P.R. Williams

Gel point and fractal microstructure of incipient blood clots are significant new markers of hemostasis for healthy and anticoagulated blood

Here we report the first application of a fractal analysis of the viscoelastic properties of incipient blood clots. We sought to ascertain whether the incipient clots fractal dimension, D(f,) could be used as a functional biomarker of hemostasis. The incipient clot is formed at the gel point (GP) of coagulating blood, the GP demarcating a functional change from viscoelastic liquid to a viscoelastic solid. Incipient clots formed in whole healthy blood show a clearly defined value of D(f) within a narrow range that represents an index of clotting in health, where D(f) = 1.74 (± 0.07). A significant relationship is found between the incipient clot formation time, T(GP), and the activated partial thromboplastin time, whereas the association of D(f) with the microstructural characteristics of the incipient clot is supported by its significant correlation with fibrinogen. Our study reveals that unfractionated heparin not only prolongs the onset of clot formation but has a significant effect on its fractal microstructure. A progressive increase in unfractionated heparin concentration results in a linear decrease in D(f) and a corresponding prolongation in T(GP). The results represent a new, quantitative measure of clot quality derived from measurements on whole blood samples.

Dynamic stressing of a liquid-liquid interface by tension

We report experiments in which the interface between two immiscible liquids is subjected to tension by dynamic stressing. During the course of these experiments, cavitation is only observed in the stronger of the two liquids (in terms of their tensile strength). The results are explained in terms of the failure of the liquid-liquid interface under tension, and the ability of the vapour layer so created to reflect subsequent compressional waves as tension. The findings reported here support the results of earlier work in this area and their technological implications are briefly discussed.

A study of the tensile properties of liquids in confined spaces using an atomic force microscope

We report work in which an atomic force microscope (AFM) is used to stretch (and ultimately, to rupture) a thin film of liquid between a moving colloid sphere and a static plane surface. Under some circumstances, when the sphere and the surface are pulled apart sufficiently rapidly, an unexpected transient decrease in the sphere‐surface separation is recorded. The results of numerical simulations of cavitation bubble dynamics suggest that the growth of a cavitation bubble within a liquid may result in the development of sufficiently large negative pressures to account for this phenomenon. The results of separate experiments, which involve acoustic pulse propagation within metre‐long columns of liquid and high‐speed microphotography (using a novel optical system designed for this work), are used to show that the peak tensile forces recorded in the AFM experiments correspond to the development of tensile stresses that are commensurate with the fluids effective tensile strength (or ‘cavitation threshold’). The results of this study, which, to the best of our knowledge, is the first to apply the AFM in cavitation bubble dynamics work, provide evidence that, in the cavitation of liquids within confined spaces, the growth of a cavity may be more damaging than its subsequent collapse.

A new biomarker quantifies differences in clot microstructure in patients with venous thromboembolism

This study compared patients with venous thromboembolism (VTE) to non‐VTE patients using a biomarker of clot microstructure (df) and clot formation time (TGP). df was the only marker that identified a significant difference (P < 0·001) between the VTE (n = 60) and non‐VTE cohorts (n = 69). The ‘abnormal’ clot microstructures in the VTE patients suggests either inadequate response to anticoagulant therapy or the presence of a procoagulant state not detected by other markers of coagulation (i.e., International Normalized Ratio). Furthermore, elevated values of df in first time VTE patients who later develop a secondary event indicates that df may identify those at risk of recurrence.

The role of whole blood impedance aggregometry and its utilisation in the diagnosis and prognosis of patients with systemic inflammatory response syndrome and sepsis in acute critical illness

Objective To assess the prognostic and diagnostic value of whole blood impedance aggregometry in patients with sepsis and SIRS and to compare with whole blood parameters (platelet count, haemoglobin, haematocrit and white cell count). Methods We performed an observational, prospective study in the acute setting. Platelet function was determined using whole blood impedance aggregometry (multiplate) on admission to the Emergency Department or Intensive Care Unit and at 6 and 24 hours post admission. Platelet count, haemoglobin, haematocrit and white cell count were also determined. Results 106 adult patients that met SIRS and sepsis criteria were included. Platelet aggregation was significantly reduced in patients with severe sepsis/septic shock when compared to SIRS/uncomplicated sepsis (ADP: 90.7±37.6 vs 61.4±40.6; p<0.001, Arachadonic Acid 99.9±48.3 vs 66.3±50.2; p = 0.001, Collagen 102.6±33.0 vs 79.1±38.8; p = 0.001; SD ± mean)). Furthermore platelet aggregation was significantly reduced in the 28 day mortality group when compared with the survival group (Arachadonic Acid 58.8±47.7 vs 91.1±50.9; p<0.05, Collagen 36.6±36.6 vs 98.0±35.1; p = 0.001; SD ± mean)). However haemoglobin, haematocrit and platelet count were more effective at distinguishing between subgroups and were equally effective indicators of prognosis. Significant positive correlations were observed between whole blood impedance aggregometry and platelet count (ADP 0.588 p<0.0001, Arachadonic Acid 0.611 p<0.0001, Collagen 0.599 p<0.0001 (Pearson correlation)). Conclusions Reduced platelet aggregometry responses were not only significantly associated with morbidity and mortality in sepsis and SIRS patients, but also correlated with the different pathological groups. Whole blood aggregometry significantly correlated with platelet count, however, when we adjust for the different groups we investigated, the effect of platelet count appears to be non-significant.

Fractal dimension (df) as a new structural biomarker of clot microstructure in different stages of lung cancer

Venous thromboembolism (VTE) is common in cancer patients, and is the second commonest cause of death associated with the disease. Patients with chronic inflammation, such as cancer, have been shown to have pathological clot structures with modulated mechanical properties. Fractal dimension (df) is a new technique which has been shown to act as a marker of the microstructure and mechanical properties of blood clots, and can be performed more readily than current methods such as scanning electron microscopy (SEM). We measured df in 87 consecutive patients with newly diagnosed lung cancer prior to treatment and 47 matched-controls. Mean group values were compared for all patients with lung cancer vs controls and for limited disease vs extensive disease. Results were compared with conventional markers of coagulation, fibrinolysis and SEM images. Significantly higher values of df were observed in lung cancer patients compared with controls and patients with extensive disease had higher values than those with limited disease (p< 0.05), whilst conventional markers failed to distinguish between these groups. The relationship between df of the incipient clot and mature clot microstructure was confirmed by SEM and computational modelling: higher df was associated with highly dense clots formed of smaller fibrin fibres in lung cancer patients compared to controls. This study demonstrates that df is a sensitive technique which quantifies the structure and mechanical properties of blood clots in patients with lung cancer. Our data suggests that df has the potential to identify patients with an abnormal clot microstructure and greatest VTE risk.

Application of ROTEM to assess hypercoagulability in patients with lung cancer

BACKGROUND Venous thromboembolism (VTE) is common in patients with cancer, contributing significantly to morbidity and mortality Currently, no test reliably identifies patients at increased risk of developing VTE who would therefore benefit from prophylactic intervention. The aim of the current study was to evaluate rotational thromboelastometry (ROTEM) in identifying VTE risk in patients with lung cancer. We also compared parameters of ROTEM in patients with limited and extensive disease. METHODS Parameters of ROTEM were measured in 67 patients with lung cancer and 72 age-matched healthy controls and compared with conventional markers of haemostasis. Patients were followed up for 12 months and VTE incidence recorded. RESULTS Lung cancer patients had a reduced clotting time (CT), increased maximum clot firmness (MCF) and increased alpha angle compared with controls. Patients also had significantly higher levels of fibrinogen and PAI-1 than controls and in the former group there was a strong correlation between fibrinogen and both MCF and alpha angle. Six patients developed a VTE during the follow-up period and all had values for MCF at or above the upper limit of normal for EXTEM. CONCLUSIONS This study demonstrates that several ROTEM parameters are significantly different in lung cancer patients compared to healthy age-matched controls, whereas only one of the parameters measured is significantly different between extensive compared to limited disease. No differences were observed between patients who developed a VTE compared to those who did not, highlighting the limitations of ROTEM use in patients with lung cancer.

Gel-point studies in reacting systems by shear wave dispersion measurements

Abstract A study of shear wave dispersion in a gelling system shows that marked changes in dispersion occur due to the viscoelastic liquid to viscoelastic solid transition. A theoretical study suggests that an immediate pre-gel combination of liquid-like and solid-like properties might be detected by shear wave dispersion measurements. Experimental work on a system which exhibits critical gel behaviour gives a high frequency wave dispersion in good agreement with theoretical predictions. The work illustrates the interdependence of the development of the relaxation spectrum at low frequencies and the high frequency wave dispersion, and suggests that measurements of the latter might be used to determine the gel-point in some systems.

Rheology of Dilute Polymer Solutions and Engine Lubricants in High Deformation Rate Extensional Flows Produced by Bubble Collapse

We report a study of liquid jets formed by the collapse of bubbles under cavitation-generated pressure waves. Such jets involve an extensional flow which is characterized by high rates of extension, the latter being relevant to considerations of the flow of oils within dynamically loaded journal bearings. The technique reported here is found to be sensitive to the influence of extremely small concentrations of high molecular weight polymeric additive (xanthan gum). Commercial multigrade oils are also found to exhibit significantly larger resistance to extensional flow than their Newtonian counterparts and, insofar as the multigrade oils studied here are made viscoelastic by polymer additives, and possess significant levels of resistance to extension, the results provide evidence in support of a mitigating effect of viscoelasticity on cavitation, as mooted by Berker et al. [3].

Cavitation phenomena in water involving the reflection of ultrasound pulses from a free surface, or from flexible membranes

We report findings from studies of water subjected to tension by pulsed dynamic stressing which may have significance in the context of assessing the safety of biomedical applications of low-frequency ultrasound. When incident on bubbles near a free surface (or a flexible membrane), shockwaves generated by cavitation bubble collapse are found to lead to the production of liquid jets which are directed towards the surface. Tension pulses generated by reflection of these shockwaves at a free surface initiate, and propagate, the growth of further cavitation bubbles. Estimates of the tensile strength of water, Fc, from measurements of the velocity of these pulses suggest that Fc is far higher than has previously been reported for experiments involving the reflection of low-frequency ultrasound; and the estimate of Fc reported here considerably exceeds the values of tension thought to be generated by ultrasound in many biomedical applications.