This study identified gender-related differences in post-exercise peripheral blood flow and body temperature in neutral environment (21ºC). The subjects were 11 male (22 +/- 4 years) and 14 pre-ovulatory female (23 +/- 3 years) recreational runners VO2max: 62 +/- 5 mL/kg &bull; min for men and 55 +/- 5 mL/kg &bull; min for women). Forearm blood flow rectal (Trec) and forearm skin temperatures (Tsk), and forearm vascular resistance (mean arterial pressure/forearm blood flow) were measured pre-exercise (pre), immediately after (t = 0), and every 15 minutes up to 105 minutes (t = 105) post-exercise (45-minute run at 75% of VO2max). ANOVA revealed main gender effects for Trec, Tsk, and forearm blood flow (men > women) as well as for forearm vascular resistance (women > men). Compared to pre-exercise, Trec at t = 0 showed a similar increase in men (1.3ºC) and women (1.2ºC). Trec decreased thereafter to reach pre-exercise level after 25 minutes in men. In women, Trec kept decreasing to reach a lower than pre-exercise level after 60 minutes (p < 0.05). Tsk was similar at pre and t = 0 for both genders. In contrast, Tsk was lower in women than men (29.0 +/- 1.3 versus 30.7 +/- 1.5ºC) at t = 105 (p < 0.05). Forearm vascular resistance was similar in men and women pre-exercise and decreased by about 50% in both groups at t = 0. Between t = 30 and t = 105, the women increased their forearm vascular resistance up to 35% more than did the men. These observations suggest the existence of gender-related differences in thermoregulatory and cutaneous blood flow responses during recovery from submaximal exercise.

Tyrimo pagrindimas ir hipotezė. Didinti jėgai treniruotėse naudojami skirtingi svoriai, pasipriešinimas, darbo apimtis, poilsio periodai, dažnis, ir atlikimo greitis. Tradicinę treniruočių priemonę su dideliu pasipriešinimu, galime pakeisti mažu pasipriešinimu kartu apribojant raumenų kraujotaką. Hipotezė: vienkartinė 15; 10; 5 ar 3 minučių trukmės 200 mm Hg slėgio okliuzija gali turėti įtakos fiziniam darbingumui ir kraujotakos intensyvumui. Tyrimo tikslas. Išanalizuoti blauzdos raumenų arterinės kraujotakos intensyvumo kaitą ir fizinį darbingumą be ir su skirtingos trukmės 200 mm Hg slėgio okliuzijomis. Uždaviniai. 1. Nustatyti blauzdos raumenų arterinės kraujotakos intensyvumą ramybėje be ir su 200 mm Hg okliuzija. 2. Nustatyti arterinio kraujo spaudimo (AKS) kaitą ramybėje be ir su 200 mm Hg okliuzija. 3. Nustatyti blauzdos raumenų darbingumo kaitą be ir su 15min, 10 min, 5 min ir 3 min trukmės, 200 mm Hg slėgio, okliuzijomis. 4. Nustatyti blauzdos raumenų arterinės kraujotakos intensyvumą ir AKS kaitą po fizinio krūvio, be ir su 15 min, 10 min, 5 min ir 3 min trukmės, 200 mm Hg slėgio, okliuzijomis Tyrimo metodai. Dinamometrija, ergometrija, veninė okliuzinė pletizmografija, Tyrimų organizavimas. Pirmoje tyrimų dalyje kontrolinėje grupėje dalyvavo 6, o eksperimentinėje grupėje 12 vyrų sportuojančių ištvermės sporto šakose. Grupėse 20 minučių registruojama arterinė kraujotaka ramybėje, o eksperimentinėje grupėje atlikta 15 minučių 200 mm Hg slėgio okliuzija. Antroje... [toliau žr. visą tekstą] / Research background and hypothesis. Different weights, resistance, scope of work, rest periods, frequency, and performance velocity are used to increase strength in training sessions. The traditional training facility with high resistance can be replaced by low resistance while limiting muscle blood flow. Hypothesis: a single 15, 10, 5 or 3 minute 200 mm Hg occlusion pressure can affect physical working capacity and blood flow intensity. Research aim. Analyse changes in the intensity of the calf muscle arterial blood flow and physical working capacity with and without 200 mm Hg pressure occlusion of different duration. Research tasks. 1. Establish arterial blood flow of the calf muscle at rest with and without 200 mm Hg occlusion. 2. Establish changes in arterial blood pressure at rest with and without 200 mm Hg occlusion. 3. Establish changes in the calf muscle work with and without 15 min, 10 min, 5 min and 3 min 200 mm Hg pressure occlusion. 4. Establish changes in the calf muscle blood flow and arterial blood pressure after exercise, with and without 15 min, 10 min, 5 min and 3 min 200 mm Hg pressure occlusion. Research methods. Dynamometry, ergometry, venous occlusive plethysmography. Research organization. In first part of the research, the control group included six and the experimental group - 12 male athletes in endurance sports. In both groups we recorded arterial blood flow at rest for 20 min; in the experimental group we applied 15 min 200 mm Hg occlusion. In the... [to full text]

The ovary undergoes cyclic changes in follicular growth and luteogenesis due to the action of gonadotropins and steroids. The ovary and especially the corpus luteum has an exteremely high blood flow. There is a gap in our knowledge about the physiological role of the high blood flow of the corpus luteum. The production of lactate, progesterone and cyclic AMP of follicles and corpora lutea incubated in vitro was analyzed and related to the tissue content of ATP to elucidate possible connections between oxygen and substrate levels and energy consumption, steroid output and LH responsiveness in vitro. It was also considered of interest to investigate if the oxygen tensions needed for ATP and progesterone production of the follicle and the corpus luteum differed. A corpus luteum model using adult pseudopregnant rats was developed and characterized according to criteria for identification of corpora lutea as well as levels of plasma steroids and gonadotropins. In vitro progesterone production was compared to plasma progesterone levels. The absolute blood flow of corpora lutea of different ages and the response to injection of hCG, noradrenaline and antidiuretic hormone was investigated with the microsphere technique. Relative blood flow changes of follicles and corpora lutea during follicular growth and luteogenesis in vivo were studied by injecting radiolabelled microspheres to anaesthetized immature rats at different time periods after injection of an ovulatory dose of pregnant mare serum gonadotropin. This approach was chosen to investigate the possible relation between follicular/luteal blood flow, steroid output and morphology in relation to the endogenous gonadotropin surge, ovulation and luteogenesis. Hormonal stimulation by injection of hCG and noradrenaline increased total ovarian blood flow but no evidence was found for a parallelism between luteotropism and blood flow. The increasing effect of hCG on ovarian blood flow was partly due to a shunting of blood from the uterus towards the ovary. The antidiuretic hormone potently decreased ovarian and uterine blood flow by 80-90% while blood flow of some other organs (e.g. kidney and spleen) were hardly affected. The corpus luteum of pseudopregnancy was found to produce 15“ 20 times more progesterone in vitro as compared to the preovulatory follicle. The steroidogenesis and energy production of corpora lutea was found to be more sensitive to decreases in oxygen tension in terms of tissue ATP levels and LH responsiveness of progesterone production while the follicle could compensate by increasing glycolysis. A parallelism between follicular/luteal blood flow and progesterone production in vivo was found. It was shown that the formation, growth and progesterone production of the corpus luteum was accompanied by an increase in blood flow as well as vascularization as seen under the light microscope. The endogenous gonadotropin surge did not change follicular blood flow due to the development of a follicular oedema. We hypothesize that the corpus luteum function in vivo and in vitro is dependent on higher energy levels than the preovulatory follicle and that the transformation of the follicle to a corpus luteum is supported by a high nutritive blood flow possibly to support a high demand for energy-rich substrates. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1987, härtill 7 uppsatser.</p> / digitalisering@umu

The five discrete, but related studies presented in this thesis investigate several aspects of the physiology and biochemistry of whole animals, perfused and isolated tissues from fishes and other vertebrates. Important fundamental questions about tissue metabolism and energy supply and utilisation in relation to oxygen supply, in addition to applied questions relating to commercial harvesting and post-mortem muscle physiology were addressed. Oxyconformance of oxygen consumption (VO2) at low oxygen delivery rates was shown using an isolated, perfused salmon tail preparation, composed primarily of skeletal muscle. Addition of pig red blood cells to the perfusing solution at a haematocrit of 5 or 10%, increasing the capacitance, resulted in oxyregulation of VO2 by the tail tissues. Below c.60 ml O2.kg-1.h-1 of oxygen delivery, VO2 was delivery dependent. Above this value additional oxygen delivery did not increase VO2 of resting muscle above c.35 ml O2 kg-1.h-1. The preparation was validated by measuring mitochondrial activity using MTT and blood flow distribution to the red and white muscle using fluorescent microspheres. Evidence of both O2-independence of VO2 in the vasculature and strict O2-dependence of VO2 in striated muscles of fishes and a mammal is presented using isolated vascular tissue and an in vitro tissue slice model. VO2 by vessels from rat, salmon and hagfish showed varying degrees of independence between PO2s of 15-95 mmHg in vitro (1 mmHg = 0.133 kPa). Above and below these values, VO2 was highly PO2-dependent. VO2 by cardiac and skeletal muscles from rat, salmon, snapper and hagfish were shown to relate linearly to PO2 between zero and 125 mmHg. VO2 in these tissues was highly dependent on tissue type (cardiac, red and white muscle) which correlated with haem protein concentration. The increase in VO2 in muscle slice mitochondria uncoupled with FCCP and DNP ruled out diffusion-limitation as a constraint on VO2. Mitochondrial activity was constant over time and reoxygenation of the Ringer bathing the tissues after the initial run down in PO2 resulted in VO2 rates that were unchanged from the starting values, demonstrating that the tissues remained viable over time. ATP turnover in red muscle was significantly increased at 100 mmHg relative to 30 mmHg, and increased in both treatments from values at the start. Our data suggest that ATP supply and ATP demand were reduced in conjunction with falling PO2. The effects of hydrogen sulphide (H2S) (derived from Na2S) and isoeugenol exposure on activity, VO2 and ventilation frequency (Vf) in a teleost fish are reported. In the H2S treatment group (200 μM Na2S) both resting VO2 and Vf decreased after 30 minutes of exposure, concurrent with narcosis and a loss of equilibrium. These events corresponded with a significant fall in VO2 (33%) and Vf (20%) by 15 minutes, both declining further to a nadir of 40% of resting values at 30 minutes. After flushing, VO2 increased to resting levels, with Vf remaining significantly depressed until 30 minutes of recovery. Recovery was accompanied by regained mobility and equilibrium and significantly increased VO2 and Vf. Isoeugenol anaesthetised fish (0.011 g.L-1) reached stage 4-5 of anaesthesia accompanied by significant decreases in VO2 (45%) and Vf (25%) at 25 minutes, both parameters declining further to around 64% and 38% respectively by 35 minutes. Similar to H2S exposed fish, VO2 increased to resting values after flushing, followed by a significant rise in VO2. Likewise, Vf had risen to resting values post-flushing, subsequently increasing significantly during recovery. Overall, VO2 in relation to resting rate was reduced in the isoeugenol treated animals, while in H2S treated fish, exposure there was increased oxygen usage, possibly associated with a toxic effect. H2S significantly reduced cytochrome c oxidase activity in muscle and gill tissue in vitro between 69-79% at 20 μM and 77-97% at 200 μM Na2S, while isoeugenol had no effect on activity in any tissue. Calorimetric and biochemical profiles of anoxic, post-mortem white muscle from Chinook salmon subjected to rested and exhausted harvesting regimens at their acclimation temperature (10°C) are reported. Prior to harvest rested animals were anaesthetised with 0.012 g.L-1 isoeugenol without disturbance. The muscle of these animals had a high metabolic rate at the time of death, at around 400 μW.g-1, which declined rapidly over the first 12 hours to15 μW.g-1. Exhausted animals were forced to swim and were crowded before capture, resulting in an initial heat output of <10 μW.g-1. Heat output was significantly greater in the rested group at the time of death and for 7 hours post-mortem. In both groups there was an exothermic event, occurring between 4 and 6 hours post-mortem amounting to a rise of around 35 μW.g-1. A one-phase exponential decay model appropriately described the net heat output of the rested profile minus the exhausted data. Rested animals had significantly higher initial cut surface pH (7.5 vs 6.7), tissue glycogen (16 vs 2 μmol.g-1), creatine phosphate (18 vs 0.1 μmol.g-1), ATP (6 vs 3.5 μmol.g-1) and potential energy (30 vs 7 μmol.g-1) than the exhausted group, which had significantly elevated tissue concentrations of lactate (43 vs 18 μmol.g-1) and glucose (5 vs 2 μmol.g-1). Potential energy in the form of ATP, glycogen and creatine phosphate remained elevated for an extended period post-mortem in rested animals while catabolites further down the chain such as inosine, hypoxanthine and uric acid accumulated at similar rates in both groups. We examined the relationship between exogenous and endogenous H2S and oxygen partial pressure in isolated hagfish and lamprey vessels that exhibit profound hypoxic vasoconstriction (HVC). In myography studies, H2S (Na2S) dose-dependently constricted dorsal aortas (DA) and efferent branchial arteries but did not affect ventral aortas or afferent branchial arteries, which was similar to the effects produced by hypoxia. Sensitivity of H2S-mediated contraction in hagfish and lamprey DA was enhanced by hypoxia. HVC in hagfish DA was enhanced by the H2S precursor cysteine and inhibited by amino-oxyacetate (AOA), an inhibitor of the H2S-synthesising enzyme, cystathionine β-synthase, and unaffected by propargyl glycine, an inhibitor of cystathionine λ-lyase. Oxygen consumption (MO2) of hagfish DA was constant between a PO2 of 15 and 115•mmHg, decreased when PO2 <15•mmHg, and increased if PO2 exceeded 115•mmHg. 10 μmol.l-1 H2S increased and concentrations above 100 μmol.l-1 H2S decreased MO2. Consistent with the effects on HVC, cysteine increased and AOA and hydroxylamine, an inhibitor of pyridoxyl 5’-phosphate-dependent enzymes, decreased MO2. These data show that H2S is a monophasic vasoconstrictor of specific cyclostome vessels and because hagfish lack vascular NO, and vascular sensitivity to H2S was enhanced at low PO2, it is unlikely that H2S contractions are mediated by either an H2S-NO interaction or an oxidation product of H2S. These experiments provide additional support for the hypothesis that the metabolism of H2S is involved in oxygen sensing/signal transduction in vertebrate vascular smooth muscle. Together the findings of this thesis contribute to the understanding of oxygen utilisation and energetics in relation to oxygen supply in a number of tissues. These data further our understanding of respiratory physiology and may have practical applications in the seafood industry.

This investigation evaluates the influences of optical property assumptions on nearinfrared diffuse correlation spectroscopy (DCS) flow index measurements. Independent variation is induced in optical properties, absorption coefficient (μa) and reduced scattering coefficient (μs’), of liquid phantoms with concurrent measurements of flow indices. A hybrid instrument is incorporated consisting of a dual-wavelength (785 and 830 nm) DCS flow device to obtain flow indices and a frequency-domain tissue-oximeter for optical properties. Flow indices are calculated with measured μa and μs’ or assumed constant μa and μs’. Inaccurate μs’ assumptions produced much larger flow index errors than inaccurate μa. Underestimated/overestimated μs’ from -35%/+175% lead to flow index errors of +110%/-80% and underestimated/overestimated μa from -40%/+150% lead to -20%/+40%, regardless of wavelength. Analysis of a clinical study involving human head and neck tumors indicates flow index errors due to inter-patient optical property variations up to +280%. Collectively, these findings suggest that studies involving significant μa and μs’ changes should measure flow index and optical properties simultaneously to accurately extract blood flow information. This study provides unique insight through the use of liquid phantoms, hybrid instrumentation, incorporation of measurement errors and a generalization into DCS flow index errors due to the influences of optical properties.

Whole body vibration (WBV) is a technique that has been shown to induce positive blood flow changes, however little is known about the effect of different vibration amplitudes on arterial blood flow. Purpose. The purpose of this study was to determine the effect of 2 different amplitudes during an acute bout of WBV on blood flow through the popliteal artery. Methods. Thirty healthy, recreationally active subjects (15 women, 15 men) aged 19-34 years performed two, 10 - minute bouts of vibration at a frequency of 30 Hz and high amplitude (6 mm) or low amplitude (3 mm) in random order after a period of prone rest. Doppler ultrasound was used to assess changes in blood flow. Mean blood flow velocity, peak velocity, end-diastolic velocity, pulsatility index, and resistive index measures were taken immediately before vibration and immediately after. Results. Mean blood flow velocity increased after 10 minutes of WBV. Mean velocity increased more in the 6mm trial (pre= 21.6 ± 4.74 cm/s, post= 25.3 ± 6.11 cm/s) than in the 3mm trial (pre= 22.3 ± 4.33 cm/s, post= 23.5 ± 5.94 cm/s). Peak blood flow velocity increased following 10 minutes of WBV and increased more in the 6mm trial (pre= 37.1 ± 9.78 cm/s, post= 43.7 ± 10.95 cm/s) than in the 3mm trial (pre= 37.8 ± 8.92 cm/s, post= 39.4 ± 10.5 cm/s) following 10 minutes of passive WBV. Pulsatility index also increased significantly following 10 minutes of WBV and increased more in the 6mm trial (pre= 1.639 ± 0.1299, post= 1.729 ± 0.1324) than in the 3mm trial (pre= 1.660 ± 0.1219, post= 1.671 ± 0.1428). No main effects or interactions were observed for resistive index or end diastolic blood flow velocity (P>0.05). Conclusion. Ten minutes of passive WBV increases blood flow velocity. High amplitude (6 mm) produced a more pronounced increase in blood flow than the low amplitude (3 mm). Given the relationship between blood flow velocity and WBV, these results suggest that amplitude plays a role in increasing blood flow and that high amplitude (6 mm) may be more effective than low amplitude (3 mm) in improving circulation to the lower leg. / School of Physical Education, Sport, and Exercise Science

Cerebral blood flow dynamics is an essential component for preserving cerebral integrity. Cerebral blood flow abnormalities are often seen in patients with central nervous system pathologies such as epilepsy, migraine, Alzheimer's Disease, vascular dementia, stroke, and even HIV/AIDS. There is increasing clinical and experimental evidence implicating cerebral hypoperfusion during ageing. The determination of cerebral perfusion has therefore become an important objective in physiological, pathological, pharmacological, and clinical investigations. The knowledge of regional cerebral blood flow further provides useful diagnostic information and/or data for a better understanding of the complex clinical presentations in patients with neurological and psychiatric disorders. Several cerebrovasoactive drugs have found application in the clinical setting of cerebrovascular diseases such as migraine and dementia. Due to the similarities between humans and non-human primates with respect to their brains, both structurally and behaviourally, numerous studies have been conducted and several non-human primate models have been developed for physiological, pathological, pharmacological, and clinical studies, amongst others in Parkinson's disease and diabetes. The relatively large size of the Cape baboon Papio Ursinus with a weight of 27-30 kg for a large male, makes this primate especially suitable for in vivo brain studies using radiotracers and Single Photon Emission Computed Tomography (SPECT). The main aim of the current study was therefore to develop a suitable radiotracer (99m Tc-hexamethylpropylene amine oxime (HMPAO) or 99m Tc_ethyl_cysteinatedimer (ECD) or 123l-iodoamphetamine (IMP)) for adapted in vivo cerebral blood flow measurements in a non-human primate (Papio ursinus) as an investigative model. The model was to be validated and applied in various drug studies for the evaluation of pharmacological interventions. The study design made use of split-dose methodology, whereby the radiopharmaceutical (radiotracer) was administered twice during each study. The first administration was injected soon after the induction of the anaesthesia, and was followed by the first SPECT data acquisition. The second administration of the radioligand, a double dose of radioactivity with respect to the first radioligand injection, was done at a specific time during the study, which took into account the pharmacodynamics of the drug. A second SPECT data acquisition followed subsequently. The drugs that were included in the study were acetazolamide, a carbonic acid anhydrase inhibitor (often used in nuclear medicine to determine cerebral reserve); sumaptriptan, a 5-HT (serotonin) agonist used for treatment of migraine; sodium valproate (an anti-epileptic drug); nimodipine, a calcium channel blocker and nitro-glycerine, a vasodilator used for angina. Arterial blood pressures were recorded from a catheter in the femoral artery and heart rates were concurrently monitored. The split-dose method was successfully applied to develop a non-human primate cerebral blood flow model under anaesthesia. The model showed differences in cerebral perfusion of the different anaesthesia regimes. These anaesthesia data sets were suitable as control/baseline results for drug intervention studies. Acetazolamide evaluation through the split-dose method in the baboon confirmed the sensitivity of the model by presenting comparable perfusion. This result compared to those already familiar prompted the model to be applied in pharmacological intervention studies. Subsequent results of these investigations showed increases in perfusion for single drug nimodipine treatment (25%). However, nimodipine attenuated the increases in perfusion when administered in combination with acetazolamide. Sumatriptan was able to decrease and normalise the increased perfusion after long duration anaesthesia. Decreased cerebral blood flow was observed for combinations of nimodipine with sodium valproate suggesting drug-drug interaction with important clinical implications. Similar decreases were found also for sumatriptan and nitro-glycerine when administered in combination with nimodipine. Studies with the various tracers (99m Tc_HMPAO or 99m Tc_ECD or 123l_IMP) showed clear differences in the perfusion data, confirming variation in the biochemical performance of the tracers. These differences, if not taken into consideration, caution for inappropriate clinical conclusions and subsequent erroneous therapeutic decisions. Improvement of radiotracer efficacy was subsequently attempted through application of the cyclodextrine complexation approach. Although cyciodextrine technology did not markedly improve the brain disposition of the 99m Tc-ECD, protection of the tracer against degradation was demonstrated. This study encouraged further exploration of this method for protection of the tracer against chemical and metabolic degradation. The current study was aimed to develop and effectively apply a non-human primate model with nuclear medicine technology for cerebral blood flow determinations after pharmacological interventions. This was achieved through the split-dose method and dedicated computer programming, which yielded a successful model with the non-human primate under anaesthesia. The model was validated with the application of acetazolamide to confirm familiar cerebrovascular reserve results, indicating that the model is sensitive to CBF changes. The model was also effectively applied in several pharmacological intervention studies, whereby cerebropharmacodynamics of selected drugs were investigated and established. This unique model of a non-human primate, Papio ursinus for cerebral blood flow determinations has served pharmacological research successfully during the past 12 years and could do so in the future, with scope to investigate new frontiers with improved technologies. / Thesis (Ph.D. (Pharmacology))--North-West University, Potchefstroom Campus, 2004.

Studies show that vasomotor and sudomotor activity is compromised in individuals with Type 1 Diabetes (T1DM) which could lead to altered thermoregulatory function. However, recent work suggests that the impairments may only be evidenced beyond a certain level of heat stress. We therefore examined T1DM-related differences in heat loss responses of sweating and skin blood flow (SkBF) during exercise performed at progressive increases in the requirement for heat loss. Participants were matched for age, sex, body surface area and fitness cycled at fixed rates of metabolic heat production of 200, 250, and 300 W•m-2 of body surface area, each rate being performed sequentially for 30 min. Local sweat rate (LSR), sweat gland activation (SGA), and sweat gland output (SGO) were measured on the upper back, chest and forearm while SkBF (laser-Doppler) was measured on the forearm and upper back only. We found that despite a similar requirement for heat loss, LSR was lower in T1DM on the chest and forearm only, relative to Control and only different at the end of the second and third exercise periods. Differences in chest LSR were due to reduced SGA whereas the decreased forearm LSR was the result of a decrease in SGO. SkBF did not differ between groups. The reduction in the sweating response in the T1DM group was paralleled by a greater increase in core temperature. We show that T1DM impairs heat dissipation as evidenced by reductions in LSR and not SkBF. A compromised thermoregulatory response during and following physical exertion is of considerable concern due to the associated increased risk of post-exertion heat-related injury.

Thrombosis formation upon rupture or erosion of an atherosclerotic plaque can lead to occlusion of arteries. An occlusive thrombus is the most common cause of clinical events such as angina, myocardial infarction, ischemic attacks and strokes. Occlusive thrombi can cause ischemic cardiac arrest in less than an hour. Thrombosis formation requires rapid platelet accumulation rates exceeding thrombosis lysis and embolization rates. Hemodynamics greatly affects platelet accumulation rate through affecting platelet transport to the surface of a growing thrombus. The presence of red blood cells (RBCs) in blood increases platelet transport rate by several orders of magnitude compared to transport due to Brownian motion. Margination of platelets towards the vessel walls also results in higher platelet concentration at the RBC-depleted layer relative to the bulk. In this thesis, we studied the effects of hemodynamics on thrombus growth. We investigated the effects of important flow and particle properties on margination of particles in RBC suspensions by direct numerical simulation (DNS) of cellar blood flow. We derived a scaling law for margination length. Based on this scaling law, margination length increases cubically with channel height and is independent of shear rate. Using DNS, we verified the proposed scaling law for margination length in straight channels. We also showed that rigidity and size both lead to particle margination. We show that platelet margination can be explained by RBC-enhanced shear-induced diffusion of platelets in the RBC-filled region combined with platelet trapping in the RBC-free region. A simple continuum model is introduced based on the proposed mechanism. Using an experimental correlation for effective diffusivity in blood, the continuum model can recover experimental results from the literature over a wide range of tube diameters. We created an in vitro experimental model of thrombosis with and without RBCs. Surprisingly, we found that rapid thrombus growth does not require enhanced platelet transport in the presence of RBCs at high shear. Instead, our results suggest that thrombus growth rate at high shear is dependent on the availability of vWF-A1 domains as opposed to convective transport of platelets. Finally, we obtained empirical correlations for thrombus growth and lag time based on flow parameters by using an in vitro model of thrombosis. We developed a simple model for predicting thrombus formation using the obtained empirical correlations. We demonstrated the capability of the model in predicting thrombus formation over a wide range of experimental geometries. This model may be useful for designing blood-contacting devices to avoid unwanted thrombosis.

Evidence suggests that cerebral blood flow patterns accompanying a mental activity are retained in many locked-in patients. Thus, real-time monitoring with functional transcranial Doppler (TCD) together with a specific mental task could control a brain-computer interface (BCI), thereby providing self-initiated interaction. The objective of this study was to create an automatic detection algorithm to differentiate hemodynamic responses coincident with one's performance of verbal fluency (VF) versus counting tasks. We recruited 10 healthy adults who each silently performed up to 30 VF tasks and counted between each. Both middle cerebral arteries were simultaneously imaged using TCD. Linear Discriminant Analyses (LDA) successfully differentiated between VF and both prior and post counting tasks. For every participant, LDA achieved the 70% classification accuracy sufficient for BCIs. Results demonstrate automatic detection of a VF task by TCD and warrant further investigation of TCD as a BCI.