Indirect systolic and mean blood pressure determination by a new tail cuff method in spontaneously hypertensive rats

A new tail cuff method for determining systolic and mean blood pressure in rats was developed based on photoelectric detection of tail arterial blood flow and pulsatile volume oscillation. Indirect systolic and mean blood pressure measured by this method correlated well with direct systolic and mean blood pressures recorded by a transducer and polygraph after carotid artery cannulation in stroke-resistant spontaneously hypertensive rats (SHR), stroke-prone SHR and normotensive Wistar Kyoto rats. Blood pressures were sharply, and transiently raised for about 1 min when rats were picked up by an investigator to be placed in a hot box or immobilized in a restrainer for measuring blood pressure. Therefore, blood pressures should be measured at least 1 min after the rats are put in a restrainer. This new tail cuff method for measuring blood pressure provides reliable mean blood pressure readings in conscious rats.     

SURGICAL MANAGEMENT OF DISSECTING ANEURYSM—The Use of a Simplified Bypass

The alarming mortality in cases of dissecting aneurysm of the aorta has stimulated the development of a surgical technique which results in re-entry of the dissecting channel. During the operative procedure prolonged cross-clamping of the aorta is necessary. While hypothermia will provide protection to the spinal cord and kidneys during reasonable periods of aortic occlusion it will not relieve back pressure on the left ventricle.By the use of a simple bypass blood is drained from the left atrium into a reservoir and then pumped into the lower aorta via the femoral artery. Thus an adequate supply of oxygenated blood is delivered to the spinal cord and kidneys distal to the occlusion while the left ventricular pressure is decompressed to normal levels. The volume of the shunted blood is simply controlled by monitoring the brachial artery pressure with a cuff sphygmomanometer. This simplified bypass has permitted successful repair of a dissecting aneurysm with complete occlusion of the thoracic aorta for a period of two hours.     

Venous occlusion plethysmography reduces arterial diameter and flow velocity

The measurement of peripheral blood flow by plethysmography assumes that the cuff pressure required for venous occlusion does not decrease arterial inflow. However, studies in five normal subjects suggested that calf blood flow measured with a plethysmograph was less than arterial inflow calculated from Doppler velocity measurements. We hypothesized that the pressure required for venous occlusion may have decreased arterial velocity. Further studies revealed that systolic diameter of the superficial femoral artery under a thigh cuff decreased from 7.7 +/- 0.4 to 5.6 +/- 0.7 mm (P less than 0.05) when the inflation pressure was increased from 0 to 40 mmHg. Cuff inflation to 40 mmHg also reduced mean velocity 38% in the common femoral artery and 47% in the popliteal artery. Inflation of a cuff on the arm reduced mean velocity in the radial artery 22% at 20 mmHg, 26% at 40 mmHg, and 33% at 60 mmHg. We conclude that inflation of a cuff on an extremity to low pressures for venous occlusion also caused a reduction in arterial diameter and flow velocity.     

New methodology for measuring blood pressure in awake baboons with use of behavioral training techniques

Adult male baboons were behaviorally conditioned to extend an arm outside of the living cage and to accept repeated cuff inflations for manual auscultatory blood pressure measurements. Frequency distributions of systolic and diastolic blood pressure for both normotensive and renovascular hypertensive baboons generally were normally distributed. The procedure accurately tracked rapid changes in blood pressure after oral administration of antihypertensive drugs. Advantages over direct arterial cannulation for blood pressure measurement during extended, chronic experiments are discussed.     

Comparison of direct and indirect blood pressure measurement in anesthetized dogs.

This study was conducted to determine whether blood pressures and pulse rate could be determined accurately by indirect measurements from the front and hind legs of 15- to 40-kg dogs anesthetized with isoflurane. Indirect measurements from each animal were compared to direct measurements obtained from a catheter placed into the abdominal aorta via the femoral artery at four ranges of systolic pressure. When systolic pressure was above 80 mm Hg, indirect measurements were either the same as direct measurements or slightly lower. However, when systolic pressures were below 80 mm Hg, indirect systolic pressure measurements were 6 to 15% higher than direct measurements. Larger differences in diastolic pressures were found, which resulted in differences in mean pressure. The most accurate measurements were found when the cuff width-to-limb circumference ratio was between 0.4 and 0.6 and when systolic pressure was between 80 and 100 mm Hg.     

Noninvasive measurement of blood pressure in African green monkeys (Cercopithecus aethiops)

Indirect measurements of arterial blood pressure were made in African green monkeys (Cercopithecus aethiops) employing a Doppler ultrasound stethoscope and standard cuff and an Infrasonde automatic blood pressure recorder. Measurements were obtained from anesthetized (10 mg/kg ketamine (HCI) and unanesthetized (1.5 mg/kg ketamine HCI) animals. Ketamine had no significant effect on blood pressure. Indirect measurements from the brachial artery were compared with direct femoral artery measurements and with each other. Systolic blood pressures measured by the Doppler (r = .948) and Infrasonde (r = .920) methods correlated closely with direct measurements but were significantly lower than systolic blood pressures measured by the direct method. Diastolic blood pressures measured by the Infrasonde method agreed closely with direct measurements (r = .947). Systolic blood pressures measured by the indirect methods correlated closely in both anesthetized (r = .973) and unanesthetized (r = .834) animals and were not significantly different. Mean blood pressures calculated from direct and Infrasonde measurements also correlated closely (r = .963), with direct measurements being 4 mmHg higher on the average. Mean blood pressures are less influenced by methodology and are more reproducible than other pressures. These noninvasive methods can be used to obtain simple and accurate measurements of blood pressure from anesthetized and unanesthetized monkeys and are of value in long-term studies in monkeys.     

Auscultatory indirect measurement of blood pressure in dogs

An indirect method of measuring blood pressure (cuff plus stethoscope) was evaluated in 70 dogs weighing 15 to 30 kg (17.5 +/- 8.8 kg; mean +/- standard deviation). A cuff 12 cm wide was used. The measurements were most audible with the cuff on the upper foreleg of the dog and with the stethoscope placed in the medial epicondylar region just distal to the cuff. The cuff was inflated to greater than systolic pressure and allowed to deflate slowly. In 70 lightly sedated dogs, systolic blood pressures averaged 145 +/- 25 mmHg (mean +/- standard deviation) and diastolic blood pressures averaged 84 +/- 14 mmHg. Indirect measurements were compared to direct measurements (femoral arterial catheter). Systolic pressures obtained by this direct method averaged 138 +/- 29 mmHg (mean +/- standard deviation) and diastolic pressures averaged 84 +/- 17 mmHg. The correlation coefficient for systolic pressure was 0.96 and for diastolic pressure 0.97.     

Oscillometric measurement of systolic and diastolic blood pressures validated in a physiologic mathematical model

ABSTRACT: BACKGROUND: The oscillometric method of measuring blood pressure with an automated cuff yields valid estimates of mean pressure but questionable estimates of systolic and diastolic pressures. Existing algorithms are sensitive to differences in pulse pressure and artery stiffness. Some are closely guarded trade secrets. Accurate extraction of systolic and diastolic pressures from the envelope of cuff pressure oscillations remains an open problem in biomedical engineering. METHODS: A new analysis of relevant anatomy, physiology and physics reveals the mechanisms underlying the production of cuff pressure oscillations as well as a way to extract systolic and diastolic pressures from the envelope of oscillations in any individual subject. Stiffness characteristics of the compressed artery segment can be extracted from the envelope shape to create an individualized mathematical model. The model is tested with a matrix of possible systolic and diastolic pressure values, and the minimum least squares difference between observed and predicted envelope functions indicates the best fit choices of systolic and diastolic pressure within the test matrix. RESULTS: The model reproduces realistic cuff pressure oscillations. The regression procedure extracts systolic and diastolic pressures accurately in the face of varying pulse pressure and arterial stiffness. The root mean squared error in extracted systolic and diastolic pressures over a range of challenging test scenarios is 0.3 mmHg. CONCLUSIONS: A new algorithm based on physics and physiology allows accurate extraction of systolic and diastolic pressures from cuff pressure oscillations in a way that can be validated, criticized, and updated in the public domain.     

Comparison of performance of various sphygmomanometers with intra-arterial blood-pressure readings.

Seven types of sphygmomanometer were used in random order on each of nine hypertensive patients and the readings compared with simultaneous intra-arterial blood-pressure recordings. All the devices gave significantly different values for systolic pressure, and only two measured diastolic pressure without significant error. Systolic pressure was consistently underestimated (range 31-7 mm Hg), and all but one instrument overestimated diastolic pressure (range 10-2 mm Hg). The variability of readings was least with the standard mercury sphygmomanometer and the random-zero machine, while with some of the more automated devices single readings were in error up to -68/33 mm Hg. The strong correlations found between intra-arterial and cuff systolic pressures with all devices tested and significant correlations for diastolic pressure with all but one device indicate that, with one possible exception, the sphygmomanometers would give accurate results where a change in blood pressure was the main concern.     

Comparing EndoPAT and BIOPAC measurement of vascular responses to mental stress

There are currently no comparison measurements of stress‐induced changes in vascular function during acute mental stress tests to measurements made by BIOPAC MP150 systems technology, a standard polygraph device used to detect deception during polygraph examinations in military or law enforcement applications. Vascular responses to reactive hyperaemia and acute mental stress in 25 healthy subjects were measured by both peripheral arterial tonometry (EndoPAT) and a blood pressure cuff attached to a pressure transducer (BIOPAC) and compared. Reactive hyperaemia was performed at baseline and following three acute mental stress tests. There was no difference in vascular reactivity at baseline and following acute mental stress, as measured by EndoPAT or BIOPAC systems (p > 0·05). Mental stress ratios measured by EndoPAT were significantly different than those measured by BIOPAC (p < 0·01). These data suggest that EndoPAT measurements of vascular responses to acute mental stress may be more specific and sensitive than measurements using the BIOPAC system. Copyright © 2011 John Wiley & Sons, Ltd.     

Long-term cannulation of the vena cava of rats for blood sampling: local and systemic effects observed by histopathology after six weeks of cannulation.

A cannulation system with fixation by a metal cuff around the tail was used for blood sampling. The cannula was guided subcutaneously and positioned in the vena cava after entering the body via the femoral vein. Histopathology was performed after long-term cannulation of up to 35 and 45 days. The presence of the cannula in the vena cava induced endothelial hypertrophy and hyperplasia accompanied by stromal hypertrophy. The endothelial activation was not limited to the vena cava but was also observed in both the cannulated vena iliaca and the contralateral control vena iliaca, the latter showing only minor alterations. In the lung, thrombi were noted in the larger lung arteries; and foreign body emboli, probably situated in the alveolar septi, could be detected occasionally. Inflammatory reactions in the tail at the site of cuff fixation consisted of a mixture of acute and chronic inflammatory responses. The chronic inflammation extended into the tail muscles, as shown by the presence of fibrous tissue associated with muscle degeneration. In conclusion, prolonged venous cannulation in rats resulted in local alterations in the veins, small emboli in the lungs and a moderate to marked inflammation in the tail. However, the procedure itself was well tolerated by the animals.     

Venous cuff pressures from 30 mmHg to diastolic pressure are recommended to measure arterial inflow by plethysmography.

Venous occlusion strain gauge plethysmography (VOP) is based on the assumption that the veins are occluded and arterial inflow is undisturbed by the venous cuff pressure. Literature is not clear concerning the pressure that should be used. The purpose of this study was to determine the optimal venous occlusion pressure at which the highest arterial inflow is achieved in the forearm, calf, and leg by using VOP. We hypothesized that, for each limb segment, an optimal (range of) venous cuff pressure can be determined. Arterial inflow in each limb segment was measured in nine healthy individuals by VOP by using pressures ranging from 10 mmHg up to diastolic blood pressure. Arterial inflows were similar at cuff pressures between 30 and 60 mmHg for the forearm, leg, and calf. Arterial inflow in the forearm was significantly lower at 10 mmHg compared with the other cuff pressures. In addition, arterial inflows at 20 mmHg tended to be lower in each limb segment than flow at higher cuff pressures. In conclusion, no single optimum venous cuff pressure, at which a highest arterial inflow is achieved, exists, but rather a range of optimum cuff pressures leading to a similar arterial inflow. Venous cuff pressures ranging from 30 mmHg up to diastolic blood pressure are recommended to measure arterial inflow by VOP.     

Problems in the interpretation of blood pressure changes seen in rats fed a breakfast cereal

Systolic blood pressures were measured on the same animals by direct and indirect methods. A tail cuff was used for the indirect measurements, and the direct measurements were obtained with a strain gauge after a needle was inserted into a major artery. Good agreement was found between normal values and elevated pressures produced by norepinephrine, but gross differences were observed in a nutritional experiment in which oatmeal was fed. Credibility requires that blood pressure changes be demonstrated by direct as well as by indirect measurements.     

Pulsatile flow in a catheterised artery

A model is presented for the physiological problem of a catheter which is inserted in a femoral artery to measure the pressure gradient. As the catheter will modify the pressure distribution in the artery, the pressure gradient which would be recorded by a perfect pressure transducer attached to it would differ from that in the uncatheterised artery. To estimate the magnitude of this error, it is assumed that the rates of flow of blood through the catheterised and the uncatheterised artery are described by the same known periodic function of time.     

大鼠体外循环模型的建立及改进

目的对现有大鼠体外循环模型予以改进,降低模型复制难度,并使之更适合用于研究体外循环对肺功能的影响。方法成年雄性SD大鼠16只,体重300～350g,各8只分别用于建模和供血。经右颈静脉、左股静脉引流,右股动脉人工灌注建立体外循环,血气分析监测内环境变化。实验过程中,保留大鼠自主呼吸,不进行机械通气。结果成功建成8只大鼠体外循环模型并按计划顺利脱离人工循环。体外循环期间转流量为70～80mL/（kg·min）,血流动力学监测和血气分析结果基本正常。结论进一步简化了建立大鼠体外循环模型的操作,最显著的改进之处在于避免了机械通气对大鼠肺功能潜在的不良效应,从而更加适合用于研究体外循环对肺功能的影响。     

颈动脉窦内压的变化速率对反射性降压效应的影响

在成年狗身上制备右侧孤离颈动脉窦,借助灌流装置用饱和氧的任氏液对其进行灌流。灌流压为搏动性的。通过改变每搏泵出量、灌流管道的阻力和弹性来调节灌流压及其变化速率。用多导生理记录仪同步记录股动脉血压、窦内灌流压及其变化速率。本文主要观察窦内压的变化速率对降压反射的影响。在8只狗身上共进行了93次实验。结果表明,在窦内压相同的情况下,灌流压的上升速率愈快,降压效应愈明显,而其下降速率则无显著作用。已有资料证明搏动性窦内压所引起的降压效应较非搏动性压力更为明显。由此可见,狗的颈动脉窦压力感受器不仅对搏动性压力而且对其上升的变化速率也很敏感。     

Evaluation of the characteristics and performance of an automatic sphygmomanometer (Omega 1400)

24 hour pressure monitoring is a newly developing technique potentially yielding important informations in hypertensive patients. Numerous automated devices are available whose performance characteristics are poorly documented. To evaluate an automated sphygmomanometer commonly used in our Division (Omega 1400, Invivo Research Laboratories), we performed a series of measurements, simultaneously recording blood pressure in the opposite arm with a common sphygmomanometer. Each measure was then repeated reversing the position of the two devices (manual and automated), thus abolishing possible differences between the two arms. We observed a mean underestimation of 1.90 mmHg of systolic pressure and of 4.82 mmHg of diastolic blood pressure by the automated device. We conclude that the device by us evaluated is not advisable in the basal blood pressure evaluation, but useful in monitoring inpatients.     

Variability in intraosseous pressure induced by saline flush of an intraosseous cannula by multiple practitioners

Intraosseous cannulation is an accepted means to achieve vascular access when peripheral venous access is not available. It is common practice to flush the intraosseous cannula with saline prior to establishing infusions. The objective of this study was to evaluate changes in intraosseous pressure during the flush procedure and to assess the variability of pressure changes induced by different practitioners. Two intraosseous cannulas were placed in an isolated cadaveric femur collected from a swine. Intraosseous pressure and the rate of change in pressure were recorded continuously during a series of saline flushes into a distal femoral intraosseous cannula by 21 members of the veterinary research staff at the authors' institution. Median peak intraosseous pressures exceeded 600 mmHg, and an inverse relationship was noted between peak intraosseous pressure and the duration of flush. Bone marrow fat emboli were grossly evident in flush effluents and their presence was confirmed by microscopic examination. Until the practitioners were informed of the pressure changes induced by the intraosseous cannula flush, few had appreciated the magnitude of the pressures that they had generated, suggesting that an instrumented intraosseous flush preparation like the one used in this study may prove useful as a training tool for flush procedures.     

Evaluation of Compliance of Arterial Vessel Using Coupled Fluid Structure Interaction Analysis

The in vivo and ex vivo compliance of arteries are expected to be closely related and estimated. Fluid-structure interaction analysis can assess the agreement between the two compliances. To evaluate this hypothesis, a pulsatile fluid-structure interaction analysis of blood flow in femoral artery of a dog was conducted using: (1) measured in vivo mean pressure (72.5 mmHg), mean pressure drop (0.59 mmHg), mean velocity (15.1 cm/sec); and (2) ex vivo measurements of non -- linear elastic properties of femoral artery. Additional analyses were conducted for physiological pressures (104.1 and 140.7 mmHg) and blood flow using a characteristic linear pressure -- flow relationship. The computed compliance decreased from 0.198% diameter change/mmHg at 72.5 mmHg to 0.145% diameter change/mmHg at 140.7 mmHg. The computed compliance tends to match well with in vivo compliance of femoral artery at lower pressure but is overestimated at higher pressure. This suggests an alteration in the compliance of the artery during ex vivo elasticity measurements.     

Systemic circulatory effects of pentagastrin

Effects of pentagastrin on systemic circulation were studied in anesthetized cats. Systemic arterial, central venous and portal pressure were monitored with electromanometers and blood flow through the superior mesenteric artery, common carotid artery, femoral artery and ascending aorta were measured with an electromagnetic blood flow meter. Pentagastrin injected intravenously at a doses of 2.0, 4.0 and 8.0 micrograms/kg induced a dose-dependent fall in arterial pressure, heart rate and cardiac output, increased mesenteric blood flow, decreased common carotid artery blood flow, did not change femoral artery blood flow and slightly rose central venous pressure. Atropine blocked observed effects. After repeated injections of the peptide, tachyphylaxis quickly developed. The obtained results indicate that pentagastrin influences general hemodynamics probably via interaction with cholinergic receptors.