Measurement of dead space ventilation using a pHa servo-controlled ventilator

OPTIMAL RESPIRATORY CONTROL SIMULATION AND COMPARATIVE STUDY OF HYPERCAPNIC VENTILATORY RESPONSES TO EXTERNAL DEAD SPACE LOADING

There has been considerable research effort regarding ventilatory responses to breathing with an imposed external dead space, and inhalation of fixed levels of CO 2 by human subjects. A human respiratory control model incorporating the optimality hypothesis can successfully demonstrate ventilatory responses to both chemical stimuli and muscular exercise. In this study, to verify the model behavior of the optimal chemical–mechanical respiratory control model, we simulated the ventilatory control under dead space loading and CO 2 inhalation. The simulation was provided by a LabVIEW® based human respiratory control simulator and signal monitoring system. The dead space measurement was described with two distinct models, derived from Gray and Coon, and predicted behaviors with corresponding ventilatory responses were investigated and compared with experimental findings. While both dead space models produced satisfactory predictions on simulated optimal [Formula: see text] versus Pa CO 2, [Formula: see text] versus Pa CO 2, F versus PI CO 2, VT versus PI CO 2, VD-total versus VT, VD- total /VT versus VT, [Formula: see text] versus VT and [Formula: see text] versus VT relationships, Gray's model provided better correlation and more consistent results throughout most of the ventilatory responses. The study of relative behavior of respiratory signals and comparative relationship of the ventilator responses between dead space loading during rest and CO 2 inhalation will certainly provide valuable understanding of increases in central respiratory motor command output of human respiratory control, which is also associated with Dyspnea on exertion, and give potential clinical perspective to realize the impaired ability to excrete CO 2 in patients diagnosed with acute respiratory distress syndrome.

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.