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Biomedical subjects

E A Trowbridge

Publications and source records attributed to E A Trowbridge.

At least 55 records · Page 3Linked to original sources
PubMed1986

The standardisation of gauge length: its influence on the relative extensibility of natural and chemically modified pericardium.

Cyclic uniaxial load tests were performed on natural and chemically modified bovine pericardium which is used in the construction of heart valve substitutes. A template was employed to select specimens from the same sites in different pericardial sacs. When the pericardium was chemically modified by glutaraldehyde fixation as an entire sac the tissue showed increased extensibility after modification compared with the natural tissue. The undeformed stress-free length (gauge length) in both the natural and modified tissue was determined by a highly reproducible experimental method giving a coefficient of variation of less than 0.5%. Specimens excised from a natural pericardial sac demonstrated a significant increase (p less than 0.03) in length, 4.97 +/- 3.49%, after a single load cycle, compared with controls placed in isotonic saline but not mechanically tested. The test pieces had returned to their original length by 8.5 h after the mechanical test. After fixation the same specimens decreased significantly in length (p less than 0.001) by 11.18 +/- 4.28%. This shrinkage was not significantly different to that of the control specimens (11.09 +/- 2.47%) which had not been tested. Uniaxial loading of these chemically modified strips demonstrated a similar increase in tissue extensibility compared to the natural tissue if the undeformed length of the test specimen after shrinkage was used as the gauge length. After mechanical conditioning the chemically modified tissue also demonstrated a significant increase (p less than 0.001) in stress-free length (5.35 +/- 0.59% after 36 cycles, 8.92 +/- 1.50% after 2085 cycles). These deformations were not permanent. The tissue had returned to its original length after 38 h in its normal buffered glutaraldehyde storage medium. On the basis of these observations, recommendations for the clarification and standardisation of gauge length definitions were made in natural, chemically modified and mechanically conditioned tissue.

Animals↗
PubMed1986

Evidence that deformations which occur during mechanical conditioning of bovine pericardium are not permanent.

Natural and glutaraldehyde fixed bovine pericardium samples were mechanically conditioned by a cyclic uniaxial load procedure. The samples tested were controlled for both position and direction in the pericardial sac. The natural tissue demonstrated a significant increase in length and a significant decrease in width after mechanical conditioning. The deformations were not permanent. The test specimens had returned to their original length by 10.5 h after the mechanical test. The control samples of natural tissue showed no significant changes in length during this time. The chemically modified tissue showed a significant increase in length but no significant changes in width or thickness after mechanical conditioning. As in the natural tissue, the length changes were not permanent. Twenty four hours after returning the fixed tissue to its normal buffered glutaraldehyde storage medium the test samples had returned to their original length. A subsequent mechanical retest 8 d after the initial test procedure suggested that the history of the original test had been removed. These observations may be important in the interpretation of 'in vitro' hydrodynamic tests for heart valve substitutes.

Animals↗
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

Modification of the Gorlin equation for use with heart valve substitutes.

The Gorlin equation, which was used to assess the obstruction to flow by a stenosed heart valve, is based on steady flow (time independent) criteria derived from hydraulics. Recently, this equation has been used to obtain an effective orifice area for heart valve substitutes both in vitro and in vivo. In this study, a modification of the original Gorlin equation for use with heart valve substitutes considers both the pulsatility of the valvar flow and possible variations in volumetric flow waveforms induced by differences in myocardial performance. The modified equation also allows for the possibility of regurgitant flows. Its use is illustrated in a study of the hydrodynamic performance of a series of heart valve substitutes and recommendations are made concerning its application to cardiac catheterisation procedures.

Blood Flow Velocity↗
PubMed1986

Pericardial heterografts. Toward quality control of the mechanical properties of glutaraldehyde-fixed leaflets.

The mechanical properties of five different, equally distributed, and randomly oriented sites in natural and glutaraldehyde-fixed calf pericardial sacs were investigated. Identical sites in different sacs were obtained by placing a template over each sac and using the ligaments still attached to the pericardium as a reference frame. Mean maximum extension of the fixed tissue was statistically significantly greater than that of natural tissue at the same degree of stress. There was no significant difference in thickness from position to position within a sac, from sac to sac, or from the natural to fixed pericardium. However, the extensibility of one particular site was significantly greater than that of other positions in the pericardial sac. This position lay entirely in a well-defined sector that emanated radially from the pericardial ligaments. Light and electron microscopy showed no difference in collagen structure in the five positions studied. In contrast, both the content and ultrastructure of the tissue elastin differed in the region of high extensibility compared with those sites studied in the remainder of the sac. This region contained coarse condensed elastin whereas the other sites had fine elastin dispersed diffusely throughout the tissue. These results suggest that pericardial heterografts of uniform thickness may be harvested from any position in calf pericardium. However, unless the region of coarse condensed elastin is excluded, leaflets with significantly different mechanical properties may be produced.

Analysis of Variance↗
PubMed1985

Platelet volume subpopulations in acute myocardial infarction: an investigation of their homogeneity for smoking, infarct size and site.

Mean platelet volume and count were measured in three groups: patients with acute myocardial infarction, a control group with myocardial ischaemia but no infarction and an asymptomatic group of young males. Mean platelet volume was significantly larger in the myocardial infarction group compared with the ischaemic heart disease group or the asymptomatic group. Two subpopulations were present within the myocardial infarction group. One subgroup had a large mean platelet volume and low count. The other subpopulation was indistinguishable, with regard to platelet count and mean volume, from the ischaemic heart disease group. Over 60% of the myocardial infarction group lay in the area of high platelet volume and low count compared with 13% of the ischaemic heart disease control group and 38% of the asymptomatic group. Acute myocardial infarction is likely to be associated with a large mean platelet volume and low count compared with the ischaemic heart disease group. There is no statistical evidence that this condition is related to smoking or size and site of infarct. This evidence suggests that large mean platelet volume and low platelet count could be a major risk factor for myocardial infarction.

Blood Platelets↗
PubMed1985

The physics of red cell sedimentation.

Blood was withdrawn from the ante-cubital vein of five normal volunteers and the erythrocytes were washed and resuspended in isotonic saline. The rate of descent of the erythrocyte-saline boundary was measured every hour for a period of at least 4 h for different suspended cell concentrations. The velocity of this boundary remained constant during the period of observation for a specific concentration. There was, however, an experimental variation of sedimentation rate with red cell concentration. Extrapolation to zero concentration allowed the 'Svedberg constant' for normal red cells to be evaluated. A continuum physics theory was used to explain the observations. The sedimentation rate was also measured in anticoagulated whole blood. The rates of descent in whole blood and the red cell-saline suspension were significantly different. Furthermore, the erythrocyte boundary in whole blood displayed both acceleration and deceleration during the period of observation. These experiments support the concept, proposed in an earlier theoretical study, of an internal energy dissipative mechanism which occurs in heterogeneous fluids (such as blood) but not in homogeneous fluids (such as water).

Adult↗
PubMed1985

The routine measurement of platelet volume: a comparison of light-scattering and aperture-impedance technologies.

The effect of dipotassium ethylenediaminetetra-acetic acid (EDTA) on platelet count and mean volume (MPV) was evaluated using two routine measurement systems, a Coulter S Plus (Phase 1) (S+) and a Technicon H6000 (H6000). In normal subjects (n = 29) MPV increased by 17% during 39 h storage in EDTA when measured by the S+. In contrast MPV decreased by 22% when measured by the H6000. MPV differences of up to 40% were observed between the two systems. Concomitant platelet counts, in both systems, changed by less than 4%. A mathematical model of the variation of MPV with storage time was constructed, enabling experimental results to be extrapolated, with accuracy, to time zero (MPV0). The H6000 average MPV0 was significantly larger than the S+ average MPV0. Using the anticoagulant sodium citrate and prostaglandin E1 (NaCitrate-PGE1) there were no significant changes in MPV measured by the S+ during 7 h storage, although a linear decrease in platelet count was observed. A decrease in H6000 MPV was observed whether the blood was stored in EDTA or NaCitrate-PGE1. Methodology, anti-coagulation and storage time all influence MPV. Until these determinants are standardised the clinical value of MPV cannot be assessed.

Blood Platelets↗
PubMed1985

The routine measurement of platelet volume: a comparison of aperture-impedance and flow cytometric systems.

The effect of dipotassium ethylenediaminetetraaceticacid (EDTA) on the platelet count and mean volume (MPV) was evaluated using two routine measurement systems, a Coulter S Plus Phase 1 (S+) and a Technicon H6000 (H6000). In normal subjects (n = 29) MPV increased by 17% during 39 h storage in EDTA when measured by the S+. In contrast MPV decreased by 22% when measured by the H6000. MPV differences of up to 40% were observed between the two systems. Concomitant platelet counts, in both systems, changed by less than 4%. Using the anticoagulant sodium citrate and prostaglandin E1 (Na-citrate/PGE1 there were no significant changes in MPV measured by the S+ during 7 h storage, although a linear decrease in platelet count was observed. A decrease in H6000 MPV was observed whether the blood was stored in EDTA or Na-citrate/PGE1. Methodology, anticoagulation and storage time all influence MPV. Until these determinants are standardized the clinical value of MPV cannot be assessed.

Alprostadil↗
PubMed1984

Platelet production in myocardial infarction and sudden cardiac death.

Megakaryocyte cytoplasmic volumes were studied in 13 subjects 18 +/- 2 days after admittance to the coronary care unit. Seven had suffered a myocardial infarction (MI group) while six had chest pain but no recent infarction. Megakaryocytes were also studied in 10 subjects suffering coronary sudden unexpected death (CSD group) and 11 subjects suffering sudden unexpected un-natural death. There was no significant difference between the megakaryocyte cytoplasmic volume distributions of the MI and CSD groups, although they had a significantly greater mean (p less than 0.01) and range (p less than 0.001) than their respective control groups. There was no significant difference in platelet volumes observed within 24 hr of the infarct and 18 +/- 2 days later. Mean platelet volume was significantly correlated (r = 0.89, p less than 0.006) to mean megakaryocyte cytoplasmic volume in the MI group. A computer simulation of platelet production showed no significant difference between platelet volumes observed in the MI group and those estimated to be circulating before death in the CSD group.

Adult↗
PubMed1984

A computer model of the random binary sequential division of megakaryocyte cytoplasm to produce platelets.

A computer program is constructed which models the production of platelet volumes from megakaryocyte cytoplasmic volumes by random binary sequential division. The volume distributions that are produced are compared with measured platelet volume distributions in rat, rabbit and man. These platelet volume distributions depend on the fragmentation pattern and the dispersion about the mean of the Gaussian distribution of binary divisions. The results of changing one of these parameters, while keeping the other fixed, are also presented.

Animals↗
PubMed1984

The origin of platelet count and volume.

Platelet count and volume were measured in man (n = 51) and rat (n = 9). Bone marrow megakaryocyte nuclear and megakaryocyte planimetric areas were measured in man (n = 11) and rat (n = 9). Megakaryocyte cytoplasmic volumes were computed from the planimetric areas. Rat had a significantly higher (p less than 0.001) mean megakaryocyte cytoplasmic volume than man and a significantly wider range (p less than 0.01). Rat mean platelet volume was significantly lower (p less than 0.001) than man while the rat platelet count was significantly higher (p less than 0.001) than man. A computer simulation of the random binary sequential division of megakaryocyte cytoplasm was used to explain these observations. Transmission electron microscopy shows that the site of this binary sequential division is probably the pulmonary circulation. The number of circulating megakaryocytes ml-1 of blood which would maintain the observed platelet counts was computed. The ellipses of constant density associated with the bivariate Gaussian distribution of platelet count and mean volume were computed. Platelet volume distributions of 13 men within two standard deviations of the composite mean of platelet count and mean volume were used to construct the platelet volume distribution signature in normal man. A similar platelet volume distribution signature for rat was constructed. The two distributions were significantly different. Neither rat nor man had a log Gaussian platelet volume distribution, however the measured volume distributions tended towards a log Gaussian curve.

Adult↗
PubMed1984

An analysis of the platelet and polyploid megakaryocyte response to acute thrombocytopenia and its biological implications.

Thrombocytopenia was induced in rabbit by a single injection of anti-platelet serum. The circulating platelet number and concomitant mean platelet volume were measured 6 h after the injection and daily thereafter. The megakaryocyte nuclear DNA content was measured in control rabbits and after 2 h and 24 h of thrombocytopenia respectively. The observed recovery of circulating platelet number is used to construct the variation of platelet destruction rate and platelet production rate with time during thrombocytopenia. The observed rebound thrombocytosis is explained by using a balance equation of these two rates. Platelet production is linked to the megakaryocyte by physical fragmentation theory and an explanation of the observed variation of mean platelet volume is used to obtain an estimated bleeding time and circulating platelet biomass during recovery from thrombocytopenia. An interpretation is given of the homeostatic control of megakaryocytopoiesis and thrombopoiesis.

Acute Disease↗