Reliability and validity of spirometry measurements in a paperless home monitoring diary program for lung transplantation

Objective: To demonstrate that home spirometry measurements are reliable and valid and can be used as part of a home measurement monitoring system by lung transplant recipients. Design: Longitudinal, observational. Setting: University medical center. Subjects: Eighteen patients who have undergone lung transplantation; age range was 24 to 63 years (mean of 49.5 years). Outcome Measures: Reliability and validity of forced expiratory volume at 1 second (FEV₁) and forced vital capacity (FVC). Intervention: Recording of spirometry, vital signs, and symptom measures at home each day by use of a paperless electronic-diary/spirometer instrument. Results: Day-to-day variability as measured by the standard deviation ranged from 0.013 L to 0.202 L for FVC and 0.015 L to 0.117 L for FEV₁. The correlation between the two best forced expiratory maneuvers on any given day was 0.98 for both FVC and FEV₁, with percent differences between the measurements of 2% for FVC and 3% for FEV₁. The correlation between measurements performed in the pulmonary function laboratory and measurements done by the patient at home on the same day was 0.94 for FVC and 0.99 for FEV₁. Conclusions: This evaluation demonstrated that home measurements are both reliable (i.e., repeatable) and valid when compared with the 'gold standard' of the pulmonary function laboratory. The home monitoring program has been well accepted by patients, is easy to use, and provides data comparable to that collected during clinic visits.