Intra versus interregional nitrogen gradients in the single breath nitrogen test.

To investigate the genesis of cardiogenic oscillations (C.O.) and the slopes of the single-breath nitrogen test, we studied ten healthy volunteers with a modified test. This test utilized incremental volumes of air from 10% to 100% vital capacity (VC) after a nitrogen washout with oxygen. Subjects exhaled to residual volume, inspired the air volume and completed a full inspiration with oxygen. C.O. and both slopes were positive with low air volumes and negative with a VC of air. The slope of phase IV showed a linear decrease with the increasing inspired air volume, and reached zero with an air volume of 38% VC. AT higher volumes it became progressively more negative. The slope of phase III and C.O. were highly positive with 10% to 50% VC air volume then subsequently decreased. The values for C.O. and the slope of phase III were significantly different (P < 0.001) from those of the slop of phase IV and the apex-base gradients predicted by the model of Milic-Emili et al. These results suggest that intraregional gradients are significantly involved in the genesis of C.O. and the slop of phase III.