Comparing response, relaxation and measurement characteristics of balloon versus micro pressure transducer catheters

Comparing response, relaxation and measurement characteristics of balloon versus micro pressure transducer catheters

Respiratory mechanics can be assessed using oesophageal balloon catheters (BC) or catheter mounted micro-pressure transducers (MC). BC are connected by tubing to external pressure transducers, whereas MC transducers are integrated. We examined whether these different catheter designs had different characteristics. We hypothesised that MC would demonstrate faster response and relaxation characteristics and more accurate peak pressure measurements. Two experiments were performed to evaluate BC and MC which were positioned in a sealed pressurised chamber along with a reference pressure transducer (RP). Experiment 1 exposed the catheters to pressures of 25, 50, 75 and 100 cmH2O with a 0.2 s pressurisation time (PT). Experiment 2 used a constant pressure of 50 cmH2O and PT of 0.4, 0.6, 0.8 and 1 s. The 10-90% rise time, maximal rate of pressure development, half relaxation time, time constant and maximal relaxation rate were faster (P<0.01) for MC compared to BC. Latency was longer for MC by 13-15.5 ms (P<0.01) and time to peak pressure was between 18 ms slower to 19.6 ms faster (P<0.01) dependent upon PT. MC vs. RP had less fixed bias than BC vs. RP (9.6±0.1 vs. 14.5±0.1 cmH2O) and MC recorded pressures more accurately (90.4±0.3 vs. 85.5±0.3 % of RP; P<0.01). The relationship between BC and MC peak pressures was strong (r=0.85; p<0.01). Under controlled conditions, MC demonstrates more rapid response characteristics and more accurate peak pressure recordings. This research suggests that the differences in pressures observed in in vivo studies comparing BC and MC may be partially attributable to less accurate recordings of peak pressures by balloon catheters.