Fluid and solid mechanical implications of vascular stenting

Vascular stents have emerged as an effective treatment for occlusive vascular disease. Despite their success and widespread use, outcomes for patients receiving stents are still hampered by thrombosis and restensosis. As arteries attempt to adapt to the mechanical changes created by stents, they may in fact create a new flow-limiting situation similar to that which they were intended to correct. In vitro fluid mechanics and solid mechanics studies of stented vessels have revealed important information about how stents alter the mechanical environment in the arteries into which they are placed. Adverse nonlaminar flow patterns have been demonstrated as well as remarkably high stress concentrations in the vessel wall. In vivo studies of stented vessels have also shown a strong relationship between stent design and their dynamic performance within arteries. Alterations in pressure and flow pulses distal to the stent have been observed, as well as regional changes in vascular compliance. Considering the influence of flow and stress on the vascular response and the suboptimal clinical outcomes associated with stenting, knowledge gained from stent/artery mechanics studies should play an increasingly important role in improving the long-term patency of these devices. © 2002 Biomedical Engineering Society. PAC2002: 8719Rr, 8780-y, 8719Uv     

Local cerebral blood flow in gently restrained rats: effects of propranolol and diazepam

Summary The cerebrovascular consequences of the gentle restraint commonly used for the measurement of local cerebral blood flow (LCBF) in conscious rats has been tested by using two drugs, propranolol and diazepam. Propranolol induced small LCBF decreases in 7 structures suggesting that the cerebral circulation was partially controlled by the activation of intra or extracerebral aminergic pathways in this protocol. Sedative doses of diazepam reduced LCBF in most of the structures but anxiolytic doses increased it in 4 structures. This effect may be due to a regionally differentiated modification of activity in the brain due to the selective inhibition of limbic structures by diazepam. Since propranolol and diazepam induced only small changes, the LCBF of gently restrained rats appeared to be minimally affected by the stressful situation imposed by the protocol.     

Humoral indices of stress in rats

Rats, bearing chronic venous cannulas, were subjected to 30 sec of constant current grid shock at 1 of 6 intensities (0, 0.25, 0.5, 1, 2, 4 mA), after being allowed to acclimate to the test chamber overnight. Blood, sampled before and after shock, was assayed for epinephrine, norepinephrine and corticosterone. Peak levels of both catecholamines increased in a stepwise fashion (i.e., monotonically) with increasing magnitude of stress, as reflected by current intensity of foot shock. Plasma corticosterone did not increase monotonically but instead showed similar increases in the 5 groups of rats that actually received shock. These data support earlier work which indicate that plasma corticosterone is not a sensitive index of stress; this is probably the case because of the relatively narrow range of responsiveness of the adrenal cortex to ACTH. In contrast, both plasma catecholamines appear to satisfy some of the requisites for a sensitive visceral index of stress.     

Objective stress monitoring based on wearable sensors in everyday settings

Abstract

Monitoring people’s stress levels has become an essential part of behavioural studies for physical and mental illnesses conducted within the biopsychosocial framework. There have been several stress assessment studies in laboratory-based controlled settings. However, the results of these studies do not always translate effectively to an everyday context. The current state of wearable sensor technology allows us to develop systems measuring the physiological signals reflecting stress 24/7 while capturing the context. In this paper, we present a stress monitoring system that provides objective daily stress measurements in everyday settings based on three physiological signals: electrocardiogram (ECG), photoplethysmogram (PPG), and galvanic skin response (GSR) using Shimmer3 ECG, Shimmer3 GSR+, and Empatica E4 wearable sensors. We perform controlled stress assessment experiments on 17 participants in which we successfully detect stress with a 94.55% accuracy for 10-fold cross-validation and an 85.71% accuracy for subject-wise cross-validation. In everyday settings, the system assesses stress with an 81.82% accuracy. We also examine whether motion artefacts affect stress assessment and filter the low-confidence readings to minimise false alarms.     

Enhancement of attention in man with ACTH/MSH 4–10

Normal men were infused for 4 hr with ACTH/MSH 4–10 or a control solution. Behavioral testing after the infusion indicated that subjects who received ACTH/MSH 4–10 were less anxious and had better visual memory than control subjects but the predominant effect of the heptapeptide was to increase visual attention. It was specualted that ACTH/MSH 4–10 may be uniquely coded for attentional functioning.     

食管分层应力-应变研究

目的　探讨食管壁各层环向应力 应变分布特征。方法　将 8只Wister大鼠的食管标记、测量在体长度后剪下置于去钙离子Krebs液中。剪下标记的中段食管用做充压试验 ,将其在显微镜下分离成内层食管 (粘膜和粘膜下层 )和外层食管 (固有肌层 )。充压时全层和分层食管均被拉长至在体长度 ,以每分钟升高 2cmH2 O速度匀速充压。根据所测图像的几何数据计算全层和分层食管的Kirchhoff应力和Green应变。零应力状态作为计算应力和应变的基本参照状态。结果　 (1 )食管离体后较在体长度缩短 2 4%。 (2 )全层食管和分层食管的环向应力 应变曲线均符合指数方程τ =(τ +β)eα(ε-ε ) -β(判定系数 >0 .96) ,为非线性关系。 (3 )与全层食管相比 ,分层后内层食管应力 应变曲线较陡直 ,且移向左侧 ,差别有统计意义 (P <0 .0 5 ) ,外层食管的曲线移向右侧 ,差别无统计意义 (P >0 .0 5 ) ,内外两层食管的应力 -应变曲线亦有统计差别 (P <0 .0 5 )。结论　食管壁各层环向应力 -应变均符合非线性关系 ,食管内层不如外层易变形     

Die Beanspruchung des menschlichen Ellenbogengelenks

Zusammenfassung Bei 80 Objekten werden die Gelenkflächen des menschlichen Ellenbogengelenks untersucht. Die Trochlea und das Capitulum humeri sowie das Caput radii zeigen keine nennenswerten Unterschiede in der Ausdehnung der mit typischem Gelenkknorpel bedeckten Flächen. Dagegen lassen sich für die Ulnazange drei charakteristische Formgruppen abgrenzen: In 3 Fällen kann eine einheitliche Knorpelfläche beobachtet werden. Bei etwa zwei Drittel der untersuchten Objekte liegt im mittleren Bereich der Incisura trochlearis in horizontaler Richtung ein 2–5 mm breiter knorpelfreier Streifen, der den Gelenkknorpel in 2 vollständig getrennte Flächen unterteilt. Das restliche Drittel der Objekte besitzt eine unvollständige Trennung der Gelenkfläche. Unter Berücksichtigung der Vorstellungen von Pauwels über die causale Histogenese der mesenchymalen Stützgewebe sowie der Materialverteilung im Knochengewebe in Abhängigkeit von der einwirkenden Spannungsgröße werden die morphologischen Befunde den für die jeweiligen Skeletelemente von Pauwels ermittelten Spannungsdiagrammen gegenübergestellt. An der Trochlea und dem Capitulum humeri und am Caput radii findet sich eine geradezu ideale Übereinstimmung in der Ausdehnung der Knorpelfläche und der Knochendichte unter den Gelenkflächen mit den entsprechenden Spannungsdiagrammen. An der Ulna trifft dies nur für einen geringen Teil der Objekte zu. Für die unterschiedliche Ausgestaltung der Incisura trochlearis werden zwei mögliche Ursachen diskutiert: 1. die Resultierende R verharre während des Bewegungsablaufes in einzelnen Positionen innerhalb der Incisura trochlearis verschieden lange; 2. der Krümmungsradius der Trochlea humeri sei größer als derjenige im mittleren Bereich der Ulnazange, so daß hier wegen des fehlenden Kontaktes der Gelenkflächen keine Druckübertragung möglich ist.

---

The stress of the human elbow jointI. Functional morphology of the articular surfaces

Summary The articular surfaces of 80 human elbow joints are analysed. The trochlea and capitulum humeri and the caput radii of the investigated individuals show no particular differences in the extent of their surfaces covered with typical articular cartilage. On the other hand the form of the incisura trochlearis is rather variable. Three characteristic formgroups are to be discerned. In three objects a continuous cartilage surface has been observed. In 50 of the investigated joints there is a small intersection free from cartilage in the midst of the incisura trochlearis, dividing the articular cartilage in two isolated surfaces. In the rest of the analysed objects the articular surface is divided only partially. According to Pauwels' hypothesis on the causal histogenesis of the mesenchymal supporting tissues and of the density distribution of the bone dependence upon the magnitude of the local unit stress the morphological findings in the single investigated parts of the elbow joint are confronted with the corresponding stress diagram as described by Pauwels. In the trochlea and capitulum humeri and in the caput radii a nearly ideal correspondence of the extent of the articular surface and the density of the bone tissue with the unit stress diagrams are found. In the ulna this correspondence exists only in few of the analysed objects. For the different form of the incisura trochlearis two possible explanations are discussed: 1, during the motion the resultant of forces may stay for a different time in their single positions in the incisura trochlearis; 2. the curvature radius of the trochlea humeri may be greater than that one of the incisura trochlearis in the central area. So no pressure occurs in this part of the articular surface.

Mit freundlicher Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Dendritic spines in the posterodorsal medial amygdala after restraint stress and ageing in rats

Several evidences suggest that the posterodorsal medial amygdala (MePD) can be a relevant part of the rat neural circuitry for the regulation of hypothalamic neuroendocrine secretion and for ontogenetically different behavioral displays. The dendritic spine density of Golgi-impregnated neurons from the MePD was evaluated in young rats following acute or chronic restraint stress and in aged animals (24 months old). Compared to the control group, a single 1 h restraint stress session promoted a decreased spine density (p < 0.01) whereas a single 6 h restraint stress session or daily 6-h restraint sessions for 28 consecutive days did not lead to the same effect (p > 0.05). Aged rats showed no difference in this dendritic spine parameter when compared to young adults (p > 0.05). These results indicate that short-term stress (1 h) can affect MePD dendritic spines and that neural plasticity is involved with adaptive responses onwards in restrained rats. On the other hand, brain structural modifications related with ageing appear not to influence the number of certain postsynaptic sites in the MePD of rats.