Effect of nitroglycerine-induced hypotension on canine spinal cord blood flow

Twenty-four mongrel dogs were anaesthetized with pentobarbitone and morphine sulphate. Neuromuscular blockade was achieved using pancuronium. Spinal cord blood flow was measured using the radionuclide microsphere and hydrogen washout methods before, during, and following nitroglycerine-induced hypotension. Heart rate, mean arterial pressure, cardiac output, pulmonary capillary wedge pressure, and acid-base balance were determined with each measurement. Mean arterial pressure was reduced by 50%. Spinal cord blood flow, as measured by the microsphere method, increased during the period of hypotension, whereas values obtained using the hydrogen washout method were not significantly different from those at normotension. No significant change in spinal cord blood flow was detected by either method after the application of spinal distraction. Nitroglycerine acts predominantly on venous capacitance vessels and it is postulated that perfusion pressure, and therefore flow, is maintained despite a reduction in arterial pressure.