Direct effects in vivo of angiotensins I and II on the canine sinus node.

The chronotropic responses to angiotensins I and II (5 micrograms in 1 mL Tyrode's solution) injected into the sinus node artery were assessed before and after the intravenous administration of captopril (2 mg/kg) and saralasin (20 micrograms/kg) in anaesthetized dogs. The effects of angiotensin II given intravenously were also observed. The animals (n = 8) were vagotomized and pretreated with propranolol (1 mg/kg, i.v.) to prevent baroreceptor-mediated responses to increases in blood pressure. Injection of angiotensin I into the sinus node artery induced significant increases in heart rate (114 +/- 6 vs. 133 +/- 6 beats/min) and in systemic systolic (134 +/- 13 vs. 157 +/- 14 mmHg; 1 mmHg = 133.3 Pa) and diastolic (95 +/- 10 vs. 126 +/- 13 mmHg) blood pressures. Similar results were obtained when angiotensin II was injected into the sinus node artery, but intravenous injection induced changes in systolic (138 +/- 8 vs. 180 +/- 25 mmHg) and diastolic (103 +/- 8 vs. 145 +/- 20 mmHg) blood pressures only. Captopril induced a significant decrease in systolic (118 +/- 11 vs. 88 +/- 12 mmHg) and diastolic (84 +/- 9 vs. 59 +/- 9 mmHg) blood pressures without affecting the heart rate (109 +/- 6 vs. 106 +/- 6 beats/min). Saralasin produced a significant increase in systolic (109 +/- 7 vs. 126 +/- 12 mmHg) blood pressure only. Increments in heart rate and systolic and diastolic blood pressures in response to angiotensins I and II were, respectively, abolished by captopril and saralasin. It was concluded that angiotensin II has, in vivo, a direct positive chronotropic effect that can be blocked by saralasin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of direct and indirect blood pressure measurement in anesthetized dogs.

This study was conducted to determine whether blood pressures and pulse rate could be determined accurately by indirect measurements from the front and hind legs of 15- to 40-kg dogs anesthetized with isoflurane. Indirect measurements from each animal were compared to direct measurements obtained from a catheter placed into the abdominal aorta via the femoral artery at four ranges of systolic pressure. When systolic pressure was above 80 mm Hg, indirect measurements were either the same as direct measurements or slightly lower. However, when systolic pressures were below 80 mm Hg, indirect systolic pressure measurements were 6 to 15% higher than direct measurements. Larger differences in diastolic pressures were found, which resulted in differences in mean pressure. The most accurate measurements were found when the cuff width-to-limb circumference ratio was between 0.4 and 0.6 and when systolic pressure was between 80 and 100 mm Hg.     

Noninvasive measurement of blood pressure in African green monkeys (Cercopithecus aethiops)

Indirect measurements of arterial blood pressure were made in African green monkeys (Cercopithecus aethiops) employing a Doppler ultrasound stethoscope and standard cuff and an Infrasonde automatic blood pressure recorder. Measurements were obtained from anesthetized (10 mg/kg ketamine (HCI) and unanesthetized (1.5 mg/kg ketamine HCI) animals. Ketamine had no significant effect on blood pressure. Indirect measurements from the brachial artery were compared with direct femoral artery measurements and with each other. Systolic blood pressures measured by the Doppler (r = .948) and Infrasonde (r = .920) methods correlated closely with direct measurements but were significantly lower than systolic blood pressures measured by the direct method. Diastolic blood pressures measured by the Infrasonde method agreed closely with direct measurements (r = .947). Systolic blood pressures measured by the indirect methods correlated closely in both anesthetized (r = .973) and unanesthetized (r = .834) animals and were not significantly different. Mean blood pressures calculated from direct and Infrasonde measurements also correlated closely (r = .963), with direct measurements being 4 mmHg higher on the average. Mean blood pressures are less influenced by methodology and are more reproducible than other pressures. These noninvasive methods can be used to obtain simple and accurate measurements of blood pressure from anesthetized and unanesthetized monkeys and are of value in long-term studies in monkeys.     

Non-invasive blood pressure measurement in Yucatan miniature swine using tail cuff sphygmomanometry

A relatively new non-invasive method using a photo-electric flow sensor in non-heated animals, was evaluated for its accuracy in measuring systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) in 40-90 Kg normotensive and hypertensive Yucatan miniature swine. Directly measured SBP, DBP and electronically averaged MAP were recorded from chronic arterial catheters simultaneously with indirect pressures, cuff pressure and tail blood flow under various conditions. In all of the tests tail cuff SBP estimation averaged within 5% of directly measured SBP. The correlation of the two methods was significant (r = .95, P less than 0.01). Over a 60 to 202 mmHg range of blood pressure induced pharmacologically or due to DOCA hypertension, the tail cuff SBP was within 4-10% of directly measured SBP. The tail cuff method was also used to determine DBP and MAP. DBP determined from the tail cuff record was found consistently to underestimate the direct measured DBP by approximately 17%. The two methods were correlated (r = .87 P less than 0.01). The measured tail cuff MAP generally underestimated the direct MAP by approximately 5%. The correlation of directly measured MAP and tail cuff methods was significant (r = .72, P less than 0.01). These results indicated that this system may be used to accurately assess blood pressure in miniature swine.     

Venous occlusion plethysmography reduces arterial diameter and flow velocity

The measurement of peripheral blood flow by plethysmography assumes that the cuff pressure required for venous occlusion does not decrease arterial inflow. However, studies in five normal subjects suggested that calf blood flow measured with a plethysmograph was less than arterial inflow calculated from Doppler velocity measurements. We hypothesized that the pressure required for venous occlusion may have decreased arterial velocity. Further studies revealed that systolic diameter of the superficial femoral artery under a thigh cuff decreased from 7.7 +/- 0.4 to 5.6 +/- 0.7 mm (P less than 0.05) when the inflation pressure was increased from 0 to 40 mmHg. Cuff inflation to 40 mmHg also reduced mean velocity 38% in the common femoral artery and 47% in the popliteal artery. Inflation of a cuff on the arm reduced mean velocity in the radial artery 22% at 20 mmHg, 26% at 40 mmHg, and 33% at 60 mmHg. We conclude that inflation of a cuff on an extremity to low pressures for venous occlusion also caused a reduction in arterial diameter and flow velocity.     

Oscillometric measurement of systolic and diastolic blood pressures validated in a physiologic mathematical model

ABSTRACT: BACKGROUND: The oscillometric method of measuring blood pressure with an automated cuff yields valid estimates of mean pressure but questionable estimates of systolic and diastolic pressures. Existing algorithms are sensitive to differences in pulse pressure and artery stiffness. Some are closely guarded trade secrets. Accurate extraction of systolic and diastolic pressures from the envelope of cuff pressure oscillations remains an open problem in biomedical engineering. METHODS: A new analysis of relevant anatomy, physiology and physics reveals the mechanisms underlying the production of cuff pressure oscillations as well as a way to extract systolic and diastolic pressures from the envelope of oscillations in any individual subject. Stiffness characteristics of the compressed artery segment can be extracted from the envelope shape to create an individualized mathematical model. The model is tested with a matrix of possible systolic and diastolic pressure values, and the minimum least squares difference between observed and predicted envelope functions indicates the best fit choices of systolic and diastolic pressure within the test matrix. RESULTS: The model reproduces realistic cuff pressure oscillations. The regression procedure extracts systolic and diastolic pressures accurately in the face of varying pulse pressure and arterial stiffness. The root mean squared error in extracted systolic and diastolic pressures over a range of challenging test scenarios is 0.3 mmHg. CONCLUSIONS: A new algorithm based on physics and physiology allows accurate extraction of systolic and diastolic pressures from cuff pressure oscillations in a way that can be validated, criticized, and updated in the public domain.     

Central Pressure Appraisal: Clinical Validation of a Subject-Specific Mathematical Model

IntroductionCurrent evidence suggests that aortic blood pressure has a superior prognostic value with respect to brachial pressure for cardiovascular events, but direct measurement is not feasible in daily clinical practice.AimThe aim of the present study is the clinical validation of a multiscale mathematical model for non-invasive appraisal of central blood pressure from subject-specific characteristics.MethodsA total of 51 young male were selected for the present study. Aortic systolic and diastolic pressure were estimated with a mathematical model and were compared to the most-used non-invasive validated technique (SphygmoCor device, AtCor Medical, Australia). SphygmoCor was calibrated through diastolic and systolic brachial pressure obtained with a sphygmomanometer, while model inputs consist of brachial pressure, height, weight, age, left-ventricular end-systolic and end-diastolic volumes, and data from a pulse wave velocity study.ResultsModel-estimated systolic and diastolic central blood pressures resulted to be significantly related to SphygmoCor-assessed central systolic (r = 0.65 p <0.0001) and diastolic (r = 0.84 p<0.0001) blood pressures. The model showed a significant overestimation of systolic pressure (+7.8 (-2.2;14) mmHg, p = 0.0003) and a significant underestimation of diastolic values (-3.2(-7.5;1.6), p = 0.004), which imply a significant overestimation of central pulse pressure. Interestingly, model prediction errors mirror the mean errors reported in large meta-analysis characterizing the use of the SphygmoCor when non-invasive calibration is performed.ConclusionIn conclusion, multi-scale mathematical model predictions result to be significantly related to SphygmoCor ones. Model-predicted systolic and diastolic aortic pressure resulted in difference of less than 10 mmHg in the 51% and 84% of the subjects, respectively, when compared with SphygmoCor-obtained pressures.     

Individualization of transfer function in estimation of central aortic pressure from the peripheral pulse is not required in patients at rest

Central aortic pressure gives better insight into ventriculo-arterial coupling and better prognosis of cardiovascular complications than peripheral pressures. Therefore transfer functions (TF), reconstructing aortic pressure from peripheral pressures, are of great interest. Generalized TFs (GTF) give useful results, especially in larger study populations, but detailed information on aortic pressure might be improved by individualization of the TF. We found earlier that the time delay, representing the travel time of the pressure wave between measurement site and aorta is the main determinant of the TF. Therefore, we hypothesized that the TF might be individualized (ITF) using this time delay. In a group of 50 patients at rest, aged 28-66 yr (43 men), undergoing diagnostic angiography, ascending aortic pressure was 119 +/- 20/70 +/- 9 mmHg (systolic/diastolic). Brachial pressure, almost simultaneously measured using catheter pullback, was 131 +/- 18/67 +/- 9 mmHg. We obtained brachial-to-aorta ITFs using time delays optimized for the individual and a GTF using averaged delay. With the use of ITFs, reconstructed aortic pressure was 121 +/- 19/69 +/- 9 mmHg and the root mean square error (RMSE), as measure of difference in wave shape, was 4.1 +/- 2.0 mmHg. With the use of the GTF, reconstructed pressure was 122 +/- 19/69 +/- 9 mmHg and RMSE 4.4 +/- 2.0 mmHg. The augmentation index (AI) of the measured aortic pressure was 26 +/- 13%, and with ITF and GTF the AIs were 28 +/- 12% and 30 +/- 11%, respectively. Details of the wave shape were reproduced slightly better with ITF but not significantly, thus individualization of pressure transfer is not effective in resting patients.     

Cardiovascular and parasympathetic effects of dexmedetomidine in healthy subjects

We evaluated the cardiovascular effects of intravenously (i.v.) and buccally administered dexmedetomidine, a selective alpha2-adrenoceptor agonist. Six healthy male subjects were studied unmedicated and after 2 micro g/kg i.v. or buccal doses of dexmedetomidine, using repeated recordings of ECG and blood pressure. Cardiac parasympathetic activity was estimated by measurements of high-frequency (HF) heart rate variability. Intravenous, but not buccal, dexmedetomidine raised systolic blood pressure by 11 +/- 5 mmHg (mean +/- SEM) and diastolic by 16 +/- 3 mmHg (maxima at 10 min). Later on, both i.v., and buccal dexmedetomidine produced a very similar hypotensive effect: on average, >or=10 mmHg reductions in systolic and diastolic pressure at 3 h. Intravenous dosing was followed by a decline in heart rate (-11 +/- 2 beats/min) accompanied by a trend toward enhanced HF variability (maximal effect at 10 min), which probably reflected baroreflex-mediated parasympathetic efferent neuronal activation. Buccal dexmedetomidine increased significantly the HF variability (maximum at 45 min) without influencing heart rate. We conclude that dexmedetomidine, when administered by a method that avoids concentration peaks, e.g., buccal dosing, can be used to produce a prolonged augmentation of cardiac parasympathetic efferent neuronal activity.     

Subharmonic microbubble emissions for noninvasively tracking right ventricular pressures

Right heart catheterization is often required to monitor intra-cardiac pressures in a number of disease states. Ultrasound contrast agents can produce pressure modulated subharmonic emissions that may be used to estimate right ventricular (RV) pressures. A technique based on subharmonic acoustic emissions from ultrasound contrast agents to track RV pressures noninvasively has been developed and its clinical potential evaluated. The subharmonic signals were obtained from the aorta, RV, and right atrium (RA) of five anesthetized closed-chest mongrel dogs using a SonixRP ultrasound scanner and PA4-2 phased array. Simultaneous pressure measurements were obtained using a 5-French solid state micromanometer tipped catheter. Initially, aortic subharmonic signals and systemic blood pressures were used to obtain a calibration factor in units of millimeters of mercury per decibel. This factor was combined with RA pressures (that can be obtained noninvasively) and the acoustic data from the RV to obtain RV pressure values. The individual calibration factors ranged from -2.0 to -4.0 mmHg/dB. The subharmonic signals tracked transient changes in the RV pressures within an error of 0.6 mmHg. Relative to the catheter pressures, the mean errors in estimating RV peak systolic and minimum diastolic pressures, and RV relaxation [isovolumic negative derivative of change in pressure over time (-dP/dt)] by use of the subharmonic signals, were -2.3 mmHg, -0.8 mmHg, and 2.9 mmHg/s, respectively. Overall, acoustic estimates of RV peak systolic and minimum diastolic pressures and RV relaxation were within 3.4 mmHg, 1.8 mmHg, and 5.9 mmHg/s, respectively, of the measured pressures. This pilot study demonstrates that subharmonic emissions from ultrasound contrast agents have the potential to noninvasively track in vivo RV pressures with errors below 3.5 mmHg.     

Afterload and blood pressure amplitude in dilated cardiomyopathy]

The beat-to-beat variability of the diastolic blood pressure induces small variations in the afterload of the left ventricle. These variations influence myocardial contractility, and thus blood pressure amplitude. We assessed the interdependence of blood pressure and changes in the afterload. We continuously recorded blood pressure (duration 200 s, at rest) in 20 patients with dilated cardiomyopathy (ejection fraction 32 +/- 13%, left ventricular diameter 67 +/- 8 mm) and in 20 healthy volunteers. Interbeat intervals, diastolic pressures, systolic pressure amplitudes and mean slopes of systolic pressure amplitudes were measured. Correlation coefficients (r) were calculated to assess the interdependence of blood pressure amplitudes/mean systolic slopes and the preceding diastolic pressures/interbeat intervals, respectively. In healthy volunteers we found a strong interdependence between blood pressure amplitude and the preceding diastolic pressures (r = 0.62 +/- 0.21 and 0.47 +/- 0.22). Higher diastolic pressures were followed by higher blood pressure amplitudes, and by steeper slopes of the systolic peaks. In patients with dilated cardiomyopathy, such interdependence was significantly lower (r = 0.33 +/- 22 and r = 0.28 +/- 0.35), and in patients with severely reduced left ventricular function (ejection fraction < 32%) was only marginal (r = 0.23 +/- 0.27 and 0.21 +/- 0.44, respectively). The forces of the isovolumetric contraction necessary to initiate the ejection phase of the left ventricle depend on the afterload, i.e. on the diastolic pressure. The responses of amplitude and slope of the systolic blood pressure to small changes in the afterload make it possible to assess left ventricular contractility. The latter is impaired in dilated cardiomyopathy.     

A new method for measurement of blood pressure, heart rate, and activity in the mouse by radiotelemetry.

A simple and reliable means for accurate, chronic measurement of pulsatile blood pressure (BP) from conscious, freely moving laboratory mice was developed and validated. The newly developed device consists of a small (1.9 ml, 3.4 g), fully implantable radiotelemetry transmitter. Initial frequency response tests showed an adequate dynamic response; the average -3-dB point found in five transmitters was 145 +/- 14 (SD) Hz. BP, heart rate, and locomotor activity were recorded from 16 chronically (30-150 days) implanted mice. Mean arterial and pulse pressure, checked at regular intervals, ranged from 90-140 mmHg and from 30-50 mmHg, respectively, throughout the study. Transmitter BP measurements were validated against a Millar 1.4-Fr. transducer-tipped catheter. The mean error of the transmitters for diastolic pressures was +1.1 +/- 6.9 mmHg (n = 7). The error for systolic pressures was, on average, 2.7 +/- 3.9 mmHg larger. This new device accurately monitors BP, heart rate, and locomotor activity in conscious, untethered, freely moving mice living in their home cages for periods of at least 150 days.     

High altitude and blood pressure in children

We aimed to evaluate the blood pressure of children who had similar demographic characteristics but lived at different altitudes. Blood pressure of the children attending primary schools in Izmir (sea level: n = 425) and Van (altitude: 1725 m, n = 291) were measured by mercurial sphygmomanometer for this study. They were similar with respect to age, sex, weight, height, and BMI. Mean age of the children was 10.51 +/- 0.87 years (range: 9 to 12 years), and 358 (50 percent) of them were female. Mean systolic blood pressure was significantly higher in the children living in Van than in the children living in Izmir (104.72 +/- 11.2 vs. 97.96 +/- 25.5 mmHg, respectively, p < .001). Similarly mean diastolic blood pressure was significantly higher in the children living in Van than in the children living in Izmir (63.98 +/- 9.3 vs. 59.91 +/- 10.0 mmHg, respectively, p < .001). When blood pressure was evaluated with regard to height percentile, the number of children with a blood pressure over 90 percentile were 19 (4.5 percent) and 48 (16.5 percent) for systolic blood pressure, and 25 (5.9 percent) and 37 (12.7 percent) for diastolic blood pressure among the children living in Izmir and Van, respectively (p < .001). Systolic and diastolic blood pressures were found to increase in parallel to the increase in body mass index in children living in Van (r = 0.358, p < .001 and r = 0.235, p < .001, respectively). However, blood pressures were not correlated to body mass index in children living in Izmir. A difference of 1700 m in altitude was associated with higher systolic and diastolic blood pressure levels in children with similar demographic characteristics, and at this altitude, body mass index and blood pressure showed a positive correlation.     

Maternal blood pressure and fetal ultrasonography in normal baboon pregnancies

Pregnancy in baboons is characterized by lower systolic, diastolic, and mean blood pressures than in the nonpregnant state. As pregnancy progresses, diastolic and mean pressures tend to increase whereas systolic pressure remains low. Sonographic measurements of fetal growth follow a sigmoid pattern, but their increase in relation to length of gestation approximates a straight line between 6 and 21 weeks of gestation (23 to 84% of term).     

Venous cuff pressures from 30 mmHg to diastolic pressure are recommended to measure arterial inflow by plethysmography.

Venous occlusion strain gauge plethysmography (VOP) is based on the assumption that the veins are occluded and arterial inflow is undisturbed by the venous cuff pressure. Literature is not clear concerning the pressure that should be used. The purpose of this study was to determine the optimal venous occlusion pressure at which the highest arterial inflow is achieved in the forearm, calf, and leg by using VOP. We hypothesized that, for each limb segment, an optimal (range of) venous cuff pressure can be determined. Arterial inflow in each limb segment was measured in nine healthy individuals by VOP by using pressures ranging from 10 mmHg up to diastolic blood pressure. Arterial inflows were similar at cuff pressures between 30 and 60 mmHg for the forearm, leg, and calf. Arterial inflow in the forearm was significantly lower at 10 mmHg compared with the other cuff pressures. In addition, arterial inflows at 20 mmHg tended to be lower in each limb segment than flow at higher cuff pressures. In conclusion, no single optimum venous cuff pressure, at which a highest arterial inflow is achieved, exists, but rather a range of optimum cuff pressures leading to a similar arterial inflow. Venous cuff pressures ranging from 30 mmHg up to diastolic blood pressure are recommended to measure arterial inflow by VOP.     

Vagal cardiac function and arterial blood pressure stability

This study was designed to investigate the importance of vagal cardiac modulation in arterial blood pressure (ABP) stability before and after glycopyrrolate or atropine treatment. Changes in R-R interval (RRI) and ABP were assessed in 10 healthy young (age, 22 +/- 1.8 yr) volunteers during graded lower body negative pressure (LBNP) before and after muscarinic cholinergic (MC) blockade. Transient hypertension was induced by phenylephrine (1 microg/kg body wt), whereas systemic hypotension was induced by bilateral thigh cuff deflation after a 3-min suprasystolic occlusion. Power spectral densities of systolic [systolic blood pressure (SBP)] and diastolic ABP variability were examined. Both antimuscarinic agents elicited tachycardia similarly without significantly affecting baseline ABP. The increase in SBP after phenylephrine injection (+14 +/- 2 mmHg) was significantly augmented with atropine (+26 +/- 2 mmHg) or glycopyrrolate (+27 +/- 3 mmHg) and associated with a diminished reflex bradycardia. The decrease in SBP after cuff deflation (-9.2 +/- 1.2 mmHg) was significantly greater after atropine (-15 +/- 1 mmHg) or glycopyrrolate (-14 +/- 1 mmHg), with abolished reflex tachycardia. LBNP significantly decreased both SBP and RRI. However, after antimuscarinic agents, the reduction in SBP was greater (P < 0.05) and was associated with less tachycardia. Antimuscarinic agents reduced (P < 0.05) the low-frequency (LF; 0.04-0.12 Hz) power of ABP variability at rest. The LF SBP oscillation was significantly augmented during LBNP, which was accentuated (P < 0.05) after antimuscarinic agents and was correlated (r = -0.79) with the decrease in SBP. We conclude that antimuscarinic agents compromised ABP stability by diminishing baroreflex sensitivity, reflecting the importance of vagal cardiac function in hemodynamic homeostasis. The difference between atropine and glycopyrrolate was not significant.     

Labetalol: potent antihypertensive agent that blocks both alpha- and beta-adrenergic receptors.

Labetalol was administered as the sole antihypertensive agent to 20 ambulatory patients with mild to moderate hypertension. The mean systolic and diastolic blood pressures (+/- standard error of the mean) with the patients sitting fell significantly (P < 0.001), from 145.5 +/- 3.2 and 103.7 +/- 1.6 mm Hg respectively at the start of labetalol therapy (after a period free of antihypertensive medication) to 125.7 +/- 2.0 and 87.2 +/- 1.1 mm Hg by the end of the trial. The diastolic blood pressure was well controlled (90 mm Hg or less) with labetalol therapy in 90% of the patients. The medication was well tolerated, and no orthostatic fall in the diastolic blood pressure was observed. Pharmacologically labetalol most closely resembles a combination of a nonselective beta-adrenergic blocker like propranolol and a postsynaptic alpha-adrenergic blocker like prazosin.     

Catheterization of pulmonary artery in rats with an ultraminiature catheter pressure transducer

Utilizing new materials and miniaturization techniques, an ultraminiature catheter pressure transducer for catheterization of the pulmonary artery (PA) has been developed and applied in intact, spontaneously breathing, anesthetized rats. The catheter arrangement consists of three components: 1) an SPR-671 ultraminiature pressure transducer (measuring catheter), 2) a plastic introducer (sheath) that is slipped over the measuring catheter, and 3) an external wire mounted on the outside of the introducer for bending its tip. The measuring catheter is first inserted through the right jugular vein into the right ventricle. The introducer is then slipped over it. The tip of the introducer is bent so that there is an angle of approximately 90 degrees or less to the shaft. The measuring catheter is advanced across the pulmonary valve into the PA. Measurements of pulmonary arterial pressure were made in five male Long Evans (364 +/- 7 g body wt) and five female Sprague-Dawley (244 +/- 7 g body wt) rats under control conditions. The effects of infusion of norepinephrine (0.1 mg.kg(-1).h(-1) iv for 20-min duration) were tested in Long Evans rats. Pulmonary arterial systolic pressure measurements were 34.0 +/- 0.8 and 29.5 +/- 0.4 mmHg, and diastolic pressure values were 23.6 +/- 0.8 and 18.1 +/- 0.6 mmHg in male Long Evans and female Sprague-Dawley rats, respectively. Norepinephrine induced an increase in pulmonary arterial systolic (40.8 +/- 0.1 mmHg) and diastolic (28.6 +/- 0.4 mmHg) pressures and an elevation in pulmonary vascular resistance from a control value of 0.093 +/- 0.003 to 0.103 +/- 0.004 mmHg.kg.min.ml(-1).     

Non-invasive model-based estimation of aortic pulse pressure using suprasystolic brachial pressure waveforms

Elevated central arterial (aortic) blood pressure is related to increased risk of cardiovascular disease. Methods of non-invasively estimating this pressure would therefore be helpful in clinical practice. To achieve this goal, a physics-based model is derived to correlate the arterial pressure under a suprasystolic upper-arm cuff to the aortic pressure. The model assumptions are particularly applicable to the measurement method and result in a time–domain relation with two parameters, namely, the wave propagation transit time and the reflection coefficient at the cuff. Central pressures estimated by the model were derived from completely automatic, non-invasive measurement of brachial blood pressure and suprasystolic waveform and were compared to simultaneous invasive catheter measurements in 16 subjects. Systolic blood pressure agreement, mean (standard deviation) of difference was ?1 (7) mm Hg. Diastolic blood pressure agreement was 4 (4) mm Hg. Correlation between estimated and actual central waveforms was greater than 90%. Individualization of model parameters did not significantly improve systolic and diastolic pressure agreement, but increased waveform correlation. Further research is necessary to confirm that more accurate brachial pressure measurement improves central pressure estimation.     

Biofeedback of R-wave-to-pulse interval normalizes blood pressure

We investigated whether biofeedback of the R-wave-to-pulse interval, a measure related to the pulse wave velocity, enables participants with either high or low arterial blood pressure to modify their blood pressure. Twelve participants with high blood pressure (mean systolic blood pressure = 142.6 ± 13.5 mmHg; mean diastolic blood pressure = 99.9 ± 12.3 mmHg) and 10 participants with low blood pressure (mean systolic blood pressure = 104.8 ± 6.6 mmHg; mean diastolic blood pressure = 73.2 ± 4.2 mmHg) received 3 individual sessions of RPI biofeedback within a 2-week period. Participants with high blood pressure were rewarded for decreasing and participants with low blood pressure for increasing their blood pressure. Standard arm-cuff blood pressure measurements across the sessions served as dependent variables. Participants with high blood pressure achieved significant reductions of systolic (15.3 mmHg) and diastolic (17.8 mmHg) blood pressure levels from the beginning of the first to the end of the last training session. In contrast, participants with low blood pressure achieved significant increases in systolic (12.3 mmHg) and diastolic (8.4 mmHg) blood pressure levels. The degree of blood pressure changes in this study might be of clinical relevance. With prolonged and refined training regimens, even larger effects seem to be likely.