Journal of Applied Physiology, Vol 69, Issue 5 1665-1669, Copyright © 1990 by American Physiological Society
Impedance measurement during air and He-O2 breathing before and after salbutamol in normal subjects
E. F. Wouters
Department of Pulmonary Diseases, University of Limburg, Maastricht, The Netherlands.
Total respiratory resistance and reactance from 4 to 52 Hz were determined
by the method of forced pseudorandom noise oscillation in 20 normal male
subjects before and after inhalation of 0.200 mg salbutamol (albuterol) and
before and after the subjects were equilibrated with 80% He-20% O2. During
air breathing, there was a statistically significant decrease of resistance
values at lower frequencies after inhalation of salbutamol. When the
subject was equilibrated with 80% He-20% O2, total respiratory resistance
markedly decreased at all frequencies, and a negative frequency dependence
of resistance was observed between 8 and 20 Hz. Resistance values further
decreased during He-O2 breathing after inhalation of salbutamol. After
inhalation of salbutamol, reactance values increased during air and He-O2
breathing. The density-dependent decrease of the real part of impedance can
be explained by a decrease of turbulence in the larger airways. The
bronchodilating effect of salbutamol was not influenced by a change in the
physical properties of the inhaled gas. During He-O2 breathing, reactance
values significantly decreased, resulting in an increase of resonant
frequency due to a decrease of inductive reactance. It is concluded that an
increase in the capacitance of the respiratory system must be supposed to
explain the increase in reactance values after inhalation of the
beta-adrenergic agonist salbutamol.
