Summer does not always mean lower: seasonality of 24 h, daytime, and night-time blood pressure

Potential mechanisms of ischemic stroke induced by heat exposure

Recent decades of epidemiological and clinical research have suggested that heat exposure could be a potential risk factor for ischemic stroke. Despite climate factors having a minor impact on individuals compared with established risk factors such as smoking, their widespread and persistent effects significantly affect public health. The mechanisms by which heat exposure triggers ischemic stroke are currently unclear. However, several potential mechanisms, such as the impact of temperature variability on stroke risk factors, inflammation, oxidative stress, and coagulation system changes, have been proposed. This article details the potential mechanisms by which heat exposure may induce ischemic stroke, aiming to guide the prevention and treatment of high-risk groups in hot climates and support public health policy development.

Seasonal variation in ambulatory blood pressure control in patients on clinic blood pressure-guided antihypertensive treatment

BACKGROUND

We investigated seasonal variation in ambulatory blood pressure control in hypertensive patients on clinic blood pressure-guided antihypertensive treatment.

METHODS

The study participants were hypertensive patients enrolled in an 8-week therapeutic study. Antihypertensive treatment was initiated with long-acting dihydropyridine calcium channel blockers amlodipine 5 mg/day or the gastrointestinal therapeutic system (GITS) formulation of nifedipine 30 mg/day, with the possible up-titration to amlodipine 10 mg/day or nifedipine-GITS 60 mg/day at 4 weeks of follow-up.

RESULTS

The proportion of up-titration to higher dosages of antihypertensive drugs at 4 weeks of follow-up was higher in patients who commenced treatment in autumn/winter ( n  = 302) than those who commenced treatment in spring/summer ( n  = 199, 24.5 vs. 12.0%, P  < 0.001). The control rate of clinic blood pressure, however, was lower in autumn/winter than in spring/summer at 4 (56.7 vs. 70.7%, P  = 0.003) and 8 weeks of follow-up (52.5 vs. 74.9%, P  < 0.001). At 8 weeks, patients who commenced treatment in autumn/winter, compared with those who commenced treatment in spring/summer, had a significantly ( P ≤0.03) smaller daytime (mean between-season difference -3.2/-2.8 mmHg) but greater nighttime SBP/DBP reduction (3.6/1.6 mmHg). Accordingly, at 8 weeks, the prevalence of nondippers was significantly ( P  < 0.001) higher in spring/summer than in autumn/winter for both SBP (54.8 vs. 30.0%) and DBP (53.4 vs. 28.8%).

CONCLUSION

Clinic blood pressure-guided antihypertensive treatment requires a higher dosage of medication in cold than warm seasons, which may have led to over- and under-treatment of nighttime blood pressure, respectively.

Seasonality in nighttime blood pressure and its associations with target organ damage

There is some evidence that nighttime blood pressure varies between seasons. In the present analysis, we investigated the seasonal variation in ambulatory nighttime blood pressure and its associations with target organ damage. In 1054 untreated patients referred for ambulatory blood pressure monitoring, we performed measurements of urinary albumin-to-creatinine ratio (ACR, n = 1044), carotid-femoral pulse wave velocity (cfPWV, n = 1020) and left ventricular mass index (LVMI, n = 622). Patients referred in spring (n = 337, 32.0%), summer (n = 210, 19.9%), autumn (n = 196, 18.6%) and winter (n = 311, 29.5%) had similar 24-h ambulatory systolic/diastolic blood pressure (P ≥ 0.25). However, both before and after adjustment for confounding factors, nighttime systolic/diastolic blood pressure differed significantly between seasons (P < 0.001), being highest in summer and lowest in winter (adjusted mean values 117.0/75.3 mm Hg vs. 111.4/71.1 mm Hg). After adjustment for confounding factors, nighttime systolic/diastolic blood pressure were significantly and positively associated with ACR, cfPWV and LVMI (P < 0.006). In season-specific analyses, statistical significance was reached for all the associations of nighttime blood pressure with target organ damage in summer (P ≤ 0.02), and for some of the associations in spring, autumn and winter. The association between nighttime systolic blood pressure and ACR was significantly stronger in patients examined in summer than those in winter (standardized β, 0.31 vs 0.11 mg/mmol, P for interaction = 0.03). In conclusion, there is indeed seasonality in nighttime blood pressure level, as well as in its association with renal injury in terms of urinary albumin excretion. Our study shows that there is indeed seasonal variability in nighttime blood pressure, highest in summer and lowest in winter, and its association with renal injury in terms of urinary albumin excretion varies between summer and winter as well.

Climate change and cardiovascular disease: implications for global health

Climate change is the greatest existential challenge to planetary and human health and is dictated by a shift in the Earth's weather and air conditions owing to anthropogenic activity. Climate change has resulted not only in extreme temperatures, but also in an increase in the frequency of droughts, wildfires, dust storms, coastal flooding, storm surges and hurricanes, as well as multiple compound and cascading events. The interactions between climate change and health outcomes are diverse and complex and include several exposure pathways that might promote the development of non-communicable diseases such as cardiovascular disease. A collaborative approach is needed to solve this climate crisis, whereby medical professionals, scientific researchers, public health officials and policymakers should work together to mitigate and limit the consequences of global warming. In this Review, we aim to provide an overview of the consequences of climate change on cardiovascular health, which result from direct exposure pathways, such as shifts in ambient temperature, air pollution, forest fires, desert (dust and sand) storms and extreme weather events. We also describe the populations that are most susceptible to the health effects caused by climate change and propose potential mitigation strategies, with an emphasis on collaboration at the scientific, governmental and policy levels.

Seasonal variation of ambulatory blood pressure in Chinese hypertensive adolescents

BACKGROUND

Blood pressure (BP) exhibits seasonal variation with lower levels at higher temperatures and vice versa. This phenomenon affects both sexes and all age groups. So far, only a few research studies have investigated this condition in adolescents and none of them were based on hypertensive population or ever applied ambulatory blood pressure monitor (ABPM). Therefore, we carried out the first study that used ABPM to record seasonal variation of blood pressure in hypertensive adolescents.

METHODS

From March 2018 to February 2019, 649 ABPMs from hypertensive adolescents between 13 and 17 years who were referred to wear an ABPM device in Beijing and Baoding were extracted. Seasonal change in ambulatory BP value, dipping status, and prevalence of different BP phenotypes were analyzed and compared.

RESULTS

Mean age of participants was 14.9 ± 1.5 years and 65.8% of them were boys. Of the participants, 75.3% met the criteria of overweight or obesity. From summer to winter, average 24-hour, day-time, and night-time BP showed significant rise, which was 9.8/2.8, 9.8/3.0, and 10.9/3.4 mmHg, respectively. This seasonal effect on BP was not dependent on the obesity degree. In addition, higher prevalence of nondippers and risers existed in winter while white coat hypertension was more frequent in warmer seasons.

CONCLUSION

Hypertensive adolescents showed evident seasonal change in their ABPM results, which was featured by elevated BP level and more frequent abnormal dipping patterns in winter. On the contrary, higher prevalence of white coat hypertension was found in warmer seasons. Physicians should take seasonal variation into consideration when managing adolescent hypertension.

Novel insights into the association between seasonal variations, blood pressure, and blood pressure variability in patients with new-onset essential hypertension

Background

Blood pressure (BP) exhibits seasonal variations, with peaks reported in winter. However, the association between seasonal variations and blood pressure variability in patients with new-onset essential hypertension is not fully understood. This study evaluated the potential association of seasonal variations with new-onset essential hypertension.

Methods

This retrospective observational study recruited a total of 440 consecutive patients with new-onset essential hypertension who underwent 24-h ambulatory electrocardiograph (ECG) and BP measurement at our department between January 2019 and December 2019. Demographic and baseline clinical data including BP variability, heart rate variability, and blood tests were retrieved. Multivariate linear regression analysis was performed to identify factors independently associated with mean BP and BP variability.

Results

Among the 440 patients recruited, 93 cases were admitted in spring, 72 in summer, 151 in autumn, and 124 in winter. Univariate analysis revealed that systolic BP (SBP), diastolic BP (DBP), high-sensitivity C-reactive protein, SBP drop rate, DBP drop rate, 24-h standard deviation of SBP, 24-h standard deviation of DBP, 24-h SBP coefficient of variation, and 24-h DBP coefficient of variation were associated with patients admitted in winter (P < 0.05 for all). Multivariate linear regression analysis showed that winter was the influencing factor of 24-h standard deviation of SBP (B = 1.851, t = 3.719, P < 0.001), 24-h standard deviation of DBP (B = 1.176, t = 2.917, P = 0.004), 24-h SBP coefficient of variation (B = 0.015, t = 3.670, P < 0.001), and 24-h DBP coefficient of variation (B = 0.016, t = 2.849, P = 0.005) in hypertensive patients.

Conclusions

Seasonal variations are closely associated with BP variability in patients with new-onset essential hypertension. Our study provides insight into the underlying pathogenesis of new-onset essential hypertension.

Reduced nitric oxide synthesis in winter: A potential contributing factor to increased cardiovascular risk

BACKGROUND

Nitric oxide is a key signalling molecule that elicits a range of biological functions to maintain vascular homeostasis. A reduced availability of nitric oxide is implicated in the progression of cardiovascular diseases and increases the risk of pathogenic events.

AIMS

To compare the concentration of nitric oxide metabolites in healthy adults between winter and summer months.

DESIGN

An observational study of healthy adults (age 32 ± 9 years) living in central Scotland.

METHODS

Thirty-four healthy adults (13 females) were monitored for 7 days in summer and winter to record sunlight exposure (ultraviolet-A (UV-A) radiation), diet, and physical activity. At the end of each phase, blood pressure was measured, and samples of blood and saliva collected. The samples were analysed to determine the concentrations of plasma and salivary nitrate and nitrite and serum 25-hydroxyvitamin D (25(OH)D).

RESULTS

The participants maintained similar diets in each measurement phase but were exposed to more UV-A radiation (550%) and undertook more moderate-vigorous physical activity (23%) in the summer than in winter. Plasma nitrite (46%) and serum 25(OH)D (59%) were higher and blood pressure was lower in the summer compared to winter months. Plasma nitrite concentration was negatively associated with systolic, diastolic, and mean arterial blood pressure.

CONCLUSIONS

Plasma nitrite, an established marker of nitric oxide synthesis, is higher in healthy adults during the summer than in winter. This may be mediated by a greater exposure to UV-A which stimulates the release of nitric oxide metabolites from skin stores. While it is possible that seasonal variation in nitric oxide availability may contribute to an increased blood pressure in the winter months, the overall impact on cardiovascular health remains to be determined.

Seasonal variation of ambulatory blood pressure in Chinese hypertensive adolescents

BACKGROUND

Blood pressure (BP) exhibits seasonal variation with lower levels at higher temperatures and vice versa. This phenomenon affects both sexes and all age groups. So far, only a few research studies have investigated this condition in adolescents and none of them were based on hypertensive population or ever applied ambulatory blood pressure monitor (ABPM). Therefore, we carried out the first study that used ABPM to record seasonal variation of blood pressure in hypertensive adolescents.

METHODS

From March 2018 to February 2019, 649 ABPMs from hypertensive adolescents between 13 and 17 years who were referred to wear an ABPM device in Beijing and Baoding were extracted. Seasonal change in ambulatory BP value, dipping status, and prevalence of different BP phenotypes were analyzed and compared.

RESULTS

Mean age of participants was 14.9 ± 1.5 years and 65.8% of them were boys. Of the participants, 75.3% met the criteria of overweight or obesity. From summer to winter, average 24-hour, day-time, and night-time BP showed significant rise, which was 9.8/2.8, 9.8/3.0, and 10.9/3.4 mmHg, respectively. This seasonal effect on BP was not dependent on the obesity degree. In addition, higher prevalence of nondippers and risers existed in winter while white coat hypertension was more frequent in warmer seasons.

CONCLUSION

Hypertensive adolescents showed evident seasonal change in their ABPM results, which was featured by elevated BP level and more frequent abnormal dipping patterns in winter. On the contrary, higher prevalence of white coat hypertension was found in warmer seasons. Physicians should take seasonal variation into consideration when managing adolescent hypertension.

Seasonal variation in blood pressure: current evidence and recommendations for hypertension management

Blood pressure (BP) exhibits seasonal variation, with an elevation of daytime BP in winter and an elevation of nighttime BP in summer. The wintertime elevation of daytime BP is largely attributable to cold temperatures. The summertime elevation of nighttime BP is not due mainly to temperature; rather, it is considered to be related to physical discomfort and poor sleep quality due to the summer weather. The winter elevation of daytime BP is likely to be associated with the increased incidence of cardiovascular disease (CVD) events in winter compared to other seasons. The suppression of excess seasonal BP changes, especially the wintertime elevation of daytime BP and the summertime elevation of nighttime BP, would contribute to the prevention of CVD events. Herein, we review the literature on seasonal variations in BP, and we recommend the following measures for suppressing excess seasonal BP changes as part of a regimen to manage hypertension: (1) out-of-office BP monitoring, especially home BP measurements, throughout the year to evaluate seasonal variations in BP; (2) the early titration and tapering of antihypertensive medications before winter and summer; (3) the optimization of environmental factors such as room temperature and housing conditions; and (4) the use of information and communication technology-based medicine to evaluate seasonal variations in BP and provide early therapeutic intervention. Seasonal BP variations are an important treatment target for the prevention of CVD through the management of hypertension, and further research is necessary to clarify these variations.

Seasonal Variation in Masked Nocturnal Hypertension: The J-HOP Nocturnal Blood Pressure Study

BACKGROUND

Little is known about seasonal variation in nighttime blood pressure (BP) measured by a home device. In this cross-sectional study, we sought to assess seasonal variation in nighttime home BP using data from the nationwide, practice-based Japan Morning Surge-Home BP (J-HOP) Nocturnal BP study.

METHODS

In this study, 2,544 outpatients (mean age 63 years; hypertensives 92%) with cardiovascular risks underwent morning, evening, and nighttime home BP measurements (measured at 2:00, 3:00, and 4:00 am) using validated, automatic, and oscillometric home BP devices.

RESULTS

Our analysis showed that nighttime home systolic BP (SBP) was higher in summer than in other seasons (summer, 123.3 ± 14.6 mmHg vs. spring, 120.7 ± 14.8 mmHg; autumn, 121.1 ± 14.8 mmHg; winter, 119.3 ± 14.0 mmHg; all P<0.05). Moreover, we assessed seasonal variation in the prevalence of elevated nighttime home SBP (≥120 mmHg) in patients with non-elevated daytime home SBP (average of morning and evening home SBP <135 mmHg; n = 1,565), i.e., masked nocturnal hypertension, which was highest in summer (summer, 45.6% vs. spring, 27.2%; autumn, 28.8%; winter, 24.9%; all P<0.05). Even in intensively controlled morning home SBP (<125 mmHg), the prevalence of masked nocturnal hypertension was higher in summer (summer, 27.4% vs. spring, 14.2%; autumn, 8.9%; winter, 9.0%; all P<0.05). The urine albumin-creatinine ratio in patients with masked nocturnal hypertension tended to be higher than that in patients with non-elevated both daytime and nighttime SBP throughout each season.

CONCLUSIONS

The prevalence of masked nocturnal hypertension was higher in summer than other seasons and the difference proved to be clinically meaningful.

Roles of cardiovascular autonomic regulation and sleep patterns in high blood pressure induced by mild cold exposure in rats

Increased blood pressure (BP) caused by exposure to cold temperatures can partially explain the increased incidence of cardiovascular events in winter. However, the physiological mechanisms involved in cold-induced high BP are not well established. Many studies have focused on physiological responses to severe cold exposure. In this study, we aimed to perform a comprehensive analysis of cardiovascular autonomic function and sleep patterns in rats during exposure to mild cold, a condition relevant to humans in subtropical areas, to clarify the physiological mechanisms underlying mild cold-induced hypertension. BP, electroencephalography, electromyography, electrocardiography, and core body temperature were continuously recorded in normotensive Wistar-Kyoto rats over 24 h. All rats were housed in thermoregulated chambers at ambient temperatures of 23, 18, and 15 °C in a randomized crossover design. These 24-h physiological recordings either with or without sleep scoring showed that compared with the control temperature of 23 °C, the lower ambient temperatures of 18 and 15 °C not only increased BP, vascular sympathetic activity, and heart rate but also decreased overall autonomic activity, parasympathetic activity, and baroreflex sensitivity in rats. In addition, cold exposure reduced the delta power percentage and increased the incidence of interruptions during sleep. Moreover, a correlation analysis revealed that all of these cold-induced autonomic dysregulation and sleep problems were associated with elevation of BP. In conclusion, mild cold exposure elicits autonomic dysregulation and poor sleep quality, causing BP elevation, which may have critical implications for cold-related cardiovascular events.

Extreme dipping: is the cardiovascular risk increased? An unsolved issue

: Extreme dipping (i.e. a marked blood pressure fall during night-time period) is an alteration of circadian blood pressure (BP) rhythm frequently observed in the setting of systemic hypertension as well as in the general population. Some reports have suggested that cardiovascular prognosis in extreme dippers (ED) is similar as in dippers, whereas other studies have documented either a better or worse prognosis in ED. Available information on clinical and prognostic implications of ED is scanty and data provided by studies are controversial. Furthermore, a comprehensive report summarizing the key features of this BP pattern is lacking. The present review focuses on a number of issues concerning ED pattern such as the prevalence and clinical correlates, mechanisms underlying this BP phenotype association with hypertension mediated organ damage (HMOD) and prognostic value in predicting cardiovascular events and all-cause mortality. The reported prevalence of this BP rhythm alteration ranges from 5% to 30%, depending on diagnostic criteria, clinical and demographic characteristics of subjects. Most studies targeting the association of this condition with HMOD failed to find consistent findings in support of an adverse impact of ED on vascular, renal of cardiac structure and function. Available data on ED as compared to low risk reference group (i.e. dippers) do not allow to conclude that high BP variability resulting from a marked BP fall at night adversely affects cardiovascular prognosis at the community level and in the general hypertensive population. Thus, further studies aimed to assess the prognostic significance of ED as well as the impact of therapeutic interventions aimed to normalize this circadian BP pattern, are highly needed.

Seasonal variation in 24 h blood pressure profile in healthy adults- A prospective observational study

The clinical and experimental data on seasonal variation in blood pressure is mainly from office and home blood pressure (BP) monitoring studies. There are few studies from temperate climates on seasonal changes with ambulatory blood pressure (ABP) monitoring and none from India. This is a prospective, observational study among healthy adults. ABP was measured in four different seasons in 28 subjects. Mean arterial pressure (MAP), ambulatory systolic blood pressure (SBP), and ambulatory diastolic blood pressure (DBP) were significantly higher in winter compared to summer season. 24-hour MAP was lowest in summer while highest MAP was recorded in winter (97.04 ± 8.30 and 103.89 ± 8.54, respectively). The mean difference was -6.86 mm Hg (95% CI: -10.74 to -2.97, p = 0.001). This difference was mainly due to increase in day time MAP. There was no difference in 24 h systolic and diastolic blood pressure between summer and winter. There was significant difference between summer and winter in the SBP (day time) [125.61 ± 11.44 and 131.93 ± 9.46, mean difference -6.32 (95% CI: -10.69 to -1.95, p = 0.005)] and DBP (day time) [79.57 ± 9.95 and 87.07 ± 9.9, mean difference -7.50 (95% CI: -12.49 to -2.51, p = 0.003)]. The night time systolic and diastolic BP was similar during winter and summer. Thus, BP increases significantly during winter compared to summer season. This change is primarily in the day time systolic, diastolic and mean blood pressures. Larger studies are required to further validate our findings.

Hypotensive Effect of Heated Water-Based Exercise Persists After 12-Week Cessation of Training in Patients With Resistant Hypertension

BACKGROUND

Heated water-based exercise (HEx) promotes a marked reduction of blood pressure (BP), but it is not entirely clear whether its effects on BP persist after cessation of HEx.

METHODS

We analyzed the effects of cessation of HEx on 24-hour ambulatory BP monitoring (ABPM) in patients with resistant hypertension (RH). Thirty-two patients (aged 53 ± 6 years) with RH (4 to 6 antihypertensive drugs) were randomly assigned to HEx (n = 16) or control (n = 16) groups. Antihypertensive therapy remained unchanged during the protocol. The HEx group participated in 36 sessions (60 minutes) in a heated pool (32^oC [89.6°F]) for 12 weeks (training), followed by 12 weeks of cessation of training. The control group was evaluated during the same period and instructed to maintain their habitual activities.

RESULTS

HEx and control groups had similar BP levels at baseline. HEx training reduced the 24-hour systolic (-19.5 ± 4.6 vs 3.0 ± 0.7 mm Hg, P = 0.001) and diastolic BP (-11.1 ± 2.4 vs 2.06 ± 0.9 mm Hg, P = 0.001) at week 12, compared with the control group. After 12 weeks of training cessation (week 24), 24-hour BP remained significantly lower in the HEx group than in the control group (-9.6 ± 3.8 vs 6.3 ± 3.5 mm Hg, P = 0.01 and -7.5±2.2 vs 2.2 ± 1.0 mm Hg, P = 0.009, for systolic and diastolic BP, respectively), although these differences were attenuated.

CONCLUSIONS

BP remained lower after cessation of 12-week training among patients with RH who underwent HEx compared with the controls. The carryover effects of HEx on BP may help to overcome the challenging problem of exercise compliance in long-term follow-up.

Echoes from Gaea, Poseidon, Hephaestus, and Prometheus: environmental risk factors for high blood pressure

High blood pressure (BP) affects over one billion people and is the leading risk factor for global mortality. While many lifestyle and genetic risk factors are well-accepted to increase BP, the role of the external environment is typically overlooked. Mounting evidence now supports that numerous environmental factors can promote an elevation in BP. Broadly speaking these include aspects of the natural environment (e.g., cold temperatures, higher altitude, and winter season), natural disasters (e.g., earthquakes, volcanic eruptions), and man-made exposures (e.g., noise, air pollutants, and toxins/chemicals). This is important for health care providers to recognize as one (or several) of these environmental factors could be playing a clinically meaningful role in elevating BP or disrupting hypertension control among their patients. At the population level, certain environmental exposures may even be contributing to the growing pandemic of hypertension. Here we provide an updated review of the literature linking environment exposures with high BP and outline practical recommendations for clinicians.

Association Between Amplitude of Seasonal Variation in Self-Measured Home Blood Pressure and Cardiovascular Outcomes: HOMED-BP (Hypertension Objective Treatment Based on Measurement By Electrical Devices of Blood Pressure) Study

Background

The clinical significance of long‐term seasonal variations in self‐measured home blood pressure (BP) has not been elucidated for the cardiovascular disease prevention.

Methods and Results

Eligible 2787 patients were classified into 4 groups according to the magnitude of their seasonal variation in home BP, defined as an average of all increases in home BP from summer (July–August) to winter (January–February) combined with all decreases from winter to summer throughout the follow‐up period, namely inverse‐ (systolic/diastolic, <0/<0 mm Hg), small‐ (0–4.8/0–2.4 mm Hg), middle‐ (4.8–9.1/2.4–4.5 mm Hg), or large‐ (≥9.1/≥4.5 mm Hg) variation groups. The overall cardiovascular risks illustrated U‐shaped relationships across the groups, and hazard ratios for all cardiovascular outcomes compared with the small‐variation group were 3.07 (P=0.004) and 2.02 (P=0.041) in the inverse‐variation group and large‐variation group, respectively, based on systolic BP, and results were confirmatory for major adverse cardiovascular events. Furthermore, when the summer‐winter home BP difference was evaluated among patients who experienced titration and tapering of antihypertensive drugs depending on the season, the difference was significantly smaller in the early (September–November) than in the late (December–February) titration group (3.9/1.2 mm Hg versus 7.3/3.1 mm Hg, P<0.001) as well as in the early (March–May) than in the late (June–August) tapering group (4.4/2.1 mm Hg versus 7.1/3.4 mm Hg, P<0.001).

Conclusions

The small‐to‐middle seasonal variation in home BP (0–9.1/0–4.5 mm Hg), which may be partially attributed to earlier adjustment of antihypertensive medication, were associated with better cardiovascular outcomes.

Impact of seasonality and air pollutants on carotid-femoral pulse wave velocity and wave reflection in hypertensive patients

Objective

The effects of seasonality on blood pressure (BP) and cardiovascular (CV) events are well established, while the influence of seasonality and other environmental factors on arterial stiffness and wave reflection has never been analyzed. This study evaluated whether seasonality (daily number of hours of light) and acute variations in outdoor temperature and air pollutants may affect carotid-femoral pulse wave velocity (PWV) and pressure augmentation.

Design and method

731 hypertensive patients (30–88 years, 417 treated) were enrolled in a cross-sectional study during a 5-year period. PWV, central BP, Augmentation Index (AIx) and Augmentation Pressure (AP) were measured in a temperature-controlled (22–24°C) room. Data of the local office of the National Climatic Data Observatory were used to estimate meteorological conditions and air pollutants (PM₁₀, O₃, CO, N₂O) exposure on the same day.

Results

PWV (mean value 8.5±1.8 m/s) was related to age (r = 0.467, p<0.001), body mass index (r = 0.132, p<0.001), central systolic (r = 0.414, p<0.001) and diastolic BP (r = 0.093, p = 0.013), daylight hours (r = -0.176, p<0.001), mean outdoor temperature (r = -0.082, p = 0.027), O₃ (r = -0.135, p<0.001), CO (r = 0.096, p = 0.012), N₂O (r = 0.087, p = 0.022). In multiple linear regression analysis, adjusted for confounders, PWV remained independently associated only with daylight hours (β = -0.170; 95% CI: -0.273 to -0.067, p = 0.001). No significant correlation was found between pressure augmentation and daylight hours, mean temperature or air pollutants. The relationship was stronger in untreated patients and women. Furthermore, a positive, independent association between O₃ levels and PWV emerged in untreated patients (β: 0.018; p = 0.029; CI: 0.002 to 0.034) and in women (β: 0.027; p = 0.004; CI: 0.009 to 0.045).

Conclusions

PWV showed a marked seasonality in hypertensive patients. Environmental O₃ levels may acutely reduce arterial stiffness in hypertensive women and in untreated patients.

Diurnal Blood Pressure Rhythmicity in Relation to Environmental and Genetic Cues in Untreated Referred Patients

No previous study has addressed the relative contributions of environmental and genetic cues to the diurnal blood pressure rhythmicity. From 24-hour ambulatory recordings of systolic blood pressure obtained in untreated patients (51% women; mean age, 51 years), we computed the night-to-day ratio in 897 and morning surge in 637. Environmental cues included season, mean daily outdoor temperature, atmospheric pressure, humidity and weekday, and the genetic cues 14 single nucleotide polymorphisms in 10 clock genes. Systolic blood pressure averaged (±SD) 126.7±11.9 mm Hg, night-to-day ratio 0.86±0.07, and morning surge 24.8±10.7 mm Hg. In adjusted analyses, night-to-day ratio was 2.4% higher in summer and 1.8% lower in winter ( P <0.001) compared with the annual average with a small effect of temperature ( P =0.079); morning surge was 1.7 mm Hg lower in summer and 1.1 mm Hg higher in winter ( P <0.001). The other environmental cues did not add to the night-to-day ratio or morning surge variance ( P ≥0.37). Among the 14 genetic variations, only CLOCK rs180260 was significantly associated with morning surge after adjustment for season, temperature, and other host factors and after Bonferroni correction ( P =0.044). In CLOCK rs1801260 C allele carriers (n=83), morning surge was 3.7 mm Hg higher than in TT homozygotes (n=554). Of the night-to-day ratio and morning surge variance, season and temperature explained ≈8% and ≈3%, while for genetic cues, these proportions were ≈1% or less. In conclusion, environmental compared with genetic cues are substantially stronger drivers of the diurnal blood pressure rhythmicity.

Effect of Arteriovenous Anastomosis on Blood Pressure Reduction in Patients With Isolated Systolic Hypertension Compared With Combined Hypertension

Background

Options for interventional therapy to lower blood pressure (BP) in patients with treatment‐resistant hypertension include renal denervation and the creation of an arteriovenous anastomosis using the ROX coupler. It has been shown that BP response after renal denervation is greater in patients with combined hypertension (CH) than in patients with isolated systolic hypertension (ISH). We analyzed the effect of ROX coupler implantation in patients with CH as compared with ISH.

Methods and Results

The randomized, controlled, prospective ROX Control Hypertension Study included patients with true treatment‐resistant hypertension (office systolic BP ≥140 mm Hg, average daytime ambulatory BP ≥135/85 mm Hg, and treatment with ≥3 antihypertensive drugs including a diuretic). In a post hoc analysis, we stratified patients with CH (n=31) and ISH (n=11). Baseline office systolic BP (177±18 mm Hg versus 169±17 mm Hg, P=0.163) and 24‐hour ambulatory systolic BP (159±16 mm Hg versus 154±11 mm Hg, P=0.463) did not differ between patients with CH and those with ISH. ROX coupler implementation resulted in a significant reduction in office systolic BP (CH: −29±21 mm Hg versus ISH: −22±31 mm Hg, P=0.445) and 24‐hour ambulatory systolic BP (CH: −14±20 mm Hg versus ISH: −13±15 mm Hg, P=0.672), without significant differences between the two groups. The responder rate (office systolic BP reduction ≥10 mm Hg) after 6 months was not different (CH: 81% versus ISH: 82%, P=0.932).

Conclusions

Our data suggest that creation of an arteriovenous anastomosis using the ROX coupler system leads to a similar reduction of office and 24‐hour ambulatory systolic BP in patients with combined and isolated systolic hypertension.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01642498.

Effects of Baroreflex Activation Therapy on Ambulatory Blood Pressure in Patients With Resistant Hypertension

Baroreflex activation therapy (BAT) has been demonstrated to decrease office blood pressure (BP) in the randomized, double-blind Rheos trial. There are limited data on 24-hour BP changes measured by ambulatory BP measurements (ABPMs) using the first generation rheos BAT system suggesting a significant reduction but there are no information about the effect of the currently used, unilateral BAT neo device on ABPM. Patients treated with the BAT neo device for uncontrolled resistant hypertension were prospectively included into this study. ABPM was performed before BAT implantation and 6 months after initiation of BAT. A total of 51 patients were included into this study, 7 dropped out from analysis because of missing or insufficient follow-up. After 6 months, 24-hour ambulatory systolic (from 148±17 mm Hg to 140±23 mm Hg, P <0.01), diastolic (from 82±13 mm Hg to 77±15 mm Hg, P <0.01), day- and night-time systolic and diastolic BP (all P ≤0.01) significantly decreased while the number of prescribed antihypertensive classes could be reduced from 6.5±1.5 to 6.0±1.8 ( P =0.03). Heart rate and pulse pressure remained unchanged. BAT was equally effective in reducing ambulatory BP in all subgroups of patients. This is the first study demonstrating a significant BP reduction in ABPM in patients undergoing chronically stimulation of the carotid sinus using the BAT neo device. About that BAT-reduced office BP and improved relevant aspects of ABPM, BAT might be considered as a new therapeutic option to reduce cardiovascular risk in patients with resistant hypertension. Randomized controlled trials are needed to evaluate BAT effects on ABPM in patients with resistant hypertension accurately.

Seasonal Variation in Blood Pressure in 162,135 Patients With Type 1 or Type 2 Diabetes Mellitus

Seasonal variation in blood pressure (BP) has been observed in different populations. However, only few studies have focused on BP seasonality in diabetic patients. This study examined the seasonal patterns in BP in 62,589 patients with type 1 diabetes mellitus (T1DM) and in 99,546 patients with type 2 diabetes mellitus (T2DM) from the German/Austrian Diabetes Follow-up Registry. Adjusted mean BP values revealed seasonal cycles of 12 months, with higher BP in colder months. Using harmonic regression models, the estimated systolic BP difference throughout the year was 2.28/2.48 mm Hg in T1DM/T2DM (both P<.001). Interestingly, seasonal variation in diastolic BP was larger in T1DM than in T2DM (1.24/0.64 mm Hg, P<.001). A sex difference was observed in T1DM only, while age differences occurred in both types of diabetes. Correlations between BP and potentially related factors such as outdoor temperature indicated that reasons underlying BP seasonality are likely to be complex and vary by subgroup.

Summertime dosage-dependent hypersensitivity to an angiotensin II receptor blocker

Background

Summertime dips in blood pressure (BP), both in normotensive and hypertensive subjects, are well known. However, the dips are small and are not related to particular forms or doses of antihypertensive medication. Nevertheless it is the practice in some quarters to decrease antihypertensive medication in summer, and/or to increase in winter. Large scale studies being inconclusive, there are calls for long-term examination of the relationship between environmental temperature and blood pressure in single individuals under medication.

Case presentation

While analyzing data from a subject whose BP had been controlled for a decade with the angiotensin-II receptor blocker losartan, an extreme, dosage-dependent, summertime dip came to light. Downward dosage adjustment appeared essential and may have prevented hypotension-related pathology.

Conclusion

The benefits of aggressive medication (the “J curve” phenomenon) being debated, the possibility of seasonal hypersensitivity, perhaps explicable in terms of differential signaling by countervailing receptors, should be taken into account when considering dosage adjustments in hypertensive subjects.

Outdoor temperature, blood pressure, and cardiovascular disease mortality among 23 000 individuals with diagnosed cardiovascular diseases from China

Introduction

Blood pressure is a major cause of cardiovascular disease (CVD) and both may increase as outdoor temperatures fall. However, there are still limited data about seasonal variation in blood pressure and CVD mortality among patients with prior-CVD.

Methods

We analysed data on 23 000 individuals with prior-CVD who were recruited from 10 diverse regions into the China Kadoorie Biobank during 2004–8. After 7 years of follow-up, 1484 CVD deaths were recorded. Baseline survey data were used to assess seasonal variation in systolic blood pressure (SBP) and its association with outdoor temperature. Cox regression was used to examine the association of usual SBP with subsequent CVD mortality, and seasonal variation in CVD mortality was assessed by Poisson regression. All analyses were adjusted for age, sex, and region.

Results

Mean SBP was significantly higher in winter than in summer (145 vs. 136 mmHg, P < 0.001), especially among those without central heating. Above 5°C, each 10°C lower outdoor temperature was associated with 6.2 mmHg higher SBP. Systolic blood pressure predicted subsequent CVD mortality, with each 10 mmHg higher usual SBP associated with 21% (95% confidence interval: 16–27%) increased risk. Cardiovascular disease mortality varied by season, with 41% (21–63%) higher risk in winter compared with summer.

Conclusion

Among adult Chinese with prior-CVD, there is both increased blood pressure and CVD mortality in winter. Careful monitoring and more aggressive blood pressure lowering treatment in the cold months are needed to help reduce the winter excess CVD mortality in high-risk individuals.

Heated water-based exercise training reduces 24-hour ambulatory blood pressure levels in resistant hypertensive patients: a randomized controlled trial (HEx trial)

BACKGROUND

Regular exercise is an effective intervention to decrease blood pressure (BP) in hypertension, but no data are available concerning the effects of heated water-based exercise (HEx). This study examines the effects of HEx on BP in resistant hypertensive patients.

METHODS

This is a parallel, randomized controlled trial. 125 nonconsecutive sedentary patients with resistant hypertension from a hypertension outpatient clinic in a university hospital were screened; 32 patients fulfilled the study requirements. The training was performed for 60-minute sessions in a heated pool (32°C), three times a week for 12 weeks. The HEx protocol consisted of callisthenic exercises and walking inside the pool. The control group was asked to maintain habitual activities. The main outcome measure was change in mean 24-hour ambulatory BP (ABPM).

RESULTS

32 patients (HEx n=16; control n=16) were randomized; none were lost to follow-up. Office BPs decreased significantly after heated water exercise (36/12 mmHg). HEx decreased 24-hour systolic (from 137±23 to 120±12 mmHg, p=0.001) and diastolic BPs (from 81±13 to 72±10 mmHg, p=0.009); daytime systolic (from 141±24 to 120±13 mmHg, p<0.0001) and diastolic BPs (from 84±14 to 73±11 mmHg, p=0.003); and nighttime systolic (from 129±22 to 114±12 mmHg, p=0.006) and diastolic BPs (from 74±11 to 66±10 mmHg, p<0.0001). The control group after 12 weeks significantly increased in 24-hour systolic and diastolic BPs, and daytime and nighttime diastolic BPs.

CONCLUSION

HEx reduced office BPs and 24-hour ABPM levels in resistant hypertensive patients. These effects suggest that HEx may be a potential new therapeutic approach in these patients.

Season, temperature and blood pressure: a complex interaction

An increase in blood pressure values measured during winter either in the office, at home, or at ambulatory blood pressure monitoring was consistently observed. Besides potentially contributing to increase the risk for cardiovascular events during the cold season, long term blood pressure variations can influence results of clinical trials, epidemiological surveys, and require personalized management of antihypertensive medications in the single patient. Those variations are often considered as an effect of climate, due to the close correlation observed in various countries and in different settings between temperature and blood pressure among children, adults, and specially the elderly. However, obtaining true measurements of exposition is a main problem when investigating the effects of climate on human health especially when the aim is to disentangle the effects of climate from those of seasonality. The aim of the present note is not to provide a complete review of the literature demonstrating the implications of seasonal blood pressure changes in the clinical and experimental setting; rather it is to consider methodological aspects useful to investigate the interaction between seasonality and temperature on blood pressure and to make health care providers aware of the implications of environmental factors on blood pressure in clinical and research settings.

Ambulatory blood pressure changes after renal sympathetic denervation in patients with resistant hypertension

BACKGROUND

Catheter-based renal sympathetic denervation (RDN) reduces office blood pressure (BP) in patients with resistant hypertension according to office BP. Less is known about the effect of RDN on 24-hour BP measured by ambulatory BP monitoring and correlates of response in individuals with true or pseudoresistant hypertension.

METHODS AND RESULTS

A total of 346 uncontrolled hypertensive patients, separated according to daytime ambulatory BP monitoring into 303 with true resistant (office systolic BP [SBP] 172.2±22 mm Hg; 24-hour SBP 154±16.2 mm Hg) and 43 with pseudoresistant hypertension (office SBP 161.2±20.3 mm Hg; 24-hour SBP 121.1±19.6 mm Hg), from 10 centers were studied. At 3, 6, and 12 months follow-up, office SBP was reduced by 21.5/23.7/27.3 mm Hg, office diastolic BP by 8.9/9.5/11.7 mm Hg, and pulse pressure by 13.4/14.2/14.9 mm Hg (n=245/236/90; P for all <0.001), respectively. In patients with true treatment resistance there was a significant reduction with RDN in 24-hour SBP (-10.1/-10.2/-11.7 mm Hg, P<0.001), diastolic BP (-4.8/-4.9/-7.4 mm Hg, P<0.001), maximum SBP (-11.7/-10.0/-6.1 mm Hg, P<0.001) and minimum SBP (-6.0/-9.4/-13.1 mm Hg, P<0.001) at 3, 6, and 12 months, respectively. There was no effect on ambulatory BP monitoring in pseudoresistant patients, whereas office BP was reduced to a similar extent. RDN was equally effective in reducing BP in different subgroups of patients. Office SBP at baseline was the only independent correlate of BP response.

CONCLUSIONS

RDN reduced office BP and improved relevant aspects of ambulatory BP monitoring, commonly linked to high cardiovascular risk, in patients with true-treatment resistant hypertension, whereas it only affected office BP in pseudoresistant hypertension.

Seasonal variation in blood pressure is modulated by gender and age but not by BMI in a large Taiwanese population, 1996-2006

Previous research has found that blood pressure tends to be higher in winter and lower in summer. The present study examined seasonal variation in blood pressure by gender, hypertension medication, age group, and body mass index using contemporary Taiwanese data. Over 400,000 health screening records collected biennially between 1996 and 2006 were used to calculate average monthly systolic (SBP) and diastolic blood pressure (DBP) measurements. Generalized estimating equations were used to estimate the difference between the highest and lowest mean monthly blood pressure measurements. Mean monthly blood pressure measurements were higher in winter than in summer for all age groups, regardless of medication for hypertension. The largest difference in mean monthly blood pressure between summer and winter months was 5.3 mm Hg (Standard error = 0.7) for SBP and 3.2 mm Hg (Standard error = 0.7) for DBP. These differences were more pronounced: in SBP than in DBP; in men than in women; and in older than in younger participants. Body mass index was not clearly associated with seasonal variation in blood pressure. Seasonal variation in blood pressure among contemporary Taiwanese populations is modest and may only approach clinical significance for the diagnosis and treatment of hypertension and the prevention of cardiovascular disease amongst older male individuals.

Seasonal blood pressure changes: an independent relationship with temperature and daylight hours

Seasonal blood pressure (BP) changes have been found to be related to either outdoor or indoor temperature. No information regarding the independent effects of temperature measured proximally to the patient, the personal-level environmental temperature (PET), is available. Inclusion of daylight hours in multivariate analysis might allow exploring the independent interaction of BP with seasonality. To investigate whether ambulatory BP monitoring is affected by PET or by seasonality, 1897 patients referred to our hypertension units underwent ambulatory BP monitoring with a battery-powered temperature data logger fitted to the carrying pouch of the monitor. Predictors of 24-hour daytime and nighttime BP and of morning BP surge were investigated with a multivariate stepwise regression model, including age, sex, body mass index, antihypertensive treatment, office BP, ambulatory heart rate, PET, relative humidity, atmospheric pressure, and daylight hours as independent variables. At adjusted regression analysis, daytime systolic BP was negatively related to PET (-0.14; 95% confidence interval, -0.25 to -0.02); nighttime BP was positively related to daylight hours (0.63; 0.37-0.90); and morning BP surge was negatively related to daylight hours (-0.54; -0.87 to -0.21). These results provide new evidence that PET and seasonality (daylight hours) are 2 independent predictors of ambulatory BP monitoring.