Auscultatory Pressure Research Articles

Real-Time Blood Pressure Estimation From Force-Measured Ultrasound.

Our objective is to create a blood pressure measurement device, which may provide a way to easily acquire frequent measurements. Common techniques to measure blood pressure include an arterial catheter, an oscillometric pressure cuff, or an auscultatory pressure cuff. The approach takes as input ultrasound images of an artery and contact force between the ultrasound array and subject. A subject may perform the self-measurements. Image and force data is analyzed for its quality and used to provide guidance or reject poor measurements. Tissue motions, due to probe contact forces and pulsing blood pressure, are estimated from the ultrasound image. Tissues elasticities and blood pressure are found by optimally fitting the observed tissue motion versus applied forces to a table of predicted motion-pre-generated with a finite element tissue deformation model. The output of the optimization is an estimate of systolic and diastolic blood pressure, arterial stiffness, and surrounding tissue stiffness. The real-time implementation of the algorithm was validated on a cohort of 21 single-visit volunteers and on four volunteers self-monitored longitudinally. The systolic and diastolic pressures were compared to oscillometric cuff readings. Regression and Bland-Altman analyses were performed. Systolic pressure and diastolic pressure can be estimated in real-time and by the subject using this novel non-invasive ultrasound-based method (systolic accuracy/precision: -5.2mmHg/10.7mmHg; diastolic accuracy/precision: -3.9/8.0mmHg). The method occupies a middle ground between the arterial catheter and cuff-based techniques. It has the potential to give calibration-free results.

Improved aorto-ventricular matching in ischemic dilated cardiomyopathy patients after surgical ventricular restoration

Scope This paper contains (i) derivation of the aorto-ventricular matching (AVM) index in terms of the ratio of aortic elastance and LV end-systolic elastance, E aorta / E es ; (ii) procedure for determination of this index, by means of non-invasive measurements of auscultatory pressures, time-variation of blood volume ejected into the aorta, stroke volume and ejection fraction; (iii) results of improved AVM index evaluation in ischemic dilated cardiomyopathy (IDCM) patients following surgical ventricular restoration (SVR), as a result of reduced end-diastolic and end-systolic LV volumes and increased LV E es . Methodology Among the ten recruited IDCM patients, four of them underwent surgical ventricular restoration (SVR) and coronary artery bypass graft (CABG), while six of them underwent CABG alone. All patients were studied by echocardiography pre- and 4 months post-operatively; LV volumes were determined by echo Doppler. LV end-systolic elastance E es was determined from a derived expression, by employing blood pressure, stroke volume, ejection fraction, pre-ejection and systolic periods, and estimated normalized ventricular elastance at end-diastole, based on single-beat measurements. Aortic elastance E aorta was determined by means of our modified single-beat method for determining aortic pressure profile. Results In the CABG plus SVR group, the AVM index E aorta / E es was reduced by 35% from 0.93 ± 0.32 to 0.60 ± 0.33, consistent with improved aorto-ventricular matching. However, in the CABG alone group, the AVM index E aorta / E es decreased only 11% from 1.02 ± 0.24 to 0.91 ± 0.29. Conclusion There is shown to be increased value of LV E es and a more favorable decreased value of AVM index in those IDCM patients who underwent SVR.

Central Blood Pressure and Hypertension

During the 20th century, the brachial artery auscultatory method of blood pressure (BP) measurement has been the major basis for our understanding of clinical hypertension. First, the height of systolic (S) and diastolic (D) BP was used to define cardiovascular (CV) risk. Second, BP reduction by drug treatment was shown to be associated with a substantial decrease of CV risk in several varieties of high BP, including systolic hypertension in the elderly.1,2 However, drug treatment often reduced DBP more than SBP, resulting in increased pulse pressures (PP) and the related arterial stiffness. An associated increase in coronary risk was also observed.1,3 Because PP and arterial stiffness did not respond readily to drug treatment and was made even less responsive by aging, it has been suggested and shown that mechanical factors such as PP, arterial stiffness, and wave reflections, preferably measured by central (aortic or carotid) BP, should be fully investigated. Because the majority of the studies used noninvasive peripheral BPs the need arose for invasive methods to verify and validate central BP measurement in the evaluation of CV risk.4 In the present issue of this journal, Jankowski et al5 established, in a 4.5-year follow-up of 1109 patients undergoing coronary angiography, that central BP was a significant and independent predictor of CV risk, as potent as cardiac ejection fraction and more powerful than brachial sphygmomanometric measurements. For these coronary patients, the pulsatile …

Automatic blood pressure measurement: the oscillometric waveform shape is a potential contributor to differences between oscillometric and auscultatory pressure measurements

To explore the differences between oscillometric and auscultatory measurements. From a simulator evaluation of a non-invasive blood pressure (NIBP) device regenerating 242 oscillometric blood pressure waveforms from 124 subjects, 10 waveforms were selected based on the differences between the NIBP (oscillometric) and auscultatory pressure measurements. Two waveforms were selected for each of five criteria: systolic over and underestimation; diastolic over and underestimation; and close agreement for both systolic and diastolic pressures. The 10 waveforms were presented to seven different devices and the oscillometric-auscultatory pressure differences were compared between devices and with the oscillometric waveform shapes. Consistent patterns of waveform-dependent over and underestimation of systolic and diastolic pressures were shown for all seven devices. The mean and standard deviation, for all devices, of oscillometric-auscultatory pressure differences were: for the systolic overestimated waveforms, 36 +/- 28/-6 +/- 3 and 23 +/- 2/-1 +/- 3 mmHg (systolic/diastolic differences); for systolic underestimated waveforms, -21 +/- 5/-4 +/- 3 and -11 +/- 4/-3 +/- 3 mmHg; for diastolic overestimated waveforms, 3 +/- 4/12 +/- 5 and 17 +/- 6/10 +/- 2 mmHg; for diastolic underestimated waveforms, 1 +/- 4/-22 +/- 4 and -9 +/- 6/-29 +/- 4 mmHg; and for the two waveforms with good agreement, 0 +/- 6/0 +/- 3 and -2 +/- 4/-4 +/- 3 mmHg. Waveforms for which devices showed good oscillometric and auscultatory agreement had smooth envelopes with clearly defined peaks, compared with the broader plateau and complex shapes of those waveforms for which devices over or underestimated pressures. By increasing the understanding of the characteristics and limitations of the oscillometric method and the effects of waveform shape on pressure measurements, simulator evaluation should lead to improvements in NIBP devices.

Effect of the shapes of the oscillometric pulse amplitude envelopes and their characteristic ratios on the differences between auscultatory and oscillometric blood pressure measurements

Oscillometric noninvasive blood pressure (NIBP) devices determine pressure by analysing the oscillometric waveform using empirical algorithms. Many algorithms analyse the waveform by calculating the systolic and diastolic characteristic ratios, which are the amplitudes of the oscillometric pulses in the cuff at, respectively, the systolic and diastolic pressures, divided by the peak pulse amplitude. A database of oscillometric waveforms was used to study the influences of the characteristic ratios on the differences between auscultatory and oscillometric measurements. Two hundred and forty-three oscillometric waveforms and simultaneous auscultatory blood pressures were recorded from 124 patients at cuff deflation rates of 2-3 mmHg/s. A simulator regenerated the waveforms, which were presented to two NIBP devices, the Omron HEM-907 [OMRON Europe B.V. (OMCE), Hoofddorp, The Netherlands] and the GE ProCare 400 (GE Healthcare, Tampa, Florida, USA). For each waveform, the paired systolic and paired diastolic pressure differences between device measurements and auscultatory reference pressures were calculated. The systolic and diastolic characteristic ratios, corresponding to the reference auscultatory pressures of each oscillometric waveform stored in the simulator, were calculated. The paired differences between NIBP measured and auscultatory reference pressures were compared with the characteristic ratios. The mean and standard deviations of the systolic and diastolic characteristic ratios were 0.49 (0.11) and 0.72 (0.12), respectively. The systolic pressures recorded by both devices were lower (negative paired pressure difference) than the corresponding auscultatory pressures at low systolic characteristic ratios, but higher than the corresponding auscultatory pressures at high systolic pressures. Conversely, the differences between the paired diastolic pressure differences were higher at low diastolic characteristic ratios, compared with those at high diastolic characteristic ratios. The paired systolic pressure differences were within +/-5 mmHg for those waveforms with systolic characteristic ratios between 0.4 and 0.7 for the Omron and between 0.3 and 0.5 for the ProCare. The paired diastolic pressure differences were within +/-5 mmHg for those waveforms with diastolic characteristic ratios between 0.4 and 0.6 for the Omron and between 0.5 and 0.8 for the ProCare. The systolic and diastolic paired oscillometric-auscultatory pressure differences varied with their corresponding characteristic ratios. Good agreement (within 5 mmHg) between the oscillometric and auscultatory pressures occurred for oscillometric pulse amplitude envelopes with specific ranges of characteristic ratios, but the ranges were different for the two devices. Further work is required to classify the different envelope shapes, comparing them with patient conditions, to determine if a clearer understanding of the different waveform shapes would improve the accuracy of oscillometric measurements.

The Left Ventricular End-Systolic Pressure and Pressure-Volume Index. Comparison Between Invasive and Auscultatory Arm Pressure Measurements

The slope of the left ventricular (LV) end-systolic pressure-volume relation (ESPVR) has been established as a valuable clinical method to assess LV contractile function independent of LV loading factors. The purpose of the present study was to evaluate whether the ESPVR could be reliably determined from auscultatory blood pressure (BP) measurements and from LV volume measurement by contrast ventriculography (CVG). Twenty-four patients with suspected or known ischemic heart disease were studied by cardiac catheterization with simultaneous, blinded, intravascular and auscultatory pressure measurements. LV volume was determined by CVG. The auscultatory mean arterial blood pressure (MAP) derived from: [formula: see text] was found to be a useful measure of the LV end-systolic pressure in this connection. The correlation between invasively measured LV end-systolic pressure (ESP) and MAP was highly significant (r = 0.82; SEE = 6.9 mmHg; p = 0.001). The correlation between invasively and semi-invasively measured ESPVR fell close to the line of identity (r = 0.99; SEE = 0.23 mmHg.mL-1; p < 0.001). The replacement of ESP by MAP induced only a minimal error in the assessment of the ESPVR. A complete noninvasive determination of the ESPVR and LV contractility therefore seems possible by using the MAP and by measuring the end-systolic volume by radionuclide ventriculography or by echocardiography.

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.

Sphygmomanometer cuff size and the accuracy of indirect measurement of blood pressure

While it is well known that too narrow a sphygmomanometer cuff may give erroneously high indirect blood pressure readings, particularly in subjects with thick arms, it has not been generally appreciated that a cuff supplied with a rubber bag which is too short to encircle the upper arm may cause a similar error. Auscultatory pressure readings obtained with two cuffs, one with a bag 12 by 23 cm. and the other with that of 14 by 40 cm., were compared with direct intraarterial pressure recording in 53 subjects. The large bag gave systolic values 3.0 ± 1.16 mm. Hg too low, and diastolic (phase v) values 1.4 ± 1.26 mm. Hg too high. With the small bag the error depended on the site of wrapping; as applied on the biceps it gave a better agreement with the systolic (0.5 ± 1.71 mm. Hg too high), but a poorer one with the diastolic pressure (7.6 ± 2.0 mm. Hg too high). As applied on the triceps, the small bag gave systolic values 5.5 ± 1.91 mm. Hg too high; the diastolic values were also 4.6 ± 2.36 mm. Hg on the high side. With the large bag the random error was significantly smaller than with the smaller bag in either position, both for systolic and diastolic pressure. The disappearance of the sounds (phase v) was closer than muffling (phase iv) to the intraarterial diastolic pressure. In this series, the arm circumference as such had no effect on the error of the indirect blood pressure measurement. However, the thickness of the triceps skinfold was negatively correlated with the error of the systolic measurement when a small cuff was used, and with that of the diastolic phase IV measurement with both cuffs. With the large cuff and the phase V criterion, the thickness of the subcutaneous fat introduced no systematic error.

Comparison of simultaneous indirect (auscultatory) and direct (intra-arterial) measurements of arterial pressure in man: Steele, J. M.: p. 1042

While it is well known that too narrow a sphygmomanometer cuff may give erroneously high indirect blood pressure readings, particularly in subjects with thick arms, it has not been generally appreciated that a cuff supplied with a rubber bag which is too short to encircle the upper arm may cause a similar error. Auscultatory pressure readings obtained with two cuffs, one with a bag 12 by 23 cm. and the other with that of 14 by 40 cm., were compared with direct intraarterial pressure recording in 53 subjects. The large bag gave systolic values 3.0 ± 1.16 mm. Hg too low, and diastolic (phase v) values 1.4 ± 1.26 mm. Hg too high. With the small bag the error depended on the site of wrapping; as applied on the biceps it gave a better agreement with the systolic (0.5 ± 1.71 mm. Hg too high), but a poorer one with the diastolic pressure (7.6 ± 2.0 mm. Hg too high). As applied on the triceps, the small bag gave systolic values 5.5 ± 1.91 mm. Hg too high; the diastolic values were also 4.6 ± 2.36 mm. Hg on the high side.With the large bag the random error was significantly smaller than with the smaller bag in either position, both for systolic and diastolic pressure.The disappearance of the sounds (phase v) was closer than muffling (phase iv) to the intraarterial diastolic pressure.In this series, the arm circumference as such had no effect on the error of the indirect blood pressure measurement. However, the thickness of the triceps skinfold was negatively correlated with the error of the systolic measurement when a small cuff was used, and with that of the diastolic phase IV measurement with both cuffs. With the large cuff and the phase V criterion, the thickness of the subcutaneous fat introduced no systematic error.