VALIDITY OF TOTAL LUNG CAPACITY DETERMINATION BY THE SINGLE BREATH NITROGEN TECHNIQUE

  • 1 January 1980
    • journal article
    • research article
    • Vol. 61  (5) , 265-274
Abstract
Total lung capacity (TLC) derived from the single breath O2 test [TLCO2] dilution of alveolar N2 was compared to the plethysmographic TLC [TLC pleth.] in 40 healthy males aged 25-55 yr, and in 16 patients with chronic obstructive respiratory disease. In healthy subjects TLC02 was 8% less (P < 0.001) than TLC pleth. The 2 results were highly correlated (r = 0.89; P < 0.001); their difference tended to increase with age and correlated significantly with the slope of phase III (P < 0.01). In patients TLC02 underestimated the lung volume by 5-50% (average 28%) (P < 0.001), and the relation between the 2 measurements was weaker (r = 0.59; P < 0.02). The TLC02/TLC pleth. ratio was significantly related to FEV1.0% [1.0% forced expiratory volume] predicted (r = 0.68) and to specific conductance (r = 0.60); it was and highly significantly (P < 0.001) related to obstructive ventilatory impairment (r = 0.77), to distribution unevenness (r = 0.85) and overinflation (r = -0.94). Although an overestimation of lung volume by plethysmography in the presence of severe obstruction cannot be excluded, most of the discrepancy is ascribed to underestimation by single breath N2 dilution due to impaired distribution of ventilation.