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

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

Voluntary Control of Systolic Blood Pressure During Postural Change

The effects of biofeedback and voluntary control procedures on systolic blood pressure and heart rate during postural change were investigated in 30 normotensive men. Systolic pressure was measured with a continuous blood pressure tracking cuff, and blood pressure feedback was provided on a beat-to-beat basis. Postural changes in pressure, and corresponding heart rate changes, were examined in three experimental groups (N = 10 each). In two groups, subjects were given feedback training to increase or to decrease systolic blood pressure. In the third group, subjects were simply asked to increase their pressure but were not given feedback about their performance. Voluntary control of systolic pressure was attempted while subjects were seated and during postural change—sitting to standing. Subjects were also instructed to maintain voluntary blood pressure control in subsequent no-feedback test trials. During postural change, voluntary control procedures caused significant alterations in tonic levels of systolic pressure, but phasic blood pressure reactivity was unaffected. With respect to postural changes in heart rate, both tonic and phasic treatment effects were observed. Implications of the findings for basic and clinical research are discussed.     

Ambulatory instrument for monitoring indirect beat-to-beat blood pressure in superficial temporal artery using volume-compensation method

A portable instrument, based on a volume-compensation technique, is designed for ambulatory monitoring of indirect beat-to-beat blood pressure (BP) in the superficial temporal artery. The instrument consists of a small disc-type cuff and a portable unit carried by the subject. Several components are integrated in the cuff for applying counter-pressure to the artery, i.e. a reflectance-type photo-plethysmographic sensor for arterial volume detection, a pressure sensor for cuff pressure P_c measurement and a nozzle flapper-type electro-pneumatic convertor for controlling P_c. The portable unit includes volume servo control circuitry and a microprocessor-based signal-processing and recording unit. This automatically performs all the necessary measurement procedures and stores into a memory IC element the processed systolic, mean and diastolic blood pressure data, together with pulse intervals on a beat-to-beat basis from the servo-controlled P_c (indirectly measured BP waveform). With this instrument, momentary changes in BP during ambulatory situations such as bicycle ergometer exercise and daily activities including motorway driving are successfully recorded. From the results of simultaneous measurement of the subject's posture changes, the effect of posture change on blood pressure, e.g. baroreceptor-cardiac reflex, is also clearly demonstrated.     

Determination of blood pressure level and changes in physiological situations: comparison of the standard cuff method with direct intra-arterial recording

Blood pressure changes during a test series (sitting, supine, standing, bicycle ergometer test, recovery) were determined in a group of normotensive and borderline hypertensive subjects simultaneously with the continuous intra-arterial registration (Oxford method) and the indirect cuff methods. The mean method difference between the direct and indirect method varied considerably in tests, from -2.3 to 12.9 mmHg in systolic pressure and from -4.3 to 18.2 mmHg in diastolic pressure. There was also a large scatter in the method difference between subjects. Analysis of the blood pressure responses to the other tests using values measured in the sitting position as the reference also revealed considerable variation between the methods. The accuracy of the indirect method was also tested by classifying the population in two subgroups along the median (high/low group) in all tests by each method. The classification discrepancy between the methods varied from 9 to 33% in systolic pressure and from 0 to 25% in diastolic pressure. The results indicate that the data gathered using the indirect measuring method from the arterial blood pressure level and changes in varying physiological conditions may differ considerably from direct intra-arterial readings. On the other hand, the repeatability of the indirect method in stabile conditions was found to be acceptable indicating that the indirect method is useful in blood pressure follow-up.     

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

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

The beat-to-beat blood pressure response to postural change in young and elderly healthy adult males

Heart rate and blood pressure were studied with the beat-to-beat tracking cuff system in two groups (n=20 per group) of healthy, unmedicated males, one between 60 and 75 years of age and the second between 18 and 29 years of age. The study confirms the previously reported blunted heart rate response to standing and the fact that, when blood pressure is recorded by conventional means, the response exhibited during orthostasis does not differ in healthy groups of young and elderly subjects. With the tracking cuff system, however, the elderly exhibited a smaller immediate systolic and diastolic drop in response to the change to upright posture and less variability in beat-to-beat blood pressure changes. The results have implications for cardiovascular studies, where age and posture can influence both blood pressure and heart rate.This research was supported by National Heart, Lung, and Blood Institute Research Grant HL-31184-05.     

Pulse Transit Time and Blood Pressure: An Intensive Analysis

Relationships between pulse transit time (PTT) and intra-arterial systolic (SBP), diastolic (DBP), and mean arterial blood pressure (MAP) were examined in 4 subjects under three conditions: rest, paced respiration, and mental arithmetic. PTT was measured from the EKG R-wave to two peripheral pulses (brachial and radial) and from one pulse to the other. Three points on each pulse wave were used (peak, foot, slope) in the measurements, yielding nine different measures of PTT. The nine PTT measures were not consistently intercorrelated. PTTs initiated by the R-wave were moderately correlated with SBP, but not with DBP or MAP. Brachial to radial PTTs were not correlated with any measures of BP. Relationships between PTT and BP also varied from subject to subject. The limited magnitude of the correlations and their inconsistency suggest caution in the simple substitution of PTT for beat-to-beat measures of BP.     

Evaluation of a New Ambulatory Blood Pressure Monitor (Accutracker 102): Laboratory Comparisons With Direct Arterial Pressure, Stethoscopic Auscultatory Pressure, and Readings From a Similar Monitor (Spacelabs Model 5200)

Systolic (SBP) and diastolic (DBP) blood pressure levels generated by a new noninvasive ambulatory monitor, the Accutracker 102, were compared in the laboratory with intra-arterial pressure levels in 12 normotensive men, and with stethoscopic auscultatory determinations in 27 normotensive and hypertensive men and women over a wide range of within-subject pressure variations. In 11 subjects, its performance was also compared with another ambulatory monitor, the Spacelabs Model 5200. Highly positive correlations with both the intra-arterial (median r=+.90 for SBP, +.92 for DBP) and the stethoscopic standards (median r=+.93 for SBP, +.88 for DBP) were obtained using Accutracker's automatic readings (digital readout), while slightly higher correlations were obtained with hand-scoring of recorded data. The Spacelabs BP monitor also yielded readings that were highly correlated with stethoscopic readings (median r=+.83 for SBP, +.77 for DBP), although in 3 of the 11 subjects the Accutracker correlations were substantially higher than the Spacelabs correlations. Despite their generally good tracking of changes in pressure, both ambulatory monitors yielded absolute values in many subjects that differed by 5 mmHg or more from stethoscopic levels. The Accutracker's SBP levels were consistently too high and its DBP levels were occasionally too low, while Spacelabs' SBP and DBP values were too high and too low with equal frequency. However, mean deviation scores for each patient calculated from 5 concurrent ambulatory monitor and stethoscopic readings were shown to yield relatively stable correction factors for use when comparison with clinical standards is desired.     

Aortic-Radial Pulse Transit Time and ECG Q-Wave to Radial Pulse Wave Interval as Indices of Beat-By-Beat Blood Pressure Change

This study examined beat-by-beat relationships between blood pressure, the time interval from the ECG Q-wave to the radial pulse wave (QRPI), and its two components, the cardiac pre-ejection period (PEP) and aortic-radial arterial pulse transit time (AR-PTT). In 8 subjects, intra-arterial systolic (SBP) and diastolic (DBP) blood pressure, QRPI, PEP, and AR-PTT were measured during rest, mental arithmetic, cold pressor, and inhalation of amyl nitrite. Both PEP and AR-PTT varied widely during each experimental condition indicating that QRPI change reflected both PEP and AR-PTT change. AR-PTT varied inversely with SBP and DBP; PEP sometimes varied directly and sometimes inversely with both SBP and DBP. QRPI varied inversely with both SBP and DBP with the magnitude of the correlation in a particular instance depending on the relationships for that instance between blood pressure and both PEP and AR-PTT. Implications of the results for the use of either QRPI or AR-PTT as indices of blood pressure change are discussed.     

Noninvasive automatic determination of mean arterial pressure

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

Apparatus and Procedure for Training Subjects to Control Their Blood Pressure

The purpose of this study was to devise a set of apparatus and procedures for treating the blood pressure response as a free operant. The system described herein developed out of an effort to combine some features of the Harvard and Rockefeller methods into a compact and inexpensive unit that could be transported easily and eventually adapted for home use. Application of the device requires fitting the subject with a standard cuff on each arm and inflating first one and then the other for intervals of 100 sec. The systolic or diastolic blood pressure threshold is tracked by readjusting cuff pressure every 3–4 heartbeats in order to hold the intensity of the Korotkoff sounds constant. A record of blood pressure is obtained by transducing and tracing moment-to-moment changes in cuff pressure on a strip chart recorder. Scores provided by this method and those obtained with the classical Riva-Rocci procedure were found to be highly correlated.     

Vibration plethysmography: A method for studying the visco-elastic properties of finger arteries

Vibration plethysmography records changes in vascular volume produced by fast vibrations of cuff pressure. From these, waveforms of dynamic vascular compliance (DVC) are obtained. A total of 46 recordings of DVC, photo-electric plethysmogram (PG), cuff pressure (CP), and indirect blood pressure (BP) are performed on two adjacent fingers (third and fourth) in 23 healthy subjects. The shape and polarity of the DVC waveform markedly depends upon CP or transmural pressure (TP) (TP=BP-CP). The correlation coefficient between DVC and PG waveforms is nearly −1 at negative mean TP, near zero at zero TP, and approaches +1 at positive TP. For CP moving between systolic and diastolic BP, the DVC waveform shows a diastolic peak, with its maximum close to the zero value of instantaneous TP. xy-diagrams of PG against TP and of DVC against TP plotted for the diastolic phase of single pulses reveal a close coincidence of the DVC peak with the maximum slope of the PG/TP curve. A similar relationship appears when slow changes in PG and the amplitude of PG pulse waves are plotted against mean TP.     

Continuous positive airway pressure lowers blood pressure in hypertensive patients with obstructive sleep apnea

Summary Question of the study Obstructive sleep apnea (OSA) and hypertension are frequently associated and probably causally related. We investigated the influence of continuous positive airway pressure (CPAP) on blood pressure (BP) in OSA. Patients and Methods Fourty-four patients in whom CPAP-therapy had been successfully applied for treatment of OSA (median apnea-hypopopnea-index [AHI] 57.5/h) were included. Non-invasive 24-hour BP was measured at 15  min intervals before and with CPAP. Results After 1 – 3 days of CPAP, 24-hour systolic and diastolic BP in the hypertensive patients (n = 32) decreased from a median of 141 (129 – 173, 25 % – 75 % interquartile range) mmHg to 136 (118 – 157) mmHg (p = 0.004) and from 90 (80 – 107) mmHg to 88 (77 – 99) mmHg (p = 0.001), respectively, but was unchanged in the normotensives (n = 10). After 4 – 6 months of CPAP, 24-hour systolic and diastolic BP in a hypertensive subgroup (n = 19) decreased from a median of 140 (131 – 142) mmHg to 131 (122 – 143) mmHg (p = 0.01) and from 88 (86 – 94) mmHg to 84 (80 – 87) mmHg (p = 0.02), respectively, but was unchanged in a normotensive subgroup (n = 8). After long-term CPAP, there was a small weight reduction in the hypertensive patients. Subgroup analysis of 13 hypertensives with stable weight confirmed a significant BP-reduction. Conclusions In OSA with associated hypertension, CPAP has a specific BP-lowering effect. This suggests that both disorders are causally related.     

Electrical admittance cuff for non-invasive and simultaneous measurement of haematocrit, arterial pressure and elasticity using volume-oscillometric method

An improved technique based on the electrical admittance cuff was designed for the non-invasive measurement of haematocrit (Hct), together with blood pressure (BP) and arterial elasticity represented as volume elastic modulus (E_v), in human fingers. This device is made of a rigid annular chamber installed with a surrounding thin-walled tube (cuff), which is filled with electrolyte solution. A tetrapolar method is used to detect the admittance signals, both in the solution and in a finger segment placed through the cuff. With this device, it is theoretically shown that the resistivity of blood flowing into the segment is equal to that of the solution multiplied by the ratio of the admittance variation in the solution to that in the segment. Thus, the blood resistivity and therefore Hct can be non-invasively determined from the electrolyte resistivity and these two admittance variations. On the other hand, BP and E_v are also simultaneously measured from the admittance signals following the gradual change of the chamber pressure based on the volume-oscillometric method. Experiments were successfully made in 14 subjects, showing that the indirect Hct values agreed well with the direct values obtained from sampled blood and that this simle technique was significant for the non-invasive ad simultaneous measurement of these physiological variables.     

Indirect measurement of instantaneous arterial blood pressure in the rat.

We devised a hydraulic servo-control system for indirect blood pressure measurement in the rat's tail, by which beat-to-beat systolic and diastolic blood pressure can be obtained. In this method the principle of "unloading vascular wall" proposed by Shirer (1962) is employed. The proposed system is composed of a transmittance photoelectric plethysmograph with an occluding cuff, a small diaphragm actuator for compressing and decompressing the segment by the hydraulic pressure, and an electromagnetic shaker driven by a volume servo circuit in accordance with the signal from the photoelectric plethysmograph. The plethysmographic signal is clamped at a proper value corresponding to the unload vascular volume by the instantaneous hydraulic servo control. The cuff pressure thus automatically controlled follows the intra-arterial pressure in the tail segment. The accuracy of this method was evaluated in comparison with direct measurement of blood pressure recorded simultaneously from 16 unanesthetized spontaneously hypertensive and normotensive rats. Close agreement between the simultaneous data from these two methods were observed.     

Biofeedback Training of Blood Pressure: A Comparison of Three Feedback Techniques

Three biofeedback procedures were compared for their effectiveness in training subjects to modify systolic blood pressure (BP). Three groups of 6 normotensives received three training sessions using one of three types of systolic BP feedback: 1) proportional feedback at 75-sec intervals, 2) relatively continuous proportional feedback, or 3) a form of continuous binary feedback. Three subjects also completed a fourth, no-feedback, session. Each session consisted of 5 training cycles, during which the subject was first instructed to “lower” BP and then “don't lower” BP. This design permitted demonstration of subjects' ability to control BP, rather than just lowering it. Systolic and diastolic BPs were recorded, as were heart rate, respiration rate and respiration volume. The continuous binary feedback technique was most successful in producing systolic BP control, apparently due to the short feedback latency and maximal information available to subjects. Diastolic BP often increased within sessions even when systolic BP decreased. No consistent covariation between BP and other physiological responses was observed, although at times these responses varied systematically with instruction. Continued systolic BP control at diminished levels was demonstrated by subjects who completed a fourth, no-feedback, session.     

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

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

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.     

一种袖带测量过程的物理模型及基于这种模型的新型收缩压测量方法的研究

传统的波动法血压无创测量技术由于利用了统计学原理，因此必然造成测量的个体误差。本文对袖带测量的物理过程进行了研究，在首先发明了袖带波动信号无失真提取技术的基础上，提出了一种袖带测量过程的物理模型，并对这一模型进行了证实。另外，根据这一模型提出了一种人体血压的无创测量方法，该方法不像传统方法那样采用统计学原理［１］，从而避免了所有个体采用统一的血压判据而导致的个体测量误差，实际实验表明，该技术的测量准确性要优于传统的波动法测量技术，这对改善医学临床血压无创自动测量技术的现状是有很大意义的     

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.