SUMMARY Measurement of intracranial arterial blood flow velocity is a new technique with potentially a number of very useful applications. This study validates the technique by comparing it to cerebral blood flow (CBF) measured using intravenous Xenon and extracranial clearance recording. We have measured the middle cerebral artery (MCA) blood flow velocity in 17 symptomatic patients with the EME TC 264 transcranlal Doppler velocimeter and compared these measurements to the ipsilateral hemispheric cerebral blood flow measured with an intravenous Xenon 133 technique (Novo Cerebrograph 10A). Measurements were made at rest and during hypercapnia.The absolute measurement of MCA velocity and hemispheric CBF showed a poor correlation (r = 0.424, p < 0.01) due to wide between-patient variations at rest but the blood flow response to hypercapnia, expressed as a reactivity index, showed a good correlation (r = 0.849, p < 0.001).Thus changes hi MCA velocity reliably correlate with changes hi cerebral blood flow but the absolute velocity cannot be used as an indicator of CBF.Stroke which has a number of potentially useful applications. It has been advocated as a method of peroperative monitoring during carotid endarterectomy when it can provide continuous on-line information about middle cerebral artery velocity, 2 ' 3 information of particular importance when the common carotid artery is clamped in deciding which patients need shunting.4 It may also be used to predict preoperatively whether or not the use of an indwelling shunt is necessary.3 Another use for the technique has been in the assessment of cerebrovascular spasm following subarachnoid hemorrhage 6 ' 7 and furthermore measurement of blood flow velocity in the middle cerebral artery, anterior cerebral artery and posterior cerebral artery combined with common carotid compression can provide information on the integrity of the Circle of Willis. 8 In an attempt to show that Doppler measured middle cerebral artery velocity corresponds to cerebral blood flow, a number of workers have performed hypercapnia stress tests and measured the resulting increase in middle cerebral artery velocity. "11 However, this only provides indirect proof of the validity of these measurements. Therefore, we have measured the response to hypercapnia of both the middle cerebral artery velocity and the cerebral blood flow measured with an intravenous Xenon 133 technique. A good correlation between the two methods would provide direct evidence that middle cerebral artery velocity changes actually reflect changes in cerebral blood flow. Methods PatientsIn order to get a wide spread of response to hypercapnia, we have studied 17 symptomatic patients with Received December 18, 1985; accepted January 23, 1986. cerebrovascular disease aged between 41 and 70 years (mean 61); providing 34 middle cerebral arteries for study. In 11 instances, the ipsilateral internal carotid artery was totally occluded and in the remaining 23 was patent. Measurement of MCA VelocityThe probe of the EME TC 264 2...

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Venous insufficiency is a widespread condition, the prevalence of venous ulceration being 0.5-1.0 per cent in Western populations. A principal abnormality causing venous insufficiency is deep venous reflux, usually resulting from post-thrombotic valve destruction. Patients undergoing treatment for venous insufficiency should have all venous abnormalities investigated, defined and corrected where possible. Although treatment for superficial and communicating vein incompetence is available, correction of deep vein reflux has been neglected until recently. Deep vein valve physiology, the selection of patients for deep vein valve surgery and methods of valve repair and replacement are reviewed.

A technique of in situ deep venous valve construction based on vein wall intussusception is described. The technique has been used to construct a size-matched, autogenous valve in the femoral vein of the dog. Forty-one valves have been constructed. Immediately after construction, all 41 were patent at ascending phlebography and Harvey's test showed them to be competent. Descending phlebography demonstrated competence in 38 valves. Hydrostatic testing was performed on 27 valves in the vertical position at pressure gradients in the range 0.2-250 cmH2O. Of these, 24 valves were fully competent. Six valves were studied at intervals between 1 and 112 days after construction. All six were competent by Harvey's test and five were competent at descending phlebography. There was no evidence of thrombosis in any valve. This technique may be suitable for replacement of deep venous valves in patients with the calf pump failure syndrome caused by deep venous reflux.

The association between cigarette smoking and the development of atherosclerosis is well established, but the mechanism that makes cigarettes such a potent "risk factor" is not understood. There is normally a constant insudation of plasma macromolecules into the arterial wall. Fibrinogen and lipids are two of the large molecules involved in atherosclerosis. Therefore we studied the effect of cigarette smoke, nicotine, and carbon monoxide on the permeability of the canine arterial wall to 125I-labeled fibrinogen. The results show that inhaled cigarette smoke significantly and rapidly increases the permeability of the arterial wall to fibrinogen and that this effect can be produced with carbon monoxide alone but not with intravenous nicotine.