R. W. Ross Russell

EFFECT OF HÆMATOCRIT ON CEREBRAL BLOOD-FLOW IN MAN

Abstract Cerebral blood-flow (C.B.F.) was measured in 38 patients with haematocrit values (Hct) in the range 0·47-0·53 and was found to be significantly lower than in 43 patients with Hct in a lower range (0·36-0·46). After reduction of Hct in the higher Hct group by venesection, flow increased by a mean of 50%. This improvement in flow was largely due to a reduction in viscosity. Hct around the generally accepted upper limit of normal may be an important factor in the causation of occlusive vascular disease.

Cerebral haemodynamic changes after extracranial-intracranial bypass surgery.

Regional cerebral blood flow, oxygen utilisation, fractional oxygen extraction, and cerebral blood volume were measured by positron emission tomography in twelve patients with carotid artery occlusion. Follow-up studies were carried out at a mean interval of eleven weeks after extracranial-intracranial bypass surgery. Clinical improvement was observed in three patients who had presented with frequent transient ischaemic attacks. One patient with multiple vascular occlusions suffered a stroke at the time of surgery. Follow-up studies showed an increase of regional cerebral blood flow in only two of the twelve patients. In the group as a whole, there was no significant change of cerebral blood flow, oxygen consumption or fractional oxygen extraction after bypass surgery. The most consistent post-operative change, observed in eleven of the twelve patients, was a fall of cerebral blood volume in the cortical territory of the bypassed carotid artery (p less than 0.01). This effect was most marked in patients with bilateral carotid occlusion, in whom there was often an accompanying fall of blood volume in the contralateral hemisphere. The post-operative findings were consistent with an increase of regional cerebral perfusion pressure as a result of the bypass procedure. Although this effect is potentially of value, those patients with most to gain from bypass surgery may also run the highest risk of peri-operative cerebral ischaemia.

CEREBRAL BLOOD-FLOW AND VISCOSITY IN RELATIVE POLYCYTHÆMIA

Abstract Cerebral blood flow (CBF), red-cell mass, and plasma volume were measured in 39 patients with venous haematocrit values in the range 0·47-0·58. Patients with true polycythaemia were thus excluded. The 39 patients studied fell into two groups—those with a measured red-cell mass in the high-normal range and those with normal red-cell-mass values but reduced plasma-volume values (the relative-polycythaemia, low-plasma-volume group). The mean CBF was low in both the high-normal red-cell-mass (HNRCM) group (45·8 ml/100 g/min) and low-plasma-volume (LPV) group (48·8 ml/100 g/min). The haematocrit in the HNRCM group was 0·504 and in the LPV group 0·513. In a control group of subjects with a mean haematocrit of 0·421 CBF was 68·6 ml/100 g/min. Venesection was associated with a significant rise in CBF in both groups of patients—to 59·7 ml/100 g/min in the HNRCM group and 65·0 ml/100 g/min in the LPV group. Whole-blood viscosity fell significantly in both groups. Both groups demonstrated significant inverse relationships between CBF and haematocrit and between CBF and blood viscosity.

EFFECT OF ASPIRIN IN AMAUROSIS FUGAX

Abstract Two patients with amaurosis fugax were treated with 600 mg. of aspirin daily. In both patients the frequency of attacks decreased, and this response appeared to be due to the drug.

THE SOURCE OF RETINAL EMBOLI

Abstract Three types of retinal emboli are described. The first are white emboli producing segmental arterial blockage with permanent damage to inner retinal layers. These seem to have an origin in the heart in most instances and commonly occur in association with aortic stenosis. The second type consists of white plugs migrating through the retinal circulation in the space of a few minutes. These are probably platelet-fibrin masses derived from mural thrombus in the carotid. They cause transient visual symptoms and even after many attacks no permanent damage to the retina results. The third type of retinal embolism consists of small, multiple, refractile plaques partially obstructing branch retinal arterioles. These seem to be derived from ulcerating atheromatous lesions, and about half of these patients have carotid stenosis on angiography.

Reactivity of the cerebral circulation in patients with carotid occlusion.

Cerebral blood flow (CBF) and the response to hypercapnia (cerebral reactivity) have been measured in 41 patients with unilateral or bilateral internal carotid artery occlusion in an attempt to identify those with limited collateral reserve. Normocapnic CBF was within normal limits in the majority of subjects. The response to hypercapnia varied from normal to absent, with impaired reactivity becoming increasingly likely when more than one artery was diseased. In 19 patients with unilateral carotid occlusion, hemisphere reactivity was well preserved in the majority, but was significantly lower on the side of the occlusion (mean 2.9%/mm Hg) compared to the normal side (mean 3.4%/mm Hg). Reactivity on the side of the occlusion was further reduced in 15 patients with occlusion and contralateral internal carotid artery stenosis (mean 1.7%/mm Hg) and was even lower in seven patients with bilateral occlusion (mean 1.1%/mm Hg). There was no difference in reactivity between asymptomatic hemispheres in the 41 patients (mean 2.7%/mm Hg) and hemispheres in which a previous stroke had occurred (mean 2.8%/mm Hg). In contrast the response in hemispheres subject to continuing transient ischaemic attacks was significantly impaired (mean 1.6%/mm Hg), suggesting that the cerebral symptoms in some of these patients may have had a haemodynamic origin more often than suspected from the clinical history.

Cerebral and Retinal Vascular Changes in Systemic Lupus Erythematosus

A 16-year-old white boy with acute systemic lupus erythematosus (SLE) who presented with chorea and florid retinopathy died in renal failure three months after diagnosis. Pathological studies revealed two types of lesion in both the cerebral and ocular vessels. Some meningeal and choroidal vessels showed a typical vasculitis with fibrinoid necrosis, whereas other meningeal and retinal vessels were occluded by amorphous hyaline material in the absence of vasculitis.

Cardiovascular disease in patients with retinal arterial occlusion.

103 patients with retinal-artery occlusion causing permanent visual-field defect were examined clinically and angiographically to assess the extent of cardiovascular disease. The 68 patients with branch-artery occlusion had a higher prevalence of previous transient episodes, ischaemic and valvular heart-disease, and more often had an operable lesion in the carotid artery than had the 35 patients with central-artery occlusion who were more often hypertensive, had fewer warning attacks, a greater prevalence of complete carotid occlusion, and fewer operable carotid lesions. The two types of retinal vascular occlusion show aetiological differences; branch occlusion is more often embolic and should be fully investigated for carotid and cardiac disease. These measures are less often of practical importance in patients with central-artery occlusion.

Correlation of CAT scan and visual field defects in vascular lesions of the posterior visual pathways.

Thirty-nine patients with various types of isolated homonymous hemianopias resulting from ischaemic lesions in the posterior parts of the cerebral hemisphere was examined by CAT scanning. Most had localised low density lesions withing the distribution of the posterior cerebral artery. The location of the lesion (deduced from a separate anatomical study of postmortem brain cut in the plane of the CAT scanner) was correlated with visual field defects. Lesions giving rise to quadrantic defects were smaller than those causing total hemianopias; lower quadrantic defects tended to occur in superior cuts and vice versa. Macular sparing was associated with survival of the occipital pole in some instances. Bilateral cases had a higher prevalence of associated defects.

EFFECT OF HIGH HÆMATOCRIT ON ALERTNESS

Patients with high-normal or above-normal haematocrit were found to have impaired alertness when compared with a control group matched for age and occupation. On retesting the controls had improved alertness scores attributable to a practice effect; but the patients, when retested after reduction of haematocrit by venesection, had improved significantly more than the controls. Improvement in alertness correlated very well with the increase in cerebral blood flow which followed venesection. Levels of venous haematocrit that are generally accepted as normal may not necessarily be optimum.