Noninvasive,automatic 24-h ambulatory blood pressure monitoring in normotensive subjects

Summary The reliability of noninvasive, automatic blood pressure monitoring is not yet clearly established. A 24-h ambulatory blood pressure profile was obtained in 9 healthy, normotensive subjects with an automatic, noninvasive device. The blood pressure profile showed the typical circadian pattern with lower systolic and diastolic values during sleep, although pulse pressure was fairly constant (about 40 mm Hg). The systolic blood pressure rose steeply in the early morning hours — before waking up. The results were compared with simultaneous hourly readings using the auscultatory method. There were no statistically significant differences between the automatic and auscultatory readings, 13 of the 18 mean values at. different time points being within 2 mm Hg of each other. All the auscultatory means fell within the 95% confidence limits of those measured hourly by the automatic method. Although the automatic method seemed to be reliable compared with the auscultatory method, its sensitivity to motion artifacts is a disadvantage in a truly ambulatory setting.     

Tumor necrosis factor-alpha in the placenta is not elevated in pre-eclamptic patients despite its elevation in peripheral blood

PROBLEM: Tumor necrosis factor-alpha (TNF-alpha) is present in human placental and uterine cells at the early and late stages of gestation and promotes the regulation of trophoblast growth and invasion. We evaluated whether TNF-alpha levels in the placenta and blood of pre-eclamptic women differed from those with normal pregnancies. METHOD OF STUDY: The subjects were 39 pregnant women carrying single fetuses (21 normal-pregnant and 18 pre-eclamptic patients). Their average gestational age at entry was 38-39 weeks. Peripheral blood was collected before the onset of labor and separated serum was stored at -20 degrees C. A tissue segment of the placenta was cut and frozen in liquid nitrogen immediately after delivery at -80 degrees C. The frozen placental tissue was added to phosphate-buffered saline. The tissue was fully homogenized and centrifuged. Separated supernatant was stored at -80 degrees C. TNF-alpha levels in separated serum and TNF-alpha and total protein (TP) levels in separated supernatant were measured. The presence of TNF-alpha in the placenta was evaluated by immunohistochemistry in five pre-eclamptic and five normal-pregnant patients. RESULTS: Serum TNF-alpha levels were higher in pre-eclampsia than in normal pregnancies. However, TNF-alpha/TP levels in the placenta did not differ significantly between the two groups. As for TNF-alpha immunostaining of trophoblastic cells in the placenta, it was weak in three and moderate in two of the normal pregnancies, while it was absent in two, weak in one, and moderate in two in the pre-eclampsia group. CONCLUSIONS: We demonstrated no significant increase in TNF-alpha/TP levels in the placenta in pre-eclampsia despite a significant increase in serum TNF-alpha levels. There was no strong immunostaining for TNF-alpha detected by immunohistochemistry in the pre-eclampsia group. These findings suggest that TNF-alpha in the placenta is not a key cytokine to interfere with normal trophoblast invasion into the myometrium in pre-eclampsia, and that sources other than the placenta may contribute to the elevated levels of TNF-alpha found in the circulation of pre-eclamptic patients.     

优化原理与小动脉血流量─管径关系

作者假设血液为符合幂定律的非牛顿流体，对小动脉血管系统进行了详细的优化分析。导出了血流量与管径立方成正比的结论以及壁面切变率与管径无关的推论。此结果既包含了前人对于牛顿血流的研究成果，又能克服后者的不足，而与近期的生理测定一致。     

高血压急诊患者降压前后脑电图变化及临床意义

目的:观察高血压急诊快速降血压对大脑功能的影响情况。方法:监测56例病人含服 降压药前后的脑电活动和血压情况,并对所获资料进行分析。结果:2 h内收缩压(SBP)下降>5.33 kPa (40 mmHg)或舒张压(DBP)下降>4.00 kPa(30 mmHg)时,脑电图异常程度增加,θ及δ频段功率值明 显升高(P<0.01)。结论:降压急骤,可能会造成大脑功能损害     

Contribution of adrenomedullin to homeostatic response to cold stress in rat model

Acute stress known to stimulate sympathetic activity as well as the hypothalamo-pituitary–adrenal (HPA) axis, produces a significant increase in adrenomedullin (ADM) levels in the pituitary gland, plasma and adrenal glands, all of which are key components of HPA axis, suggesting a regulatory or protective role for ADM in countering HPA activation following a variety of physiological and psychological stressors. This study was conducted to assess a rat model for in depth investigation of biochemical mechanisms and consequences of cold stress. Four groups of Sprague–Dawley rats were observed for their serum total protein, glucose, trigliceride and cholesterol levels as well as their blood pressures after housing at room temperature, administration of ADM (1.0 nm/kg), exposing to cold stress (8 °C for 48 h) and exposing to ADM injection in addition to cold stress. The results suggest that application of ADM in addition to cold stress may act via receptors on different end-organs and causes altered metabolic regulation taking partial or total occupation of ADM receptors, stimulated in response to cold application induced physiologic ADM release before pharmacological ADM administration.     

Hemodynamic and hormonal responses to lower body negative pressure in men with varying profiles of strength and aerobic power

Hemodynamic, cardiac, and hormonal responses to lower-body negative pressure (LBNP) were examined in 24 healthy men to test the hypothesis that responsiveness of reflex control of blood pressure during orthostatic challenge is associated with interactions between strength and aerobic power. Subjects underwent treadmill tests to determine peak oxygen uptake ( O_2max) and isokinetic dynamometer tests to determine knee extensor strength. Based on predetermined criteria, subjects were classified into one of four fitness profiles of six subjects each, matched for age, height, and body mass: (a) low strength/average aerobic fitness, (b) low strength/high aerobic fitness, (c) high strength/average aerobic fitness, and (d) high strength/high aerobic fitness. Following 90 min of 0.11 rad (6°) head-down tilt (HDT), each subject underwent graded LBNP to –6.7 kPa or presyncope, with maximal duration 15 min, while hemodynamic, cardiac, and hormonal responses were measured. All groups exhibited typical hemodynamic, hormonal, and fluid shift responses during LBNP, with no intergroup differences between high and low strength characteristics. Subjects with high aerobic power exhibited greater (P < 0.05) stroke volume and lower (P < 0.05) heart rate, vascular peripheral resistance, and mean arterial pressure during rest, HDT, and LBNP. Seven subjects, distributed among the four fitness profiles, became presyncopal. These subjects showed greatest reduction in mean arterial pressure during LBNP, had greater elevations in vasopressin, and lesser increases in heart rate and peripheral resistance. Neither O_2max nor leg strength were associated with fall in arterial pressure or with syncopal episodes. We conclude that interactions between aerobic and strength fitness characteristics do not influence responses to LBNP challenge.     

Haemodynamic model of a unilateral iliac stenosis with an aortoiliac bypass

A hydrodynamic model for the part of the human arterial network below the renal arteries has been constructed using specially fabricated distensible tubes and a pulsatile pump to simulate an aortoiliac bypass. The experiments and the computer model indicated that no ‘steal’ occurred due to the insertion of the bypass graft. Also, the results showed that the length of the stenosis had a non-systematic apparent effect on the physiological significance of the obstruction and that the kinetic power represented only a small percentage of the total power. The total power efficiency of the bypass graft was unaffected by its elastic properties. The experimental investigation also indicated that the pressure drop across the stenosis was considerably larger than the drop calculated using the Poiseuille flow relationship when the stenosis was severe. Therefore, a critical arterial stenosis value cannot be defined as an obstruction of a constant percentage reduction of luminal area. It varies directly with the effective cross-sectional area and inversely with the flow rate. The value of angiography in assessing the functional significance of any arterial stenosis is there-fore limited. A better method for evaluation requires quantitative measurements of local blood pressure and blood flow, not only at rest, but also under conditions creating augmented flows due to exercise.     

Vortex Shedding in Steady Flow Through a Model of an Arterial Stenosis and Its Relevance to Mural Platelet Deposition

In this study, the development of unsteady vortical formations in the separated flow region distal to a stenosis throat is presented and compared with the platelet deposition measurements, to enhance our understanding of the mechanisms involved in platelet kinetics in flowing blood. Qualitative and quantitative flow visualization and numerical simulations were performed in a model of a streamlined axisymmetric stenosis with an area reduction of 84% at the throat of the stenosis. Measurements were performed at Reynolds numbers (Re), based on upstream diameter and average velocity, ranging from 300 to 1800. Both the digital particle image visualization method employed and the numerical simulations were able to capture the motion of the vortices through the separated flow region. Periodic shedding of vortices began at approximately Re=375 and continued for the full range of Re studied. The locales at which these vortices are initiated, their size, and their life span, were a function of Re. The numerical simulations of turbulent flow through the stenosis model entailed a detailed depiction of the process of vortex shedding in the separated flow region downstream of the stenosis. These flow patterns were used to elucidate the mechanisms involved in blood platelet kinetics and deposition in the area in and around an arterial stenosis. The unsteady flow development in the recirculation region is hypothesized as the mechanism for observed changes in the distribution of mural platelet deposition between Re=300, 900, and 1800, despite only a marginal variation in the size and shape of the recirculation zone under these flow conditions. © 1999 Biomedical Engineering Society. PAC99: 8719Uv, 8710+e     

Measurement of venous oxyhaemoglobin saturation in the adult human forearm by near infrared spectroscopy with venous occlusion

Measurement of the oxygenation of the peripheral tissues provides useful information about tissue perfusion. A method is described for the measurement of peripheral venous oxyhaemaglobin saturation (SvO₂) in the adult forearm by a non-invasive technique, near infrared spectroscopy (NIRS) with venous occlusion. A series of studies is performed on healthy adults to compare measurements of forearm SvO₂ made by NIRS with measurements of superficial venous SvO₂ made by co-oximetry, and to study the effect of different optode spacings. There is a significant correlation between forearm SvO₂ measured by NIRS and SvO₂ of superficial venous blood measured by cooximetry (n=19, r=0.7, p<0.0001). Higher values for SvO₂ were obtained using a 2.5 cm spacing than with a 4 cm spacing (mean difference=4.1% (95% Cl 1.4%–6.8%) n=16). This difference is likely to have been due to a more superficial volume of tissue being studied with the closer optode spacing. Peripheral SvO₂ can be measured non-invasively using NIRS with venous occlusion. It may prove to be a useful method to study circulatory disturbances.     

Fuel kinetics during intense running and cycling when fed carbohydrate

On two occasions, six well-trained, male competitive triathletes performed, in random order, two experimental trials consisting of either a timed ride to exhaustion on a cycle ergometer or a run to exhaustion on a motor-driven treadmill at 80% of their respective peak cycling and peak running oxygen (VO_2max) uptakes. At the start of exercise, subjects drank 250 ml of a 15 g·100 ml^–1 w/v [U-¹⁴C]glucose solution and, thereafter, 150 ml of the same solution every 15 min. Despite identical metabolic rates [VO₂ 3.51 (0.06) vs 3.51 (0.10) 1·min^–1; values are mean (SEM) for the cycling and running trials, respectively], exercise times to exhaustion were significantly longer during cycling than running [96 (14) vs 63 (11) min; P < 0.05]. The superior cycling than running endurance was not associated with any differences in either the rate of blood glucose oxidation [3.8 (0.1) vs 3.9 (0.4) mmol· min^–1], or the rate of ingested glucose oxidation [2.0 (0.1) vs 1.7 (0.2) mmol· min^–1] at the last common time point (40 min) before exhaustion, despite higher blood glucose concentrations at exhaustion during running than cycling [7.0 (0.9) vs 5.8 (0.5) mmol·1^–1; P < 0.05]. However, the final rate of total carbohydrate (CHO) oxidation was significantly greater during cycling than running [24.0 (0.8) vs 21.7 (1.4) mmol C₆·min^–1; P < 0.01]. At exhaustion, the estimated contribution to energy production from muscle glycogen had declined to similar extents in both cycling and running [68 (3) vs 65 (5)%]. These differences between the rates of total CHO oxidation and blood glucose oxidation suggest that the direct and/or indirect (via lactate) oxidation of muscle glycogen was greater in cycling than running.