The same experiments will be performed as described in Exp. 1A, but, in addition, in these experiments venous blood will be sampled each minute before, during, and after CO exposures. Relevant “normalized” inspired CO concentrations to be plugged into the CFK equation will be determined using approaches obtained in Exp. 1A. Other terms—lung diffusing capacity, alveolar partial pressure of O2, and mean pulmonary capillary O2Hb% saturation—can be assumed. A normal pulmonary dead space can be assumed to allow calculation of alveolar ventilation from total ventilation measurements. In these short time-duration experiments, venous blood COHb levels reflect uptake and time-dependent mixing in body stores, including blood and muscle myoglobin stores. Because the CFK equation assumes complete mixing in body stores, measured blood COHb levels used in comparing values calculated using the CFK equation should be obtained at least 5 minutes after cessation of CO uptake. COHb values calculated using the CFK equation will be plotted versus measured venous blood COHb.
These experiments will be similar to those described above except that inspired CO will be kept constant after a step increase and effects of changes in ventilation on CO uptake and increases in blood COHb will be determined. These experiments will be performed with the subject standing or running on a treadmill. After a control rest period, subjects will start exercising using estimates of work performed by armored-vehicle personnel. After increased ventilation has become constant, CO will be added to inspired air giving concentrations of 50 to 200 parts per million (ppm). This will be followed by reducing the workload to resting level and removal of CO from inspired gas. Venous blood will be taken every minute for COHb analysis. CO uptake will be determined as above from measurements of inspired and mixed expired gas CO concentration. Repeats of these experiments at different workloads and time durations, will allow determination of effects of rapid changes in ventilation on CO uptake and on blood COHb levels.
To evaluate the CFK equation, the same approach as above will be used. Inspired CO is the constant value used in each run, and alveolar ventilation is the measured value minus the assumed dead space. COHb calculated using the CFK equation will be compared with measured venous blood COHb obtained 5 minutes after removal of CO from inspired gas.
The goal of these experiments is to duplicate experiments described in Experiments 1 and 2 but under conditions of simultaneous rapid changes in ventilation and inspired CO. After control data are obtained, the subjects will start exercising, and inspired CO will be increased. CO increases in different experiments will be in the same range as found during and following canon firing. This will be followed by cessation of both exercise and CO exposure. The approaches used to compare venous COHb increases with those predicted by the CFK equations will be identical to those described above.