Regional blood flow in respiratory muscles during partial ventilatory assistance in rabbits

We tested the hypothesis that even partial ventilatory assistance would reduce respiratory muscle blood flow to levels similar to those found during control mechanical ventilation (CMV). Three levels of pressure support ventilation (PSV) and 2 CMV settings were compared in 10 rabbits. PSV 0, 6, and 12 cm H2O, under continuous positive airway pressure mode, were applied, and then pressure control ventilation (PCV) values of 6 (36 breaths/min) and 12 cm H2O (18 per breaths/min) were applied to each CMV setting with a muscle relaxant. Using colored microspheres, we measured regional tissue blood flow in respiratory muscles, lower extremities, kidney, and liver. Regional tissue blood flow in the diaphragm during PSV6, PCV6, and PCV12 were less than those during PSV0. During PSV12, blood flow in the crural diaphragm was more than that during PCV12 and similar to that during PSV0. Whereas the transdiaphragmatic pressure of PSV6 was -0.8 +/- 1.6 cm H2O, that of PSV12 was -3.1 +/- 2.4 cm H2O. Inspiratory asynchrony, arising from an ineffective triggering effort, was observed in PSV12. The ventilatory settings did not affect blood flow of the lower extremities, liver, and kidney. In conclusion, ventilatory settings affected blood flow in the diaphragm. At certain PSV settings, blood flow in the diaphragm was minimal.