Automated rodent respiratory monitor and histogram computer--a preliminary report

The system described in this paper was designed to monitor total inhaled volume (V), tidal volume (VT), and respiratory frequency (f) of Fisher rats before, during, and after exposure to cigarette smoke. The systems consists of three major subsystems: plethysmograph, analog signal conditioner, and histogram computer. The volume type whole body plethysmograph incorporates a rubber nose seal. Tidal flow rate (V) from the tube, measured by a pneumotachometer, is integrated by the signal conditioning system to obtain VT and V. Both V and V are displayed on a strip chart recorder. A rat will often exhibit considerable sniffing, especially in the presence of cigarette smoke. Consequently, average tidal volume (VT) and average respiratory frequency (f) are not accurate measurements of typical VT and f. Sensitivity of the system to changes in typical VT and f is important snce the system will be used to evaluate the effects of subtle differences in types of experimental cigarettes. A microprocessor was used in conjunction with a cathode ray tube to compute and display both the VT and respiratory period (T = 1/f) as histograms. From the histograms the most common (typical) VT (mode of the histogram) and the most common T can be easily observed and recorded. The histogram computer also calculates and digitally displays VT and f.