Increases in core temperature counterbalance effects of haemoconcentration on blood viscosity during prolonged exercise in the heat

Hormonal Control of Blood Viscosity

The hemodynamic milieu differs throughout the vascular tree because of varying vascular geometry and blood velocities. Accordingly, the risk of turbulence, which is dictated by the Reynolds and Dean numbers, also varies. Relatively high blood viscosity is needed to prevent turbulence in the left ventricle and aorta, where high-velocity blood changes direction several times. Low blood viscosity is needed in the capillaries, where erythrocytes pass through vessels with a diameter smaller than their own. In addition, higher blood viscosity is necessary when the cardiac output and peak blood velocity increase as a part of a sympathetic response or anemia, which occurs following significant hemorrhage. Blood viscosity, as reflected in systemic vascular resistance and vascular wall shear stress, is sensed, respectively, by cardiomyocyte stretching in the left ventricle and mechanoreceptors for wall shear stress in the carotid sinus. By controlling blood volume and red blood cell mass, the renin-aldosterone-angiotensin system and the systemic vascular resistance response control the hematocrit, the strongest intrinsic determinant of blood viscosity. These responses provide gross control of blood viscosity. Fine-tuning of blood viscosity in transient conditions is provided by hormonal control of erythrocyte deformability. The short half-life of some of these hormones limits their activity to specific vascular beds. Hormones that modulate blood viscosity include erythropoietin, angiotensin II, brain natriuretic factor, epinephrine, prostacyclin E2, antidiuretic hormone, and nitric oxide.

Effects of supplementing processed velvet beans (Mucuna pruriens L. DC. var. utilis) on nutrients intakes, growth performance, and blood profile in goats

Ruminant production in West Africa faces both qualitative and quantitative feeding constraints during the dry season and animal diseases in smallholder farms. High-protein legume seeds can represent an alternative and sustainable feed that could enhance animal performance. The use of legume beans, limited by their anti-nutritional factor contents, can be improved through different detoxification methods. The study evaluated the effects of processed velvet beans compared to raw velvet beans on the nutritive value of the beans, nutrient intakes, growth performance, and blood profile in West African Dwarf (WAD) goats. Four diets were tested, including 22.22% of raw velvet beans (RW diet), soaked beans (SK diet), boiled beans (BL diet), or roasted beans (RT diet). Twenty WAD goats of 6.85 ± 0.93 kg of body weight were divided equally into 4 groups and fed one of the four experimental diets. The processing method affects the crude protein content of velvet beans; in particular, tannin content was reduced with soaking or boiling. Dry matter and nutrient intakes resulted significantly (p < 0.05) higher in the SK diet compared to the control. Daily weight gain was highest in SK and RT diets and lowest in BL and the control diets RW. Therefore, the FCR was highest in BL and lowest in SK diets. In addition, SK diet showed the lowest feeding cost (1046.70 XOF/kg WG in SK). Our study revealed that processed velvet beans obtained using simple methods (e.g., soaking, boiling, or roasting) could be used as low-cost protein supplements in smallholder farms to enhance goats' performance. The soaking method appears the simplest and cheapest process that smallholder farmers can easily use to enhance goats' productivity and improve their livelihoods.

Emerging Microfluidic Devices for Sample Preparation of Undiluted Whole Blood to Enable the Detection of Biomarkers

Blood testing allows for diagnosis and monitoring of numerous conditions and illnesses; it forms an essential pillar of the health industry that continues to grow in market value. Due to the complex physical and biological nature of blood, samples must be carefully collected and prepared to obtain accurate and reliable analysis results with minimal background signal. Examples of common sample preparation steps include dilutions, plasma separation, cell lysis, and nucleic acid extraction and isolation, which are time-consuming and can introduce risks of sample cross-contamination or pathogen exposure to laboratory staff. Moreover, the reagents and equipment needed can be costly and difficult to obtain in point-of-care or resource-limited settings. Microfluidic devices can perform sample preparation steps in a simpler, faster, and more affordable manner. Devices can be carried to areas that are difficult to access or that do not have the resources necessary. Although many microfluidic devices have been developed in the last 5 years, few were designed for the use of undiluted whole blood as a starting point, which eliminates the need for blood dilution and minimizes blood sample preparation. This review will first provide a short summary on blood properties and blood samples typically used for analysis, before delving into innovative advances in microfluidic devices over the last 5 years that address the hurdles of blood sample preparation. The devices will be categorized by application and the type of blood sample used. The final section focuses on devices for the detection of intracellular nucleic acids, because these require more extensive sample preparation steps, and the challenges involved in adapting this technology and potential improvements are discussed.

From Localized Mild Hyperthermia to Improved Tumor Oxygenation: Physiological Mechanisms Critically Involved in Oncologic Thermo-Radio-Immunotherapy

(1) Background: Mild hyperthermia (mHT, 39-42 °C) is a potent cancer treatment modality when delivered in conjunction with radiotherapy. mHT triggers a series of therapeutically relevant biological mechanisms, e.g., it can act as a radiosensitizer by improving tumor oxygenation, the latter generally believed to be the commensurate result of increased blood flow, and it can positively modulate protective anticancer immune responses. However, the extent and kinetics of tumor blood flow (TBF) changes and tumor oxygenation are variable during and after the application of mHT. The interpretation of these spatiotemporal heterogeneities is currently not yet fully clarified. (2) Aim and methods: We have undertaken a systematic literature review and herein provide a comprehensive insight into the potential impact of mHT on the clinical benefits of therapeutic modalities such as radio- and immuno-therapy. (3) Results: mHT-induced increases in TBF are multifactorial and differ both spatially and with time. In the short term, changes are preferentially caused by vasodilation of co-opted vessels and of upstream normal tissue vessels as well as by improved hemorheology. Sustained TBF increases are thought to result from a drastic reduction of interstitial pressure, thus restoring adequate perfusion pressures and/or HIF-1α- and VEGF-mediated activation of angiogenesis. The enhanced oxygenation is not only the result of mHT-increased TBF and, thus, oxygen availability but also of heat-induced higher O₂ diffusivities, acidosis- and heat-related enhanced O₂ unloading from red blood cells. (4) Conclusions: Enhancement of tumor oxygenation achieved by mHT cannot be fully explained by TBF changes alone. Instead, a series of additional, complexly linked physiological mechanisms are crucial for enhancing tumor oxygenation, almost doubling the initial O₂ tensions in tumors.

Intravascularly infused extracellular matrix as a biomaterial for targeting and treating inflamed tissues

Decellularized extracellular matrix in the form of patches and locally injected hydrogels has long been used as therapies in animal models of disease. Here we report the safety and feasibility of an intravascularly infused extracellular matrix as a biomaterial for the repair of tissue in animal models of acute myocardial infarction, traumatic brain injury and pulmonary arterial hypertension. The biomaterial consists of decellularized, enzymatically digested and fractionated ventricular myocardium, localizes to injured tissues by binding to leaky microvasculature, and is largely degraded in about 3 d. In rats and pigs with induced acute myocardial infarction followed by intracoronary infusion of the biomaterial, we observed substantially reduced left ventricular volumes and improved wall-motion scores, as well as differential expression of genes associated with tissue repair and inflammation. Delivering pro-healing extracellular matrix by intravascular infusion post injury may provide translational advantages for the healing of inflamed tissues 'from the inside out'.

Exercise-related hemoconcentration and hemodilution in hydrated and dehydrated athletes: An observational study of the Hungarian canoeists

Hemoconcentration during exercise is a well-known phenomenon, however, the extent to which dehydration is involved is unclear. In our study, the effect of dehydration on exercise-induced hemoconcentration was examined in 12 elite Hungarian kayak-canoe athletes. The changes of blood markers were examined during acute maximal workload in hydrated and dehydrated states. Dehydration was achieved by exercise, during a 120-minute extensive-aerobic preload. Our research is one of the first studies in which the changes in blood components were examined with a higher time resolution and a wider range of the measured parameters. Hydration status had no effect on the dynamics of hemoconcentration during both the hydrated (HS) and dehydrated (DHS) load, although lower maximal power output were measured after the 120-minute preload [HS Hemoglobin(Hgb)Max median 17.4 (q1 17.03; q3 17.9) g/dl vs. DHS HgbMax median 16.9 (q1 16.43; q3 17.6) g/dl (n.s); HS Hematocrit(Hct)Max 53.50 (q1 52.28; q3 54.8) % vs. DHS HctMax 51.90 (q1 50.35; q3 53.93) % (n.s)]. Thirty minutes after the maximal loading, complete hemodilution was confirmed in both exercises. Dehydration had no effect on hemoconcentration or hemodilution in the recovery period [HS HgbR30' 15.7 (q1 15.15; q3 16.05) g/dl (n.s.) vs. DHS HgbR30' 15.75 (q1 15.48; q3 16.13) g/dl (n.s.), HS HctR30' 48.15 (q1 46.5; q3 49.2) % vs. DHS HctR30' 48.25 (q1 47.48; q3 49.45) % (n.s.)], however, plasma osmolality did not follow a corresponding decrease in hemoglobin and hematocrit in the dehydrated group. Based on our data, metabolic products (glucose, lactate, sodium, potassium, chloride, bicarbonate ion, blood urea nitrogen) induced osmolality may not play a major role in the regulation of hemoconcentration and post-exercise hemodilution. From our results, we can conclude that hemoconcentration depends mainly on the intensity of the exercise.

Hemodynamical analysis of MHD two phase blood flow through a curved permeable artery having variable viscosity with heat and mass transfer

A numerical investigation of MHD blood flow through a stenosed permeable curved artery has been done in this study. Blood flow is considered in two-phases; core and plasma region, respectively. Viscosity of the core region is considered as temperature-dependent, while constant viscosity is considered in plasma region. The governing equations of the proposed two-phase blood flow model are considered in the toroidal coordinate system. The second-order finite difference method is adopted to solve governing equations with [Formula: see text] tolerance in the iteration process. A comparative study of Darcy number (Da) is performed to understand the influence of permeable and impermeable wall conditions. The effect of various physical parameters such as magnetic field (M), viscosity variation parameter ([Formula: see text]), Darcy number (Da), heat source (H) and chemical reaction parameter ([Formula: see text]) is displayed graphically on the flow velocity, temperature, concentration, wall shear stress and frictional resistance profiles. A comparison with published work has also been displayed through the graph to validate the present model, and it is in fair agreement with the existing work. The present study suggested that the curvature and permeability of the arterial wall raise the risk of atherosclerosis formation, while the implication of heat source on the blood flow lower this risk.

High-Resolution Dynamics of Hemodilution After Exercise-Related Hemoconcentration

Purpose: Hemoconcentration during acute intense exercise is intensively investigated, while the rearrangement of hematological parameters during the recovery period is less understood. The aim of our study was to understand the mechanisms of hemodilution after short-term dynamic exercise. Methods: Twelve euhydrated male kayak athletes and 6 untrained controls were examined on a spiroergometer. In addition to the continuous recording of circulatory parameters, blood samples were taken at rest, at maximum load, and during restitution with a dense sampling frequency. Hemoglobin, hematocrit, osmolality, blood components, and core temperature were measured. Results: The hemoconcentration, independently of training status, reached its maximum (athletes Δ9.59% [4.18%] vs controls Δ11.85% [2.71%]) in the first minute of the recovery period. There was a significant increase in core temperature, reducing the viscosity of blood and promoting tissue oxygenation. High cardiac output and the increased blood flow compensate for viscosity being elevated by hemoconcentration during exercise. Hemoconcentration was maintained for 7 to 10 minutes and then diluted back to baseline 30 minutes after exercise. Temporarily higher viscosity during reduced cardiac output may result in a critical hemoconcentration zone, elevating the risk of circulatory overload. Elite athletes have a faster cardiac output decrease compared with that of hemodilution, making the circulation more vulnerable. We supposed that hemodilution was guided independently by plasma- and erythrocyte-related effectors. Conclusions: After high-intensity dynamic acute exercise, hemodilution is driven by independent factors, and a critical hemoconcentration zone may be formed during the recovery period in trained elite athletes.

Standardization for obtaining blood viscosity: A systematic review

INTRODUCTION

There is evidence to suggest that blood viscosity (BV) is involved in several pathological processes. In this review, we evaluated the different methods of BV acquisition, analyzing the sample storage time, the storage temperature, the acquisition time, the acquisition temperature, sample volume, and shear rates, in order to standardize this technique.

METHODS

We selected 50 articles with methods of obtaining BV, evaluating pathologies through BV, comparing rheological equipment, monitoring, and regulating BV.

RESULTS AND CONCLUSION

Measurements should be obtained as soon as possible, to reduce hemorheological changes. It is necessary to refrigerate them at 4°C when the storage time is long. The acquisition time is related to the equipment used. BV measurements at 37°C will represent the real BV in vivo more faithfully. In order to understand the BV phenomena, the shear rates must be between 0.1 and 1000 s-1. There is a wide variety of equipment available for measuring the BV.

Distinct contributions of skin and core temperatures to flow-mediated dilation of the brachial artery following passive heating

The primary determinant of vascular adaptations to lifestyle interventions, such as exercise and heat therapy, is repeated elevations in vascular shear stress. Whether skin or core temperatures also modulate the vascular adaptation to acute heat exposure is unknown, likely due to difficulty in dissociating the thermal and hemodynamic responses to heat. We found that skin and core temperatures modify the acute vascular responses to passive heating irrespective of the magnitude of increase in shear stress.

Endothelial function and shear stress in hypobaric hypoxia: time course and impact of plasma volume expansion in men

High-altitude exposure typically reduces endothelial function, and this is modulated by hemoconcentration resulting from plasma volume contraction. However, the specific impact of hypobaric hypoxia independent of external factors (e.g., cold, varying altitudes, exercise, diet, and dehydration) on endothelial function is unknown. We examined the temporal changes in blood viscosity, shear stress, and endothelial function and the impact of plasma volume expansion (PVX) during exposure to hypobaric hypoxia while controlling for external factors. Eleven healthy men (25 ± 4 yr, mean ± SD) completed two 4-day chamber visits [normoxia (NX) and hypobaric hypoxia (HH; equivalent altitude, 3,500 m)] in a crossover design. Endothelial function was assessed via flow-mediated dilation in response to transient (reactive hyperemia; RH-FMD) and sustained (progressive handgrip exercise; SS-FMD) increases in shear stress before entering and after 1, 6, 12, 48, and 96 h in the chamber. During HH, endothelial function was also measured on the last day after PVX to preexposure levels (1,140 ± 320 mL balanced crystalloid solution). Blood viscosity and arterial shear stress increased on the first day during HH compared with NX and remained elevated at 48 and 96 h (P < 0.005). RH-FMD did not differ during HH compared with NX and was unaffected by PVX despite reductions in blood viscosity (P < 0.05). The stimulus-response slope of increases in shear stress to vasodilation during SS-FMD was preserved in HH and increased by 44 ± 73% following PVX (P = 0.023). These findings suggest that endothelial function is maintained in HH when other stressors are absent and that PVX improves endothelial function in a shear-stress stimulus-specific manner.NEW & NOTEWORTHY Using a normoxic crossover study design, we examined the impact of hypobaric hypoxia (4 days; altitude equivalent, 3,500 m) and hemoconcentration on blood viscosity, shear stress, and endothelial function. Blood viscosity increased during the hypoxic exposure and was accompanied by elevated resting and exercising arterial shear stress. Flow-mediated dilation stimulated by reactive hyperemia and handgrip exercise was preserved throughout the hypoxic exposure. Plasma volume expansion reversed the hypoxia-associated hemoconcentration and selectively increased handgrip exercise flow-mediated dilation.

Effects of electrolyzed hydrogen water ingestion during endurance exercise in a heated environment on body fluid balance and exercise performance

Electrolyzed hydrogen water (EHW) is generated at a cathode. It contains many hydrogen molecules with high alkaline properties. The physiological effects of ingesting EHW during endurance exercise are unclear. The purpose of this study was to determine the effects of ingesting EHW during endurance exercise in a heated environment on body fluid balance and exercise performance. Twelve triathletes (20.0 ± 1.3 years, 171 ± 6 cm, 60.6 ± 3.9 kg, V̇O_2max 67.1 ± 3.8 mL/kg/min) performed pedaling exercise for 60 min at 65% of V̇O_2max consuming either purified water (CON trial) or EHW (EHW trial) and then conducted an incremental pedaling test. Blood parameters, tissue temperature, and respiratory variables were determined during 60 min of exercise. The time to exhaustion (TTE) during the incremental pedaling test was also determined. Body weights were 1.1 ± 0.4 kg lower after exercise, with no significant differences between trials. Plasma volume and serum osmolality and blood sodium and potassium concentrations significantly changed with exercise, but no significant differences were observed between trials. The pH, blood lactate and bicarbonate concentrations, and changes in skin and muscle temperature did not significantly differ between the two trials. Energy expenditure during exercise was significantly (P = 0.04) lower in the EHW trial (13.2 ± 0.5 kcal/min) than in the CON trial (13.7 ± 0.4 kcal/min). TTE did not significantly differ between the trials. In conclusion, EHW ingestion during endurance exercise in a heated environment decreased energy expenditure but did not affect body fluid balance or exercise performance. Abbreviations: CON: control trial; CV: coefficient of variation; EHW: electrolyzed hydrogen water; HR: heart rate; RPE: rating of perceived exertion; SE: standard error; TP: total protein; TTE: time to exhaustion.

Blood Rheology: Key Parameters, Impact on Blood Flow, Role in Sickle Cell Disease and Effects of Exercise

Blood viscosity is an important determinant of local flow characteristics, which exhibits shear thinning behavior: it decreases exponentially with increasing shear rates. Both hematocrit and plasma viscosity influence blood viscosity. The shear thinning property of blood is mainly attributed to red blood cell (RBC) rheological properties. RBC aggregation occurs at low shear rates, and increases blood viscosity and depends on both cellular (RBC aggregability) and plasma factors. Blood flow in the microcirculation is highly dependent on the ability of RBC to deform, but RBC deformability also affects blood flow in the macrocirculation since a loss of deformability causes a rise in blood viscosity. Indeed, any changes in one or several of these parameters may affect blood viscosity differently. Poiseuille's Law predicts that any increase in blood viscosity should cause a rise in vascular resistance. However, blood viscosity, through its effects on wall shear stress, is a key modulator of nitric oxide (NO) production by the endothelial NO-synthase. Indeed, any increase in blood viscosity should promote vasodilation. This is the case in healthy individuals when vascular function is intact and able to adapt to blood rheological strains. However, in sickle cell disease (SCD) vascular function is impaired. In this context, any increase in blood viscosity can promote vaso-occlusive like events. We previously showed that sickle cell patients with high blood viscosity usually have more frequent vaso-occlusive crises than those with low blood viscosity. However, while the deformability of RBC decreases during acute vaso-occlusive events in SCD, patients with the highest RBC deformability at steady-state have a higher risk of developing frequent painful vaso-occlusive crises. This paradox seems to be due to the fact that in SCD RBC with the highest deformability are also the most adherent, which would trigger vaso-occlusion. While acute, intense exercise may increase blood viscosity in healthy individuals, recent works conducted in sickle cell patients have shown that light cycling exercise did not cause dramatic changes in blood rheology. Moreover, regular physical exercise has been shown to decrease blood viscosity in sickle cell mice, which could be beneficial for adequate blood flow and tissue perfusion.

Effect of heat exposure and physical exercise until exhaustion in normothermic and hyperthermic conditions on serum, sweat and urinary concentrations of magnesium and phosphorus

AIM

The aim of this survey was to ascertain the difference in the levels of Magnesium (Mg) and Phosphorus (P) after an exercise test in normothermia and hyperthermia before and after heat acclimation in comparison to their respective pre-test values.

METHODS

Twenty-nine male university students were divided into an Experimental Group (EG) (n = 15) and a Control Group (CG) (n = 14). All of them voluntarily participated in this investigation. Both groups performed an incremental test until exhaustion on a cycloergometer in normothermia (22 °C) and hyperthermia (42 °C). EG underwent 9 sessions of heat acclimation (100 °C) in a sauna (Harvia C105S Logix Combi Control; 3-15 W; Finland). Once the experimental period was completed, all initial measurements were carried out again under identical conditions. Urine and blood samples were obtained before and after each trial. Sweat samples were collected at the end of every test performed in hyperthermia. The samples were frozen at -80 °C until further analysis by ICP-MS.

RESULTS

Lower seric Mg levels were observed in both groups at the end of pre-acclimation tests. After acclimation, only EG experimented a decrease of Mg in serum after testing (p < .01). The urinary excretion was unaffected in the pre-acclimated period, but EG experimented an increase in Mg after trials in the post-acclimation evaluation (p < .01). Mg sweat loss decreased significantly after heat acclimation (p < .05). P did not undergo changes, except in its urinary excretion, which was elevated after the normothermia trial in the post-acclimation period (p < .05).

CONCLUSIONS

It seems that exercise in hyperthermia altered Mg status but not P homeostasis. Additionally, heat acclimation reduces Mg losses in sweat while increasing its loss in urine. Thus, Mg supplementation should be considered in unacclimated and acclimated subjects if physical exercise is going to be performed in hyperthermic conditions.

Influence of a physical exercise until exhaustion in normothermic and hyperthermic conditions on serum, erythrocyte and urinary concentrations of magnesium and phosphorus

AIM

The aim of this study was to evaluate the effect of the performance of a maximal exercise test until exhaustion in normothermic and hyperthermic conditions on body concentrations of magnesium (Mg) and phosphorus (P).

METHODS

19 adult males (age: 22.58 ± 1.05 years) performed two maximum incremental exercise tests on a cycloergometer separated by 48 h. The first was performed in normothermia (22 ± 2 °C) and the second in hyperthermic conditions induced with a sauna (42 ± 2 °C). Blood and urine samples were taken before and after each test.

RESULTS

The tests in hyperthermia did not produce ergospirometric alterations or a noticeable cardiovascular drift. Serum Mg concentrations underwent a reduction after the stress test in hyperthermia (p > 0.05) but not in normothermia. Nevertheless, urinary and erythrocyte concentrations of Mg, and urinary, erythrocyte and serum concentrations of P did not undergo alterations in either conditions.

CONCLUSIONS

It seems that exercise in hyperthermic conditions induces a tissue redistribution of Mg in the body, a fact which was not observed in normothermic conditions.

Rat red blood cell storage lesions in various additive solutions

BACKGROUND

Small rodent models are routinely used to evaluate the safety and efficacy of blood transfusions. Limited comprehensive literature exists about effect of different storage solutions in rat red blood cells (RBCs) characteristics. RBCs undergo time dependent biochemical and biophysical changes during storage known as hypothermic storage lesions (HSLs).

OBJECTIVE

This study evaluates the effects of RBC additive solutions (AS) during storage of rat RBCs.

METHODS

Blood was leukoreduced and stored as per manufacturer instructions at 4°C up to 42-days. Three solutions, CPDA-1; AS-1; and AS-7 (SOLX), were evaluated. Biochemical parameters measured included extracellular K+, pH, hemolysis, 2,3-diphosphoglycerate (2,3-DPG), oxygen affinity, ATP, and lactate. Mechanical properties measured included RBC deformability, elongation index (EI), RBC membrane shear elastic modulus (SEM), mean corpuscular volume (MCV), viscosity, and aggregability.

RESULTS

There were no differences in biochemical or mechanical parameters at baseline or after one week of storage. However, after two weeks, AS-7 preserved biochemical and mechanical properties as compared to CPDA-1 and AS-1. Changes were observed to be significant after 14-days of storage. AS-7 prevented extracellular K+ increase, reduced acidosis, showed lower hemolysis, preserved ATP and 2,3-DPG levels (consequently oxygen affinity), and reduced lactate. AS-7, when compared to CPDA-1 and AS-1, prevented the reduction in RBC deformability and was found to preserve the EI at multiple shear stresses, the membrane SEM, the aggregability and viscosity.

DISCUSSION

Rat RBCs stored with AS-7 presented reduced changes in biochemical and mechanical parameters, when compared with rat RBCs stored in CPDA-1 and AS-1, after as early as two weeks of storage.

Effects of stiffness and volume on the transit time of an erythrocyte through a slit

By using a fully coupled fluid-cell interaction model, we numerically simulate the dynamic process of a red blood cell passing through a slit driven by an incoming flow. The model is achieved by combining a multiscale model of the composite cell membrane with a boundary element fluid dynamics model based on the Stokes flow assumption. Our concentration is on the correlation between the transit time (the time it takes to finish the whole translocation process) and different conditions (flow speed, cell orientation, cell stiffness, cell volume, etc.) that are involved. According to the numerical prediction (with some exceptions), the transit time rises as the cell is stiffened. It is also highly sensitive to volume increase inside the cell. In general, even slightly swollen cells (i.e., the internal volume is increased while the surface area of the cell kept unchanged) travel dramatically slower through the slit. For these cells, there is also an increased chance of blockage.