Ambulatory monitoring for prediction of cardiac and cerebral events

Heritability of ambulatory and beat-to-beat office blood pressure in large multigenerational Arab pedigrees: the 'Oman Family study'

OBJECTIVE

To estimate the heritability of ambulatory blood pressure (BP), heart rate (HR), and beat-to-beat office BP and HR in an isolated, environmentally and genetically homogeneous Omani Arab population.

METHODS

Ambulatory BP measurements were recorded in 1,124 subjects with a mean age of 33.8 ± 16.2 years, using the auscultatory mode of the validated Schiller ambulatory BP Monitor. Beat-to-beat BP and HR were recorded by the Task Force Monitor. Heritability was estimated using quantitative genetic analysis. This was achieved by applying the maximum-likelihood-based variance decomposition method implemented in SOLAR software.

RESULTS

We detected statistically significant heritability estimates for office beat-to-beat, 24-hour, daytime, and sleep HR of 0.31, 0.21, 0.20, and 0.07, respectively. Heritability estimates in the above mentioned conditions for systolic BP (SBP)/diastolic BP (DBP)/mean BP (MBP)were all significant and estimated at 0.19/0.19/0.19, 0.30/0.44/0.41, 0.28/0.38/0.39, and 0.21/0.18/0.20,respectively. Heritability estimates for 24-hour and daytime ambulatory SBP, DBP, and MBP ranged from 0.28 to 0.44, and were higher than the heritability estimates for beat-to-beat recordings and sleep periods,which were estimated within a narrow range of 0.18-0.21.

CONCLUSION

In this cohort, because shared environments are common to all, the environmental influence that occurs is primarily due to the variation in non-shared environment that is unique to the individual. We demonstrated significant heritability estimates for both beat-to-beat office and ambulatory BP and HR recordings, but 24-hour and daytime ambulatory heritabilities are higher than those from beat-to-beat resting levels and ambulatory night-time recordings.

The reproducibility of ethnic differences in the proportional awake-sleep blood pressure decline among women

A growing body of evidence indicates that African Americans (AA), on average, have a smaller proportional decline in blood pressure (BP) from waking to sleep than European Americans (EA), but this difference is largely based on correlational data from a single assessment day. The persistence of this difference over repeated sampling is not well established. The purpose of this study was to evaluate whether ethnic differences in the awake-sleep BP decline between AA and EA persisted over three monthly assessments. The subjects were 47 AA (age = 39.7 +/- 8.7) and 92 EA (age = 37.4 +/- 9.2) normotensive women. Subjects had 24-h ambulatory BP monitoring done on midweek workdays at 1-month intervals for three consecutive months. The proportional decline in BP was calculated as follows: (average awake - average sleep)/average sleep. The persistence of ethnic differences was evaluated using repeated-measures ANCOVA and by examining Bland-Altman plots. The ANCOVA results revealed that overall, the proportional decline of AA women was less than that of EA women for both SBP (P < 0.038) and DBP (P < 0.083), consistent with previous research, and that there were also no significant ethnic differences by monthly assessment. Bland-Altman plots revealed that overall and by ethnicity, the proportional decline in BP among individual subjects over the 3 months was also reproducible. These results suggest that the ethnic difference in awake-sleep BP between AA and EA women persists over time and that the awake-sleep decline in BP among individuals, whether AA or EA, is also reproducible.

Relationship between waking-sleep blood pressure and catecholamine changes in African-American and European-American women

BACKGROUND

A blunted decline in waking to sleep blood pressure (BP) is more common in African-American (AA) than European-American (EA) women. The causes of reduced BP 'dipping' in AA women are not known, although several factors including ethnic differences in catecholamine sensitivity have been suggested. The purpose of this study was to investigate the possible contribution of catecholamine influences on BP to ethnic differences in BP dipping in a sample of working women.

PARTICIPANTS AND METHODS

Healthy female participants wore ambulatory BP monitors over the course of 1 work day and night. Urine samples for assay of epinephrine and norepinephrine were collected at work (approximately 11.00-15.00 h), home (approximately 06.00-22.00 h) and during sleep (approximately 22.00-06.00 h). Analysis of covariance was used to assess the relationships between changes in BP and the catecholamines by ethnicity.

RESULTS

AA women (n=51; age=38.9+/-8.5 years) had smaller proportional BP changes from work to sleep and home to sleep than EA women (n=110; age=37.1+/-9.2 years). Overall, the work to sleep change in epinephrine excretion was positively associated with changes in both SBP (P<0.003) and DBP (P<0.001); however, there was an ethnic difference in the epinephrine-BP relationship. For AA women, these associations were highly positive and significant, but for EA women, there was little correlation. Nonetheless, the analysis also revealed that overall, the work to sleep BP changes were not directly related to ethnic differences in catecholamine variation.

CONCLUSION

The AA-EA difference in waking-sleep BP changes (dipping) is not directly related to ethnic differences in catecholamine variation; however, AA seem to have a greater BP sensitivity to epinephrine.

Type D personality as a prognostic factor in heart disease: assessment and mediating mechanisms

Type D personality, a synergy between negative affectivity and social inhibition, has established itself as a serious risk factor for morbidity and mortality in patients suffering from cardiovascular disease. In this review, we summarize studies on the validity of the assessment methods of Type D, emphasizing its role as an independent vulnerability factor in the progression of cardiovascular disease. We further present evidence on the physiological characteristics that accompany the 2 psychological traits negative affectivity and social inhibition and may mediate the relation between personality and prognosis in heart disease. Further research needs to determine the mechanisms by which Type D affects the course and outcome of cardiovascular disease as well as how Type D patients may benefit from psychosocial intervention.

Comparison of time and frequency domain measures of RSA in ambulatory recordings

The extent to which various measures of ambulatory respiratory sinus arrhythmia (RSA) capture the same information across conditions in different subjects remains unclear. In this study the root mean square of successive differences (RMSSD), peak valley RSA (pvRSA), and high frequency power (HF power) were assessed during ambulatory recording in 84 subjects, of which 64 were retested after about 3 years. We used covariance structure modeling to test the equality of the correlations among three RSA measures over two test days and three conditions (daytime sitting or walking and nighttime sleep) and in groups with low, medium, and high mean heart rate (HR), or low, medium, and high mean respiration rate (RR). Results showed that ambulatory RMSSD, pvRSA, and HF power are highly correlated and that their correlation is stable across time, ambulatory conditions, and a wide range of resting HR and RR values. RMSSD appears to be the most cost-efficient measure of RSA.

The BpTRU automatic blood pressure monitor compared to 24 hour ambulatory blood pressure monitoring in the assessment of blood pressure in patients with hypertension

BACKGROUND

Increasing evidence suggests that ABPM more closely predicts target organ damage than does clinic measurement. Future guidelines may suggest ABPM as routine in the diagnosis and monitoring of hypertension. This would create difficulties as this test is expensive and often difficult to obtain. The purpose of this study is to determine the degree to which the BpTRU automatic blood pressure monitor predicts results on 24 hour ambulatory blood pressure monitoring (ABPM).

METHODS

A quantitative analysis comparing blood pressure measured by the BpTRU device with the mean daytime blood pressure on 24 hour ABPM. The study was conducted by the Centre for Studies in Primary Care, Queen's University, Kingston, Ontario, Canada on adult primary care patients who are enrolled in two randomized controlled trials on hypertension. The main outcomes were the mean of the blood pressures measured at the three most recent office visits, the initial measurement on the BpTRU-100, the mean of the five measurements on the BpTRU monitor, and the daytime average on 24 hour ABPM.

RESULTS

The group mean of the three charted clinic measured blood pressures (150.8 (SD10.26) / 82.9 (SD 8.44)) was not statistically different from the group mean of the initial reading on BpTRU (150.0 (SD21.33) / 83.3 (SD12.00)). The group mean of the average of five BpTRU readings (140.0 (SD17.71) / 79.8 (SD 10.46)) was not statistically different from the 24 hour daytime mean on ABPM (141.5 (SD 13.25) / 79.7 (SD 7.79)). Within patients, BpTRU average correlated significantly better with daytime ambulatory pressure than did clinic averages (BpTRU r = 0.571, clinic r = 0.145). Based on assessment of sensitivity and specificity at different cut-points, it is suggested that the initial treatment target using the BpTRU be set at <135/85 mmHG, but achievement of target should be confirmed using 24 hour ABPM.

CONCLUSION

The BpTRU average better predicts ABPM than does the average of the blood pressures recorded on the patient chart from the three most recent visits. The BpTRU automatic clinic blood pressure monitor should be used as an adjunct to ABPM to effectively diagnose and monitor hypertension.

Heritability of daytime ambulatory blood pressure in an extended twin design

The present study estimated the genetic influences on ambulatory systolic and diastolic blood pressure, and on hypertensive status derived from ambulatory levels, in a family sample of 535 twins and 257 singleton siblings. This "extended twin design" was used to explicitly test the possibility that results obtained in singleton siblings are different from those obtained in twins. To examine the effects of excluding (medicated) hypertensive subjects, the genetic analyses were first performed under strict exclusion (medication and/or blood pressure >135/85 mm Hg), then without the medicated subjects, and, finally, without any exclusion. For the latter analysis, the untreated blood pressure values in subjects using antihypertensive medication were estimated by augmenting the observed blood pressure by the published efficacy of the specific antihypertensive medication used. No evidence was found for differential means, variances, or covariances of ambulatory blood pressure in singletons compared with twins. This indicates that estimates of heritability of ambulatory blood pressure from twin studies can be generalized to the singleton population. Heritability of hypertension, defined as a mean daytime blood pressure >135/85 mm Hg or antihypertensive medication use, was 61%. Genetic contribution to ambulatory blood pressure was highest when all subjects were included (systolic, 44% to 57%; diastolic, 46% to 63%) and lowest under strict exclusion (systolic, 32% to 50%; diastolic, 31% to 55%). We conclude that exclusion of (medicated) hypertensives removes part of the true genetic variance in ambulatory blood pressure.