Organ blood flow during high-frequency ventilation at low and high airway pressure in dogs

Using the radiolabeled microsphere technique, the authors studied hemodynamic variables and regional blood flow to multiple peripheral organs during conventional positive-pressure ventilation (CV) and high-frequency ventilation (HFV) at low and high mean airway pressure (P(aw)). Twenty supine anesthetized, paralyzed dogs were ventilated using CV (14-16 breaths/min) and HFV (rate = 10 Hz) in random order. In the first group (low P(aw), n = 10), P(aw) was maintained at 3 cmH₂O during CV and HFV. In the second group (high P(aw), n = 10), P(aw) was increased to 13 cmH₂O during CV and HFV. Pulmonary capillary wedge pressure and right atrial pressure remained constant during low and high P(aw) trials. No differences in heart rate, systemic arterial pressure, intracranial pressure, or cardiac output were noted during CV and HFV within the low and high P(aw) groups. In addition, blood flow to multiple peripheral organs during CV and HFV remained constant within each P(aw) group, except for a small decrease in cerebellar blood flow during HFV at high P(aw). Comparison of hemodynamic measurements during high and low P(aw) trials showed a significant decrease in hepatic arterial and outer kidney cortical flow at high P(aw). Total cerebral blood flow was decreased at high P(aw), as were regional flows to diencephalon, midbrain, pons, medulla, and cerebellum. However, these differences were not attributable to differences in cerebral perfusion pressure or intracranial pressure, and cerebral oxygen delivery was not different between high P(aw) and low P(aw) groups. It is concluded that under conditions of similar P(aw) in anesthetized dogs, HFV does not significantly alter hemodynamic patterns or regional circulation relative to CV.