ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Computer analysis of spontaneous cardiovascular beat-by-beat variability has gained wide credibility as a means of inferring disturbances of autonomic cardiovascular regulation in a variety of cardiovascular conditions, including hypertension, myocardial infarction and heart failure. Recent applications of spectral analysis to muscle sympathetic nerve activity (MSNA) offer a new approach to a better understanding of the relationship between cardiovascular oscillations and autonomic regulation. However, areas of uncertainty and unresolved debates remain, mostly concerning different methodologies and interpretative models that we will consider in this article. Perusal of all available literature suggests that average sympathetic nerve activity and its oscillatory components, although correlated to some extent, are likely to provide different types of information. In addition, the specific experimental context is of paramount importance, as the rules that seem to govern the relationship between average and oscillatory properties of MSNA appear to be different in usual conditions and in conditions of extremes of activation or disease. In general, dynamic experiments, such as with graded tilt or with vasoactive drugs, are more suited to investigations of the complexity of autonomic regulation than are static comparisons. In addition, because the information is spread across variables and is affected by a potentially large error, it appears that several different techniques should be perceived as complementary rather than as mutually exclusive. Available evidence suggests that low-frequency and high-frequency oscillations in peripheral signals of variability might have a predominantly central, rather than a peripheral, origin and that this applies in particular to low-frequency oscillations. A crucial point in the assessment of the meaning of spectral components relates to consideration of the varying level of very-low-frequency noise, and the mathematical manipulation of derived indices, particularly using a normalization procedure. This appears easier to obtain with auto-regressive than with fast Fourier techniques. With this approach, discrepant interpretations seem to be resolved, provided adequate care is taken in separating direct physiological data from derived meaning, which relates to hidden information and neural codes; in the case of sympathetic discharge, the latter display greater complexity than simple average spike activity per unit time. Accordingly we believe, in conclusion, that the judicious use of spectral methodology, in addition to other techniques, might provide unprecedented, useful insights into autonomic cardiovascular regulation, in both physiopathological and clinical circumstances.

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Blood pressure fall at night is commonly used to classify subjects as 'dippers' or 'non-dippers'. Such a classification is poorly reproducible, however, due to interference by a number of confounders. These include methodological problems with ambulatory blood pressure monitoring at night due to a variable hydrostatic difference between the arm cuff and the heart. Even correcting for this variable, however, does not significantly improve the reproducibility of the nocturnal blood pressure fall, which probably depends to a large extent on other factors, such as the level of daytime activity and differences in sleep patterns.

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

ObjectivesTo investigate the influence of different supine body positions on blood pressure measured by an ambulatory device.Design and methodsTwenty hypertensive and 20 normotensive subjects of a tertiary hospital outpatient clinic participated. Blood pressure was measured with an ambulatory blood pressure device while lying in the back, left side, right side and abdominal positions. The distance between the antecubital fossa and sternum was measured in all four body positions. An expected blood pressure difference between the arm of measurement and the right atrium (i.e. the midsternum) was calculated for the different body positions.ResultsWhen blood pressure was measured in side position at the left arm in hypertensive subjects, the mean systolic and diastolic blood pressure differences (± SD) between the left arm in the lower position and in back position at the same arm were +5/+4 (8/6) mmHg. These differences were −14/−17 (6/4) mmHg for the left arm lying above heart level in side position. Values of the right arm in hypertensives and the measurement at both arms in normotensive subjects yielded similar differences.ConclusionsBody and arm position can both significantly influence the ambulatory blood pressure and therefore the day-night difference. This comprises one of the main reasons for the moderate individual reproducibility of the blood pressure fall at night.

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

BackgroundNocturnal blood pressure readings may be influenced by body position because of variation in the vertical distance between heart and cuff level.ObjectivesTo quantify the effect of body position on nocturnal blood pressure and to assess whether this effect influences the reproducibility of nocturnal blood pressure.Patients and methodsIn 16 individuals (three normotensive and 13 hypertensive) 24 h ambulatory measurement of blood pressure and body position was performed twice, separated by an interval of 2–6 weeks. Body position was measured with five acceleration sensors, which were mounted on the trunk and legs.ResultsDuring the first night, 43 ± 31% of blood pressure values were measured while participants were in the supine position, 29 ± 28% when they were lying on their side with the cuffed arm down and 28 ± 29% when they were lying on their side with the cuffed arm up. During the second night these percentages were 40 ± 29%, 32 ± 29% and 28 ± 25% respectively. Blood pressure readings obtained while individuals were lying with the cuffed arm up were about 10 mmHg lower than those obtained with the individual in either the supine position or lying with the cuffed arm down. After correction for the underestimation attributable to ‘cuff-up’ readings, nocturnal blood pressure increased by 3 mmHg and the number of non-dippers increased from two to four. Correction did not affect the reproducibility of nocturnal blood pressure measurements (standard deviation of the differences 8.3 mmHg for systolic and 6.0 mmHg for diastolic blood pressure after correction). Dipping status was reproduced in 88% of individuals before correction, and in 87% after correction.ConclusionsUnder ambulatory conditions, a highly variable but sometimes substantial number of blood pressure readings are taken with the cuffed arm above heart level. These readings result in underestimation of nocturnal blood pressure and hence influence dipper-non-dipper classification. However, body position does not seem to have an important influence on the reproducibility of nocturnal blood pressure or dipping status.

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

ObjectiveTo investigate whether measurement of blood pressure at home (HBP) and by ambulatory monitoring (ABP) are reliable alternatives to the traditional strategy for the diagnosis of hypertension based on blood pressure measurement on repeated clinic visits (CBP).DesignComparison of the diagnosis of hypertension based on HBP (on six workdays) or ABP monitoring (two occasions) with that based on CBP (five visits within 3 months).SettingOutpatient hypertension clinic.ParticipantsWe enrolled 133 individuals with a diastolic CBP of 90–115 mmHg on the initial visit.Main outcome measuresCBP, HBP and ABP values, and the diagnosis of hypertension.ResultsHypertension was diagnosed in 70, 63 and 56% of individuals using the CBP, ABP and HBP methods respectively (P= 0.04). Agreement in the diagnosis of hypertension between all three methods was found in 59% of individuals. Disagreement between CBP and ABP was found in 27%, between CBP and HBP in 29% and between ABP and HBP in 26% of individuals. The sensitivity, specificity and positive and negative predictive values of ABP to diagnose hypertension correctly were 76, 67, 85 and 53% respectively; for HBP the respective values were 69, 77, 88 and 51%. The same parameters for HBP compared with ABP in the detection of white-coat hypertension were 61, 79, 48 and 86% respectively.ConclusionsIndiscriminate use of HBP or ABP monitoring in the evaluation of all individuals with high blood pressure will probably result in confusion and therefore should be discouraged. However, in the detection of white-coat hypertension, HBP appears to be useful as a screening test, which, if positive, requires confirmation with ABP monitoring.

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

ObjectivesTo examine the relationship between indicators at birth and adult blood pressure and risk for developing hypertension at two age levels.DesignOriginal midwife records of 438 women born at term participating in a prospective population study in Göteborg, Sweden with blood pressure and hypertension assessment at both 50 and 60 years of age.ResultsSystolic blood pressure at both age levels showed a U-shaped relationship to weight and length at birth. Hypertension prevalence at 60 years was significantly and inversely related to both weight and length at birth, but not at 50 years. Significantly higher risk for hypertension was found in the lowest birth weight quintile [odds ratio (OR) = 2.0, 95% confidence interval (CI) 1.1–3.8] and lowest birth length tertile (OR = 1.8, 95% CI 1.1–3.0), in relation to the middle quintile/tertile, with or without adjustment for adult body size (as body mass index), at 60 years but not at 50 years. At 50 years, hypertension risk decreased by 3% (95% CI 0.92–1.01) for every 100 g increase in birth weight and 6% (95% CI 0.83–1.05) per cm birth length. At age 60 years, hypertension risk decreased by 4% (95% CI 0.92–0.99) per 100 g birth weight and 10% (95% CI 0.81–0.99) per cm length.ConclusionsSize at birth was a predictor of hypertension risk in women at 60 years but not 50 years. This study supports the hypothesis that poor fetal growth, as measured by low weight or length at birth, may contribute to the development of hypertension in later life and that this relationship became stronger with age.

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

ObjectiveTo determine whether there is a relationship between season of birth and adult blood pressure, as a possible early determinant of later blood pressure.DesignWe studied 572 men, aged 45–64 years, whose blood pressure was measured in standardized manner as part of a nation-wide survey in Spain. To analyse the seasonal variation in blood pressure, a linear regression was performed, adjusting for age, height, body mass index, occupation and rural or urban residence.ResultsWe found seasonal variation in mean systolic blood pressure, with maxima in adults born in autumn and winter, and minima in those born in spring and summer. The greatest difference in systolic blood pressure occurred between adults born in spring (134.1 mmHg) and those born in autumn (140.3 mmHg). After adjustment, the difference in means between spring and autumn was 5.9 mmHg (95% confidence interval 0.7 to 11.1 mmHg,P= 0.03).ConclusionsThis study demonstrated differences in systolic blood pressures of adult men according to the Jose season of their birth. Although this relationship is compatible with several hypotheses, the difference found between spring and autumn, partially independent of some other factors, might indicate that the extent of early exposure to sunlight is implicated in determining later blood pressure. This needs further investigation.

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

ObjectivesTo test whether the Glu298Asp polymorphism of the endothelial nitric oxide synthase (eNOS) gene is of functional relevance in humans by altering endothelium-dependent vasodilation.BackgroundThe Asp298 variant of the eNOS gene product has been associated with arterial hypertension, coronary artery disease and myocardial infarction. The pathogenetic mechanism has not yet been elucidated. Since endothelium-dependent vasodilation has been shown to be impaired in these disorders, we hypothesized that the Glu298Asp polymorphism of the eNOS gene influences endothelium-dependent vasodilation.MethodsIn 80 patients with normal or elevated cholesterol, endothelium-dependent and -independent vasodilation was assessed. Forearm blood flow was measured by plethysmography in response to intra-arterial (i.a.) infusion of 12 and 48 μg/min acetylcholine and 3.2 and 12.8 μg/min nitroprusside, respectively. NG-monomethyl-L-arginine (L-NMMA) in doses of 4, 8 and 16 μmol/min was infused to test basal nitric oxide (NO) production and release. Genomic DNA was extracted from blood samples to determine the Glu298Asp polymorphism of the eNOS gene at position 1917 G/T after BanII restriction.ResultsBaseline parameters (age, gender, blood pressure, body mass index, cholesterol level) were similar across the genotypes. Genotype frequencies did not deviate from the Hardy-Weinberg equilibrium. No differences in forearm blood flow to i.a. acetylcholine (average increase: + 554 ± 371±), nitroprusside or L-NMMA infusion were found across the eNOS genotypes, neither for endothelium-dependent or endothelium-independent vasodilation, nor for basal NO production and release. Our sample size ofn= 80 had a power of > 80 > (α = 0.20) with aPvalue < 0.05 (β = 0.05) to detect a 200% difference in forearm blood flow response to 48 μg/min acetylcholine.ConclusionsAt a power of 80%, we can exclude a relevant effect on endothelium-dependent vasodilation due to the eNOS Glu298Asp polymorphism. Thus, our functional genetic study does not suggest any biological effect of the eNOS Glu298Asp genotype on the cardiovascular system via an influence on endothelium-dependent vasodilation.

ISSN:0263-6352    

出版商:OVID    

年代:2000

数据来源: OVID