Maxillary sinus mucosal blood flow during nasal vs tracheal respiration

Objective: To determine the effect of changes from nasal to tracheal respiration on maxillary sinus mucosal blood flow in rabbits with unobstructed sinus ostia. Design: Animals underwent tracheotomy with a T tube, and then a small window of intact maxillary sinus mucosa was exposed. Mucosal blood flow was recorded during normal nasal respiration using laser- Doppler velocimetry. At hourly intervals, respiration was changed from the nasal to the tracheal route and then back again. Subjects: Ten anesthetized rabbits were used: 5 underwent single and 4 underwent multiple shifts in the respiratory route, while 1 was monitored continuously during long-term nasal breathing only. Results: A significant decrease in maxillary sinus blood flow occurred on switching from nasal to tracheal respiration and a significant increase in blood flow occurred on return to nasal respiration. Where multiple switches were made, blood flow changes diminished in magnitude, but significant decreases (nasal to tracheal) or increases (tracheal to nasal) were evident in all cases. Conclusions: It is proposed that the maxillary sinus may act in an accessory capacity to the nose for humidification of inspired air via secretions liberated from the sinus ostium. Furthermore, we suggest that nasal airflow is involved with the reflex regulation of sinus blood flow, probably via stimulation of sensory receptors in the nasal cavity. Reduced maxillary sinus mucosal blood flow may thus contribute to supra-systemic levels of antral carbon dioxide. Since elevated carbon dioxide levels have been shown to reduce maxillary sinus mucociliary activity in vitro, nasal airflow compromise may contribute to the initiation of a cascade of pathophysiological events leading to acute sinusitis.