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A head-out exercise body plethysmograph has been developed to facilitate investigations of the extrathoracic airways. An airtight seal around the neck is provided by a pliable sheet of dental dam braced by a tubular bean bag. A set of bicycle pedals is connected by a chain drive, axle, and wall-mounted sealed ball bearing to an external ergometer. The box is air-conditioned to allow exercise up to work loads of 200 W with a temperature increase of less than 1 degree C above ambient laboratory readings. Nose, mouth, and extrathoracic airways are easily accessible for airflow and pressure measurements. O2, CO2, and humidity levels of respired air are not disturbed, verbal communication with the subject is possible, and the subject is unlikely to feel claustrophobic. The plethysmograph has a flat frequency response to 4.2 Hz; it thus functions accurately in both resting and exercise measurements of respiratory minute ventilation. The plethysmograph can also be used for determinations of nasal and oral airflow and pressure, and the study of breathing patterns.
Niinimaa et al. (1979) studied this question.