The abdominal muscles in anaesthesia and after surgery G.B. Drummond  British Journal of Anaesthesia  Volume 91, Issue 1, Pages 73-80 (July 2003) DOI: 10.1093/bja/aeg145 Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 1 Abdominal muscle activity during anaesthesia. Top trace: gastric pressure. Middle trace is respiratory flow (inspiration down). Bottom trace, left: electromyogram of lateral abdominal (probably external oblique) muscles: this is integrated after the second respiratory cycle. Note the decrease in abdominal pressure at the onset of inspiration: this represents abdominal relaxation. At end inspiration, abdominal pressure increases as the diaphragm descends, and decreases as the diaphragm relaxes. From Freund, Roos, and Dodd,32 with permission from the publisher. British Journal of Anaesthesia 2003 91, 73-80DOI: (10.1093/bja/aeg145) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 2 Abdominal pressure (measured from the bladder) in a patient 6 h after abdominal hysterectomy, receiving morphine by patient controlled analgesia. Lower trace is respiratory flow at the nose, inspiration down. There is mild inspiratory obstruction, shown by the flattened trace. (a) Onset of inspiration: abdominal pressure decreases. (b) End-inspiration with pressure generated by diaphragm descent, followed by increase in expiration from abdominal muscle action (G. B. Drummond, unpublished data). British Journal of Anaesthesia 2003 91, 73-80DOI: (10.1093/bja/aeg145) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 3 The actions of diaphragm and abdominal muscles. Top: diaphragm activity will apply traction upwards to the costal insertions, if the diaphragm is impeded in its descent by a rigid abdomen. At the same time, abdominal pressure increase is transmitted through the pleural sulcus (‘zone of apposition’) to act to expand the lower ribcage. Bottom: the abdominal muscles can apply traction to the rib margins and pull them down and in. At the same time, increased abdominal pressure acts to distend the lower ribs and force the diaphragm cranially. The net movement depends on the relative action of the different abdominal muscles. British Journal of Anaesthesia 2003 91, 73-80DOI: (10.1093/bja/aeg145) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 4 Diagrammatic representation of spirometry traces from Bergman6 and Kallos et al.46 At induction of anaesthesia, there is a prompt decrease in FRC, which does not change further after giving a neuromuscular blocking agent. In contrast, during anaesthesia with fentanyl, FRC is increased after neuromuscular block, indicating the loss of abdominal muscle contraction. British Journal of Anaesthesia 2003 91, 73-80DOI: (10.1093/bja/aeg145) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions

Fig 5 An example of distortion of the abdomen. Control breath: unloaded. Loaded breath: breathing through an expiratory resistance. Heavy solid line is tidal volume, thin solid line is height of central abdomen, interrupted line height of lateral abdomen. During a control breath, both central and lateral abdomen move out in synchrony. With the added load, paradoxical inward motion of the central abdomen is noted, because the central abdomen protruded during active expiration. Data from Drummond and Duffy.24 British Journal of Anaesthesia 2003 91, 73-80DOI: (10.1093/bja/aeg145) Copyright © 2003 British Journal of Anaesthesia Terms and Conditions