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The determination of O(2) consumption by using arteriovenous O(2) content differences is dependent on accurate oxyhemoglobin saturation measurements. Because swine are a common experimental species, we describe the validation of CO-oximeter for porcine-specific oxyhemoglobin saturation. After developing a nonlinear mathematical model of the porcine oxyhemoglobin saturation curve, we made 366 porcine oxyhemoglobin saturation determinations with a calibrated blood-gas analyzer and a porcine-specific CO-oximeter. There was a high degree of correlation with minimal variability (r(2) = 0.99, SE of the estimate = 5.2%) between the mathematical model and the porcine-specific CO-oximeter measurements. Bland-Altman comparison showed that the CO-oximeter measurements were biased slightly lower (-0.4 vol%), and the limits of agreement (+/-2 SD) were 0.7 and -1.5 vol%. This is in contrast to a 10-20 vol% error if human-specific methods were used. The results show excellent agreement between the nonlinear model and CO-oximeter for porcine-specific oxyhemoglobin saturation measurements. In contrast, comparison of the porcine-specific oxyhemoglobin saturations with saturations obtained by using human methods highlights the necessity of species-specific measurement methodology.

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Micrococcus radiodurans, irradiated aerobically in phosphate buffer, exhibits a phasic response to x-irradiation during its growth cycle. The culture progresses from a relatively sensitive state during the exponential portion of the growth cycle to a highly resistant state during the stationary phase. The shift in resistance is characterized by a marked extension of the shoulder of the survival curve and a threefold increase in the LD99 from 250 kR to over 700 kR. The resistant state appears to be a metastable condition, readily induced in exponential-phase cultures and easily reversed in stationary-phase cultures. Similar variations are not elicited in response to ultraviolet irradiation. The phasic response does not appear to be the result of a low-molecular-weight extractable sulfhydryl radioprotective agent.

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