Measurement of flow through perfused bronchial segments: optimization of flow head resistance.

Techniques for measuring flow, for example through perfused bronchial segments, frequently use a flow head as the sensing device. The sensitivity of these instruments to changes in airway resistance is dependent on the flow head resistance. This study aims to quantify the effect of flow head resistance on sensitivity and flow, allowing optimization of flow head resistance. A mathematical model of the perfused bronchial segment preparation was constructed and used to explore the effect of flow head resistance on sensitivity. The model's assumptions were experimentally tested using segments of pig bronchus, perfused through the lumen with Krebs solution. The model suggests a complex relationship between flow head resistance and sensitivity that has a distinct maximum when approximately half of the total resistance is present in the flow head. Furthermore, the maximum sensitivity was found to be proportional to the resting flow. Regression between experimentally derived sensitivities and modelled predictions was linear, with a correlation coefficient of 0.93. We have defined the optimum recording conditions for study of flow through isolated bronchial segments.