Breath-by-breath measurement of respiratory functions: instrumentation and applications.

Abstract

Study of dynamic as well as stable-state ventilatory responses to changes in respiratory stimuli are becoming increasingly inportant in attempts to explore the control of pulmonary ventilation. Instrumentation is described for accurate automatic measurement of breath-by-breath respiratory minute volume (VE), respiratory frequency (f), and tidal volume (TV). Use of the instrument in the study of pharmacological actions and in the investigation of physiological mechanisms is described. The action of a recycling, water-sealed, dual spirometer unit upon a potentiometer provides a voltage accurately proportional to tidal volume. An electromechanical divider unit stimultaneously measures the period (P) of a respiration and computes respiratory minute volume and respiratory frequency on a breath-by-breath basis as the ratios VT P = VE and I P = f. Appropriate voltages are sampled and clamped at the end of each breath for recording. As described, tidal volumes in the range 0-4L and respiratory frequencies from 7-110 breaths min can be measured with an accuracy of + 2% of full scale easily attainable. Also described is an electronic tidal volume accumulator which permits measurement of time-average values.