Assessment of Respiratory Mechanics in Mice Using Estimated Input Impedance Without Redundancy

Abstract

The forced oscillation technique (FOT) is a noninvasive method to assess respiratory mechanics. The most widely used commercial ventilator in rodents based on FOT (flexiVent, SCIREQ, Canada) applies a 3-s broadband volume disturbance to estimate the impedance of respiratory entry. The constant phase model (CPM) is adjusted to the impedance of respiratory entry, estimating physiologically significant parameters related to conservative and dissipative properties. Volume disturbance is the overlap of two 2-s epochs (0–2 s and 1–3 s) with a 1-s overlap, improving input estimation respiratory impedance. In this work, the CPM parameters of the small animal ventilator were compared to assess the similarity with the CPM parameters of the calculated signal stretches and whether the parameters of one of these stretches can be used in place of those generated by the ventilator. Respiratory mechanics was evaluated in eleven senescence-accelerated mice (SAMR1) under the administration of methacholine (MCh) by continuous infusion. The impedance of respiratory entry was calculated from three volume disturbances (0–2 s, 1–3 s and 0–3 s). The aim of this work was to evaluate if there are statistical differences between the parameters of the CPM of the sections of 0–2 and 1–3 s compared with that of 0–3 s. The results suggest a similarity between the parameters for increasing doses of MCH and the dissipative parameters for all three signals, while the conservative parameters tends to remain constant until the last but one dose. The plateau analysis showed statistical differences between the doses, while in the ways of adjusting the signals to the CPM they did not present statistical differences ($p < 0.0001$). In conclusion, we were able to verify that a 2-s period that forms the three-second broadband signal is capable of providing CPM parameters without losing a significant amount of physiological information from the animal.