Flow and volume dependence of respiratory mechanical properties studied by forced oscillation

Abstract

The influence of inspiratory and expiratory flow magnitude, lung volume, and lung volume history on respiratory system properties was studied by measuring transfer impedances (4-30 Hz) in seven normal subjects during various constant flow maneuvers. The measured impedances were analyzed with a six-coefficient model including airway resistance (Raw) and inertance (Iaw), tissue resistance (Rti), inertance (Iti), and compliance (Cti), and alveolar gas compressibility. Increasing respiratory flow from 0.1 to 0.4 1/s was found to increase inspiratory and expiratory Raw by 63% and 32%, respectively, and to decrease Iaw, but did not change tissue properties. Raw, Iti, and Cti were larger and Rti was lower during expiration than during inspiration. Decreasing lung volume from 70 to 30% of vital capacity increased Raw by 80%. Cti was larger at functional residual capacity than at the volume extremes. Preceding the measurement by a full expiration rather than by a full inspiration increased Iaw by 15%. The data suggest that the determinants of Raw and Iaw are not identical, that airway hysteresis is larger than lung hysteresis, and that respiratory muscle activity influences tissue properties.

Variations in airways impedance during respiratory cycle derived from combined measurements of input and transfer impedances

“…2) which, analysed with equation 6, corresponded mostly to negative flow dependence (table 3). This finding is in agreement with the observations of OOSTVEEN et al [21] who derived Iaw from 4-30 Hz Ztr data obtained during constant-flow inspiratory and expiratory manoeuvres. During inspiration Iaw decreased from 2.12 Pa·s 2 ·L -1 at 0.1 L·s -1 to 1.79 hPa·s 2 ·L -1 at 0.4 L·s -1 ; the changes, however, were smaller during the expiratory phase (2.15 and 1.91 Pa·s 2 ·L -1 at 0.1 and 0.4 L·s -1 , respectively), which is at variance with the present observations.…”

“…In another work from the same laboratory [18] The analysis revealed some negative volume dependence of Raw, which is consistent with previous data. OOST-VEEN et al [21] reported a decrease with volume of airway resistance derived from transfer impedance during inspiratory manoeuvres. PESLIN et al [18] reported values of K 3 ranging from about -0.3 to -0.7 for inspiration and -0.8 to -1.4 hPa·s·L -2 for expiration.…”

Partitioning of airway and respiratory tissue mechanical impedances by body plethysmography

“…6), the analysis showed the expected effect, namely, a marked decrease in Xti at all frequencies, corresponding to a large increase of Eti. Interestingly, Xaw was almost unchanged, although it represented at low frequencies only a small part of the total reactance; this is in agreement with observations showing that Iaw varies little with lung volume (17) and strongly supports a very good separation between the two components. Elastic loading also significantly increased Raw, which is consistent with the decreased TGV.…”

Respiratory Muscle Power and the Slow Component of O2 Uptake

“…Commensurate with these rising flows was a timedependent increase in pulmonary resistance (i.e., RL,I and RL,E) over the V O 2sc phase, exacerbating the amount of resistive work expended per breath. The increase in RL,I during severe work rate transitions was probably due to a flow-dependent phenomenon, which may be attributed to the development of turbulent flow within larger-diameter airways (3,29). The increase in RL,E over the V O 2sc phase, on the other hand, was likely the result of a greater mechanical constraint on breathing during severe cycling trials, namely, the development of EFL.…”