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Postprandial effects on twitch transdiaphragmatic pressure

¹ Respiratory Muscle Laboratory, Dept of Respiratory Medicine and Allergy, Guy's, King's and St Thomas' School of Medicine, and ² Royal Brompton Hospital, London, UK

CORRESPONDENCE: W. Man, Respiratory Muscle Laboratory, Dept of Respiratory Medicine, King's College Hospital, Bessemer Road, London, SE5 9PJ, UK. Fax: 44 2073463589. E-mail: William.man@kcl.ac.uk

Keywords: magnetic stimulation, phrenic nerves, transdiaphragmatic pressure

Received: December 13, 2001
Accepted March 4, 2002

W. Man is a Clinical Research Training Fellow of the Medical Research Council (UK).

Twitch transdiaphragmatic pressure (P_di,tw), measured following magnetic stimulation of the phrenic nerves, is used to assess diaphragm strength, contractility and fatigue. Although the effects of posture, lung volume and potentiation on P_di,tw are well described, it is not known whether the degree of gastric filling affects the measurement.

P_di,tw was recorded in seven healthy volunteers on two occasions with antero-lateral magnetic stimulation of the phrenic nerves. On the first occasion, the subjects had fasted for at least 8 h, whilst on the second occasion, measurements were made after each subject had eaten a substantial meal sufficient to produce a feeling of satiation.

Mean postprandial unpotentiated and potentiated P_di,tw were significantly greater than corresponding fasting P_di,tw in all seven volunteers (29.8 versus 25.7 cmH₂O and 38.9 versus 34.4 cmH₂O, respectively). This was due to a significantly increased gastric pressure component (1.10 versus 0.84 and 0.94 versus 0.78, respectively), and reduced abdominal compliance (36 versus 62 mL·cmH₂O^–1). Twitch oesophageal pressure was preserved (15.0 versus 15.4 cmH₂O).

The postprandial state increases twitch transdiaphragmatic pressure, and this should be taken into account when using twitch transdiaphragmatic pressure to follow-up patients or to assess the effects of interventions on diaphragm contractility.

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