Pulmonary function assessment by whole-body plethysmography in restrained versus unrestrained mice

The evaluation of pulmonary physiological measurements in laboratory animals is an essential tool in many biomedical and toxicological research areas. Recently, an unrestrained single chambered whole-body plethysmograph that utilizes a barometric analysis technique to quantify pulmonary physiological values has gained widespread use. However, results generated with the single chamber plethysmograph have come under increased scrutiny because airflow in the lung is indirectly measured. The purpose of the present study was to use mice with known interstrain differences in pulmonary physiology (A/J, BALB/c, CD-1, and B6C3F1) and compare the physiological data generated with a single chamber plethysmograph to data obtained in the widely accepted double chamber noninvasive airway mechanics (NAM) plethysmograph in which the animals are restrained.

Animals were placed into the plethysmographs and baseline physiological data acquired. The mice were then subjected to challenge with aerosols generated from isotonic saline (control) and methacholine solutions of increasing concentration (2.5-320 mg/ml) for 3 min for determination of the concentration of methacholine that induced a 200% increase in airway resistance (PC(200)R).

Repeated physiological measurements on the same animals in both the single and double chamber plethysmographs demonstrated that each instrument generated reproducible baseline physiological data. However, comparison of physiological data generated with the double-chambered instrument to that generated with the single chamber plethysmograph revealed several significant differences. While the single chamber plethysmograph appeared to give inaccurate measurements of tidal volume, it provided much better analysis of airway reactivity based on PC(200)R results. In contrast, the double chamber plethysmograph provided accurate physiological data such as tidal volume and respiratory rate, but provided inaccurate and irreproducible airway reactivity results based on PC(200)R.

Our results indicate that the choice of single or double chamber plethysmograph for physiological measurements should be linked to the study objectives and the type of data required.