Estimation of mean arterial pressure from the oscillometric cuff pressure: comparison of different techniques

Mean arterial pressure (MAP) is determined in most automated oscillometric blood pressure devices, but its derivation has been little studied. In this research, different techniques were studied and compared with the auscultatory technique. Auscultatory systolic and diastolic blood pressure (SBP and DBP) were obtained in 55 healthy subjects by two trained observers, and auscultatory MAP was estimated. Automated MAP was determined by six techniques from oscillometric cuff pressures recorded digitally and simultaneously during manual measurement. MAPs were derived from the peak and foot of the largest oscillometric pulse, and from time domain curves fitted to the sequence of oscillometric pulse amplitudes (4th order and three versions of the 6th order polynomial curve). The agreement between automated and auscultatory MAPs was assessed. Compared with the auscultatory MAP, the automated MAP from the baseline cuff pressure at the peak of the 6th order polynomial curve had the smallest mean paired difference (−1.0 mmHg), and smallest standard deviation of paired differences (3.7 mmHg). These values from the peak of the largest oscillometric pulse were −1.3 and 6.2 mmHg, respectively. Determining MAP from a model of the oscillometric pulse waveform had the smallest differences from the manual auscultatory technique.     

Different responses of Finapres and the oscillometric finger blood pressure monitor during intensive vasomotion

Two different techniques for non-invasive beat-to-beat finger arterial blood pressure monitoring are compared in six healthy volunteers during local hand heating from 21 to 38^°C. The degree of peripheral vasoconstriction was established by recording the thumb pulp skin blood flow with a laser Doppler instrument. For time episodes without vasoconstriction no systematic difference in the readings of beat-to-beat mean blood pressure of the two monitors was found (the oscillometric device UT9201 minus Finapres differencewas 0.3 mm Hg, SD 0.3). For the episodes with vasoconstriction the difference was statistically significant (6.7 mm Hg, SD 2.0). The oscillometric device minus Finapres difference and the laser Doppler signal were found to be inversely correlated, the correlation coefficient varying from - 0.28 to - 0.67. A disagreement between the readings of the instruments during intensive vasomotion is assumed to be caused mainly by the tendency of the oscillometric method to overestimate the finger mean blood pressure under the condition of peripheral vasoconstriction.     

Hemodynamic responses to hypoxia and hyperoxia in calves at sea level and altitude

Summary Hemodynamic studies were done in nine male Holstein calves, born at sea level, at 250 m (P _B 740 mm Hg) and in eight of these calves after 2 and 4 weeks at 3400 m altitude (P _B 510 mm Hg). Cardiac index (CI) decreased significantly as compared to sea level after 2 weeks at altitude and it was further decreased after 4 weeks. This reduction in CI resulted from decreased stroke index (SI) with unchanged heart rate (HR). Mean pulmonary arterial pressure (PAM) rose from 26 mm Hg at sea level to 63 and 74 mm Hg after 2 and 4 weeks at 3400 m, respectively. Both pulmonary arterial systolic and diastolic pressures were substantially increased at altitude, the diastolic relatively more than the systolic pressure (4.5 fold increase vs. 2.5 fold). Aortic blood pressures (systolic, diastolic and mean) did not change significantly at 3400 m. Right ventricular (systolic) and atrial (mean) pressures increased at altitude.During acute severe hypoxia (P _{IO 2} 55 mm Hg) at sea level CI remained essentially unchanged, while SI and HR, respectively, decreased and rose significantly; PAM was double the normoxic value. Acute hypoxia after 4 weeks at 3400 m did not elicit significant changes in blood gases and pH, CI, SI and HR while PAM increased by 25 mm Hg. There were slight reductions in CI, SI, HR and PAM during acute hyperoxia at sea level. Hyperoxia after 4 weeks at altitude did not change CI, while SI rose significantly; PAM decreased by 30 mm Hg. Apparently, the Holstein calf has a highly reactive pulmonary vascular bed to acute and chronic hypoxia which could make this cattle breed more susceptible to right heart failure during exposure to chronic hypoxia at high altitude.     

Validation of a new noninvasive method to measure blood pressure and assess baroreflex sensitivity in preterm infants during sleep

STUDY OBJECTIVES: Accuracy and precision of a noninvasive device for continuously measuring blood pressure (BP) (Finometer, FMS, The Netherlands) during sleep was assessed in preterm infants. DESIGN: Absolute BP beat-to-beat values, interbeat changes, measurement precision, and baroreflex sensitivity were compared with BP measurements from intraarterial catheters. PARTICIPANTS: Ten preterm infants (gestational age 27-36 weeks; birth weight 964-2620 gm) were studied in the neonatal intensive care unit. MEASUREMENTS AND RESULTS: The 2 modes of BP measurement were compared in 2-minute epochs (n = 10-12/infant). Mean arterial pressure, systolic arterial pressure, and diastolic arterial pressure were analyzed beat to beat, and baroreflex sensitivity was assessed using spontaneous sequence analysis. Mean differences for absolute BP (mm Hg) were as follows: mean arterial pressure, 3 (limits of agreement, -1 to 8); systolic arterial pressure, -4 (-8 to 1); and diastolic arterial pressure, 7 (4 to 10). Mean differences and limits of agreement for interbeat changes were essentially 0 for mean arterial pressure, systolic arterial pressure, and diastolic arterial pressure. Precision (+/- 95% confidence intervals, mm Hg) for the Finometer were mean arterial pressure +/- 7, systolic arterial pressure +/- 8, and diastolic arterial pressure +/- 6. Precision was greater for the arterial catheter (mean arterial pressure +/- 3, systolic arterial pressure +/- 4, and diastolic arterial pressure +/- 4). Baroreflex sensitivity calculated from the Finometer BP was (mean +/- SEM, ms/mm Hg) 1.74 +/- 0.23 and, from the catheter system, BP was 1.56 +/- 0.21 (p value NS). CONCLUSIONS: The Finometer provides accurate measurements of beat-to-beat BP and baroreflex sensitivity. The ability to continuously measure BP and baroreflex sensitivity during sleep in infants may provide vital clues into pathologic conditions associated with impaired autonomic control during sleep.     

Different responses of Finapres and the oscillometric finger blood pressure monitor during intensive vasomotion

Two different techniques for non-invasive beat-to-beat finger arterial blood pressure monitoring are compared in six healthy volunteers during local hand heating from 21 to 38 degrees C. The degree of peripheral vasoconstriction was established by recording the thumb pulp skin blood flow with a laser Doppler instrument. For time episodes without vasoconstriction no systematic difference in the readings of beat-to-beat mean blood pressure of the two monitors was found (the oscillometric device UT9201 minus Finapres difference was 0.3 mm Hg, SD 0.3). For the episodes with vasoconstriction the difference was statistically significant (6.7 mm Hg, SD 2.0). The oscillometric device minus Finapres difference and the laser Doppler signal were found to be inversely correlated, the correlation coefficient varying from -0.28 to -0.67. A disagreement between the readings of the instruments during intensive vasomotion is assumed to be caused mainly by the tendency of the oscillometric method to overestimate the finger mean blood pressure under the condition of peripheral vasoconstriction.     

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.     

Validation of automated oscillometric sphygmomanometer (HDBPM) for arterial pressure measurement during haemodialysis

An HDBPM oscillometric sphygmomanometer used for the automatic measurement of arterial blood pressure is evaluated according to the ANSI/AAMI SP10-1992 standard. The accuracy of the HDBPM is ascertained by comparing it against the standard Riva-Rocci ascultatory method. Following the ascultatory method, two independent observers use the HDBPM devise to simultaneously measure the arterial blood pressure in 92 subjects of varying ages and having different blood pressures and arm sizes. High agreement is found when comparing the observers' pressure determinations (within 10 mmHg for 100% of observations). Correlation between the average of two ascultatory determinations and the HDBPM is high both for the systolic (r=0.98) and diastolic (r=0.94) pressures. The mean of the differences between the pressures measured by the observers and the HDBPM device are 0.2 mmHg (systolic) and −0.4 mmHg (diastolic). The percentages of readings within 10 mmHg between those taken by the observers and those taken by the HDBPM are 88% (systolic) and 97% (diastolic). These results largely satisfy current requirements.     

Gender effects on blood pressures obtained during an on-campus screening

In a blood pressure screening of 167 male and female college students, we varied the gender of the screener to evaluate gender effects on blood pressure. Four repeated determinations of resting systolic and diastolic blood pressure were obtained with an automated oscillometric device in a quiet semi-darkened room. Analysis of systolic blood pressure indicated a significant interaction between screener gender, subject gender, and repeated determinations. Screener/subject gender concordance produced relatively stable systolic blood pressures across four repeated determinations. Gender discordance resulted in larger changes in systolic pressures across the four determinations. This pattern was not obtained with diastolic pressures. Measures of recent stress and somatic anxiety interacted with gender effects on blood pressure. These gender effects on systolic blood pressure may explain, in part, higher reported incidence of "white coat hypertension" in females.     

The relation between blood pressure and mortality due to coronary heart disease among men in different parts of the world. Seven Countries Study Research Group

BACKGROUND: Elevated blood pressure is known to be a risk factor for death from coronary heart disease (CHD). However, it is unclear whether the risk of death from CHD in relation to blood pressure varies among populations. METHODS: In six populations in different parts of the world, we examined systolic and diastolic blood pressures and hypertension in relation to long-term mortality from CHD, both with and without adjustment for variability in blood pressure within individual subjects. Blood pressure was measured at base-line in 12,031 men (age range, 40 to 59 years) who were free of CHD. During 25 years of follow-up, 1291 men died from CHD. RESULTS: At systolic and diastolic blood pressures of about 140 and 85 mm Hg, respectively, 25-year rates of mortality from CHD (standardized for age) varied by a factor of more than three among the populations. Rates in the United States and northern Europe were high (approximately 70 deaths per 10,000 person-years), but rates in Japan and Mediterranean southern Europe were low (approximately 20 deaths per 10,000 person-years). However, the relative increase in 25-year mortality from CHD for a given increase in blood pressure was similar among the populations. The overall unadjusted relative risk of death due to CHD was 1.17 (95 percent confidence interval, 1.14 to 1.20) per 10 mm Hg increase in systolic pressure and 1.13 (95 percent confidence interval, 1.10 to 1.15) per 5 mm Hg increase in diastolic pressure, and it was 1.28 for each of these increments after adjustment for within-subject variability in blood pressure. CONCLUSIONS: Among the six populations we studied, the relative increase in long-term mortality due to CHD for a given increase in blood pressure is similar, whereas the absolute risk at the same level of blood pressure varies substantially. If the absolute risk of CHD is used as an indication for antihypertensive therapy, these findings will have major implications for treatment in different parts of the world.     

Application of art,science and gumption in the care of the disabled

Non-invaswe oscillometric blood pressure and pulse measured by an Omron HEM-703CP monitor were compared with arterial values obtained from direct measurements of the radial artery. An excellent correlation and agreement was found between the two methods (systolic r=0.99; diastolic r=0.97; pulse r=0.99), although there was some variability among individual subjects. The range of difference between them was 0 to l. mmHg for systolic and—6 to + 5mmHg for diastolic pressures. When tested on the bench using the Metron QA-1280 non-invasive blood pressure analyser the HEM-703CP monitor rarely exhibited errors exceeding 2–3 mmHg over a measurement range of 50–200 mmHg.     

Elevated arterial blood pressure in cardiac tamponade.

BACKGROUND. In cardiac tamponade cardiac output falls, but peripheral vascular resistance increases, so that systemic blood pressure may be maintained at normal or near-normal levels. We recently observed a patient with cardiac tamponade whose blood pressure was markedly elevated. METHODS. To determine the frequency of elevated blood pressure in patients with cardiac tamponade and their hemodynamic characteristics, we studied 18 consecutive patients with cardiac tamponade from a variety of causes using right heart catheterization. RESULTS. Six of the 18 patients had systolic arterial blood pressures ranging from 150 to 210 mm Hg (mean [+/- SD], 176 +/- 26) and diastolic pressures ranging from 100 to 130 mm Hg (mean, 113 +/- 14). All six had previously been hypertensive. After pericardiocentesis there was a significant decrease in blood pressure (to 139 +/- 13 mm Hg systolic, P less than 0.05; and 83 +/- 6 mm Hg diastolic, P less than 0.01) and peripheral vascular resistance (from 2150 +/- 588 to 1207 +/- 345 dyn.sec.cm-5, P less than 0.01). Cardiac output increased in all six. The other 12 patients, 3 of whom had a history of hypertension, had significant increases in cardiac output and systolic blood pressure (from 119 +/- 13 to 127 +/- 7 mm Hg, P less than 0.05) after pericardiocentesis, whereas peripheral vascular resistance decreased. Both groups had similar degrees of cardiac tamponade, as indicated by measurements of cardiac output and intrapericardial, right atrial, and pulmonary-artery wedge pressures. CONCLUSIONS. Elevated blood pressure may occur in some patients with cardiac tamponade who have preexisting hypertension. Moreover, blood pressure may fall after pericardiocentesis in patients who have elevated blood pressure associated with tamponade.     

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.     

Theory of the oscillometric maximum and the systolic and diastolic detection ratios

It is proposed that the maximum in cuff pressure oscillations during oscillometry is due to the buckling of the brachial artery under a cuff. This theory is investigated by means of a mathematical model of oscillometry that includes the mechanics of the occlusive arm cuff, the arterial pressure pulse waveform, and the mechanics of the brachial artery. A numerical solution is provided for the oscillations in cuff pressure for one cycle of cuff inflation and deflation. The buckling pressure is determined from actual arterial data and the von Mises buckling criteria. The buckling of an artery under a cuff occurs near — 2 to 0 mm Hg transmural pressure. This effect corresponds with a maximum arterial compliance and maximum cuff pressure oscillations when cuff pressure is nearly equal to mean arterial pressure (MAP), in support of the suggested theory. The model was also found to demonstrate the basic characteristics of experimental oscillometry, such as an increasing and decreasing amplitude in oscillations as cuff pressure decreases, the oscillations that occur when cuff pressure is above systolic pressure, maximum oscillation amplitudes in the range of 1 to 4 mm Hg, and an oscillatory maximum at cuff pressure equal to MAP. These findings support the case that the model is representative of oscillometry. Finally, the model predicted values for the systolic and diastolic detection ratios of 0.593 and 0.717, respectively, similar to those found empirically. These ratios alter with blood pressure, but the tightness of the cuff wrap did not change their value.     

The effects of calcium supplementation on ambulatory blood pressure in African-American adolescents.

This longitudinal trial investigated the effects of calcium supplementation on the mean 24-hour blood pressure in African-American adolescents. Subjects were self-identified African-American adolescents from a high school in a suburb of Los Angeles, California. The subjects were randomly placed in a placebo or treatment group (placebo versus 1.5 g of calcium/day x 4 weeks). Follow-up mean 24-hour ambulatory blood pressure (ABP) for both the treatment and control groups was lower than the baseline mean 24-hour ABP. In the treatment group, there was a decrease of 2.2 mm Hg in the mean systolic blood pressure and 0.7 mm Hg in the diastolic blood pressure. Relative to the placebo group, the net change in ABP was -1.7 mm Hg for systolic blood pressure and -0.5 mm Hg for the diastolic blood pressure. There was no statistically significant effect of calcium supplementation on the 24-hour mean ABP. The net effect of supplementation on ABP during waking and sleeping hours also was not significant.     

Oscillometric blood pressure devices and simulators: measurements of repeatability and differences between models

PRIMARY OBJECTIVE: To measure the repeatability and pressure pulse envelope of simulators used for testing oscillometric non-invasive blood pressure (NIBP) devices; to study the effect of different envelopes on NIBP devices, and to measure the difference between NIBP devices due to different oscillometric algorithms. METHODS: Three different models of NIBP simulator and 18 different patient monitors with NIBP function were studied. We developed a pressure measurement system (accuracy 0.048?mmHg) to measure the repeatability of simulators. The effect of changing the envelope was measured by using three simulators with one NIBP device. Differences between 18 NIBP devices were measured using one simulator at seven blood pressure settings. MAIN OUTCOMES AND RESULTS: Simulators generate repeatable pressure pulse envelopes (< 0.2 mmHg) but the magnitude and shape depends on the model of simulator. Oscillometric NIBP devices are highly repeatable (< 2 mmHg) when presented with a repeatable pressure pulse envelope, but different devices employ different algorithms and give different results. For a simulated standard blood pressure setting of 120/80 mmHg, estimates of systolic pressure ranged from 112.6 to 126.6 mmHg (sd of 3.0 mmHg), and diastolic pressure ranged from 74.8 to 86.9 mmHg (sd of 3.5 mmHg). CONCLUSIONS: Simulators and NIBP devices are sufficiently repeatable for clinical use, but further systematic clinical studies are required to better characterize the pressure pulse envelope for different patient groups.     

Theoretical analysis of non-invasive oscillometric maximum amplitude algorithm for estimating mean blood pressure

A theoretical analysis is performed to evaluate the effect of arterial mechanical and blood pressure pulse properties on the accuracy of non-invasive oscillometric maximum amplitude algorithm (MAA) estimates of the mean blood pressure obtained using air-filled occlusive cuffs. Invasively recorded blood pressure pulses, selected for their varied shapes, are scaled to simulate a wide range of blood pulse pressures (diastolic blood pressure minus systolic blood pressure). Each scaled blood pressure pulse is transformed through an exponential model of an artery to create a series of blood volume pulses from which a simulated oscillometric waveform is created and the corresponding MAA estimate of the mean blood pressure and error (mean blood pressure minus MAA estimate) are determined. The MAA estimates are found to depend on the arterial blood pressure. The errors are found to depend on the arterial mechanical properties, blood pressure pulse shape and blood pulse pressure. These results suggest that there is no direct relationship between the mean blood presure and MAA estimate, and that multiple variables may affect the accuracy of MAA estimates of the mean blood pressure obtained using air-filled occlusive cuffs.     

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.     

A real-time pressure algorithm

A digital computer algorithm is described for real-time detection of critical points in the arterial pressure signal. Two externally selected parameters allow for filtering without loss of high frequency components. The accuracy of the algorithm was tested on 1005 cycles. Worse case a verage error was 2 mm Hg for diastolic pressure, 4 mm Hg for peak systolic pressure, and 11 msec in the placement of the dicrotic notch, Stability of the algorithm was shown by detection of 1004 of the 1005 cycles with two false positive cycles. A relative error bound is given for the Kouchoukos pulse contour formula for the estimate of stroke volume. The bound is a function of the notch placement relative error.     

Culture,skin color,and arterial blood pressure in Brazil

Populations of African descent in North and South America have higher mean blood pressures and higher rates of hypertension than populations of European descent or populations in Africa. Within populations of African descent, darker skinned persons have higher blood pressures than lighter skinned persons. Whether examined within or between populations, there is an interaction between skin color and socioeconomic status (SES) in relation to blood pressure, with persons with dark skin color and low SES having the highest blood pressures. This interaction was examined in Brazil using a measure of a cultural dimension of SES called “cultural consonance in lifestyle.” This measure was derived using cultural consensus analysis linked with social survey data. It was found that darker skinned Brazilians with lower cultural consonance in lifestyle had adjusted systolic blood pressures 16.2 mm Hg higher than darker skinned Brazilians with higher cultural consonance (P < .01); the corresponding difference in adjusted diastolic blood pressure was 9.7 mm Hg (P < .04). The differences for lighter skinned Brazilians were 6.4 mm Hg (P < .02) and 1.0 mm Hg (not significant), respectively. These results could be due either to an interaction of genetic predisposition and SES, or the result of a socially and culturally‐mediated process. Given that cultural consonance in lifestyle measures the ability of the person to live up to cultural norms, and given the existence of racial stratification in Brazil, it is argued that a social and cultural mediation of the relationship is more plausible. Am. J. Hum. Biol. 11:49–59, 1999. © 1999 Wiley‐Liss, Inc.     

Talking Effect and White Coat Phenomenon in Hypertensive Patients

Both white coat effect (the tendency of blood pressure to rise during a medical visit) and talking effect were analyzed in 42 patients with essential hypertension. Blood pressure was measured during the clinic visit and over the subsequent 24-hour ambulatory period, with the physician performing 49 ± 4 measurements for each patient. Three silent periods and two talking periods (stress and relaxation) were randomly allocated in a crossover design and studied, using analysis of variance. During the initial 11-minute silent period, systolic/diastolic blood pressures increased by 6 mm Hg/5 mm Hg. During the subsequent talking periods, these variations were significantly greater: +22 mm Hg/+17 mm Hg. Measures of systolic/diastolic blood pressure were higher during stressful talking than during relaxed talking. The talking and its emotional contents seemed to explain 70% of the white coat phenomenon. To minimize the white coat phenomenon in the clinic, physicians, nurses, and clinicians are advised to measure blood pressure during an initial period of silence.