Lack of interaction between adenosine-induced vasodilatation and carotid baroreflex-induced changes in sympathetic activity in dog hindlimb artery

In anaesthetized dogs, a hindlimb was vascularly isolated and perfused at a constant flow rate of 7.7 +/- 1.9 ml min-1 100 g-1 (mean +/- S.E.M.; n = 5) through the femoral artery. The carotid sinuses were isolated and perfused at high (greater than 145 mmHg) or low (less than 75 mmHg) pressure to enable reflex sympathetic tone on the hindlimb vessels to be controlled. Both vagi were sectioned in the neck and mean aortic blood pressure was held constant by connection of the aorta to a reservoir. The responses to infusion of three doses of adenosine at high and low carotid sinus pressures were not significantly different: infusion of 0.60 +/- 0.16 microM-adenosine reduced femoral arterial perfusion pressure (FAPP) by 11.6 +/- 3.2% (n = 6) at high carotid sinus pressure and by 12.6 +/- 5.1% (n = 4) at low carotid sinus pressure, while 4.71 +/- 0.49 microM-adenosine reduced FAPP by 20.8 +/- 4.8% (n = 6) at high carotid sinus pressure and by 20.7 +/- 4.8% (n = 6) at low carotid sinus pressure; 50.1 +/- 7.3 microM-adenosine reduced FAPP by 36.7 +/- 5.5% (n = 6) at high carotid sinus pressure and by 27.7 +/- 7.8% (n = 5) at low carotid sinus pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of pulsatile with nonpulsatile mechanical support in a porcine model of profound cardiogenic shock

The aim of this study was to examine whether pulsatility by intraaortic balloon counterpulsation (IABP) is an important adjunct to the treatment of profound cardiogenic shock (CS) with a widely used, nonpulsatile centrifugal pump (CP). In each of 18 anesthetized, open chest pigs, the outflow cannula of the CP was inserted in the aortic arch through the right external carotid artery, and the inflow cannula of the CP was placed in the left atrium. A 40 cc IABP was subsequently placed in the descending aorta through the left external carotid artery. CS was induced by occlusion of coronary arteries and the infusion of propranolol and crystalloid fluid. Mean aortic pressure, pulse pressure, aortic end diastolic pressure, left ventricular end diastolic pressure, right atrial pressure, and heart rate were monitored. Cardiac output and left anterior descending artery flow were measured with a transit time ultrasound flowmeter. During profound CS, life sustaining hemodynamics were maintained only with the support of the assist devices. Hemodynamic support with the CP was associated with a nearly nonpulsatile flow and a pulse pressure of 7 +/- 4 mm Hg, which increased to 33 +/- 10 mm Hg (p = 0.000) after combining the CP with the IABP. Compared with the hemodynamic support offered by the CP alone, addition of the IABP increased mean aortic pressure from 40 +/- 15 to 50 +/- 16 mm Hg (p = 0.000), cardiac output from 810 +/- 194 to 1,200 +/- 234 ml/min (p = 0.003), and left anterior descending artery flow from 26 +/- 10 to 39 +/- 14 ml/min (p = 0.001). In profound CS, mechanical support provided by a continuous flow CP is enhanced by the added pulsatility of the IABP.     

Mechanism of intrarenal blood flow redistribution after carotid artery occlusion.

Bilateral carotid artery occlusion results in an increase in mean arterial pressure, an increase in renal sympathetic nerve activity, and a redistribution of renal blood flow from inner to outer cortex. To elucidate the mechanism of the renal blood flow redistribution, carotid artery occlusion was performed in anesthetized dogs with the left kidney either having renal perfusion pressure maintained constant (aortic constriction) or having alpha-adrenergic receptor blockade (phenoxybenzamine); the right kidney of the same dog served to document the normal response. When renal perfusion pressure was maintained constant, renal blood flow distribution (microspheres) was unchanged by carotid artery occlusion. In the presence of renal alpha-adrenergic receptor blockade, carotid artery occlusion elicited the usual redistribution of renal blood flow from inner to outer cortex. The redistribution of renal blood flow observed after carotid artery occlusion is mediated by the increase in renal perfusion pressure rather than the increase in renal sympathetic nerve activity.     

Blood flow redistribution during spontaneous wheel walk of the rat

Changes in regional blood flow and arterial pressure in the rat during spontaneous walk in a wheel were observed. An electromagnetic flow probe was implanted around the carotid, superior mesenteric, or renal artery, or the terminal aorta and a catheter for pressure measurement was inserted into the terminal aorta or the common carotid artery. The wheel had a diameter of 35 cm and rotated passively as the rat walked. When hindquarter (terminal aortic) flow increased markedly during wheel walk, carotid flow decreased, superior mesenteric flow decreased or remained unchanged, and renal flow did not change. Arterial pressure remained almost unchanged and heart rate increased an average of about 10%. Semiquantitative considerations indicated that arterial pressure was maintained in the face of the profuse increase in hindquarter flow during wheel walk by an increase in cardiac output rather than shifts of blood flow from other regions.     

Unusual aortic arch variation: distal origin of common carotid arteries

As part of a larger study, the aortic arch and its branches were removed en bloc at autopsy from men of Japanese ancestry born in Hawaii. Of the 193 arterial trees examined, 182 (94.3%) had a typical branching pattern (e.g., brachiocephalic trunk, left common carotid, and left subclavian arteries, in that order). Two specimens had only two branches arising from the aortic arch, a common trunk uniting the brachiocephalic and left common carotid arteries and a left subclavian artery. Nine individuals (4.6%) had four branches off the aortic arch; in eight of these cases (4.1%), the left vertebral artery originated directly off the aortic arch just proximal to, or as a common trunk with, the left subclavian artery. A unique aortic arch branching pattern was found in one of these men. The four arteries arising from the arch of the aorta were, in sequence: right subclavian, left subclavian, right common carotid, and left common carotid. The literature on aortic arch variations is reviewed and the possible embryonic development of these branching patterns and their clinical significance is discussed briefly.     

Regional difference in sympathetic vasoconstrictor tone in conscious rats

Regional differences in sympathetic vasoconstrictor tone were studied in conscious rats. In each rat an electromagnetic flow probe was chronically implanted around the common carotid, superior mesenteric, or renal artery, or the terminal aorta. An indwelling catheter for the measurement of arterial pressure was inserted into the terminal aorta via the right femoral artery. Peripheral resistance was calculated by dividing arterial pressure by flow. The per cent decrease in peripheral resistance on the ganglion blockade with hexamethonium bromide was used as a measure of regional sympathetic vasoconstrictor tone. A significant decrease in peripheral resistance, assumed to indicate a substantial tonic discharge to resistance vessels, was observed in conscious rats only in the carotid and renal areas and not in the superior mesenteric and hindquarter (supplied by the terminal aorta) areas. Since ganglion blockade also diminished the sum of the mean regional flows, cardiac output was estimated to decrease on the ganglion blockade. This suggests that capacitance vessels are also receiving a sizable vasoconstrictor tone, because the ganglion blockade did not elevate right atrial pressure. Pentobarbital anesthesia markedly inhibited the assumed tone to the renal area and was estimated to newly generate a tone to the hindquarters.     

Redistribution of cardiac output during grooming of the rat

Changes in blood flow in the carotid, superior mesenteric, or renal artery or terminal aorta during grooming were measured in the conscious rat with a chronically implanted electromagnetic flow probe. Arterial pressure was measured simultaneously with an indwelling catheter. During grooming, carotid flow almost doubled and arterial pressure rose slightly, while hindquarter (terminal aortic) flow decreased by an average of about 20%. Superior mesenteric flow decreased occasionally and renal flow remained almost unchanged. Heart rate increased by an average of about 10%. An increase in carotid flow during grooming was similarly observed after cervical sympathectomy. After ganglion blockade with hexamethonium, grooming did not decrease hindquarter flow any more. These findings suggest that during grooming a substantial amount of blood flow is switched from the hindquarters to the carotid areas, to achieve a redistribution of cardiac output largely by excitation of the respective regional sympathetic and parasympathetic fibers and that sympathetic vasoconstrictor fibers supplying different vascular areas are controlled by separate pathways from separate neuron groups.     

The effect of common carotid artery occlusion on blood pressure in the barodenervated cat

A 12% blood pressure elevation was found during common carotid occlusion in the barodenervated, thoracotomised cat under Nembutal anaesthesia. This rise in blood pressure appeared to be the net result of an 18% increase of total peripheral resistance and a concomitant 5% decrease of mean aortic flow.When the occlusions were repeated after ganglionic blockade similar values were found, indicating that the increase in resistance had not resulted from reflex vasoconstriction. To test if this increase of total peripheral resistance was caused by a mechanical exclusion, Ohm's law for parallel resistances was applied to the systemic tree to calculate the rise in resistance due to obstruction of the carotid flow. The results thus obtained matched the observed increase of peripheral resistance.It is concluded that common carotid artery occlusion can be used to test completeness of barodenervation in the cat, if an increase in blood pressure of about 12% is allowed for.     

Circulating catecholamines and control of plasma renin activity in conscious dogs.

Uninephrectomized dogs were prepared with indwelling catheters in the aorta, inferior vena cava (IVC), and renal artery, and after recovery they were studied in the conscious state. Basal aortic epinephrine and norepinephrine concentrations were 57 +/- 11 and 101 +/- 18 pg/ml, respectively. Elevation of epinephrine concentration to over 2,000 pg/ml by IVC infusion resulted in a sustained 3.5-fold increase in plasma renin activity (PRA), with only a transient decrease in arterial blood pressure. The PRA response to epinephrine was completely blocked by l-propranolol; isoproterenol increased PRA more than did epinephrine. Increasing norepinephrine concentration to 1,600 pg/ml by IVC infusion resulted in only a 1.5-fold increase in PRA. Infusion of epinephrine or norepinephrine directly into the renal artery to achieve similar increments of renal arterial concentration did not increase PRA. Insulin injection or hemorrhage resulted in elevations of arterial epinephrine (but not norepinephrine) concentration greater than the concentrations achieved during IVC infusion in these studies. We conclude that circulating epinephrine in the physiologic range plays a role in the control of PRA by activation of an extrarenal beta-receptor.     

Application of electrocapacitography to investigation of cephalic and cerebral circulation in the rabbit

Electrocapacitography devised for medical purposes by Hatakeyama was applied as a noninvasive volumetric method to investigate circulation in the rabbit head and brain. The effective electric capacitance was measured by means of a highly sensitive device. An electrocapacitogram (ECPG) of the head, considered to reflect the volume of intracranial as well as extracranial blood vessels, varied rhythmically with cardiac beat and respiratory movement. In general, the pulsatile variations of ECPG in synchronization with cardiac beat (ECPG pulse) bore a resemblance to arterial pulse. Occlusion of the common carotid artery caused the ECPG level corresponding to mean vascular volume to fall markedly and in most cases the amplitude of ECPG pulse was diminished. By rapid infusion of 5 ml of the blood into intracranial blood vessels via the internal carotid artery or into extracranial blood vessels via the external carotid artery, ECPG level was raised transitorily, the effect of extracranial infusion being larger than that of intracranial infusion. Stimulation of the central cut end of the cervical sympathetic nerve reduced ECPG level considerably. This response was greatly diminished by carotid occlusion and sometimes a temporary rise of ECPG was observed at the beginning of the stimulation. In several cases the effect was reversed completely by carotid occlusion and an increase of ECPG during the stimulation was observed. These findings suggest the existence of a sympathetic vasoconstrictor in the head as well as a sympathetic vasodilator of the brain, although in confirmation of this review further investigation is required. ECPG of the head is demonstrated to be a useful method for investigating circulation in the head including brain.     

颅内压升高引起神经源性肺水肿的发病机理

家兔两侧顶骨部蜘网膜下腔注入抗凝兔血,从颅内压(ICP)升高到60mmHg至140mmHg时,颈内动脉血流量(ICABFV)急剧降低,颈交感神经自发性放电频率、血浆去甲肾上腺素和肾上腺素含量、动脉血压均急剧增高,与ICP升高前比较,相差均非常显著(P<0.01)。ICP140mmHg持续2～5min随着动脉血压降低,ICABFV进一步减少,在5～20min内动物死亡。左心房、室显著扩张,肺静脉淤血,发生了严重的出血性肺水肿。ICP升高时,由股动脉抽血使动脉血压保持在ICP升高前的水平,可以防止神经源性肺水肿(NPE)的发生。实验结果提示了ICP升高使脑血液供给急剧减少,引起交感神经兴奋性增高,儿茶酚胺释放增多,从而使动脉血压急剧升高,左心负荷过重,由于血液动力性机理,导致NPE的发生。     

Neurohumoral mechanisms in acute aortic coarctation in conscious and anesthetized dogs

To study the interactions of the renin-angiotensin system, sodium balance, and the sympathetic nervous system in the development of coarctation hypertension, an aortic gradient was created with a pneumatic cuff in 11 chronically instrumented conscious dogs. Significant hypertension associated with a significant rise in plasma renin activity and sodium retention occurred within 48 h. Competitive angiotensin II blockade caused a greater decrease in arterial pressure after coarctation than before coarctation. In contrast, plasma norepinephrine decreased significantly from control levels after coarctation, and alpha-adrenergic blockade with phentolamine caused less of a decrease in arterial pressure than before coarctation. This decrease in sympathetic activity was also accompanied by a decreased blood pressure response to pressor doses of angiotensin II and methoxamine after coarctation. To assess carotid baroreceptor influence on acute coarctation hypertension, aortic blood pressure responses to pressor agents were determined in 12 chlorolose-urethan-anesthetized dogs while carotid sinus pressure was independently varied. Maintaining carotid pressure at control levels after aortic constriction restored blood pressure responses to pressor agents to before-coarctation levels. These results suggest that 1) activation of the renin-angiotensin system and sodium retention contribute to the development of coarctation hypertension, and 2) there is a carotid sinus baroreceptor-mediated decrease in alpha-adrenergic activity with acute coarctation hypertension.     

Cardiac end-diastolic dilation during acute blood pressure elevation is inotropy dependent

To examine if the degree of left ventricular (LV) end-diastolic dilation during an acute blood pressure elevation is inotropy dependent, the descending thoracic aorta was occluded before and during a continuous isoproterenol infusion into the left coronary artery in 10 open-chest pigs. The increase in peak LV systolic pressure and in LV tension-time-index induced by aortic occlusion, were equal before and during the isoproterenol infusion. Left and right ventricular (RV) segment lengths were continuously recorded in the free walls of both ventricles, by an ultrasonic technique. A slight fall in LV end-diastolic segment length by the intracoronary isoproterenol infusion was corrected by an i.v. saline infusion. Left ventricular end-diastolic volume was therefore equal at both levels of inotropy when the aorta was occluded, and the heart rate was kept constant by right atrial pacing. At control inotropy, aortic occlusion induced a rise in LV end-diastolic segment length; 6.0 (4.0-8.2)% (median and 95% confidence interval), compared with the smaller (P less than 0.05) increase of 3.8 (2.6-5.5)% during isoproterenol infusion. The end-systolic segment length increased more (P less than 0.01) at control inotropy than during intracoronary isoproterenol infusion: 10.9 (6.9-14.4)% and 4.1 (1.5-7.4)%, respectively. In the RV, both end-diastolic and end-systolic segment length increased slightly during aortic occlusion but only at control inotropy. Thus during an acute blood pressure elevation, the end-diastolic and end-systolic ventricular volumes are better maintained at high than at control inotropy.     

A case of the right aortic arch with the left subclavian artery as its last branch]

A case of the right aortic arch with the left subclavian artery as its last branch was found in an 80-year-old Japanese female cadaver during the 1990 dissection for students. The main findings were as follows. The ascending aorta arose from the left ventricle and ran right and upward to the level of the intervertebral disc between the 2nd and 3rd thoracic vertebrae. It then curved right and backward to form the aortic arch. The aortic arch joined the thoracic aorta that descended along the right side of the vertebral column and crossed obliquely the vertebral column at the level of the 8th thoracic vertebra. Finally it entered the abdomen through the aortic hiatus behind the esophagus. Four branches were given off from the aortic arch in the following order from left to right: the left common carotid, the right common carotid, and the right subclavian and the left subclavian arteries. The left subclavian artery, which had an aortic diverticulum at the origin of the aortic arch, ran left and upward behind the esophagus. The ligamentum arteriosum connected the left pulmonary artery with the aortic diverticulum of the left subclavian artery. The left common carotid artery, which normally had no branches before entering the cranium, gave off an accessory esophageal branch about 20 mm distally from its origin. The right and left vertebral arteries entered the transverse foramen of the 6th cervical vertebra. The left recurrent laryngeal nerve hooked around from the left dorsal to the right ventral part of the ligamentum arteriosum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional distribution of vasoconstrictor tone in acute spinal rats

Rats, chronically instrumented with an electromagnetic flow probe around the carotid, superior mesenteric, or renal artery, or the terminal aorta as well as having an arterial and venous catheter, were anesthetized with either and submitted to high spinal cord transection. One hour later, when the rats had recovered consciousness and the arterial pressure had recovered partially, hexamethonium was intravenously injected for ganglionic blockade. Peripheral resistance (arterial pressure/regional flow) was decreased significantly by ganglionic blockade in the carotid and renal areas but not in the superior mesenteric and hindquarter (terminal aortic) areas. This suggests the presence of sizable vasoconstrictor tone to resistance vessels in the carotid and renal areas but not in the superior mesenteric and hindquarter areas in the acute spinal rat. This distribution of vasoconstrictor tone is similar to that in intact conscious rats in the resting state and suggests the possibility that the vasoconstrictor tone for resistance vessels in intact rats is also for the most part generated in the spinal cord. Spinal transection decreased blood flow in all the four regions, suggesting a decrease in cardiac output due to dilation of capacitance vessels. It is possible that, in intact rats at rest, the so-called medullary vasomotor center is sending tonic impulses for the most part to capacitance vessels.     

Comparison of aortic and carotid baroreflexes in the dog

1. Experiments with vascularly isolated, blood-perfused aortic arch and carotid sinus preparations in sixteen dogs have provided evidence which suggests that, in the reflex regulation of normal arterial blood pressure, the aortic and carotid baroreflexes are not equivalent.2. Two different techniques were used. In one, a steel cannula was inserted into the ascending aorta and arch and fixed in position by ligatures about the aorta. The blood-filled space (aortic jacket) thus created could be distended with known pressures; the cardiac output passed through the cannula into the descending aorta. In the other, an extracorporeal circulation utilizing an isolated heart-lung preparation was used to separately perfuse the carotid sinuses, aortic arch, and systemic circulation of a test dog.3. Independent open-loop analysis of the aortic and carotid baroreflexes in each dog indicated that they were essentially similar in their over-all modus operandi but that there were quantitative differences between them which would suggest a predominant role for the carotid sinus reflex in the control of normal blood pressure.4. The carotid sinus Blutdruck-charakteristik curve was symmetrical about the range of normal blood pressure for the dog while the aortic arch curve was displaced to the right.5. The carotid sinus system had the greater gain (with reference to limb vascular resistance) and exhibited a greater maximal capacity to alter vascular resistance reflexly.6. When the carotid and aortic systems were activated simultaneously by distension, the reflex depressor responses were summed, essentially by a process of simple addition. A carotid-induced pressor response obscured a simultaneous aortic-induced depressor response of equal magnitude.7. In five dogs studied, the functional reflexogenic area of the aortic arch did not extend distally beyond the origin of the left subclavian artery.     

Contributions of blood drainage from the liver,spleen and intestines to cardiac effects of aortic occlusion in the dog

By occluding the descending thoracic aorta, blood transferred from the lower to the upper part of the body increases left ventricular end-diastolic volume and maintains stroke volume despite a rise in systolic left ventricular pressure (LVP) of about 60 mmHg. Seventy percent of the blood drained stems from the splanchnic circulation. To examine which splanchnic organs contribute to the cardiac effects, selective occlusions were performed during ultrasonic measurements of spleen and liver dimensions and left ventricular myocardial chord length (MCL) in atropinized, open-chest dogs. Drainage of 15±2 ml from the spleen accounted for 18±4% of the increase in end-diastolic MCL, whereas liver dimensions remained unaltered. Similar results were obtained during aortic occlusion at high inotropy (isoproterenol infusion). it was ascertained by occlusion of the coeliac and mesenteric arteries that about 50% of the cardiac response to aortic occlusion was due to drainage from the intestines and the aorta. Liver blood volume could be reduced by combined occlusion of the aorta and portal vein or coeliac and mesentenc arteries and was sensitive to changes in pressure in the inferior vena cava, but did not contribute to the cardiac response to aortic occlusion.     

内皮细胞的形态和排列与血液动力学关系的探讨

对２５例第２￣１０个月人胚胎主动脉及其分支处的内皮细胞形态进行了扫描电镜观察，可见胸、腹主动脉内皮细胞呈梭形和长梭形，主动脉弓的内皮细胞短，核突出。无名动脉、左颈总动脉及左锁骨下动脉分支口之间，两肋间动脉分支口处的内皮细胞形态、排列及损伤程度差异很大。本文用血流动力学的理论对此进行了讨论。     

Reflex sympathetic changes in aortic diastolic pressure-diameter relationship.

In anesthetized vagotomized cats with the chest opened and artificially ventilated, aortic blood pressure (AP) and external diameter (AD; ultrasound technique) were measured in the proximal third of the descending thoracic aorta. Slow sinusoidal oscillations (0.2-0.3 Hz in aortic volume were produced by a piston pump connected to a femoral artery. Diastolic pressure-diameter relationship (PDR) curves were obtained during control conditions and during stimulation of either the cut central end of the left inferior cardiac nerve (ICN) or the decentralized thoracic sympathetic chain (SC). In six cats with both carotid arteries occluded ICN stimulation reflexly shifted the PDR curves to lower diameters for any given pressure (mean deltaAD 3.2% at control AP). A smaller response to ICN stimulation was obtained in five cats with one patent carotid artery (mean deltaAD 2.3% at control AP). Stimulation of sympathetic efferents to the aorta (SC) caused similar responses in five animals (mean deltaAD 3.4% at control AP). This reflex control of the thoracic aorta may be involved in cardioaortic coupling and may influence the sensitivity of aortic mechanoreceptors.