USE OF TWITCH PRESSURES TO ASSESS DIAPHRAGMATIC FUNCTION AND CENTRAL DRIVE

Transdiaphragmatic pressures generated by phrenic nerve twitches have been proposed as a means to assess diaphragmatic function and central drive, but their validity and reliability have not been determined. We evaluated diaphragmatic twitch and twitch occlusion measurements in a rabbit model of diaphragmatic contractile dysfunction and diaphragmat ic fatigue to determine whether 1) diaphragmatic twitch pressures accu rately assess changes in low- and high-frequency diaphragm trains duri ng the development of, and recovery from, contractile fatigue; 2) twit ch occlusion measurements accurately quantify the intensity of central drive to the diaphragm; and 3) twitch measurements are affected by th oracoabdominal binding or twitch potentiation. Single-twitch and 20-Hz double- and triple-twitch pressures accurately reflected changes in l ow-frequency diaphragm train pressures, whereas only 80-Hz triple-twit ch pressures accurately reflected changes in high-frequency trains. Tw itch occlusion measurements of central drive closely mirrored central drive as reflected by phrenic nerve recordings and only slightly under estimated the absolute intensity of central drive. Thoracoabdominal bi nding increased twitch and train pressures, and repetitive electrical stimulations further potentiated twitch pressures. However, twitch pot entiation and a lack of thoracoabdominal binding had no affect on twit ch measurements of diaphragmatic function during the induction and rec overy from fatigue or on twitch occlusion measurements of intensity of central drive. Thus, twitch measurements can be used to accurately as sess diaphragmatic low- and high-frequency fatigue and to quantify the intensity of central drive to the diaphragm.