Effect of methacholine on low-frequency mechanics of canine airways and lung tissue

Abstract

We measured tracheal flow, tracheal pressure, and alveolar capsule pressure in four anesthetized paralyzed tracheostomized open-chest dogs. Lung impedance between 0.12 and 4.88 Hz was measured with a forced volume oscillation technique before and after the intravenous administration of methacholine (MCh). Before MCh administration, lung impedance was well described by a model featuring a single airway leading to an alveolar region surrounded by tissue with a continuous distribution of viscoelastic time constants as used by Hantos et al. (J. Appl. Physiol. 68: 849-860, 1990). After MCh, however, this model gave a poor fit to the impedances. The impedances were well accounted for, however, when the model was enhanced to include an extra time constant term, which we suspect is required to account for the uneven ventilation distribution produced by MCh. Airway impedance before MCh administration was well described by a simple resistance-inertance model, but a model incorporating serial inhomogeneity of ventilation was again required after MCh. Our results support those of previous studies indicating that the impedance of the normal dog lung is well described by a homogeneously ventilated viscoelastic tissue model. In contrast, our results after MCh administration show strong evidence of marked regional ventilation inhomogeneity in addition to the rheological properties of the tissues.

Influence of inertance on respiratory mechanics measurements in mechanically ventilated puppies

“…Other investigators have reported that models which include terms for bronchial compliance, peripheral resistance, inhomogeneity or tissue properties may be superior to a SCM. 3,11,12 The visco-elastic tissue properties of the respiratory tissues do contribute to the behaviour of the respiratory system. The SCM does not include a parameter for visco-elasticity so the contribution of viscoelasticity to energy dissipation is included in the estimates of resistance, elastance and inertance.…”

Pendelluft is not the major contributor to respiratory insufficiency in dogs with flail chest: a mathematical analysis

“…Airway flow (9) was measured with a Fleisch #2 pneumotachograph connected to a differential piezoresistive transducer (Microswitch 163PC01D36, Honeywell, Tokyo, Japan). The pneumotachograph was, in turn, connected to a three-way valve which made it possible to switch between a mechanical ventilator (EVA-900, Aika, Tokyo, Japan) and a volume oscillator described elsewhere [4]. Tracheal pressure (Ptr) was measured by a piezoresistive pressure transducer (1CS 13 002G, ICSensors, Milpitas, CA, USA) at a side port of the tracheal cannula.…”

“…Zcw has the same structure as ZL except the lack in the resistance corresponding to R1 in ZL. Zvc has only one element of elastance Mechanical impedance of the respiratory system (ZRS) was measured in a frequency range between 0.15 and 6.65Hz bY a pseudorandom forced oscillation method as described previously [4,5]. Briefly, mechanical ventilation Was stopped at end expiration and the the intact subsystem which consists of lung with a resistance (RL) and an elastance (EL) enclosed by a chest wall.…”

“…The measurement was repeated five times with a 2-rain interval of mechanical ventilation between each run, and five sets of measured signals were ensemble averaged. ZRS was computed with the averaged signals using an auto-and cross-correlation method [4] [(zero end-expiratory pressure (ZEEP) control condition]. Following the measurements, the dogs were ventilated with a positive end-expiratory pressure (PEEP) of 5cmH20 and ZRS measurements were repeated (PEEP control).…”

“…We fitted a model to the measured ZRs using a nonlinear least-squares technique described by Sato et al [4]. The model consists of five compartments as illustrated in Fig.…”