The magnitude (1Z,81) and phase angle (0r8) of the total respiratory impedance (Zr,), from 3 to 45 Hz, were rapidly obtained by a modification of the forced oscillation method, in which a random noise pressure wave is imposed on the respiratory system at the mouth and compared to the induced random flow using Fourier and spectral analysis. No significant amplitude or phase errors were introduced by the instrumentation. 10 normals, 5 smokers, and 5 patients with chronic obstructive lung disease (COPD) were studied. Measurements of Zr, were corrected for the parallel shunt impedance of the mouth, which was independently measured during a Valsalva maneuver, and from which the mechanical properties of the mouth were derived. There were small differences in Zr, between normals and smokers but both behaved approximately like a second-order system with 0r8 = 00 in the range of 5-9 Hz, and Or, in the range of +40°at 20 Hz and +60°at 40 Hz. In COPD, Or, remained more negative (compared to normals and smokers) at all frequencies and crossed 0 between 15 and 29 Hz. Changes in Zr,, similar to those in COPD, were also observed at low lung volumes in normals. These changes, the effects of a bronchodilator in COPD, and deviations of Zr, from second-order behavior in normals, can best be explained by a two-compartment parallel model, in which time-constant discrepancies between the lung parenchyma and compliant airways keep compliant greater than inertial reactance, resulting in a more negative phase angle as frequency is increased. INTRODUCTIONThe description of the respiratory system in terms of electrical analogs (1) by Otis et al. (2) and others (3-15),

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Nasal mucous velocity was estimated by following the motion of radiopaque discs of Teflon by means of a fluoroscopic image intensifier. From 5 to 10 discs were deposited on the superior surface of the inferior turbinate with a forceps. No local anesthesia was employed and the subjects experienced no discomfort. The linear velocity of the discs was obtained by playing the videotape onto a television monitor, measuring distance with a ruler, and dividing by elapsed time. Duplicate runs of 1-2 min, 15 min apart were very reproducible but runs at 4-h intervals or daily over a 5-day period had a coefficient of variation of 30%. Average nasal velocity for individual ranged from 0 to 22.5 mm/min and group means ranged from 6. 8 to 10.8 mm/min. There was no statistically significant difference in nasal mucous velocity between young and elderly subjects nor was there a sexual difference. The saccharin test of nasal mucous transport was unsatisfactory because of inability to repeat the test more often than 1-2 h and its propensity to produce mild discomfort in a significant number of subjects. Saccharin times did not correlate significantly with values of nasal mucous velocity.

In six normal upright subjects, a 100 mol bolus-composed of equal parts of neon, carbon monoxide, and acetylene (Ne, CO, and C(2)H(2))-was inspired from either residual volume (RV) or functional residual capacity (FRC) during a slow inspiration from RV to total lung capacity (TLC). After breath holding and subsequent collection of the exhalate, diffusing capacity and pulmonary capillary blood flow per liter of lung volume (D(L)/V(A) and Q(C)/V(A)) were calculated from the rates of CO and C(2)H(2) disappearances relative to Ne. The means: D(L)/V(A) = 5.26 ml/min x mm Hg per liter (bolus at RV), 6.54 ml/min x mm Hg per liter (at FRC); Q(C)/V(A) 0.537 liters/minute per liter (bolus at RV), 0.992 liters/minute per liter (at FRC). Similar maneuvers using Xenon-133 confirmed that, during inspiration, more of the bolus goes to the upper zone if introduced at RV and more to the lower, if at FRC. A lung model has been constructed which describes how D(L)/V(A) and Q(C)/V(A) must be distributed to satisfy the experimental data. According to this model, there is a steep gradient of Q(C)/V(A), increasing from apex to base, similar to that previously determined by other techniques-and also a gradient in the same direction, although not as steep, for D(L)/V(A). This more uniform distribution of D(L)/V(A) compared with Q(C)/V(A) indicates a vertical unevenness of diffusing capacity with respect to blood flow (D(L)/Q(C)). However, the relative degree of vertical unevenness of D(L)/V(A) compared with Q(C)/V(A) can account only in part for previous observations attributed to the inhomogeneity of D(L)/V(A) and Q(C)/V(A). Thus, a more generalized unevennes of these ratios must exist throughout the lung, independent of gravitation.

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