Pressure and temperature patterns under the ischial tuberosities

A study was conducted to investigate the pressure relief patterns under the ischial tuberosities in group of 12 paraplegic subjects. A small electrical pressure transducer was taped over each ischial tuberosity, and each subject had a thermistor taped near one tuberosity. The subjects were instrumented in the morning and allowed to go about their normal activities for the day sitting on a 4-inch foam cushion. The subjects sat at pressures greater than 150, greater than 90, and greater than 30 mmHg for 17.6 percent, 53.5 percent, and 91.8 percent of the time, respectively. The subjects sat on the average for 10.1 min without doing a pushup with a duration greater than 1 sec and sat on the average for 29.6 min without doing a pushup with a duration greater than 5 sec. Two of the subjects sat for periods greater than 60 min for greater than 75 percent of the time (ignoring pushups less than 5 sec) and greater than 65 percent of the time ignoring pushups less than 1 sec. The average time between pushups was within the generally accepted limits to prevent ulcers--10-30 minutes. A few of the subjects had occasional long periods of uninterrupted pressure greater than what is thought to be required to produce ulcers--and did not develop them.