Hyatt's Interpretation of Pulmonary Function Tests by Scanlon Paul D.;

Author:Scanlon, Paul D.;
Language: eng
Format: epub
Publisher: Wolters Kluwer
Published: 2020-09-15T00:00:00+00:00

FIG. 9-3 Classic instrument used to measure maximal static expiratory and inspiratory pressures. The expiratory gauge measures 0 to +300 cm H2O, and the inspiratory gauge 0 to −300 cm H2O. Gauges are alternately connected to the cylinder by a three-way stopcock, as indicated by the arrows on the right-hand gauge (A). The side view (B) shows the small 2-mm hole at the distal end of the metal tube. A piece of firm rubber tubing is attached to the proximal end of the cylinder.

Maximal inspiratory pressure (PImax) is measured by having the patient exhale to residual volume, hold the tubing against the lips, and suck as hard as possible. Again, the greatest negative pressure sustained for a similar interval is recorded. The small 2-mm hole at the distal end ensures that the device is measuring the pressure developed in the lung by the inspiratory muscles. Without it, if the patient closes the glottis and sucks with the cheeks, a very large negative pressure can be developed. The leak prevents this from happening because the pressure produced by sucking with a closed glottis decreases rapidly and cannot be sustained. To ensure accuracy, the patient must exert maximal effort. Herein lies a shortcoming of the test. These efforts can be uncomfortable. Some patients are unable, or unwilling, to make such effort. Enthusiastic coaching by the technician is essential.

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