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.     

Criteria for set point estimation in the volume clamp method of blood pressure measurement.

When blood pressure is measured in the finger using the volume clamp method the value at which the vascular volume is clamped is of crucial importance. Since the discovery of the method, several criteria of finding a correct set point have been elaborated: 1. The volume oscillations reach their maximum amplitude at cuff pressure equalling mean blood pressure. 2. The form of the diastolic portion of volume pulsations changes if the cuff pressure moves around the mean blood pressure. 3. The set point can be positioned at one third of the arterial volume. 4. The dynamic vascular compliance (DVC) may be continuously measured as the instantaneous amplitude of vascular volume oscillations is elicited by a relatively small and rapid vibration of the cuff pressure. The shape of the DVC pulse characteristically depends on the transmural pressure (TP): at negative TP (cuff pressure exceeding the blood pressure) it shows a distinct positive systolic peak, at positive TP the polarity of the DVC pulse is reversed. In contrast to the first three ways to find the set point, the last one may operate even in closed-loop performance, i.e. during the blood pressure measurement.     

Exercise reduces arterial pressure augmentation through vasodilation of muscular arteries in humans

Exercise markedly influences pulse wave morphology, but the mechanism is unknown. We investigated whether effects of exercise on the arterial pulse result from alterations in stroke volume or pulse wave velocity (PWV)/large artery stiffness or reduction of pressure wave reflection. Healthy subjects (n = 25) performed bicycle ergometry. with workload increasing from 25 to 150 W for 12 min. Digital arterial pressure waveforms were recorded using a servo-controlled finger cuff. Radial arterial pressure waveforms and carotid-femoral PWV were determined by applanation tonometry. Stroke volume was measured by echocardiography, and brachial and femoral artery blood flows and diameters were measured by ultrasound. Digital waveforms were recorded continuously. Other measurements were made before and after exercise. Exercise markedly reduced late systolic and diastolic augmentation of the peripheral pressure pulse. At 15 min into recovery, stroke volume and PWV were similar to baseline values, but changes in pulse wave morphology persisted. Late systolic augmentation index (radial pulse) was reduced from 54 +/- 3.9% at baseline to 42 +/- 3.7% (P < 0.01), and diastolic augmentation index (radial pulse) was reduced from 37 +/- 1.8% to 25 +/- 2.9% (P < 0.001). These changes were accompanied by an increase in femoral blood flow (from 409 +/- 44 to 773 +/- 48 ml/min, P < 0.05) and an increase in femoral artery diameter (from 8.2 +/- 0.4 to 8.6 +/- 0.4 mm, P < 0.05). In conclusion, exercise dilates muscular arteries and reduces arterial pressure augmentation, an effect that will enhance ventricular-vascular coupling and reduce load on the left ventricle.     

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 determination of diastolic, mean and systolic blood pressure--a numerical model

A theoretical model of oscillometric blood pressure measurement is presented. Particular emphasis is paid to the collapse behavior of the artery, and an exponential volume-pressure curve is used. The results of this study suggest that mean blood pressure can be accurately predicted from the peak of the oscillometric curve if corrections related to the cuff pressure waveform are applied. It is also shown, however, that systolic and diastolic pressure may not in general be accurately determined from fixed amplitude ratios based on the oscillometric peak due to the sensitivity of the method to variations in blood pressure waveform, pulse pressure, and arterial compliance. No simple procedures are found to correct for these effects.     

Biomechanical characterization of ventricular–arterial coupling during aging: A multi-scale model study

Left ventricular–arterial (VA) coupling has been recognized to be of great significance in understanding both the global and local mechanical performance of the circulatory system. In this study, a closed-loop multi-scale model of the human cardiovascular system is established for the purpose of studying the coupled VA hemodynamic changes during aging. Obtained results show that age-associated changes in arterial properties have some negative but relatively small influences on left ventricular (LV) mechanical performance, whereas they progressively increase LV and aortic systolic pressures, and aortic pulse pressure during aging. Wave analysis reveals that increased aortic characteristic impedance and premature wave reflection induced by arterial stiffening are two coexistent factors responsible for aortic systolic hypertension and increased aortic pulse pressure at old age. In contrast, aortic dilatation can partly counteract the negative influences of arterial stiffening. Coupled LV-systolic and arterial stiffening (a constant VA coupling index) well preserves LV mechanical performance given normal LV diastolic function during aging, but with a concomitant further elevation of LV and aortic systolic pressures. Furthermore, it is found that the states of arterial, LV-systolic and diastolic stiffness can be distinguished by investigating the sensitivity of LV-systolic pressure to various cardiac indices.     

Wave reflection augments central systolic and pulse pressures during facial cooling

Cardiovascular events are more common in the winter months, possibly because of hemodynamic alterations in response to cold exposure. The purpose of this study was to determine the effect of acute facial cooling on central aortic pressure, arterial stiffness, and wave reflection. Twelve healthy subjects (age 23 +/- 3 yr; 6 men, 6 women) underwent supine measurements of carotid-femoral pulse wave velocity (PWV), brachial artery blood pressure, and central aortic pressure (via the synthesis of a central aortic pressure waveform by radial artery applanation tonometry and generalized transfer function) during a control trial (supine rest) and a facial cooling trial (0 degrees C gel pack). Aortic augmentation index (AI), an index of wave reflection, was calculated from the aortic pressure waveform. Measurements were made at baseline, 2 min, and 7 min during each trial. Facial cooling increased (P < 0.05) peripheral and central diastolic and systolic pressures. Central systolic pressure increased more than peripheral systolic pressure (22 +/- 3 vs. 15 +/- 2 mmHg; P < 0.05), resulting in decreased pulse pressure amplification ratio. Facial cooling resulted in a robust increase in AI and a modest increase in PWV (AI: -1.4 +/- 3.8 vs. 21.2 +/- 3.0 and 19.9 +/- 3.6%; PWV: 5.6 +/- 0.2 vs. 6.5 +/- 0.3 and 6.2 +/- 0.2 m/s; P < 0.05). Change in mean arterial pressure but not PWV predicted the change in AI, suggesting that facial cooling may increase AI independent of aortic PWV. Facial cooling and the resulting peripheral vasoconstriction are associated with an increase in wave reflection and augmentation of central systolic pressure, potentially explaining ischemia and cardiovascular events in the cold.     

Model for post-occlusive reactive hyperemia as measured noninvasively with pressure pulse waveform

Post-occlusive reactive hyperemia is a noninvasive maneuver to assess microvascular reactivity related to the bioavailability and/or bioactivity of endothelial-derived factors. The inability to respond to endogenous vasodilator substances is mostly described by a low peak flow after an event associated with a peak flow. The aim of this study is to propose a model to describe post-occlusive responses observed in the pressure waveforms after occlusion release. Model variables were investigated in search of those representatives of the endothelial response to the ischemic process. Radial pressure pulse waveforms were acquired in the anterior region of the wrist, superficial to the radial artery, using a piezoelectric transducer acquired by a 12 bits acquisition board model at a sampling rate of 1.0 kHz to increase the temporal resolution. The occlusion maneuver was performed using an arm-cuff placed over the brachial artery. A time series of pulse pressure (PP) values, calculated from successive values of beat-to-beat systolic and diastolic pressures, was found to be a useful variable representing blood pressure signal in the model. This data time series of the pulse pressure presents reduced initial values compared with the baseline measurement, and an increasing value until a steady state behavior was sustained after approximately 60 s. This behavior for the pulse pressure series was described by a hyperbolic tangent model with parameters K (rate of change of PP), PP₀ (first value of PP after cuff release), and ΔPP (change in PP). The model was applied to pulse pressure signals from normotensive and hypertensive subjects. The observed responses between groups suggest that PP₀ and ΔPP are related to an endothelial response to the ischemic process and could be used as a clinical tool to assess endothelial function in hypertension.     

Assessment of central haemomodynamics from a brachial cuff in a community setting

ABSTRACT: BACKGROUND: Large artery stiffening and wave reflections are independent predictors of adverse events. To date, their assessment has been limited to specialised techniques and settings. A new, more practical method allowing assessment of central blood pressure from waveforms recorded using a conventional automated oscillometric monitor has recently been validated in laboratory settings. However, the feasibility of this method in a community based setting has not been assessed. METHODS: One-off peripheral and central haemodynamic (systolic and diastolic blood pressure (BP) and pulse pressure) and wave reflection parameters (augmentation pressure (AP) and index, AIx) were obtained from 1,903 volunteers in an Austrian community setting using a transferfunction like method (ARCSolver algorithm) and from waveforms recorded with a regular oscillometric cuff. We assessed these parameters for known differences and associations according to gender and age deciles from <30 years to >80 years in the whole population and a subset with a systolic BP < 140 mmHg. RESULTS: We obtained 1,793 measures of peripheral and central BP, PP and augmentation parameters. Age and gender associations with central haemodynamic and augmentation parameters reflected those previously established from reference standard non-invasive techniques under specialised settings. Findings were the same for patients with a systolic BP below 140 mmHg (i.e. normotensive). Lower values for AIx in the current study are possibly due to differences in sampling rates, detection frequency and/or averaging procedures and to lower numbers of volunteers in younger age groups. CONCLUSION: A novel transfer-function like algorithm, using brachial cuff-based waveform recordings, provides robust and feasible estimates of central systolic pressure and augmentation in community-based settings.     

人上臂加压时的脉波分析

将与动脉脉波测定装置相连的袖带,缠绕于上臂,借助袖带充气给袖带部位的动脉加压。当袖带内压从收缩压水平缓缓下降时,可以记录到一系列逐渐变化着的动脉脉波,与以前在动物动脉外直接描记到的脉波群相似。用“脉波分析法”可以获得袖带部位的收缩压和舒张压值。与柯氏音法比较,在105次体力负荷前后的12名健康人测定中,收缩压与舒张压的相关系数分别为0.98和0.97。分析“0 波”,尚可获得容积变化的信息,并能测得同时发生的压力变化值。进而可将此两值代入动脉顺应指数(I_C)式。20名正常人87次测定的I_C值,远高于20名高血压患者 78次测定的结果(P<0.001)。I_C值的降低与眼底动脉硬化的程度有关。此方法具有简易、无创伤的优点。     

Central Pressure Appraisal: Clinical Validation of a Subject-Specific Mathematical Model

IntroductionCurrent evidence suggests that aortic blood pressure has a superior prognostic value with respect to brachial pressure for cardiovascular events, but direct measurement is not feasible in daily clinical practice.AimThe aim of the present study is the clinical validation of a multiscale mathematical model for non-invasive appraisal of central blood pressure from subject-specific characteristics.MethodsA total of 51 young male were selected for the present study. Aortic systolic and diastolic pressure were estimated with a mathematical model and were compared to the most-used non-invasive validated technique (SphygmoCor device, AtCor Medical, Australia). SphygmoCor was calibrated through diastolic and systolic brachial pressure obtained with a sphygmomanometer, while model inputs consist of brachial pressure, height, weight, age, left-ventricular end-systolic and end-diastolic volumes, and data from a pulse wave velocity study.ResultsModel-estimated systolic and diastolic central blood pressures resulted to be significantly related to SphygmoCor-assessed central systolic (r = 0.65 p <0.0001) and diastolic (r = 0.84 p<0.0001) blood pressures. The model showed a significant overestimation of systolic pressure (+7.8 (-2.2;14) mmHg, p = 0.0003) and a significant underestimation of diastolic values (-3.2(-7.5;1.6), p = 0.004), which imply a significant overestimation of central pulse pressure. Interestingly, model prediction errors mirror the mean errors reported in large meta-analysis characterizing the use of the SphygmoCor when non-invasive calibration is performed.ConclusionIn conclusion, multi-scale mathematical model predictions result to be significantly related to SphygmoCor ones. Model-predicted systolic and diastolic aortic pressure resulted in difference of less than 10 mmHg in the 51% and 84% of the subjects, respectively, when compared with SphygmoCor-obtained pressures.     

A simple method for obtaining blood pressure in rhesus monkeys (Macaca mulatta).

A relatively simple procedure was devised to obtain blood pressures in rhesus monkeys. This procedure utilized a polygraph, pulse transducer, pressure transducer, blood pressure mixer unit, and pediatric sphygmomanometer cuff. Previous attempts to auscultate the Korotkoff sounds by use of a sphygmomanometer cuff and stethoscope were unsuccessful. Blood pressure can be obtained by cannulation of the femoral artery, but repeated puncture may cause serious trauma to the arterial wall. This procedure was developed and used in our laboratory to obtain repeated blood pressures over a 90-da period. Results from using the cuff and polygraph have been shown to correlate favorably with cannulation of the femoral artery.     

Blood pressure in young adults as influenced by copper and zinc intake

The relationship of copper and zinc status with blood pressure in young adults was studied (N=59). Copper and zinc status was assessed through analysis of serum, urine, hair, and diet records. Males (N=27) had greater systolic and pulse pressures than females (N=32). Multiple regression analysis suggested that males and higher caloric and dietary copper intakes were the predominant factors associated with higher systolic and diastolic pressures, whereas higher dietary zinc intakes were associated with lower pressures. Higher urine zinc excretion rates and serum zinc concentrations were associated with higher diastolic pressures. The sex variable was the strongest factor affecting pulse pressures, with males having higher pulse pressures. Serum zinc concentrations had an inverse relationship to pulse pressures. The data suggest that the weight/height index and age had a low association with blood pressure in this normotensive sample.     

Noninvasive cardiovascular phenotyping in mice

With the growth of genetic engineering, mice have become common as models of human diseases, which in turn has stimulated the development of techniques to monitor and image the murine cardiovascular system. Invasive methods are often more quantitative, but noninvasive methods are preferred when measurements must be repeated serially on living animals during development or in response to pharmacological or surgical interventions. Because of the small size and high heart rates in mice, high spatial and temporal resolutions are required to preserve signal fidelity. Monitoring of body temperature and the electrocardiogram is essential when animals must be anesthetized for a measurement or other procedure. Several other groups have developed cardiovascular imaging modalities suitable for murine applications, and ultrasound is the most widely used. Our group has developed and applied high-resolution Doppler probes and signal processing for measuring blood velocity in the heart and peripheral vessels of anesthetized mice noninvasively. We can measure cardiac filling and ejection velocities as indices of systolic and diastolic ventricular function and for timing of cardiac events; velocity pulse arrival times for determining pulse-wave velocity and arterial stiffness; peripheral velocity waveforms as indices of arterial resistance, compliance, and wave reflections; stenotic velocities for estimation of pressure drop and detection of vorticity; and tail artery velocity for determining systolic and diastolic blood pressure using a pressure cuff. These noninvasive methods are convenient and easy to apply and have been used to detect and evaluate numerous cardiovascular phenotypes in mutant mice.     

Changes in oscillometric pulse amplitude envelope with cuff size: implications for blood pressure measurement criteria and cuff size selection

Oscillometric blood pressures are derived from the amplitude envelope of oscillometric pulses generated in an occlusive cuff during cuff inflation or deflation; one factor which will affect the characteristics of these pulses is the size of the cuff bladder. Because limiting values are stipulated in recommendations and standards for bladder sizes, there is a wide variety of acceptable cuff sizes for any particular application. An experimental and theoretical study was undertaken to show the dependence of oscillometric blood pressures on bladder size. Actual cuff-arm compliance data were obtained from two subjects for two cuffs of different bladder size. Theoretical analysis was then applied to the data to predict the effects of different bladder sizes on the characteristics of the pulses. The results show that cuff-arm compliance and bladder size interact to affect the pulse amplitude and hence oscillometric blood pressure determination. These results suggest that blood pressures obtained using the oscillometric method may vary depending on cuff size, and in particular that replacement cuffs for oscillometric non-invasive blood pressure monitors should be chosen carefully.     

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.     

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.     

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.     

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.     

The technique of detecting systolic and diastolic pressure from the transducer output of a PC-based blood pressure monitoring system

A pressure to voltage transducer is used along with a cuff, in a PC-based blood pressure and pulse rate monitoring system for human body. During the blood pressure measurement cycle, the output voltage of the pressure to voltage transducer is recorded digitally using a data acquisition system. The recorded data are then analyzed using software routines to determine the blood pressure and pulse rate of the person under test. However, it is difficult to identify the points of systole and diastole correctly from the recorded data. This paper presents the technique that may be used to determine the systolic and diastolic pressure from the collected data.