Abstract
Humidification of inspired gas is important for patients receiving respiratory support. High-flow nasal cannula (HFNC) effectively provides temperature and humidity-controlled gas to the airway. We hypothesized that various levels of gas humidification would have differential effects on airway epithelial monolayers. Calu-3 monolayers were placed in environmental chambers at 37°C with relative humidity (RH) < 20% (dry), 69% (noninterventional comparator), and >90% (HFNC) for 4 and 8 hours with 10 L/min of room air. At 4 and 8 hours, cell viability and transepithelial resistance measurements were performed, apical surface fluid was collected and assayed for indices of cell inflammation and function, and cells were harvested for histology (n = 6/condition). Transepithelial resistance and cell viability decreased over time (P < 0.001) between HFNC and dry groups (P < 0.001). Total protein secretion increased at 8 hours in the dry group (P < 0.001). Secretion of interleukin (IL)-6 and IL-8 in the dry group was greater than the other groups at 8 hours (P < 0.001). Histological analysis showed increasing injury over time for the dry group. These data demonstrate that exposure to low humidity results in reduced epithelial cell function and increased inflammation.
Highlights
Humidification of inspired gas is important for patients receiving respiratory support with nasal cannulae or mechanical ventilation
Calu-3 monolayers exposed to the gases with relative humidity (RH) of less than 20% and more than 90% (HFNC group) showed decreased transepithelial resistance (TER) (P < 0.001) over time
Two-way analyses of variance (ANOVA) demonstrated an interaction for humidification and time of exposure (P < 0.001) whereby the TER did not change over time in the noninterventional comparator group but decreased in both the High-flow nasal cannula (HFNC) and dry groups
Summary
Humidification of inspired gas is important for patients receiving respiratory support with nasal cannulae or mechanical ventilation. The inspired gas is heated and humidified by the nasal mucosa [1]. Previous studies demonstrated that just five minutes of respiration using ambient gas with no heating or humidification in ventilated infants resulted in a significant decrease in both pulmonary compliance and Pulmonary Medicine conductance [8]; cool, dry air induces a bronchoconstriction response, which is associated with muscarinic receptors in the nasal mucosa [9]. A clinical study that compared the effect of heat and moisture exchangers and heated humidifiers showed that heat and moisture exchangers generated inadequate airway humidification resulting in high incidence of endotracheal tube occlusion [10]
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