A SMALL ANIMAL PLETHYSMOGRAPH/EXPOSURE TUBE FOR DETERMINATION OF RESPIRATORY MECHANICS DURING EXPOSURE, USING A NONINVASIVE METHOD TO MEASURE INTRAPLEURAL PRESSURE

Abstract

The real-time measurement of changes in respiratory mechanics, primarily dynamic compliance (C dyn) and airway resistance (R L) , is often used to assess the pulmonary toxicity of inhaled materials, irritants thought to cause reactivity response in the airways. Simple volume displacement plethysmography for measurement of ventilation in spontaneously breathing animals can be adapted for the determination of C dyn and R L by including measurement of intrapleural pressure (Ppl). Accurate estimates of Ppl can be obtained by measurement of esophageal pressure (Pes) using transoral insertion of a water-filled catheter. Measurement of Pes does not require surgical intervention as is often required for the measurement of Ppl directly. However, the use of conventional head-out plethysmography to measure ventilation and respiratory mechanics during exposure usually precludes the use of a transoral esophageal catheter to measure Pes. Thus, invasive methods must be used to measure Ppl. The combination headout plethysmograph/nose-only exposure tube (PET), described in this article is suitable for the measurement of R L and C dyn using transoral catheterization for the determination of Pes during exposure. In addition to avoidance of surgical intervention, use of the PET does not interfere with the animal's normal breathing or require extraordinary procedures for connection to a nose-only exposure chamber. Ventilation, breath waveform, and respiratory mechanics measurements in 36 Long-Evans rats demonstrated that neither short-term restraint in the PET nor subsequent insertion of the esophageal catheter significantly altered ventilation or individual breath structure. R L and C dyn measured in normal rats using the PET did not differ from R L and C dyn determined using more traditional plethysmographic methods.