Characterization of a density-corrected ultrasonic pneumotachometer for horses.

A density-corrected ultrasonic pneumotachometer designed specifically for horses (UF202) was evaluated and characterized with the aid of a custom-built apparatus. UF202 provided voltage outputs for airflow through and gas density within the flowhead. Baseline stability for flow channel output (VUF202) was < 0.35% full scale (FS), and VUF202 was linear over a range of +/- 50 l/s (R2 > or = 0.9976). Under optimal conditions, VUF202 accuracy was determined to be +/- 1.00% FS and repeatability was +/- 0.78% FS. VUF202 resolution was 24 ml/s. The rise time for VUF202 was 18 ms, and the -3-dB point was 18 Hz; digital compensation provided a flat frequency response to 32 Hz. VUF202 gain appeared to be stable over a period of 8 days. Density channel output (PUF202) was linear over a range of 1.11-1.23 g/l (R2 > or = 0.9645). PUF202 accuracy was calculated to be +/- 0.50% FS, and PUF202 repeatability was determined to be +/- 0.30% FS. Resistance of the flowhead was determined to be 0.013 cmH2O.l-1.s at a flow of 40 l/s. On the basis of this study, we conclude that UF202 should facilitate accurate measurement of breath-by-breath airflow of exercising horses.