An Evaluation of the Respiradyne II Spirometer

Abstract

We evaluated the accuracy and precision of a prototype Respiradyne II spirometer. Methods: To evaluate the Resting Ventilation Mode, we used four test signals from an Emerson IMV ventilator with respiratory rates of 10-25 cycles/min, tidal volumes of 0.25-1.0 L, and inspiratory times of 1-2 s. The signals were measured by 10 Respiradyne II sensors and compared to measurements made by a Tissot spirometer. To evaluate the Pulmonary Function Mode, we used nine combinations of test signals from a Dixie TTL Training test lung with resistances of 2.33-28.24 cm H₂O/L/s and volumes of 1-5 L, as well as a tenth signal generated by a healthy male volunteer. Each signal was measured three times by each sensor and compared to measurements made by an 8-L Stead-Wells spirometer. To evaluate the Maximum Voluntary Ventilation Mode, we used four test signals generated by an Emerson IMV ventilator with volumes of about 20, 30, 40, and 50 L/min. These signals were measured by 10 Respiradyne II sensors and compared to measurements made by a Tissot spirometer. To evaluate the Negative Inspiratory Force Mode, we simultaneously depressurized the Respiradyne II and a U-tube mercury manometer to negative pressures of 0-100 cm H₂O. Results: There was good overall correlation and acceptable agreement between the Respiradyne II and the Tissot for the Resting Ventilation and Maximum Voluntary Ventilation modes; and there was good correlation between the negative pressures measured by the Respiradyne II and the U-tube manometer. In the Pulmonary Function Mode the accuracy of the Respiradyne met ATS standards for FVC and PEF, but not for FEV₁ and FEF_25-75%. The greatest differences occurred for FEF_25-75%, which the Respiradyne tended to underestimate. The precision of the Respiradyne II was also acceptable. Conclusions: Although we do not believe that the Respiradyne II is acceptable as a diagnostic spirometer, we do believe that its accuracy and precision are adequate for bedside assessment.