The presented data are the mean values of a/ distributions taken in duplicate. 13The duplicate samples were processed separately, resulting in two a/ distributions for each condition investigated in this study. a/ distributions were estimated as previously described by Wagner et al . For each inert gas retention (the ratio of the gas concentration in arterial to that in mixed venous blood) and excretion (the ratio of the gas concentration in expired gas to that in mixed venous blood) were calculated. Therefore, the tidal volume has a dead space. Physiologic dead space is defined as the volume of gas that is inspired but takes no part in gas exchange in the airways and alveoli. is referred to as physiologic dead space. The expiratory tubing and the mixing box for the expired gas samples were heated above body temperature to avoid a loss of the more soluble gases in condensed vapor. Ventilation of nonperfused alveoli and the airways, because neither accomplishes exchange of the respiratory gases. Samples of arterial and mixed venous blood and mixed expired gas were collected simultaneously at each study point during several respiratory cycles and analyzed immediately by gas chromatography. Briefly, 45 min before the first blood sampling, an isotonic saline solution equilibrated with six inert gases (sulfur hexaflouride, ethane, cyclopropane, halothane, ether, and acetone) was infused into a peripheral vein at a constant rate of 4 ml/min.

A/ distributions were analyzed using the multiple inert gas elimination technique (MIGET). During conventional ventilation of preterm infants, dead space washout by deliberate leakage flow was studied experimentally.

Dead space ventilation med student