Plug Effect of Erythrocytes in Capillary Blood Vessels

As an idealized problem of the motion of blood in small capillary blood vessels, the low Reynolds number flow of plasma (a newtonian fluid) in a circular cylindrical tube involving a series of circular disks is studied. It is assumed in this study that the suspended disks are equally spaced along the axis of the tube, and that their centers remain on the axis of the tube and that their faces are perpendicular to the tube axis. The inertial force of the fluid due to the convective acceleration is neglected on the basis of the smallness of the Reynolds number. The solution of the problem is derived for a quasi-steady flow involving infinitesimally thin disks. The numerical calculation is carried out for a set of different combinations of the interdisk distance and the ratio of the disk radius to the tube radius. The ratio of the velocity of the disk to the average velocity of the fluid is calculated. The different rates of transport of red blood cells and of plasma in capillary blood vessels are discussed. The average pressure gradient along the axis of the tube is computed, and the dependence of the effective viscosity of the blood on the hematocrit and the diameter of the capillary vessel is discussed.     

Assaying the Effect of Levodopa on the Evaluation of Risk in Healthy Humans

In humans, dopamine is implicated in reward and risk-based decision-making. However, the specific effects of dopamine augmentation on risk evaluation are unclear. Here we sought to measure the effect of 100 mg oral levodopa, which enhances synaptic release of dopamine, on choice behaviour in healthy humans. We use a paradigm without feedback or learning, which solely isolates effects on risk evaluation. We present two studies (n = 20; n = 20) employing a randomised, placebo-controlled, within-subjects design. We manipulated different dimensions of risk in a controlled economic paradigm. We test effects on risk-reward tradeoffs, assaying both aversion to variance (the spread of possible outcomes) and preference for relative losses and gains (asymmetry of outcomes - skewness), dissociating this from potential non-specific effects on choice randomness using behavioural modelling. There were no systematic effects of levodopa on risk attitudes, either for variance or skewness. However, there was a drift towards more risk-averse behaviour over time, indicating that this paradigm was sensitive to detect changes in risk-preferences. These findings suggest that levodopa administration does not change the evaluation of risk. One possible reason is that dopaminergic influences on decision making may be due to changing the response to reward feedback.     

Generation of Nitric Oxide by Peripheral Blood Leukocytes and Platelets in Healthy Humans and Patients with Thermal Trauma

The generation of nitric oxide (NO) by human peripheral blood leukocytes and platelets has been studied in healthy subjects and patients with burns (with the affected area varying from 10 to 45% of the body surface). Differential centrifugation was used to isolate leukocytes and platelets from the blood. The leukocyte suspension was diluted with a complete medium to a concentration of 1 × 10⁷ cells/ml, and the platelet suspension, to 1 × 10⁸ cells/ml; the suspensions were then cultured for 15 h (37°C). The concentration of nitrite, an NO metabolite, was determined using the Griss reaction. The relative production of NO by leukocytes of healthy subjects and patients was 0.75 ± 0.06 and 2.93 ± 0.16 mol/l, respectively (p < 0.001), and its relative production by platelets of healthy subjects and patients was 2.15 ± 0.14 and 3.62 ± 0.13 mol/l, respectively (p < 0.01). The absolute generation of NO by leukocytes of healthy subjects and patients is 0.47 ± 0.05 and 3.02 ± 0.28 mol/l, respectively (p < 0.001), and its absolute generation by platelets of healthy subjects and patients was 7.70 ± 0.55 and 14.68 ± 0.84 mol/l, respectively (p < 0.001). Thus, the absolute production of NO by platelets is 16 times higher than the absolute production of NO by leukocytes of healthy subjects. Stress increases the generation of NO by both leukocytes and platelets. The absolute generation of NO by platelets in thermal trauma is positively correlated with the plasma content of fibrinogen in the patients.     

正常猕猴与人视网膜血管的比较

目的比较正常猕猴与人视网膜血管的异同,为进一步利用猕猴建立动物模型来研究视网膜血管打下基础。方法取健康成年猕猴眼球6只和人角膜移植供体剩余眼杯8只的视网膜,用ADP酶法进行血管染色,对两者视网膜血管的走行、血管分级、毛细血管分层以及黄斑区血管拱环等进行比较,测量结果进行统计学检验。结果猕猴与人的视网膜铺片经ADP酶法染色后见视网膜血管自穿出视盘后的一级血管逐渐分支变细,直至五级血管即毛细血管;在视盘旁、赤道部、周边部两者血管面积百分比没有差异;视盘旁血管分为多层,赤道部有两层,且深浅层间相互交通,周边部仅见一层毛细血管且较稀疏;两者黄斑区毛细血管均较密集,有形态完整呈不规则状的血管拱环,血管面积百分比以及血管拱环的面积、周长和直径没有差异。结论猕猴与人在视网膜血管走行、分级、毛细血管分层以及黄斑区血管拱环等多方面有良好的相似性,可用作人类视网膜血管、尤其是黄斑区视网膜血管研究的良好动物模型。     

The Effect of Age and Gender on 37 Chemical Element Contents in Scalp Hair of Healthy Humans

The effect of age and gender on minor and trace element contents in the scalp hair of 80 relatively healthy 15- to 55-year-old women and men was investigated. Contents or upper limit of contents of 37 chemical elements in the scalp hair were determined by instrumental neutron activation analysis. Mean values (M ± SΕΜ) for the mass fraction of Ag, Au, Ba, Br, Ca, Ce, Cl, Co, Cr, Eu, Fe, Hf, Hg, I, K, La, Lu, Mg, Mn, Na, Rb, Sb, Sc, Se, Sm, Sr, Th, and Zn (milligrams per kilogram of dry hair) were 0.191 ± 0.018, 0.0102 ± 0.0014, 6.33 ± 0.68, 3.59 ± 0.26, 1320 ± 110, 0.369 ± 0.055, 1245 ± 133, 0.0707 ± 0.0054, 2.78 ± 0.22, 0.0082 ± 0.0021, 88.2 ± 6.7, 0.040 ± 0.012, 0.145 ± 0.009, 6.93 ± 1.05, 146 ± 14, 0.238 ± 0.025, 0.0030 ± 0.0007, 163 ± 17, 2.29 ± 0.30, 344 ± 31, 0.65 ± 0.10, 0.062 ± 0.005, 0.0100 ± 0.0012, 0.248 ± 0.008, 0.0090 ± 0.0010, 45.7 ± 3.5, 0.0168 ± 0.0019, and 154 ± 3, respectively. The upper limits of contents of Cd, Cs, Gd, Nd, Ta, Tb, Tm, and Yb were ≤0.17, ≤0.013, ≤0.104, ≤0.19, ≤0.011, ≤0.0048, ≤0.0057, and ≤0.0047, respectively. In all hair samples, the contents of As was under detection limits <0.01. The tendency for the Ce, La, and Th content to increase with age was found in the human hair, but statistically significant changes were shown for females only. The mass fraction of Rb in the male scalp hair increases and of Cl decreases with age. It was shown that higher Au, Ca, Mg, and Sr mass fractions as well as lower Cl, Fe, I, Sc, Se, and Sm content were typical of female hair as compared to those in male hair.     

Correlation between the Quantity of White Blood Cells and Their Volume Distribution Parameters in Humans

Using correlation and factor analyses, the following parameters were studied in males and females: correlations between the white blood cell (WBC) count; mean neutrophil, lymphocyte, and monocyte volume; volume variation; asymmetry coefficients; and volume distribution excess in populations of WBCs. A clear interrelationship between the quantity and the volume, i.e., the quality, was shown. The cosubordination relationship involves all studied classes of WBCs appearing as a parameter correlation within the distinct classes as well as between different classes. This phenomenon is strongly sex-specific. The relative quantity or cell volume is changed together with the concerted behavior of other WBC classes, i.e., content, volume, and distribution of the cells. It is suggested that such functional alterations are compensatory in nature and facilitate optimization of the capillary blood flow.     

Optic Nerve Head Blood Flow Autoregulation during Changes in Arterial Blood Pressure in Healthy Young Subjects

Aim

In the present study the response of optic nerve head blood flow to an increase in ocular perfusion pressure during isometric exercise was studied. Based on our previous studies we hypothesized that subjects with an abnormal blood flow response, defined as a decrease in blood flow of more than 10% during or after isometric exercise, could be identified.

Methods

A total of 40 healthy subjects were included in this study. Three periods of isometric exercise were scheduled, each consisting of 2 minutes of handgripping. Optic nerve head blood flow was measured continuously before, during and after handgripping using laser Doppler flowmetry. Blood pressure was measured non-invasively in one-minute intervals. Intraocular pressure was measured at the beginning and the end of the measurements and ocular perfusion pressure was calculated as 2/3*mean arterial pressure –intraocular pressure.

Results

Isometric exercise was associated with an increase in ocular perfusion pressure during all handgripping periods (p < 0.001). By contrast no change in optic nerve head blood flow was seen. However, in a subgroup of three subjects blood flow showed a consistent decrease of more than 10% during isometric exercise although their blood pressure values increased. In addition, three other subjects showed a consistent decline of blood flow of more than 10% during the recovery periods.

Conclusion

Our data confirm previous results indicating that optic nerve head blood flow is autoregulated during an increase in perfusion pressure. In addition, we observed a subgroup of 6 subjects (15%) that showed an abnormal response, which is in keeping with our previous data. The mechanisms underlying this abnormal response remain to be shown.     

Blood Vessel Adaptation with Fluctuations in Capillary Flow Distribution

Throughout the life of animals and human beings, blood vessel systems are continuously adapting their structures – the diameter of vessel lumina, the thickness of vessel walls, and the number of micro-vessels – to meet the changing metabolic demand of the tissue. The competition between an ever decreasing tendency of luminal diameters and an increasing stimulus from the wall shear stress plays a key role in the adaptation of luminal diameters. However, it has been shown in previous studies that the adaptation dynamics based only on these two effects is unstable. In this work, we propose a minimal adaptation model of vessel luminal diameters, in which we take into account the effects of metabolic flow regulation in addition to wall shear stresses and the decreasing tendency of luminal diameters. In particular, we study the role, in the adaptation process, of fluctuations in capillary flow distribution which is an important means of metabolic flow regulation. The fluctuation in the flow of a capillary group is idealized as a switch between two states, i.e., an open-state and a close-state. Using this model, we show that the adaptation of blood vessel system driven by wall shear stress can be efficiently stabilized when the open time ratio responds sensitively to capillary flows. As micro-vessel rarefaction is observed in our simulations with a uniformly decreased open time ratio of capillary flows, our results point to a possible origin of micro-vessel rarefaction, which is believed to induce hypertension.     

The Effect of Lipemia on Peripheral Blood Flow

The effect of lipemia on peripheral blood flow was studied in patients with and without peripheral vascular disease. Blood flow was measured by venous occlusion plethysmography in the calf and/or finger four to six hours after a fatty meal and after intravenous heparin. The abolition of postprandial lipemia by heparin was determined by measuring the plasma lactescence.Heparin resulted in no change in finger flow of either group or in calf flow in the control group. In nine out of 10 patients with occlusive vascular disease of the legs, it resulted in a small but significant increase of calf blood flow. No such alteration was found when heparin was given following a non-fatty meal.In 12 patients with intermittent claudication the clearing of postprandial lipemia by heparin caused prolongation of claudication time, as measured by the appearance of pain on treadmill exercise.It is concluded that, in some cases, postprandial lipemia is associated with a decrease in blood flow in a limb which is already the site of occlusive vascular disease.     

褪黑素对人体睡眠和血压的影响

昼夜节律遵循体内的生物钟规律,调节着机体多种功能和代谢过程,如血压、睡眠周期和体温等,睡眠周期表现出明显的昼夜节律,血压的变化也遵循24小时昼夜模式.研究表明,昼夜节律异常是睡眠障碍和心血管疾病的危险诱因之一.昼夜节律的起搏点受褪黑素的调节,而褪黑素的合成和分泌也具有昼夜节律性.内源性褪黑素可以通过多种方式增强人类节律系统的功能,外源性褪黑素作为一种时相药,可以对人体昼夜节律紊乱产生调节作用.越来越多的研究发现,褪黑素与睡眠和血压的变化有紧密的联系,深入研究褪黑素在其中的作用有利于阐明该类疾病的发生机制.本文旨在就褪黑素对人体睡眠和血压的影响作一综述.