L. Symon

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.

PRESSURE WAVES IN SO-CALLED LOW-PRESSURE HYDROCEPHALUS

Abstract Episodes of raised intracranial pressure were discovered in patients who were thought to have low-pressure hydrocephalus. Possibly these episodes identify patients in whom continuing deterioration may be expected, and the long-term measurement of intracranial pressure in such patients may be valuable in deciding which of them should have a ventriculo-atrial shunt operation.

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 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.

REGIONAL CEREBRAL BLOOD-FLOW IN TRANSIENT ISCHÆMIC ATTACKS

Abstract Regional cerebral blood-flow (R.C.B.F.) was measured by the intra-carotid xenon-133 technique in a series of 11 patients who had recently experienced a transient ischaemic cerebrovascular attack. 7 patients showed persistent disturbance of R.C.B.F.—in 1 case as long as ninety days after the last attack.

Viscosity, cerebral blood flow and haematocrit in patients with paraproteinaemia

It has been suggested that blood viscosity is involved in the control of cerebral blood flow (CBF) (Thomas et al. 1977a, b, Humphrey et al. 1979). CBF, using the intravenous Xenon133 technique, blood viscosity and haematocrit were measured in 21 patients with elevated viscosity due to paraproteinaemia and found to be the same as in normal subjects. However, the paraproteinaemic patients were anaemic with a mean haematocrit of 0.342. This degree of anaemia would normally be associated with a high CBF.

Cerebral blood flow, haematocrit and viscosity in subjects with a high oxygen affinity haemoglobin variant

The cerebral blood flow is low in primary polycythaemia, and it has been suggested that this is due to the increase in viscosity which accompanies the elevated haematocrit. In the present study cerebral blood flow has been measured by a non‐invasive 133Xenon technique in six subjects with an elevated haematocrit secondary to a haemoglobin variant with increased oxygen affinity. Flow was significantly higher than normal and 81 % higher than in 11 subjects of comparable age, matched for haematocrit and viscosity, but without the haemoglobin variant. In patients with this unusual type of polycythaemia, cerebral blood flow is high despite the elevated blood viscosity and the implications of these results are discussed.

Regional cerebral blood flow in completed strokes and transient ischemic attacks: A clinical correlation

m The first question the clinician confronted with a diagnostic problem asks himself is “Where is the lesion?’ If a method of investigation that purports to detect focal disturbances is used, the clinician will similarly ask, “Does it localize the disturbance accurately?’ Focal abnormalities seen on cerebral angiography have been found to correspond to the anatomic site of the lesion as determined by the neurologic signs and symptoms accompanying completed strokes.’.’ Measurements of regional cerebral blood flow (rCBF) by ‘”Xenon clearance after intracarotid injectiong have shown focal changes; both focal decrease and focal increase of flow have been recorded in completed stroke^.^-^ Persistent disturbance of rCBF in a proportion of patients who had experienced transient ischemic attacks (TIA) as long as 90 days before rCBF measurement has been shown.: The relationship between these disturbances of rCBF and the clinically determined site of the lesion in completed strokes (CS) and T I A is the subject of this study.

The development of cerebral collateral circulation following occlusion of vessels in the neck: An experimental study in baboons

Abstract In a series of baboons, both carotid and vertebral vessels have been ligated successively, and the development of collateral circulation was assessed by repeated measurements of ophthalmic artery pressure. Some months after ligation of all the neck vessels, pressure in the ophthalmic artery had risen to 50% of normal. Six months after four-vessel ligation had been completed, middle cerebral arterial pressure and regional venous oxygen tension (Po2) in one cerebral hemisphere were measured directly. The response of cerebral arterial pressure and cerebral venous Po2 to vascular occlusion demonstrated that a state of continuing partial vasodilatation existed in the brains of these animals. The relevance of these observations to human cerebral vascular disease is discussed.

The Effect of Changes in Cerebral Blood Flow on Compartmental Weight

Results of regional cerebral blood flow (rCBF) studies at two levels of arterial CO2 tension (PaCO2) are presented which suggest that the measurement of the proportion of gray and white matter by two-compartmental analysis of clearance curves does not strictly represent the true anatomical proportions of gray and white matter—at any rate, in patients with ischemic cerebrovascular disease.