EFFECTS OF MECHANICAL UNLOADING LOADING ON RESPIRATORY LOOP GAIN AND PERIODIC BREATHING IN MAN/

We investigated the effect of mechanical unloading and loading on Chey ne-Stokes respiration (CSR) in seven intubated patients with preexisti ng CSR. For mechanical loading patients had to breathe against the res istance of the endotracheal tube. For mechanical unloading patients we re supported with a volume-proportional pressure support in the propor tional assist ventilation (PAV) mode whilst the flow-dependent (nonlin ear) endotracheal tube resistance was continuously compensated for by means of the automatic tube compensation (ATC) mode. Mechanical unload ing aggravated CSR as revealed by a prolongation of apnea time and by an increase in the so-called strength index whereas mechanical loading shortened apnea time and decreased strength index. To test whether th e observed changes are caused by the effect of mechanical unloading/lo ading on respiratory loop gain (relationship between minute ventilatio n and arterial CO2 tension), the response of respiratory loop gain on mechanical unloading/loading was determined in five healthy subjects ( without CSR). In each subject, mechanical unloading increased respirat ory loop gain whereas mechanical loading decreased it. (C) 1998 Elsevi er Science B.V. All rights reserved.