Respiration Physiology, 80 (1990) 193-202 193 Elsevier RESP 01649 Influence of lung volume and rib cage configuration on transdiaphragrnatic pressure during phrenic nerve stimulation in man Anne Mier, Conor Brophy, John Moxham and Malcolm Green Brompton Hospital, London, U.K. (Accepted 16 February 1990) Abstract. Transdiaphragmatic pressure was recorded during bilateral supramaximal percutaneous phrenic nerve stimulation at 1 Hz (twitch Pdi) to investigate the effect of lung volume and rib cage configuration on diaphragm contractility in man. Stimulations were performed 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 manoeuvres.Twitch Pdi at FRC was 24.4 cm H20. At lung volumes above FRC, twitch Pdi decreased by 7.04 + 3.2 cm HaO per litre of volume change. At lung volumes below FRC, twitch Pdi increased by 12.4 _+8.6 cm HzO per litre of volume change. When the diaphragm was lengthened during an isovolume manoeuvre 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. Animal, man; Diaphragm, contractility, dependence on lung volume; Lung volume, influence on diaphragmatic contractility; Phrenic nerve, stimulation, transdiaphragmatic pressure; Pressure, esophageal, gastric, transdiaphragmatic; Rib cage configuration, influence on diaphragm contractility; Technique in respiratory physiology,phrenic nerve stimulation (electric) Previous studies both in vitro and in vivo have demonstrated that the force developed by the diaphragm depends on muscle length. The tension generated by the diaphragm has been noted to decrease as diaphragm length shortens and the length tension properties of the mammalian diaphragm in vitro have been shown to be similar to those of intact limb muscles and to be similar between species (McCully and Faulkner, 1983). Other studies in cats and man have demonstrated that twitch tension during submaximal unilateral phrenic nerve stimulation decreases as lung volume increases (Pengelly et al., 1971). The force-length relationship of the diaphragm was further demonstrated during Correspondence to: A. Mier, Department of Medicine, Charing Cross Hospital, Fulham Palace Road, London W6, U.K. 0034-5687/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)