Measuring lung mechanics of expiratory tidal breathing with non-invasive breath occlusion

Abstract

Background and objective: Lung mechanics measurements provide clinically useful information about disease progression and lung health. Currently, there are no commonly practiced methods to non-invasively measure both resistive and elastic lung mechanics during tidal breathing, preventing the important information provided by lung mechanics from being utilised. This study presents a novel method to easily assess lung mechanics of spontaneously breathing subjects using a dynamic elastance, single-compartment lung model. Methods: A spirometer with a built-in shutter was used to occlude expiration during tidal breathing, creating exponentially decaying flow when the shutter reopened. The lung mechanics measured were respiratory system elastance and resistance, separated from the exponentially decaying flow, and interrupter resistance calculated at shutter closure. Progressively increasing resistance was added to the spirometer mouthpiece to simulate upper airway obstruction. The lung mechanics of 17 healthy subjects were successfully measured through spirometry. Results: N = 17 (8 female, 9 male) healthy subjects were recruited. Measured decay rates ranged from 5 to 42/s, subjects with large variation of decay rates showed higher muscular breathing effort. Lung elastance measurements ranged from 3.9 to 21.2 cmH 2 O/L, with no clear trend between change in elastance and added resistance. Resistance calculated from decay rate and elastance ranged from 0.15 to 1.95 cmH 2 Os/L. These very small resistance values are due to the airflow measured originating from lowresistance areas in the centre of airways. Occlusion resistance measurements were as expected for healthy subjects, and increased as expected as resistance was added. Conclusions: This test was able to identify reasonable dynamic lung elastance and occlusion resistance values, providing new insight into expiratory breathing effort. Clinically, this lung function test could impact current practice. It does not require high levels of cooperation from the subject, allowing a wider cohort of patients to be assessed more easily. Additionally, this test can be simply implemented in a small standalone device, or with standard lung function testing equipment.

Respiratory pressure and split flow data collection device with rapid occlusion attachment

“…Rapid expiratory occlusion (REO), also termed ‘the interrupter technique’, is a method to identify passive mechanics (elastance and resistance) from shutter instances, or shuttering, in expiration, which theoretically allows the simultaneous identification of respiratory mechanics without identifiability trade-off [13] , [14] . Prior REO methods have proven these mechanics are identifiable using such occlusion data [1] , [13] , [14] . However, implementation of REO without excessive expiratory resistance during standard 100 ms duration shutter instances has proven difficult, and they often result in additional patient effort in reaction to this 100 ms expiratory flow limitation, which in turn impacts model identifiability and relevance as these active expiratory terms are not included in the model [1] , [13] , [14] .…”

“…Prior REO methods have proven these mechanics are identifiable using such occlusion data [1] , [13] , [14] . However, implementation of REO without excessive expiratory resistance during standard 100 ms duration shutter instances has proven difficult, and they often result in additional patient effort in reaction to this 100 ms expiratory flow limitation, which in turn impacts model identifiability and relevance as these active expiratory terms are not included in the model [1] , [13] , [14] .…”

“…This work presents a shuttering device for REO to be used in conjunction with a venturi-based flow meter, which has been adapted from previous designs for similar applications [15] , [16] . The REO attachment is developed using a camera shutter to generate measurably shorter shutter instance durations than the prior 100 ms standard [1] , [13] , [14] . The hypothesis is the profile of a longer occlusion could be predicted or estimated from a shorter occlusions profile uncorrupted by patient effort due to its short duration.…”

“…The hypothesis is the profile of a longer occlusion could be predicted or estimated from a shorter occlusions profile uncorrupted by patient effort due to its short duration. Thus, such a rapid occlusion aims to reduce subject-specific muscular reactions to shuttering [1] to improve the identification of passive, model-based respiratory mechanics in resting breathing.…”

Respiratory monitoring dataset, with rapid expiratory occlusions, over increasing positive airway pressure ventilation

“…Passive mechanics can be difficult to elucidate from passive breathing modes [4] , [5] , [6] . A rapid expiratory occlusion (REO) device was used, based on the ‘interrupter technique’ principle which fits passive mechanics to 100ms occlusions [ 1 , [7] , [8] , [9] ]. The shorter REO instances were implemented to identify passive mechanics without the patient-effort dynamics in response to a perceptible occlusion [3] .…”