Influence of lung volume and rib cage configuration on transdiaphragmatic pressure during phrenic nerve stimulation in man

Abstract

Transdiaphragmatic pressure was recorded during bilateral supramaximal percutaneos phrenic nerve stimulation at 1 Hz (twitch Pdii) to investigate the effect of lung volume and rib cage configuration on diaphragm contractility in man. Stimulatons were perfomed in 5 normal supine subjects at resting end expiration (FRC) and at lung volumes above and below FRC, during relaxation against a closed airway and during isovolume manœuvres. Twitch Pdi at FRC was 24.4 cm H 2O. At lung volumes above FRC, twitch Pdi decreased by 7.04±3.2 cm H 2O per litre of volume change. At lugn volumes below FRC, twitch Pdi increased by 12.4±8.6 cm H 2O per litre of volume change. When the diaphragm was lengthened during an isovolume manœuvre at FRC, twitch Pdi increased. A similar relationship between lung volume and twitch Pdi was obtained during stimulations performed with abdominal binding. These results demonstrate that the pressure developed by the diaphragm during phrenic nerve stimulation is significantly affected both by increases and decreases in lung volume and by the rib cage configuration at which stimulation is performed.