Edwin M. Wilson

Regional Cerebral Blood Flow by 133Xenon Inhalation

Repeated measurements of regional cerebral blood flow (rCBF) were made by the short (ten minutes) 133Xenon inhalation technique and bicompartmental analysis in 11 patients with cerebrovascular disorders, mainly acute cerebral infarction. rCBF was measured 3 to 11 times during one to two weeks. The blood flow of the fast compartment (f1) was calculated as well as the relative weight of this compartment (w1, assumed to correspond to gray matter). In addition a new flow index, the Initial Slope Index (ISI) modified for the inhalation technique, was used. This index of predominantly gray matter flow was calculated from a one-minute epoch of the early part of the clearance curve corrected for recirculation. In three of the patients the f1 and ISI varied in parallel and the w1 showed generally only minor variations from one measurement to the other. However, in the other eight patients fluctuation of the w1 and f1 values were seen which often showed no meaningful relation to the clinical course. The observed w1 changes indicated that some tissues (slowly perfused gray matter and/or rapidly perfused white extracerebral tissues) fluctuate between the fast and the slow compartment. In such cases the f1 values obtained cannot be used for comparison between measurements, since they represent flow rates of varying tissues and do not always represent a true gray matter blood flow. In these patients the ISI, which is independent of such weight changes, showed moderate and clinically likely variations.

133Xenon inhalation method. Analysis of reproducibility: some of its physiological implications.

Regional cerebral blood flow (rCBF) was simultaneously measured at seven locations in each hemisphere by the Obrist 133Xenon inhalation method. In each of 35 healthy right-handed subjects two rest measurements were performed on consecutive days. The data analysis comprises the two-compartmentally derived parameters for flow (f1), relative tissue weight (w1), and fractional flow (FF1) respectively of the first compartment, and in addition the initial slope index (ISI). At each detector location the coefficient of variation (C.V.) of the change from first to second measurement was on average 10.4% (ISI), 14.2% (f1), 7.2% (w1), and 2.9% (FF1) respectively. However, when each regional measurement was expressed as a percentage of its hemispheric mean, the C.V. of the intermeasurement change was on average 4.4% (ISI), 7.0% (f1), 7.7% (w1), and 1.9% (FF1) respectively; that of the hemispheric means of ISI, f1, and FF1 was found to be distinctly larger, whereas that of w1 was about equal in size. The interhemispheric coefficient of variation for the change of the hemispheric means from first to second measurement was only 2.3% (ISI), 4.4% (f1), 1.6% (w1), and 1.1% (FF1) respectively. The findings suggest that (1) the variability of rCBF from subject to subject and in consecutive measurements in the same subject is to a substantial degree of physiological origin, and that (2) there are two determinants of rCBF which may operate independently: a determinant of the hemispheric mean level, probably a single determinant for both hemispheres, and a set of determinants for each separate regions superimposed on the hemispheric mean level.

Regional cerebral blood flow comparison of right and left hand movement

Regional cerebral blood flow measurements were made in normal right-handed subjects by the 133 xenon inhalation method at rest and during movement of either hand. Left hand movement evoked a prominent focal flow increase in the right hemisphere in the Rolandic region. During right hand movement, there was a smaller and not statistically significant increase in left hemisphere Rolandic region. This suggests that more effort is required of right-handed subjects to move the left hand than the right, or that motor organization differs for left and right hand movements. Of several flow indices tested, there was little difference among gray matter flow rate, the product of gray matter flow and relative weight, the mean regional flow, and the initial slope index, all reflecting the flow changes with nearly equal sensitivity. The gray matter weight and fractional flow did not change consistently during hand movement.

Measurement of regional blood flow by the 133Xenon inhalation method with an on-line computer☆

Abstract A computer based multidetector system was developed for the measurement of regional cerebral blood flow ( r CBF) by the 133 Xenon inhalation technique. The computer portion of the system is characterized by on-line data acquisition, rapid data analysis and presentation of results. Special system features include programs which automatically determine end-tidal Xenon concentrations during the saturation and desaturation phases of the flow measurement and which provide for automatic background subtraction, and a special purpose counter-digital multiplexor-computer interface. The system provides convenience in handling acutely ill patients, and assures reproducible positioning for serial measurements. Typical output format and partial results from 150 patient and normal subject measurements are presented.

Validation of Jugular Venous Flow as an Index of Total Cerebral Blood Flow

Values of total cerebral blood flow in man measured by the indicator dilution method are compared with values of total internal jugular venous flow measured by the thermal dilution method. Except in the case of an extremely labile cerebral hemodynamic state, the results agree within the accuracy of the two methods, suggesting that for the supine patient total internal jugular venous flow provides a good index of total cerebral flow. The relatively short measurement time associated with nondiffusible indicators (dye or thermal dilution) facilitates detection of transient changes in total CBF or differential jugular flow that would tend to be averaged out with diffusible indicator methods. A mathematical analysis of the potential errors in the computation of total flow using the average of bilateral jugular venous dilution curves from a unilateral internal carotid injection is presented. This error can be partially corrected if the ratio of flow in one internal jugular to total flow is known. An analysis of potential computational errors under nonsteady state flow conditions (change in flow during the period between alternate carotid injections) is presented. Such flow changes can effect substantial errors in the computation of individual hemispheric or internal jugular flow and smaller errors in the computation of total flow.

133Xenon inhalation method: significance of indicator maldistribution for distinguishing brain areas with impaired perfusion. An index for total flow.

This paper introduces a new index for the assessment of regional cerebral blood flow. The index is proportional to total flow, and is obtained from the ratio of regional count rate to arterial indicator input to a region. This index is a more sensitive indicator of impaired perfusion than the traditional flow rate indices which express flow per unit mass of tissue per minute. It accounts for brain tissue partly or totally deprived of its blood supply. Examples of clinical application are reported. A good correlation with the findings of computer-assisted tomography has been found.

Bilateral Jugular Venous Blood Flow by Thermal Dilution

Measurements of internal jugular venous flow were made in 12 patients with severe cerebral vascular disease. Flow rates were determined by the thermal dilution method, using room temperature physiological (heparinized) saline as an indicator infused at a constant rate. The major sources of error (indicator mixing) were studied under highly controlled in vitro experiments. Total jugular venous outflow was substantially below mean values of total cerebral flow for normal subjects and somewhat below the mean values for demented patients. Free communication between the two jugular veins via the torcular was observed in all patients. Following unilateral venous compression, the differential shift to the contralateral vein was not always equal to the precompression total flow. This would seem to indicate that this maneuver produces some diversion of flow to other venous channels and suggests that total cerebral blood flow can be obtained reliably only through bilateral measurements.

An Improved Thermal Dilution Method for Measuring Jugular Venous Flow

The local thermal dilution method of performing serial bilateral measurements of internal jugular venous flow is significantly improved by injecting a bolus of saline rather than by using a continuous injection of saline. New thermistor catheter designs maintain the proper separation between the sites of injection and of sampling and require only a single insertion per side. The method measures mean flow rates over a two-second to three-second interval. Measurements were made in 14 patients with cerebrovascular disease. Studies of five patients are presented to illustrate the value of the method for assessing internal jugular venous hemodynamics. Positive response to injection of acetazolamide was noted in four of these five patients. Cyclic variations in jugular flow were observed in one patient with Cheyne-Stokes respiration. Occasional retrograde flow in one jugular vein was recorded in another patient.

The Use of STA-MCA Bypass in the Evaluation of rCBF

Objective means of evaluating patients who have undergone surgical procedures designed to augment collateral blood supply to the brain are necessary if these patients are to be assessed by means other than ongoing clinical examination and repeated angiography. We have studied seven consecutive patients selected for superficial temporal artery-middle cerebral artery (STA-MCA) bypass by clinical and angiographic criteria using 133xenon clearance as assessed by the inhalation technique.

Comparison of external lung monitoring with end-tidal air detection using the 133xenon inhalation method.

When the 133Xe inhalation method is employed for measuring regional cerebral blood flow, the arterial 133Xe concentration is usually approximated by the end-tidal air concentration. However, this approximation may be invalid in the presence of certain lung pathologies or when the breathing pattern is irregular. Jaggi and Obrist, using an intravenous injection of 133Xe, suggested that the counts detected by an external lung probe could provide an alternative estimate for arterial blood concentration once the noise produced by 133Xe in superficial tissues is removed from the signal. A mathematical model, based on hypotheses similar to theirs is presented here together with a new computational procedure for removing the noise. Results from normal rest studies on ten healthy young males indicate that the approximations for arterial blood concentration obtained from end-tidal air and from corrected lung counts are not equivalent when 133Xe is administered by inhalation. The concentration-time curves have different shapes, and these differences are reflected in blood flow values computed by head channel. However, there is no effect on comparisons between homologous regions of the left and right hemispheres.