Frequency responses of infant air-balloon versus liquid-filled catheters for intra-esophageal pressure measurement

Amplitude and phase frequency response characteristics of infant air- balloon catheters (IABC) of differing French gauge (FG) sizes and brands were quantified to determine their suitability for measuring dynamic intra- esophageal pressure (P(es)) accurately. Frequency response performances of matching IABC and water-filled catheters (WFC) were also compared using the swept sine wave technique. The maximum respiratory rate within which IABCs could potentially measure P(es) within a 5% error limit was calculated (F(RR)). Frequency responses of IABCs greater than FG size 5 exhibited underdamped resonant properties, while smaller FG size IABCs exhibited near- critical damping or overdamping. IABCs maintained uniform amplitude frequency responses up to 25 Hz, demonstrating the ability to measure P(es) potentially up to 148 breaths/min within a 5% error limit. The frequency response performance of FG size 6 IABCs was similar to that of FG size 10 IABCs. Compared with matching WFCs, the frequency response performance of IABCs was significantly superior, the frequency response variability within IABC samples was lower, and IABC correlation between FG size and F(RR) was advantageously lower than for WFCs. F(RR) values for differing IABC brands and FG sizes era presented. We conclude that IABCs manufactured to infant- appropriate balloon specifications exhibit significantly superior frequency response characteristics compared with matching WFCs. Measurement accuracy is not improved using IABCs greater than FG size 6. Inexpensive intra-esophageal IABCs are technically suitable for the accurate measurement of dynamic P(es) during high-frequency respiratory mechanics encountered during infant artificial ventilation.