Tissue oxygen tension and blood-flow changes in rat incisor pulp with graded systemic hyperoxia

The role of oxygen in the regulation of the pulpal microcirculation is unknown. This investigation is aimed to measure tissue oxygen tension and blood-flow changes in the pulp of rat lower incisors during graded systemic hyperoxia, and to determine the response of the pulpal vasculature to various oxygen tensions. Twenty-four Sprague-Dawley rats were anaesthetized and artificially ventilated with the appropriate gas mixture. Recessed oxygen-sensitive microelectrodes were used to measure pulpal tissue oxygen tension via a small access cavity filled with saline on the labial surface of the incisor. A laser Doppler flowmeter was used to record pulpal blood-flow. Inspired oxygen was increased stepwise from 20 to 100% in 20% steps. Systemic blood-gas concentrations were measured at each step. Systemic arterial oxygen tension at 100% oxygen ventilation reached 481.2 +/- 30.7% of the baseline at 20% oxygen breathing (n=21). Pulpal tissue oxygen tension did not change significantly whereas pulpal blood-flow fell dose-dependently to 74.6 +/- 5.0% at 100% oxygen ventilation (n=21). Systemic hyperoxia, therefore, induces a significant reduction in pulpal blood-flow whereas pulpal tissue oxygen tension remains relatively stable, indicating an oxygen-dependent local regulatory mechanism.