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Biomedical subjects

J F Martin

Publications and source records attributed to J F Martin.

At least 217 records · Page 12Linked to original sources
PubMed1987

Regional myocardial blood flow, function and metabolism using phosphorus-31 nuclear magnetic resonance spectroscopy during ischemia and reperfusion in dogs.

Postreperfusion regional myocardial dysfunction may be associated with depletion of high energy phosphate compounds during ischemia and with their relatively slow repletion during reperfusion. However, few studies have correlated relatively rapid changes in regional myocardial function (sonomicrometers) and blood flow (microspheres) with high energy phosphate concentrations measured using phosphorus-31 nuclear magnetic resonance spectroscopy in intact large animal models of regional myocardial ischemia. The left anterior descending coronary artery of mongrel dogs was abruptly occluded for 17.1 +/- 1.9 minutes and then completely released; measurements were made for an additional 22 minutes. Transmural blood flow decreased from 1.07 +/- 0.25 to 0.25 +/- 0.10 ml/(min X g) and holosystolic expansion was observed in all dogs (segmental systolic shortening decreased from 9.3 +/- 3.7 to -6.3 +/- 6.0%). Phosphocreatine (PCr) measured during 4.4 minute sampling intervals decreased to steady state within the first sampling period after occlusion and was 45.9 +/- 17.0% of control at the end of the occlusion, whereas beta-adenosine triphosphate (beta-ATP) reached its lowest level early after reperfusion (72.7 +/- 13.3% of control). The ratio of PCr to inorganic phosphate (Pi) decreased during the occlusion (3.34 +/- 0.75 versus 1.01 +/- 0.61) but returned to control level early during reperfusion. The ratio of PCr to beta-ATP also decreased during coronary occlusion (2.16 +/- 0.39 versus 1.29 +/- 0.39) but did not return to control level during reperfusion. Significant correlations were observed between the intensity of ischemia (reduced blood flow) and reductions in regional contractile function, PCr, beta-ATP, myocardial pH and the increase in Pi during the coronary occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Platelets in idiopathic thrombocytopenic purpura are increased in size but are of normal density.

To determine whether platelet size and volume are related to one another or to platelet age, subpopulations of platelets from patients with idiopathic thrombocytopenic purpura (ITP) have been produced on the basis of density using Percoll gradients. The density distribution of platelets from patients with ITP and from patients with other forms of thrombocytopenia (thought to be nonimmune in nature) was the same as in normal controls. However, the platelets in each density subpopulation from ITP patients were increased in size. beta-thromboglobulin (beta TG) content of platelets from each patient group and the normals increased with density and tended to be higher in ITP than in normal controls. beta TG concentration per unit platelet volume and its level in plasma were similar in ITP patients and in normal controls. This suggests that the apparently normal density of ITP platelets was not a result of degranulation of large, dense platelets. Thus platelet size and density are independently determined and the increased size of platelets in immune thrombocytopenia may be the result of abnormalities in their production.

Blood Platelets↗
PubMed1987

Efficient plasmid transformation of the beta-lactam producer Streptomyces clavuligerus.

The conditions for optimal formation and regeneration of protoplasts of Streptomyces clavuligerus were established. The optimal temperature for regeneration of protoplasts and for transformation was 26 degrees C in three different regeneration media. The best efficiency of transformation was obtained with 40% polyethylene glycol 1000. The efficiencies of regeneration and transformation increased greatly when protoplasts were obtained from cultures in the early stationary phase of growth. The number of transformants per assay increased linearly with rising concentrations of protoplasts. However, the number of transformants per protoplast decreased at concentrations of protoplasts above 1.5 X 10(9). The total number of transformants rose linearly at increasing plasmid DNA concentrations, but the number of the transformants per microgram of DNA became constant at concentrations above 1 microgram of DNA. Transformation frequencies as high as 5 X 10(5) transformants per microgram of DNA were obtained when plasmid pIJ702 was isolated from S. clavuligerus but not when isolated from Streptomyces lividans.

Anti-Bacterial Agents↗
PubMed1987

Platelet count is positively correlated with white cell count and red cell count.

Platelet count is positively correlated with the white cell count in healthy males aged 20-68 years (p less than 0.002) and in healthy medical students of both sexes aged 18-22 years (p less than 0.0001). Platelet count is also positively correlated with red cell count in healthy males (p less than 0.02). Red cell count is positively correlated with white cell count in the older healthy males (p less than 0.02) and in the male medical students (p less than 0.003). These findings provide support for the concept of a single hormone-dependent pluripotent stem cell whose effect is seen concomitantly in all circulating blood cells. The white cell count and platelet count correlation is less significant in the males aged 35 or above which may represent the development of pathological mechanisms.

Adolescent↗
PubMed1986

Prolonged bleeding time, reduced platelet aggregation, altered PAF-acether sensitivity and increased platelet mass are a trait of asthma and hay fever.

In a case control study 31 asymptomatic patients with asthma and/or hay fever and 31 normal controls had their bleeding time measured using the Simplate II device and venostasis. Mean bleeding time in the atopic group (527 s) was significantly prolonged compared to the controls (393 s) (p less than 0.0005). Platelet aggregation to collagen and ADP (but not to PAF-acether) was significantly depressed in the atopics. Mean circulating platelet mass was significantly greater in atopics than in the controls (p = 0.006). Stepwise multiple regression analysis showed that within the control group bleeding time was best predicted by platelet mass (p = 0.007). No such relationship was found in the atopics. However stepwise multiple regression analysis showed that bleeding time in the atopics (but not in the controls) was best predicted by PAF-acether induced platelet aggregability (p less than 0.05). In neither group was bleeding time related to collagen induced platelet thromboxane B2 production. It is hypothesised that in respiratory atopy the depressed aggregatory function of platelets is not compensated for sufficiently by an increase in platelet mass, leading to prolongation of the bleeding time. This haemostatic imbalance, whose cause remains to be established, appears to constitute a trait of atopy.

Adenosine Diphosphate↗
PubMed1986

Transmission line matching of surface coils.

Tuning of surface coils is often difficult to accomplish in vivo since the exact coil loading is impossible to predict in advance. This technical difficulty was obviated through use of a transmission line matching scheme. This technique has been successfully used at a variety of frequencies for imaging and spectroscopy.

Adult↗
PubMed1986

Platelet volume heterogeneity in acute thrombocytopenia.

Platelet volume and count were measured by aperture impedance techniques in rats during acute thrombocytopenia 2, 6, 12 and 24 h and 3, 6, 9 and 11 days after a single injection of anti-platelet serum (APS). Platelet volume heterogeneity was quantified by four statistical parameters: the measure of central tendency, dispersion, asymmetry and convexity. None of the volume distributions, including the controls, was log Gaussian. Mean platelet volume increased for the first 6 h post APS and then started to decrease although the platelet count had not started to rise. There was an initial increase, followed by a smooth decrease to control values, in the coefficient of variation (suggesting an initial increased dispersion about the mean platelet volume) with concomitant decreases in asymmetry and convexity. In contrast the age of the platelets immediately after the APS injection must have a decreased dispersion about the mean age compared with control values. These facts are used to show that young platelets are not synonymous with large platelets even under the stress of acute thrombocytopenia and support the concept that thrombopoiesis is the dominant factor in determining platelet volume heterogeneity.

Animals↗
PubMed1986

Relationship of platelet-associated immunoglobulin G and platelet protein to platelet size and density in normal individuals and patients with thrombocytopenia.

Total platelet-associated immunoglobulin G (PA-IgG) and platelet volume and protein content in normal individuals and in patients with idiopathic thrombocytopenic purpura (ITP) and other thrombocytopenias of presumed nonimmune origin have been measured on platelets separated into subpopulations on the basis of density on continuous polyvinylpyrrolidone (Percoll) gradients. In all subjects PA-IgG per platelet was primarily found in the lightest platelets at levels up to sevenfold greater than in the heavier platelets. PA-IgG level per platelet was raised in light platelets in 29% of patients with thrombocytopenia and in heavy platelets in 60%. In almost half of these instances the PA-IgG level fell to within the normal range when considered in relation to either platelet volume or protein content. PA-IgG levels of patients with untreated ITP did not differ significantly from those with treated ITP or thrombocytopenia of other causes. Mean platelet volume and protein content of the total platelet population of all subjects showed significant linear correlation (P less than 0.01). Thus PA-IgG of both controls and patients with thrombocytopenia of all causes is preferentially located in the lightest platelets, but increases in PA-IgG in immune thrombocytopenias occur more frequently in the heavier platelets. These findings suggest that part of the process of IgG accumulation by platelets is the same in normal individuals as in patients with thrombocytopenia.

Adolescent↗
PubMed1985

Shortened bleeding time in acute myocardial infarction and its relation to platelet mass.

The bleeding time, using the Simplate method, horizontal incision, and venostasis, was measured in a study of 51 patients admitted to a coronary care unit within 12 hours of the onset of chest pain. The bleeding time was significantly shorter in the 28 patients who were found to have definite myocardial infarction compared with the 23 others with chest pain but no definite infarction (p less than 0.0005). A bleeding time of less than 212 seconds correctly classified 84% of patients (sensitivity for definite myocardial infarction 89%) presenting to the coronary care unit with chest pain. Multiple regression analysis showed the bleeding time in all patients to be determined independently (and with high significance) by the following variables in order of importance: diagnostic group, platelet mass (platelet count X mean volume), and age. Packed cell volume was not a significant determinant. In the group with definite myocardial infarction considered alone the same order of variables was observed in predicting bleeding time, but none of them was significant. A major variable reducing bleeding time in acute myocardial infarction remains to be determined. There was no association between bleeding time and creatine phosphokinase activity or infarct size in the group with definite myocardial infarction.

Aged↗
PubMed1985

Liquid crystal thermography as a screening test for deep-vein thrombosis.

The accuracy of liquid crystal colour thermography and clinical examination was compared with that of X-ray venography in 80 patients clinically suspected of having unilateral, lower-limb, deep-vein thrombosis. The clinical examination was not helpful in diagnosis. Of the 35 patients with confirmed deep-vein thrombosis, 34 had a positive thermogram, giving a sensitivity of 97%. 17 false-positive thermograms gave a specificity of 62%. The predictive value of a negative thermogram was 96.5%. Liquid crystal colour thermography is a quick, inexpensive, non-invasive investigation that might be useful as a screening test in patients suspected of having unilateral, lower-limb, deep-vein thrombosis. A diagnostic scheme starting with liquid crystal thermography and followed by 99mTc venoscanning might obviate the need for X-ray venography in almost 80% of patients with suspected deep-vein thrombosis.

Adolescent↗