The isometric force transducers (Grass FT-03C; Grass, Quincy, MA, USA) were connected to two custom-made preamplifiers (Biomedical Engineering, Flinders University) and then to a PowerLab (model 16/35, AD Instruments, Bela Vista, NSW, Australia) and a Macintosh computer running Labchart version 6 (AD Instruments, NSW, Australia). Two high resolution manometry catheters were used to record intraluminal muscle contractions. The first, used for 12 recordings, was a fibre-optic catheter with 72 pressure sensors spaced at 1cm intervals. The fibre-optic catheter was attached to a spectral interrogator unit (FBG-scan 804; FOS&S, Geel, Belgium) and pressures were recorded in real time on a custom-written LabVIEW program (National Instruments, Austin, TX, USA). The second catheter, used for 22 recordings, was a commercially available, solid state high-resolution impedance manometry catheter (Sandhill Scientific, Unisensor USA Inc.) with 32 pressure sensors spaced at 1cm intervals. Pressure data was acquired at 10Hz using InSIGHTTM (Sandhill Scientific, Unisensor USA Inc.). Impedance data was not used in this study. Pressure data acquired by either catheter was exported as text (*.txt) files for analysis in custom-made PlotHRM software developed by the authors (LW), written in Matlab (Mathworks, MA, USA) and Java (Sun Microsystems, CA, USA.