Am. J. Respir. Crit. Care Med., Vol 149, No. 5, 05 1994, 1342-1347.
Airway and tissue responses during hyperpnea-induced constriction in guinea pigs
T Nagase, MJ Dallaire and MS Ludwig
Meakins-Christie Laboratories, McGill University, Montreal, Quebec, Canada.
It has been reported that hyperpnea-induced bronchoconstriction in guinea
pigs is a potential model for exercise-induced asthma in humans. On the
basis of recent studies that show increases in tissue resistance after
allergen exposure in sensitized rats, we hypothesized that lung tissues
might also be involved in the pathophysiology in this asthma model. We
measured tracheal pressure (Ptr) and alveolar pressure (PA) using alveolar
capsules in open-chested, mechanically ventilated (respiratory frequency
[f] = 1 Hz, tidal volume [VT] = 9 ml/kg, positive end-expiratory pressure
[PEEP] = 4 cm H2O) guinea pigs under control conditions (regular breathing
of warm, humidified air) and after dry gas hyperpnea challenge (HC, mixture
of 95% O2 and 5% CO2, 150 breaths/min, 7 min). We calculated lung elastance
(EL) and resistance of lung (RL), tissue (Rti), and airway (Raw) by fitting
the equation of motion to changes in Ptr and PA. To assess the effects of
volume history, we applied a single deep inflation (three times VT) in five
HC animals. We performed morphometric analysis in five control and five HC
animals, freezing the lungs with liquid nitrogen and processing the tissues
via freeze substitution. HC significantly increased RL, Rti, Raw, and EL
(424 +/- 62, 771 +/- 230, 287 +/- 33, 259 +/- 31% baseline, respectively).
A deep inflation reduced RL, Rti, Raw, and EL by 30 +/- 4, 31 +/- 4, 29 +/-
6, 23 +/- 5%, respectively. In HC animals, the degree of airway
constriction was most prominent in the larger airways; extensive tissue
distortion was also observed.(ABSTRACT TRUNCATED AT 250 WORDS)
