Systemic arterial pH servocontrolled ventilator simulation of the respiratory control system

The terminology 'isocapnic hyperpnea' has been used to describe the ability of the respiratory control system to increase ventilation in response to inhalation of low levels of CO2 without an apparent change in the error signal (arterial pH or PCO2). Recently a control system for the systemic arterial pH (pHa) servocontrol of mechanical ventilation has been developed. The combination of proportional and integral control used produced a system by which the desired set point was maintained with virtually a zero steady-state error. The purpose of these experiments was to use this system to produce isocapnic hyperpnea in response to low levels of inspired CO2 and thus to demonstrate how, through integral control, a biological system could produce a particular response without an apparent change in the controlled variable. Adding 1.0 to 3.5% CO2 to the inspired gas of dogs connected to the pHa servocontrolled ventilator produced increases in minute ventilation with little or no change in pHa or PaCO2. Whether such a control system has any relevance to the physiological control system is questionable. It does however allow a unique way of investigating the possibilities by which the physiological system may work.