A general purpose microprocessor for spirometry.

A portable, inexpensive microprocessor is described for on-line spirographic analysis of FVC and its time derivatives and MVV, using a primary flow or volume signal. Resolution is +/- 0.02 L and maximal collection time 66 seconds. Algorithms according to the Snowbird Conference recommendations include back extrapolation, "end of test" determination and the selection criteria for satisfactory tests, and best FVC, FEV1 and other flow rates. Differentiation is digital and flow-volume outputs are available. Actual, predicted and percent predicted values for children or adults are displayed, or can be printed together with an interpretation and a flow-volume loop. Four hundred tests with a Stead-Wells spirometer, a pneumotachograph and a turbinometer using an explosive decompression FVC simulator showed standard deviations of +/- 0.04 L or L/sec or less, except for peak flow. Differences between microprocessor values and tracing analyses were less than 0.04 L. MVV with a reciprocating pump equalled exactly the MVV calculated from stroke volume and frequency (r = .999) from 8 to 325 L/min. Tests of 168 patients were comparable to the calibration devices.