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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Schematic diagram of the APD showing pneumotach to measure flow rate, pressure transducer to measure mouth pressure, and the rotating wheel to perturb the airflow.
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Figure 1: Schematic diagram of the APD showing pneumotach to measure flow rate, pressure transducer to measure mouth pressure, and the rotating wheel to perturb the airflow.

Mentions: Subjects breathe normally into a disposable cylindrical mouthpiece attached to the APD (Figure 1). The air flow path from the mouth then enters the pneumotachograph and pressure transducers, where pressure and air flow are measured. A series of perturbations is created by a rotating segmented wheel that partially obstructs air flow. The depths of airflow and pressure perturbations depend on the levels of respiratory resistance and resistance of the device. Respiratory resistance can be calculated after measuring the resistance of the wheel and pneumotachograph with each perturbation. Real time measurements of respiratory resistance are displayed on the computer screen with each perturbation. At the end of 100 perturbations, average respiratory resistance, calculated by averaging inhalation and exhalation resistances, is displayed. It is necessary, with any new technology, to determine its limitations of use and its performance under non-ideal conditions. This is certainly true for technology intended for the clinical setting.


Testing limits to airflow perturbation device (APD) measurements.

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

Schematic diagram of the APD showing pneumotach to measure flow rate, pressure transducer to measure mouth pressure, and the rotating wheel to perturb the airflow.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Schematic diagram of the APD showing pneumotach to measure flow rate, pressure transducer to measure mouth pressure, and the rotating wheel to perturb the airflow.
Mentions: Subjects breathe normally into a disposable cylindrical mouthpiece attached to the APD (Figure 1). The air flow path from the mouth then enters the pneumotachograph and pressure transducers, where pressure and air flow are measured. A series of perturbations is created by a rotating segmented wheel that partially obstructs air flow. The depths of airflow and pressure perturbations depend on the levels of respiratory resistance and resistance of the device. Respiratory resistance can be calculated after measuring the resistance of the wheel and pneumotachograph with each perturbation. Real time measurements of respiratory resistance are displayed on the computer screen with each perturbation. At the end of 100 perturbations, average respiratory resistance, calculated by averaging inhalation and exhalation resistances, is displayed. It is necessary, with any new technology, to determine its limitations of use and its performance under non-ideal conditions. This is certainly true for technology intended for the clinical setting.

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