Respiratory tubes with a length of 35mm and diameters of 10, 15, and 20mm were made for experimental purpose, and both the static$(P_s);and;dynamic(P_D)$ pressures were simultaneously measured for steady flow rates ranging 1-12//sec. Least squares analysis resulted successful fitting of $P_s;and;P_D$ data with quadratic equations with correlation coefficients higher than 0.99(P<0.0001). The spirometric measurement standards of the American Thoracic Society(ATS) were applied to $P_s$ data, which demonstrated the smallest tube diameter of 15mm to satisfy the ATS standards. The maximum $P_D$ value of the velocity type transducer(the functional single use respiratory air flow tube) with the diameter of 15mm was estimated to be approximately $75cmH_2O$, implying more than 7 times larger sensitivity than the widely used pneumotachometers. These results showed that the velocity type respiratory air flow transducer is a unique device accomplishing miniaturization with the sensitivity increased, thus would be of great advantage to develop portable medical devices.