A NEW INSTRUMENT FOR THE MEASUREMENT OF RIB CAGE AND ABDOMEN CIRCUMFERENCE VARIATION IN RESPIRATION AT REST AND DURING EXERCISE

A simple and inexpensive new extensometer for measuring changes in che st wall circumference during human respiratory movements is presented. The instrument detects the delay between ultrasound emission and rece ption at opposite ends of two rubber tubes encircling the rib cage and abdomen. Assuming a two degree of freedom model of the chest wall and employing an isovolume procedure for determination of volume-motion c oefficients, extensometer estimation of tidal volume (V-T) from change s of rib cage and abdomen circumference was compared with spirometer m easurements at rest and during exercise on a cycle ergometer (55-155 W ) in six subjects and, in four of them, on a treadmill (4-12 km . h(-1 )). In three subjects hypercapnic hyperpnoea at rest was also studied. The slopes of the linear relationship between extensometer and spirom eter V-T (litres) averaged 0.9967 (SD 0.0117) (r(2) = 0.995-0.998; n = 90-143) for cycle ergometer exercise, 1.0072 (SD 0.0078)(r(2) = 0.991 -0.998; n = 75-93) for treadmill exercise and 0.9942 (SD 0.0188) (r(2) = 0.997-0.998; n = 18-25) for hypercapnic hyperpnoea. In all instance s the slope of the regression line was consistent with the model of th e identity line (slope = 1). The changes in end-expiratory lung volume between respiration at rest and during exercise were determined by th e extensometers, and were nearly identical (98.4% on average) to those measured with the spirometer (r(2) = 0.945; n = 24). It is concluded that determination of chest wall circumference with this new instrumen t is suitable for quantitative measurement of ventilation and lung vol ume variations in humans under most physiological conditions.