Comparison of pulsed versus continuous oxygen delivery using realistic adult nasal airway replicas

Abstract

BackgroundPortable oxygen concentrators (POCs) typically include pulse flow (PF) modes to conserve oxygen. The primary aims of this study were to develop a predictive in vitro model for inhaled oxygen delivery using a set of realistic airway replicas, and to compare PF for a commercial POC with steady flow (SF) from a compressed oxygen cylinder.MethodsExperiments were carried out using a stationary compressed oxygen cylinder, a POC, and 15 adult nasal airway replicas based on airway geometries derived from medical images. Oxygen delivery via nasal cannula was tested at PF settings of 2.0 and 6.0, and SF rates of 2.0 and 6.0 L/min. A test lung simulated three breathing patterns representative of a chronic obstructive pulmonary disease patient at rest, during exercise, and while asleep. Volume-averaged fraction of inhaled oxygen (FiO2) was calculated by analyzing oxygen concentrations sampled at the exit of each replica and inhalation flow rates over time. POC pulse volumes were also measured using a commercial O2 conserver test system to attempt to predict FiO2 for PF.ResultsRelative volume-averaged FiO2 using PF ranged from 68% to 94% of SF values, increasing with breathing frequency and tidal volume. Three of 15 replicas failed to trigger the POC when used with the sleep breathing pattern at the 2.0 setting, and four of 15 replicas failed to trigger at the 6.0 setting. FiO2 values estimated from POC pulse characteristics followed similar trends but were lower than those derived from airway replica experiments.ConclusionFor the POC tested, PF delivered similar, though consistently lower, volume-averaged FiO2 than SF rates equivalent to nominal PF settings. Assessment of PF oxygen delivery using POC pulse characteristics alone may be insufficient; testing using airway replicas is useful in identifying possible cases of failure and may provide a better assessment of FiO2.

In Vitro–In Silico Comparison of Pulsed Oxygen Delivery From Portable Oxygen Concentrators Versus Continuous Flow Oxygen Delivery

“…In Chen et al, 10 testing was limited to a single POC evaluated at 2 integer pulse settings, one high (6) and one low (2). It was found that intersubject variability among 15 airway geometries had only a small (Ͻ5% coefficient of variation) impact on volume-averaged F IO 2 values.…”

“…It was found that intersubject variability among 15 airway geometries had only a small (Ͻ5% coefficient of variation) impact on volume-averaged F IO 2 values. 10 Therefore, it was deemed reasonable to use only a single representative replica for comparative testing in the present work. A single replica was selected on the criterion that the volume-averaged F IO 2 value obtained by using this replica (for either continuous flow oxygen or pulse flow) was closest to the average value obtained across the set of 15 replicas.…”

“…The challenge of establishing equivalence between continuous flow oxygen and nominal pulse flow device settings on different devices is well known 5,9 and provides motivation for the development of physiologically representative in vitro testing methods. Chen et al 10 recently outlined a methodology to compare pulse flow oxygen delivery from a commercially available POC with continuous flow oxygen delivery from a stationary cylinder by using a set of 15 realistic airway replicas. Use of these replicas, together with a lung simulator in in vitro experiments allowed for precise control of simulated breathing parameters in anatomically representative models of the upper airways and made it possible to account for potential intersubject variability due to variance in airway geometries as well as allowing modes of failure to be assessed when a POC failed to detect an inspiratory effort.…”

“…By measuring the real-time oxygen concentration at the airway replica outlet (representative of the trachea) during inspiration, a volume-averaged F IO 2 was obtained that represented the fraction of oxygen contained in a given inhaled tidal volume (V T ). 10 In other words, these volumeaveraged F IO 2 values represent the ratios between the total volume of inhaled oxygen (including both supplemental oxygen and oxygen in the entrained air) and the inhaled V T , and provide a common basis for comparison between pulse flow and continuous flow oxygen. 10 In building on this recent work, the present study had 2 primary objectives.…”

“…10 In other words, these volumeaveraged F IO 2 values represent the ratios between the total volume of inhaled oxygen (including both supplemental oxygen and oxygen in the entrained air) and the inhaled V T , and provide a common basis for comparison between pulse flow and continuous flow oxygen. 10 In building on this recent work, the present study had 2 primary objectives. The first was to compare the performance of several POCs against each other and against continuous flow oxygen by using volume-averaged F IO 2 at the trachea as a measure of oxygen delivery.…”