Electromagnetic blood flowmetry in small vessel surgery. An experimental study

A tribute to Helge Nornes

This supplement of the Acta Neurochirurgica is dedicated to professor Helge Nornes on the occasion of his retirement. Helge Nornes started his neurosurgical training in Oslo in 1965. In 1980 he was offered the neurosurgical chair of Bern, Switzerland, where he stayed until 1983 when his old university called him back to the chair at the National Hospital in Oslo, a position he filled until he retired last year. The present paper briefly reviews examples of his contributions to neurosurgery and to the understanding of intracranial pathophysiology, including the transcranial doppler, the miniature transducer for intracranial pressure monitoring, his observations on intracranial pressure and internal carotid blood flow during subarachnoid haemorrhage, intracranial arterial blood flow in patients undergoing aneurysm surgery, his studies of the pathophysiology of arteriovenous malformations, the introduction of intraoperative Doppler recordings during surgery for aneurysms and arteriovenous malformations, and his methods for evaluating collateral circulation prior to internal carotid artery occlusion.

Flow field mapping in the anesthetized rat

This study measured the hemodynamics of peripheral arterial sites in the rat, using 20 MHz pulsed ultrasonic Doppler velocimeter (PUDVM) methods. The lower extremities of 14 male Sprague-Dawley rats were studied. The targeted sites included the abdominal aorta, external iliac, proximal femoral, mid-femoral, and saphenous arteries. The hemodynamic variables of pulse period, maximum centerline velocity, lumen diameter, and mean volumetric flow were calculated interactively from temporal-spatial plots of local velocity distributions. An analysis of variance revealed significant differences between right and left sides for lumen diameter (P = 0.028) and mean volumetric flow (P less than 0.0001). The analysis showed no statistical difference for pulse period (P = 0.0836) among sites. However, three distinct groupings of sites: 1) abdominal aorta, 2) external iliac, proximal femoral, and mid-femoral arteries, and 3) saphenous artery were noted for the remaining hemodynamic variables (P less than 0.05). These results indicate that three hemodynamically distinct regions are available for microvascular research in the rat lower extremity arterial tree.

Intraoperative measurement of cortical blood flow adjacent to cerebral AVM using laser Doppler velocimetry

Standard methods for measurement of cerebral blood flow (CBF) are not optimal for continuous intraoperative recording. Laser Doppler velocimetry has been used for evaluation of microcirculatory flow in a variety of human tissues, including skin, muscle, and retina. The authors report the use of this technique for measuring flow in human cerebral cortex. The physiological changes associated with excision of a cerebral arteriovenous malformation are interpreted using CBF recorded intraoperatively with the laser Doppler probe.

Peripheral hemodynamic stability during prolonged anesthesia in the rat

The present study tests the hypothesis that peripheral hemodynamics in the rat femoral artery remain relatively stable during 3 hours of general anesthesia. Hemodynamic variables (pulse period, maximal centerline velocity, lumen diameter, and mean volumetric flow) were measured by the 20 MHz-pulsed ultrasonic Doppler velocimeter method at 30-minute intervals. The hemodynamic variables were not statistically different during the duration of the study. The mean values were pulse period 160 +/- 2 msec, maximal centerline velocity 37.0 +/- 1.9 cm/sec, lumen diameter 0.94 +/- 0.03 mm, and mean volumetric flow 1.92 +/- 0.19 cc/min.

Hemodynamic aspects of cerebral arteriovenous malformations

Local hemodynamics were studied in 16 patients undergoing total extirpation of cerebral arteriovenous malformation (AVM). Directional Doppler technique was used for the registration of blood velocities in vessels feeding and draining the AVM. Calculated flow in single feeding arteries ranged from 3 to 550 ml/min (average, 180 ml/min). An estimation of total AVM flow was possible in nine patients, and ranged from 150 to more than 900 ml/min (average, 490 ml/min). Pressure recordings were made from feeding arteries at their entrance to the AVM. This pressure was well below the systemic arterial blood pressure in all cases, and ranged from 40 to 77 mm Hg (average, 56 mm Hg). On temporary occlusion, this stump pressure instantly rose to from 55 to 95 mm Hg (average, 76 mm Hg). Draining vein pressure before occlusion ranged from 8 to 23 mm Hg (average, 15 mm Hg), and fell to zero in all patients when the AVM was occluded. These data and other clinical observations are discussed with regard to adjacent brain-tissue perfusion, and with special emphasis on the circulatory breakthrough that can follow the occlusion of these high-capacity shunts.

Intraoperative evaluation of cerebral hemodynamics using directional Doppler technique. Part 1: Arteriovenous malformations

The use of a pulsed echo Doppler technique during surgery for cerebral arteriovenous malformation is described. The equipment and the methods employed are presented. The main advantages are easy determination of flow direction and pattern of the vasculature involved, allowing a precise discrimination between inflow and outflow channels. Deep-seated malformations, not visible at the brain surface, can be located with the Doppler technique. The ultrasound probe was placed on the brain surface with a slight pressure on the intact pia mater. The precise direction and depth of the malformation could be determined in relation to the recording site. This facilitated the planning of cortical incisions, identification of vessels involved, and the vascular procedure to be employed.

Cerebral arterial blood flow and aneurysm surgery. Part 1: local arterial flow dynamics

Cerebral arterial blood flow was monitored in 22 patients undergoing surgery for intracranial saccular aneurysms. An electromagnetic flow probe was used to record the internal carotid artery (ICA) flow in the neck or intracranially in seven patients. The ICA flow ranged between 100 and 175 ml/min (average 144 ml/min). Intracranial flow measurements with specially designed probes were made in 17 patients. The middle cerebral artery (MCA) showed flow values between 75 and 120 ml/min (average 97 ml/min). Flow figures recorded from the proximal anterior cerebral artery (ACA) were lower (average 65 ml/min), and had a wider range from 30 to 110 ml/min. Test occlusion of the terminal ICA showed a retrograde flow in the proximal ACA to the MCA ranging from 15 to 125 ml/min (average 78 ml/min). This test was used to investigate the collateral potential of the anterior portion of the circle of Willis, which is essential to the decision of whether to undertake trap ligation procedures in this location. Flow monitoring in the parent vessel was also of use in some patients to assess flow conditions after the clipping of the aneurysm neck.