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Biomedical subjects

J Megerman

Publications and source records attributed to J Megerman.

50 records · Page 3Linked to original sources
PubMed1983

The effect of halothane anesthesia on platelet aggregation in vivo: decreased deposition on polytetrafluoroethylene arterial grafts in dogs.

The technique of gamma-imaging can be used to study the deposition of 111In-labeled platelets onto synthetic arterial grafts in vivo. Recent results suggested that platelet uptake on polytetrafluoroethylene (PTFE) grafts might depend on the choice of anesthetic. To evaluate the effect of anesthesia a series of experiments was performed in seven dogs wherein each animal served as its own control. The first of paired femoral or carotid PTFE grafts was inserted with the animal under pentobarbital anesthesia, and the graft was imaged for 90 minutes. A second graft was then inserted after at least 1 hour of halothane anesthesia. The mean activity ratio (describing platelet deposition) in the grafts inserted when only pentobarbital anesthesia was used was 7.04 +/- 0.55, compared to 1.20 +/- 0.07 in the grafts inserted with halothane anesthesia (P less than 0.01). Halothane anesthesia led to significantly decreased platelet uptake on canine PTFE arterial grafts. This effect was reversible, though not immediately, with no significant difference in graft activity noted by the day following surgery.

Anesthesia, Inhalation↗
PubMed1982

Current PTFE grafts: a biomechanical, scanning electron, and light microscopic evaluation.

Two currently available brands of PTFE grafts (Goretex and Impra) were studied in a canine femoral artery model to determine whether changes in the manufacturing processes of the two grafts, which increased their strength, had altered the biophysical properties and the histological reactivity of either graft. Both grafts were found to be similar except for differences in their suturability. Their in vivo dynamic compliances were almost identical (1.2 +/- 0.35 vs. 1.2 +/- 0.45). (Scanning electron microscopy showed endothelialization of the grafts only adjacent to the anastomoses, and light microscopy demonstrated similar degrees of histologic incorporation by the host tissues, though of slower tempo than that previously described. These results are examined and discussed with regard to the suitability of this model for characterizing new arterial prostheses of small to medium diameter.

Animals↗
PubMed1981

Polymerization of myosin from smooth muscle of the calf aorta.

Myosin from smooth muscle of the calf aorta has been found to be similar to rabbit skeletal muscle myosin in molecular weight, sedimentation coefficient, and amino acid composition. When dialyzed at low ionic strength, it also forms polymers that exist in equilibrium with the "monomer", the position of this equilibrium being sensitive to ionic strength, pH, and hydrostatic pressure. The self-association reactions for smooth muscle myosin differ, however, from those observed for skeletal muscle myosin in several ways: (1) aorta myosin polymerizes at a higher ionic strength to form a smaller polymer; (2) between pH 6 and 8, only one polymer boundary is observed; (3) the result of varying total protein concentration on the myosin-polymer equilibrium cannot be analyzed by the Gilbert theory for a simple two-species system, as was possible with skeletal myosin. This more complex polymerization behavior may be related to differences in the mode of assembly between smooth and skeletal muscle myosin.

Amino Acids↗
PubMed1981

Anatomic localization of atherosclerotic lesions by hemodynamic tests.

Use of noninvasive tests to assess the severity of lower-extremity occlusive lesions is generally accepted. To evaluate the effectiveness of noninvasive vascular-laboratory tests in locating atherosclerotic lesions, the results of hemodynamic studies in 100 patients were reviewed by both skilled observers and a vascular computer, and compared with angiograms. The results of the comparison suggest a remarkable sensitivity of the vascular-laboratory tests in locating significant arterial obstructions, and underscore that the great predictive value of a negative results gives the physician reliable information on the patency of a given arterial segment. Computer interpretation proved less accurate than that of the vascular-laboratory personnel.

Adult↗
PubMed1980

Matched elastic properties and successful arterial grafting.

Clinical results from medium- and small-caliber arterial bypass grafts are unsatisfactory. Since elastic properties of grafts tested experimentally have been correlated with patency results, the compliance of the human femoral artery was compared with grafts currently in use: human saphenous vein (HSV), knitted Dacron (DAC), glutaraldehyde-treated umbilical cord vein (DBM), bovine heterograft, and expanded polytetrafluoroethylene (PTFE). This was correlated with clinical patency data for the different conduits in the femoropopliteal position. Increased patency correlated with a decreasing disparity between host artery and graft compliance. After two years, patency rates of the more compliant materials (HSV, DBM) exceeded 80%, while less than 45% of the incompliant grafts (DAC, PTFE) remained patent. Thus, clinical performance with synthetic grafts might be improved by use of prostheses in which the viscoelastic characteristics match those of arteries more closely.

Actuarial Analysis↗
PubMed1980

Complementary methods for evaluating carotid stenosis: a biophysical basis for ocular pulse wave delays.

Attempts to noninvasively estimate the significance of carotid arterial stenoses have resulted in a recent technological explosion. Ocular pulse wave timing [oculoplethysmography (OPG) pulse delay] has been strongly promulgated but also criticized on theoretical grounds and for lack of physiologic validation. Audiofrequency analysis of carotid bruits (carotid phonoangiography CPA) has been combined with OPG allegedly to improve accuracy. To evaluate these methods in a controlled model, we studied the effects of graded unilateral stenoses in the canine carotid artery on physiological parameters and associated OPG and CPA recordings. Arterial compliance was calculated from simultaneous diameter and pressure recordings distal to the stenosis. OPG time delay correlated directly with reductions in flow and pressure and with increasing arterial compliance (P less than 0.01). Thus, the delay is caused at least partially by a decreased pulse wave velocity, resulting from the increased compliance distal to stenoses associated with a significant pressure gradient. OPG is most discriminating for stenoses of higher grades. Because bruits arise from flow disturbances that occur even with moderate degrees of stenosis, CPA provides diagnostic information before profound flow reduction occurs. This study illustrates the value of complementary methods for analyzing complex hemodynamic phenomena and provides evidence to support use of the pulse delay concept to diagnose arterial disease.

Angiography↗
PubMed1979

In vivo measurement of blood vessel wall thickness.

To understand the mechanical properties of arteries and vascular grafts, it is crucial that the wall thickness in these vessels be known. Unfortunately, all availble methods for measuring this parameter require the removal of the vessel, which precludes the study of such vessels as a function of time. A new radiographic technique for measuring the wall thickness of arteries and vascular grafts in vivo, utilizing contrast materials injected into the vessel lumen and applied to the outer surface of the vessel, is described. Radiographs are obtained with a portable X-ray machine and analyzed using a calibrated microscope. The technique has been successfully applied to the in vivo measurement of wall thickness in canine arteries, veins, and experimental vascular grafts. It is concluded that the method provides better than 95% accuracy in a variety of vessels and that it can be used to study changes in vascular grafts after their implantation into the arterial circulation.

Angiography↗
PubMed1977

Assembly of smooth muscle myosin into side-polar filaments.

The in vitro assembly of myosin purified from calf aorta muscle has been studied by electron microscopy. Two types of filament are formed: short bipolar filament similar to those formed from skeletal muscle myosin, and longer "side-polar" filaments having cross bridges with a single polarity along the entire length of one side and the opposite polarity along the other side. Unlike the case with skeletal myosin filaments, antiparallel interactions between myosin molecules occur along the whole length of side-polar filaments. The side-polar structure may be related to the in vivo form of myosin in vertebrate smooth muscle.

Animals↗
PubMed1975

Myosin from arterial smooth muscle: isolation following actin depolymerization.

The contractile proteins from arterial smooth muscle are highly soluble, and can be extracted at I = 0.05. However, they can be precipitated by a prolonged dialysis at pH 6 to give an actomyosin with a high, although variable, actin:myosin ratio. The sedimentation behavior of this actomyosin at high ionic strength was examined as a function of pH, protein concentration and composition by preparative ultracentrifugation. Comparisons with synthetic skeletal muscle actomyosins of similar composition demonstrated significant differences in the behaviors of these two systems. It was found that much smooth muscle actomyosin is not dissociated by normally relaxing conditions, and that it sediments at a slower rate than F-actin. The solubility of the supernatant protein (a myosin-enriched actomyosin) in 0.2 M K Cl (pH 7) depended on the pH during centrifugation. A lower solubility was associated only with a higher actin concentration in the supernatant, suggesting a dependence on actin repolymerization. Pure myosin was selectively precipitated from the supernatant by polyethylene glycol-6000, but only when the protein was soluble at low ionic strength. The solubility of purified myosin was similar to that of myosin from striated muscles. A relationship between the presence of depolymerized actin and the high solubility of smooth muscle contractile proteins is suggested.

Actins↗
PubMed1974

Force-generating capacity and contractile protein content of arterial smooth muscle.

After correction for extracellular space (40%) determined from electron micrographs, the maximum isometric force developed by strips prepared from the media of the hog carotid artery (2.2 x 10(6) dyn/cm(2)) can be extrapolated to give a value of 3.7 x 10(6) dyn/cm(2) for the smooth muscle component of the strip. Three independent estimates of the myosin content of the smooth muscle cells were made based on (a) exhaustive extraction and purification with estimates of preparative losses, (b) the myosin catalyzed ATPase activity of media homogenates, and (c) quantitative densitometry of the peaks containing myosin, actin, and tropomyosin after disk electrophoresis of sodium dodecyl sulfate-treated media homogenates. The results were consistent and gave a myosin content of 5-10 mg/g media, or 8-17 mg/g cell. Method (c) gave myosin:actin:tropomyosin weight ratios of 1:3.2:0.8. Although measured force developed by the smooth muscle cell exceeds that of mammalian striated muscle, the myosin content in smooth muscle is about five times lower. The actin content of smooth muscle is relatively high. The actin and myosin contents are consistent with thick and thin filament ratios observed in electron micrographs of vascular smooth muscle.

Actins↗
PubMedDate not supplied

In vivo determination of human arterial compliance: preliminary investigation of a new technique.

PURPOSE: To obtain more detailed information about the dynamic mechanical properties of human arteries in vivo, using a new technique based on intravascular ultrasound. (IVUS). METHODS: Arterial compliance was measured in the common and/or external iliac arteries of 6 patients using an IVUS device, concurrently obtained intraarterial pressure measurements, and a video motion analysis system. RESULTS: Compliance decreased with increasing vessel diameter and mean arterial pressure. Pre- and postangioplasty measurements were obtained in 2 patients but did not demonstrate a consistent change in compliance following angioplasty. CONCLUSION: We conclude that IVUS provides an accurate means for in vivo determination of human arterial compliance, the practical value of which needs to be established.

Adult↗
PubMedDate not supplied

New access device for hemodialysis.

A new subcutaneous device (Dialock; Biolink Corp., Middleboro, MA) provides vascular access to patients who currently require hemodialysis (HD). The device consists of a port-like valve, implanted subcutaneously below the clavicle, which provides a linear flow passage to two catheters placed in the right atrium via the jugular vein. The valve is accessed percutaneously with needle-cannulas that functionally convert the device to twin catheters for connecting the patient to the HD lines. Interdialytic patency is maintained using a standard heparin lock. The device has been implanted in 10 outpatients under local anesthesia, with almost immediate use for HD (median, 3 days) and has functioned successfully for more than 6 months (mean +/- SD, 4.0 +/- 1.7; > 400 dialysis sessions). Blood flows over 300 ml/min were consistently achieved (average, 320 +/- 50) with venous and arterial pressures of 197 +/- 42 mmHg and -241 +/- 31 mmHg, respectively. After 40 patient-months, condition of the needle puncture sites remains satisfactory. Four systemic infections have occurred in three patients; all have resolved without the need for device removal. There have been no infections at the puncture sites. One patient whose heparin lock was not changed for 23 days (for reasons unrelated to the device) required fibrin sheath stripping of his catheters. Patient and nurse acceptance has been excellent. The device may offer substantial improvement over conventional devices for HD access.

Adult↗
PubMedDate not supplied

Adjunctive antibiotic/anticoagulant lock therapy in the treatment of bacteremia associated with the use of a subcutaneously implanted hemodialysis access device.

To improve vascular access for hemodialysis, a new device (Dialock Hemodialysis Access System, Biolink Corporation, Middleboro, MA) has been developed. Implanted subcutaneously, the device is accessed by percutaneous puncture. Attached to the device are two catheters that are implanted into the superior vena cava or right atrium. Clinical results thus far have been promising. However, use of this device is not free from infectious complications. In the present pilot study, 25 maintenance hemodialysis patients were implanted with 26 Dialock devices. The incidence of bacteremia was 2.9/1,000 catheter days. In 14 episodes of bacteremia in 8 patients the infection was successfully treated with a combination of systemic antibiotic treatment and adjunctive antibiotic/anticoagulant lock therapy. The lock therapy entailed the instillation of both an antibiotic and an anticoagulant into the device. We believe that the antibiotic/anticoagulant lock technique is an effective, adjunctive therapeutic modality in the treatment of infections related to the use of indwelling vascular access devices.

Anti-Bacterial Agents↗