Tracer Washout Research Articles

Correlates of Diuretic Renography in Experimental Hydronephrosis

We studied the correlations between diuretic renographs and kidney function in experimental hydronephrosis in rabbits. Features of furosemide-stimulated 99mTc-diethylenetriamine-pentaacetic acid renographs were compared to the growth rate, thirst test and endogenous creatinine clearance rate in a chronic solitary-kidney animal model. Intravenous pyelograms, done four weeks after laparotomy, left nephrectomy, bladder resection and constriction of the right pyeloureteric junction, showed signs of obstruction in all the 12 animals of the experimental group. An absent tracer washout after intravenous furosemide, found in five animals, was associated with retarded growth, isosthenuria and an abnormal creatinine clearance. In all of the other seven animals, a distinct tracer washout after intravenous furosemide was accompanied with a normal growth rate and creatinine clearance. However, no one of these seven animals had a normal ability to retain water and concentrate urine in the thirst test. We conclude that, in this experimental model, a furosemide-induced tracer washout from the kidney pelvis cannot be taken as a proof of the absence of any upper urinary tract obstruction.

Multicompartment analysis of blood flow and tissue perfusion employing D2O as a freely diffusible tracer: a novel deuterium NMR technique demonstrated via application with murine RIF-1 tumors.

Deuterium NMR is employed in concert with multicompartment kinetic analysis for measurement of tissue blood flow and perfusion through a bolus administration of D2O as a freely diffusible tracer. The traditional single-compartment and two-compartment in-parallel flow models with no tracer recirculation are briefly discussed. The two-compartment in-series flow model with recirculation is developed to account for reflow of the stable (slowly excreted) deuterium tracer. With this model a monoexponential tracer washout curve is predicted. The rate of blood flow and tissue perfusion is readily extracted by three-parameter monoexponential analysis of the residue decay curve. A three-compartment model with recirculation, incorporating one compartment in-series with two compartments in-parallel, is developed for analysis of biexponential tracer washout curves. With this model the flow rates through the two in-parallel compartments (i.e., fast and slow) and the volume fractions of these two compartments are obtained by five-parameter biexponential analysis of the residue decay curve. Application of these multicompartment tracer-recirculation flow models is demonstrated with in situ determinations of murine RIF-1 tumor blood flow and tissue perfusion. The blood flow rates determined by deuterium NMR and analyzed by the multicompartment flow models agree well with those determined by others using radiolabels. A companion article (S.-G. Kim and J.J.H. Ackerman, Cancer Res. 48, 3449-3453, 1988) discusses in more depth the practical aspects of applying these multicompartment models to tumor blood flow measurement.

Permeability to Ca2+ of the acetylcholine receptor channel of denervated mouse muscles in the presence of Na+ and of some other cations.

Calcium uptake caused by exposure to azelainylcholine and the additional membrane slope conductance caused by the same agonist were compared in partially depolarized mouse soleus muscles denervated for 3-5 days. Ca uptake was estimated from the amount of 45Ca retained after a 2 min exposure to the tracer (1 min in the presence of azelainylcholine) and a subsequent 17 min period of tracer washout. The amount taken up in the presence of Na+ was 0.152 m mole/kg fresh muscle. The uptake was by about 60% higher when Na+ was replaced by N-methyl-D-glucamine. For 10 other monovalent cations Ca uptake was less than with Na. Ca uptake was not related to the molecular weight, size or structure of the cation. The slope conductance in the presence of 10 microM azelainylcholine was 4 microseconds and it was 21% of that value when Na+ was replaced by N-methyl-D-glucamine, i.e. conductance was decreased when Ca uptake was increased. This discrepancy points to a major difference in the way cations such as Ca2+ and K+ pass the receptor channel.

Bolus technique for assessing distribution of inspired gas during tidal breathing.

The washout of an insoluble tracer from the lung may be represented by a model with two ventilatory compartments representing poorly and better-ventilated regions. Using boli of a second insoluble gas delivered at a given point during inspirations of a multibreath washout test, the proportions of labeled inspired ventilation reaching the poorly and well-ventilated regions may be determined by analyzing the kinetics of the exhaled tracer. We studied eight normal subjects breathing through large-bore solenoid valves controlled to maintain tidal volume at 600 or 900 ml. Boli consisting of 15 ml of 80% He-20% O2 were delivered over 75 ms; this labeled approximately 125 ml of inspired gas. Boli were delivered after 50 ml had been inspired to mark early inspiration and after 300 ml had been inspired to mark midinspiration. Using 900-ml tidal breaths, late inspiration was marked by boli delivered at 600 ml. Subjects were studied in the seated and the supine positions. In both positions, significantly more of the early breath went to the poorly ventilated compartment. Several possible physiological mechanisms, singly or in combination, could account for these observations, but differences in dead space path length are most likely involved.

In vivo opioid receptor occupation in the rat brain following exercise

The effects of prolonged swim-stress (2 h and 1 h) upon brain opioid receptor binding of tritiated [3H]diprenorphine were investigated in male Sprague-Dawley rats. This was accomplished by injecting the label intravenously immediately following the swim, then allowing 20 min for tracer washout from non-specific binding sites, sacrificing the animal, dissecting the brain into several discrete areas (medulla-pons, mid-brain, mesolimbic, caudate, thalamus, and hypothalamus), and subsequently preparing homogenates from each brain area. Data were obtained from scintillation counting of the homogenates. A separate support experiment measured circulating beta-endorphin endorphin like immunoreactivity immediately following 2 h of swim-stress. Blood-borne beta-endorphin levels were significantly enhanced by the swim. Additionally, [3H]diprenorphine binding was insignificantly elevated following the 1-h swim and significantly greater in 5 of 6 brain areas examined subsequent to the 2-h swim. Greater availability of opioid receptors to allow enhanced binding of [3H]diprenorphine may have been caused by decreased competition for available receptors from endogenously produced peptides or possibly by alterations in receptor-binding characteristics. These proposed explanations await further investigation. As a result of these studies, we conclude: exercise-induced enhancement of peripheral beta-endorphin probably does not have a supraspinal action; and prolonged swim-stress apparently alters opioid receptor occupancy in the rat brain, and this effect may be dependent upon exercise duration.

Phloem Unloading within the Seed coat ofPisum sativumObserved using Surgically Modified Seeds

Phloem unloading in pea seed coats was observed by removing the embryos from developing seeds and washing the attached coats with a weakly buffered solution. The quantity of labelled photosynthate appearing in the washing solution varied immediately when the solute concentration was changed, and is shown to be an osmotic response. This response is predicted by the Münch theory of phloem transport with concentration dependent unloading. Respiratory inhibitors and the sulphydryl modifying reagent PCMBS had a slow effect upon the washout of tracer, which arrived within the seed coat prior to inhibitor application, but completely stopped any washout of tracer arriving after its application. This time-course suggests that the inhibitors were not directly inhibiting unloading, but preventing further tracer from entering the region of unloading within the seed coat. Phloem unloading within the seed coats of Pisum appears to be passive and not dependent upon a PCMBS-sensitive carrier.

Local Regulation of Cutaneous Blood Flow in Psoriasis

Local regulation of cutaneous blood flow (CBF), i.e., the venoarteriolar reflex mechanism and the autoregulation response, was studied in 27 patients with psoriasis using atraumatic epicutaneous 133Xe-labeling tracer washout technique. Venous stasis of 40 mm Hg induced a significant reduction in CBF--as in normal subjects (i.e., a vasoconstrictor response)-in both involved psoriatic skin (0.47 +/- SEM 0.04, p less than 0.0001) and uninvolved psoriatic skin (0.38 +/- SEM 0.03, p less than 0.0001). The vasoconstrictor response to neural blockade with lidocaine was investigated in two control experiments in psoriatic skin. It was found to be normal: neural blockade with lidocaine 2 cm outside the measured field did not affect the vasoconstrictor response, whereas local infiltration with lidocaine did block the vasoconstrictor reflex. Limb elevation of 40 cm above heart level induced a 2-fold significant increase in the CBF of involved psoriatic skin in 10 patients. This response is a paradoxical deviation from normal local autoregulation of the CBF (p less than 0.002). Limb elevation had no significant influence on CBF of uninvolved psoriatic skin, indicating a normal autoregulation of the CBF. The paradoxical increase in CBF during limb elevation in involved psoriatic skin was not influenced by local neural blockade with lidocaine, or by local neural and vascular, smooth muscle blockade obtained by injection of lidocaine and papaverine. The results indicate that the reason for this paradoxical phenomenon might be due to the special morphology of the capillaries of involved psoriatic skin.

Mixing efficiency as estimated by nonlinear least squares

The suitability of a statistical technique known as nonlinear least squares for use in estimating mixing coefficients was evaluated by fitting models to residence time distribution curves. The washout curves were generated by adding slug inputs of tracers to three different reactors. Each of the reactors, used to treat wastewaters, was a different size and represented a different degree of mixing.Three models, described in the paper, were examined for use in conjuction with the nonlinear least squares technique. They included the axial dispersion, N-tanks-in-series, and Cholette–Cloutier models. The form of the equation for the axial dispersion model depends on the boundary conditions for the reactor being studied. For reactors which cannot be classified as "open" vessels, the required analytical solutions either do not exist or are not suitable for use with the nonlinear least squares technique.Mixing coefficients for the N-tanks and Chollette–Cloutier models were obtained from the tracer washout curves for the three reactors. The residual sum of squares based on nonlinear least squares estimates for the model parameters was compared with the sum of squares obtained using more conventional methods for estimating the parameters. The existence of trailing tails on the tracer curves resulted in misleading parameter estimates for the two models using conventional techniques. Keywords: mixing, least squares, tracer, dispersion, short-circuiting, deadspace.

Measurement of regional myocardial perfusion using collimated miniature radiation detectors and the method of 133-xenon washout.

A new approach to the measurement of local myocardial perfusion based on the application of highly-collimated miniature cadmium telluride radiation detectors to measure washout of 133-Xenon from well-defined tissue volumes is presented. Single-hole collimators with length/diameter ratios of 1 (L = 4 mm, D = 4 mm) and 4 (L = 12 mm, D = 3 mm) were employed as prototype designs. The probe field of view was characterized theoretically using a spherical model of the myocardium in conjunction with experimental point source response measurements for each collimator. Method evaluation using two medium resolution collimators (L/D = 1) was effected by performing left main and circumflex coronary artery perfusion studies at controlled but variable flows in the dog heart. An excellent correlation (r greater than 0.99) between actual and estimated perfusion determined from 65 washout curves over the flow range 0.38 to 3.18 ml/min/gm was demonstrated. The ability to resolve regional flow differences was verified by measuring tracer washout from circumflex and left anterior descending regions of the myocardium, using two high resolution collimators (L/D = 4), in a preparation where the left main coronary artery was cannulated and a snare was placed around the circumflex coronary artery to selectively reduce flow to that region.

Role of myocardial ischemia in the genesis of stress-induced S-T segment elevation in previous anterior myocardial infarction

This study tests the hypothesis that myocardial ischemia is responsible for exercise-induced S-T segment elevation in patients with previous anterior myocardial infarction (MI). Exercise stress testing in conjunction with thallium imaging of the myocardium was performed in 28 patients with previously documented anterior MI. Thallium images were analyzed by computer for the presence of initial uptake defects and evidence of abnormal clearance of the isotope from the myocardium (that is, imaging evidence of ischemia). Total S-T segment elevation (∑ST) in precordial leads V1 to V6 at rest was subtracted from ∑ST at peak stress in order to quantitate the extent of S-T elevation induced by stress (ΔST). Two groups of patients were identified; 1 with stress-induced S-T elevation (Group I, ΔST ≥ 4.0 mm) and 1 without this abnormality (Group II, ΔST < 4.0 mm). Evidence of abnormal thallium washout from myocardial scan segments occurred in 12 of 15 Group I patients versus 9 of 13 Group II patients (difference not significant). In addition, abnormal tracer washout from anterolateral or septal scan segments occurred in 5 patients in each group. Likewise, abnormal thallium clearance from inferior or posterior scan segments occurred in 8 of 15 Group I patients versus 7 of 13 Group II patients (difference not significant). The patient with the greatest amount of stress-induced S-T elevation (S-T 11.5 mm) had no evidence of ischemia during the stress test. However, Group I patients did have larger anterolateral plus septal initial thallium uptake defect scores than did those of Group II (10 of 15 with defect score ≥ 350 in Group I versus 1 of 13 in Group II, p <0.002). Similarly, resting left ventricular ejection fraction ≥ 30% was present in only 4 of 15 Group I patients versus 13 of 13 in Group II (p <0.001). Finally, multiple stepwise linear regression analysis demonstrated that ΔST correlated best with the extent of initial anterolateral plus septal thallium uptake defect score (F = 17.3, p < 0.001) and to a lesser extent with resting ejection fraction (F = 5.2, p < 0.05) and change in heart rate from rest to peak stress (F = 8.1, p < 0.01; corrected multiple correlation coefficient = 0.76, p < 0.001). Thus, in patients with previous anterior MI (1) exercise-induced myocardial ischemia occurs as often with as without S-T segment elevation, (2) myocardial ischemia is not required for the production of stress-induced S-T segment elevation, and (3) stress-induced S-T elevation primarily reflects the extent of previous anterior wall damage and to a lesser extent an increase in heart rate between rest and peak stress.

Regional variation of left ventricular transit time in normal ventricles and those with abnormalities of contraction.

Thirty-three subjects were studied by first pass radionuclide angiography. The extrapolated monoexponential tracer washout slopes from septal, lateral, and apical segments of the left ventricle were measured. In 13 subjects with normal left ventricles, as assessed by ejection fraction estimation and phase analysis, there was no difference between septal and lateral segments but, in each case, apical washout was significantly prolonged. In 20 subjects with abnormal ventricles washouts were, in general, slower than those of the normal ventricles. Apical washout was still the slowest but the difference between base and apex was less pronounced. In contrast to the normal ventricles, differences appeared between septal and lateral segments. The left ventricle is a poor mixing chamber. Pools of relative stasis exist at the apex of both normal and abnormal ventricles and within the body of the chamber in the latter.

Diffusional and compartmental models for tracer washout records of Na in dog carotid

This paper re-examines studies of Na kinetics in canine carotid arterial wall previously reported by three groups of investigators. The similarities and differences in experimental and analytical approaches for Na arterial wall washout therein are reviewed. Major conclusions are: (1) A three-compartment model in series is adequate for all short and long (after subtracting the small slow exponential) records. (2) Values for the diffusion coefficient, however, varied markedly among the different groups. (3) A continuous sampling method as opposed to an intermittent one measures better the kinetics of a rapidly exchanging ion as Na +. (4) Models based on individual washout records are better than those based on ensemble averaging. Characterization of sets of results in terms of mean values for comparing parameters provides significant potential for distinguishing quantitative features between control and treated sets despite inadequacies in data sampling or model specifications.

Evaluation of 133Xe washout kinetics by controlled pig liver perfusion in vivo

The interpretation of multiexponential curves from hepatic tracer washout for estimation of hepatic blood flow (THBF) was investigated, using hepatic 133Xe washout during controlled portal and arterial perfusion of liver in anesthetized pigs. Variations of (1) THBF from 25 to 210 ml/min × 100 g, (2) the proportion of portal to arterial flow, and (3) the site of tracer application were performed. After portal injection the tracer curves were in most cases multiexponential; their analysis revealed that calculation of THBF using k values based on the monocompartmental hypothesis always grossly overestimated total flow. Estimation of THBF by height/area ( H A ), however, reflected the total flow in all cases. Only when hypoventilation or elevation of hepatic venous pressure was performed, did calculation of THBF from k values and H A values reveal similar results. THBF when estimated from H A and from indocyanine green dye extraction gave identical results, both in the controlled perfused liver and in the intact animal. Washout curve analysis after arterial Xe application showed neither a correlation with the total nor with the arterial flow, indicating incomplete mixing of both blood flow components. It is concluded that liver perfusion is multicompartmental and blood flow through the portal and arterial vascular bed is incompletely mixed. Therefore, THBF can be calculated only after portal tracer injection and when the mean transit time concept is applied.

Nutrient pathways of the cruciate ligaments. An experimental study using the hydrogen wash-out technique.

We used the hydrogen wash-out technique to determine the rate of wash-out of an inert tracer from the posterior cruciate ligament in dogs and rabbits after we had detached the ligament from bone and synovial structures, and after we had isolated it from the synovial tissue with aluminum foil. These rates were compared with those from controls and no differences could be found between them. The uptake of tritiated proline administered intravenously was also shown not to be significantly different in the detached ligament as compared with an intact ligament. Isolation of the ligament from contact with the synovial lining prevented the uptake of hydrogen. Cruciate ligaments removed from the knee and placed in the suprapatellar pouch appeared viable after eight to ten days. These findings suggest that diffusion can serve as a major pathway for delivery of nutrients to the cruciate ligaments.

States of myocardial metabolism related to ischemia.

Energy metabolism of the heart in ischemia is mainly characterized by oxygen deficiency and lack of lactate removal. However, under certain circumstances substrate deficiency might contribute to disturbances of energy supply as well. Capillary permeability was determined from tracer washout kinetics of isolated hearts. Regulation of mitochondrial respiration was estimated from the relationship of phosphorylation potential vs. oxygen consumption. The results obtained suggest that at least under experimental conditions substrate supply at the level of capillary exchange can be a rate-limiting figure, as well as substrate supply at the mitochondrial level, i.e., NADH supply. The latter was inferred from the effects of cobalt and strontium ions on the regulation of respiration.

Multiexponential and multicompartmental approaches for analysis of tracer washout data from animal tissues

A comparison is made between multiexponential and multicompartmental analyses of tracer washout data from biological tissues. Various analytical and computer methods are used to explore the relations between kinetic parameters of three-compartment models and parameters of three-exponential functions fitted to typical observed tracer washout records and also to examine relations between kinetic parameters of the same three-compartment models determined analytically and numerically. It is concluded that exponential factors and coefficients cannot always be equated respectively with compartmental transport rate constants or compartment sizes. Sufficient analytical and computer methodologies exist so that selection of meaningful biological models should not be hampered by a lack of appropriate solution procedures.

Low molecular weight intracellular iodocompounds with long intrathyroidal half-life: remnants of thyroglobulin hydrolysis?

In this paper additional information on low molecular weight, soluble, intrathyroidal iodocompounds with slow metabolic rate is provided. These compounds have previously been localized autoradiographically within the follicular cells. Radioiodide was administered to rats on a normal iodine intake (6--7 microgram/day) for 80 days to approach isotopic equilibration of the intrathyroidal iodine with the dietary radioiodide. When the isotope was omitted from the diet the intrathyroidal radioiodine was released with an apparent half-life of approximately 12 days. When the individual soluble components carrying radioiodine were analyzed after separation on Sephadex G-200, different apparent half-lives were found, the half-life of thyroglobulin (Tgb) being roughly 10 days and that of the low molecular weight iodocomounds being in the order of 60 to 100 days or more. In addition to the soluble low molecular weight iodocompounds, the radioactivity in the particulate fraction increased by 100% during the tracer washout when compared to Tgb and the total soluble fraction. The soluble slow turnover iodocompounds contained a higher percentage of carbohydrate and total iodine than Tgb, while the relative amounts of each sugar analyzed (hexoses, fucose, hexosamine and sialic acid) were close to those in Tgb. Sephadex G-25 chromatography of the low molecular weight iodocompounds obtained after Sephadex G-200 separation resulted in the separation of 4 peaks. Two peaks identified as iodopeptides could be further analyzed. The carbohydrate composition of these peptides was similar to that of 2 glycopeptides obtained after in vitro enzymatic hydrolysis of purified Tgb with pronase. Slow equilibration with radioiodine, long apparent intrathyroidal half-life and carbohydrate content similar to that of Tgb, taken together with previously published data on intracellular localization of soluble intrathyroidal iodocompounds, suggest that the low molecular weight iodocompounds are products of in vivo hydrolysis of engulfed Tgb droplets.

Blood flow in proximal femur of the dog determined by the local 133Xe injection method.

A new approach for measuring blood flow in bone is presented. It consists of the local injection of 133Xe into the proximal femur of adult beagles and the external measurement of isotope washout curves. The curves were analyzed using a two-compartment exponential model. The half-times for the tracer washout from the fast and slow compartment were 3.34 +/- 0.48 min and 33.6 +/- 11.7 min (mean +/- 1 S.D.) respectively. Blood flow was calculated using a measured blood to bone partition coefficient of 1.55 ml/g. The mean blood perfusion in proximal femur of the dog was 10.8 +/- 4.3 ml/100 g/min (mean +/- 1 S.D.). This value agrees well with most estimates of bone circulation. Due to rapid disappearance of 133Xe the method is easy to repeat and is thus suitable for physiological studies of local blood flow in bones.

Nutrition of Flexor Tendons in Monkeys

The hydrogen washout technique was used to investigate the role of synovial diffusion versus vascular perfusion in the nutrition of monkey flexor tendons within the digital sheath. There was no significant difference in the uptake and washout of hydrogen tracer by tendons in contact with synovium but detached from the surrounding vasculature, compared to control tendons. However, there was insignificant uptake of tracer by tendons with intact vasculature, but separated from synovium. Synovial diffusion is a primary nutrient pathway of monkey flexor tendons within the digital sheath.

Physiology and theory of tracer washout techniques for the estimation of myocardial blood flow: Flow estimation from tracer washout

The time course of washout of tracer from the myocardium provides an estimate of the flow per unit volume when the blood-tissue exchange is flow-limited. Methods of testing for the flow-limitation and for the absence of influences of low permeability or diffusion on the washout include the uses of paired or multiple tracers and the examination for similarity of the shapes of the residue function or washout curves at varied coronary blood flows. A conceptual framework for these studies is provided by a clearance-flow diagram for the myocardium where capillaries are long compared to radial intercapillary distances. This anatomic-physiologic framework coupled with a probabilistic, general analytical approach and with various experimental approaches to tracer studies of mass transport through the heart provides a general basis for methods of estimating myocardial blood flow in the whole organ and in its component regions.