Limits...
Testing limits to airflow perturbation device (APD) measurements.

Lopresti ER, Johnson AT, Koh FC, Scott WH, Jamshidi S, Silverman NK - Biomed Eng Online (2008)

Bottom Line: 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 cmH2O.sec/L, respectively).Although breathing through a 52 cm length of flexible ventilator tubing reduced the APD measurement from 4.0 cm H2O.sec/L for the control to 3.6 cm H2O.sec/L for the tube, the difference was not statistically significant.

View Article: PubMed Central - HTML - PubMed

Affiliation: Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA. erikalopresti@yahoo.com

ABSTRACT

Background: 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.

Method: 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.

Results: All leaks reduced APD resistance measurement values. Leaks represented by two 3.2 mm diameter tubes reduced measured resistance by about 10% (4.2 cmH2O.sec/L for control and 3.9 cm H2O.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 cmH2O.sec/L, respectively). Mouth resistance measured with a cardboard mouthpiece gave an APD measurement of 4.2 cm H2O.sec/L and mouth resistance measured with an oronasal mask was 4.5 cm H2O.sec/L; the two were not significantly different. Nose resistance measured with the oronasal mask was 7.6 cm H2O.sec/L. Adding airflow resistances of 1.12 and 2.10 cm H2O.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 H2O.sec/L. Although breathing through a 52 cm length of flexible ventilator tubing reduced the APD measurement from 4.0 cm H2O.sec/L for the control to 3.6 cm H2O.sec/L for the tube, the difference was not statistically significant.

Conclusion: 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.

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Diagram of the mouthpiece used to test the effect of leaks around the mouth. Small tubes on either side of the mouth provided leakage paths. This mouth piece was used in place of the regular mouthpiece with the APD.
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Figure 2: Diagram of the mouthpiece used to test the effect of leaks around the mouth. Small tubes on either side of the mouth provided leakage paths. This mouth piece was used in place of the regular mouthpiece with the APD.

Mentions: At Station 1, subjects used four different mouthpieces. The first was the control mouthpiece, a simple cardboard cylinder that fit over the APD pneumotach. The other three mouthpieces had small, medium, and large leaks composed of a pair of 2 cm long tubes of 3.2, 4.8, and 6.4 mm (1/8, 3/16, and 1/4 inches) internal diameters respectively (Figure 2). The size of each leak was constructed to give a leak resistance to APD resistance ratio of about 1:1, 1:2, and 1:20. For each APD measurement, subjects placed their mouths securely over the mouthpiece and breathed normal breaths for approximately 1 minute with their hands holding cheeks stable to minimize vibrations. Subjects completed two measurement replications with the control mouthpiece, two measurements with the small, medium, and large leak mouthpieces, and finally two more replications with the control mouthpiece. Control replications before and after the leaky mouthpieces were made to detect changes to respiratory resistance that might have resulted from hyperventilation when compensating for the leaks.


Testing limits to airflow perturbation device (APD) measurements.

Lopresti ER, Johnson AT, Koh FC, Scott WH, Jamshidi S, Silverman NK - Biomed Eng Online (2008)

Diagram of the mouthpiece used to test the effect of leaks around the mouth. Small tubes on either side of the mouth provided leakage paths. This mouth piece was used in place of the regular mouthpiece with the APD.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2600779&req=5

Figure 2: Diagram of the mouthpiece used to test the effect of leaks around the mouth. Small tubes on either side of the mouth provided leakage paths. This mouth piece was used in place of the regular mouthpiece with the APD.
Mentions: At Station 1, subjects used four different mouthpieces. The first was the control mouthpiece, a simple cardboard cylinder that fit over the APD pneumotach. The other three mouthpieces had small, medium, and large leaks composed of a pair of 2 cm long tubes of 3.2, 4.8, and 6.4 mm (1/8, 3/16, and 1/4 inches) internal diameters respectively (Figure 2). The size of each leak was constructed to give a leak resistance to APD resistance ratio of about 1:1, 1:2, and 1:20. For each APD measurement, subjects placed their mouths securely over the mouthpiece and breathed normal breaths for approximately 1 minute with their hands holding cheeks stable to minimize vibrations. Subjects completed two measurement replications with the control mouthpiece, two measurements with the small, medium, and large leak mouthpieces, and finally two more replications with the control mouthpiece. Control replications before and after the leaky mouthpieces were made to detect changes to respiratory resistance that might have resulted from hyperventilation when compensating for the leaks.

Bottom Line: 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 cmH2O.sec/L, respectively).Although breathing through a 52 cm length of flexible ventilator tubing reduced the APD measurement from 4.0 cm H2O.sec/L for the control to 3.6 cm H2O.sec/L for the tube, the difference was not statistically significant.

View Article: PubMed Central - HTML - PubMed

Affiliation: Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA. erikalopresti@yahoo.com

ABSTRACT

Background: 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.

Method: 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.

Results: All leaks reduced APD resistance measurement values. Leaks represented by two 3.2 mm diameter tubes reduced measured resistance by about 10% (4.2 cmH2O.sec/L for control and 3.9 cm H2O.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 cmH2O.sec/L, respectively). Mouth resistance measured with a cardboard mouthpiece gave an APD measurement of 4.2 cm H2O.sec/L and mouth resistance measured with an oronasal mask was 4.5 cm H2O.sec/L; the two were not significantly different. Nose resistance measured with the oronasal mask was 7.6 cm H2O.sec/L. Adding airflow resistances of 1.12 and 2.10 cm H2O.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 H2O.sec/L. Although breathing through a 52 cm length of flexible ventilator tubing reduced the APD measurement from 4.0 cm H2O.sec/L for the control to 3.6 cm H2O.sec/L for the tube, the difference was not statistically significant.

Conclusion: 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.

Show MeSH
Related in: MedlinePlus