Flow limitation in anesthetized rhesus monkeys: A comparison of rapid thoracoabdominal compression and forced deflation techniques

Rapid thoracoabdominal compression (RTC) and forced deflation (FD) allow the examination of maximal expiratory flow-volume (MEFV) curves in animals and human infants unable to generate a voluntary maximal expiratory maneuver. We compared flows generated by these two techniques and by constructing isovolume pressure flow (IVPF) curves examined each method's potential to produce flow limitation. RTC and FD were performed in seven intubated rhesus monkeys from +40 cm H₂O inspiratory pressure with deflation pressures ranging from -20 to -100 cm H₂O and jacket pressures from +20 to + 100 cm H₂O (arms outside jacket). We also performed RTC maneuvers in all monkeys with the arms inside the jacket at + 100 cm H₂O jacket pressure. Maximal expiratory flows achieved by FD and RTC were analyzed at isovolume points. Both techniques produced flow limitation conditions over the last 25% of the MEFV curve. Individual IVPF curves generated by the two techniques demonstrated remarkable differences in shape and flow rates. Maximal transpulmonary pressures achieved with FD were higher than those with RTC in this experiment. Negative effort dependence was observed with higher deflation pressures in the majority of the monkeys. Flows achieved by RTC with the arms in were lower than those achieved with the arms out when compared at identical pressure gradients. We conclude that the difference in expiratory flow rates at isovolume-pressure points is most likely related to different effects on the behavior of intrapulmonary airways and choke point characteristics by the two techniques.