The technique of detecting systolic and diastolic pressure from the transducer output of a PC-based blood pressure monitoring system

A pressure to voltage transducer is used along with a cuff, in a PC-based blood pressure and pulse rate monitoring system for human body. During the blood pressure measurement cycle, the output voltage of the pressure to voltage transducer is recorded digitally using a data acquisition system. The recorded data are then analyzed using software routines to determine the blood pressure and pulse rate of the person under test. However, it is difficult to identify the points of systole and diastole correctly from the recorded data. This paper presents the technique that may be used to determine the systolic and diastolic pressure from the collected data.     

A simple method for obtaining blood pressure in rhesus monkeys (Macaca mulatta).

A relatively simple procedure was devised to obtain blood pressures in rhesus monkeys. This procedure utilized a polygraph, pulse transducer, pressure transducer, blood pressure mixer unit, and pediatric sphygmomanometer cuff. Previous attempts to auscultate the Korotkoff sounds by use of a sphygmomanometer cuff and stethoscope were unsuccessful. Blood pressure can be obtained by cannulation of the femoral artery, but repeated puncture may cause serious trauma to the arterial wall. This procedure was developed and used in our laboratory to obtain repeated blood pressures over a 90-da period. Results from using the cuff and polygraph have been shown to correlate favorably with cannulation of the femoral artery.     

Blood pressure and heart rate determination by radiotelemetry in mice

Mice are not commonly used in cardiovascular physiology, especially in space physiology because of methodological problems. The initial studies that have monitored arterial pressure and heart rate in mice used the tail cuff plethysmography method or classical catheterization techniques with a catheter liable to an external pressure transducer. But for long term arterial pressure measurements the studies have been facilitated by the development of radiotelemetry. This is a less constraining method as classical one allowing to monitor in continuous in freely moving animal blood pressure, heart rate and temperature. This technique allows to record these parameters thank to an implanted transmitter without physical connection with the monitoring system. The aim of this work was to valid the use of the radiotelemetry in mice to evaluate arterial blood pressure and heart rate during different stress conditions (but only control data are described in this paper).     

Model for post-occlusive reactive hyperemia as measured noninvasively with pressure pulse waveform

Post-occlusive reactive hyperemia is a noninvasive maneuver to assess microvascular reactivity related to the bioavailability and/or bioactivity of endothelial-derived factors. The inability to respond to endogenous vasodilator substances is mostly described by a low peak flow after an event associated with a peak flow. The aim of this study is to propose a model to describe post-occlusive responses observed in the pressure waveforms after occlusion release. Model variables were investigated in search of those representatives of the endothelial response to the ischemic process. Radial pressure pulse waveforms were acquired in the anterior region of the wrist, superficial to the radial artery, using a piezoelectric transducer acquired by a 12 bits acquisition board model at a sampling rate of 1.0 kHz to increase the temporal resolution. The occlusion maneuver was performed using an arm-cuff placed over the brachial artery. A time series of pulse pressure (PP) values, calculated from successive values of beat-to-beat systolic and diastolic pressures, was found to be a useful variable representing blood pressure signal in the model. This data time series of the pulse pressure presents reduced initial values compared with the baseline measurement, and an increasing value until a steady state behavior was sustained after approximately 60 s. This behavior for the pulse pressure series was described by a hyperbolic tangent model with parameters K (rate of change of PP), PP₀ (first value of PP after cuff release), and ΔPP (change in PP). The model was applied to pulse pressure signals from normotensive and hypertensive subjects. The observed responses between groups suggest that PP₀ and ΔPP are related to an endothelial response to the ischemic process and could be used as a clinical tool to assess endothelial function in hypertension.     

Telemetered epidural pressure.

An implantable transducer capable of telemetering epidural brain pressure during long periods of time is described. The transducer is constructed from conventionally available materials, and routine workshop techniques are used. The coplanarity principle has been applied while the described mounting clamp allows discrete positioning of the transducer relative to the brain. Basically, the transducer consists of a coil-capacitor circuit in which alterations of epidural pressure induce changes in capacity and, thus, the transducer's resonance frequency. An external electromagnetically coupled impedance-measuring device converts the resonance frequency to a pressure analogous voltage. In vitro tests showed that the transducer had good accuracy and reliability for a period of more than 1 month. An in vivo experiment with a cat showed that the measured epidural pressure was linearly related to ventricular fluid pressure.     

Noninvasive pressure pulse waveform analysis of flow-mediated vasodilation evoked by post-occlusive reactive hyperemia maneuver

Post-occlusive reactive hyperemia (PORH) assesses flow-mediated vasodilation at microvascular level due to bioactivity of endothelial-derived factors. Ordinary augmentation index that quantifies endothelial response is based on an ensemble-averaged waveform that limits its short-time application. This study proposes a mathematical model and two corresponding indices to evaluate arterial pressure response after blood flow restoration. Radial pressure pulse waveforms were acquired by a 12 bits acquisition board at a sampling rate of 1.0 kHz using a piezoelectric transducer. Signals were stored during 30 s at baseline condition and 60 s after 5-min occlusion using an arm-cuff placed over the brachial artery. In both conditions, the pressure pulse waveform presents systolic and diastolic phases with progressive and regressive pulse waveforms, respectively. Changes in pulse wave morphology were also observed and comprised attenuation of the pulse pressure amplitude (markedly first and second systolic peaks). This characteristic of the pulse pressure was described by the time-domain summation of two pairs of Gaussian-like waveforms (representing independent progressive and regressive components) with parameters related to amplitude, time lag, and duration for each component. A steepest descent optimization routine was used to fit the model parameters to experimental data of normotensive and subjects with hypertension. The optimized parameters were used to calculate two indices, RIx_1,2 (second-to-first systolic peak ratio) and RIx_1,3 (first diastolic-to-first systolic ratio). The observed responses between groups suggest that RIx_1,2 is related to an endothelial response to the ischemic process and could be used as a clinical tool to assess endothelial function in hypertension.     

Comparison of simultaneous measurement of mouse systolic arterial blood pressure by radiotelemetry and tail-cuff methods

Radiotelemetry of mouse blood pressure accurately monitors systolic pressure, diastolic pressure, heart rate, and locomotor activity but requires surgical implantation. Noninvasive measurements of indirect systolic blood pressure have long been available for larger rodents and now are being reported more frequently for mice. This study compared mouse systolic arterial blood pressure measurements using implanted radiotelemetry pressure transducer with simultaneous tail-cuff measurements in the same unanesthetized mice. The pressure range for comparison was extended by inducing experimental hypertension or by observations of circadian elevations between 3 AM and 6 AM. Both trained and untrained tail-cuff operators used both instruments. Every effort was made to follow recommended manufacturer's instructions. With the initial flow-based tail-cuff instrument, we made 671 comparisons (89 sessions) and found the slope of the linear regression to be 0.118, suggesting poor agreement. In an independent assessment, 277 comparisons (35 sessions) of radiotelemetry measurements with the pulse based tail-cuff instrument were made. The slope of the linear regression of the simultaneous measurements of systolic pressures was 0.98, suggesting agreement. Bland-Altman analysis also supported our interpretation of the linear regression. Thus although reliable systolic pressure measurements are possible with either tail-cuff or radiotelemetry techniques, in our hands some tail-cuff instruments fail to accurately detect elevated blood pressures. These data, however, do not distinguish whether this instrument-specific tail-cuff failure was due to operator or instrument inadequacies. We strongly advise investigators to obtain an independent and simultaneous validation of tail-cuff determinations of mouse blood pressure before making critical genotyping determinations.     

The relationship between body mass index, blood pressure and pulse rate among normotensive and hypertensive participants in the third National Health and Nutrition Examination Survey (NHANES).

Obesity is associated with high insulin and leptin levels. Studies also suggest that high levels of insulin and leptin increase sympathetic nervous system (SNS) activity and engender increased chronotropy, vasoconstriction and antinatriuresis that may contribute to the pathogenesis of obesity related hypertension. Sympathetic modulation of cardiovascular responses requires good baroreceptor sensitivity and optimal vascular compliance. The vascular changes associated with isolated systolic hypertension (ISH) have been shown to modify baroreceptor sensitivity and vascular compliance and may mitigate sympathetic modulation of cardiovascular responses and attenuate the hypertensive effect of obesity. The purpose of this study is to examine the differences in the relationship between body mass index, pulse rate (PR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) among participants with normal blood pressure and ISH using data from the third National Health and Nutrition Examination Survey. Data from 13,761 non-institutionalized adults 18 years and older not receiving antihypertensive therapy were analyzed. Results showed that PR, SBP and DBP increase with increasing BMI. The rise in PR, SBP and DBP with BMI is higher among participants with normal blood pressure than among those with ISH. We concluded that increasing level of obesity is associated with a rise in pulse rate and blood pressure but the effect of obesity on blood pressure and pulse rate might be weaker among participants with ISH.     

Role of the renal nerves in blood pressure in male and female SHR

Female spontaneously hypertensive rats (SHR) have lower blood pressures than males. The renin-angiotensin system plays an important role in the sexual dimorphism of blood pressure in SHR. The sympathetic nervous system can stimulate renin release, and, therefore, the present study was performed to determine whether the renal sympathetic nerves play a role in the sexual dimorphism of blood pressure in SHR. Male and female SHR underwent bilateral kidney denervation or sham surgery, and, 2 wk later, mean arterial pressure (MAP) and pulse interval were recorded, and baroreflex sensitivity (BRS) was measured by the sequence technique. Left ventricle index (LVI) was also calculated. MAP was higher in sham-operated males than females (182 +/- 5 vs. 169 +/- 4 mmHg; P < 0.01), but, despite the higher MAP in males, LVI was significantly greater in female rats. BRS was not different between sham-operated male and female SHR. Following bilateral renal denervation, MAP was decreased by a similar percentage (8-10%) in males (169 +/- 2 mmHg) and females (152 +/- 3 mmHg), whereas LVI was reduced only in female SHR. BRS was not altered by renal denervation in either sex. These data indicate that renal nerves play a role in the control of blood pressure in SHR independent of sex, but do not play a role in mediating the sex differences in blood pressure.     

Lowering of blood pressure in hypertensive rats by SKF 64139 and SKF 72223

The effects of a centrally acting phenylethanolamine N-methyl-transferase (PNMT) inhibitor, SKF 64139, and of its analog, SKF 72223, which is devoid of PNMT inhibitory activity on blood pressure and heart rate, were investigated in spontaneously hypertensive rats (SHR) and in DOCA-salt hypertensive rats. SKF 64139 lowers blood pressure and decreases pulse rate, while SKF 72223 lowers blood pressure and transiently increases pulse rate in SH-rats and in DOCA-salt hypertensive rats. SKF 72223 has no effect on blood pressure or heart rate in normotensive Wister-Kyoto rats. These results suggest that the antihypertensive action elicited by these two tetrahydroisoquinoline (TIQ) derivatives is not due to lowering of central epinephrine (E) levels. To determine whether the cardiovascular response elicited by SKF 72223 is due to stimulation of presynaptic alpha 2-adrenoreceptors, or to blockade of alpha 1-adrenoreceptors, we have examined its effect in combination with the partial alpha 2-agonist clonidine, or with the alpha 1-antagonist prazosin. The administration of clonidine slightly decreases the antihypertensive action of SKF 72223. The clonidine induced reduction in pulse rate is reversed by SKF 72223. In animals pretreated with prazosin, SKF 72223 elicits an additional decrease in blood pressure. Since SKF 64139 and SKF 72223 interact with alpha 2-adrenoreceptors, it is suggested that blockade of peripheral vascular alpha 2-adrenoreceptors might be in part responsible for their antihypertensive action. However, the antihypertensive action of these two drugs might also be due to some central mechanisms.     

Pulse wave analysis as an experimental tool to clinical application: past and present (review)

Pulse examination by palpation of a peripheral artery against a bony prominence is the most commonly used and widely accepted method. However this is subjective and thus prone to errors. Although pulse waveform was recorded in the 19th century, it did not gain popularity because of inconvenience in using the recording instruments and the absence of a sound theory to explain the wave forms recorded. Sphygmomanometry for recording blood pressure gained popularity as it was easy to record and had a sound theoretical background. Sphygmomanometry provides two extreme values of blood pressure but does not give a true representation of the blood pressure changes occurring in the entire cardiac cycle. Recently there has been resurgence in the analysis of the graphical recording of the pulse wave. Photoplethysmography is becoming a widely accepted technique in assessing the volume pulse. The whole review is about historical background, non-invasive methods of pulse recording, relation of the digital volume pulse to the pressure pulse and the advantages of recording the pressure pulse.     

Exercise reduces arterial pressure augmentation through vasodilation of muscular arteries in humans

Exercise markedly influences pulse wave morphology, but the mechanism is unknown. We investigated whether effects of exercise on the arterial pulse result from alterations in stroke volume or pulse wave velocity (PWV)/large artery stiffness or reduction of pressure wave reflection. Healthy subjects (n = 25) performed bicycle ergometry. with workload increasing from 25 to 150 W for 12 min. Digital arterial pressure waveforms were recorded using a servo-controlled finger cuff. Radial arterial pressure waveforms and carotid-femoral PWV were determined by applanation tonometry. Stroke volume was measured by echocardiography, and brachial and femoral artery blood flows and diameters were measured by ultrasound. Digital waveforms were recorded continuously. Other measurements were made before and after exercise. Exercise markedly reduced late systolic and diastolic augmentation of the peripheral pressure pulse. At 15 min into recovery, stroke volume and PWV were similar to baseline values, but changes in pulse wave morphology persisted. Late systolic augmentation index (radial pulse) was reduced from 54 +/- 3.9% at baseline to 42 +/- 3.7% (P < 0.01), and diastolic augmentation index (radial pulse) was reduced from 37 +/- 1.8% to 25 +/- 2.9% (P < 0.001). These changes were accompanied by an increase in femoral blood flow (from 409 +/- 44 to 773 +/- 48 ml/min, P < 0.05) and an increase in femoral artery diameter (from 8.2 +/- 0.4 to 8.6 +/- 0.4 mm, P < 0.05). In conclusion, exercise dilates muscular arteries and reduces arterial pressure augmentation, an effect that will enhance ventricular-vascular coupling and reduce load on the left ventricle.     

Influence of 50-Hz electric and magnetic fields on human blood pressure

This investigation studied the effects of 50-Hz electric and magnetic fields on the pulse rate and blood pressure in humans. Electrocardiograms (ECG) and the blood pressure of 41 male volunteers were recorded using ambulatory methods. Twenty-six subjects were measured in and outside real fields and 15 subjects in and outside `sham' fields. The results of the ECG recordings have been presented earlier. This article deals with the analysis of the blood pressure measurements. Measurement took 3 hrs. First, the subjects spent 1 h outside the fields, then 1 h in real or `sham' fields, followed by 1 h outside the fields. The electric field strength varied from 3.5 to 4.3 kV/m and the magnetic flux density from 1.4 to 6.6 μT. When analysing the blood pressure, which was measured with a non-invasive cuff method, it could not be shown that the fields (<4.3 kV/m and <6.6 μT) affected diastolic or systolic blood pressure. Received: 6 June 1994 / Accepted in revised form: 11 March 1996     

Effect on intra-arterial blood pressure of slow release metoprolol combined with placebo or chlorthalidone.

Thirty patients with essential hypertension participated in a double blind crossover trial in which they were randomly allocated to treatment with either once daily slow release metoprolol (200 mg) with placebo or once daily slow release metoprolol (200 mg) with chlorthalidone (25 mg). Ambulatory intra-arterial blood pressure was recorded continuously for 24-48 hours before treatment and two months after each change in regimen. The response of blood pressure and pulse rate to a standard exercise protocol that included supine rest and tilt, isometric, and dynamic bicycle exercise was measured during the same recording periods. Both treatments appreciably reduced blood pressure and pulse rate; mean daytime intra-arterial blood pressure was reduced from 174/95 mm Hg to 158/85 mm Hg by metoprolol plus placebo and to 143/78 mm Hg by metoprolol plus chlorthalidone. This reduction with the combined treatment was significantly greater than with metoprolol and placebo (p systolic = 0.001, p diastolic = 0.004). Mean night time pressures were reduced from 148/78 mm Hg to 139/75 mm Hg by metoprolol plus placebo and to 116/61 mm Hg by metoprolol plus chlorthalidone. Again the reduction in blood pressure was significantly greater with combined treatment (p less than 0.001) than with metoprolol plus placebo. Once daily slow release metoprolol is effective in controlling blood pressure, but this effect is greatly enhanced by the addition of a diuretic.     

Microwave-induced pressure waves in a model of muscle tissue

Microwave-induced mechanical stress waves were studied in simulated muscle tissue. Pulsed microwave energy at 5.655 GH_z induced pressure waves that were recorded with a hydrophone transducer. Each pulse produced a peak power density greater than 1.5 kW/cm². Microwave absorption measurements within the model showed energy deposition to be mostly confined to a region within 2 cm of the irradiated surface. The average specific absorption rate (SAR) at the surface of the sample was about 100 W/kg. The microwave-induced stress wave propagated at a velocity of 1,600 m/sec with peak pressures of approximately 300 pascals and was detectable after having traveled a total distance of 0.61 m on a path that included two reflections at model-container interfaces.     

Pulse Wave Velocity Testing in the Baltimore Longitudinal Study of Aging

Carotid-femoral pulse wave velocity is considered the gold standard for measurements of central arterial stiffness obtained through noninvasive methods¹. Subjects are placed in the supine position and allowed to rest quietly for at least 10 min prior to the start of the exam. The proper cuff size is selected and a blood pressure is obtained using an oscillometric device. Once a resting blood pressure has been obtained, pressure waveforms are acquired from the right femoral and right common carotid arteries. The system then automatically calculates the pulse transit time between these two sites (using the carotid artery as a surrogate for the descending aorta). Body surface measurements are used to determine the distance traveled by the pulse wave between the two sampling sites. This distance is then divided by the pulse transit time resulting in the pulse wave velocity. The measurements are performed in triplicate and the average is used for analysis.     

Transducer for monitoring respiration during imaging procedures

A transducer system for monitoring respiration is described; it uses a ‘liquid column’ sensor with a remote integrated circuit pressure module. It was designed primarily for non-invasive monitoring and control of respiration during diagnostic imaging procedures, but has also found applications in other areas, e.g. physiotherapy and pulse monitoring. The device is a new version of a system developed several years ago and takes advantage of relatively low cost commercial ‘building blocks’. The output is an analogue voltage (from a low impedance source) capable of driving a wide range of recorders, amplifiers and computer interfaces. Reference is also made in the text to a bio-feedback signal processing and display unit (described elsewhere) which, when used with this transducer, provides a versatile respiratory control system.     

Velocity pulse advances pressure pulse by close to 45 degrees in the rat pial arterioles

In order to clarify the phase relationship between velocity pulse and pressure pulse propagating along microvessels, the red cell velocity and intravascular pressure were simultaneously measured in the rat pial arterioles of 41-53 microm in diameter with a high temporal resolution by a laser-Doppler anemometer and a servo-null micropressure system. It was found that the velocity pulse preceded the pressure pulse in all the measured arterioles by 18.7-35.6 ms. The corresponding phase difference was 43.6+/-6.9 degrees (mean +/- SD), which is not statistically different from 45 degrees. The value is consistent with the phase difference predicted for the blood flow in microvessels with a small reflection coefficient at frequencies as low as the heart rate of the rats. The present results suggest that the upstream changes in blood flow are transmitted by the velocity pulse faster than by the pressure pulse in the microvasculature.     

Evaluation of a new tail-cuff method for blood pressure measurements in rats with special reference to the effects of ambient temperature

We evaluated a recently developed tail-cuff apparatus for the indirect blood pressure measurement in rats with special reference to the effects of ambient temperature. For this purpose, we designed two preparations 1) an intact preparation to determine the effect of ambient temperature on blood pressure measurements and 2) an anesthetized and catheterized preparation for comparison of the values of blood pressure obtained by the indirect and by the direct method. This apparatus also required enough pulse volume oscillations to measure the accurate value of blood pressure. Sufficient pulse volume oscillations were obtained within 20 min at 30 and 40 degrees C. At 40 degrees C, the values of blood pressure, pulse rate and rectal temperature were significantly higher than those at 30 degrees C. Correlation between blood pressure and rectal temperature was significant, and blood pressure increased with rectal temperature dependently. The values of the indirect measurement were close to the values measured directly, and these correlations were highly significant. Thus, we showed the effects of temperature for indirect blood pressure measurement. This tail-cuff apparatus could measure the accurate value of indirect blood pressure without thermal stress at 30 degrees C.     

Non-invasive quantification of peripheral arterial volume distensibility and its non-linear relationship with arterial pressure

Arterial wall function is associated with different physiological and clinical factors. Changes in arterial pressure cause major changes in the arterial wall. This study presents a simple non-invasive method to quantify arterial volume distensibility changes with different arterial pressures.The electrocardiogram, finger and ear photoplethysmogram were recorded from 15 subjects with the right arm at five different positions (90°, 45°, 0°, ?45° and ?90° referred to the horizontal level). Arm pulse propagation time was determined by subtracting ear pulse transit time from finger pulse transit time, and was used to obtain arterial volume distensibility. The mean arterial blood pressure with the arm at the horizontal level was acquired, and changes with position were calculated using the hydrostatic principle that blood pressure in the arm is linearly related to its vertical distance from the horizontal level.The mean arm pulse propagation times for the five different positions were 88, 72, 57, 54 and 52 ms, with the corresponding mean arterial volume distensibility of 0.234%, 0.158%, 0.099%, 0.088% and 0.083% per mmHg. For all consecutive changes in arm position, arm pulse propagation time and arterial volume distensibility, were significantly different (all probability P<0.05). The slopes of arm pulse propagation time and arterial volume distensibility against arterial pressure decreased significantly between each consecutive arm position from 90° to ?45° (all P<0.01), indicating significant non-linearity.The experimental results fitted the physiological exponential model and Langewouters’ arctangent model well, and were also comparable to published data with arterial volume distensibility approximately tripling for transmural pressure changes from 101 to 58 mmHg.In conclusion, the inverse and non-linear relationship between arterial volume distensibility and arterial pressure has been quantified using a simple arm positioning procedure, with the greatest effect at low pressures. This work is an important step in developing a simple non-invasive technique for assessing peripheral arterial volume distensibility.