Red cell aggregation and viscoelasticity of blood from seals, swine and man

Alginate/xanthan gum hydrogels as forensic blood substitutes for bloodstain formation and analysis

Understanding the behaviour of human blood outside of the body has important implications in forensic research, especially related to bloodstain pattern analysis (BPA). The design of forensic blood substitutes (FBSs) can provide many advantages, including the incorporation of multiple physiological components for use as safe and reliable materials for forensic applications. In this work, we present the design of synthetic alginate and xanthan gum-based hydrogels that contain electrosprayed microparticles (MPs) with and without crosslinked DNA. In addition to the MPs, the alginate/xanthan gum FBS materials include fillers to alter the physical appearance and fluid properties of the material. The optimized FBS consisted of alginate (1% w/v) and xanthan gum (5.0 × 10^-3% w/v), 2 mM CaCl₂, ferric citrate (0.5% w/v), magnesium silicate (0.25% w/v), Allura Red dye (2% w/v), 0.025% v/v Tween 20 and 9.5% v/v MPs. The FBS was tested in passive dripping experiments relevant to BPA scenarios at various impact angles. The spreading ratio (D_s/D₀) was determined for 90° stains made on a paper surface and compared to bovine blood where the FBS was shown to simulate accurate and predictable spreading behaviour. In addition, we simulated other common BPA scenarios (e.g., impact patterns) and evidence processing potential. The FBS could be swabbed, and the DNA could be extracted, amplified, and genotyped analogous to human blood evidence. A stability test was also conducted which revealed a shelf-life of over 4 weeks where the material remains relevant to human blood at physiological temperature.

Whole bovine blood use in forensic research: Sample preparation and storage considerations

Mammalian whole blood sources are often used for forensic research and training when human samples cannot be sourced. While porcine, ovine and equine blood have been shown to be viable alternatives to whole human blood for forensic purposes, procurement can still pose a problem, especially for smaller and remote institutions. This work explores the use of whole bovine blood for basic bloodstain simulation. Sample preparation through the addition of ACD-A anticoagulant was optimized and storability was explored. Viscosity, surface tension, density, and packed cell volume, four fluid properties relevant to bloodstain pattern analysis, were monitored over four days and in two temperature conditions. Linear mixed models accounting for variation in the donor demonstrated that these fluid properties of the bovine blood changed predictably over time and with temperature. Whole bovine blood with 12.5% v/v ACD-A was found to be viable for use in basic bloodstain simulation at ambient and physiological temperature.

Effects of a TASER® conducted energy weapon on the circulating red-blood-cell population and other factors in Sus scrofa

In previous studies hematocrit has been consistently increased in an anesthetized animal model after exposures to TASER(®) conducted energy weapons (CEWs). In the present study we analyzed changes in blood cell counts and red blood cell membrane proteins following two 30-s applications of a TASER C2 device (which is designed for civilian use). Hematocrit increased significantly from 33.2 ± 2.4 (mean ± SD) to 42.8 ± 4.6 % immediately after CEW exposure of eleven pigs (Sus scrofa). Red blood cell count increased significantly from 6.10 ± 0.55 × 10(12)/L to 7.45 ± 0.94 × 10(12)/L, and mean corpuscular volume increased significantly from 54.5 ± 2.4 fl to 57.8 ± 2.6 fl. Mean corpuscular hemoglobin concentration decreased significantly from 20.5 ± 0.7 to 18.5 ± 0.6 mM. Thirty protein spots (from two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis, selected for detailed comparison) exhibited greater densities 30-min post-exposure compared with pre-exposure values. A greater number of echinocytes were observed following CEW exposure. On the basis of these results it appears that, during the strong muscle contractions produced by TASER CEWs, a specific population of red blood cells (RBCs) may be released from the spleen or other reservoirs within the body. The total time of CEW exposure in the present study was relatively long compared with exposures in common law-enforcement scenarios. Despite statistically significant changes in red blood cell counts (and other measures directly related to RBCs), the alterations were short-lived. The transient nature of the changes would be likely to counteract any potentially detrimental effects.

Evaluation of two devices for point-of-care testing of haemoglobin in neonatal pigs

In veterinary medicine, point-of-care testing (POCT) techniques have become popular, since they provide immediate results and only small amounts of blood are needed. However, their accuracy is controversial. Pigs are often used for research purposes and accurate measurement of haemoglobin (Hb) is important during invasive procedures. The aim of this study was to evaluate two different Hb POCT devices in neonatal pigs. A prospective study with 57 pigs of 3-6 weeks of age, weighing 4.1-6.2 kg (median 5.1 kg) was performed. Fifty-seven blood samples were analysed for Hb using a conductivity-based and a photometrical POCT device and compared with a photometrical reference method. Statistical analysis was performed with Bland-Altman analysis, Spearman correlation and Passing-Bablok regression analysis. Hb values ranged from 32 to 108 g/L (median 80 g/L) using the reference method. The bias of the photometrical method (HemoCue(®)) to the reference method was -1 g/L, with limits of agreement (LOA) of -7 to 6 g/L. The conductivity-based method (i-STAT(®)) had a bias of -15 g/L with LOA from -24 to -6 g/L. There was a significant association between protein values and the bias of i-STAT versus CellDyn (r(2) = 0.27, P < 0.05) but not with the bias of HemoCue versus CellDyn (r(2) = 0.001, P = 0.79). The lower the protein values were, the lower the Hb values were measured by the i-STAT. The conductivity-based measurement of Hb constantly underestimated Hb values, whereas the photometrical method demonstrated a better accuracy and is therefore more reliable for on-site measurement of Hb in pigs.

Increased hematocrit after applications of conducted energy weapons (including TASER(®) devices) to Sus scrofa

Conducted energy weapons (CEWs) are used by law enforcement personnel to incapacitate individuals quickly and effectively, without intending to cause lethality. CEWs have been deployed for relatively long or repeated exposures in some cases. In laboratory animal models, central venous hematocrit has increased significantly after CEW exposure. Even limited applications (e.g., three 5-sec applications) resulted in statistically significant increases in hematocrit. Preexposure hematocrit was significantly higher in nonsurvivors versus survivors after more extreme CEW applications. The purpose of this technical note is to address specific questions that may be generated when examining these results. Comparisons among results of CEW applications, other electrical muscle stimulation, and exercise/voluntary muscle contraction are included. The anesthetized swine appears to be an acceptable animal model for studying changes in hematocrit and associated red blood cell changes. Potential detrimental effects of increased hematocrit, and considerations during law enforcement use, are discussed.

Blood rheology in marine mammals

The field of blood oxygen transport and delivery to tissues has been studied by comparative physiologists for many decades. Within this general area, the particular differences in oxygen delivery between marine and terrestrial mammals has focused mainly on oxygen supply differences and delivery to the tissues under low blood flow diving conditions. Yet, the study of the inherent flow properties of the blood itself (hemorheology) is rarely discussed when addressing diving. However, hemorheology is important to the study of marine mammals because of the critical nature of the oxygen stores that are carried in the blood during diving periods. This review focuses on the essential elements of hemorheology, how they are defined and on fundamental rheological applications to marine mammals. While the comparative rationale used throughout the review is much broader than the particular problems associated with diving, the basic concepts focus on how changes in the flow properties of whole blood would be critical to oxygen delivery during diving. This review introduces the reader to most of the major rheological concepts that are relevant to the unique and unusual aspects of the diving physiology of marine mammals.

Viscosity of Animal Erythrocyte Suspensions mixed with a Perflurocarbon Emulsion

Artificial blood substitutes (ABS) offer an alternative to donated blood. Increasing the oxygen carrying capacity of blood plasma through the addition of a Perfluorocarbon emulsion (PFE) is one approach in creating a blood substitute. The peripheral resistance of the circulatory system may be altered depending on the rheological properties of the ABS. Measurements of the rheological behavior of mixtures of a PFE, Oxygent, and erythrocyte suspensions were conducted at room temperature at different hematocrits using sheep (nonaggregating) and swine (aggregating) erythrocytes. The pure PFE was found to be shear thinning. Adding 6 and 12 g per 100 mL of sheep blood at the various hematocrits increased the viscosity of the suspension from as low as 4% (6 g PFE/40% Hct) to as high as 26.5% (12 g PFE/plasma). The nonaggregating sheep erythrocyte and PFE mixtures exhibited Newtonian behavior. Shear thinning behavior continued upon addition of 6 and 12 g per 100 mL of swine blood at the various hematocrits, with a slight increase in viscosity in most cases. It was observed that adding 12 g of PFE (approximately 3 x intended clinical dose) to 40% Hct swine blood at room temperature led to a significant decrease in viscosity.

Blood values of juvenile northern elephant seals (Mirounga angustirostris) obtained using a portable clinical analyzer

BACKGROUND

Sick, injured, or orphaned juvenile northern elephant seals (Mirounga angustisrostris) treated at rehabilitation centers frequently present with abnormalities in blood sodium, potassium, chloride, BUN, and glucose concentrations, and HCT. These abnormalities could be detected rapidly using a portable blood analyzer, but results with this analysis method do not necessarily equate with those obtained using other techniques.

OBJECTIVE

The objective of this study was to better assess the clinical relevance of values obtained from a portable analyzer and to compare the results with values obtained using more common methods of analysis.

METHODS

Heparinized whole blood samples were collected from 20 rehabilitated juvenile northern elephant seals. A portable clinical analyzer (i-STAT, i-STAT Corp, East Windsor, NJ, USA) was used to establish baseline values. Serum biochemical values were obtained using an automated chemical analyzer (Olympus AU5200, Olympus America, Melville, NY, USA). HCT was determined using EDTA whole blood and a cell counter.

RESULTS

Using the portable analyzer, mean (minimum-maximum) values were obtained for sodium, 143 (132-146) mmol/L; potassium, 4.4 (3.9-5.8) mmol/L; chloride, 106 (101-109) mmol/L; BUN, 1.8 (1.1-2.4) mmol/L; glucose, 7.55 (5.99-8.49) mmol/L; and HCT, 0.55 (0.52-0.61) L/L. Average differences between methods were small for potassium (-0.45 mmol/L), BUN (0.1 mmol/L), and HCT (0.037 L/L) but were large for sodium (-6.8 mmol/L), chloride (-6.4 mmol/L), and glucose (-0.56 mmol/L).

CONCLUSIONS

These results suggest that the i-STAT portable analyzer could be useful for clinically assessing juvenile elephant seals. However, when making medical decisions, the clinician should be aware of differences associated with various analyzers and sample types.

Inhibition of red cell aggregation prevents spontaneous echocardiographic contrast formation in human blood

BACKGROUND

Spontaneous echocardiographic contrast (SEC) is a pattern of blood echogenicity that has been attributed to ultrasonic backscatter from blood cell aggregates that form under low shear conditions. Patients with left atrial SEC have an increased thromboembolic risk. This study examined the role of red cell and platelet aggregates in the pathogenesis of SEC in human blood and the effects on SEC of antithrombotic therapy and red cell disaggregatory agents.

METHODS AND RESULTS

Blood echogenicity was examined with the use of quantitative videodensitometry over a controlled range of flow velocities in an in vitro model characterized by nonlaminar flow conditions. One hundred ninety study samples were prepared from single fresh blood donations (40 to 120 mL) from 24 healthy volunteers and 11 patients. Whole blood echogenicity was unaltered by depletion of platelets, stimulation of platelet aggregation with adenosine diphosphate, or inhibition of platelet aggregation with aspirin. Low flow-related echogenicity increased with increasing hematocrit (P<.001) but was abolished when red cells were lysed selectively with saponin (P<.001). In the presence of red cells, low flow-related echogenicity increased with increasing fibrinogen concentration (P<.001) and with plasma paraproteins. Low flow-related echogenicity in whole blood was unaltered by heparin and warfarin but was reduced in a dose-dependent manner by dextran 40 (40 mg/mL, 70% reduction, P<.001) and poloxamer 188 (8 mg/mL, 47% reduction, P<.001), which inhibited red cell aggregation.

CONCLUSIONS

These results support protein-mediated red cell aggregation as the mechanism of SEC in human blood. Inhibition of red cell aggregation, indexed by resolution of SEC, may provide an alternative to anticoagulant and antiplatelet therapy to reduce cardiac thromboembolic risk.

In vivo and in vitro studies on the mechanism and clinical significance of spontaneous echocardiographic contrast in patients with atrial dysrhythmias

The pathogenesis of spontaneous echocardiographic contrast (SEC) is complex and multifactorial. Although originally described in low-flow state situations such as in the left atrium of patients with mitral stenosis or in the false lumen of patients with aortic dissection, its detection is highly dependent on technical factors such as the frequency of the transducer used. Multiple blood components have been implicated in SEC formation and erythrocyte aggregation currently appears to be the most likely mechanism. SEC is related to atrial fibrillation and is commonly found in patients with thrombus or prior history of thromboembolism. In addition, it may represent a prognostic marker for patients with atrial fibrillation because patients with SEC have a higher incidence of subsequent thromboembolic events. Therapeutic options include anticoagulation and, perhaps, antiplatelet therapy. Further prospective studies are necessary to better define SEC pathogenesis and treatment.

Quantification of blood echogenicity: evaluation of a semiquantitative method of grading spontaneous echo contrast

Spontaneous echo contrast (SEC) is an echogenic, swirling pattern of blood flow which may be observed by transesophageal echocardiography (TEE) in the left atrium in low flow states, such as atrial fibrillation (AF). The presence of SEC has been proposed as a marker of increased thromboembolic risk. Evaluation of the severity of SEC might be useful in stratification of thromboembolic risk. The aim of this study was to validate a semiquantitative method of grading SEC against quantitative videodensitometric analysis. TEE studies were performed in 50 patients with AF. The severity of left atrial SEC was graded by three independent observers and by videodensitometry. There was a strong, positive correlation between the semiquantitative grades of SEC and quantitative videodensitometric scores (r = 0.85, P < 0.0001). Inter- and intraobserver correlations in the grading of SEC were very high (observer 1 vs. 2: r = 0.98, P = 0.0001; observer 1 vs. 3: r = 0.93, P = 0.0001; observer 1 vs. 1: r = 0.97, P = 0.0001). Semiquantitative grading of SEC can be performed rapidly and reliably by experienced observers. These results support the use of semiquantitative grading in studies of the pathogenesis and prognostic implications of SEC.

Echocardiographic "smoke" is produced by an interaction of erythrocytes and plasma proteins modulated by shear forces

OBJECTIVES

This study was designed to determine the blood elements responsible for spontaneous echocardiographic contrast.

BACKGROUND

Spontaneous contrast or "smoke" is an echocardiographic image usually found in low flow conditions. Two blood elements, erythrocytes and platelets, have been related to the generation of smoke.

METHODS

The echogenicity of porcine blood products was assessed in static and flow conditions and was graded on a digitized videodensity computer program that assigned a score of 0 for black and 100 for white images. Blood elements were circulated from a small tube (4-mm diameter) into a larger cylindric chamber (30-mm diameter) under controlled flow rate conditions. The following blood products were studied: whole blood, platelet-depleted blood, platelet-rich plasma, platelet-poor plasma, erythrocytes suspended in saline solution, adenosine diphosphate (ADP) added to platelet-rich plasma, and saline solution as a control medium.

RESULTS

As blood flow was increased in 30 ml/min increments from 0 to 180 ml/min, whole blood echo videodensity (scale 0 to 100) progressively decreased in the larger tube from 38 and 42 to 20, 12, 14, 16 and 14, respectively. When flow increased from 0 to 30 ml/min in the smaller tube, corresponding to a wall shear rate of 0 to 80 s-1, the blood entering the chamber was completely echolucent. The echogenicity of blood products in the larger tube was for static flow (0 ml/min) and high flow (180 ml/min), respectively: platelet-depleted blood = 36 and 14; platelet-rich plasma = 2 and 2; platelet-poor plasma = 0 and 0; erythrocytes in saline solution = 8 and 12; ADP added to platelet-rich plasma = 0 and 15; saline solution = 0 and 0. Because platelets alone were nonechogenic but platelet-depleted blood produced a flow-dependent echogenicity similar to that produced by whole blood, platelets may not be involved in the production of smoke. However, when platelets were aggregated by ADP, they were echogenic but in dense clumps and in a flow-independent pattern not typical of the smokelike images. Erythrocytes suspended in saline solution had an intermediate density image.

CONCLUSIONS

Echogenic smoke appears to be due primarily to the interaction of red blood cells and plasma proteins at low flow and low shear rate conditions.