A method for measurement of arterial concentration of cerebral blood flow tracer for autoradiographic experiments

A new method for continuous monitoring of the concentration of 131I-labelled iodoantipyrine during an autoradiographic local cerebral blood flow (LCBF) experiment is described. During infusion of iodoantipyrine, radioactivity in an external femoral arteriovenous loop is monitored by a scintillation detector. Data is collected with a variable time base, and the arterial activity curve displayed visually in its entirety. The main advantage of this method is that there is no blood loss. It will therefore be of particular importance in dual-label autoradiography. This method can also be used for other gamma-emitting blood flow tracers, e.g. 123I-iodoantipyrine.

Influence of the input function on the calculation of the local cerebral metabolic rate for glucose in the deoxyglucose method

We describe here a modification of Sokoloff's deoxyglucose method which requires fewer blood samples but does not diminish accuracy. To calculate the local cerebral metabolism for glucose (LCMRglu), the input function containing the initial peak must be known. This requires many blood samples for accurate definition. To estimate the influence of the peak on the LCMRglu, a dummy input function was generated by extrapolating the data points after 2 min back to 0 min. Next, a biexponential curve, fitted to a reduced number of samples, was applied for the input function. The error introduced into the LCMRglu by using these different approximations was analyzed with an error function derived from an operational equation. The results indicate that the error of LCMRglu caused by neglecting the peak is less than 3%. Furthermore, the error of LCMRglu resulting from use of the biexponential approximation is a function of LCMRglu: the error decreases as the LCMRglu increases and remains at less than 3% even when only seven data points are used (half the usual number of the standard method). Finally, the LCMRglu was calculated by the biexponential curve-fitting, using the experimental data, and compared with that calculated by Sokoloff's computer program. Both methods were in good agreement. This modified method offers great advantage for simultaneous measurement of CMRglu, CBF, and other physiological parameters by means of the multiple tracer autoradiographic technique in the small laboratory animal.

Ventricular size and cerebral blood flow following subarachnoid hemorrhage

The relationship among ventricular size on computed tomography (CT), the clinical status of the patient, and cerebral blood flow alterations in subarachnoid hemorrhage is examined. Fifty patients with subarachnoid hemorrhage underwent a total of 71 cerebral blood flow measurements and 115 CT scans. Flow was measured noninvasively using 133Xe inhalation. It is demonstrated that increasing ventricular size is accompanied by clinical deterioration and also by a reduced flow. The effects of the various lesions (as demonstrated by CT) on cerebral perfusion are examined. Of the 23 patients scanned 5 days or less after hemorrhage, 12 had subarachnoid blood visible on the scan. These 12 had flows that averaged 20% lower than the other 11 when examined 6 to 17 days after the hemorrhage. Ventricular enlargement is more prevalent in the first week after the hemorrhage than in the second. Also, blood flow is maximally reduced at the end of the first week following hemorrhage.

Effect of therapy on cerebral blood flow following aneurysm surgery

The authors report on a patient with a ruptured anterior communicating aneurysm treated surgically on the day following her subarachnoid hemorrhage (SAH). Repeated measurements of cerebral blood flow (rCBF) were carried out using the inhalational Xenon 133 method. Dramatic acute increases in rCBF occurred, coincident with clinical improvement, following mannitol, CSF drainage and dopamine. Later, further elevation to normal levels occurred following ventriculoperitoneal shunting.

Effects of venesection on cerebral function in chronic lung disease

Regional cerebral blood flow measurements and neuropsychological testing were conducted before and after venesection on 6 patients with polycythemia secondary to chronic obstructive pulmonary disease. Venesection resulted in lowered viscosity and hematocrit, and an accompanying improvement in cerebral perfusion and mental function. Blood flow was significantly increased in the left cerebral hemisphere following phlebotomy, and there was significant improvement in sensory/mental function. Cerebral function would appear to be related to blood flow alterations influenced by the viscosity of the blood.

The relationship between cerebral blood flow and the EEG in normals

Using the Xe133 inhalation technique, measurements of the blood flow to the left and right parietal and temporal regions of the cerebrum were obtained in 5 healthy individuals while simultaneously recording their EEGs. Up to 3 measurements were obtained from each of the subjects the first while they were mentally at rest and the others while they were engaged in prescribed forms of mental activity. Relationships between the measured blood flow through grey matter, initial slope index, relative grey weight, percent grey flow and power in the delta, delta-theta, alpha, beta and gamma rhythms of the EEG were examined. The results showed that for the subject group as a whole there was a strong correlation between the power present in the low frequency components of EEG and the grey flow and relative grey weight parameters of blood flow. On an individual basis, the observed relationships were highly variable particularly at high flow rates and at low relative grey weights, but became much more definitive at low flows and high weights. The results as they relate to previous work of this kind are discussed.

Effects of secondary polycythemia on cerebral blood flow in chronic obstructive pulmonary disease

Cerebral blood flow was measured before and after venesection in 6 patients with chronic obstructive pulmonary disease and secondary polycythemia. The hematocrit was decreased from a mean of 59.6 to 43.9%, and whole blood viscosity was decreased by 35%. The supratentorial blood flow increased 78.2% (p < 0.005) after venesection; subtentorial flow also increased, but not significantly. The improvement in cerebral blood flow appeared to be related to a decrease in blood viscosity, because pulmonary function and arterial blood gases did not change significantly. There was subjective improvement in all patients, and this improvement might have been due to the increased supratentorial blood flow.

Evaluation of cerebral blood flow in arteriovenous malformations by the xenon 133 inhalation method

Fifteen regional cerebral blood flow studies (rCBF) were conducted on 14 patients with arteriovenous malformations (AVM). Only one patient was studied at the time of a hemorrhage. None of the patients were operated upon. All patients had angiographically demonstrated lesions. All the CT scans performed demonstrated the lesions. rCBF was increased in the involved hemisphere compared to the non-involved hemisphere and the difference was greater when the malformations were superficial. There was a higher incidence of high flow regions in the involved hemisphere of patients with AVMs compared to our normal control group and patients with subarachnoid hemorrhage (SAH) from aneurysms. Flow rates within the involved hemisphere demonstrated abnormal distributions and greater variability than normals. Some peaks previously demonstrated in the intra-arterial flow studies are not apparent using the inhalation method. This non-invasive technique has a potential to provide additional useful information on the natural history of this disorder.

Regional cerebral blood flow in patients with aneurysms: estimation by Xenon 133 inhalation

Seventy six regional cerebral blood flow (rCBF) studies were conducted on 32 patients who had a total of 39 aneurysms. Twenty three of these patients were studied pre- and post-operatively. Normal values were obtained from a control group of 33 subjects, each of whom underwent one rCBF study. Flow was reduced following subarachnoid hemorrhage (SAH); it increased significantly post-operatively. Lower flows were associated with poorer clinical grades. There was a greater variation in regional distribution of flow immediately following SAH than in normals or in patients who had recovered from the acute phase. rCBF studies correlated with CT scans demonstrated that a progressive increase in ventricular size was accompanied by a progressive reduction in flow. In addition, intraventricular hemorrhage (IVH) was associated with a significant reduction in cerebral blood flow (CBF). No significant correlation between CBF and spasm was demonstrable.