Design and calibration of unicapillary pneumotachographs

Abstract

This study presents a method for design and calibration of unicapillary 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 minimal interference with animal's respiratory mechanics and gas exchange. A third-order polynomial calibration (Pol) of the pressure-flow relationship was employed and compared with linear calibration (Lin). Tests were done for conditions of ambient pressure (Pam) and positive pressure (Ppos) ventilation at different flow ranges. A physical model designed to match normal and low compliance in rats was used. At normal compliance, Pol provided lower errors than Lin for mixed (1-12 ml/s), mean (4-10 ml/s), and high (8-12 ml/s) flow rate calibrations for both Pam and Ppos inspiratory tests (P < 0.001 for all conditions) and expiratory tests (P < 0.001 for all conditions). At low compliance, they differed significantly with 8.6 +/- 4.1% underestimation when Lin at Pam was used in Ppos tests. Ppos calibration, preferably in combination with 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 useful for improvement of flow and volume measurements in small animals during both Pam and Ppos ventilation.

Gas exchange during exercise in different evolutional stages of chronic Chagas' heart disease

“…The VIT 2000 software employed for processing the signals and calculating the cardiopulmonary exercise test parameters was developed and tested in the laboratory of pulmonary engineering of the Biomedical Engineering Program of COPPE-UFRJ 12 . The flow signal was calculated with a third-order polynomial adjustment 13 , and the gas sample suctioned during the analysis of gas concentrations was compensated by the respiratory mass spectrometer (1 mL.s -1 ). V IC and V EC were calculated through trapezoidal numerical integration and expressed in BTPS (37°C, 760mmHg, and saturated with water vapor) for each respiratory cycle.…”

“…V IC and V EC were calculated through trapezoidal numerical integration and expressed in BTPS (37°C, 760mmHg, and saturated with water vapor) for each respiratory cycle. Instantaneous gas viscosity was calculated and employed to correct its effect in gas flows and volumes 13 , and to estimate the time delay between gas flow and concentrations 14 necessary for calculating the partial respiratory gas volumes. These were expressed in STPD (0°C, 760mmHg, dry) and obtained by numerical integration of the product of the gas flow and fractions, and these signals were previously synchronized.…”

Continuous positive airway pressure setups evaluated at simulated exercise conditions

“…The flow rate was calibrated according to the technique described by Giannella-Neto et al (1998), and the P ao was calibrated against a reference manometer RT-200 (Timeter Instrument, USA). In all cases, the baselines of the signals were measured prior to the experiments and were subtracted from the signals during off-line processing.…”

Design and nonlinear modeling of a sensitive sensor for the measurement of flow in mice

“…Indeed, the design and implementation of flow sensors for rodents has already been shown to be feasible. For instance, Giannella-Neto et al (Giannella-Neto et al 1998) designed and calibrated an effective rat pneumotachograph based on rigorous design criteria considering laminar flow, measurable pressure difference, and minimal gas exchange and interference with the rodent’s respiratory mechanics. In the characterization of the rat pneumotachograph, the nonlinear pressure-flow characteristics of the device were accounted for via a nonparametric polynomial model, and an important conclusion was the importance of nonlinear calibration for accurate flow measurements.…”