Abstract
Background: Oscillometry has been used to evaluate changes in pulmonary function in subjects with obstructive lung disease, and to a lesser extent in restrictive lung process. Spirometry also informs on lung disease, but results can be variable depending on patient effort and instruction. We hypothesize that reactance measured at 5 Hz (X5) could be a more sensitive measure of lung restriction and decreased compliance than forced vital capacity (FVC) measured by spirometry. As part of a parallel study to evaluate closed loop logic of an oxygen delivery system in volunteers subjected to hypoxia with and without chest restriction, we compared the sensitivity of X5 and FVC to evaluate the degree of chest restriction.
Methods: Five healthy volunteers were selected, screened, and consented at UTMB’s Clinical Research Center (IRB# 18-0007). Each volunteer underwent two randomized hypoxia studies with or without an extra-thoracic restriction device. Restriction was achieved by placing a belt around the thoracic cavity to simulate low compliance or chest wall restriction. To evaluate the degree of restriction, FVC was measured with spirometry and airway resistance and lung reactance were measured with the forced oscillometry technique (FOT). Spirometry with and without extra-thoracic restriction was measured with a portable Koko Spirometer. FOT was assessed with the Resmon Pro. Other variables measured during hypoxia studies included end-tidal CO2, SpO2, oxygen flow, tidal volume (VT), respiratory rate (RR) and minute ventilation (MV). An anesthesiologist was present and monitored the volunteers throughout the study. Hypoxia was discontinued if SpO2 decreased below 70% for more than 3 min or volunteers became symptomatic (intolerant).
Results: Application of restriction significantly decreased FVC (non-restriction: 5.54 ± 0.53L vs restriction: 4.65 ± 0.33 L; P < 0.001). X5 also became more negative with restriction (non-restriction: -0.67 cm H2O/L/s vs restriction: -1.47 cm H2O/L/s; P< 0.004). The average change in FVC was 28% while for X5 it was 113%.
Conclusions: Assessment of lung function can be done easily, reproducibly, and with minimal patient instruction or effort using FOT. X5 correlates with changes in chest wall compliance that result in a restrictive process as measured by spirometry. X5 appears to be a more sensitive measure of changing respiratory system compliance and could be useful in following post-COVID-19 patients complaining of continuing dyspnea.
Airway resistance and reactance measured by Forced Oscillometry Technique using Resmon Pro.
Footnotes
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