Noninvasive,automatic 24-h ambulatory blood pressure monitoring in normotensive subjects

Summary The reliability of noninvasive, automatic blood pressure monitoring is not yet clearly established. A 24-h ambulatory blood pressure profile was obtained in 9 healthy, normotensive subjects with an automatic, noninvasive device. The blood pressure profile showed the typical circadian pattern with lower systolic and diastolic values during sleep, although pulse pressure was fairly constant (about 40 mm Hg). The systolic blood pressure rose steeply in the early morning hours — before waking up. The results were compared with simultaneous hourly readings using the auscultatory method. There were no statistically significant differences between the automatic and auscultatory readings, 13 of the 18 mean values at. different time points being within 2 mm Hg of each other. All the auscultatory means fell within the 95% confidence limits of those measured hourly by the automatic method. Although the automatic method seemed to be reliable compared with the auscultatory method, its sensitivity to motion artifacts is a disadvantage in a truly ambulatory setting.     

Effect of a newly developed charging chamber for the treatment of hypotension during hemodialysis

We developed a new method of hemodialysis using a charging chamber for treatment of hemodialysis patients with hypotension occurring during the latter half of hemodialysis (collapse). The purpose of this method was to recover systolic blood pressure (BP) by returning a part of blood within the chamber into the body circulation when hemodialysis collapse occurred. Using this method, systolic BP recovery (DeltaBP) in ten hemodialysis patients (4 males, 6 females, mean age 66.0 years old) was compared to a control group treated with intravenous administration of 20 ml of 10% NaCl. When hemodialysis collapse occurred, 60 ml of blood within the chamber in this method and 20 ml of 10% NaCl intravenously in the control group were administered and systolic BP was measured 20 minutes later. The results showed that DeltaBP using this method was 26.0 mm Hg (ANOVA: p = 0.0072), while in the control group it was 30.2 mm Hg (ANOVA: p = 0.0003), and there was no significant difference between the systolic BP recovery of both groups (paired t test: p = 0.4196).     

Continuous estimation of systolic blood pressure using the pulse arrival time and intermittent calibration

A continuous noninvasive method of systolic blood pressure estimation is described. Systolic blood pressure is estimated by combining two separately obtained components: a higher frequency component obtained by extracting a specific frequency band of pulse arrival time and a lower frequency component obtained from the intermittently acquired systolic blood pressure measurements with an auscultatory or oscillometric system. The pulse arrival time was determined by the time interval from QRS apex in electrocardiogram to the onset of photoplethysmogram in a fingertip beat-by-beat via an oximetric sensor. The method was examined in 20 patients during cardiovascular surgery. The estimated values of systolic blood pressure were compared with those measured invasively using a radial arterial catheter. The results showed that the correlation coefficients between estimated values and invasively obtained systolic blood pressure reached 0.97±0.02 (mean±SD), and the error remained within ±10% in 97.8% of the monitoring period. By using a system with automatic cuff inflation and deflation to acquire intermittent systolic blood pressure values, this method can be applicable for the continuous noninvasive monitoring of systolic blood pressure.     

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.     

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.     

Effect of serial arm ischemic preconditioning sessions on the systemic blood pressure of a normotensive subject

Remote ischemic preconditioning (RIPC) consists of repeated 5' periods of blood pressure (BP) cuff inflations applied to the upper arms at pressures above the systolic blood pressure (SBP), interspersed with 5' periods of reperfusion have been shown to benefit the ischemic and infarcted myocardium in animal experiments, and human clinical experience. Serial sessions of RIPC, as described, were applied to the arms of a normotensive subject. RIPC resulted in a statistically significant mean drop of the SBP by >6mm Hg, of the diastolic BP by >3mm Hg, and of the pulse pressure by 3mm Hg, 30' after RIPC, with some evidence for a delayed effect in the ensuing days following RIPC. RIPC exerts an immediate BP lowering effect and possibly has a prolonged delayed such influence on BP. This newly described herein phenomenon needs to be corroborated and explored for its potential value in the physiology of BP regulation and the pathophysiology and therapy of hypertension.     

Effects of relative blood volume-controlled hemodialysis on blood pressure and volume status in hypertensive patients

In hypertensive hemodialysis (HD) patients, dry weight reduction to normalize blood pressure (BP) often results in increased frequency of HD hypotension. Because HD with blood volume tracking (BVT) has been shown to improve intra-HD hemodynamic stability, we performed a prospective, randomized study to test whether BVT is more effective than standard hemodialysis (SHD) in the management of hypertension by dry weight reduction. After a run-in period of 4 weeks on SHD, 28 patients were randomly assigned for a 12-week treatment period with either SHD (n = 14) or BVT (n = 14). The mean pre-HD and post-HD weight did not change over time in either group. In the BVT group, pre-HD systolic and diastolic BP decreased on average 22.5 mm Hg and 8.3 mm Hg, respectively (both p < 0.05), whereas BP did not change in the SHD group. Extracellular water and cardiothoracic ratio decreased significantly (all p < 0.05) in the BVT group but not in the SHD group. Brain natriuretic peptide levels declined only in the BVT group, without reaching statistical significance. The frequency of HD hypotensive episodes decreased significantly (p < 0.05) in the BVT group and was unchanged in the SHD group. HD with BVT was associated with a significant reduction in pre-HD BP. At the same time, the frequency of intra-HD hypotensive episodes decreased. Although the mean weight did not change, the reductions in cardiothoracic ratio and extracellular water suggest that HD with BVT resulted in optimization of volume status.     

Cardiovascular reactions induced by unpredictable, predictable, and controllable painful stimuli during sphygmomanometry.

Sphygmomanometry is the most common technique of blood pressure (BP) determination. In order to study effects of predictability and controllability in sphygmomanometric BP measurements, 72 normotensive healthy subjects were examined. BP was determined continuously and non-invasively using a Finapres device (Penaz-technique) and by sphygmomanometry. Five sphygmomanometric measurements took place, during the fourth the arm cuff was inflated to 300 mmHg, the others were done with a pressure of 175 mmHg. Subjects were randomly assigned to one of three groups: In one group the recordings were unpredictable to the subject, in the second group measurements were announced 1 min before cuff inflation took place, and in the third group, subjects could decide when the sphygmomanometric recordings should occur. With unpredictable measurements systolic and diastolic BP decreased (approx. 5 mmHg). When sphygmomanometric recordings were controllable or predictable to the subject BP remained relatively stable. We would suggest that automatic BP devices (e.g. in ambulatory BP monitoring) should generally work with acoustic signals, making cuff inflation predictable for the subject.     

Relationship of blood pressure and pump flow in an implantable centrifugal blood pump during hypertension

The purpose of this study was to evaluate the real time relationship between pump flow and pump differential pressure (D-P) during experimentally induced hypertension (HT). Two calves (80 and 68 kg) were implanted with the EVA-HEART centrifugal blood pump (SunMedical Technology Research Corp., Nagano, Japan) under general anesthesia. Blood pressure (BP) in diastole was increased to 100 mm Hg by norepinephrine to simulate HT. Pump flow, D-P, ECG, and BP were measured at pump speeds of 1,800, 2,100, and 2,300 rpm. All data were separated into systole and diastole, and pump flow during HT was compared with normotensive (NT) conditions at respective pump speeds. Diastolic BP was increased to 99.3+/-4.1 mm Hg from 66.5+/-4.4 mm Hg (p<0.01). D-P in systole was under 40 mm Hg (range of change was 10 to 40 mm Hg) even during HT. During NT, the average systolic pump flow volume was 60% of the total pump flow. However, during HT, the average systolic pump flow was 100% of total pump flow volume, although the pump flow volume in systole during HT decreased (33.1+/-5.7 vs. 25.9+/-4.0 ml/systole, p<0.01). In diastole, the average flow volume through the pump was 19.6+/-6.9 ml/diastole during NT and -2.2+/-11.1 ml/diastole during HT (p<0.01). The change in pump flow volume due to HT, in diastole, was greater than the change in pump flow in systole at each pump speed (p<0.001). This study suggests that the decrease of mean pump flow during HT is mainly due to the decrease of the diastolic pump flow and, to a much lesser degree, systolic pump flow.     

Blood flow and oxygen consumption with near-infrared spectroscopy and venous occlusion: spatial maps and the effect of time and pressure of inflation

We have measured the local blood flow (BF) and oxygen consumption (OC) in the human calf muscle using near-infrared spectroscopy during venous occlusion. Venous occlusion was achieved by inflating a pneumatic cuff around the thigh of the subject. We have investigated the influence of the inflation time and cuff pressure on the recovered values of BF and OC. We have found that if the cuff pressure is increased from a threshold pressure (approximately 30 mm Hg) to a critical pressure (approximately 45 mm Hg) in less than about 6 s, one measures the same values of BF and OC independent of the total inflation time and final cuff pressure. We also report nine-pixel spatial maps of BF and OC to show that this technique can lead to spatially resolved measurements of blood flow and oxygen consumption in tissues.     

Tracking-Cuff System for Beat-to-Beat Recording of Blood Pressure

A system is described for the automatic beat-to-beat tracking of blood pressure (BP) based on the detection of Korotkoff sounds. Upon each detection, a discrete adjustment in cuff pressure is made prior to the next cardiac cycle. In comparison with other continuous tracking systems, digital control allows for estimation of systolic BP based on precise knowledge of cuff pressure at each heart beat. Simultaneous recordings of intra-arterial pressure (radial artery) and systolic pressure measured with the tracking system were made in 4 subjects during 1-min trials of resting, paced respiration, and mental arithmetic. Correlations of the paired measures of intra-arterial and cuff pressure for 27 trials varied from .46 to .90 (median = .72). The standard error of estimate of intra-arterial systolic BP varied from 1.8 to 6.3 mmHg (median = 3.6). The system can be used without discomfort to track systolic BP for 60 and 120 sec in experiments involving repeated cuff inflations. Critical features and advantages of the tracking-cuff system for blood pressure measurement and biofeedback are discussed.     

Catecholamine responses to histamine infusion in man

To evaluate the effects of histamine-induced hypotension on plasma catecholamine levels, eight normal men, aged 20 to 40 years, were infused with incremental doses of histamine starting at 0.2 microgram/kg/min at a 30 degree tilt position with monitoring of blood pressure (BP) and heart rate. Histamine dosage was increased every 5 minutes by 0.1 to 0.2 microgram/kg/min until mean BP fell greater than 15 mm Hg or a dosage of 1.6 micrograms/kg/min was reached. Plasma catecholamine samples were taken between the fourth and fifth minute of each histamine dosage. Identical measurements were made during nitroglycerin-induced hypotension in these subjects. Histamine produced threefold greater increases in heart rate and plasma norepinephrine (NE) levels than did nitroglycerin for comparable decreases in BP. Although NE levels increased twofold to fivefold from baseline with histamine infusion, epinephrine levels increased minimally at the highest doses or not at all. Our data demonstrate that histamine selectively releases NE from adrenergic nerve terminals without significant adrenal catecholamine release. We suggest that neural NE release plays an important role in the cardiac effects of histamine.     

Hormone replacement therapy reduces mean 24-hour blood pressure and its variability in postmenopausal women with treated hypertension

BACKGROUND: The rate and severity of hypertension increase dramatically after menopause. Complications seem to be more frequent and marked in hypertensive patients with greater blood pressure (BP) variability, and antihypertensive treatment does not easily reduce this variability. The effect of hormone replacement therapy (HRT) on BP and its variability is not well understood in moderate to severe hypertension, but estrogen may have calcium channel-blocking properties. Cardiovascular events occur more frequently in the morning, likely in part because of a rise in BP. DESIGN: We prospectively studied 34 postmenopausal women with treated hypertension (mean age = 53 years) and receiving a cyclic combination of estradiol and norgestrel for 19 weeks with 24-h ambulatory BP monitoring. RESULTS: Mean daily BP and its variability decreased significantly with HRT (149.3 +/- 6.1 mm Hg vs. 140.3 +/- 8.5 mm Hg [p < 0.001]; diastolic: 95.4 +/- 4.7 mm Hg vs. 92.4 +/- 7.2 mm Hg [p < 0.05]). There was also a significant decrease in the early morning BP values after HRT (154.0 +/- 6.9 mm Hg vs. 145.6 +/- 11.0 mm Hg [p < 0.001]; diastolic: 98.0 +/- 4.8 mm Hg vs. 95.1 +/- 10.0 mm Hg [p < 0.05]). Subjects who were taking calcium channel blockers (n = 11) had only half the reduction in 24-h systolic BP compared with those who were not taking calcium channel blockers (5.3 mm Hg vs. 10.5 mm Hg), and the reduction in those who were taking calcium channel blockers failed to reach statistical significance. CONCLUSIONS: Our results demonstrate that HRT may have a role in decreasing the severity of hypertension, and the mechanism of its action might be through calcium channels.     

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.     

Relationship of clinic, ambulatory, and laboratory stress blood pressure to left ventricular mass in overweight men and women with high blood pressure

OBJECTIVE: This study was designed to evaluate the relationship between left ventricular (LV) mass and blood pressure (BP) recorded in the following contexts: in the clinic, using standard auscultatory procedures, during a typical day using ambulatory BP monitoring, and in the laboratory environment during behavioral stress testing. METHODS: Ninety-seven men and women with clinic systolic blood pressure (SBP) of 130 to 180 mm Hg and/or diastolic blood pressure (DBP) of 85 to 110 mm Hg and mild to moderate obesity were included in the study. Laboratory stressors included the following tasks: Public Speaking; Anger Interview; Mirror Trace; and Cold Pressor. LV mass was measured using echocardiography and adjusted for body size by dividing by height(2.7) to yield LV mass index (LVMI). RESULTS: LVMI was positively correlated with clinic SBP (r = 0.24, p <.05), ambulatory SBP (r = 0.34, p <.01), and aggregated laboratory stress SBP (r = 0.28, p <.01). Of the individual stressors, only SBP responses to the Mirror Trace and Cold Pressor tasks were independently correlated with LVMI (r = 0.35 and 0.34, respectively, p values <.01). Hierarchical regression analyses revealed that laboratory stress SBP remained a significant predictor of LVMI, after controlling for BMI and clinic pressure. CONCLUSIONS: These findings suggest that cardiovascular responses to behavioral stress are associated with individual differences in LVMI in men and women with high blood pressure who are overweight. Laboratory studies of behavioral stress may help promote our understanding of the pathophysiology of LVH.     

Long-term ambulatory monitoring of indirect arterial blood pressure using a volume-oscillometric method

A new portable instrument equipped with a microprocessor was designed for the long-term ambulatory monitoring of indirect arterial pressure in the human finger at desired intervals using a volume-oscillometric technique. All the necessary procedures such as (1) programmed control of cuff pressure, (2) detection of the systolic end-point and the point of maximum amplitude of arterial volume pulsations, (3) reading of the cuff pressures corresponding to these two points, (4) its processing and (5) recording of the systolic and mean pressure together with heart rate on a digital memory integrated circuit were performed automatically. After the monitoring, the data were reproduced and analysed by a conventional personal computer. Simultaneous comparison of the data with direct measurement, operation and evaluation of this instrument, and ambulatory monitoring were carried out. With this instrument noninvasive and accurate monitoring of arterial pressure could be made in unrestricted subjects during daily activities.     

Indomethacin induced hypotension in sodium and volume depleted rats

Summary After a single oral dose of 4 mg/kg indomethacin (IDM) to sodium and volume depleted rats plasma renin activity (PRA) and systolic blood pressure fell significantly within four hours. In sodium repleted animals indomethacin did not change systolic blood pressure (BP) although plasma renin activity was decreased.Thus, indomethacin by inhibition of prostaglandin synthesis may diminish the blood pressure maintaining effect of the stimulated renin-angiotensin system in sodium and volume depletion.Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

The effects of avoidance and conflict schedules on the blood pressure and heart rate of rats

Two studies examined the cardiovascular response to aversive conditioning as a function of the degree of control over the stressor. Experiment 1 used 24 normotensive rats assigned to 3 groups: experimental, yoked, and non-shock restraint control. Triplets of rats were exposed to signalled avoidance for 3 weeks. Experimental animals were required to turn a wheel to avoid shocks to themselves and their yoked partners. Direct cardiovascular monitoring via aortic catheters during the final avoidance session revealed that both systolic and diastolic blood pressure (BP) increased significantly in experimental and yoked rats during avoidance but remained elevated throughout avoidance and post-avoidance only in the yoked animals. Experimental rats also exhibited a significant increase in HR during early avoidance. Experiment 2 assessed the cardiovascular response to a reduction in the controllability of the stressor by exposing 24 rats, assigned to groups as above, to 11 weeks of conflict and avoidance conditioning. Indirect systolic BP was significantly higher in experimental and yoked rats as compared to controls when averaged over the 11 weeks of stress. Experimental and yoked rats also had significantly more hypertensive systolic BP readings (SBP≥150 mm Hg), 34% and 38% respectively, than controls (13%). Direct cardiovascular monitoring during a final conflict session showed sustained increases in systolic and diastolic BP during conflict and post-conflict for both experimental and yoked rats, attaining significance, however, only in the yoked group. These studies suggest that the opportunity to cope moderates the systolic BP response to aversive stimulation and the loss or lack of such opportunity leads to a significant increase in the number of hypertensive blood pressure readings.     

Correlation between luminal hydrostatic pressure and proximal tubular fluid reabsorption in the rat kidney

Summary Split-drop experiments were performed to evaluate the effect of changes in luminal hydrostatic pressure on net fluid reabsorption in proximal convoluted tubules of the rat kidney. While hydrostatic pressure in control droplets averaged 28.9±1.03 mm Hg, it increased to a mean of 65.2±3.3 mm Hg during pressure elevation and fell to 10.8±1.04 mm Hg during pressure reduction. In paired measurements in identical tubules net fluid absorption changed from a control value of 2.96±0.14 nl/min·mm to 3.88±0.14 nl/min·mm when luminal pressure was elevated. During pressure reduction net fluid absorption fell from a control of 2.98±0.09 nl/min·mm to 2.26±0.13 nl/min·mm (P<0.001). This dependency of fluid absorption upon hydrostatic pressure was not greatly affected by the finding that microphotography overestimated the true intradroplet volume by 31% during control and by 30.2% and 50% during elevated and reduced pressure respectively. From the relation between the changes of net absorption and luminal hydrostatic pressure an apparent hydraulic conductance of 0.04 nl/min·mm Hg was estimated.     

Effect of repeated measurements of blood pressure on blood pressure in essential hypertension: Role of anxiety

Over the past years, we repeatedly observed that of the hypertensive population entered into our behavioral treatment programs, more than half were actually false hypertensives. With repeated measurements of blood pressure (BP), only one-third remained hypertensive, while two-thirds showed a significant decrease in BP. The purpose of this study was to determine which factors correlate with the decrease in BP and could be useful in distinguishing the true and the false hypertensives. Of the 24 patients in this study, 15 decreased their mean arterial pressure by at least 5 mm Hg during a 6-week period of home and clinic BP measurement, while 9 did not. The 9 patients with BPs that did not change had lower State Anxiety, Trait Anxiety scores, lower diastolic BP, and lower heart rates compared to the group whose BPs decreased. These results suggest that under certain conditions a relationship exists between anxiety and elevated blood pressure. In a segment of the hypertensive population, anxious patients may be placed on inappropriate anti-hypertensive medication if a BP measurement period is not conducted before intervention.