Velocity Perfusion Research Articles

A novel method of doppler signal quantification for metastatic neck node evaluation

Problem: Vascularization and oxygenation are important factors for radiosensitivity. The authors investigate the use of a novel ultrasound technique for the assessment of vascularization and oxygenation in metastatic neck nodes. Methods: Seventeen patients with neck metastases of squamous cell head and neck cancer were investigated by Color Duplex sonography and polarography. Intranodal perfusion was measured by a novel technique using a dynamic signal quantification (Pixelfux). With this approach perfusion intensity, perfused area, flow velocity, resistance index (RI), and pulsatility index (PI) could be evaluated in a predefined region of interest. PO2 was measured in the same nodes with polarography. The data were correlated using Pearson‘s test. Results: In metastatic lymph nodes the hypoxic fraction <10 mmHg demonstrated a significantly inverse correlation with the intranodal perfusion (r = 0.54, P < 0.024). Nodes with a perfusion velocity <0.05 cm/sec had larger hypoxic areas ( P < 0.006). Statistically significant differences existed between nodes in stage N1 and N2/3 for PI ( P < 0.028) and RI ( P < 0.048). Conclusion: The new sonographic technique demonstrates a significant correlation between tumor perfusion and oxygenation. This noninvasive technique allows not only the assessment of size, localization, and shape in neck nodes but also an evaluation of functionally important tumoral parameters. Significance: The method offers novel noninvasive means for monitoring perfusion and oxygenation of tumors via commonly available ultrasound equipment. It can be helpful for therapy monitoring in head and neck cancers. Support: Chameleon Software Corp. provided the Pixelflux software application free of charge for this study.

Quantitative analysis of three-dimensional fluid flow in rotating bioreactors for tissue engineering.

Tissue engineering has emerged as a viable alternative to the problem of organ and tissue shortage. Our laboratory has developed matrices for bone tissue engineering based on sintered spherical particles and, using bioreactor technology, has demonstrated the ability to produce highly mineralized matrices in vitro. In this study, porous microcapsule scaffolds were developed for bone tissue engineering in the high aspect ratio vessel rotating bioreactor. The motion of individual microcapsules as well as scaffolds in the bioreactor were studied by numerical simulation and in situ imaging analysis. Results show that spherical microcapsules with density less than the surrounding fluid exhibited two motions: (1) a periodic circular orbit with tangential speed equal to the free fall speed of the particle, and (2) an inward radial migration of the circular orbit toward the center of the bioreactor vessel. Lighter-than-water scaffolds were fabricated by sintering poly(lactic-co-glycolic acid) hollow microcarriers with diameter from 500 to 860 microm into a fixed three-dimensional geometry with approximately 30% pore volume and 180 to 190 microm median pore size. Scaffolds were fabricated with aggregate densities ranging from 0.65 g/mL and 0.99 g/mL by appropriate combinations of hollow and solid microcarriers within the scaffold. Scaffold velocity in the bioreactor for the above range of densities was accurately predicted by numerical simulation and ranged from 100 mm/s to 3 mm/s. Maximum shear stress estimation due to media flow over the exterior of the scaffold ranged from 0.3 N/m(2) to 0.006 N/m(2). Internal perfusion velocity through scaffolds also was calculated and ranged from 13 mm/s to 0.2 mm/s. Estimates of maximum interior shear stress ranged from 0.03 to 0.0007 N/m(2). These analytical methods provide an excellent vehicle for the study of bone tissue synthesis in three-dimensional culture with fluid flow.

Echocardiographic comparison of the standard end-hole cannula, the soft-flow cannula, and the dispersion cannula during perfusion into the aortic arch

Background Dislodgement of aortic arch atheroma caused by a perfusion “jet” from the aortic cannula may be a major cause of atheroemboli during coronary artery surgery when using cardiopulmonary bypass (CPB). Two very different cannulas, the Soft-Flow aortic cannula and the Dispersion cannula, which have been designed to reduce exit velocity (cm/s) during perfusion, are compared with a standard steel tip cannula and to each other. Methods To demonstrate any significant differences transesophageal echocardiography (TEE) was used to measure exit velocity of each cannula at a distance of 1, 2, and 3 cm from the tip and compare flow morphology within the aortic arch. Nine patients in whom the cannula tip could be identified and colored Doppler imaging could demonstrate representative morphology were randomly assigned into one of three groups of 3 patients each: group I, a standard steel-tip end-hole cannula (7.3 mm); group II, the Soft-Flow cannula (8.0 mm); and group III, the Dispersion cannula (8.0 mm). Results The standard steel tip cannula demonstrated a long narrow perfusion jet. The Soft-Flow cannula morphology was made up of multiple smaller exiting jets. The Dispersion cannula demonstrated a broad wedge-shaped perfusion pattern. Perfusion hemodynamics (cardiopulmonary bypass hematocrit in d/L, cardiopulmonary bypass blood flow in L/m, mean arterial pressure during cardiopulmonary bypass mm Hg, and perfusion line pressure in mm Hg) were not significantly different between each group. The mean velocities between group I (318 ± 63 cm/s at 1 cm, 296 ± 60 cm/s at 2 cm, 271 ± 85 cm/s at 3 cm) and group II (351 ± 31 cm/s at 1 cm, 240 ± 103 cm/s at 2 cm, 171 ± 120 cm/s at 3 cm) were not statistically different. Group III (the Dispersion cannula) demonstrated significantly reduced velocities (174 ± 22 cm/s at 1 cm, 138 ± 23 cm/s at 2 cm, 90 ± 36 cm/s at 3 cm) when compared with the other two groups ( p < 0.05, analysis of variance). Conclusions The Dispersion cannula is significantly different with a lower perfusion velocity and the elimination of the exiting jet or jets. This cannula warrants further clinical study as it may reduce atheroemboli during cardiopulmonary bypass.

Therapeutic angiogenesis/arteriogenesis in the chronic ischemic rabbit hindlimb: effect of venous basic fibroblast growth factor retroinfusion.

Therapeutic induction of angiogenesis has been shown in experimental hindlimb ischemia. An alternative to targeting the ischemic hindlimb tissue via the severely stenosed or occluded artery consists in the intact venous system, e.g., by retroinfusion. We tested whether basic fibroblast growth factor (bFGF) enhances angiogenesis induction. Therefore, we applied bFGF retrogradely as compared to intramuscular application. Furthermore, we assessed whether bFGF-induced angiogenesis was enhanced by low-dose VEGF coapplication. Chronic hindlimb ischemia in rabbits was established by excision of the femoral artery at day 0 (d0). At d7, baseline collateral number in the ischemic limb and collateral flow velocity of contrast agent (frame count score) were assessed. Thereafter, saline solution (control group) or bFGF (20 microg/kg) with or without VEGF (10 microg/kg) was retroinfused through the femoral vein. Alternatively, bFGF (20 microg/kg) was injected into thigh and calf muscles. At d35, collateral growth and flow velocity were quantified, and tissue samples were analyzed for capillary density. In the untreated control group, capillary/muscle fiber (C/FM) ratio of the ischemic limb was 0.87 +/- 0.12, and collateral number as well as frame count score at -d35 did not change compared to d7 (107% +/- 7% and 109% +/- 10% of baseline, respectively). Retrograde application of bFGF induced capillary and collateral growth (C/FM ratio 1.56 +/- 0.19 and frame count 161% +/- 29% of baseline), resulting in enhanced flow velocity (143% +/- 13%), similar to the intramuscular application of bFGF. Additional low-dose VEGF retroinfusion did not further increase capillary/collateral growth (1.49 +/- 0.08 and 172% +/- 26%) nor perfusion velocity (149% +/- 7%). The authors conclude that bFGF retroinfusion is a feasible approach of inducing angiogenesis and arteriogenesis in an ischemic hindlimb, resulting in increased blood perfusion, which was not further extended by additional low-dose VEGF coapplication.

Effects of perfusion rate on permeability of frog and rat mesenteric microvessels to sodium fluorescein.

The permeability, P(S), to sodium fluorescein (Stokes-Einstein radius = 0.45 nm) has been measured in single mesenteric capillaries of pithed frogs and anaesthetised rats as perfusion velocity, U, was varied over a range from 400 up to 2000-10,000 microm s(-1). P(S) increased linearly with U. In 20 frog capillaries, mean (+/- S.E.M.) P(S) (in microm s(-1)) = 9.35 (+/- 1.55)U x 10(-5) + 0.244 (+/- 0.0291). Similarly, in nine rat venules, mean P(S) = 1.62 (+/- 0.385)U x 10(-4) + 0.375 (+/- 0.025). The flow-dependent component of permeability could be reversibly abolished in frog capillaries by superfusing with 100 microM noradrenaline and by superfusing rat venules with the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine (20 microM). It was shown that changes in microvascular pressure accompanying changes in U during free perfusion could account for only 15 % of the changes in P(S), i.e. 85 % of the changes in P(S) were changes in the permeability coefficient itself. A comparison between the changes in P(S) with U and the previously described changes in microvascular permeability to K(+) with U, suggest that if the flow-dependent component of permeability is modelled as a population of pores of constant size, these have radii of 0.8 nm. Such a pathway would limit flow-dependent permeability to small hydrophilic molecules and have minimal effect on net fluid exchange.

Influence of the endothelial glycocalyx on cerebral blood flow in mice.

The endothelial surface layer (glycocalyx) of cerebral capillaries may increase resistance to blood flow. This hypothesis was investigated in mice by intravenous administration of heparinase (2500 IU/kg body weight in saline), which cleaves proteoglycan junctions of the glycocalyx. Morphology was investigated by transmission electron microscopy. Cerebral perfusion velocity was recorded before and during heparinase or saline treatment using laser-Doppler flowmetry. In addition, cerebral blood flow (CBF) was measured 10 minutes after heparinase or saline treatment using the iodo[14C]antipyrine method. Laser-Doppler flowmetry and CBF measurements were performed during normocapnia and severe hypercapnia (PCO2: 120 mm Hg). After heparinase, morphology showed a reduced thickness of the glycocalyx in cortical microvessels by 43% (P < 0.05) compared with saline-treated controls. Under normocapnic conditions, a 15% (P < 0.05) transient increase of cerebral flow velocity occurred 2.5 to 5 minutes after heparinase injection. Laser-Doppler flow and CBF returned to control values ten minutes after the injection. However, during severe hypercapnia, heparinase treatment resulted in a persisting increase in laser-Doppler flow (6%, P < 0.05) and CBF (30%, P < 0.05). These observations indicate the existence of a flow resistance in cerebral capillaries exerted by the glycocalyx. The transient nature of the CBF increase during normocapnia may be explained by a vascular compensation that is exhausted during severe hypercapnia.

A new concept of bioartificial liver based on a fluidized bed bioreactor.

Many bioartificial livers have been developed, but most of them suffer from difficulty when being scaled up and from poor efficiency of mass transfer between the plasma and the immobilized hepatocytes. We present a new concept of bioartificial liver based on the fluidized bed motion of hepatocytes entrapped in alginate beads. The bioreactor is designed to offer stable behavior. The maximum fluid perfusion velocity is determined to avoid any bead release from the bioreactor. The fluidized bed height depends on the amount of beads and the velocity employed. Under the optimized operating conditions, the mass transfer between perfusion fluid and beads is very efficient; only 10 min are necessary to reach concentration equilibrium. Hence, this fluidized bed bioartificial liver appears to be a promising tool for a liver support system in the treatment of acute liver failure.

Regional distribution of cerebral blood volume and cerebral blood flow in newborn piglets—effect of hypoxia/hypercapnia

The relationship between regional parenchymal cerebral blood volume (CBV), regional cerebral blood flow (CBF) and the calculated mean transit time (MTT) was investigated in 14 newborn piglets. The effects of combined hypoxic hypoxia ( p aO 2=32±5 mm Hg) and hypercapnia ( p aCO 2=68±5 mm Hg) were measured in seven animals. Remaining animals served as the control group. During baseline conditions the highest CBF and CVB values were found in the lower brainstem and cerebellum, whereas white matter exhibited the lowest values ( p<0.05). MTT was prolonged within the cerebral cortex (2.34±0.42 s −1) compared with the thalamic MTT (1.53±0.38 s −1) ( p<0.05). Under moderate hypoxia/hypercapnia, a CBF increase to the forebrain ( p<0.05) resulted in an elevated brain oxygen delivery ( p<0.05) and so CMRO 2 remained unchanged. Moreover, a moderate increase of CBV and a marked shortening of MTT occurred ( p<0.05). The CBV increase was higher in structures with lowest baseline values, i.e., thalamus (66% increase) and white matter (62% increase) ( p<0.05). MTT was between 22% of baseline in the lower brainstem and 49% in white matter ( p<0.05). We conclude that under normoxic and normocapnic conditions the newborn piglets exhibit a comparatively enlarged intraparenchymal CBV. Moderate hypoxia and hypercapnia induced a marked increase in cerebral blood flow which appears to be caused by an increased perfusion velocity, expressed by a strongly reduced mean transit time and by a concomitant CBV increase.

Ocular Blood Flow Velocities in Patients With Proliferative Diabetic Retinopathy After Panretinal Photocoagulation

Color Doppler imaging allows for simultaneous two-dimensional anatomical imaging and Doppler measurement of blood-flow velocity. Because hemodynamic changes have been seen in diabetic patients after photocoagulation by other techniques, the author compared 25 eyes of 25 patients with proliferative diabetic retinopathy before and 6 months and 1 year after panretinal photocoagulation with a matched control group of 30 eyes of 30 healthy volunteers. The ophthalmic artery, short posterior ciliary artery, central retinal vessels, and vortex veins of all patients were examined, and the systolic, diastolic, and mean arterial velocities were measured. Panretinal photocoagulation was performed with these parameters: 800-1000 spots, 0.1 second, 500 μm argon laser. The blood velocity was significantly lower in diabetic patients than in normals in the ophthalmic artery and the central retinal artery. After treatment, blood-flow velocities were significantly lower than before photocoagulation in the ophthalmic artery, the central retinal artery and the central retinal vein. No statistically significant differences were found between 6 months and 1 year after panretinal photocoagulation. No significant correlations were found between age and blood velocities in diabetics and healthy volunteers. Eyes with proliferative diabetic retinopathy showed lower ocular perfusion velocities than normals in the ophthalmic artery and the central retinal artery. Photocoagulation resulted in a reduction in ocular bloodflow velocities in the ophthalmic artery, the central retinal artery and the central retinal vein; these values did not change significantly during 1 year of follow-up.

Color Doppler ultrasound studies of benign and malignant lymph nodes

Color-coded duplex sonography is being increasingly used in the head and neck as another method for diagnosis of such disorders as stenosis of arteries or veins or hemangiomas. A possible additional advantage of testing is the ability to differentiate benign from malignant tumors. Since the underlying cause of a suspicious lesion is most important for treatment strategies, we investigated histologically-proven benign and malignant cervical lymph nodes for determining the value of color-coded duplex sonography. In the present study, 135 patients (45 women and 90 men; ages 30-63 years) with palpable cervical lymph nodes were examined with both ultrasound and color-coded duplex sonography. Afterwards, lymph nodes were removed by open biopsies or neck dissections. The histological results were then compared to perfusion velocities and pulsation indices from the color-coded duplex sonography. However, no significant differences were found between the benign and malignant nodes. When comparing perfusion and color, each group was seen to be non-homogeneous and no typical distribution of vascularization was demonstrable. Findings showed that color-coded duplex sonography is currently not an accurate indicator of lymph node pathology.

Ocular blood flow velocities in patients with proliferative diabetic retinopathy after scatter photocoagulation. Two years of follow-up.

Color Doppler imaging allows for simultaneous two-dimensional anatomic imaging and Doppler measurement of blood flow velocity. Because hemodynamic changes have been seen in diabetic patients after photocoagulation by other techniques, the authors compared 25 eyes with proliferative diabetic retinopathy before, 6 months after, 1 year after, and 2 years after panretinal photocoagulation with a matched control group of 30 healthy volunteers (55 eyes). The ophthalmic artery, short posterior ciliary artery, central retinal vessels, and vortex veins of all patients were examined, and the systolic, and diastolic, and mean arterial velocities were measured. Panretinal photocoagulation was performed with these parameters: 800-1000 spots, 0.1 second, 500-microns argon laser. Student's t test revealed that the perfusion velocity was significantly lower in diabetic patients than in healthy controls (V systolic in the ophthalmic artery: 31.7 +/- 6.7 cm/s vs. 36.6 +/- 7.0 cm/s, respectively, P = 0.03). After treatment, blood flow velocities were significantly lower than before photocoagulation (V systolic in the ophthalmic artery: 6 months after treatment, 26.9 +/- 7.2 cm/s, P = 0.018; 1 year after photocoagulation, 25.5 +/- 7.0 cm/s, P = 0.009; and 2 years after photocoagulation, 25.7 +/- 6.8 cm/s, P = 0.01). No statistically significant differences were found between 6 months, 1 year, and 2 years after panretinal photocoagulation. No significant correlations were found between patient age and blood velocities in diabetics and healthy volunteers. Eyes with proliferative diabetic retinopathy showed lower ocular perfusion velocities than controls. Photocoagulation resulted in a reduction in ocular blood flow velocities; these values did not change during 2 years of follow-up.

Evaluation of the extent and timing of the coronary hyperemic response to dipyridamole: A study with transesophageal echocardiography and positron emission tomography with oxygen 15 water

Coronary flow reserve may be measured with Doppler-derived coronary blood-flow velocity or scintigraphic assessment of myocardial perfusion. The purpose of this study was to compare coronary flow velocity and perfusion measures of flow reserve with respect to their extent and time course. Coronary flow velocity reserve in the proximal left anterior descending coronary artery measured by pulsed-wave Doppler at transesophageal echocardiography, with measures of perfusion reserve obtained in the corresponding territory, were measured by a standard O15 water technique at positron emission tomography. Eighteen male volunteers underwent both tests on different days in random order, with dipyridamole stress (0.56 mg/kg). After correction of resting flow and perfusion measurements to a standard cardiac workload (to compensate for heterogeneity in hemodynamics between the two studies), coronary flow reserve was calculated as the ratio between dipyridamoleand corrected resting flow. The uncorrected perfusion reserve measured by positron emission tomography was 3.7 +/- 1.2, compared with a corrected perfusion reserve of 2.3 +/- 0.7. This correlated with a corrected flow velocity reserve of 2.9 +/- 1.0 at transesophageal echocardiography (R = 0.92; p < 0.001). The mean difference between these results was 0.58 +/- 0.41; discrepant results occurred at higher flows, in the presence of discordant blood pressure responses to stress, and because of intersubject variations in the timing of the peak coronary flow response, which were detected by continuous monitoring at transesophageal echocardiography. Measurement of coronary flow reserve at transesophageal echocardiography correlates well with measurements at positron emission tomography, and discrepancies are minimized if measurements are taken at the same time after dipyridamole.

Carbon monoxide: an endogenous modulator of sinusoidal tone in the perfused rat liver.

Heme oxygenase is a heme-oxidizing enzyme which generates biliverdin and carbon monoxide (CO). The present study was designed to elucidate whether CO endogenously produced by this enzyme serves as an active vasorelaxant in the hepatic microcirculation. Microvasculature of the isolated perfused rat liver was visualized by dual-color digital microfluorography to alternately monitor sinusoidal lining and fat-storing Ito cells. In the control liver, the CO flux in the venous effluent ranged at 0.7 nmol/min per gram of liver. Administration of a heme oxygenase inhibitor zinc protoporphyrin IX (1 microM) eliminated the baseline CO generation, and the vascular resistance exhibited a 30% elevation concurrent with discrete patterns of constriction in sinusoids and reduction of the sinusoidal perfusion velocity. The major sites of the constriction corresponded to local sinusoidal segments colocalized with Ito cell which were identified by imaging their vitamin A autofluorescence. The increase in the vascular resistance and sinusoidal constriction were attenuated significantly by adding CO (1 microM) or a cGMP analogue 8-bromo-cGMP (1 microM) in the perfusate. From these findings, we propose that CO can function as an endogenous modulator of hepatic sinusoidal perfusion through a relaxing mechanism involving Ito cells.

Prostaglandin modulation of the gastric vasculature and mucosal integrity in cirrhotic rats

Gastric bleeding is a frequent occurrence in cirrhotic patients and may be related to altered microcirculatory responses to luminal irritants and/or vasoactive mediators. Because gastric prostaglandin synthesis has been reported to be altered in cirrhosis, we have examined the role of prostaglandins in modulating gastric perfusion velocity and mucosal integrity in cirrhotic rats. Cirrhosis was induced by bile duct ligation. Gastric perfusion velocity was measured in an ex vivo gastric chamber preparation by laser-Doppler flowmetry. The responsiveness of the mucosa to topical application of 20% ethanol was assessed. Effects of pretreatment with indomethacin or misoprostol were also determined. Gastric and hepatic prostaglandin E2 syntheses were significantly depressed (by approximately 60%) in cirrhotic vs. normal rats. Administration of indomethacin (7.5 mg/kg) to normal rats did not significantly affect gastric perfusion velocity, but in cirrhotic rats it caused a 45% reduction (P < 0.05). Topically applied misoprostol produced significantly greater (2- to 5-fold) increases in gastric perfusion velocity in cirrhotics than in controls. Cirrhotic rats were significantly more susceptible to gastric injury induced by topically applied 20% ethanol than were controls. These results suggest that gastric perfusion velocity in cirrhotic rats is modulated by endogenous prostaglandins to a much greater degree than in controls. Gastric vascular hyperresponsiveness to misoprostol may be attributable to an adaptive response to depressed endogenous prostaglandin synthesis in the cirrhotic animals.

Hypoxia Increases Velocity of Blood Flow through Parenchymal Microvascular Systems in Rat Brain

The postulation that hypoxia increases local cerebral blood flow (lCBF) mainly by perfusing more capillaries (the capillary recruitment hypothesis) was tested in awake adult male Sprague-Dawley rats exposed to 10% O2 and control rats. The [14C]iodoantipyrine technique was used to measure lCBF. Local cerebral blood volume was determined by measuring plasma and red cell distribution spaces within the brain parenchyma with 125I-labeled serum albumin (RISA) and 55Fe-labeled red cells (RBC), respectively. Tissue radioactivity in 44 brain areas was estimated by quantitative autoradiography. Hypoxia raised lCBF by 25-90% in all brain areas. In about one-quarter of the brain areas, the rise in blood flow was associated with a small increase in microvascular plasma and blood volumes. This change in blood volume, which could be the result of perfusing more parenchymal microvessels and/or increasing parenchymal microvessel diameter, is not sufficient to account for the observed rise in lCBF. In the remaining areas the RISA, RBC, and blood spaces were either unchanged or only marginally increased by hypoxia. For this hypoxic perturbation, the major mechanism of raising blood flow appears to be increased velocity of microvessel perfusion and not perfusion of more capillaries. These findings provide only limited support for the capillary recruitment hypothesis.

A perfusion system for preparing the victim and the ischemic limb for reimplantation

We have developed and tested an original perfusion system for rapid and effect ive simultaneous preparation of the victim and the traumatically amputated limb, after a long period of ischemia, for reimplantation. The extracorporeal circuit of the circulatory system (Fig. 1) includes the main drainage channels 3 and 6, reservoirs for holding the perfusion fluid 7 and 14, peristaltic (roller) pumps 8 and 15, a column 9 containing the hemosorbent, a low-output membrane oxygenator with heat exchanger (LMO-HE) (International Standard) 10, the isolated donor's spleen 11, an ultraviolet source (UVS) 12 for irradiating the blood, the rotor of the RK-0.5 blood fractionator 13, and transducers for measuring perfusion pressure 16 and temperature 17 and 18. During development of the system we initially assumed that the hemosorbent and living isolated hepatocytes can temporarily perform the detoxicating function of the liver. Besides this function, hepatocytes utilize toxic substrates of lipoprotein complexes, which are essential for the restoration of disturbed metabolic processes (aerobic oxidation, etc.) in cells. The action of the donor's spleen, UV irradiation, the AUVM-Dnepr -MN-1 activated carbon fiber adsorbent, and of dioxidine was aimed at neutralizing the damaging action of microorganisms and leading to their elimination. In addition, the UVS stimulates processes of energy metabolism and oxidative phosphorylation, as well as transmembrane mass exchange in isolated hepatocytes, and this must unquestionably make the working of the whole system more efficient. The perfusion medium was obtained by diluting whole blood by one-third of its volume with native plasma, and also by adding heparin in a dose of 5000 U and 30 mi of a 1% solution of dioxidine for every 400 ml of fluid. The final hematoerit reading of the perfusion fluid was 28-32%. The extracorporeal circulation was filled with perfusion fluid, the volume of which corresponded to the mass of the amputated limb (1:1). The temperature of the perfusion fluid entering the main artery was 37"C, the perfusion pressure was 70-80 mm Hg, and the volume velocity of regional perfusion was 40-60 ml/(min.kg). The pO 2 of the perfusion fluid entering the arterial system of the amputated limb fluctuated from 160 to 300 mm Hg. The duration of isolated regional perfusion of the amputated limb and of the limb stump below the tourniquet was 1 h. The AUVM-Dnepr -MN-I activated carbon-f iber adsorbent, soaked with 1% dioxidine solution, was applied to the infected wound surface of the amputated limb. The extracorporeal system (Fig. 1) works in the following way. Perfusion fluid draining from the veins of the limb and stump enters the first reservoir 7, which may be equipped with a volume self-regulator, and it is pumped from the reservoir by the pump 8, through the column 9, which has a volume of 100-250 ml, and which is filled with hemosorbent ( S K N I K or SKN-2K) . Next, at the rate of 30-40 ml/min the perfusion fluid passes through the blood chamber of the LMO-HE (International Standard) chamber 10, where it is saturated with oxygen and heated. The perfusion fluid then passes through the regional vascular bed of the isolated donor's spleen 11 and, passing through the UV source 12, it enters the rotor 13 of the RK-0.5 blood fractionator, containing 100-350 ml of a dense suspension of hepatoeytes. The speed of rotation of the rotor is 600-800 rpm. The design of the RK-0.5 rotor is intended to ensure direct contact between the flowing perfusion fluid and hepatocytes. After the rotor the perfusion fluid drains into the second reservoir 14, which may be equipped likewise with a servo-operated volume regulator. From the reservoir the perfusion fluid is pumped by the roller pump 15 into the arteries of the isolated limb and stump. Isolated living xenogeneic hepatocytes were isolated by a combined enzymic-mechanical method [1, 2]. During regional perfusion of the limb, a dense suspension of hepatocytes containing 2 x 108 cells in 10 mi was used. Hepatocytes kept in the extracorporeal circuit by centrifugal force or by capsules of semipermeable membrane functioned actively on direct contact with the perfusion fluid throughout the period of perfusion (results of electron-

Transcranial Doppler Monitoring of Cerebral Flow Velocities during Surgical Occlusion of the Carotid Artery

Abstract Transcranial Doppler (TCD) was used to assess collateral flow and to quantitate perfusion velocity changes in a group of 18 patients requiring temporary or permanent surgical occlusion of the internal carotid artery for treatment of their cerebrovascular lesions. Velocity measurements were correlated with times of occlusion and neurological outcome in order to assess safe vessel occlusion times and the need for an intraoperative shunt. These data were used to calculate a perfusion velocity index (PVi), which indicated that values &amp;gt;2 were well tolerated, and values of &amp;lt;1 were associated with ischemic signs. In addition, preoperative TCD examinations were combined with compressive maneuvers of the carotid artery in the neck to evaluate the feasibility of carotid clamp ligation for the treatment of giant intracranial aneurysms deemed unsuitable for direct clipping. When maintenance of neurological function and intracranial vessel flow velocities were found to be normal, with aneurysmal flow velocities of zero, ligation of the carotid artery could safely be undertaken. Finally, TCD allowed continuous surveillance of cerebral hemodynamics, which gave immediate assurance of postoperative ICA patency, as well as the ability to identify high velocity states associated with hyperperfusion syndromes, which occurred in two patients.

Transcranial Doppler monitoring of cerebral flow velocities during surgical occlusion of the carotid artery.

Transcranial Doppler (TCD) was used to assess collateral flow and to quantitate perfusion velocity changes in a group of 18 patients requiring temporary or permanent surgical occlusion of the internal carotid artery for treatment of their cerebrovascular lesions. Velocity measurements were correlated with times of occlusion and neurological outcome in order to assess safe vessel occlusion times and the need for an intraoperative shunt. These data were used to calculate a perfusion velocity index (PVi), which indicated that values greater than 2 were well tolerated, and values of less than 1 were associated with ischemic signs. In addition, preoperative TCD examinations were combined with compressive maneuvers of the carotid artery in the neck to evaluate the feasibility of carotid clamp ligation for the treatment of giant intracranial aneurysms deemed unsuitable for direct clipping. When maintenance of neurological function and intracranial vessel flow velocities were found to be normal, with aneurysmal flow velocities of zero, ligation of the carotid artery could safely be undertaken. Finally, TCD allowed continuous surveillance of cerebral hemodynamics, which gave immediate assurance of postoperative ICA patency, as well as the ability to identify high velocity states associated with hyperperfusion syndromes, which occurred in two patients.

Tube flow of human blood at near zero shear.

Pressure-velocity relations were obtained in vertical and horizontal glass tubes (I.D. 26 to 83 micron) perfused with normal human blood at feed hematocrits between 0.25 and 0.65. Perfusion pressures used corresponded to wall shear stresses up to 0.27 dyn cm-2. Red cell velocity measurements were made both immediately following implementation of perfusion pressure (with red cells still disaggregated) and in a steady state situation (with red cells aggregated). Analysis of the slopes of the linear relations between perfusion pressure and velocity showed apparent viscosity to decrease with the manifestation of red cell aggregation. In horizontal tubes, sedimentation and aggregation occurred simultaneously, and apparent viscosity increased due to axial asymmetry of cell concentration. Evidence for a yield shear stress (flow stagnation at positive driving pressure) was not observed.

Factors Influencing Development and Survival of Pacific Herring (Clupea harengus pallasi) Eggs and Larvae to Beginning of Exogenous Feeding

The euryplastic Pacific herring (Clupea harengus pallasi) generally encounters temperatures ranging between 0 and 10 °C throughout its distribution during the maturation and spawning of adults, incubation of eggs, and hatching of larvae. For many Asian stocks these events occur in the lower half of the temperature range; with North American stocks they tend to occur in the upper half of the range. In British Columbia waters, salinities associated with these events (range, optimum) are spawning (2.6–28.7‰, 27–28.7‰), [Formula: see text] fertilization of eggs (4.5–42‰, 12–15‰), and maximum total hatch and hatch of viable larvae (4.5–42‰, 12–17‰). A low/low–high/high interaction between salinity and temperature also influences total hatch, hatch of viable larvae, and salinity tolerance of larvae. In addition, the following implications arise regarding aspects of the Pacific herring reproductive cycle, based on previously published and new data, and on speculative inference. The response of Pacific herring to salinity and temperature appears to have a commanding influence on the reproductive cycle and, thereby, on distribution of the species. Survival of eggs on substrate, related to respiratory activity, appears to be influenced by the transport and perfusion velocity of interstitial water in an egg mass. Such transport may involve perivitelline fluid colloid osmotic pressure; natural convection; the surge associated with wave action, beach slope, and depth; and possibly differences in resistance to convective flow of deoxygenated water from an egg mass based on orientation of the substrate. These relations would be modified by variations in deposition intensity (number of egg layers) and packing density (eggs per unit volume), and both factors may affect survival of occluded eggs in an egg mass differentially, depending on the substrate used. A review of data on salinity tolerance of herring larvae indicates that a variety of dosage-mortality techiques has been used, leading to noncomparable estimates of response. An assessment of upper incipient lethal salinities will require standardization of such techniques. Recent studies show that salinity tolerance of larvae is influenced significantly by salinity–temperature conditions during egg incubation. At usual incubation conditions in British Columbia waters, the upper boundary of larval tolerance is estimated as 27.5–31.7‰ S (72-h LC10). depending on incubation history. The fate of Pacific herring larvae carried into the higher salinities of offshore waters has been controversial. In the Strait of Georgia, British Columbia, substantial offshore dispersion of larvae occurs where surface conditions generally are 27–28.6‰ and 9–10 °C in the early larval period. Although these salinities are near the upper boundary of salinity tolerance, larvae sampled in offshore waters (1981) had an apparent mean age of 15 d and were actively feeding and growing. From rates of disappearance of larvae in the offshore waters (9% wk) and inshore waters (45% wk) we conclude that usual surface salinities and food supply in the open waters of the Strait were not a dominant influence on larval survival. Assuming the larvae remain in the upper 10 m, we suspect their disappearance, at least offshore, to be largely the result of predation.