Measurement of respiratory resistance in anesthetized subjects

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Abstract
Theoretical calculations predict that volume of gas in the thorax should vary exponentially with time during a passive exhalation. It should, therefore, be possible to calculate respiratory resistance without measuring gas flow rates by determination of the time constant of a passive exhalation. In the present study the essentially exponential character of passive exhalations in anesthetized, paralyzed patients was experimentally verified. Mean respiratory resistance, calculated from simultaneous measurement of transthoracic pressure and gas flow in 12 anesthetized subjects was 5.8 cm H2/liter per sec at a flow of 0.5 liter/sec. In the same subjects, respiratory resistance calculated using total compliance and time constant of exhalation was 5.5 cm H2O/liter per sec. Calculation or respiratory resistance in anesthetized, paralysed, or otherwise apneic subjects using total compliance and time constant of exhalation is a valid, simple, and objective method which eliminates necessity for measuring gas flow rates. Magnitude of resistance in anesthetized subjects in the present study is in close agreement with that reported by several other investigators in conscious subjects.

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