Usefulness of the Impulse Oscillometry System in Graft Function Monitoring in Lung Transplant Recipients

After successful lung transplantation, patients are monitored for chronic lung allograft dysfunction. Pulmonary function tests and 6-minute-walk tests are commonly used for functional graft monitoring. As these methods require substantial effort, however, many patients are unable to complete testing fully. The impulse oscillometry system is a noninvasive method that requires minimal patient cooperation and is suitable for use for patients incapable of strenuous activity. We compared impulse oscillometry system with pulmonary function tests and 6-minute-walk tests to determine if impulse oscillometry system could serve as a substitute measure.

This prospective, observational study evaluated 25 consecutive patients (19 men, median age 54.5 years) admitted to a single institution from January to October 2016 (double-lung = 13, single-lung = 13). Patients were assessed using pulmonary function tests, impulse oscillometry system, and 6-minute-walk tests.

Eighty-eight percent of patients reached high-resonance frequency (F_res) and, in 84% of patients, the value of Ax (area of reactance) increased above the norm (N < 0.33 kPa/L) indicating peripheral airways obstruction. High resistance of small airways, measured with an R5 - R20 difference, followed higher Ax values. The increase of resistance at 5 Hz in 31% of patients (R5 >150% predicted value) also indicated small airway obstruction. Airway obturation in patients with elevated Ax and R5 was confirmed by decreased FEV₁ (<75% predictive value) and FEV₁/FVC ratio in 38% of patients.

Study results confirm the impulse oscillometry system method could be a substitute for pulmonary function tests in determining the occurrence of chronic lung allograft dysfunction. 6-minute-walk tests showed neither strong correlations regarding impulse oscillometry system and pulmonary function tests nor any base for differentiation of results regarding main factor codes.