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J C Barbenel

Publications and source records attributed to J C Barbenel.

At least 55 records · Page 3Linked to original sources
PubMed1988

Mouthpiece forces produced while playing the trumpet.

A transducer for measuring the force applied to the trumpet mouthpiece during performance is described. The device allowed the players to perform on their own instrument and in their usual manner. The results of tests on 60 subjects showed that during playing the force between the mouthpiece and instrument increased with increasing loudness and ascending pitch but that there was no significant correlation between mouthpiece force and proficiency or style. The maximum force which the players could tolerate was greater for high proficiency players than for medium.

Biomechanical Phenomena↗
PubMed1987

Effect of dipyridamole on spontaneous platelet aggregation in whole blood decreases with the time after venepuncture: evidence for the role of ADP.

Spontaneous platelet aggregation (SPA) was studied in human whole blood at 3, 5, 10, 20, 30, 40, and 60 minutes after venepuncture. Using a whole blood platelet counter, SPA was quantified by measuring the fall in single platelet count upon rollermixing aliquots of citrated blood at 37 degrees C. The extent of SPA increased with the time after venepuncture, with a correlation coefficient of 0.819. The inhibitory effect of dipyridamole (Dipy) on SPA was studied: (a) 10 microM at each time interval; (b) 0.5-100 microM at 3 and 30 minutes and (c) 15 microM in combination with 100 microM adenosine, 8 microM 2-chloroadenosine (2Clad, an ADP receptor blocker) and 50 microM aspirin. There was a rapid decrease in the inhibitory effect of Dipy with the time after venepuncture; the correlation coefficient was -0.533. At all the concentrations studied, Dipy was more effective at 3 minutes than at 30 minutes after venepuncture. A combination of Dipy with adenosine, 2ClAd or aspirin was a more effective inhibitor of SPA than either drug alone. However, when 15 microM Dipy and 10 microM Ad were added together, the inhibitory effect of Dipy was not increased significantly, suggesting that Dipy inhibits platelet aggregation independent of Ad. The increase in SPA with the time after venepuncture was abolished when blood was taken directly into the anticoagulant containing 5 microM 2ClAd. It is suggested that ADP released from the red blood cells is responsible for the increased platelet aggregability with the time after venepuncture and makes a serious contribution to the artifacts of in vitro platelet function studies.

2-Chloroadenosine↗
PubMed1987

Red blood cells mediate spontaneous aggregation of platelets in whole blood.

The influence of red blood cells on spontaneous platelet aggregation (SPA) has been studied ex vivo. Platelet aggregation was quantified by measuring the fall in single platelet count using a new whole blood platelet counter. When aliquots of whole blood and autologous platelet rich plasma (PRP) were roller-mixed at 37 degrees C, a marked fall in platelet count occurred in whole blood due to SPA but platelet count remained almost unchanged in PRP. When blood from healthy young controls, aged 20-35 years, was compared with healthy old controls, aged 48-80 years, and patients with thrombotic complications, the extent of SPA was in the order: thrombotic patients greater than old controls greater than young controls. Prostacyclin and the new stable prostacyclin analogue Iloprost, at 8 nM effectively inhibited SPA. 2-Chloroadenosine (10 microM) which is an inhibitor of ADP-induced platelet aggregation was also an effective inhibitor of SPA. Acetylsalicylic acid (56 microM) and the thromboxane A2 receptor blocker BM13.177 (0.5 microM) only partially inhibited SPA. ADP from red blood cells is suspected to mediate red cell-induced SPA. However, the possibility that the red cells have an important physical role in SPA cannot be ruled out.

2-Chloroadenosine↗
PubMed1987

Comparison of inhibitory actions of prostacyclin and a new prostacyclin analogue on the aggregation of human platelet in whole blood.

Prostacyclin (PGI2), an unstable endogenous prostanoid, is a potent vasodilator and inhibitor of platelet aggregation. The use of exogenous PGI2 as an antithrombotic agent is limited by its chemical instability and lack of dissociation between its vasodilatory and antithrombotic actions. Iloprost (ZK36374) is a recently developed, chemically stable, carbacyclin analogue of PGI2. Preliminary evaluation studies have shown a significant dissociation between vasodilatory and antithrombotic actions of Iloprost. We have compared the effects of PGI2 and Iloprost on platelet aggregation in human whole blood. Platelet aggregation was induced by ADP (4 microM), adrenaline (Adr, 0.4 microM) and arachidonic acid (AA, 0.4 mM). Aggregation was quantified as a fall in the number of single platelets counted using the Clay Adams Ultra Flo 100 whole blood platelet counter. In the absence of any PGI2 or Iloprost, each aggregating agent induced up to an 80% fall in the number of single platelets counted. When blood was pre-incubated with PGI2 (1-6 nM) or Iloprost (1-6 nM), aggregation responses to all three aggregating agents were inhibited in a dose-dependent manner. Iloprost was equipotent to PGI2 against ADP-induced aggregation but was more potent than PGI2 against Adr- and AA-induced aggregation. It is concluded that Iloprost, as a chemically stable PGI2 analogue, may be superior to PGI2 as an antithrombotic agent.

Adenosine Diphosphate↗
PubMed1986

A critical investigation into the existence of circulating platelet aggregates.

By a method of counting single platelets in diluted whole blood, platelet aggregates were quantified ex-vivo. Four groups: 20 thrombotic patients, 10 non-thrombotic patients, 10 healthy old controls and 10 healthy young controls were included in the study. Using a 19 gauge needle, with and without tubing, venous blood was taken into buffered EDTA, as a disaggregating agent and buffered EDTA-formalin, as the fixative. The amount of platelet aggregates quantified was affected by the quality of venepuncture or the rate of blood flow through the needle, but was unaffected by the presence of the tubing. There was no statistically significant difference between the four groups, in terms of the platelet aggregates quantified, but scanning electron microscopy revealed the presence of irreversible aggregates, composed of platelet red and white blood cells, in the blood of a greater number of thrombotic patients than non-thrombotic or healthy controls. Platelet aggregates were also quantified in aliquots of platelet rich plasma, and were found to be significantly greater than the corresponding values in whole blood. The difference appeared to be due to increased viscosity of the plasma, induced by the fixative which reduces platelet mobility during centrifugation. It is concluded that the platelet aggregates which disaggregate in buffered EDTA may represent an artifact of blood collection; the irreversible aggregates are suspected to represent the in vivo circulating aggregates.

Adult↗
PubMed1986

Mobility of elderly patients in bed. Measurement and association with patient condition.

Measurements were made of the overnight mobility of a group of elderly hospital patients whose clinical status had been assessed using the Norton clinical assessment score. The number of movements on the first two nights after admission differed from subsequent nights. There was a significant correlation between mobility and patient condition on all nights except the second. Patients assessed as being at high risk of developing pressure sores made fewer movements; mobility criteria are presented for detecting these individual patients.

Aged↗
PubMed1986

Modeling transient heat transfer through the skin and superficial tissues--1: Surface insulation.

Two models of transient heat transfer through the skin and superficial tissues are presented. One model comprises a finite slab and semi-infinite slab, representing the epidermis and subdermal tissues, respectively, and a heat-generating interface representing the thermal effect of blood flow through the dermis. A model is also considered where the three tissue regions are represented more conventionally by three finite slabs. A transient problem arising from surface insulation is examined and analytical solutions derived from the first model are compared with numerical solutions derived from the second.

Body Temperature Regulation↗
PubMed1985

Further studies on the role of red blood cells in spontaneous platelet aggregation.

The influence of red blood cells on platelet aggregation has recently been a subject of considerable interest. We have studied the effect of red cells on spontaneously formed platelet aggregates in rotating vials at 37 degrees C. Platelet aggregation was quantified by measuring the fall in number of single platelets with a whole blood platelet counter. Autologous packed red cells, platelet rich plasma and platelet free plasma were used to reconstitute aliquots of blood with constant platelet count but 0-60% haematocrit (Hct). The fall in platelet count was minimal at zero Hct, increased markedly with the Hct in the anaemic range and less markedly in the normal to polycythaemic ranges of Hct. Scanning electron microscopic observation of whole blood showed the presence of small platelet aggregates after about 3 mins rotation and very large aggregates after about 12 mins. ADP from red cells has been implicated in triggering platelet aggregation in whole blood. Whether aggregates are formed as a result of ADP leaking from the red cells or by their jostling physical action on the platelets is discussed. The marked effect of the red cells on spontaneous platelet aggregation however, justifies the manipulation of the Hct as a useful therapeutic option in the control of thrombotic and bleeding tendencies.

Adult↗
PubMed1985

Effects of time-varying magnetic fields on fibroblast growth.

L929 mouse fibroblasts were exposed to sinusoidally varying magnetic fields. Compared with controls the exposed cells showed differences in morphology, clustering and orientation with respect to the magnetic fields and an increased mitotic rate. These effects are time dependent, but occurred at frequencies of 10 and 27 MHz.

Animals↗
PubMed1985

Nitrous oxide and wound healing.

Following a paravertebral surgical incision, mature, female rats under ether anaesthesia were exposed to either 3% nitrous oxide, continuously for 48 h, or 50% nitrous oxide, 4 h each day for 7 days. For each exposure group, a similar number of rats was exposed to atmospheres containing no nitrous oxide. Wound healing was assessed by measurement of the breaking strengths of wound samples. No statistically significant influence on breaking strength could be attributed to nitrous oxide following either exposure sequence.

Animals↗
PubMed1984

A comparison of spontaneous platelet aggregation in whole blood with platelet rich plasma: additional evidence for the role of ADP.

ADP, generated from red blood cells is believed to be responsible for the spontaneous aggregation of platelets in whole blood. This notion is based mainly on the use of enzymes which remove ADP. We have studied spontaneous platelet aggregation in whole blood and autologous platelet rich plasma obtained from 12 healthy male and female volunteers. Platelet aggregation was quantitated by measuring the fall in the number of single platelets counted using a whole blood platelet counter (Ultra Flo 100). In a rotating tube model, the mean fall in the number of platelets due to spontaneous aggregation was 56% in whole blood but, only 3% in platelet rich plasma prepared from the same blood samples. Spontaneous platelet aggregation in whole blood was unaffected by apyrase grade I, but was reduced to 15% by apyrase grade II, to 38% by creatine phosphokinase/creatine phosphate and to 9% by pyruvate kinase/phosphoenolpyruvate. The results of this study provide additional evidence that ADP generated in whole blood triggers the spontaneous aggregation of platelets.

Adenosine Diphosphate↗
PubMed1984

Effect of prostacyclin (epoprostenol) on the aggregation of human platelets in whole blood in vitro.

Prostacyclin (PGI2) is a potent endogenous inhibitor of platelet aggregation. The effect of PGI2 on platelet aggregation and disaggregation in whole human blood was studied at 37 degrees C in vitro. Aggregation or disaggregation was quantified by counting single platelets using the recently developed Ultra Flo 100 Whole Blood Platelet Counter. Aggregation of platelets in whole blood was induced by arachidonic acid (AA, 400 microM), adenosine 5'-diphosphate (ADP, 10 microM), thrombin (0.1 U/ml) and collagen (1 microgram/ml). At peak aggregation, each aggregating agent induced about a 90% fall in the number of single platelets counted. When whole blood was pre-incubated with PGI2 (0.5-8 nM), it dose dependently inhibited aggregation of platelets induced by all four aggregating agents. Platelet aggregates induced by ADP or thrombin could rapidly be disaggregated by PGI2 added to blood at peak aggregation. Disaggregation of collagen-induced platelet aggregation by PGI2 was slow and minimal and it was completely ineffective in disaggregating AA-induced platelet aggregates. Unlike platelet-rich plasma, which is routinely used to study platelet aggregation, the present whole-blood method allows red and white blood cells to exert their influences on platelet function, and is an important step towards a physiological state for evaluating the effects of pharmacological agents on platelets in whole blood in vitro and ex vivo.

Adenosine Diphosphate↗
PubMed1984

Effects of diabetic control and biosynthetic human insulin on blood rheology in established diabetics.

Blood rheology (blood viscosity, haematocrit, plasma viscosity, erythrocyte sedimentation and deformability) was measured in 22 diabetics in a study to compare animal insulins with biosynthetic human insulin. All rheological variables were significantly abnormal in the diabetics when compared with matched normal controls, and were not influenced by the type of insulin injected. However, blood rheology was related to diabetic control, as judged by glycosylated haemoglobin levels; when diabetic control was worst (mean glycosylated haemoglobin 11%), blood viscosity was significantly higher and red cell deformability significantly lower than when control was at its best (mean glycosylated haemoglobin 9.5%). A similar correlation between mean red cell deformability and mean glycosylated haemoglobin was found when individual diabetics were compared (r = 0.66; p less than 0.001). The occurrence of abnormal blood viscosity and red cell deformability during periods of poor diabetic control may contribute to the development of diabetic vascular complications.

Adolescent↗
PubMed1983

The novel effect of a new prostacyclin analogue ZK36374 on the aggregation of human platelets in whole blood.

Platelet aggregation was studied at 37 degrees C in citrated whole human blood, using the Ultra Flo 100 Whole Blood Platelet Counter. Aggregation was measured as a fall in the number of single platelets following addition of an aggregating agent. At peak aggregation, the fall in the number of platelets induced by ADP (10 microM), collagen (1 microgram/ml) or thrombin (0.2 U/ml) was about 90%. When blood was incubated with the prostacyclin-analogue ZK36374, the aggregation responses to ADP, collagen and thrombin were reduced with IC50's = 0.5, 1.5 and 3 nM respectively and the corresponding IC100's were: 1, 3 and 12 nM. When ZK36374 was added at peak aggregation, the number of single platelets increased significantly due to disaggregation of preformed platelet aggregates. It is concluded that the present technique represents a rapid, sensitive and more physiological approach for investigating the effects of pharmacological agents on platelet aggregation.

Adenosine Diphosphate↗
PubMed1983

Platelet aggregation studies in whole human blood.

Since the development of the photometric aggregometer, platelet aggregation studies are routinely performed on platelet-rich plasma (PRP). We have studied platelet aggregation in fresh citrated whole human blood using the recently developed Ultra Flo 100 Whole Blood Platelet Counter. Aggregation of platelets in whole blood was induced with adenosine 5'-diphosphate (ADP; 0.25-10 microM), collagen (0.25-1.0 microgram/ml) and thrombin (0.05-0.2U/ml). Platelet aggregation induced by ADP and thrombin was maximum within 1 min, and that of collagen within 3 mins. Aggregation responses to low concentration of ADP and thrombin were rapidly reversible, whereas responses to collagen and high concentrations of ADP and thrombin were virtually irreversible. The aggregation of platelets was indicated by a fall in platelet count; confirmed by scanning electron micrographs which revealed the presence of large aggregates of platelets, and was prevented when blood was treated with EDTA as anticoagulant. The present technique appears to be rapid, sensitive and reliable; and allows direct measurement of platelet aggregation and disaggregation in whole blood in vitro and ex-vivo.

Adenosine Diphosphate↗
PubMed1982

Uniaxial tension test of human skin in vivo.

The application of uniaxial tension in vivo is a common test method for investigating mechanical properties of the skin. This paper reports an investigation of the strain distributions on the skin surface produced by such a test method. The strains were shown to be non-homogeneous with major concentrations being present near the area of load application. At all sites within the test area, axial, lateral and shear strains were present but their magnitude depended both on their position within the test site and the overall extension. The axial and lateral strains were largest and most uniformly distributed within the area bounded by th loading tabs. The shear strains, however, were smallest in the are bounded by the tabs. The distribution of the three strains became similar if they were referred to the principal axes. The area of skin within the strained area became larger as the overall deformation increased because additional skin was recruited from the sites lateral to the strained area. The general form of the load/strain relations and lateral contractions were site- and extension-dependent, but were similar to those found in vitro.

Abdomen↗