Relationship of transcranial Doppler flow velocities and arteriovenous malformation feeding artery pressures.

BACKGROUND AND PURPOSE

Feeding mean arterial pressure immediately proximal to the nidus of arteriovenous malformations may influence the frequency of spontaneous intracerebral hemorrhage. This study assessed the usefulness of transcranial Doppler ultrasound velocities as a noninvasive estimate of feeding mean arterial pressure.

METHODS

We studied 41 patients undergoing 73 staged treatments of arteriovenous malformations with endovascular embolization, surgery, or both. Before treatment during the awake state, transcranial Doppler mean and peak velocities were recorded in proximal Willisian vessels. During superselective angiography with the patient under conscious sedation or during surgery with the patient under general anesthesia, feeding mean arterial pressure was measured through a 1.5F transfemoral intracranial microcatheter or a 26-g needle by direct puncture. Measurement of insonated artery diameter was possible in 41 embolizations, and a flow velocity index (mL/min) and Reynolds' number were estimated.

RESULTS

Mean +/- SEM feeding mean arterial pressure was 38 +/- 2 mm Hg at a systemic mean arterial pressure of 77 +/- 2 mm Hg; mean velocity was 102 +/- 4 cm/s. There was an inverse correlation between feeding mean arterial pressure and parent artery mean velocity (y = -0.74x + 130, r = .35, P = .0025). The best correlation was for the first treatment in each patient (n = 27) using the highest peak velocity obtainable in a Willisian vessel ipsilateral to the arteriovenous malformation (y = -1.61x + 221, r = .62, P = .0005). Flow velocity index (775 +/- 106 mL/min) did not correlate with feeding mean arterial pressure, but there was a weak correlation with Reynolds' number (y = -12x + 1616, r = .27, P = .1283). Mean Reynolds' number was 1257 +/- 119.

CONCLUSIONS

Transcranial Doppler mean velocity is correlated with feeding mean arterial pressure but only weakly predictive. Considerations influencing the relation of distal feeding mean arterial pressure to proximal mean velocity might include the influence of other fistulae in the circuit between major inflow and outflow channels as well as turbulent flow at vascular branch points between point of insonation and the nidus, as suggested by Reynolds' number values of more than 400.