A Critical Study of the Response of Manometers to Forced Oscillations

A new pump has been designed to generate a sinusoidal pressure, or flow, of constant amplitude up to 90 c/s. Some of the technical problems of this design are discussed, and compared with other pumps that have been used. The cause of possible errors in manometric measurement is discussed with emphasis on the necessity for the scrupulous elimination of any trace of air bubbles. At 90 c/s transducers of the P23 type, connected directly to the pump, showed a response within 5% of the true amplitude; the type SF-1 was within 1% at this frequency. The P23 type manometers were tested with standard cardiac catheters, and with two specimens of polyethylene tubing. The results show that, when bubbles are carefully eliminated, these manometers are capable of giving a result within 5% of the true value to above 15 c/s with all the cardiac catheters tested. The modification of the transducer behaviour by the catheter is discussed briefly, but for practical purposes cardiac catheters may be treated as virtually rigid tubes.