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S F Mohammad

Publications and source records attributed to S F Mohammad.

88 records · Page 5Linked to original sources
PubMedDate not supplied

Scaling of hemolysis in needles and catheters.

Hemolysis in clinical blood samples leads to inaccurate assay results and often to the need for repeated blood draws. In vitro experiments were conducted to determine the influence on hemolysis in phlebotomy needles and catheters of pressure difference, cannula diameter, and cannula material. Fresh blood from five human volunteers was forced from a syringe inside a pressurized chamber through 14, 18, and 22 gauge 304 stainless steel needles and polyurethane and Teflon catheters, all 40 mm long. Hemolysis was measured in the samples by a spectrophotometer. It was found that hemolysis increased with increases in pressure difference and cannula diameter and no consistent trend could be identified with regard to cannula material. The pressure differences required for significant hemolysis were above those typical of clinical venipuncture blood draws. While there was substantial variability among individuals, the hemolysis values scaled with exponent S = (t/t0)[(tau/tau0)-1]2, where t is the characteristic duration of shear, t0 is a time constant, tau is the wall shear stress, and tau0 is the wall shear stress threshold below which no hemolysis occurs. A hemolysis threshold including both time and shear stress was also defined for S = constant. The threshold implies that a threshold shear stress exists below which erythrocytes are not damaged for any length of exposure time, but that red cells may be damaged by an arbitrarily short period of exposure to sufficiently large shear stress.

Analysis of Variance↗
PubMedDate not supplied

Animal implantation results with the Utah-100 total artificial heart.

The Utah-100 total artificial heart was designed to have increased reliability over the Jarvik-7 total artificial heart, achieve better fit, and minimize device associated thrombus formation, without decreasing the function. The Utah-100 heart was tested in 28 calves and 3 sheep. The smallest animal at the time of implantation weighted 54 kg. Mean survival duration was 78 days (range, 1-331 days), with 14 animals surviving longer than 60 days. Multiple organ function was maintained satisfactorily with the Utah-100 artificial heart, and mean plasma free hemoglobin values in the calves that survived longer than 100 days were less than 10 mg/dl. Hemorrhage was the main cause of death in animals dying within 30 days after implantation (5/13, 38%); infection was another primary cause of death or termination (4/31, 13%). Deaths due to mechanical failure occurred from valve or diaphragm failure in two cases, yielding a 91% reliability at a 90% confidence level for 60 days' support. No animal died because of driver or other technical failure. Utah-100 hearts showed superior antithrombogenicity in the connector and valve-related areas when compared with the results of the Jarvik-7 heart, which was also fabricated and implanted in our laboratory (p less than 0.01). With these test results, the authors anticipate that the Utah-100 heart will be a safe and effective device for interim use as a bridge to heart transplantation.

Animals↗
PubMedDate not supplied

SPUU-PEO-heparin graft copolymer surfaces. Patency and platelet deposition in canine small diameter arterial grafts.

The influence of an SPUU-PEO-Heparin (B-PEO-HEP) copolymer coated blood contacting surface on patency and platelet deposition in small diameter (4 mm i.d.) Biomer grafts was investigated using a canine model. Grafts were implanted in the bilateral carotid and femoral arteries. B-PEO-HEP coated grafts still showed patency after 3 days. Control Biomer grafts occluded before 24 hr. (postoperatively). SEM of the luminal surfaces of the Biomer grafts demonstrated large amounts of adherent platelets with distorted morphologies, while B-PEO-HEP grafts did not. In platelet studies, B-PEO-HEP grafts showed significantly less platelet adhesion than Biomer grafts. The improved blood compatibility of B-PEO-HEP graft co-polymer coatings attests to their usefulness for coating or casting.

Animals↗
PubMedDate not supplied

Microbially infected thrombus in animals with total artificial hearts.

In a retrospective study of 330 animals with total artificial hearts (TAH), 103 (31%) had microbially infected thrombi (MIT). The incidence of MIT approximated 75% in the animals surviving more than 100 days. The most common pathogen isolated from animals with MIT was Pseudomonas. Most thrombi appeared to have originated from valve junctions and connectors. Methods to prevent MIT should be aimed at eliminating thrombus formation by improved design and materials and controlling the route of bacterial colonization. These findings suggest that bacterial interaction with the thrombus, device-related bacterial colonization, host immunomodulation, and gut barrier function after TAH implantation need further study.

Animals↗
PubMedDate not supplied

Differential light scattering cuvettes for the measurement of thromboemboli in high shear blood flow systems.

Newly developed optical scattering cuvettes were constructed as a modification of our existing 1.0 mm and 3.0 mm internal diameter (ID) cuvettes to facilitate the measurement of platelet microemboli ranging from 20 microns to 1,000 microns diameter in whole blood in 0.9 mm ID flows ranging from 250 to 4,000 ml/min. A perturbation solution to the one-speed radiative transport equation was used in the design and calibration of these cuvettes. A series of tests were performed with these cuvettes in an extracorporeal left ventricular assist device bovine model, and in a recirculating closed-loop flow system containing anticoagulated whole baboon blood, to determine to what extent they affect platelet and erythrocyte function ex vivo and in vitro. Serial hemolysis tests, thromboxane radioimmunoassay measurements, platelet counts, and activated partial thromboplastin times were measured. All of these tests with cuvettes in the extracorporeal and in vitro circuits were statistically indistinguishable from baseline measurements, suggesting the usefulness of this system for the measurement of microemboli in blood-contacting materials of extracorporeal circuits and cardiac assist devices.

Animals↗
PubMedDate not supplied

Light scattering detection of microemboli in an extracorporeal LVAD bovine model.

Thromboembolization studies were performed on two calves supported by extracorporeal left ventricular assist devices (LVAD) using a light scattering (He Ne Laser) microemboli detector (LSMD). The LSMD system was placed on the outflow cannula of the LVAD in the extracorporeal loop of each animal. The measurements included the size, number, and rate of production of circulating microemboli in the range 20 microns less than microemboli diameter less than 1,000 microns. These data were compared to independently and concurrently obtained measurements of emboli shear rate (CPF), platelet count, red blood count (RBC), leukocyte count (WBC), plasma free hemoglobin, factors XIII, X, and V, and sorbitol dehydrogenase. Embolic number and volume were seen to be most dynamic in the very early phases of acute thromboembolization (0-40 minutes) with a peak embolic response within the first 30 minutes. The dynamics of reduced emboli volume, rather than number, may be implicated in the later stages of the thromboembolic passivation of these ventricles. The LSMD results generally showed an inverse correlation of microemboli volume rate with CPF measurements for each ventricle. LSMD, CPF, and leukocyte and platelet counts, showed a direct correlation with reduced counts for each additional ventricle for both calves. Factor XII was seen to have a more direct correlation in time with LSMD measurements for each ventricle than other parameters under investigation. This study represents the first time laser scattering and filtration methods have been applied simultaneously with hematologic assays in order to study the dynamics of device associated thrombogenesis.

Animals↗
PubMedDate not supplied

Heparin neutralization of antiplatelet effect of aspirin and dipyridamole.

Heparin is used as an anticoagulant for treatment or prevention of thromboembolism. Heparin has been shown also to 1) stimulate platelet aggregation and platelet release reaction, 2) enhance thromboxane A2 production in platelets, and 3) neutralize prostacyclin, a potent inhibitor of platelet aggregation. In the light of these observations, the effect of heparin on two commonly used antiplatelet agents, aspirin and dipyridamole, was investigated. It was noted that heparin reversed the antiplatelet effect of both aspirin and dipyridamole although the effect was relatively more pronounced with aspirin. Presence of aspirin in blood in vitro as well as in vivo resulted in the inhibition of release reaction and the secondary wave of platelet aggregation. In the presence of heparin, platelets previously treated with aspirin showed nearly normal platelet aggregation as well as the release reaction. This reversal by heparin of the inhibitory effect of aspirin was dose dependent; the neutralization of inhibitory effect being more pronounced as the concentration of heparin was increased at a given concentration of aspirin. The neutralization of antiplatelet effect of aspirin was observed in vitro as well as in vivo and whether heparin was added before or after the addition of aspirin. These observations suggest the need for caution in the event heparin and antiplatelet agents are administered concurrently.

5-Hydroxytryptophan↗
PubMedDate not supplied

Enhanced bacterial adhesion on surfaces pretreated with fibrinogen and fibronectin.

The effect of certain plasma proteins on the adhesion of Pseudomonas aeruginosa and Staphylococcus epidermidis on polyurethane, polyvinylchloride, or glass was investigated. Test surfaces were treated with serum, plasma, albumin, immunoglobulin G, fibrinogen, or fibronectin. Using a specially designed test chamber, surfaces previously treated with test proteins were incubated with bacterial suspension. During the experiment, the test chamber was placed on a rotator to prevent settling of bacteria. At the end of the experiment, each test well was rinsed repeatedly to remove non-adherent bacteria. The number of bacteria adherent to the test surfaces was quantitated by a combination of methods including microscopic counting of cells, scintillation counting and autoradiography. It was noted that a greater number of bacteria adhered to surfaces coated with fibrinogen or fibronectin whereas surfaces treated with serum showed reduced bacterial adhesion. The inhibitory effect of serum appeared more pronounced with S. epidermidis when compared with P. aeruginosa under identical experimental conditions. Scanning electron microscopy revealed that adherent bacteria were randomly distributed on the test surfaces and appeared to replicate while still adherent. These observations suggested that bacterial adhesion to biomaterials can be significantly influenced by the composition of the adsorbed proteins at the interface.

Adsorption↗
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A pulmonary mock circulation model for a better understanding of protamine reversal of heparin.

Neutralization of heparin by protamine is a common procedure following extracorporeal circulation (cardiopulmonary bypass) of blood. Protamine administration has been shown to cause serious hemodynamic derangement in some patients. Obstruction of the pulmonary vascular bed following protamine administration has been suggested to be the primary cause of hemodynamic changes. The present study was undertaken to test the hypothesis that macromolecular complexes formed between cationic protamine with anionic heparin or other plasma components cause the obstruction of the vascular bed. An in vitro mock circulation model was designed to examine the formation of such complexes. In this model, blood or plasma was passed through a glass bead column at a constant flow rate while the pressure between the syringe pump and the column was closely monitored. No increase in pressure was noted when blood, plasma or saline alone or with added heparin were passed through the column. Addition of protamine to either blood or plasma resulted in a significant increase in the pressure; this increase was even greater when heparin was also present in the test medium. That the increase in pressure was due to the obstruction of the column was confirmed by using 1251-protamine and documenting that complexes formed between protamine and plasma proteins/heparin were retained in the column. These observations suggested that protamine formed large insoluble complexes with plasma proteins. Heparin appeared to help consolidate these complexes thus causing a rapid increase in the pressure. This may explain why the hemodynamic changes following protamine administration are more pronounced in patients with circulating heparin.

Blood↗
PubMedDate not supplied

Adaptive responses of total artificial heart animals to treadmill exercise.

The hemodynamic and metabolic adaptations to exercise in five calves implanted with the Utah-100 total artificial heart (TAH) were investigated. The outputs of the left and right ventricles (LCO, RCO) were measured with a cardiac output monitoring and diagnostic unit (COMDU). Arterial and venous oxygen content (CaO2, CvO2) and blood lactate levels (Lac) were measured by blood gas analysis and enzymatic methods. Oxygen consumption (VO2), oxygen delivery (DO2), oxygen extraction rate (EO2), index of metabolic adequacy (IMA), and systemic and pulmonary vascular resistance (SVR, PVR) were calculated. The intensity of exercise was categorized into three horizontal grades: low speed (LS) 0.7-1.0 mph, medium speed (MS) 1.0-1.4 mph, and high speed (HS) 1.4-1.8 mph, each for 30 min. During LS, MS, and HS exercise, the LCO, RCO, LAP, RAP, VO2, DO2, and EO2 all increased, and the SVR and PVR decreased. During exercise, there was a positive correlation between DO2, EO2, and VO2. The blood pH, BE, SBE, and lactate levels were within normal ranges, and the IMA exceeded 1.5, denoting that tissue perfusion was adequate and anaerobic metabolism did not occur. This study implies that Utah-100 TAH animals could physiologically accommodate to exercise with an intensity of up to 1.8 mph for 30 min by increasing cardiac preload, cardiac output, oxygen delivery, and oxygen extraction rate, and by decreasing systemic and pulmonary vascular resistance without transition to anaerobic metabolism.

Animals↗