Pulmonary mechanics by spectral analysis of forced random noise.

Abstract

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),

Assessment of Central Airway Obstruction Using Impulse Oscillometry Before and After Interventional Bronchoscopy

“…The pattern of frequency dependence of resistance in variable CAO is much like that of an upper airway shunt. [23][24][25] or as is seen in patients with COPD, in whom the resistance at 5 Hz is higher than the resistance at 20 Hz. 23,[26][27][28] When forced oscillations are applied to measure the impedance of the respiratory system, part of the air flow generated by the loudspeaker does not enter the lower airways and is lost in motions of the upper airway walls.…”

Servo-Controlled Pneumatic Pressure Oscillator for Respiratory Impedance Measurements and High-Frequency Ventilation

“…1 Moreover, their use in humans or large animals require high-powered electrical driving amplifiers, capable of dissipating over 200 W. 28 Regardless of the method employed to acquire respiratory impedance data, a more vexing problem is the ability of either approach to make oscillatory measurements while the lungs are maintained at a specified mean volume or pressure. Since lung volume can significantly impact respiratory impedance, 22 the ability to provide forced oscillations at different lung volumes or mean airway pressures is useful in understanding the impact of PEEP, periodic sighs, and recruitment/derecruitment manuevers on dynamic lung mechanics. Previous forced oscillation studies have relied on the manual adjustment of small bias flows into the breathing circuit to compensate for leaks and to maintain specified lung volumes during oscillatory excitations.…”

Respiratory system impedance in patients with acute left ventricular failure: pathophysiology and clinical interest.

“…'1 ' 14, 24, 25 In other studies, Zrs indexes have been proposed that are based on a simple series resistance, compliance, and inertance lung model.26 '27 However, in a nonhomogeneous lung, more complicated models with parallel compartments must be used, 14,15,28 although their application is still hazardous. 16 Michaelson, 14 Landser,29 Nagels,0 Pimmel,3' and Hayes24 and their colleagues have published measurements obtained in patients with obstructive disease over a large frequency range. Their results suggest that, in those patients, the modifications of Zrs at frequencies lower than 20 Hz should be distinguished from those above 20 Hz since they likely originate 392 from different pathophysiologic mechanisms.…”

“…The difference observed between our group 1 and 2 patients is not due to a particular observation tilting the mean in small groups. In particular, there is no The negative slope of resistance at low frequencies associated with a low reactance is not specific to pulmonary vascular congestion and has been described in obstructive lung diseases 14,24,29,30 Mechanical inhomogeneities of the lung and upper airways have usually been invoked to interpret this characteristic Zrs frequency dependence.11 14,30 According to the model described by Mead,3 an increase in slope of resistance vs frequency could be associated with an increase of resistance of the small airways. Numerous animal4'1 and human studies'8 have shown that pulmonary vascular congestion could induce small airways dysfunction, as shown by an increase in closing volume and peripheral airways resistance and by a decrease in dynamic compliance.…”