A NEW CAPACITANCE PLETYSMOGRAPH FOR RESPIRATORY MONITORING IN UNRESTRAINED SMALL ANIMALS, AND ITS APPLICATION TO THE BRONCHIAL HISTAMINE CHALLENGE TEST

Abstract

A new capacitance pletysmograph to monitor respiration in unrestrained small animals was developed. It measures the change of electrical capacitance between the animal and a surrounding fixed electrode. The output of this device is stable and proportional to the change of capacitance.
In the balloon model, there was high correlation between the changes of volume and capacitance. In comparing signals of a capacitance pletysmograph with signals of a pneumotachograph in four guinea-pigs, their tracings were very similar and their phases correlated well.
In bronchial histamine challenge tests, attacks were precipitated in eleven out of twelve cases. In four of them, simultaneous monitoring with a pneumotachograph was done. Prior to the attack, which was recognized by eye, flat end-expiratory phases appeared in all the provoked cases. Hysteresis was observed in the X-Y tracing of the volume integrated from the flow vs. capacitance. In the course of the attacks, paradoxical changes in the end-expiratory phases and increments of hysteresis were observed.
The onset and grading of asthmatic attacks could be distinguished precisely with this system. Comparison with the pneumotachograph was useful to analyse the mechanism of the asthma attack in the experimental model.