LAUSR

In recent years, the mechanical input impedance of the respiratory system (Zrs) determined using the technique known as oscillometry has been gaining traction as a clinical diagnostic tool to complement conventional spirometry. Nevertheless, despite currently approved oscillometry devices being relatively compact and portable, they are still too heavy and bulky to be used in an ambulatory hands-free setting, mostly because of the mass of the motor and power supply. We therefore explored the possibility of using the subject's own respiratory musculature as the power source for creating flow oscillations at the mouth. We measured reference Zrs in 8 normal volunteers by having them breathe tidally into a piston-driven oscillator powered by an external motor. We fit the measured Zrs to the single-compartment model of the respiratory system characterized by the three parameters resistance (Rrs), elastance (Ers) and inertance (Irs). We then compared these parameter values to those obtained with two commercially available mucus-clearing devices that generate oscillations when expiratory flow drives a flapper valve. The estimates of Rrs agreed mostly within ± 1 cmH2O.s.L-1, which is usefully accurate for most clinical needs. Ers and Irs agreed less well because the breath-driven oscillators provided data at essentially a single frequency close to the resonant frequency of the respiratory system. Nevertheless, we conclude that perturbing respiratory air flow and pressure with a breath-driven oscillator has the potential to provide measurements of Zrs, possibly serving as the basis for a light-weight ambulatory oscillometry system.