Is blood pressure variability related to activity of the sympathetic system?

Correlation between short-term blood pressure variability parameters with mobil-O-graph pulse wave velocity

Background

Blood pressure variability (BPV) and arterial stiffness show an association with increased cardiovascular events. Evidences demonstrated an association between higher short-term systolic BPV and stiffer arteries. There is no previous study assessed the correlation between BPV and arterial stiffness measured by a Mobil-O-Graph device. We issued to evaluate the correlation between short-term BPV parameters and Mobil-O-Graph pulse wave velocity (PWV) among suspected hypertensive individuals under treatment.

Methods

Mobil-O-Graph device estimated arterial stiffness (oscillometric PWV [oPWV]) in 649 individuals, and they recorded 24-h ambulatory BP; 428 had suspected hypertension and 221 under treatment. We analyzed the correlation between oPWV and measures of BPV: SD of 24 h BP (24-h SD), SD of daytime BP (daytime-SD), and SD of nighttime BP (nighttime-SD), weighted SD of 24-h BP (wSD), coefficient of variation of 24-h BP (CV 24-h) and average real variability (ARV).

Results

Oscillometric PWV showed a positive correlation with all systolic BPV measures, in both groups. Among suspected hypertensives: 24-h SD, r = 0.30; SD daytime-SD, r = 0.34; nighttime-SD, r = 0.16; wSD, r = 0.30; CV 24-h, r = 0.24; ARV, r = 0.22. In the treated individuals: 24-h SD, r = 0.46; daytime-SD, r = 0.47; nighttime-SD, r = 0.35; wSD, r = 0.50; CV 24-h, r = 0.43; ARV, r = 0.37, all P < 0.001. Diastolic BPV demonstrated association with some measures of BPV. In suspected hypertensive group: nighttime-SD, r = 0.13; wSD, r = 0.10, both P < 0.001. And in treated individuals: daytime-SD, r = 0.23; wSD, r = 0.22; CV 24-h, r = 0.19 (all P < 0.001), ARV, r = 0.15 (P < 0.05). Systolic daytime-SD in suspected and diastolic CV 24-h in treated group independently predicted oPWV.

Conclusion

We observed a positive and independent correlation between Mobil-O-Graph pulse wave velocity and BPV measures, strong to systolic BPV and weak to diastolic BP.

Home blood pressure on winter mornings could be exaggerated: A comparison with summer mornings

PURPOSE

Self-measured blood pressure at home (HBP) is quite important for the management of hypertension. We hypothesized that winter HBP measured according to the recommendation of the guidelines, but not HBP measured inside bed before getting up, is elevated in response to cold ambient temperatures in winter. This study aimed to investigate differences in HBP measured before and after getting up in winter and summer.Methods: Hypertensive subjects whose blood pressure was stably controlled were enrolled (n = 46, 73 years). They were instructed to measure HBP while in bed just after waking (HBP-bed), in addition to the ordinary HBP measurement in the morning (HBP-morning) according to the guidelines. The mean value of HBP for 7 consecutive days before the day of a regular hospital visit was considered as the HBP of each subject, and characteristics of the winter and summer BPs were investigated.Results: HBP-morning was significantly higher (P < .001) in winter than in summer, but HBP-bed was lower in winter than in summer (P < .05). HBP-morning was significantly higher than HBP-bed in winter, while HBP-morning was not different from HBP-bed in summer, resulting in greater changes in HBP after getting up in winter than in summer (P < .0001). Changes in HBP after getting up were significantly correlated with serum creatinine levels and the urinary albumin-to-creatinine ratio.Conclusions: These findings imply that elevated HBP-morning in winter reflects the response of BP to cold after getting up. Seasonal profiles of HBPs before and after getting up should be noted in the management of hypertension.

Blood pressure variability with different measurement methods: Reliability and predictors. A proof of concept cross sectional study in elderly hypertensive hospitalized patients

Blood pressure variability (BPV) is an independent cardiovascular risk factor in hypertensive patients. The best method for quantifying BPV is still an object of debate. The existence of different BPV patterns, particularly age and arterial stiffness related, is postulated. Our aims were:Cross-sectional study in 108 elderly hypertensive hospitalized patients. Each patient underwent blood pressure measurements with 5 different modalities: 24 hour BP and pulse wave velocity (PWV) monitoring (24hBPM), measurement by nurses or physicians, self-measurement and beat-to-beat monitoring. Differences between maximum and minimum values (ΔBP), averages of the absolute differences between consecutive values (ARV) and coefficients of variation (CV) were calculated.ΔBP showed the wider values' dispersion (Δ systolic blood pressure (SBP): 66.4 ± 22.9 and Δ diastolic blood pressure [DBP]: 45.0 ± 13.5 mmHg). ARV and CV were highest with nurses' measurements (SBP-ARV 9.2 ± 6.2; DBP-ARV 6.9 ± 5.2; SBP-CV 7.6 ± 5.3; DBP-CV 9.6 ± 5.5). The strongest correlation was found comparing physicians' SBP measurements and 24hBPM ARVs (R2 0.23, P <.05). 24hBPM ΔSBP in a multivariate analysis was significantly associated with age (β -3.85, SE 0.83; P <.001) and PWV (β 20.29, SE 3.70; P <.001). Calcium antagonists were associated with a lower ΔSBP (β -14.6, SE 6.1, P <.05) while diuretics and alpha-blockers with a significant increase (β 14.4 SE 5.4, P <.01; β 26.9 SE 11.7, P <.05).Age, PWV, diuretics, alpha-blockers, but also measurements obtained by nurses, increase BP variability while calcium antagonists reduce it. BP profiles in elderly in-hospital patients potentially provide important information; they should, however, be interpreted cautiously.

Morning surge in blood pressure and blood pressure variability in Asia: Evidence and statement from the HOPE Asia Network

Hypertension is a major risk factor for cardiovascular and cerebrovascular diseases. To effectively prevent end-organ damage, maintain vascular integrity and reduce morbidity and mortality, it is essential to decrease and adequately control blood pressure (BP) throughout each 24-hour period. Exaggerated early morning BP surge (EMBS) is one component of BP variability (BPV), and has been associated with an increased risk of stroke and cardiovascular events, independently of 24-hour average BP. BPV includes circadian, short-term and long-term components, and can best be documented using out-of-office techniques such as ambulatory and/or home BP monitoring. There is a large body of evidence linking both BPV and EMBS with increased rates of adverse cardio- and cerebrovascular events, and end-organ damage. Differences in hypertension and related cardiovascular disease rates have been reported between Western and Asian populations, including a higher rate of stroke, higher prevalence of metabolic syndrome, greater salt sensitivity and more common high morning and nocturnal BP readings in Asians. This highlights a need for BP management strategies that take into account ethnic differences. In general, long-acting antihypertensives that control BP throughout the 24-hour period are preferred; amlodipine and telmisartan have been shown to control EMBS more effectively than valsartan. Home and ambulatory BP monitoring should form an essential part of hypertension management, with individualized pharmacotherapy to achieve optimal 24-hour BP control particularly the EMBS and provide the best cardio- and cerebrovascular protection. Future research should facilitate better understanding of BPV, allowing optimization of strategies for the detection and treatment of hypertension to reduce adverse outcomes.

24-Hour Blood Pressure Variability Assessed by Average Real Variability: A Systematic Review and Meta-Analysis

Background

Although 24‐hour blood pressure (BP) variability (BPV) is predictive of cardiovascular outcomes independent of absolute BP levels, it is not regularly assessed in clinical practice. One possible limitation to routine BPV assessment is the lack of standardized methods for accurately estimating 24‐hour BPV. We conducted a systematic review to assess the predictive power of reported BPV indexes to address appropriate quantification of 24‐hour BPV, including the average real variability (ARV) index.

Methods and Results

Studies chosen for review were those that presented data for 24‐hour BPV in adults from meta‐analysis, longitudinal or cross‐sectional design, and examined BPV in terms of the following issues: (1) methods used to calculate and evaluate ARV; (2) assessment of 24‐hour BPV determined using noninvasive ambulatory BP monitoring; (3) multivariate analysis adjusted for covariates, including some measure of BP; (4) association of 24‐hour BPV with subclinical organ damage; and (5) the predictive value of 24‐hour BPV on target organ damage and rate of cardiovascular events. Of the 19 assessed studies, 17 reported significant associations between high ARV and the presence and progression of subclinical organ damage, as well as the incidence of hard end points, such as cardiovascular events. In all these cases, ARV remained a significant independent predictor (P<0.05) after adjustment for BP and other clinical factors. In addition, increased ARV in systolic BP was associated with risk of all cardiovascular events (hazard ratio, 1.18; 95% confidence interval, 1.09–1.27). Only 2 cross‐sectional studies did not find that high ARV was a significant risk factor.

Conclusions

Current evidence suggests that ARV index adds significant prognostic information to 24‐hour ambulatory BP monitoring and is a useful approach for studying the clinical value of BPV.

Association between beat-to-beat blood pressure variability and vascular elasticity in normal young adults during the cold pressor test

The beat-to-beat blood pressure (BP) monitoring parameters, such as average beat-to-beat BP, BP variability (BPV), could have an influence on the vascular elasticity. This study hypothesized that the elevated beat-to-beat BPV could evoke the reduction of the vascular elasticity independent of BP levels. We measured the beat-to-beat BP recordings and total arterial compliance (TAC), which was used to assess the vascular elasticity, in 80 young healthy adults during the cold pressor test (CPT). The CPT included 3 phases: baseline phase, cold stimulus phase, recovery phase. Six parameters were used to estimate BPV. In bivariate correlation analysis, TAC showed a significant correlation with systolic BP (SBP) and diastolic BP (DBP) in the cold stimulus phase; and 4 indices of SBP variability (SBPV) were associated with TAC (r = 0.271∼0.331, P ≤ 0.015) in the recovery phase; similarly, 2 indices of DBP variability (DBPV) were also correlated with TAC (r = 0.221∼0.285, P ≤ 0.048) in the recovery phase. In multivariate regression analysis, DBPV (β = 0.229, P = 0.001) was a determinant of TAC independent of average DBP, sex, and weight. In addition, both beat-to-beat BP and BPV values increased in the cold stimulus phase (P < 0.01); whereas, the TAC decreased in the cold stimulus phase (P < 0.01). In conclusion, these data suggest that the beat-to-beat DBPV shows an independent association with the vascular elasticity in young normal adults during the CPT.

Blood pressure variability in risk stratification: What does it add?

1. In this minireview we address the predictive value of blood pressure variability, over and beyond level of pressure, in randomly selected population samples. All reviewed studies had sufficient power, long follow-up duration and a wide age range. 2. We assessed blood pressure variability derived from home visit, self-measured home pressure and 24 h ambulatory monitoring. The conclusions are based mainly on novel indices of blood pressure variability: variability independent of the mean, difference between maximum and minimum blood pressure and average real variability. 3. None of these variability indices or morning surge in blood pressure substantially refined risk profiling over and beyond the blood pressure level. 4. In risk stratification, clinicians should concentrate on blood pressure level, the predominant risk factor modifiable by lifestyle measures and antihypertensive drug treatment.

Within-subject blood pressure level--not variability--predicts fatal and nonfatal outcomes in a general population

To assess the prognostic significance of blood pressure (BP) variability, we followed health outcomes in a family-based random population sample representative of the general population (n=2944; mean age: 44.9 years; 50.7% women). At baseline, BP was measured 5 times consecutively at each of 2 home visits 2 to 4 weeks apart. We assessed within-subject overall (10 readings), within- and between-visit systolic BP variability from variability independent of the mean, the difference between maximum and minimum BP, and average real variability. Over a median follow-up of 12 years, 401 deaths occurred and 311 participants experienced a fatal or nonfatal cardiovascular event. Overall systolic BP variability averaged (SD) 5.45 (2.82) units, 15.87 (8.36) mmHg, and 4.08 (2.05) mmHg for variability independent of the mean, difference between maximum and minimum BP, and average real variability, respectively. Female sex, older age, higher-mean systolic BP, lower body mass index, a history of peripheral arterial disease, and use of β-blockers were the main correlates of systolic BP variability. In multivariable-adjusted analyses, overall and within- and between-visit BP variability did not predict total or cardiovascular mortality or the composite of any fatal plus nonfatal cardiovascular end point. For instance, the hazard ratios for all cardiovascular events combined in relation to overall variability independent of the mean, difference between maximum and minimum BP, and average real variability were 1.05 (0.96-1.15), 1.06 (0.96-1.16), and 1.08 (0.98-1.19), respectively. By contrast, mean systolic BP was a significant predictor of all end points under study, independent of BP variability. In conclusion, in an unbiased population sample, BP variability did not contribute to risk stratification over and beyond mean systolic BP.

Ambulatory blood pressure of adults in Ohasama, Japan

We performed a cross-sectional study in a small town in northern Japan to evaluate the distribution, reference values, and daily variation in ambulatory blood pressure. A total of 705 subjects (229 men aged 61.3 +/- 13.4 years [mean +/- SD] and 476 women aged 57.5 +/- 13.3 years; 41.1% of the regional adult population, n = 1716), including those treated with antihypertensive drugs (n = 231, 66.5 +/- 9.5 years) as well as untreated subjects (n = 474, 55.0 +/- 13.5 years), participated in the study. Both ambulatory and screening blood pressures were measured in 659 subjects. Ambulatory blood pressure was measured with an automatic device (Colin ABPM-630). The 24-hour ambulatory blood pressure in the total population was 121.7 +/- 13.0/71.1 +/- 7.6 mm Hg (95th percentile value [95%] = 146/85 mm Hg). The corresponding value in the untreated subjects was 119.4 +/- 12.5/70.1 +/- 7.4 mm Hg (95% = 144/83 mm Hg). The 24-hour average ambulatory blood pressure was 118.0 +/- 11.1/69.4 +/- 6.8 mm Hg (95% = 139/81 mm Hg) in subjects identified as normotensive by their screening blood pressure (n = 448, 57.2 +/- 13.1 years) and 133.6 +/- 14.2/78.9 +/- 8.8 mm Hg in those identified as hypertensive by their screening blood pressure (n = 73, 63.1 +/- 10.6 years). Based on the mean+SD of the 24-hour ambulatory blood pressure in the normotensive subjects by their screening blood pressure (129/76 mm Hg), the 24-hour ambulatory blood pressures in 25 (34.2%) of these 73 hypertensive subjects by screening blood pressure were below this level. Nine (2%) of 448 normotensive subjects by screening blood pressure were above the mean+2 SDs (140/83 mm Hg) of the 24-hour ambulatory blood pressure in the normotensive group by screening blood pressure. Ambulatory and screening blood pressures increased with age. The age-dependent increase in ambulatory blood pressure was less apparent in men. The 24-hour average pulse rate decreased with age. The daily variation in ambulatory blood pressure (standard deviation) increased with age, whereas that of pulse rate decreased with age. Increases in blood pressure variation were observed in nighttime and daytime blood pressure values. The differences between day versus night ambulatory blood pressures decreased with age in men but not in women.(ABSTRACT TRUNCATED AT 400 WORDS)

Does anxiety or cardiovascular reactivity have a causal role in hypertension?

Anxiety, stress, and cardiovascular reactivity (CVR) are variously believed to play a role in sustained hypertension. Although acute anxiety or stress elicits acute pressor responses, there is little support for their significant role in sustained hypertension. Anxiety correlates poorly with CVR, and blood pressure levels and anxiolytics do not sustain blood pressure lowering in subjects with hypertension-associated anxiety. Chronic anxiety disorders tend to be characterized by relatively low blood pressure and prevalence of sustained hypertension. Blood Pressure Regulation in hypertension is normal, and normo- and hypertensives have similar ambulatory blood pressure variability. Laboratory CVR fails to predict variability in natural environments, hyperreactors do not exhibit increased variability in natural environments, and the increased variability and ambulatory reactivity that is "accounted for" by laboratory responses is small. These findings do not support the belief that hypertension is related to a summation of heightened pressor responses over time. Antihypertensives normalize elevated blood pressures but do not alter CVR in the laboratory or variability in natural environments, probably because of a dual central regulation of resting and reactive blood pressures. Psychological stress responses result from selective neuronal activation rather than from generalized sympathetic neural responses or dysregulation. Differences in blood pressure responses during various emotions are only quantitative, with no specificity of sympathoadrenal or emotional responses to stressors. It may be time to regard reactive cardiovascular responses as physiological, rather than as psychological, and to require much stronger evidence to confirm causal roles of anxiety, stress, and reactivity in sustained hypertension.

Effects of carotid sinus nerve stimulation at different times in the respiratory and cardiac cycles on variability of heart rate and blood pressure of normotensive and renal hypertensive dogs

It was the purpose of the present study to determine (1) whether or not there exists a common respiratory and cardiac cycle time effect of the baroreceptor control of heart rate (HR) and blood pressure (BP) in spontaneously breathing anaesthetized dogs and (2) whether this effect, if present, is abnormal in dogs with renal hypertension. The baroreflex responses were evoked by brief low-intensity electrical carotid sinus nerve stimulation (CSNS) triggered by the R-wave in the electrocardiogram with an adjustable delay (0-210 ms) and positioned in either inspiration or expiration. All baroreceptor afferent nerves were intact. Brief CSNS had no noticeable effect on breathing. The responses of means of HR, respiratory sinus arrhythmia (RSA), and systolic and diastolic respiratory blood pressure waves (RBPWsyst, RBPWdiast) to CSNS were not different for normotensive and hypertensive dogs. No cardiac, but a small respiratory cycle time effect on means of HR, BPsyst and BPdiast was observed. The magnitude of RSA and RBPWdiast was markedly enhanced for expiratory CSNS at each delay after the R-wave. Inspiratory CSNS diminished the magnitude of RSA and RBPW only if applied during systole, and become ineffective for delays greater than 200 ms after the R-wave. During both respiratory phases, CSNS was elevated at times of central presentation of the natural sinoaortal baroreceptor discharges (120 ms and 70 ms, respectively). The magnitudes of RSA and RBPW were influenced simultaneously and in the same way by CSNS throughout. It is concluded that, under the present experimental conditions, RSA and RBPW have a common central origin.

Adrenergic and vagal influences on blood pressure variability

The present paper reviews our recent studies set up to define the role of sympathetic and vagal nervous influences on blood pressure variability. Blood pressure and its variability was measured in men by Arteriosonde or by Portometer (the latter recording 12 hours ambulatory blood pressure) and in the dog by intraarterial recordings. It was shown that sympathetic nerves do not influence variability as no change was seen with drugs acting on either beta (atenolol, metoprolol, propranolol) or alpha adrenergic receptors (prazosin, phentolamine, guanfacine). Also no correlation was found with plasma catecholamines or sympathetic function tests. By contrast, clear inhibition was demonstrated with atropine indicating an important role of vagal nerves on variability. However, in men, inhibition was not complete with atropine; thus, also other mechanisms play a role but these are, at present, largely unknown.

Intermittent ambulatory blood pressure recordings in children. Methodological aspects and influence of family history on hypertension

In 100 children of different school classes (10-12 years, participation rate ca. 50%) ambulatory blood pressure (BP) was recorded by a semi-automatic non-invasive device (Remler system). BP was measured every 1/2 h between 2 and 7.30 p.m. During each measurement the children protocolled their activity. These BP recordings were repeated five times at monthly intervals in 86 children. In the same children casual and near basal BP was determined. The mean ambulatory BP was 103/64 +/- 7/6 mm Hg. The average retest reliability of the monthly mean values was r = 0.57 for systolic and r = 0.45 for diastolic BP. The variability of BP (standard deviation) was not reproducible. Data recording failed in 32% of all single systolic and in 42% of all single diastolic BP measurements. These drop-outs were caused by inappropriate use rather than technical problems. There was a relationship between procolled activities and systolic BP. On average, ambulatory BP was lower than BP under standardized conditions. Under all conditions, children with hypertensive parents exhibited a 6 mm Hg higher systolic BP than children without a similar family history. No sex differences were found.

Detection of a diurnal rhythm in arterial blood pressure in the evaluation of 24-hour antihypertensive therapy

Uncertainty in defining hypertensive disease makes a prolonged study of blood pressure pattern necessary, using continuous or semicontinuous blood pressure recordings. Its pathophysiological meaning involves data sufficiently indicative of blood pressure profile with reference to the continuous stimulations of different intensity and duration, which are met by subjects both in their daily activities and in the passage from an active life to sleep. Such a parameter is, in fact, an indispensable premise for a correct course of therapy. The aim of our work was at first the detection of a diurnal rhythm in blood pressure, using data obtained in a 24-h ambulatory monitoring away from the conditioning of different activities and daily routine. We have employed three groups of 34 males each. The first group consisted of hypertensive outpatients, while hospitalized subjects comprised the second group. The third group was composed of normal subjects. Furthermore, after finding this system productive, we started studying whether this rhythm of blood pressure could be modified under the influence of a single administered drug dose, and whether information obtained could be easily interpreted. We studied 12 male patients with essential hypertension, which had been untreated. Each patient underwent three 24-h blood pressure ambulatory monitorings. Two different doses of nifedipine (10 and 20 mg) were randomly administered to each of the patients at the beginning of the second and third readings. We observed a significant fall in systolic blood pressure and a minor decrease in diastolic blood pressure after administration of a single 10 mg nifedipine tablet.

Basal blood pressure variability and reactivity of blood pressure to emotional stress in essential hypertension

Blood pressure variability under basal conditions and blood pressure reactivity to emotional stress were studied in 38 hypertensives and 13 normotensives. Systolic basal blood pressure variability correlated with systolic blood pressure reactivity. Variability increased with higher basal blood pressure. Thus in the hypertension group the blood pressure variability was greater than in the normotension group. Besides, the hypertension group showed a greater reactivity of systolic blood pressure to emotional stress, too. An influence of age on basal blood pressure, blood pressure variability, and reactivity could be evaluated; but no influence of sex on these parameters was detected. The results indicate that variability and reactivity of blood pressure can be referred to a common central nervous blood-pressure-regulating mechanism. As both parameters are increased in hypertension, a greater lability of blood pressure must be assumed. This greater lability may be attributed to a stronger neurogenic influence or to structural changes of peripheral blood vessels.

Diurnal variations of cardiac rhythm, arterial pressure, and urinary catecholamines in borderline and established essential hypertension

Ambulatory continuous ECG and arterial pressure (BP) were recorded simultaneously (Delmar Avionics Pressurometer II) for 24 hours in 13 age-matched normotensive subjects, 11 patients with borderline hypertension (HBP), and in 10 patients with uncomplicated established essential HBP. Urinary concentrations of epinephrine, norepinephrine, and dopamine were simultaneously collected over four successive 4-hour periods and one 8-hour period. Prevalence and total number of ventricular and supraventricular ectopic beats was low and not affected by arterial BP. Twenty-four-hour rate (HR) and 4-hourly excretion of epinephrine, norepinephrine, and dopamine were comparable between normotensive and HBP persons and no correlation between urinary catecholamines and arterial BP (systolic, diastolic, or mean), HR, or prevalence of ectopic beats was found in any of the three groups or in the total study population. We conclude that HBP patients without ECG evidence of left ventricular hypertrophy do not have a higher prevalence of supraventricular or ventricular ectopic beats. Urinary catecholamines are not related to circadian fluctuations or variability in arterial BP, HR, or prevalence of ectopic beats.

Blood-pressure response to swimming in ice-cold water

The cardiovascular responses to cold were studied in a group of 28 subjects who enjoyed swimming in ice-cold water in winter ("ice-bears"). History and clinical examination had revealed no abnormalities except hypertension (180/105 mm Hg) in 1, while 3 other subjects had a diastolic value of 95 mm Hg. Systolic blood-pressure increased significantly while the subjects were waiting undressed in cold air in the cabin by the pond. Neither immersion nor swimming in the ice-cold water caused further increase in systolic blood-pressure, and diastolic blood-pressure showed only a modest rise. 4 min later, blood-pressure had returned to control values. Electro and vector cardiographic signs remained unchanged. Although very high pressures were recorded in several subjects, no signs of left ventricular hypertrophy or of cardiovascular of cerebrovascular damage could be detected.