Studies of experimental cervical spinal cord transection. Part IV. Effects of cervical spinal cord transection on myocardial blood flow in anesthetized dogs

Effects of cervical cord transection on total and regional myocardial blood flow and coronary vascular resistance were studied in anesthetized dogs using 15-μm microspheres. Left atrial catheters were inserted by thoracotomy in 10 dogs and iodine-125-labeled microspheres were injected to measure baseline tissue blood flows by means of the reference flow technique. Four dogs then underwent laminectomy of the C-6 vertebra (control group), and six underwent laminectomy and cord transection (experimental group). Microspheres labeled with cerium-141, strontium-85, and scandium-46 were injected at 15, 30, and 120 minutes, respectively, after surgical intervention. The dogs were sacrificed, and the radioisotope content of specimens of epicardial, mid-myocardial, and endocardial tissues was determined by differential spectrometry, and tissue blood flow was calculated in relation to arterial reference specimens. No significant differences in baseline endocardial, epicardial, or mid-myocardial blood flow were detected between the control and experimental groups. Tissue blood flows fell significantly in all regions (p < 0.05 or less) at 15, 30, and 120 minutes after transection. No major alteration of the endocardial/epicardial flow ratio occurred, and no electrocardiographic or pathological evidence of ischemia was seen. When corrected for variations in systemic arterial pressure, no differences in coronary vascular resistance between control and cord-transected dogs were observed. These findings suggest that the decreased coronary blood flow following cervical cord transection is secondary to decreased mean arterial pressure rather than to altered coronary vascular resistance. Pharmacological augmentation of perfusion pressure may therefore be necessary to maintain adequate coronary blood flow in patients with acute cord injury who have pre-existent cardiac disease.