Single cuff comparison of two methods for indirect measurement of arterial blood pressure: standard auscultatory method versus automatic oscillometric method

Noninvasive Blood Pressure Estimation Using Ultrasound and Simple Finite Element Models

OBJECTIVE

Many commercially available arterial blood pressure measurement devices suffer from a range of weaknesses. For example, common weaknesses include being inaccurate, invasive, and ad hoc; many also require explicit user calibration or cut off blood flow to a limb. A novel algorithmic approach is presented to accurately estimate systolic and diastolic blood pressure in a way that does not require any explicit user calibration, is noninvasive, and does not cut off blood flow.

METHODS

The approach uses ultrasound images of the arterial wall and corresponding contact force data to obtain blood pressure estimates. To acquire data, an ultrasound probe was placed on the patient's carotid artery and the contact force was increased from 1.5 to 12 N. The artery was then algorithmically segmented from the recorded DICOM B-Mode data. The segmentation data and the contact force were used as input into the Levenberg-Marquardt optimization method to solve for the parameters, including blood pressure, of a simple finite element model of the carotid artery.

RESULTS

The algorithm was validated on 24 healthy volunteers. Algorithm arterial blood pressure predictions were compared to oscillometric blood pressure cuff readings. Regression and Bland-Altman analyses were performed on the data.

CONCLUSION

Both systolic pressure and diastolic pressure can be estimated using this novel noninvasive ultrasound-based method (systolic accuracy/precision: $-$ 2.36 mmHg/10.21 mmHg; diastolic accuracy/precision: $-$ 0.32/8.23 mmHg).

SIGNIFICANCE

The method occupies a clinical middle ground between the arterial catheter and cuff-based techniques. It has the potential to give accurate results for patients with hypertension and atherosclerosis.

Just one drop: the significance of a single hypotensive blood pressure reading during trauma resuscitations

BACKGROUND

Single, isolated hypotensive blood pressure (BP) measurements frequently are ignored or considered "erroneous." Although their clinical significance remains unknown, we hypothesized that single, isolated hypotensive BP readings during trauma resuscitations signify the presence of severe injuries that often warrant immediate intervention.

METHODS

A prospective observational study was performed on all trauma patients admitted from June 2008 to January 2009. Patients with a single systolic blood pressure (SBP) reading <110 mm Hg during their trauma resuscitation were evaluated, and demographics, hemodynamics, resuscitation (fluids, blood products, and duration), injuries, and operative or endovascular management were analyzed. Single and multiple variable logistic regression analyses were performed. Cutpoint analysis of the entire range of lowest single SBP measurements determined which SBP value best predicted the need for immediate therapeutic intervention.

RESULTS

Patients (n = 145) were predominantly male (77.2%) but age (mean, 35.1 +/- 15.3 years) and injury mechanisms varied (penetrating, 46.2%; blunt, 53.8%). Cutpoint analysis determined that a single SBP reading <105 mm Hg best predicted the need for immediate therapeutic intervention. Although 38.1% patients with isolated SBP <105 mm Hg measurements underwent immediate therapeutic operative or endovascular procedures, only 10.4% (p < 0.001) with isolated SBP >or=105 mm Hg required these procedures. Patients were 12.4 times (confidence interval: 2.6-59.2; p = 0.002) more likely to undergo immediate therapeutic intervention than those with a single SBP >or=105 mm Hg.

CONCLUSIONS

Single, isolated hypotensive BP measurements during trauma resuscitations should not be ignored or dismissed. Instead, our results suggest that a single SBP reading <105 mm Hg is associated with severe injuries that often require immediate operative or endovascular treatment and surgical intensive care unit admission.

Comparison of the Automated Oscillometric Method With the Gold Standard Doppler Ultrasound Method to Access the Ankle-Brachial Pressure Index

Objective: Despite its screening interest, the ankle-brachial pressure index (ABPI) remains uncommon in general practice, because it needs training and specific devices as Doppler. Easier methods such as the use of automated oscillometric devices may facilitate the peripheral arterial diseases (PADs) screening. We wanted to assess the reliability of the automated oscillometric measurement of the ABPI, compared with the gold standard Doppler ultrasound measurement. Patients and Method: In 287 patients aged 65 years or older without diagnosed PAD, we performed ABPI measurements with oscillometric and Doppler devices. Reproducibility was assessed by the intraclass correlation coefficient of agreement (R) and the Bland and Altman method. Results: The intermethod reliability was bad (R = .346, 95% CI = (0.268-0.420)), with a large confidence interval of the individual differences between the 2 methods: 95% CI = (—0.183-0.346). Conclusion: Automatic oscillometric devices cannot be recommended as reliable methods for ABPI measurement.

Influence of Contact Forces on Wrist Photo plethysmography – Prestudy for a Wearable Patient Monitor / Einfluß von Kontaktkräften auf die photoplethysmografische Pulsmessung am Handgelenk – Vorstudie zu einem tragbaren Patientenmonitor

The practical setting shows that gentle manual pressure on a photosensor suffices to improve the detectability of arterial pulses, but changes in the pressure applied may also produce signal artefacts. To study these effects, stepwise increasing contact forces (0.5 to 4 N) were applied to a photosensor placed over the radial artery. Additionally, the influence of optical coupling between sensor and skin surface was examined by introducing an elastic distance ring. The AC and DC components from the recorded photoplethysmogram were analysed. The AC component (absorption due to arterial pulsation) increased with the pressure applied; at lower forces (0.5 to 3 N) an introduction of the ring enhanced this effect. The characteristic of the DC component (backscattering from non-pulsating tissues) depends on optical coupling: without the ring the DC component increased stepwise with force (slope 0.035 V/N), but with the ring in place this component decreased (slope -0.075 V/N). Since the sensitivity of the pulse signal to artifacts is related to the slope of the DC component, such artefacts can be minimized by making the slope small. The utilization of these results to improve pulse detection and reduce motion artefacts in a wearable wrist device is discussed.

Are Automated Blood Pressure Measurements Accurate in Trauma Patients?

BACKGROUND

Automated blood pressure (BP) determinations by oscillometry are reported to be as accurate as invasive monitoring for systolic pressures as low as 80 mm Hg. Automated BP devices are widely used by prehospital providers and in hospital operating rooms, emergency departments, and intensive care units, although the accuracy of automated BP has not been demonstrated in trauma patients. We hypothesized that automated BP is less accurate than manual BP in trauma patients. The purpose of this study was to determine the accuracy of automated BP versus manual BP in trauma patients.

METHODS

A retrospective review of patients who met trauma activation criteria admitted to a Level I trauma center over a 30-month period was conducted. Patients were included if both manual BP and automated BP were measured within 5 minutes of admission. Additional data collected included Injury Severity Score, base deficit, and emergency department resuscitation volume. Statistical analysis was performed using paired t test, chi2, and linear regression analysis. Significance was attributed to a value of p < 0.05.

RESULTS

From January 2000 through June 2002, 388 patients met inclusion criteria. Patients were grouped by manual BP levels: group 1, BP < or = 90 mm Hg (n = 92); group 2, BP 91-110 mm Hg (n = 119); and group 3, BP > or = 110 mm Hg (n = 177). The mean automated BP measurements were significantly higher than the manual measurements in groups 1 and 2 (26 and 16 mm Hg, respectively; p < 0.001). Of the 92 patients with manual BP < or = 90, 45 (49%) had automated BP > or = 100. The base deficit (-5, -3, and -2 for groups 1, 2, and 3, respectively; p < 0.01), Injury Severity Score (30, 25, and 18; p < 0.01), and volume of resuscitative fluid and blood (p < 0.001) all decreased with higher BP group.

CONCLUSION

Injury severity, degree of acidosis, and resuscitation volume were more accurately reflected by manual BP. Automated BP determinations were consistently higher than manual BP, particularly in hypotensive patients. Automated BP devices should not be used for field or hospital triage decisions. Manual BP determinations should be used until systolic blood pressure is consistently > or = 110 mm Hg.

Comparison of ankle-brachial pressure index measurements using an automated oscillometric device with the standard Doppler ultrasound technique

BACKGROUND

The aim of the present study was to assess the accuracy of an automated oscillometric device (DINAMAP) in measuring ankle-brachial pressure index (ABPI) in the clinical setting. Results were then compared to those obtained using the standard Doppler technique.

METHODS

A prospective comparative study of 50 healthy volunteers was carried out using a standard ward DINAMAP machine, hand-held Doppler and a 14 cm sphygmomanometer cuff. Three consecutive pressure readings were taken from all four limbs of the volunteers using both Doppler and DINAMAP techniques. The two techniques were carried out by different investigators who were blind to the findings of the other. The ABPI was calculated for each technique and the two techniques were compared.

RESULTS

There was no significant agreement between the ABPI readings obtained by DINAMAP and those obtained by the standard Doppler technique. There was also a substantial variation in pressure readings produced by the DINAMAP for a given limb as measured by intraclass correlation of the three readings taken.

CONCLUSIONS

There is no role for standard automated oscillometric devices in the calculation of ABPI in the vascular clinic.

Social support and age-related differences in cardiovascular function: an examination of potential mediators

The investigators examined the potential influence of social support on age-related differences in resting cardiovascular function and the potential mediators responsible for such associations in 67 normotensive women and men. Consistent with prior research, age predicted increased resting systolic blood pressure (SBP) and diastolic blood pressure (DBP). More importantly, regression analyses revealed that social support moderated age-related differences in resting SBP and DBP, as age predicted higher resting blood pressure for individuals low in social support, but was unrelated to blood pressure for individuals high in social support. An examination of potential pathways revealed that these results were not mediated by various health-related variables, personality factors, or psychological processes. Implications for the study of social support and health are discussed.

The correlation of ankle oscillometric blood pressures and segmental pulse volumes to Doppler systolic pressures in arterial occlusive disease

PURPOSE

This study was designed to evaluate the accuracy and failure rates of automatically collected oscillometric ankle systolic pressures (Psys) and pulse volumes (Pvol) using a new algorithm as compared with Psys obtained by standard manual Doppler-and-cuff technique.

METHODS

One hundred ten consecutive patients at a vascular laboratory had brachial and ankle Psys measured with the two methods. Pvol at or near the mean arterial pressure was also obtained automatically by the oscillometric device.

RESULTS

Both methods showed a 6.6% failure rate when measuring Psys at the ankle. Oscillometric Psys measurement was possible when Doppler Psys failed as a result of nonoccluding arteries. No difference was found between the two methods in occluding limbs with ankle-brachial indexes of 1.30 or more. Sequential brachial Psys values had a mean difference (Doppler-oscillometric) or 2 +/- 10.9 mm Hg and a correlation coefficient (r) of 0.92. Measurements at the ankle had a mean difference of -8.4 +/- 16.8 mm Hg and r = 0.90. These differences were not statistically significant. Mean arterial pressure Pvol recorded at the ankle also correlated with ankle Doppler Psys (r = 0.71) and showed a 1.9% failure rate.

CONCLUSION

Both automatic oscillometric plethysmographic Psys and Pvol at the ankle are shown to correlate well with Doppler-and-cuff Psys in patients with vascular disease. Oscillometric measurements can replace Doppler measurements in most clinical situations.

Postural effects on diastolic blood pressure are differently recorded by a non-invasive ambulatory blood pressure monitor and a standard auscultatory device

The aim of this study was to determine the influence of change of posture on blood pressure as recorded with an automatic ambulatory blood pressure monitor and a standard auscultatory device. The blood pressure difference between sitting and supine and between standing and supine posture was 1.1/3.9 and 6.5/6.3 mmHg, respectively, for the monitor recordings, and 0.7/6.7 and 7.9/14.8 mmHg, respectively, for the standard recordings. All differences were significant, except the systolic blood pressure difference between sitting and supine posture. There were no significant differences in systolic blood pressure between monitor and standard recordings in any posture. The corresponding differences in diastolic blood pressure were significant in sitting (-4.6 mmHg) and standing postures (-10.3 mmHg), but not in supine posture (-1.8 mmHg). It is concluded that a change of posture contributes to blood pressure variability, and agreement between diastolic blood pressure in supine subjects, as recorded by an ambulatory monitor and a standard device, does not necessarily mean agreement in standing (or sitting) subjects.

Measuring ankle systolic blood pressure: validation of the Dinamap 1846 SX

Clinical and epidemiologic situations requiring repeated measurements of blood pressure in the lower extremity are increasingly incorporating automated measurement devices; however, no device has been validated adequately for ankle blood pressure. This study evaluates the Dinamap 1846 SX against Doppler ultrasound in determining ankle systolic blood pressure (SBP) and compares a parallel with contour wrapping technique for applying the blood pressure cuff. Ankle SBP was measured on 71 adult volunteers by both devices simultaneously, for each cuff wrap. Averages of three readings were compared to evaluate Dinamap versus Doppler SBP estimates and to assess any cuff wrap effect. Multiple linear regression was used to assess potential effect modifiers. Instrument differences (Dinamap minus Doppler) for the parallel wrap (95% confidence intervals in parenthesis) were -1.5 mmHg (-3.1, 0.0) and -3.9 mmHg (-5.6, -2.2) for the contour wrap. Wrap effect differences (contour minus parallel) for the Doppler were -4.9 mmHg (-6.3, -3.5) and -7.2 mmHg (-8.7, -5.8) for the Dinamap. Degree of ankle taper was a strong modifier of cuff effect for the Dinamap but not for the Doppler: adjusted cuff effect with the Dinamap ranged from -3 to -10 mmHg. Measurement precision (within-person reproducibility, measured by within-person standard deviation [sigma 2] and reliability coefficient [R]) was higher for the Dinamap than the Doppler technique, lowest for the parallel wrap and Doppler configuration (sigma 2 = 5.4 mmHg, R = 0.88) and greatest for the contour wrap and Dinamap (sigma 2 = 4.0 mmHg, R = 0.94). In conclusion, cuff-wrapping technique can generate SBP differences of greater magnitude than instrument differences. Conditional on the use of the contour wrap, and by virtue of its high repeatability and ease of operation, the Dinamap is a useful tool for epidemiologic study and the clinical assessment of peripheral arterial disease.

Cardiac cycle phase uncertainty: another source of error in indirect blood pressure measurement

Cardiac cycle phase uncertainty causes a small error in indirect estimation of arterial blood pressure by sphygmomanometry. A simple analysis yields a statistical description of the error and a rule for its reduction: correct bias by adding to the systolic estimate and subtracting from the diastolic estimate one-half of the per-cardiac-cycle cuff deflation decrement. If several measurements are taken, the least-square estimate is approximately the arithmetic mean of the greatest and least of the bias corrected estimates.

The Dinamap 1846SX automated blood pressure recorder: comparison with the Hawksley random zero sphygmomanometer under field conditions

STUDY OBJECTIVE

The aim was to compare the performance of the Dinamap 1846SX automated oscillometric blood pressure recorder with that of the Hawksley random zero sphygmomanometer during use under field study conditions.

DESIGN

Two independent within subject measurement comparisons were made, one in adults and one in children, each conducted in three stages over several months while the Dinamap instruments were being used in epidemiological field surveys.

SETTING

The studies were done in outpatients clinics (adults) and primary schools (children).

PARTICIPANTS

141 adults (20-85 years) and 152 children (5-7 years) took part.

MEASUREMENTS AND MAIN RESULTS

In adults a pair of measurements was made with each instrument, the order alternating for consecutive subjects. In children one measurements was made with each instrument, in random order. Measurements with the Dinamap 1846SX were higher than those with the random zero sphygmomanometer both in adults (mean difference 8.1 mm Hg; 95% CI 6.5 to 9.7 mm Hg) and in children (mean difference 8.3 mm Hg; 95% CI 6.9 to 9.7 mm Hg). Diastolic measurements were on average very similar both in adults and in children. The results were consistent at all three stages of both studies. The differences in systolic measurement were independent of blood pressure level. However, the extent of agreement in diastolic pressure depended on the diastolic blood pressure level; in both studies Dinamap diastolic measurements were higher at low diastolic pressures while random zero diastolic measurements were higher at high diastolic pressures.

CONCLUSIONS

Systolic measurements made with the Dinamap 1846SX instrument are not directly comparable with those of the Hawksley random zero sphygmomanometer and are unlikely to be comparable with those of earlier Dinamap models. These differences have important implications for clinical practice and for comparisons of blood pressure measurement between epidemiological studies. However, the consistency of measurement by the Dinamap 1846SX over time suggests that the instrument may have a place in standardised blood pressure measurement in the research setting.

Blood pressure monitoring: automated oscillometric devices

An understanding of the principles of blood pressure measurement with automated oscillometric devices (e.g., Dinamap) allows a user to realize the purpose and level of accuracy for which the equipment is designed. Good technique cells for various actions: (1) using a cuff of proper size (too large a cuff will generally work acceptably, but too small a cuff will yield erroneously high readings); (2) squeezing all of the residual air out of the cuff before applying it to the arm or leg; (3) wrapping the cuff snugly around the arm or leg; (4) instructing the patient to refrain from talking or moving and letting nothing press against the cuff during measurement; (5) keeping the cuff and heart at the same horizontal level. (6) When instrument malfunction is suspected, first checking the status of the patient (not the status of the instrument) to be sure that a clinical emergency is not causing the suspected "malfunction"; (7) repeating a reading several times when it is suspicious and, if necessary, modifying the measurement conditions by using, for example, different limbs or different cuffs until the question is resolved; and (8) remembering that a leak in the cuff, hoses, or connection can cause an unexpected malfunction.

Measurement of blood pressure during the intraoperative period

For the monitoring of arterial blood pressure in the peri-operative period, three different methods are available. The classical approach is the indirect measurement employing a cuff applied to the upper arm as described by RIVA-ROCCI, known as sphygmomanometry. Thanks to the development of automatic devices employing the oscillometric principle, measurement of the mean arterial pressure has now become possible, blood pressure monitoring simplified, and documentation made easy. The particular indications for direct arterial pressure measurement are very low, very high, and widely fluctuating pressure, as well as major and prolonged surgery. Furthermore, arterial catheterisation provides the additional advantage of permitting blood gas analysis, while, properly employed, the rate of associated complications is low. Recently, it has become possible to perform continuous recording of the blood pressure with a non-invasive method known as servo-plethysmomanometry. The device employed for this method (Finapres) measures the pressure in the arteries of a finger using a small cuff incorporating a photoplethysmograph. Experience to date with this method in clinical usage is good. It is thus to be expected that the technique will in future offer an alternative to invasive methods of blood pressure measurement in many cases.

Arterial blood pressure and its measurement

Pressure is defined as force per unit area. The actual value of the recorded pressure depends on dynamic influences, like acceleration and friction in a moving fluid, and on static influences like the effect of a gravitational field. In the arterial system, four mechanisms exert the main influence on the measured pressure: (1) cardiac output and peripheral resistance, on which the mean value of the pressure depends; (2) the flow amplitude and the characteristic impedance of the artery, on which the pressure amplitude depends; (3) the orthostatic pressure component; (4) the local velocity of flow, on which the recorded pressure depends, and is described by the Bernoulli equation. Under normal conditions, this influence is rather small. The measurement of arterial pressure can be done either invasively or with one of the following noninvasive methods: occlusive cuff method, vascular unloading, arterial tonometry, or measurement of the arterial pulse wave velocity. Each of these methods has certain advantages and disadvantages. It seems necessary to point out the fact that due to wave reflections in the arterial system, pressure values depend on local influences and differ from location to location. Most markedly, the influence of wave reflection can be demonstrated proximally, as well as distally, to the occlusive cuff in the Riva Rocci method. Once the blood pressure has been measured in a person, the problem of the assessment and interpretation of the measured values has to be considered. According to the decision of the WHO, certain limits are defined which permit a distinction between normotension and hypertension. In each case, of course, a physician has to consider the importance of individual conditions.

A comparison of blood pressure measurements obtained with the Dinamap 845XT, the standard mercury sphygmomanometer and the London School of Hygiene device

Blood pressure measurements obtained with the Dinamap 845XT Vital Signs monitor were compared with measurements obtained with a standard mercury sphygmomanometer and a London School of Hygiene mercury sphygmomanometer in a group of 31 normotensive and hypertensive subjects. The experimental design allowed reading to be taken with all 3 devices at approximately the same time. 12 sets of readings were obtained with each device in each subject. Although inter-device differences estimated from analysis of variance were small (less than 2 mmHg after allowing for calibration differences) differences between measurements taken simultaneously with the 3 devices were often substantial. Agreement between the two mercury sphygmomanometers was better than that between either sphygmomanometer and the Dinamap. This may be a reflection of fundamental differences between auscultatory and oscillometric measurements. Differences between devices were unrelated to blood pressure level. The observed variability within subjects was similar with each device.

Computerized home telemetry of maternal blood pressure in hypertensive pregnancy

We have developed a telemetric technique whereby maternal blood pressure, which is self-measured by pregnant women in their own homes using a Dinamap 1846 automated blood pressure recorder, can then be transmitted over the commercial telephone network into the Rosie Maternity Hospital in Cambridge, where it is computer-processed. The maternal blood pressure is then reviewed by the obstetrician as part of the clinical management protocol. We have used this telemetric technique on 90 occasions, from the homes of 10 pregnant hypertensive women. On almost every occasion, the blood pressure measured at home was lower than that previously measured in the hospital antenatal clinic. This technique offers great promise, both in terms of health economics and also in terms of reducing pregnant women's unhappiness about their being admitted to hospital whenever they exhibit moderate to severe hypertension in the antenatal clinic. Indeed, in the antenatal period, home telemetry should allow the vast majority of hypertensive pregnancies to be managed just as safely at home as in hospital. In the management of high risk pregnancy, home telemetry of maternal blood pressure complements three other home telemetric techniques which have already been described: fetal heart rate, maternal blood glucose and uterine contractions.