Automatic noninvasive measurement of systolic blood pressure using photoplethysmography

Background

Systolic blood flow has been simulated in the abdominal aorta and the superior mesenteric artery. The simulations were carried out using two different computational hemodynamic methods: the finite element method to solve the Navier Stokes equations and the lattice Boltzmann method.

Results

We have validated the lattice Boltzmann method for systolic flows by comparing the veloCity and pressure profiles of simulated blood flow between methods. We have also analyzed flow-specific characteristics such as the formation of a vortex at curvatures and traces of flow.

Conclusion

The lattice Boltzmann Method is as accurate as a Navier Stokes solver for computing complex blood flows. As such it is a good alternative for computational hemodynamics, certainly in situation where coupling to other models is required.     

Effect of eicosapentaenoic acid on central systolic blood pressure

Central systolic blood pressure (C-SBP) has been shown to be a better predictor of cardiovascular risk than brachial SBP. In this study, the effects of eicosapentaenoic acid (EPA) on C-SBP were compared with pravastatin. Twenty-four patients with hyperlipidemia were assigned 13 to receive 1800 mg/day EPA (EPA group) and 11 to receive 10 mg/day pravastatin (pravastatin group) for 3 months. In the EPA group, there were no changes in the LDL–cholesterol level. However, the radial augmentation index (AI) and C-SBP decreased after treatment by 5.7% (p<0.01) and 8.7% (p<0.001), respectively. Moreover, systolic and diastolic brachial BPs decreased by 7.1% and 8.0%, respectively (p<0.01 for both). In the pravastatin group, the LDL–cholesterol level decreased by 29.5% (p<0.001). However, there were no significant changes in brachial BP, AI and C-SBP between. These results suggested that EPA but not pravastatin may reduce cardiac afterload by reducing vascular reflected waves and lowering C-SBP.     

Automatic noninvasive measurement of systolic blood pressure using photoplethysmography

Background  

Automatic measurement of arterial blood pressure is important, but the available commercial automatic blood pressure meters, mostly based on oscillometry, are of low accuracy.     

Excess diet copper increases systolic blood pressure in rats

Twenty Wistar and 20 Spontaneously Hypertensive Rats were divided into two diet copper intake groups at 5 wk of age. One group was fed 18 mg Cu as cupric carbonate/kg feed and the other group 100 mg Cu/kg feed. The basal diet was formulated after the AIN-76 diet. Animals were fed their respective diets until 20 wk of age. At age 8, 14, and 20 wk rats were placed in metabolic cages and food and water consumption as well as urine output were quantitated. Systolic blood pressures were measured triweekly by the tail-cuff method. Rats fed 100 mg Cu/kg feed showed an increase in systolic pressure compared to rats fed 18 mg Cu/kg feed. The increase was more pronounced for the Wistar strain. Body weights, urine output, and feed and water consumption did not differ (p>0.05) by copper intake. Rats fed 100 mg Cu/kg feed did have greater hemoglobin levels. Heart: body and liver: body weight strain differences were apparent. This study demonstrated increased blood pressure in rats fed excess diet copper.     

Thermal stress elevates the systolic blood pressure of spontaneously hypertensive rats

The effect of thermal stress on the systolic blood pressure of spontaneously hypertensive rats (SHR) and normotensive rats (WKY) of the Wistar/Kyoto strain was compared using our newly-developed indirect method which does not require heating of the animal to measure its blood pressure. The blood pressure of SHR increased significantly at 30°C and reached a maximum increase of about 20% at 32°C in 16 minutes in spite of the fact that the heart rate was decreased. In contrast to SHR, the systolic pressure of WKY did not change significantly after 30 minutes at 34°C or 36°C.     

Learned control of systolic blood pressure raising and lowering in rhesus monkeys

Three male monkeys (Macaca mulatta) were operantly conditioned to raise and lower systolic blood pressure (SP). All animals were trained in three stages: first to lower, then to raise systolic pressure, and finally to alternate these two behaviors. All monkeys learned the task and performed reliably in all stages. Diastolic pressure (DP) usually paralleled systolic pressure but changed much less than SP. Heart rate (HR) always fell below baseline in lowering sessions, and in two of the three animals during raising sessions as well. These findings support our earlier results which showed that monkeys could learn to control heart rate. This animal model should permit detailed studies of the hemodynamic mechanisms mediating learned control of systolic pressure.     

The sex-specific impact of systolic hypertension and systolic blood pressure on arterial-ventricular coupling at rest and during exercise

In healthy subjects the arterial system and the left ventricle (LV) are tightly coupled at rest to optimize cardiac performance. Systolic hypertension (SH) is a major risk factor for heart failure and is associated with structural and functional alterations in the arteries and the LV. The effects of SH and resting systolic blood pressure (SBP) on arterial-ventricular coupling (E(a)I/E(LV)I) at rest, at peak exercise, and during recovery are not well described. We noninvasively characterized E(a)I/E(LV)I as end-systolic volume index/stroke volume index in subjects who were normotensive (NT, n = 203) or had SH (brachial SBP > or =140 mmHg, n = 79). Cardiac volumes were measured at rest and throughout exhaustive upright cycle exercise with gated blood pool scans. E(a)I/E(LV)I reserve was calculated by subtracting peak from resting E(a)I/E(LV)I. At rest, E(a)I/E(LV)I did not differ between SH and NT men but was 23% (P = 0.001) lower in SH vs. NT women. E(a)I/E(LV)I did not differ between SH and NT men or women at peak exercise or during recovery. Nevertheless, E(a)I/E(LV)I reserve was 61% (P < 0.001) lower in SH vs. NT women. Similarly, resting SBP (as a continuous variable) was not associated with E(a)I/E(LV)I in men (beta = -0.12, P = 0.17) but was inversely associated with E(a)I/E(LV)I in women (beta = -0.47, P < 0.001). SH and a higher resting brachial SBP are associated with a lower E(a)I/E(LV)I at rest in women but not in men, and SH women have an attenuated E(a)I/E(LV)I reserve. Whether a smaller E(a)I/E(LV)I reserve leads to functional limitations warrants further examination.     

Genome-wide linkage scan for genes affecting longitudinal trends in systolic blood pressure

Only one genome scan to date has attempted to make use of the longitudinal data available in the Framingham Heart Study, and this attempt yielded evidence of linkage to a gene for mean systolic blood pressure. We show how the additional information available in these longitudinal data can be utilized to examine linkages for not only mean systolic blood pressure (SBP), but also for its trend with age and its variability. Prior to linkage analysis, individuals treated for hypertension were adjusted to account for right-censoring of SBP. Regressions on age were fitted to obtain orthogonal measures of slope, curvature, and residual variance of SBP that were then used as dependent variables in the model-free linkage program SIBPAL. We included mean age, gender, and cohort as covariates in the analysis. To improve power, sibling pairs were weighted for informativity using weights derived from both the marker and trait. The most significant results from our analyses were found on chromosomes 12, 15, and 17 for mean SBP, and chromosome 20 for both SBP slope and curvature.     

Association of interarm systolic blood pressure difference with atherosclerosis and left ventricular hypertrophy

An interarm systolic blood pressure (SBP) difference of 10 mmHg or more have been associated with peripheral artery disease and adverse cardiovascular outcomes. We investigated whether an association exists between this difference and ankle-brachial index (ABI), brachial-ankle pulse wave velocity (baPWV), and echocardiographic parameters. A total of 1120 patients were included in the study. The bilateral arm blood pressures were measured simultaneously by an ABI-form device. The values of ABI and baPWV were also obtained from the same device. Clinical data, ABI<0.9, baPWV, echocariographic parameters, and an interarm SBP difference ≥10 mmHg were compared and analyzed. We performed two multivariate forward analyses for determining the factors associated with an interarm SBP difference ≥10 mmHg [model 1: significant variables in univariate analysis except left ventricular mass index (LVMI); model 2: significant variables in univariate analysis except ABI<0.9 and baPWV]. The ABI<0.9 and high baPWV in model 1 and high LVMI in model 2 were independently associated with an interarm SBP difference ≥10 mmHg. Female, hypertension, and high body mass index were also associated with an interarm SBP difference ≥10 mmHg. Our study demonstrated that ABI<0.9, high baPWV, and high LVMI were independently associated with an interarm SBP difference of 10 mmHg or more. Detection of an interarm SBP difference may provide a simple method of detecting patients at increased risk of atherosclerosis and left ventricular hypertrophy.     

Segregation analysis of systolic and diastolic blood pressure in Middle Dalmatia Island population

A complex segregation analysis of systolic and diastolic blood pressure has been performed on pedigree data from rural populations inhabiting Middle Dalmatian islands of Brac, Hvar and Korcula and the Peljesac peninsula. The purpose of the performed analysis was to possibly elucidate a signal of a large-effect gene responsible for high prevalence of hypertension present in this population (the age-adjusted prevalence of developed hypertension being 31.82% in males and 28.23% in females). The analysis was performed on a sample of 389 two- and three-generation families consisting of 2 to 19 observed individuals (1126 examinees in total, 526 males and 600 females, aged 17 to 83). Since the examinees were randomly selected from census data encompassing 22.6% of the total population--the family relations having been established afterwards--the selected sample can be considered representative for the examined populations. By applying the usual transmission probability tests, the major gene model has been accepted for systolic as well as for diastolic blood pressure. The most parsimonious models showed that: (a) inheritance of blood pressure in the Middle Dalmatia population can be attributed to the effect of a major gene responsible for 34% (systolic) and 36% (diastolic) blood pressure variation; (b) alleles of that major gene act in co-dominant fashion; (c) allele frequency for high blood pressure (A2) is 18% (systolic) and 15% (diastolic blood pressure); and (d) the residual (non-major gene) familial correlation is negligible and can be constrained to zero. Since the results are also indicating heterogeneity within the sample in the genetic determination of the systolic blood pressure, the obtained results thus justify further search for the most promising subpopulation for incoming genetic epidemiological investigations of hypertension.     

Linkage analysis of systolic blood pressure: a score statistic and computer implementation

A genome-wide linkage analysis was conducted on systolic blood pressure using a score statistic. The randomly selected Replicate 34 of the simulated data was used. The score statistic was applied to the sibships derived from the general pedigrees. An add-on R program to GENEHUNTER was developed for this analysis and is freely available.     

Distribution of changes in systolic blood pressure and waist circumference--indicators for primary prevention

Eliminating or diminishing risk behaviors that lead to cardiovascular diseases could be achieved through primary prevention during the general practice visits. However, there is difference in effectiveness of preventive measure while there are no symptoms, and reactive response when burden of diseases start to show. We analyzed trends in gender and age--pattern changes of systolic blood pressure and waist circumference, as a reflection of primary prevention. Results show increase of values for both indicators in both genders, through youngest and middle age groups. In the oldest group stagnation and even decrease of values is evident. These results signal possible absence of primary prevention in younger age groups and some action when symptoms occur. It is hard to distinguish weather lower values is consequence of medication or lifestyle change. The absence of primary prevention is usually missed opportunity that is charged later both to the patient and health care system.     

Relation between birth weight at term and systolic blood pressure in adolescence.

OBJECTIVE--To examine whether birth weight is related to systolic blood pressure during adolescence. DESIGN--Retrospective (comparative) cohort study. The observers who traced and studied the subjects were unaware of their case-control status. SUBJECTS--330 subjects were born in Cardiff in 1975-7. Cases who were low birth weight at term (< 2500 g) were matched with controls of normal birth weight (3000-3800 g) at term. MAIN OUTCOME MEASURES--Systolic blood pressure measured by random zero sphygmomanometry in the subject''s right arm with the subject supine, corrected for size and age. RESULTS--The mean age at examination was 15.7 years. The mean systolic blood pressure of the cases was 105.8 mm Hg and of the controls 107.5 mm Hg. The corrected difference (95% confidence interval) in systolic blood pressure between the cases and controls was 1 mm Hg (-3 to +1 mm Hg; two tailed probability 0.33). CONCLUSION--Systolic blood pressure in adolescents of low birth weight is not significantly different from that of adolescents of normal birth weights.