DESIGN AND CALIBRATION OF UNICAPILLARY PNEUMOTACHOGRAPHS

This study presents a method for design and calibration of unicapillar y pneumotachographs for small-animal experiments. The design, based on Poiseuille's law, defines a set of internal radius and length values that allows for laminar flow, measurable pressure differences, and min imal interference with animal's respiratory mechanics and gas exchange . A third-order polynomial calibration (Pol) of the pressure-flow rela tionship was employed and compared with linear calibration (Lin). Test s were done for conditions of ambient pressure (Pam and positive press ure (Ppos) ventilation at different flow ranges. A physical model desi gned to match normal and low compliance in rats was used. At normal co mpliance, Pol provided lower errors than Lin for mixed (1-12 ml/s), me an (4-10 ml/s), and high (8-12 ml/s) flow rate calibrations for both P am and Ppos inspiratory tests (P < 0.001 for all conditions) and expir atory tests (P < 0.001 for all conditions). At low compliance, they di ffered significantly with 8.6 +/- 4.1% underestimation when Lin at Pam was used in Ppos tests. Ppos calibration, preferably in combination w ith Pol, should be used in this case to minimize errors (Pol = 0.8 +/- 0.5%, Lin = 6.5 +/- 4.0%, P < 0.0005). Nonlinear calibration may be u seful for improvement of flow and volume measurements in small animals during both Pam and Ppos ventilation.