A short rebreathing protocol (SRP) to speed up the measurement of functional residual capacity (FRC)

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Background: Measurement of FRC is an essential component of lung function assessment. Multiple breath nitrogen washout (MBNW) is widely used for this, but the measurement is more time-consuming than body plethysmography and requires a continuous supply of oxygen. We have developed a short rebreathing protocol (SRP) to reduce the gas equilibration time and remove the need for a continuous oxygen supply. Aim: To compare FRC values obtained using the SRP with those obtained by full MBNW. Methods: Healthy non-smokers undertook both SRP and full MBNW on each of two visits. SRP involved a short period of steady-state air-breathing, followed by 80 seconds of rebreathing from a 5L anaesthetic bag filled to ~0.75 GLI-predicted FRC with 100% oxygen (Fig 1A); MBNW involved steady-state air-breathing followed by 5 minutes of 100% oxygen from large gas cylinders. FRC was calculated by computed cardiopulmonography (doi: 10.1152/japplphysiol.00436.2022), a novel technique employing laser absorption spectroscopy and a precision flow meter to measure and model gas exchange within the main airway accurately. Results: A Bland-Altman plot of data from 12 participants is shown in Fig 1B. There was a strong correlation between the two methods (r=0.95, p<0.001) with no significant difference between them (F=2.868, p=0.117). Conclusion: SRP may provide a faster alternative to full MBNW for measuring FRC. erj;66/suppl_69/PA639/F1 F1 F1

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