Tracking of airway and tissue mechanics during TLC maneuvers in mice.
A tracking impedance estimation technique was developed to follow the changes in total respiratory impedance (Zrs) during slow total lung capacity maneuvers in six anesthetized and mechanically ventilated BALB/c mice. Zrs was measured with the wave-tube technique and pseudorandom forced oscillations at nine frequencies between 4 and 38 Hz during inflation from a transrespiratory pressure of 0-20 cmH2O and subsequent deflation, each lasting for approximately 20 s. Zrs was averaged for 0.125 s and fitted by a model featuring airway resistance (Raw) and inertance, and tissue damping and elastance (H). Lower airway conductance (Glaw) was linearly related to volume above functional residual capacity (V) between 0 and 75-95% maximum V, with a mean slope of dGlaw/dV = 13.6 +/- 4.6 cmH2O-1. s-1. The interdependence of Raw and H was characterized by two distinct and closely linear relationships for the low- and high-volume regions, separated at approximately 40% maximum V. Comparison of Raw with the highest-frequency resistance of the total respiratory system revealed a marked volume-dependent contribution of tissue resistance to total respiratory system resistance, resulting in the overestimation of Raw by 19 +/- 8 and 163 +/- 40% at functional residual capacity and total lung capacity, respectively, whereas the lowest frequency reactance was proportional to H; these findings indicate that single-frequency resistance values may become inappropriate as surrogates of Raw when tissue impedance is changing.
Hantos
Zoltán
Z
Dept. of Medical Informatics, Univ. of Szeged, Korányi fasor 9, H-6720 Szeged, Hungary. hantos@dmi.u-szeged.hu
Collins
Rachel A
RA
Turner
Debra J
DJ
Jánosi
Tibor Z
TZ
Sly
Peter D
PD
D000403:Airway Resistance; D000818:Animals; D005260:Female; D008170:Lung Compliance; D051379:Mice; D008807:Mice, Inbred BALB C; D008954:Models, Biological; D010827:Physiology / Q000379:methods*; D012123:Pulmonary Ventilation; D014109:Total Lung Capacity