Studies of experimental cervical spinal cord transection. Part I: Hemodynamic changes after acute cervical spinal cord transection.

Two distinct and sequential patterns of hemodynamic alteration were observed after acute cervical spinal cord transection in anesthetized dogs. Interruption of the cord initially caused a 45% increase in mean arterial pressure (p less than 0.01), a 34% increase in systemic vascular resistance (p less than 0.05), and a 92% increase in left ventricular dp/dt (p less than 0.01), reflecting a generalized sympathetic response to trauma. Concomitant bradycardia and escape arrhythmias suggested relative parasympathetic hyperactivity. Resolution of the brief pressor response was followed by a second, more prolonged, period characterized by a fall in arterial pressure to 71% of control levels (p less than 0.05), a 16% decrease in systemic vascular resistance, and a 58.5% decrease in left ventricular dp/dt (p less than 0.01). These latter hemodynamic changes are consistent with sympathetic denervation and failure of regulatory mechanisms mediated by both alpha- and beta-adrenergic peripheral vascular and myocardial receptors.