Circadian heart rate and blood pressure variability considered for research and patient care

Mutation of the circadian clock gene Per2 alters vascular endothelial function

BACKGROUND

The circadian clock regulates biological processes including cardiovascular function and metabolism. In the present study, we investigated the role of the circadian clock gene Period2 (Per2) in endothelial function in a mouse model.

METHODS AND RESULTS

Compared with the wild-type littermates, mice with Per2 mutation exhibited impaired endothelium-dependent relaxations to acetylcholine in aortic rings suspended in organ chambers. During transition from the inactive to active phase, this response was further increased in the wild-type mice but further decreased in the Per2 mutants. The endothelial dysfunction in the Per2 mutants was also observed with ionomycin, which was improved by the cyclooxygenase inhibitor indomethacin. No changes in the expression of endothelial acetylcholine-M3 receptor or endothelial nitric oxide synthase protein but increased cyclooxygenase-1 (not cyclooxygenase-2) protein levels were observed in the aortas of the Per2 mutants. Compared with Per2 mutants, a greater endothelium-dependent relaxation to ATP was observed in the wild-type mice, which was reduced by indomethacin. In quiescent aortic rings, ATP caused greater endothelium-dependent contractions in the Per2 mutants than in the wild-type mice, contractions that were abolished by indomethacin. The endothelial dysfunction in the Per2 mutant mice is not associated with hypertension or dyslipidemia.

CONCLUSIONS

Mutation in the Per2 gene in mice is associated with aortic endothelial dysfunction involving decreased production of NO and vasodilatory prostaglandin(s) and increased release of cyclooxygenase-1-derived vasoconstrictor(s). The results suggest an important role of the Per2 gene in maintenance of normal cardiovascular functions.

Circadian rhythm of maternal blood pressure and fetal growth

This study aimed at examining any relation between the circadian variation in blood pressure (BP) in human pregnancy and fetal growth. A prospective study included 52 pregnant women monitored during the third trimester of pregnancy. There were 33 uncomplicated pregnancies with normal fetal growth (Group 1) and 19 pregnancies complicated by intrauterine growth retardation (IUGR), confirmed at birth (Group 2). Ten women (five in each group) had pregnancy-induced hypertension. All women were hospitalized and followed a similar daily routine. BP was recorded with an automatic wearable device. Measurements were obtained every 20 min for 24 +/- 1 h. BP profiles were analyzed by conventional statistical methods and by cosinor, involving the least squares fit of cosine curves with an anticipated period (24 h) to the data. BP parameters, fetal outcome, demographic and obstetric characteristics were compared between the two groups. Logistic regression and multivariate analyses were used to assess factors putatively associated with fetal outcome. The circadian amplitude of diastolic BP was found to be larger in normotensive women with IUGR. As gauged by odds ratios (OR), the circadian amplitude of diastolic BP (OR = 1.7, 95% CI: 1.1-2.8; P = 0.03) and hematocrit (OR = 1.4, 95% CI: 1.0-1.9; P = 0.04) were the only variables positively and independently associated with IUGR. In the presence of maternal hypertension, the circadian amplitude of systolic BP was negatively associated with IUGR (OR = 0.7, 95% CI: 0.5-1.0; P = 0.03). A larger circadian variation in diastolic BP, rather than a difference in the mean value of systolic or diastolic BP, was found to be statistically significantly associated with IUGR. This study adds another condition in which the circadian BP amplitude constitutes a harbinger of elevated risk, apart from an association with a shortened lifespan in the absence or presence of malignant hypertension and with an increased risk of stroke and nephropathy reported earlier.

Losing harmonic stability of arterial pulse in terminally ill patients

OBJECTIVE

To measure the coefficient of variation of the harmonic magnitude (HCV) of the radial arterial pulse before death of cancer patients.

METHODS

We non-invasively recorded the radical arterial pulse of 21 end-stage cancer patients, 31 healthy subjects, and 47 outpatient department (OPD) patients. During the 2-week study, eight cancer patients expired.

RESULTS

There were no considerable differences in diastolic or systolic blood pressure between cancer patients and other subjects; however, all six HCVs were significantly higher in the cancer patients (P<0.05). Within the cancer patient group, the first and second HCV were notably higher in the patients that expired (P<0.05), and the first to fourth HCVs were significantly increased on their last day (P<0.05). In the control healthy subjects and the OPD group, the HCVs were below 5 and 8%, respectively. In the cancer patients, the third to sixth HCVs were higher than 15%. On the last day of the cancer patients that expired, even the first and second HCVs were higher than 15%.

CONCLUSIONS

During the dying process, the traditional diastolic and systolic blood pressure did not show significant changes; however, all the harmonic components gradually lost their stability. The HCVs, which increased first for the high-frequency components and then the low-frequency components, could quantitatively reflect the severity of different stages of illness.

Increased concentrations of lipoprotein(a), circadian rhythms and metabolic reactions evoked by acute myocardial infarction, associated with acute reactions in relation to large breakfasts

Of 54 patients with acute coronary artery disease (CAD) that were included in this study, 41 patients had acute myocardial infarction (AMI), five patients possible MI, four patients unstable angina and the remaining four angina pectoris. The control subjects (n = 85) were randomly selected from the general population of the city of Moradabad of similar age range after exclusion for CAD (n = 9), diabetes (n = 6) and excess intake of trans fatty acids (n = 20). The incidence of lipoprotein(a) excess (> 30 mg/dl; 42.6 vs 24.7%; P < 0.05) and mean concentration of lipoprotein(a) (Lp[a], 6.4 mg/dl, 95% confidence interval: 2.8-10.5; P < 0.05) was significantly greater in the acute CAD group compared with control subjects. Mean total cholesterol and triglycerides were significantly higher and mean nitrite level lower in the study group as compared with the control group.There was a significant greater incidence of cardiac events in the second quarter of the day compared with the fourth quarter. Lp(a), triglycerides, blood glucose, plasma insulin, malondialdehyde, diene conjugates, TBARS and TNF-alpha and IL-6 levels, which were significantly greater during the acute phase, showed a significant decline and serum nitrite and coenzyme Q demonstrated an increase at 4 weeks of follow-up when the acute reactions evoked by MI had been controlled. Large breakfasts were a predisposing factor for cardiac events in the second quarter of the day and it was significantly associated with metabolic reactions. The findings indicate that acute reactions as a result or as circadian rhythms appear to be important in the pathogenesis of AMI-associated complications and that a large breakfast in association with nitrite deficiency may further trigger the circadian rhythms. However, more studies in a larger number of subjects would be necessary in order to confirm our findings.

Can brain dysfunction be a predisposing factor for metabolic syndrome?

The various mechanisms that may explain the association between brain dysfunction and the pathogenesis of metabolic syndrome (MS) leading to cardiovascular disease and type 2 diabetes have been reviewed. A Medline search was conducted until September 2003, and articles published in various national and international journals were reviewed. Experts working in the field were also consulted. Compelling evidence was found that saturated and total fat and low dietary n-3 fatty acids and other long-chain polyunsaturated fatty acids (PUFAs) in conjunction with sedentary behavior and mental stress combined with various personality traits can enhance sympathetic activity and increase the secretion of catecholamine, cortisol and serotonin, all of which appear to be underlying mechanisms involved in MS. Excess secretion of these neurotransmitters in conjunction with underlying long-chain PUFA deficiency may damage the neurons in the ventromedial hypothalamus and insulin receptors in the brain, in particular during fetal life, infancy and childhood, and lead to their dysfunction. Since 30-50% of the fatty acids in the brain are long-chain PUFAs, especially omega-3 fatty acids which are incorporated in the cell membrane phospholipids, it is possible that their supplementation may have a protective effect. Omega-3 fatty acids are also known to enhance parasympathetic activity and to increase the secretion of anti-inflammatory cytokines as well as acetylecholine in the hippocampus. It is possible that a marginal deficiency of long-chain PUFAs, especially n-3 fatty acids, due to poor dietary intake during the critical period of brain growth and development in the fetus, and later in the infant and also possibly in the child, adolescent and adult may enhance the release of tumor necrosis factor-alpha (TNF-alpha) interleukin (IL)-1, 2 and 6 and cause neuronal dysfunction. Experimental studies indicate that ventromedial hypothalamic lesions in rats induce hyperphagia, resulting in glucose intolerance and insulin resistance. Treatment with neuropeptide Y abolished hyperphagia and ob mRNA (leptin mRNA) in this animal model. Long-term infusion of norepinephrine and serotonin into the ventromedial hypothalamus impaired pancreatic islet function inasmuch as ventromedial hypothalamic norepinephrine and serotonin levels were elevated in hyperinsulinemic and insulin-resistant animals. Treatment with insulin was associated with restoration of hypothalamic neurotransmitter abnormalities, indicating that ventromedial hypothalamus dysfunction can impair pancreatic beta cells resulting in metabolic abnormalities consistent with MS. Treatment with omega-3 fatty acids, beta blockers, ACE inhibitors, estrogen, and meditation may have a beneficial effect on insulin receptors and ventromedial hypothalamic dysfunction. However, no definite or precise insight into the pathophysiological link between MS, brain function and nutrition is available. Despite this, epidemiological studies and intervention trials indicate that treatment with n-3 fatty acids may be adopted in clinical practice and used to direct therapy for prevention of type 2 diabetes, hypertension, coronary artery disease (CAD), and atherosclerosis, thereby indicating that MS may also respond to this treatment.

Prediction of gestational hypertension or intrauterine fetal growth restriction by mid-trimester 24-h ambulatory blood pressure monitoring

OBJECTIVES

To investigate clinical impact of 24-h ambulatory blood pressure monitoring (ABPM) on the prediction of hypertensive disorders of pregnancy and IUGR.

METHODS

ABPM was performed in 334 normotensive non-proteinuric nulliparous women at 20 weeks' gestation. Arterial blood pressure patterns were analyzed by chronobiometry.

RESULTS

Women who developed idiopathic IUGR (21) or PIH (33) showed a 24-h diastolic blood pressure mean significantly higher than the controls (69.2+/-1.8 mmHg and 73.5+/-6.2 vs. 62.2+/-1.5). Women with subsequent IUGR also showed a modification in BP rhythm. The most effective cut-off levels of 24-h diastolic blood pressure mean proved to be 67 for IUGR and 68 for hypertension.

CONCLUSIONS

ABPM in the second trimester reliably predicts idiopathic IUGR and PIH. Both patients destined to develop gestational hypertension and those destined to develop IUGR show similar elevations in 24-h diastolic mean at 20 weeks' gestation.