Effects of isoflurane on arterial blood pressure, heart rate, and phrenic nerve discharge in the decerebrate rat.

Background: The potent inhalational anesthetic isoflurane has widespread use in experimental investigations. Intratracheal administration of the agent attenuates breathing, blood pressure, heart rate, and baroreflex control of heart rate. Concurrent effects of potent inhalational anesthetics on hemodynamic waves and neural respiratory output have yet to be systematically interrogated.

Objectives: We sought to determine the effects of administering isoflurane to unanesthetized decerebrate animals upon breathing, dynamic arterial pressure magnitude, and ventricular depolarization frequency.

Methods And Results: Experiments were conducted on ten unanesthetized decerebrate Sprague-Dawley adult male rats. Saturation of a hyperoxic gas mixture with 2.0% isoflurane in supracollicularly decerebrate rats having undergone successful weaning from isoflurane anesthesia quantally reduced phrenic nerve bursting frequency and coupling with the ventilator cycle from 1:1 to 1:2 and prolonged phrenic expiratory duration, though failed to modify phrenic inspiratory burst amplitude or duration. Isoflurane also reduced dynamic arterial pressure magnitude and heart rate, increased heart rate variability, and reduced blood pressure variability.

Conclusions: Use of unanesthetized decerebrate preparations eschewing the confounding effects of anesthesia upon neural networks may prudently supplant the use of anesthetized animals when seeking to mechanistically interrogate propriobulbar interneuronal microcircuit oscillators constituting the respiratory rhythm and pattern generator, sympathetic oscillators, and cardiovagal premotoneurons.