Search for Optimal Frequencies and Amplitudes of Therapeutic Electrical Carotid Sinus Nerve Stimulation by Application of the Evolution Strategy

In humans, electrical, bipolar, bilateral carotid sinus nerve stimulation (CSNS; impulse duration 0.35 ms) was applied, using frequencies between 10 and 110 Hz and voltages between individual thresholds and maximal amplitudes of stimulation. Ten anginal patients and two hypertensive patients were studied at an interval of up to 12 years after implantation of electrodes and a radiofrequency receiver for chronic therapeutic CSNS. In search of combinations of frequency and voltage of CSNS, eliciting largest ("optimal") depressor responses of blood pressure and heart rate in the individual patient, Rechenberg's evolution strategy was applied. This strategy simulates mutation and selection of biological evolution. In each patient and on each test stimulation, a value of quality was computed from actual heart rate and blood pressure values as a selection criterion for the strategy. Either responses to uninterrupted CSNS were investigated, while stimulation parameters were adjusted every 3 min, according to the strategy, or responses to 3 min of CSNS after a change in stimulation parameters were compared to intercalated 3-min control periods. In each patient, one or more combined settings of frequency and voltage elicited "optimal" responses. In principle, "optimal" CSNS frequencies ranged between 35 and 105 Hz with large interindividual differences. Due to chronic implantation of electrodes and technical features of radiofrequency transmitted stimulation energy, interindividually different voltages led to an optimal response to CSNS. Also according to the present results, the frequency of CSNS has to be determined individually. It is concluded that the evolution strategy was applied successfully, because voltage and frequency settings leading to "optimal" responses were found within 90-180 min, whereas intraindividual systematic investigations would not be feasible due to their necessarily very long duration. So far, only short-term responses have been evaluated. A broader use of the strategy in other applications is encouraged, as for example in pacemaker optimization and especially in functional electrostimulation.     

Effects of calcitonin gene-related peptide on canine cerebral artery strips and the in-vivo vertebral blood flow in dogs

Summary The effects of calcitonin gene-related peptide (CGRP) on canine cerebral arteries and on vertebral blood flow were investigated in-vivo and in-vitro and the findings compared with the effects of vasoactive intestinal peptide (VIP) and substance P. Administration of CGRP into the vertebral artery caused a dose-dependent and long-lasting increase in blood flow. The in-vivo vasodilatory effects of substance P and VIP were short-lasting. CGRP (0.1 to 100 nmol/l) elicited a concentration-dependent relaxation of the isolated middle cerebral and basilar arteries when the tissues were precontracted by exposure to prostaglandin F₂ (PGF₂). This effect was not antagonized by propranolol, atropine, tetrodotoxin, (N-Ac-Tyr¹, D-Phe²)-growth hormone-releasing factor(1–29)-NH₂ or (D-Pro², D-Trp^7,9) substance P. CGRP also reduced concentration-dependently the contraction of cerebral arteries induced by KCl or 9,11-epithio-11,12-metano-thromboxane A₂ (STXA₂). Mechanical removal of the endothelium did not abolish the vasodilatory response to CGRP. In PGF₂-contracted canine cerebral arteries, VIP (0.1 to 100 nmol/l) was less potent a vasodilator than CGRP. At low concentrations (0.01 to 1 nmol/l) substance P elicited a rapid and short-lasting relaxation, and in the absence of endothelium this relaxation disappeared. These findings are clear evidence that CGRP modulates vascular tone.     

Dopamine inhibits prostaglandin F2α-induced depolarization of rabbit jejunal arteries via activation of DA1-receptors

Summary In rabbit jejunal arteries, the membrane potential of single smooth muscle cells decreased on the application of noradrenaline 3 mol/1. LY 171555 1 mol/1 did not change, whereas SKF 38393 10 mol/1 reversed the effect of noradrenaline. When prostaglandin F₂ (PGF₂) was used to evoke depolarization in the presence of prazosin 0.1 mol/1, rauwolscine 1 mol/1 and propranolol 1 mol/1, both SKF 38393 10 mol/1 and dopamine 10 mol/1 repolarized the membrane. SCH 23390 1 mol/1 antagonized the effects of SKF 38393 10 mol/1 and dopamine 10 mol/1. Thus, the change in membrane potential is mediated by a DA₁-recep-tor.     

AN ARTERIAL PERFORMANCE INDEX

INTRODUCTIONWhenpulsatingbloodflowsthroughtheartery,thearterialwallwilldilateandcontractperiodicallybecauseoftheelasticityofarterialwallandtheperipheralresistance'Thisensuresthecontinuityofbloodflowandthelocalbloodpressurenotchangingtoomuch.Ifthearterialwallispathologicallychanged,causingthechangeoftheelasticityofarterialwall,theperformanceofarterywillbeaffected'Atpresent,thecomplianceiswidelyusedtoevaluatethedistensibilityofarterialwass[1],butitcannotevaluatethetotalperformanceofartery'T…     

下鼓室的应用解剖

目的　探讨颈动脉管、颈静脉窝与下鼓室的变异关系 ,为此区域手术提供可靠的解剖学资料。方法　在XSQ～Ⅱ型手术显微镜下解剖观察了 2 0 0例颞骨标本的下鼓室 ,并用游标卡尺对有关结构进行了测量。结果　下鼓室纵径 0 2 8mm ,横径为 0 85mm ,深为 1 2 8mm。下鼓室底与颈静脉窝相毗邻者见 93 0 %。当颈静脉窝大而上隆时 ,窝顶与鼓室间以薄骨板分隔 ,骨板最薄时仅为 0 2 0mm。颈静脉窝顶突入鼓室腔者占 1 2 5 % ,窝顶有骨质缺损者见 4 0 %。鼓室底与颈动脉管关系随颈动脉位置变化而异 ,有 6 8 0 %的标本颈动脉管位于岬下缘前 1 / 3区 ,4 0 %的标本颈动脉管占据范围达岬下缘后 1 / 3区。结论　下鼓室与颈静脉窝及颈动脉管存在着多种变异关系 ,下鼓室手术及静脉窝区手术应避免损伤颈静脉球及颈内动脉等结构     

Arterial endothelial function in a porcine model of early stage atherosclerotic vascular disease

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the United States and is projected to become the leading cause of mortality in the world. Atherosclerosis is the most important single factor contributing to this disease burden. In this study, we characterize relationships between endothelial dysfunction and vascular disease in an animal model of diet-induced, early-stage atherosclerotic vascular disease. We tested the hypothesis that hypercholesterolaemia induces vascular disease and impairs endothelium-dependent relaxation (EDR) in conduit arteries of adult male Yucatan pigs. Pigs were fed a normal fat (NF) or high fat cholesterol (HFC) diet for 20-24 weeks. Results indicate that, while the HFC diet did not alter EDR in femoral or brachial arteries, EDR was significantly decreased in both carotid and coronary arteries. Sudanophilic fatty streaks were significantly present in the abdominal aorta and common carotid artery. Histopathology revealed increased intima-media thickness (IMT) and foam cell accumulation in Stary Stage I-III lesions in the abdominal aorta, common carotid artery and femoral arteries. In the coronary arteries, the accumulation of foam cells in Stary Stage I and II lesions resulted in a trend for increased IMT. There was no evidence of vascular disease in the brachial arteries. These results indicate that early stages of CVD (Stary Stage I-III) precede decreases in EDR induced by HFC diet, because femoral arteries exhibited foam cell accumulation and an increased IMT but no change in endothelial function.     

Role of the mesenteric arteries in the arterial blood supply to the lower limbs

Summary The arteries of the gut, and in particular in the inferior mesenteric artery (a. mesenterica inferior), normally play a minimal role in supplying blood to the lower limbs. However, this is far from being the case in aorto-iliac obstruction. The anatomical anastomoses between the intestinal arterial system and the arteries of the lower limb hypertrophy and in one case out of ten become predominant.In the present study the path taken and the relations of the collaterals of the intestinal arteries and of their anastomoses have been traced, and several collateral pathways are described.

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Rôle des artères mésentériques dans la revascularisation artérielle des membres inférieurs

Résumé Les artères digestives, et en particulier l'artère mésentérique inférieure (a. mesenterica inferior), jouent à l'état normal un rôle minime dans la vascularisation des membres inférieurs. Il n'en est pas de même en cas d'oblitération aorto-iliaque. Les anastomoses anatomiques entre le système artériel digestif et les artères du membre inférieur s'hypertrophient et, dans un cas sur 10, deviennent prédominantes.Dans cette étude, le trajet et les relations des collatérales des artères digestives et leurs anastomoses sont étudiés. Plusieurs voies collatérales sont possibles.

     

Hypertension and sleep apnoea

SUMMARY  Epidemiological data indicate a link between sleep-disordered breathing and elevation of arterial pressure. Previous studies suggest increased activity of the sympathetic nervous system in patients with sleep apnoea. The response of muscle sympathetic nerve activity was further investigated in normal, awake subjects following exposure to 20 minutes of asphyxia. Sympathetic nerve traffic increased during exposure and remained elevated even after the return to room air breathing. These findings raise the possibility that this sustained elevation of sympathetic nerve traffic could play a role in the development of daytime hypertension in patients with sleep-disordered breathing.     

A mixture of experts network structure for modelling Doppler ultrasound blood flow signals

Mixture of experts (ME) is a modular neural network architecture for supervised learning. This paper illustrates the use of ME network structure to guide modelling Doppler ultrasound blood flow signals. Expectation-Maximization (EM) algorithm was used for training the ME so that the learning process is decoupled in a manner that fits well with the modular structure. The ophthalmic and internal carotid arterial Doppler signals were decomposed into time-frequency representations using discrete wavelet transform and statistical features were calculated to depict their distribution. The ME network structures were implemented for diagnosis of ophthalmic and internal carotid arterial disorders using the statistical features as inputs. To improve diagnostic accuracy, the outputs of expert networks were combined by a gating network simultaneously trained in order to stochastically select the expert that is performing the best at solving the problem. The ME network structure achieved accuracy rates which were higher than that of the stand-alone neural network models.     

Sympathetic a-adrenergic control of large-bore arterial vessels,arterioles and veins,and of capillary pressure and fluid exchange in whole-organ cat skeletal muscle

The sympathetic nervous control of the vascular bed of cat gastrocnemius muscle was studied with a new whole-organ technique which permits simultaneous, continuous and quantitative measurements of capillary pressure (P_c), capillary fluid exchange and resistance reactions in the whole vascular bed and in its three consecutive sections: large-bore arterial vessels (> 25 μm), arterioles (< 25 μm) and veins. The results demonstrated a distinct neural control of all three consecutive vascular sections, graded in relation to the rate of nerve excitation up to maximum at 16 Hz. Stimulation at high rates, which in the steady state caused an average rise of overall regional resistance from 15.3 to 120 PRU (7.8-fold increase), thus raised large-bore arterial vessel resistance from 8.8 to 64 PRU (7.3-fold increase), arteriolar resistance from 4.5 to 49 PRU (10.9-fold increase) and venous resistance from 2.0 to 7 PRU (3.5-fold increase). The rate of resistance development (PRU s^-1) of the sympathetic constrictor response was much higher in the arteriolar than in the other sections, which indicates that the neural control is especially prompt and efficient in the arterioles. A passive component was shown to contribute to the described responses only on the venous side, but in no case by more than 10% of the total sympathetic venous resistance response, which thus is mainly active. Of special functional importance was that the new technique provided information about the adrenergic control of P_c, in absolute figures. From the control value of 19 mmHg, graded sympathetic stimulation caused a graded decline in P_c, at maximum constriction by about 7 mmHg. This resulted in marked net transcapillary fluid absorption, in turn increasing plasma volume.