Pulmonary resistance in dogs: a comparison of xenon with nitrous oxide.

Xenon (Xe) may cause an increase in airway resistance due to its high density and viscosity. The object of this study was to examine the effects of Xe on pulmonary resistance using dog models with normal and methacholine-treated airways. During anaesthesia 22 mongrel dogs' tracheas were intubated and the lungs were mechanically ventilated with 70% N2/30% O2 as a control gas. The gases 70% nitrous oxide (N2O), 50% N2O, 70% Xe and 50% Xe were administered in a random order for 25 min. Bronchoconstriction was produced by a continuous infusion of methacholine, 0.22 mg.kg-1.hr-1. Pulmonary resistance (RL) was calculated by the isovolume method using flow at the airway opening, volume and transpulmonary pressure. In normal dogs, RL breathing 70% Xe (mean +/- SEM, 0.84 +/- 0.12 cm H2O.L-1.sec-1) was greater (P < 0.05) than with 70% N2O, 50% N2O or control gas (0.61 +/- 0.08, 0.59 +/- 0.06 and 0.62 +/- 0.06 cmH2O.L-1.sec-1). Breathing 50% Xe the RL (0.77 +/- 0.10 cmH2O.L-1.sec-1) was not different from 50% N2O or control. Methacholine infusion increased RL 3.92 +/- 1.98 (mean +/- SD) times. The RL breathing 50% Xe (2.55 +/- 0.44 cmH2O.L-1.sec-1) was not greater than during 50% N2O or control (2.08 +/- 0.33 and 2.13 +/- 0.33 cmH2O.L-1.sec-1) in methacholine-treated dogs. The data suggest that inhalation of high concentrations of Xe increases airway resistance, but only to a modest extent in dogs with normal or methacholine-treated airways.