The Effect of Mouth Opening on Two Types of Non-Invasive Respiratory Therapy

A series of models was run to investigate the effect that the extent to which a patient’s mouth is open has on two types of non-invasive respiratory therapy, with CO₂ remaining at end-exhale being the metric for comparison. Provisions were made to precisely vary the area through which flow could exit the mouth of a realistic airway geometry. Mouth openings of 0, 2, 5, 10, 20, 30, 40, and 100 percent were tested with a coarse mesh, and mouth openings of 5, 10, 20, 30, and 100 were tested with a fine mesh. The two types of therapy tested were High Flow Nasal Cannula (HFNC) oxygen therapy and High Velocity Nasal Insufflation (HVNI), with both therapies set to deliver flow rates of 35 lpm. Results are conveyed in HFNC CO₂ remaining - HVNI CO₂ remaining. For the fine models, a maximum discrepancy between therapy types was found at a mouth opening of 20 percent, at which point there was a difference of 3.65 mg. For coarse models, the mouth opening of maximum discrepancy was 10 percent, at which point there was a difference of 2.81 mg. The difference between therapy types was found to be strongly affected by the mouth opening percent of the patient, with the higher velocity flow of HVNI being less affected by the decreasing size of the mouth opening down to a 20% opening, after which both therapy types were severely affected by the mouth closing.