Tritium used for estimation of right-to-left shunts

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Abstract
A method is described for estimating right-to-left shunts through the determination of the recovery of intravenously injected tritium gas in the arterial blood. Tritiated water was used as an indicator of the dilution that would have occurred had no loss of tritium gas taken place in the alveoli. In normal man, average recovery values obtained were: 1.1% during normal respiration, 0.6% during hyperventilation, 0.9% during inspiratory apnea and 1.8% during expiratory apnea. In two patients with congenital heart disease large recovery values were found with right-to-left shunt, agreeing with the shunt estimates obtained using oxygen analysis. While no significant diffusion limitation at the alveolar membrane can be supposed to occur normally, a significant back pressure results from the gradually increasing alveolar tritium concentration. This factor is presumably responsible for the greater part of the recovery found in normal man, while a smaller part may be due to actual bypassing of the alveoli. On the basis of the experiments it is estimated that in normal man 0.3% of the blood entering the right side of the heart reaches the left side without passing air-filled alveoli. Submitted on November 5, 1960