Respiratory flow integrator with improved stability.

A circuit was designed for integrating respiratory flow signals over time to produce volume signals. The circuit involves a simple integrator and three compensation subcircuits which control integrator drift caused by ambient temperature changes, flow signal base-line errors, and random signal errors. A functional unit built according to the circuit design requires initial adjustment, but no further adjustment before or during sustained use. Integration errors are typically less than 1%. The only flow signal requirements are that they be bidirectional and within the human physiological frequency range.