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

BACKGROUND: Portable oxygen concentrators (POCs) deliver oxygen in intermittent pulses. The challenge of establishing equivalence between continuous flow oxygen and nominal pulse flow settings on different POCs is well known. In vitro bench measurements and in silico mathematical modeling were used to compare the performance of 4 POCs versus continuous flow oxygen by predicting the F-IO2 at the trachea and entering the acini. METHODS: Each of the 4 POCs was connected to a 3-dimensional printed replica of a human adult nasal airway via nasal cannula. A test lung simulated 3 breathing patterns representative of a patient with COPD at rest, during exercise, and while asleep. POCs were tested for each breathing pattern at all integer pulse flow settings. Volume-averaged F-IO2 was calculated by analyzing oxygen concentrations and inhalation flow over time. In vitro oxygen waveforms were then combined with a single-path mathematical model of the lungs to assess oxygen transport through the conducting airways. In vitro experiments and mathematical modeling were repeated for continuous flow oxygen. RESULTS: Continuous flow oxygen consistently delivered more (>2% absolute) oxygen in terms of volume-averaged F-IO2 for all nominally equivalent pulse flow settings of >2. Differences were also observed when comparing performances between different POCs, particularly at high device settings (5 and 6). Simulations showed that efficiency of delivery to the acinar region of the lungs was higher in pulse flow than in continuous flow oxygen but that continuous flow oxygen generally delivered a higher absolute volume of oxygen. Differences in absolute oxygen delivery per breath between continuous flow oxygen and pulse flow were smaller for acinar delivery than for tracheal delivery. CONCLUSIONS: Significant differences in POC performance based on volume-averaged F-IO(2) were found between pulse flow and continuous flow oxygen, and among pulse flow modes in different POCs. Although pulse flow was a more efficient mode of delivery than continuous flow oxygen, continuous flow oxygen delivered a greater absolute volume of oxygen per breath.