Accommodation of the abdomen to its content: Integrated abdomino-thoracic response

Background We previously showed that changes in intra-abdominal content induce a volume-dependent muscular response of the anterior abdominal wall and the diaphragm. We aimed to determine the contribution of the thorax to abdominal accommodation and the influence of the intra-abdominal expansion rate. Methods Gas (1440mL total load) was infused into the colon of nine healthy subjects, while abdomino-thoracic perimeters (by tape measure), electromyography (EMG) activity of the diaphragm (via six ring electrodes over an esophageal tube in the hiatus), intercostals and anterior abdominal wall (via five pairs of surface electrodes) and the position of the diaphragm by ultrasonography were measured. Infusion rates of 24, 48, and 96mLmin -1 were tested on separate days. Key Results Gas infusion induced anterior abdominal wall contraction (18±1% EMG increment; P<0.001) with relatively modest girth increment (4.9±0.9mm; P=0.001), diaphragmatic relaxation (by 15±1%; P<0.001) with cephalad displacement (by 23±6mm; P=0.005), and intercostal contraction (by 19±2%; P<0.001) with increased thoracic perimeter (by 2.0±0.5mm; P=0.009). Responses were similar with the three infusion rates. Conclusions & Inferences Accommodation of intra-abdominal loads involves a volume-related integrated abdomino-thoracic response regardless of the expansion rate. © 2011 Blackwell Publishing Ltd.