Search PubMed⌕ Search

Biomedical subjects

B Klitzman

Publications and source records attributed to B Klitzman.

At least 55 records · Page 3Linked to original sources
PubMed1993

Patency and blood flow in gas denucleated arterial prostheses.

Biomaterials exposed to blood often fail due to thrombosis. Gas nuclei (air) in the material are thrombogenic and a potential cause of failure. The effects of gas nuclei on patency and blood flow were studied in 4 mm diameter arterial grafts (Gore ePTFE; Johnson and Johnson Vitagraft ePTFE; Bard ACG EXS) in the femoropopliteal position of dogs. Control and denucleated (air-free) grafts were implanted bilaterally. Grafts were denucleated by immersion in degassed saline and exposure to 4 torr vacuum and 3,000-20,000 psig pressure. Graft patency was determined at harvest in 46 dogs. Blood flow was measured with acoustic flow probes in eight dogs. Denucleated graft patency was 60% after 2 days of implant while control patency was 22% (P < .05). Measured blood flow was higher in denucleated grafts than in control grafts (P < .02) in 4 of 5 dogs which had significantly different flows. Patency and flow decreased to zero for both control and denucleated grafts over periods of up to 80 days. Air in the control grafts may have been absorbed within several days, leading to late similarity with the denucleated grafts. Thus, removing the air from 4 mm ePTFE grafts decreased acute thrombosis and increased the patency.

Animals↗
PubMed1993

Quantification of in vitro endothelial cell adhesion to vascular graft material.

This study tests the hypothesis that denucleating vascular graft material and binding cell adhesion molecules increases endothelial attachment. Removal of gas nuclei (denucleation) increases the available surface area of biomaterials for modification and/or cell adhesion, while adhesion molecules provide specific attachment sites. Microvascular endothelial cells (MVEC) were isolated from fat, fluorescently labeled, and allowed to settle onto expanded polytetrafluoroethylene (ePTFE) vascular patches. Patch treatments included fibronectin alone (F), gas denucleation followed by fibronectin (D/F), denucleation followed by the surfactant tridodecylmethylammonium chloride (TDMAC) (D/T), denucleation followed by TDMAC followed by fibronectin (D/T/F), or denucleation followed by TDMAC followed by a synthetic polymer with numerous arginine-glycine-aspartic acid sequences (D/T/R). After 1 h of incubation, the 45 mm2 patch area covered with microvascular endothelial cells was assessed using computer-aided fluorescence microscopy. Initial graft coverage with D/T (26.2 +/- 2.4 mm2) and D/T/F (25.9 +/- 2.1 mm2) was better than with F (16.8 +/- 2.5 mm2) (P < .05). Patches were then exposed to a detachment stress and coverage was again measured. Following stress, coverage was greater with D/T (20.7 +/- 3.4 mm2) and D/T/F (20.7 +/- 2.0 mm2) than with D/T/R (8.4 +/- 1.8 mm2) or F (3.6 +/- 0.9 mm2) (P < .001). Percent retention of cells following stress was better with D/T and D/T/F than with D/T/R, D/F, or F (P < .0001). Scanning electron micrographs were consistent with the qualitative findings. The results indicate that TDMAC alone or with fibronectin increases adhesion of human microvascular endothelial cells to denucleated ePTFE.

Amino Acid Sequence↗
PubMed1993

Measurement of material extravasation in microvascular networks using fluorescence video-microscopy.

We have developed a new method using fluorescence videomicroscopy to quantitate the extravasation of intravenously injected materials. This method can measure the relative plasma concentration of, and the vascular permeability to, these materials in microcirculatory preparations which contain multiple blood vessels in a field of view. The image of a tissue area containing multiple blood vessels is recorded via a SIT camera immediately before, and for an extended period after, the intravenous injection of a bolus of fluorescent test tracers. The videotape is analyzed off-line. At various time points, the light intensities of the entire tissue area and of several spots over selected vessels are measured. These measurements are then used to calculate the fluorescent light intensities arising from the tracers inside vessels (Iv) and in the interstitial region (Ii). Iv represents the relative amount of the tracers in the plasma, and Ii represents that in the interstitium. Iv and Ii are used to calculate an average permeability (P) for the vessels in the observed region. The benefit of this method is that it can be used to compare permeability of various tissues of interest or to serially evaluate changes in P in the same tissue over time. In this study, it was applied to measuring P to albumin as well as to liposomes in granulating and implanted tumor tissues in a rat skin flap window chamber. Changes in permeability to a small molecule (sulforhodamine B) before and during bradykinin application were also measured. The results of these experiments indicate that the relative plasma concentrations predicted by this method conformed well to those measured directly from blood samples, and the measured permeability values were consistent with previously published data. Therefore, this method provides a valid approach for quantitatively measuring the extravasation of intravenously injected molecular and colloidal materials in microcirculatory preparations. The method has a set of defined experimental conditions and assumptions that cannot be violated, however, or erroneous results can be obtained.

Animals↗
PubMed1993

Tissue oxygenation and blood flow on specialized and conventional hospital beds.

Despite the widespread use of specialty bed products, the physiological mechanism of their benefit has not been evaluated. In this study, healthy subjects were used to study transcutaneous oxygen tension (TcPo2) and laser Doppler blood flow in pressure sore-prone areas on air-fluidized, low-air-loss, and adjustable air-mattress beds relative to a standard hospital mattress with and without an egg-crate mattress overlay. Measurements were obtained over the sacrum with the subject in the prone and supine positions, and over a greater trochanter with the subject in the prone and 90-degree lateral positions. Our results on healthy volunteers suggest that the specialty bed products maintain TcPo2 better than a standard bed when tissue is weighted. Further, the Clinitron had significantly higher TcPo2 when weighted than each of the other beds. Laser Doppler blood flow was much more variable. The weighted trochanter on the standard bed had the lowest blood flow, which is consistent with the TcPo2 readings. However, the variability made the laser Doppler flow data less valuable than the TcPo2. In conclusion, these data indicate that several products, particularly the Clinitron, maintain TcPo2 of weight-bearing tissue, which may be an important mechanism in protecting against pressure sores.

Beds↗
PubMed1992

Diminished leukocyte-endothelium interaction in tumor microvessels.

Leukocyte-endothelium interaction in vivo consists of the rolling of leukocytes along the vascular wall and, under certain conditions, their adherence to endothelial cells. In a rat tumor microcirculation model (mammary adenocarcinoma implanted in rat skinfold window chamber), we demonstrated that this interaction, measured as flux of rolling leukocytes and density of adhering leukocytes, was significantly reduced in tumor microvessels compared to normal microvessels, both under control conditions and during inflammation induced by N-formylmethionylleucylphenylalanine (1 microM), bacterial lipopolysaccharide (1 microgram/ml), or tumor necrosis factor alpha (500 units/ml). We also measured the blood flow shear rate in the tumor and normal microvessels and found that the difference in shear rate between the two types of microvessels could not account for the differences in leukocyte-endothelium interaction. The diminished leukocyte-endothelium interaction in tumors under various stimulated conditions suggests that a number of adhesion molecules may not be expressed properly on tumor endothelial cells.

Adenocarcinoma↗
PubMed1992

Effects of chronic hypoxia on capillary flow and hematocrit in rat skeletal muscle.

The cremasteric microcirculation was studied in rats exposed to chronic hypoxia. Control male weanling Sprague-Dawley rats (n = 8) were raised for 42-49 days at 752 mmHg. Hypoxic rats (n = 9) were reared for 3 days at 551 mmHg, 4 days at 461 mmHg, 3 days at 371 mmHg, and 31-38 days at 311 mmHg (6,000 m). Red blood cells labeled with fluorescein isothiocyanate were injected. The exposed cremaster was observed using fluorescence microscopy. Rats acutely breathed 10, 21, and 30% O2 spontaneously in random order. Hypoxia-adapted animals had greater (P less than 0.01) red cell flux (10.6 +/- 1.0 vs. 5.7 +/- 0.4/s), capillary hematocrits, capillary-to-systemic hematocrit ratios (0.42 +/- 0.02 vs. 0.33 +/- 0.02), and reduced red cell spacing (11.4 +/- 1.3 vs. 22.3 +/- 2.0 microns) than controls under 21% O2. Chronically hypoxic rats also demonstrated significantly (P less than 0.05) larger capillary diameters (6.52 +/- 0.04 vs. 6.15 +/- 0.06 microns) and greater perfused (135 +/- 5 vs. 94 +/- 3 mm/mm3) and anatomic (182 +/- 5 vs. 151 +/- 8 mm/mm3) microvessel length-densities at 21% O2. Results were generally similar for 10 and 30% O2. Bulk capillary blood flow was significantly (P less than 0.01) greater in controls (2.75 +/- 0.32 vs. 1.87 +/- 0.12 pl/s) only under 30% O2. Our experiments demonstrate that numerous physiological, in addition to anatomic, alterations can occur in the cremasteric microcirculation in response to chronic hypoxia.

Adaptation, Physiological↗
PubMed1992

Effects of the calcium channel blocker flunarizine on the hemodynamics and oxygenation of tumor microvasculature.

Flunarizine is a diphenylpiperazine calcium entry blocker that has been shown previously to increase tumor blood flow and sensitivity to radiotherapy via reduction in the radiobiologically significant hypoxic fraction. Two mechanisms of action have been proposed previously (vasodilation, altered blood viscosity), but no studies have been performed to examine its mechanisms of action in vivo. Such information would be invaluable in determining the role of flunarizine in multimodality approaches to reduce tumor hypoxia. Fisher-344 rats bearing R3230Ac tumors transplanted into dorsal flap window chambers were used to examine microcirculatory changes after administration of flunarizine (1.0 mg/kg, iv). The drug increased the diameters of the microvasculature and red cell velocities specifically in central tumor regions (producing an average increase in vessel flow by a factor of 1.96), which was accompanied by an increase in perivascular pO2 of 12 mm Hg, on the average. The drug did not change the diameters of tumor "feeding" vessels, nor did it change vascular length densities. Thus the improvement in central tumor blood flow and oxygenation could not be attributed to dilation of feeding vessels. The oxygen-carrying capacity of the blood was not altered either since hemoglobin saturation (measured in vitro) and the hematocrits of the microvasculature were unchanged after drug administration. Therefore, by a process of elimination, the most likely explanation for the effect of the drug is modification of blood viscosity. Additional studies are under way in this laboratory to examine whether changes in viscosity occur after flunarizine administration.

Adenocarcinoma↗
PubMed1992

Perivascular oxygen tensions in a transplantable mammary tumor growing in a dorsal flap window chamber.

Fischer 344 rats with R3230 Ac mammary carcinomas implanted in dorsal flap window chambers served as a model to obtain measurements of perivascular and stromal oxygen tension in normal and tumor tissues using Whalen recessed-tip microelectrodes (3- to 6-microns tip). Perivascular measurements were made adjacent to vessels with continuous blood flow. Thus the measurements and models provided are reflective of conditions leading to chronic hypoxia. Perivascular oxygen tensions averaged 72 +/- 13 mmHg in normal tissue vessels adjacent to tumor, 26 +/- 5 mmHg in tumor periphery, and 12 +/- 3 mmHg in tumor central vessels. There was a significant trend toward lower perivascular oxygen tensions in the tumor center (Kruskal-Wallis test, P = 0.002). A similar tendency was seen with a limited number of stromal measurements. Krogh cylinder models, which incorporate these data for perivascular oxygen tension, along with morphometric data obtained from the same tumor model suggest that hypoxic regions will exist between tumor vessels in the tumor center unless O2 consumption rates are well below 0.6 ml/100 g/min. The low perivascular measurements observed near the tumor center combined with the theoretical considerations suggest, for this model at least, that tissue oxygenation may best be improved by increasing red cell velocity and input pO2 and reducing oxygen consumption. The low perivascular oxygen tensions observed near the center also suggest that conditions conducive to increased red cell rigidity exist, that drugs which can decrease red cell rigidity could improve tumor blood flow and oxygenation, and that the endothelium of those vessels may be susceptible to hypoxia-reoxygenation injury.

Animals↗
PubMed1992

Effects of bradykinin on the hemodynamics of tumor and granulating normal tissue microvasculature.

Bradykinin (BK) is an important endogenous mediator of microvascular flow modulation. Since the structure of the microcirculation is very different in tumor tissues than in normal tissues, bradykinin may elicit different responses in tumors. This study was designed to test the hypothesis that local administration of bradykinin increases blood flow preferentially in normal tissue relative to adjacent tumor tissue, resulting in a "vascular steal" phenomenon. Microvessel diameters (D), velocities (Vc), length densities, shear rates, and intermittent flow frequencies were measured every 10 min before, during, and after 40 min exposure to BK in rats with dorsal flap window chambers 9 days after tumor implantation. Separate studies were made of normal vessels outside the tumor margin, the hypervascular tumor periphery, and the tumor center. Bradykinin was administered with a suffusion medium flowing over the tissue at 1-2 ml/min with a BK concentration of 1.6 x 10(7) M. Administration of BK created five distinct changes in normal and tumor vessel function that varied over time, but coincidentally reached a maximum effect after 20 min exposure to BK. In normal vessels, increased Vc and D led to increased flow, which reached a peak 20 min after onset of suffusion with BK. In contrast, in centrally located tumor vessels, decreased D and Vc were observed in most vessels during the initial 10-20 min of suffusion. In addition, there was a significant increase in intermittent flow frequency in tumor central vessels, which peaked after 20 min of suffusion with BK. These five separate observations that coincided at 20 min of suffusion are consistent with a "vascular steal" phenomenon. The increase in normal microvessel D and Vc at 20 min suggests that BK causes vasodilation in arterioles. The coincident decrease in tumor microvessel D and Vc suggests that tumor feeding vessels are less able to respond to BK by vasodilating. The concomitant increase in intermittent flow frequency in tumor vessels suggests that a reduction in pressure drop occurred after 20 min exposure to BK, which is also consistent with "vascular steal." Since BK is also known to increase vascular permeability, it is possible that increases in interstitial fluid pressure brought on by exposure to BK contributed to the observed reduction in tumor blood flow. In normal vessels, reduced D and Vc, relative to peak values, were noted after 40 min suffusion with BK. Adherence of leukocytes to the vessel walls was prominent and microthrombi were also observed during this period. No evidence of such adhesion was seen in tumor vessels, although microthrombi were observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenocarcinoma↗
PubMed1991

Quantification of gas denucleation and thrombogenicity of vascular grafts.

In vitro methods were developed to measure the air content of vascular graft walls and the thrombogenicity of this air. Gas content (volume %) of expanded polytetrafluoroethylene (ePTFE) grafts from different sources ranged from 75.5 +/- 0.4% to 61.8 +/- 0.3%. Exposure of Vitagraft ePTFE to a vacuum prior to saline immersion replaced 87.5% of the gas nuclei with saline (denucleation). Acetone and ethanol immersion produced 98.9% and 94.3% denucleation, respectively. Denucleation was essentially complete when vacuum exposure was followed by hydrostatic pressure treatment at 500 psig or greater. The influence of gas content on thrombogenicity was determined by immersing graft samples in whole canine blood and weighing the adherent thrombus. Denucleation significantly reduced adherent thrombus weight compared with control grafts (p less than 0.001). Air in Vitagraft walls was responsible for 84% of the adherent thrombus weight at four minutes. The described methods could be employed to assess the hemocompatibility of various biomaterials.

Adhesiveness↗
PubMed1991

Establishment of normal ranges of laser Doppler blood flow in autologous tissue transplants.

Over a 3-year period, 136 patients were monitored following free autologous tissue transplantation using a laser Doppler flowmeter linked to a computerized data-acquisition system. This monitoring system has indicated perfusion compromise in free flaps more rapidly than clinical observation alone. Most important, this has resulted in an increase in salvage rate from 50.0 to 82.4 percent. In addition, our overall success rate has increased from 92.6 to 97.8 percent since introducing this monitor clinically. Computerization also has facilitated the collection of data, which has enabled us to establish expected values for postoperative blood flow in several types of donor tissues used for microvascular reconstruction. Finally, this computerized monitoring system has relieved personnel from basing decisions on subjective data.

Adult↗
PubMed1991

Reconstruction of rat femoral veins with microvascular prostheses.

Synthetic conduits have not been suitable for microvascular reconstruction owing primarily to their high thrombogenicity. Vein replacements are the most vulnerable to thrombosis because of their low shear rates and low pressure. Experimental replacement of microvenous segments with prosthetic segments has shown little success. Recent technological advances in biomaterials and control of thrombogenesis provide the potential for success in the development of venous prostheses. The purpose of this study was to assess the use of nonbiodegradable composite polyurethane microvascular prostheses for reconstruction of rat femoral veins. Rat femoral venous defects of 10 mm were reconstructed with autogenous vein (n = 12), unprocessed plain polyurethane (n = 5), and nonbiodegradable composite polyurethane (n = 31). Patency was evaluated by direct observation and proximal venous milking tests. The patency rate of composite grafts was not significantly different from that of isotopic vein (p = 0.5, Fisher's exact test), and both had higher patency than unprocessed polyurethane (p less than 0.01). Composite grafts were examined sequentially using light and scanning electron microscopy. Grafts were fully endothelialized between the first and third months. The neointimal, neomedial, and neoadventitial layers could be seen more distinctly over time. New opportunities in reconstructive microsurgery may be opened by microvascular prostheses that are complaint and thromboresistant.

Animals↗
PubMed1990

Quantification of neutrophil adhesion to skeletal muscle venules following ischemia-reperfusion.

Ischemia-reperfusion is encountered in a wide variety of surgical situations. The damage resulting from ischemia-reperfusion may be due, in part, to the infiltration and activation of neutrophils into the reperfused tissue. The purpose of the study was to examine ischemia-reperfusion induced neutrophil activation in skeletal muscle. In control muscles, ischemia in the hamster right cremaster muscle was produced for 5 min after an initial 2 hr 55 min perfusion period. In ischemic muscles, ischemia was produced for 3 hr prior to reperfusion. After the clamps were removed, a video recording of the cremaster microvasculature was made using intravital fluorescence microscopy. Acridine orange was infused intravenously 10 min prior to video recording in order to selectively label and enhance the contrast of neutrophils. The number of neutrophils rolling along the endothelium of 40 to 60 microns-diameter venules in a 1-min period increased from 9.0 in control animal cremaster venules to 24.1 following ischemia-reperfusion (p less than .05; n = 11). The ischemia-reperfusion model developed in this study allows for the direct quantification of neutrophil adhesion in skeletal muscle and can be further used to assess pharmacologic minimization of neutrophil-mediated damage in skeletal muscle.

Animals↗
PubMed1990

Acute difluoromethylornithine treatment increases skin flap survival in rats.

Difluoromethylornithine (DFMO) pretreatment for 7 days improved survival of rat abdominal skin flaps in previous studies. The purpose of this study was to determine if acute administration of DFMO enhances survival. Each rat had a 7 x 7-cm abdominal skin flap raised on a single epigastric neurovascular pedicle. Within 1 minute of pedicle ligation, the rats were given 0, 1, or 4 gm/kg of body weight of DFMO intraperitoneally. Putrescine was administered to additional rats alone or with DFMO. After 48 hours, the percentage of flap survival was estimated using fluorescein injection and planimetry to quantify the perfused and unperfused areas. Flap survival increased from 71 +/- 3% in controls to 83 +/- 2% and 92 +/- 3% in rats treated with 1 and 4 gm/kg of DFMO, respectively (p less than 0.005). Putrescine reversed the protective effect of DFMO, suggesting a specific polyamine-related mechanism. This study indicates that there may be both short- and long-term polyamine pools through which DFMO acts. In summary, DFMO may prove to be important in preventing cell death following acute ischemia.

Animals↗
PubMed1990

Toxic effects of catecholamines on skin.

The purpose of this study was to examine the effects of catecholamines on skin necrosis independent of their vasoactive effects. Rat abdominal or human breast skin was excised, pinned flat, and incubated at 37 degrees C for 6 hours in a buffered salt solution containing catecholamine. At 0.1 and 6 hours the lactate dehydrogenase (LDH) released from the skin and appearing in the buffer was determined spectrophotometrically. All groups showed similar LDH levels at 0.1 hour. Rat skin treated with greater than or equal to 10(-7) M epinephrine (33 times less than the 1:200,000 used clinically) or greater than or equal to 10(-5) M norepinephrine showed a significant increase in the LDH released at 6 hours versus controls (18.75 +/- 1.25 versus 13.75 +/- 1.25 and 29.25 +/- 2.96 versus 22.00 +/- 1.96 IV, respectively). Total tissue LDH levels were not significantly different at 0.1 or 6 hours. The toxic effect of epinephrine was eliminated by the addition of propranolol or selective beta 2 blockade, but not by alpha or beta 1 blockade. Therefore, this effect appears to be mediated largely by beta 2 receptors. Similar toxic effects were seen in human breast skin treated with 1:200,000 epinephrine and were blocked with propranolol. Phenylephrine at 1:20,000 demonstrated toxicity, but angiotensin II and vasopressin did not. These studies indicate that addition of catecholamine to ischemic rat or human skin accelerates skin death within 6 hours, but that the toxicity can be reversed with beta blockade.

Angiotensin II↗
PubMed1990

Laser Doppler blood flow measurements of common cutaneous donor sites for reconstructive surgery.

The purpose of this study was to evaluate cutaneous blood flow in regions commonly used as donor sites in reconstructive surgery in order to better establish normal flow ranges. Flow was measured with the TSI Laserflo BPM 403 in 27 healthy volunteers and compared to the flow in uncomplicated postoperative autologous tissue transplants. The forehead produced the highest flow, with an average value of 6.50 +/- 0.31 (mean +/- SE), and the dorsalis pedis had the lowest flow, with an average value of 0.60 +/- 0.04. Gender differences were noted in the latissimus dorsi, pectoralis major, and rectus abdominis areas. There were no significant differences between smokers and nonsmokers, hand dominance, musculocutaneous and fasciocutaneous tissues, or supine and sitting body positions. Flow levels in volunteers were similar to those in postoperative surviving autologous tissue transplants. The site-specific flow and flow changes over long time periods (hours) have helped clinical monitoring of 77 patients in the last 24 months. In every case identified by the flowmeter as decreased perfusion, a definite etiology for low reduction was documented. Complications occurred in 12 patients, and the rate of salvaging compromised tissue has increased from 50 percent using temperature monitoring and clinical observation to 83 percent with the computerized laser Doppler flowmeter.

Blood Flow Velocity↗
PubMed1990

Stimulation of DNA synthesis in human epidermis by UVB radiation and its inhibition by difluoromethylornithine.

The purpose of this study was to determine whether the rate of DNA synthesis in human skin could be increased by UVB radiation and to determine the potential for reversing the stimulatory effects of UVB radiation by alpha-difluoromethylornithine (DFMO). Split-thickness facial skin was grafted onto athymic CD-1 Nu/Nu mice on the anterolateral dorsal surface. Following graft healing for 6 weeks, grafts were treated with 0%, 2%, or 5% DFMO (a potent inhibitor of polyamine biosynthesis) and subsequently irradiated with 0.15 J/cm2 of UVB light. Two days after UVB exposure, [3H]thymidine was injected and the grafts were dissected and counted. Ultraviolet radiation significantly increased thymidine incorporation, indicating increased DNA synthesis. The stimulatory effects of UV radiation were significantly reduced by topical application of 5% DFMO. Thus administration of DFMO most likely decreased the polyamine level and decreased the rate of DNA synthesis, which may have caused a decreased rate of epidermal proliferation. Thus the topical application of DFMO may prove beneficial for UVB exposure and other hyperproliferative states where a decrease in the rate of cell turnover might be desirable.

Aged↗