Automated system for measurement of mechanics of breathing

We describe a complete automated system for measurement of total respiratory resistance and compliance, and of pulmonary resistance and compliance in humans and anesthetized animals. The device for testing the chest-lung system consists of a sinusoidal pump with a stroke adjustable from 20 ml to 600 ml over a cycling frequency of 0.3 to 30 Hz. Pressure and flow or volume are inputted into an analog network for wave shaping, then to an arithmetic unit composed of sample-and-hold amplifiers, peak, minimum and zero detecting circuits, an analog division circuit, and a digital logic processor. The computer takes the peak-to-peak amplitude of one of two sinusoidal inputs at 0.3 to 10 Hz and the corresponding amplitude of the other input in the presence of a.c. noise and d.c. shifts, divides one into the other, and displays an answer on a digital voltmeter. In addition, the analog output is displayed on the cathode-ray tube of a storage oscilloscope. Plots of total resistance and pulmonary resistance are recorded as a function of lung volume in both humans inspiring voluntarily as well as anesthetized dogs inflated by positive pressure from the test apparatus. Total and pulmonary dynamic compliance, as a function of breathing frequency, can only be measured by the computer if a symmetrical waveform is presented to it. This cannot be achieved in spontaneously breathing subjects but is accomplished in apneic animals by producing sinusoidal oscillations from the test apparatus. Our on-line method for measurement of total respiratory resistance is now used in the Clinical Pulmonary Laboratory for experimental work, and we are in the process of obtaining values in normal subjects.