Abstract
A new method has been developed to measure airway functions in unanaesthetized, unrestrained guinea-pigs. The technique utilizes a specially designed pneumotachograph that is placed inside the trachea, and a saline-filled balloon, placed inside the pleural cavity. The pneumotachograph consists of a stainless steel cylinder with coaxial and perpendicular tubes attached to it, measuring the total pressure and the lateral pressure in the trachea, respectively. Via air-filled silicon conducting tubes, subcutaneously driven and permanently attached to the neck of the animal, the pressures are fed into a differential pressure transducer, yielding a pressure difference proportional to the airflow in the trachea. Via a saline-filled tubing, the pleural balloon is similarly attached to the neck of the animal, and pleural pressure ( P pl) is measured using a second pressure transducer. These data permit calculation of airway functions in conscious, unstressed animals. Control values for airway resistance ( R AW), P pl, tidal volume and respiratory frequency are all in the range of results reported previously for this species. A very significant correlation between R AW and P pl ( P < 0.001) was observed, indicating that sole P pl-measurement can be used as a relatively simple and sensitive method to assess bronchial obstructive reactions in unrestrained guinea-pigs. Using a specially designed provocation cage, which allowed the animals to remain in a stress-free, unrestrained condition, the method has been successfully applied for the assessment of the dose-dependent bronchoconstrictor sensitivity to histamine as well as to allergen-induced early and late phase airway reactions. Because chronically instrumented animals can be monitored repeatedly for extended time periods, intra-individual comparisons of airway responses to different pharmacological and immunological stimuli, and to drug treatment, are feasible, while this model may also be suitable for the study of chronic asthma.
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