of carbon monoxide (CO) reduces maximum exercise duration in both normal and ischemic heart patients. At high COHb levels in normal subjects, brain function is also affected and behavioral performance is impaired.These are findings from published experiments that are, due to ethical or practical considerations, incomplete in that higher or lower ranges of COHb, and exercise have not been well studied. To fill in this knowledge base, a whole-body human physiological model was used to make estimates of physiological functioning by the simulation of parametric exposures to CO and various exercise levels. Ischemic heart disease was simulated by introducing a stenosis in the left heart arterial supply. Brain blood flow was also limited by such a stenosis. To lend credibility to such estimation, the model was tested by simulating experiments from the published literature. Simulations permitted several new conclusions. Increases in COHb produced the largest decreases in exercise duration when exercise was least strenuous and when COHb was smallest. For ischemic heart disease subjects, the greatest change in exercise duration produced by COHb increase was when ischemia and COHb was smallest. Brain aerobic metabolism was unaffected until COHb exceeded 25%, unless the maximum brain blood supply was limited by a stenosis greater than 50% of normal. For higher levels of stenosis, aerobic brain metabolism was reduced for any increase in COHb level, implying that behavior would be impaired with no "threshold" for COHb.

A review of the experimental evidence on the toxicokinetics of carbon monoxide: the potential role of pathophysiology among susceptible groups

“…An example is the setting Health Canada guidelines, which use an adapted CFK equation that incorporates parameters to account for CO in alveoli and CO-bound heme proteins in extravascular spaces [ 14 ]. Fewer studies, however, have attempted to model the effects of specific physiological deficits on CO-COHb relationships [ 76 ]. Benignus and Coleman 2010 [ 76 ] used a whole-body physiological model, which uses a form of the CFK equation, to simulate effects of CO on exercise duration among healthy persons and those with vascular disease at different exercise levels.…”

“…Fewer studies, however, have attempted to model the effects of specific physiological deficits on CO-COHb relationships [ 76 ]. Benignus and Coleman 2010 [ 76 ] used a whole-body physiological model, which uses a form of the CFK equation, to simulate effects of CO on exercise duration among healthy persons and those with vascular disease at different exercise levels. Stenosis of the left heart arterial supply was introduced to simulate IHD, and stenosis of the cerebral arteries to simulate reductions in brain flow.…”