The Morning Blood Pressure Surge: Therapeutic Implications

Hypertension: Causes and Consequences of Circadian Rhythms in Blood Pressure

Hypertension is extremely common, affecting approximately 1 in every 2 adults globally. Chronic hypertension is the leading modifiable risk factor for cardiovascular disease and premature mortality worldwide. Despite considerable efforts to define mechanisms that underlie hypertension, a potentially major component of the disease, the role of circadian biology has been relatively overlooked in both preclinical models and humans. Although the presence of daily and circadian patterns has been observed from the level of the genome to the whole organism, the functional and structural impact of biological rhythms, including mechanisms such as circadian misalignment, remains relatively poorly defined. Here, we review the impact of daily rhythms and circadian systems in regulating blood pressure and the onset, progression, and consequences of hypertension. There is an emphasis on the impact of circadian biology in relation to vascular disease and end-organ effects that, individually or in combination, contribute to complex phenotypes such as cognitive decline and the loss of cardiac and brain health. Despite effective treatment options for some individuals, control of blood pressure remains inadequate in a substantial portion of the hypertensive population. Greater insight into circadian biology may form a foundation for novel and more widely effective molecular therapies or interventions to help in the prevention, treatment, and management of hypertension and its related pathophysiology.

Implications of Circadian Rhythm in Stroke Occurrence: Certainties and Possibilities

Stroke occurrence is not randomly distributed over time but has circadian rhythmicity with the highest frequency of onset in the morning hours. This specific temporal pattern is valid for all subtypes of cerebral infarction and intracerebral hemorrhage. It also correlates with the circadian variation of some exogenous factors such as orthostatic changes, physical activity, sleep-awake cycle, as well as with endogenous factors including dipping patterns of blood pressure, or morning prothrombotic and hypofibrinolytic states with underlying cyclic changes in the autonomous system and humoral activity. Since the internal clock is responsible for these circadian biological changes, its disruption may increase the risk of stroke occurrence and influence neuronal susceptibility to injury and neurorehabilitation. This review aims to summarize the literature data on the circadian variation of cerebrovascular events according to physiological, cellular, and molecular circadian changes, to survey the available information on the chronotherapy and chronoprophylaxis of stroke and its risk factors, as well as to discuss the less reviewed impact of the circadian rhythm in stroke onset on patient outcome and functional status after stroke.

Blood Pressure Management in Stroke

Hypertension is a well-established and modifiable risk factor for stroke and other cardiovascular diseases. Notably, stroke is the second leading cause of death worldwide and the second most common cause of disability-adjusted life-years. As such, we provide a viewpoint on blood pressure management in stroke and emphasize blood pressure control or management for first and recurrent stroke prevention, acute stroke treatment, and for prevention of cognitive impairment or dementia.

Early morning-Best time window of hourly 24-hour ambulatory blood pressure in relation to hypertensive organ damage: The Japan Morning Surge-Home Blood Pressure study

The correlations between organ damage and hourly ambulatory blood pressure (BP) have not been established. The patients were 1464 participants of the Japan Morning Surge-Home Blood Pressure (J-HOP) study participants who underwent ambulatory BP monitoring. The hourly systolic BP (SBP) at x o'clock was defined as the average of SBP values measured at times x - 30 minutes, x, and x + 30 minutes. The mean age was 64.8 ± 11.6 years. The percentage of male participants was 47.8%. The left ventricular mass index (LVMI) was significantly associated with SBP at 6 o'clock (r = 0.166, P < 0.001). The carotid intima-media thickness was significantly associated with SBP at 5 o'clock (r = 0.196, P < 0.001). After adjustment for age, sex, smoking, hyperlipidemia, diabetes mellitus, antihypertensive drug use, clinic SBP, and 24-hour ambulatory SBP, the correlations of the LVMI and hourly SBP at 6 o'clock remained significant (beta coefficient = 0.125, P < 0.01). In conclusion, morning ambulatory systolic BP especially at 5 and 6 o'clock was independently associated with organ damage.

Morning Blood Pressure Surge Relates to Autonomic Neural Activity in Young Non-Dipping Adults: The African-PREDICT Study

BACKGROUND

It is well established that an exaggerated morning blood pressure surge (MBPS) is associated with an increased risk for cardiovascular disease development in hypertensive individuals. However, in non-dipping individuals, a lower surge was reportedly associated with increased cardiovascular risk. Sympathetic nervous system activity is involved in 24-hour blood pressure fluctuations, including night-time dipping and the MBPS. To better understand this interaction, we investigated associations of MBPS with heart-rate variability and baroreceptor sensitivity in young healthy dippers and non-dippers.

METHODS

We included black and white men and women (n=827), aged 20-30 years and determined the MBPS using two formulas: the sleep-trough and dynamic morning surge. For autonomic function we determined baroreceptor sensitivity and heart-rate variability.

RESULTS

The majority of non-dippers in this population were black (70.4%), presenting lower sleep-trough and dynamic morning surge (all p<0.001). Heart-rate variability was comparable between dippers and non-dippers, whereas baroreceptor sensitivity was higher in non-dippers (p=0.021). Despite a suppressed MBPS profile in non-dippers, we found both sleep-trough (β=-0.25; p=0.039) and dynamic morning surge (β=-0.14; p=0.047) to be inversely and independently associated with 24-hour heart-rate variability (total power). These results were absent in dippers.

CONCLUSIONS

In conclusion, we found a higher night-time blood pressure coupled with lower MBPS in young healthy non-dippers. Furthermore, this lower MBPS was independently and negatively associated with autonomic neural activity, suggesting increased autonomic function involvement in MBPS suppression of non-dippers. The predictive value of suppressed nocturnal dipping pattern should be investigated while taking autonomic neural activity into account.

Circadian Variation of Stroke Onset: A Hospital-Based Study

Aims and background.

The circadian pattern of stroke occurrence variation has been recognized with certain differences between authors and stroke types. The underlying reason may be related to exogenous factors (cyclic physical activity, including sleep–awake cycles and assuming the up-right posture) and endogenous factors, with their diurnal variation (blood pressure, hemostatic balance, autonomic system activity). The aims of the present study are to investigate the existence of a circadian variation of stroke and the possible differences between stroke subtypes in the Cluj Napoca area.

Materials and method.

The stroke event data were acquired from the Patient Records of a consecutive series of 1083 patients admitted through the Emergency Room at Neurology Departments I and II of the District Hospital of Cluj Napoca, between 1 January 2012 and 31 December 2012. The classifiable onset time was assigned to one of four six-hour intervals: 00.01–06.00 (night), 06.01–12.00 (morning), 12.01–18.00 (afternoon) and 18.01–24.00 (evening). Demographic data and vascular risk factors were recorded.

Results.

All three stroke types (ischemic stroke, hemorrhagic stroke and subarachnoid hemorrhage) have shown a circadian variation regarding their occurrence, with the peak of incidence in the morning and the nadir during nighttime. This circadian pattern is independent by demographic factors and vascular risk factors.

Conclusion.

Our study confirmed the circadian variation of onset occurrence for all stroke subtypes. Some triggering factors promote ischemic stroke and prevent hemorrhagic stroke. The diurnal pattern of variation with the higher incidence in the morning and the lower in the night may lead to chrono-therapeutic and preventive approach (chrono-therapy of the risk factors), which targets the period of the highest vulnerability after awaking.

Influences of the circadian clock on neuronal susceptibility to excitotoxicity

Stroke is the third leading cause of death and the primary cause of morbidity in the United States, thus posing an enormous burden on the healthcare system. The factors that determine the risk of an individual toward precipitation of an ischemic event possess a strong circadian component as does the ischemic event itself. This predictability provided a window of opportunity toward the development of chronopharmaceuticals which provided much better clinical outcomes. Experiments from our lab showed for the first time that neuronal susceptibility to ischemic events follows a circadian pattern; hippocampal neurons being most susceptible to an ischemic insult occurring during peak activity in a rodent model of global cerebral ischemia. We also demonstrated that the SCN2.2 cells (like their in vivo counterpart) are resistant to excitotoxicity by glutamate and that this was dependent on activation of ERK signaling. We are currently working on elucidating the complete neuroprotective pathway that provides a barricade against glutamate toxicity in the SCN2.2 cells. Our future experiments will be engaged in hijacking the neuroprotective mechanism in the SCN2.2 cells and applying it to glutamate-susceptible entities in an effort to prevent their death in the presence of excitotoxicity. Despite the advancement in chronopharmaceuticals, optimal clinical outcome with minimal adverse events are difficult to come by at an affordable price. Superior treatment options require a better understanding of molecular mechanisms that define the disease, including the role of the circadian clock.

Benefits of once-daily therapies in the treatment of hypertension

In patients with hypertension, 24-hour blood pressure control is the major therapeutic goal. The number of daily doses is one characteristic of an antihypertensive agent that may affect the adequacy of 24-hour control. One measure of therapeutic coverage is the 24-hour trough-to-peak ratio, which determines the suitability of an agent for once-daily administration. The closer an agent is to a 100% trough-to-peak ratio, the more uniform the 24-hour coverage and therefore blood pressure control. High trough-to-peak ratio, long-acting antihypertensive medications lower blood pressure more gradually, which reduces the likelihood of adverse events attributable to abrupt drug action that occurs with shorter-acting agents. In hypertension, the natural diurnal variation of blood pressure may be altered, including elevated nighttime pressures. An optimal once-daily hypertension therapy would not only lower blood pressure but also normalize any blunted circadian variations in blood pressure. The benefits of once-daily agents with sustained therapeutic coverage may also be explained, in part, by increased patient adherence to simpler regimens as well as lower loss of blood pressure control during virtually inevitable intermittent noncompliance. Studies have demonstrated that once-daily antihypertensive agents have the highest adherence compared with twice-daily or multiple daily doses, including greater adherence to the prescribed timing of doses.

An Emerging Role for Understanding Orthostatic Hyp'er'tension in the Cardiorenal Syndrome

Orthostatic hypertension (OHT) is a clinically important problem increasingly recognized in persons with borderline hypertension, diabetes mellitus, and autonomic neuropathies, and in the elderly. Moreover, the association of OHT with progression of target end-organ damage, especially coronary heart disease and chronic kidney disease (CKD), and the attendant increased cardiovascular disease (CVD) and CKD risk, is gaining attention but is still underappreciated. There are various mechanisms that contribute to the development of OHT: excessive vascular adrenergic sensitivity, baroreceptor reflex abnormalities, and inappropriate activation of the renin-angiotensin-aldosterone system, which are also mechanisms that lead to cardiorenal metabolic disease (CRS). While the evidence is compelling for the clinical importance of OHT, more investigation is needed to evaluate the effects of OHT on CKD and CVD. The notion that the development of OHT is a risk factor for the development of CRS raises the need for further clinical and investigational attention to this clinical dilemma.

Potential roles of melatonin and chronotherapy among the new trends in hypertension treatment

The number of well-controlled hypertensives is unacceptably low worldwide. Respecting the circadian variation of blood pressure, nontraditional antihypertensives, and treatment in early stages of hypertension are potential ways to improve hypertension therapy. First, prominent variations in circadian rhythm are characteristic for blood pressure. The revolutionary MAPEC (Ambulatory Blood Pressure Monitoring and Cardiovascular Events) study, in 3000 adult hypertensives investigates, whether chronotherapy influences the cardiovascular prognosis beyond blood pressure reduction per se. Second, melatonin, statins and aliskiren are hopeful drugs for hypertension treatment. Melatonin, through its scavenging and antioxidant effects, preservation of NO availability, sympatholytic effect or specific melatonin receptor activation exerts antihypertensive and anti-remodeling effects and may be useful especially in patients with nondipping nighttime blood pressure pattern or with nocturnal hypertension and in hypertensives with left ventricular hypertrophy (LVH). Owing to its multifunctional physiological actions, this indolamine may offer cardiovascular protection far beyond its hemodynamic benefit. Statins exert several pleiotropic effects through inhibition of small guanosine triphosphate-binding proteins such as Ras and Rho. Remarkably, statins reduce blood pressure in hypertensive patients and more importantly they attenuate LVH. Addition of statins should be considered for high-risk hypertensives, for hypertensives with LVH, and possibly for high-risk prehypertensive patients. The direct renin inhibitor, aliskiren, inhibits catalytic activity of renin molecules in circulation and in the kidney, thus lowering angiotensin II levels. Furthermore, aliskiren by modifying the prorenin conformation may prevent prorenin activation. At present, aliskiren should be considered in hypertensive patients not sufficiently controlled or intolerant to other inhibitors of renin-angiotensin system. Third, TROPHY (Trial of Preventing Hypertension) is the first pharmacological intervention for prehypertensive patients revealing that treatment with angiotensin II type 1 receptor blocker attenuates hypertension development and thus decreases the risk of cardiovascular events.

Management of hypertension in the outpatient setting

The treatment of hypertension on an outpatient basis should be approached in a systematic manner. The diagnosis of hypertension should always be verified first before treatment is initiated and, where indicated, a workup should be done. Lifestyle modifications should be considered in all patients with hypertension. Blood pressure can be brought to goal in the majority of patients if antihypertensive medications are correctly dosed or combined. As blood pressure is brought to goal in the patient with hypertension, ongoing attention should be directed to long-term adherence to therapy.