Volume of trapped gas in lungs of healthy humans.

The volume of trapped gas (Vtg) that could be mobilized by maximal breaths at the end of a nitrogen washout to 2% N2 was measured in 70 healthy women and 62 healthy men while seated. The average Vtg was found to be 102 +/- 21 (SD) ml in men and 73 +/- 18 ml in women. The Vtg was positively related to total lung capacity (TLC) (r = 0.67; P less than 0.001). An average percent Vtg/TLC of 1.4 +/- 0.31 (DS) % was applicable to both sexes. Vtg/TLC (%) was positively related to age (4 = 0.45; P less than 0.001). The error of a single determination was 8 ml, i.e., the reproducibility was very high. The existence of lung compartments that are unventilated or extremely underventilated may explain part of the physiological alveolararterial O2 difference. An increase in Vt has been found to be a very sensitive sign of subclinical bronchospasm.