To investigate the premise that levels of endogenous volatile organic compounds (VOC) in breath reflect those in blood, the concentration of acetone and isoprene were measured in radial arterial blood, peripheral venous blood and breath samples from ten healthy volunteers. Coefficients of repeatability as a percentage of mean are less than 30% in breath but greater than 70% in blood. The volunteer-mean ratios of arterial to venous blood concentration are 1.4 (0.9-2.1) for acetone and 0.55 (0.3-1.0) for isoprene. Concentration in breath showed a significant inter-subject correlation with concentration in arterial blood (CAB) for acetone but not for isoprene. Arterial blood/breath ratios are 580 (280-1060) for acetone and 0.47 (0.22-0.77) for isoprene. The sample-mean blood/breath ratio was used to calculate an estimate of CAB and the standard deviation of this estimate was lower than that of arterial blood measured directly. For most subjects, estimated CAB was within uncertainty limits of the actual CAB. Owing to the poor repeatability of VOC concentrations from consecutive blood samples, and the capacitive effects of the lung, this study suggests that breath VOC measurements may provide a more consistent measure than blood measurements for investigating underlying physiological function or pathology within individuals.
If brain venous outflow Tdegrees (JB) accurately reflects brain Tdegrees, NP Tdegrees is a safe surrogate indicator of cooling. During rewarming, all peripheral sites underestimate brain temperature and caution is required to avoid hyperthermic arterial inflow, which may inadvertently, result in brain hyperthermia.
Low-concentration inhaled nitric oxide is as effective as sodium nitroprusside and prostacyclin in reducing transpulmonary gradient and pulmonary vascular resistance, and is highly pulmonary vasoselective.
The performance of three electrodes used for transcutaneous carbon dioxide (tcPCO2) monitoring is compared in 15 healthy volunteers and 26 critically ill adults. All three electrodes showed good correlation between tcPCO2 and arterial blood PCO2 (PaCO2) with a correlation coefficient (r) greater than 0.86. There was little difference in the performance characteristics of the three monitors. They may be usefully employed to estimate PaCO2 values when used with a modified calibration recommended by the manufacturers.
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