Ventilation, perfusion, and cardiogenic oscillations of the single-breath N2 test

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Abstract
The mirror image of the single-breath N2 test (SB-N2) can be obtained after the N2 is removed from the lungs by 100% O2 washout and a vital capacity of air inspired. In 10 normal subjects studied with this technique (SB-R), phase IV and cardiogenic oscillations (CO) were similar in magnitude but reversed in direction to the SB-N2 values. The slope of phase III was also reversed, but its values were 35% smaller than in SB-N2 (P < 0.01). In a 2nd group of 10 normal human subjects, the effect of a 60 s end-inspiratory breath hold on both SB-N2 and SB-R was studied. With each technique, breath holding had no influence on phase IV and its slope. The slope of phase III decreased by 32% in SB-N2 and 44% in SB-R (P < 0.001). The magnitude of CO was not altered by breath holding in SB-N2 but increased by 72% in SB-R (P < 0.001). Certain differences in the N2 gradients responsible for each parameter are implied. The data can be used to identify the ventilation and perfusion characteristics of lung regions that decrease their emptying during cardiac systole and thus give rise to CO.