Loop - Gain of the CO 2 Ventilatory Control System

SuwA, K. and MATSUSHITA, F. Open Loop-Gain of the CO2 Ventilatory Control System. Tohoku J. exp. Med., 1985, 147 (1), 97-106 We devised a method of measuring the open-loop gain for C02-ventilatory feedback control system. The procedure is to gradually increase then decrease the PIco2 while measuring Picoz and PAco2. We theorized that the gain is aPIco2/aPAco2-1. We measured this gain in 11 young healthy subjects and found the value to be 3.24, quite different from what had been reported so far by a conventional method. The conventional method calculates the gain as the ratio of the slope of C02-response curve (s) over that of metabolic hyperbola. Analysis revealed that the conventional method requires an accurate knowledge of s-value at the very operating point. The assumption that the CO2 response curve is linear down to the operating point is probably the source of error. The open-loop gain for CO2 ventilatory control is in the order of 3, from which we may extrapolate that the slope of C02-response curve at the operating point is much flatter than the normal value of more than 21/min/mmHg2 open-loop gain ; ventilatory response for C02; feedback control ; operating point