26 research outputs found
Testing limits to airflow perturbation device (APD) measurements
<p>Abstract</p> <p>Background</p> <p>The Airflow Perturbation Device (APD) is a lightweight, portable device that can be used to measure total respiratory resistance as well as inhalation and exhalation resistances. There is a need to determine limits to the accuracy of APD measurements for different conditions likely to occur: leaks around the mouthpiece, use of an oronasal mask, and the addition of resistance in the respiratory system. Also, there is a need for resistance measurements in patients who are ventilated.</p> <p>Method</p> <p>Ten subjects between the ages of 18 and 35 were tested for each station in the experiment. The first station involved testing the effects of leaks of known sizes on APD measurements. The second station tested the use of an oronasal mask used in conjunction with the APD during nose and mouth breathing. The third station tested the effects of two different resistances added in series with the APD mouthpiece. The fourth station tested the usage of a flexible ventilator tube in conjunction with the APD.</p> <p>Results</p> <p>All leaks reduced APD resistance measurement values. Leaks represented by two 3.2 mm diameter tubes reduced measured resistance by about 10% (4.2 cmH<sub>2</sub>O路sec/L for control and 3.9 cm H<sub>2</sub>O路sec/L for the leak). This was not statistically significant. Larger leaks given by 4.8 and 6.4 mm tubes reduced measurements significantly (3.4 and 3.0 cm cmH<sub>2</sub>O路sec/L, respectively). Mouth resistance measured with a cardboard mouthpiece gave an APD measurement of 4.2 cm H<sub>2</sub>O路sec/L and mouth resistance measured with an oronasal mask was 4.5 cm H<sub>2</sub>O路sec/L; the two were not significantly different. Nose resistance measured with the oronasal mask was 7.6 cm H<sub>2</sub>O路sec/L. Adding airflow resistances of 1.12 and 2.10 cm H<sub>2</sub>O路sec/L to the breathing circuit between the mouth and APD yielded respiratory resistance values higher than the control by 0.7 and 2.0 cm H<sub>2</sub>O路sec/L. Although breathing through a 52 cm length of flexible ventilator tubing reduced the APD measurement from 4.0 cm H<sub>2</sub>O路sec/L for the control to 3.6 cm H<sub>2</sub>O路sec/L for the tube, the difference was not statistically significant.</p> <p>Conclusion</p> <p>The APD can be adapted for use in ventilated, unconscious, and uncooperative patients with use of a ventilator tube and an oronasal mask without significantly affecting measurements. Adding a resistance in series with the APD mouthpiece has an additive effect on resistance measurements, and can be used for qualitative calibration. A leak size of at least the equivalent of two 3.2 mm diameter tubes can be tolerated without significantly affecting APD measurements.</p