Is oscillometric ankle pressure reliable in leg vascular disease?

The objective of the study was to evaluate the validity of oscillometric systolic ankle pressure in symptomatic leg arterial occlusive disease. Ankle pressure measurements using oscillometric curves obtained using a standard 12-cm cuff with a specially designed device for signal processing were validated against the continuous wave (CW) Doppler technique. Thirty-four subjects without signs or symptoms of peripheral vascular disease (68 legs) and 47 patients with leg ischaemia (85 legs) varying from moderate claudication to critical ischaemia were examined. The oscillometric curves were analysed using several algorithms reported in the literature, based on the assumption that maximum oscillations are recorded near mean arterial pressure. In normals, reasonable agreement between CW Doppler and oscillometric methods was seen. When an algorithm that determined the lowest cuff pressure at which maximum oscillations occurred, and a characteristic ratio for systolic pressure of 0.52 was used, the mean difference between CW Doppler and oscillometry was 1.7 mmHg [range -19 to +27, limits of agreement (2 SD) 21.1 mmHg]. In ischaemic legs, oscillometry overestimated systolic ankle pressure by a mean of 28.8 mmHg [range -126 to +65, limits of agreement 82.8 mmHg]. The difference was more pronounced among patients with critical ischaemia compared with claudicants, and also more evident among diabetics. The error of oscillometric pressure determination in subjects with leg arterial disease inversely increased with CW Doppler ankle pressure. In 39% of the recordings in legs with a CW Doppler systolic pressure below 100 mmHg, the oscillometric mean arterial pressure was higher than the recorded CW Doppler systolic pressure. In conclusion, the oscillometric method to determine systolic ankle pressure, based on the concept of maximum cuff oscillations occurring near mean arterial pressure, is not reliable in leg arterial disease, usually overestimating ankle pressure.     

Interference resistance in automated oscillometric sphygmomanometers

Conclusions 1. Parameters of valid signal in oscillometric methods of measurement of arterial blood pressure depend on values of diastolic and pulse arterial blood pressure, heart rate, type of elasticity and collapse of the humeral artery, volume of the artery, volume of the blood pressure cuff, and the ratio of the duration of arterial pressure oscillations to valid signal period. The peak amplitude of the valid signal varies over a range from 0.31 to 7.34 mm Hg, and heart rate varies from 0.66 to 3.33 Hz. The characteristic point for determining systolic arterial blood pressure is the maximum of the envelope of the “negative” part of oscillometric signals, and for diastolic arterial blood pressure is the maximum rate of the decrease of the envelope of the “positive” part of oscillometric signals. The correlation coefficient between experimental signal and theoretical calculations was found to be 0.84. 2. Two types of interferences, related to breathing and movement of patient, have the largest affect on the results of arterial blood pressure measurements by the oscillometric method. 3. An interference-rejecting algorithm was developed for measuring systolic and diastolic arterial blood pressure. The algorithm was implemented in prototype models of the SA-02 and SA-03 automated sphygmomanometers. Clinical trial of the SA-02 automated sphygmomanometer revealed overall error in determination of systolic and diastolic arterial blood pressure in a sample of 144 patients to beS=6.6 mm Hg for systolic arterial blood pressure andS=6.4 mm Hg for diastolic arterial blood pressure. The results of the trial meet the requirements of the United States standard. Scientific Research Institute for Medical Instrument Engineering, Moscow. Translated from Meditsinskaya Tekhnika, No. 3, pp. 19–28, May–June, 1993.     

Non-invasive measurement of systolic blood pressure on the arm utilising photoplethysmography: development of the methodology

Photoplethysmography (PPG) can be used to measure systolic blood pressure at the brachial artery. With a specially designed probe, positioned in the most distal position beneath a pressure cuff on the upper arm, this is possible. The distance between the light source (880 nm) and the photodetector was 20 mm. A test was performed on neuro-intensive care patients by determining blood pressure from the PPG curves, and, when it was compared with systolic blood pressure obtained from inserted indwelling arterial catheters, a correlation factor of r=0.95 was achieved. The difference between blood pressure obtained using PPG and invasive blood pressure measurement was 3.9±9.1 mmHg (mean±SD), n=19. The depth to the brachial artery was 13.9±4.1 mm (mean±SD), n=18. A digital PPG system utilising pulsating light was also developed.     

Vibration technique for indirect measurement of diastolic arterial pressure in human fingers

Diastolic pressure P_d was indirectly measured by vibrating a finger artery with a 10 Hz sinusoidal pressure variation during a gradual increase (or decrease) in occlusive cuff pressure P_c. Pulsatile arterial volume changes on which sinusoidal variations are superimposed were detected by a transmitted infra-red photoelectric plethysmograph (TIPP). It is known that volume change in an artery shows a maximum amplitude at the transmural pressure P_t level equal to 0 mm Hg due to the nonlinear viscoelastic properties of the arterial wall. For the same reason, the amplitude of the sinusoidal volume variation reached its maximum at the end-diastolic phase, when P_c was controlled to be exactly equal to P_d. The indirect P_d values determined from P_c were compared with those simultaneously measured by a direct method in rabbit forelegs and by the volume-compensation method in human fingers. Using the principle of the volume oscillometric method systolic and mean pressures were also determined by this system.     

Osler's maneuver and pseudohypertension

We describe a simple bedside procedure (which we call "Osler's maneuver") that differentiates patients with true hypertension from those whose blood pressure is spuriously elevated because of excessive sclerosis of the large arteries ("pseudohypertension"). The maneuver is performed by assessing the palpability of the pulseless radial or brachial artery distal to a point of occlusion of the artery manually or by cuff pressure. We classified 24 elderly hypertensive patients as either Osler-positive (n = 13) or Osler-negative (n = 11), and measured their intraarterial pressure, arterial compliance, and systemic hemodynamics. Patients with pseudohypertension (Osler-positive) had falsely elevated blood-pressure readings, with a difference of 10 to 54 mm Hg between cuff and intraarterial pressure. Arterial compliance was lower in Osler-positive subjects and correlated with the difference between cuff and intraarterial pressures, indicating that the stiffer the artery, the more pronounced the degree of pseudohypertension. Pseudohypertension is common in the elderly and becomes more severe as arterial compliance decreases and sclerosis of large arteries progresses.     

Perceived Changes in the Intensity oi Arterial Pulsations as a Function oi Applied Cufi Pressure

A psychophysical scaling procedure was employed to investigate subjects' ability to discriminate pulsatile arterial sensations produced by applying an occluding cuff about the upper arm. Subjects (n = 8) were exposed to 5 presentations of 7 occluding cuff pressure levels ranging from above systolic to below diastolic arterial pressure. During each cuff inflation, subjects were instructed to attend to the pulsating sensations in the arm. When the cuff deflated, subjects adjusted the volume ofa tone to a level that matched their subjective estimate of pulsation intensity. Consistent with previous reports, subjects perceived maximum intensity pulsations when cuff pressure approximated calculated mean arterial pressure (MAP), 1/3 (systolic -diastolic) + diastolic. The perceived intensity ofthe sensations decreased monotonically as cuff pressure was varied in either the systolic or diastolic direction producing a highly symmetrical function on both sides of MAP. The gradient of arterial pulsations produced by the occluding cuff pressure, the accuracy of the judgments ofthe intensity of perceived pulsations, and the possibility that these pulsations may he more physiologically related to the hemodynamics of blood flow, suggest that these sensations may be employed as a more effective discriminative stimulus in a blood pressure biofeedback procedure.     

Cuff sphygmomanometry: Theoretical analyses for determining differences between diastolic and systolic arterial pressures and the corresponding cuff pressures in terms of quantities that can be measured on line

In conventional cuff sphygmomanometry the operator monitors the cuff pressure at the onset of the appearance and muffling of Korotkoff sounds, and associates them with the desired brachial arterial systolic and diastolic pressures. Based on stability analyses of the brachial arterial-cuff system, the differences between these monitored cuff pressures or the auscultatory pressures and the actual brachial arterial pressures have been shown to be functions of the geometrical, material and vibratory parameters of the brachial artery. This information delineates the importance of knowing these differences, for obtaining accurate measures of the brachial arterial pressures. Hence, in order to facilitate and provide the basis for the calculation of these differences in an online arrangement which can be used clinically, in this paper we express the modulus of elasticity of the tube material in terms of the velocities of pulse propagation in circular-cylindrical and biconcave-cylindrical tubes, at systole and diastole; the pulse velocity is in turn expressed in terms of quantities which can be measured online, namely the cuff width and the dominant frequency f of the disturbance, and hence of the Korotkoff sounds. We have further invoked experimental observations obtained by others during the laboratory simulation of Korotkoff sounds to delineate the values of the geometrical parameters of the brachial artery-cuff system and finally to obtain expressions for the differences between the auscultatory and direct brachial arterial pressures in terms of the measurable cuff width and the dominant frequency of the Korotkoff sounds; the paper hence concerns theoretical analyses for obtaining the actual systolic and diastolic brachial arterial pressures in terms of quantities that can be measured online.     

An Integrative Model of the Cardiovascular System Coupling Heart Cellular Mechanics with Arterial Network Hemodynamics

The current study proposes a model of the cardiovascular system that couples heart cell mechanics with arterial hemodynamics to examine the physiological role of arterial blood pressure (BP) in left ventricular hypertrophy (LVH). We developed a comprehensive multiphysics and multiscale cardiovascular model of the cardiovascular system that simulates physiological events, from membrane excitation and the contraction of a cardiac cell to heart mechanics and arterial blood hemodynamics. Using this model, we delineated the relationship between arterial BP or pulse wave velocity and LVH. Computed results were compared with existing clinical and experimental observations. To investigate the relationship between arterial hemodynamics and LVH, we performed a parametric study based on arterial wall stiffness, which was obtained in the model. Peak cellular stress of the left ventricle and systolic blood pressure (SBP) in the brachial and central arteries also increased; however, further increases were limited for higher arterial stiffness values. Interestingly, when we doubled the value of arterial stiffness from the baseline value, the percentage increase of SBP in the central artery was about 6.7% whereas that of the brachial artery was about 3.4%. It is suggested that SBP in the central artery is more critical for predicting LVH as compared with other blood pressure measurements.     

New oscillometric method for indirect measurement of systolic and mean arterial pressure in the human finger. Part 1: Model experiment

To analyse the mechanism of the occurrence of the maximum volume pulsation in an artery during the application of counterpressure, the static, and dynamic pressure-volume (P-V) relationship was measured in excised arterial segments placed in a compression chamber. Teh volume change caused by perfusing the segment with a sinusoidal pump was detected by an infrared photoelectric plethysmograph during the application of counterpressure. It was revealed that the characteristic change in the amplitude of volume pulsation in response to the gradual change in the counterpressure was due to the nonlinearity of the P-V relation of the artery, and that the value of the counterpressure showing the maximum pulsation amplitude was coincided with the mean arterial pressure. From this evidence it was concluded that the maximum volume pulsation occurs when the transmural pressure was equal to zero, i.e. the arterial wall isunloaded. Based on the results a new oscillometric method for the indirect measurement of systolic and mean arterial pressure in an arterial segment was designed. Through the comparison of data with the actual pressure produced by perfusing the segment, it was demonstrated that systolic and mean arterial pressure can be indirectly measured by this technique within ±3 mm Hg error.     

Comparison of oscillometric pulse amplitude envelopes recorded from the locally compressed radial arteries

Simultaneously recorded oscillometric envelopes, obtained pneumo- and photoplethysmographically from a small local pad-type pneumatic cuff on the left and from a larger cuff on the right radial artery, were compared in 17 healthy subjects. For oscillometric estimation, specific fixed ratios based on evidence in the literature were used. The obtained envelopes for each person were shifted and aligned at the point of upper arm mean arterial pressure for this person, thus eliminating the brachial-to-radial mean blood pressure gradient and possible left–right difference. In this way, the shape of differently recorded envelopes as a determinant of the accuracy of oscillometric estimation was studied. Results showed an advantage of photoplethysmographically compared to pneumoplethysmographically recorded envelopes. For a smaller cuff (diameter 40 mm), the mean difference in mm Hg ‘oscillometric estimate minus auscultatory reference’ and standard deviation were in the case of photo recording for systolic and diastolic pressures ?0.6 (6.3) and 1.2 (3.4), respectively. In the case of pneumo recording, these parameters were considerably larger, being 12.1 (11.9) and ?6.2 (10.9), respectively. For a larger cuff the same tendency was revealed. Photo recording was found to be less sensitive to alterations in the cuff size and characteristic ratios.     

Effect of tissue mechanical properties on cuff-based blood pressure measurements

This paper presents a 3D finite element upper arm model, validated by experiments as well as clinical data, used to study the error introduced in blood pressure measurements due to variability of arm tissue mechanical properties. The model consists of three separate cylindrical parts: soft tissue, bone and brachial artery. The artery volume changes under the cuff are used to represent the cuff pressure oscillations for analyzing blood pressure measurements. These oscillation trends are identical to observed clinical data. Also an upper arm simulator is designed and built for model validation. The model shows that the variation of soft tissue compressibility introduces an error up to 5% in blood pressure measurements. It is also revealed that the variation of the brachial artery and arm tissue stiffness has an insignificant effect on oscillometric blood pressure measurement method.     

Noninvasive Measurement of the Human Brachial Artery Pressure–Area Relation in Collapse and Hypertension

A noninvasive method to obtain pressure–lumen area (P-A) measurements of the human brachial artery is introduced. The data obtained from this method are analyzed using a mathematical model of the relationship between vessel pressure and lumen area including vessel collapse and hypertension. An occlusive arm cuff is applied to the brachial artery of ten normal subjects. The cuff compliance is determined continuously by means of a known external volume calibration pump. This permits the computation of the P-A curve of the brachial artery under the cuff. A model is applied to analyze the P-A relation of each subject. The results show that the lumen area varies considerably between subjects. The in vivo resting P-A curve of the brachial artery possesses features similar to that of in vitro measurements. A primary difference is that the buckling pressure is higher in vivo, presumably due to axial tension, as opposed to in vitro where it is near zero or negative. It is found that hypertension causes a shift in the P-A curve towards larger lumen areas. Also, the compliance–pressure curve is shown to shift towards higher transmural pressures. Increased lumen area provides an adaptive mechanism by which compliance can be maintained constant in the face of elevated blood pressure, in spite of diminished distensibility. © 1998 Biomedical Engineering Society. PAC98: 8745Hw, 8710+e     

Error Mechanisms of the Oscillometric Fixed-Ratio Blood Pressure Measurement Method

The oscillometric fixed-ratio method is widely employed for non-invasive measurement of systolic and diastolic pressures (SP and DP) but is heuristic and prone to error. We investigated the accuracy of this method using an established mathematical model of oscillometry. First, to determine which factors materially affect the errors of the method, we applied a thorough parametric sensitivity analysis to the model. Then, to assess the impact of the significant parameters, we examined the errors over a physiologically relevant range of those parameters. The main findings of this model-based error analysis of the fixed-ratio method are that: (1) SP and DP errors drastically increase as the brachial artery stiffens over the zero trans-mural pressure regime; (2) SP and DP become overestimated and underestimated, respectively, as pulse pressure (PP) declines; (3) the impact of PP on SP and DP errors is more obvious as the brachial artery stiffens over the zero trans-mural pressure regime; and (4) SP and DP errors can be as large as 58 mmHg. Our final and main contribution is a comprehensive explanation of the mechanisms for these errors. This study may have important implications when using the fixed-ratio method, particularly in subjects with arterial disease.     

用有创血压验证示波法测量血压的准确性

本文用山羊有创血压作对比研究了示波法无创测量血压的准确性.示波法一般通过袖带放气过程中脉搏波包络线顶点来估计平均压,而用幅度系数算法来估计收缩压和舒张压.虽然示波法能提供较为准确的平均压,但是估计收缩压和舒张压却存在较大误差.用5只山羊进行了试验,以研究幅度系数在不同个体之间的变异性.在用示波法测量山羊血压的同时记录山羊的有创血压.根据放气过程中的袖带内脉搏波包络线和用有创法得到的收缩压和舒张压,计算出每只羊的幅度系数.结果显示5只羊的幅度系数呈现出较大的离散性.究其根源在于,幅度系数法采用的系数是用统计方法得到的,它针对群体而不是个体,是一种经验算法.采用幅度系数算法的示波法血压测量技术不够准确,必须寻找一种新的血压测量方法.     

Evaluation of the harmonized alert sensing technology device for hemodynamic monitoring in chronic hemodialysis patients

The Harmonized Alert Sensing Technology (HASTE) device was developed to overcome the primary shortcomings of interval based noninvasive blood pressure (BP) monitoring. This study was conducted to assess the reliability of the HASTE system compared with standard cuff BP values in patients on hemodialysis. A total of 1,370 HASTE measurements were compared with oscillometric standard cuff systolic BP values in 42 sessions of 15 patients on hemodialysis. The average discrepancy between the HASTE and cuff systolic BP was 1.41 +/- 16.90 mm Hg. Compared with cuff measurements, 31% of systolic BP fell within a range of 5 mm Hg difference, 57% of systolic BP fell within 10 mm Hg, and 73% of systolic BP fell within a 15 mm Hg band. According to British Hypertension Society standards or Association for the Advancement of Medical Instrumentation criteria, the current HASTE method did not perform well. Technology to provide noninvasive hemodynamic monitoring is, however, in its developmental stage. The effort at continuous systolic pressure monitoring using existing, readily available, and frequently used techniques is exciting. Although the HASTE system as currently configured and calibrated did not adequately perform, variations in site analysis and conversion factors may increase pressure sensitivity and tracking over the course of a standard dialysis treatment.     

Measurement of arterial pressures in intact rabbits

Summary Measurement of arterial blood pressure in intact rabbits is described by Korotkov's method. Animals were fixed to a special stand during investigation. A pneumatic cuff, measuring 2.7×10 cm, was applied to the shoulder. Korotkov's sounds were auscultated with a phonendoscope on the radial artery from the medial surface of the elbow joint. Systolic pressure in adult rabbits ranged from 110 to 140 mm Hg, while the diastolic was from 95 to 120 mm Hg.Presented by Active Member Academy of Sciences, USSR V. V. Parin     

Myocardial ferritin content is closely related to the degree of ischaemia

Aims: The mechanical properties of arteries play a major role in the regulation of blood pressure and cardiac performance. The effect of sympathetic stimulation on the mechanical properties of the proximal brachial artery was analysed in 18 healthy volunteers, nine young (25 ± 2 years) and nine elderly (69 ± 2 years). Methods: A non‐invasive ultrasonic echo‐tracking system for measurement of systolic/diastolic variation of the proximal brachial artery diameter in combination with intra‐arterial pressure measurements was used to determine wall mechanics. The pressure–diameter (P–D) relationship, distensibility coefficient (DC), compliance coefficient (CC) and stiffness(β) were obtained at rest and during sympathetic stimulation induced by lower body negative pressure (LBNP). Results: The peripheral vascular resistance increased by 100 and 72%, respectively in the young and elderly during LBNP (P < 0.001). Simultaneously, the mechanical properties of the proximal brachial artery remained unaltered, as estimated from both P–D relationship and stiffness in young (β‐index rest: 5.2 ± 0.9, LBNP: 5.5 ± 1.3, NS) as well as elderly (β‐index rest: 13.6 ± 4.6, LBNP: 16.1 ± 4.7, NS). Conclusions: LBNP‐induced sympathetic activation does not change proximal brachial artery mechanics, in contrast to earlier reports on the muscular distal brachial artery. This may imply that the transition between elastic and muscular artery behaviour is within the length of the brachial artery, where the site of transition from elastic to muscular wall structure needs to be specified in future studies.     

Vascular Unloading Method for Noninvasive Measurement of Instantaneous Arterial Pressure: Applicability in Psychophysiological Research

A new method proposed previously by us (1980) was described to evaluate its applicability in psychophysiological research. In this method, beat-to-beat systolic and diastolic pressure as well as the pressure waveform can be measured noninvasively in the human finger. By use of a hydraulicservosystem, the photoplethysmographically detected vascular volume changes associated with intraarterial pressure in the finger are compensated by an applied counterpressure (cuff pressure) to maintain a proper value corresponding to the unloaded vascular volume. At this state the controlled cuff pressure follows instantaneously the intraarterial pressure. Comparison data were obtained by direct measurement of blood pressure in the brachial artery in 3 normotensive and 3 hypertensive subjects. High correlations between the two measures were obtained in each subject under various conditions. By maintaining circulation in the finger, this method enables the noninvasive and continuous measurement of instantaneous arterial pressure for more than one hour without much discomfort. This indirect method should be useful in many areas of psychophysiological research.     

Changes in central artery blood pressure and wave reflection during a cold pressor test in young adults

The relative contribution of sympathetic nervous system (SNS)-induced increase in peripheral vascular resistance on central artery blood pressure (BP) and aortic wave reflection (augmentation index; AIx) is not completely understood. Central BP and wave reflection characteristics were measured using radial artery applanation tonometry before, during a 3-min cold pressor test (CPT), and 90 and 180-s post-CPT in 15 young, healthy adults (25 +/- 1 years). The CPT resulted in a greater magnitude of change in the estimated aortic systolic (31 vs. 23%, P < 0.05) and pulse (31 vs. 13%, P < 0.05) BP compared with the change in brachial artery BP. Additionally, the CPT resulted in an increased mean arterial pressure (MAP) (P < 0.05) and AIx (10 +/- 2 vs. 26 +/- 2%, P < 0.05). The change in MAP during the CPT was correlated to the change in AIx (r = 0.73, P < 0.01) and inversely related to roundtrip duration of the reflected wave to the periphery and back (r = -0.57, P < 0.05). The present study suggests that cold pressor testing results in a significant increase in arterial wave reflection intensity, possibly due to an increased MAP. However, the greater increase in systolic and pulse BP in the central compared with the peripheral circulation suggests that increased central artery wave reflection intensity contributes to increased left ventricular myocardial oxygen demand during CPT-induced hypertension.     

Noninvasive automatic determination of mean arterial pressure

A new instrument for the indirect noninvasive measurement of mean arterial pressure (m.a.p.) has been constructed and evaluated in man. The instrument does not require an external microphone or transducer and determines m.a.p. rather than systolic and diastolic pressure. Instead, the method employs the point of maximal oscillations as an indicator of m.a.p. The instrument automatically inflates a standard blood pressure cuff and determines the m.a.p. by measuring the cuff pressure oscillations as the cuff pressure is reduced by discrete increments. Cuff deflation in discrete increments, instead of continuously, allows the oscillation data obtained at each cuff pressure to be tested for artefacts and averaged, greatly enhancing artefact-rejection ability. The m.a.p. is selected as the lowest cuff pressure at which the oscillation amplitude is a maximum. The instrument was tested on the bicep and ankle in a series of 28 studies involving 17 human subjects with intra-arterial catheters. Averaging the mean errors from each of the 28 studies, there was an overall mean error of — 0·23 mmHg, with a standard deviation of 4·21 mmHg. The correlation coefficient was 0·98. The instrument was found to give good results in a wide variety of clinical subjects and physiologic states.