ABSTRACT
Aims
To explore the relationship between diurnal blood pressure (BP) pattern and season.
Methods
A total of 6765 eligible patients (average age 57.35 ± 15.53 years; male 51.8%; hypertensives 68.8%) from 1 October 2016 to 6 April 2022 were enrolled, who were divided into four dipper groups, dipper, non‐dipper, riser, and extreme‐dipper, according to the diurnal BP pattern calculated using their ambulatory BP monitoring data. The season which the patient was in was determined by the time of ambulatory BP monitoring examination.
Results
Among the 6765 patients, 2042 (31.18%) were grouped into dipper, 380 (5.6%) into extreme‐dipper, 1498 (22.1%) into riser and 2845 (42.1%) into non‐dipper. Only the dipper subjects showed age difference among seasons, with the average age significantly lower in winter. There was no seasonal difference in age for the other types. No seasonal difference was revealed in gender, BMI, hypertension or not. Diurnal BP patterns significantly differed among seasons (P < .001). Post hoc tests with Bonferroni correction indicated the significantly different diurnal BP pattern between any two seasons (P < .001), but not between spring and autumn (P = .257), and the significance of the P value was assessed at 0.008 (0.05/6) after Bonferroni correction. Multinomial logistic regression suggested season as an independent contributor to diurnal BP pattern.
Conclusion
Diurnal BP pattern is influenced by season.
Introduction
A continuous variation of blood pressure (BP) rather than a static state leads to physiological adaptability (Citation1–3). Variation in BP is considered BP variability (BPV), which is classified into short-term BPV (beat-to-beat, minute-to-minute, hour-to-hour, and day-to-night changes) and long-term BPV (days, weeks, months, seasons, and even years). It has been demonstrated as the result of complex interactions between extrinsic environmental and behavioral factors and intrinsic cardiovascular regulatory mechanisms (Citation2).
BP variation within 24 h demonstrates an obvious circadian rhythm, which is higher during the day and lower at night (Citation1,Citation4,Citation5). The physiological decline in BP at night results in a dipper shape of 24-h BP curve, which can be determined by the records of ambulatory BP monitoring (ABPM). According to the decreasing ratio of night-time BP [(day-time BP – night-time BP)/day-time BP × 100%], the diurnal BP pattern can be categorized into four subtypes: dipper (10%−20%), non‐dipper (0%−10%), riser, or reverse dipper (<0%), extreme‐dipper (>20%). Evaluating the diurnal BP pattern makes a prominent sense for clinics. The non‐dipper and riser are associated with the increased risk of target organ damage and cardiovascular and cerebrovascular death (Citation6,Citation7). It is suggested diurnal BP pattern serve as a reference to individually optimize the anti-hypertension medication regimen (Citation2,Citation8).
BPV has been a research hotspot up to now, especially in seasons. Although it has received a wide discussion, most are focused on day-time BP. Whether the diurnal BP pattern vary with seasons has rarely been reported. Therefore, this study is carried out to explore this issue through a cross-sectional comparison based on 6765 patients’ ABPM data.
Material and methods
Study design and study subjects
All ABPM data and general data (age, gender, height and weight) from the outpatient BP management system of the First Affiliated Hospital of Chongqing Medical University from and aborted on 1 October 2016 to 6 April 2022 were derived, covering a total of 23 382 patients. According to ABPM guidelines (Citation1,Citation9,Citation10), ABPM records with the obtained valid readings of more than 70% of the setting were considered eligible, or ≥20 valid day-time with ≥7 valid night-time readings. A total of 6765 eligible ABPM records were finally enrolled. According to diurnal BP pattern, the data were divided into dipper group, extreme‐dipper group, riser group and non‐dipper group.
The study was approved by the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University (2020-758).
24-h ABPM
ABPM was recorded by the same automatic device (W-BMP; Standard Medical, Jiangsu, China), which was programmed to measure every half hour. The recorded data were automatically stored in the memory of the device and uploaded to the BP management system, which automatically calculated the mean BP and the decreasing ratio of night-time BP, where the systolic and diastolic BP were separately calculated.
Assessment of BP and diurnal BP pattern
The diagnostic thresholds for hypertension of day-time, morning, night-time and 24 h were 135/85 mmHg, 135/85 mmHg, 120/70 mmHg and 130/80 mmHg, respectively. The mean BP (either systolic or diastolic BP) above the diagnostic threshold at any given time period was determined as hypertension, and those below the diagnostic threshold for all given time period were determined as the normal BP. According to the 2020 Chinese Hypertension League Guidelines on Ambulatory BP Monitoring, day-time was from 8:00 to 20:00, morning was from 6:00 to 10:00 and night-time was from 23:00 to 5:00 the next day (Citation10).
According to the decreasing ratio of night-time BP ([day-time BP – night-time BP]/day-time BP × 100%), the diurnal BP pattern could be assessed as dipper (10%−20%), non‐dipper (0%−10%), riser dipper (<0%) and extreme‐dipper (>20%). The inconsistence between decreasing ratio of systolic and diastolic BP could possibly result from the following: one of the two was dipper, the other subtype was taken as the final assessment result; neither were dipper, the assessment was conducted based on the systolic BP.
Statistical analysis
All statistical analysis was performed using SPSS version 23.0 (SPSS, Chicago, IL). A 2-sided P value <0.05 was considered statistically significant. Continuous variables were shown as mean ± standard deviation and compared using analysis of variance, categorical variables were shown as percentages and assessed using the chi-square test. Post hoc tests were performed using Bonferroni correction, the significance of the P value was assessed at 0.008 (0.05/6), as pairwise comparisons were performed for six times between the four groups, and the comparison of diurnal BP patterns between any two seasons were also conducted six times. Multinomial logistic regression was used to investigate diurnal BP patterns and their associated factors (season, age, BP); dipper was used as a reference.
Results
Study subjects’ characteristics
Among the 6765 patients, 2042 (31.18%) were identified as dipper, 380 (5.6%) as extreme‐dipper, 1498 (22.1%) as riser and 2845 (42.1%) as non‐dipper. Only the dipper subjects showed age difference among seasons, with the average age significantly lower in winter; there was no seasonal difference in age for the other types. And no seasonal difference was revealed in gender, BMI, hypertension or not. Diurnal BP patterns significantly varied among seasons (P < .001) (). Post hoc tests with Bonferroni correction showed the significantly differences between any two seasons (P < .001) but not between spring and autumn (P = .257) ().
Table 1. Characteristics of all study subjects.
Table 2. Characteristics of dipper subjects.
Table 3. Characteristics of extreme‐dipper subjects.
Table 4. Characteristics of riser subjects.
Table 5. Characteristics of non-dipper subjects.
Table 6. Comparison of constituent ratio of subtypes of diurnal BP pattern between any two seasons.
Seasonal differences in diurnal BP pattern
Multinomial logistic regression was performed to investigate the diurnal BP patterns and their associated factors, taking dipper as the reference group (). Season emerged as an independent influencing factor. And age was independently associated with non‐dipper and riser but not with extreme‐dipper. Performing stratification by age, the constituent ratios of each subtype of the diurnal BP pattern in summer and winter were calculated. Percentage bar charts of diurnal BP patterns are plotted in .
Figure 1. Comparison of constituent ratio of subtypes of diurnal BP pattern in each age categories between summer and winter.
Table 7. Multinomial logistic regression showing the association between diurnal BP pattern and their associated factors.
Discussion
The guidelines at present tend to be focused on day-time BP, where BP levels generally serve as the key to primary and secondary prevention of cardiovascular disease, since the current view of adverse cardiovascular consequences of hypertension is considered to absolutely depend on BP value but could not stop the exploration on BPV (Citation1,Citation2). Multiple studies have demonstrated an increased risk of target organ damage in people with non-dipper BP, such as the increased left ventricular mass index and left ventricular hypertrophy, the increased carotid intima-media thickness, carotid plaque, stroke, microprotein and retinopathy (Citation11–15).
The present study revealed the increased proportion of non-dipper and riser with age in both normal BP patients and hypertensive patients, while extreme-dipper showed no correlation with age. It has also been revealed that the proportion of non-dipper and riser was increased in summer taking dipper and winter as reference, which was reversed in extreme-dipper.
Some studies have shown decreased nocturnal sympathetic nerve activity in the extreme-dipper population, while the day-time sympathetic nerve activity is low in the non-dipper population, relatively activated in the night-time. The diurnal variation of autonomic nerve activity in the non-dipper population was weakened. Compared with people with drop in normal BP at night, non-dipper patients showed an elevated frequency of involuntary awakenings at night accompanied with poor sleep quality. The improved sleep quality and the reduced nocturnal activity may contribute to normalizing the circadian rhythm of non-dipper patients (Citation16). In addition, melatonin has a correlation with the circadian rhythm of BP. Studies have demonstrated more melatonin secretion in the night among dipper hypertension patients and normal BP patients, while it significantly reduced in the night among non-dipper hypertension patients (Citation17).
Although it was a simple cross-sectional study, the remarkable sample size is powerful to preliminarily reflect the influence of season on diurnal BP pattern. The drawback of this study is the lack of clinical data such as smoking, alcohol consumption, diabetes, dyslipidemia, and pre-history of cardiovascular disease. Further studies are required to provide more evidence of the clinical value of the diurnal BP pattern. In conclusion, season was identified as an independent contributor to diurnal BP pattern.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Funding
References
- Kario K, Shin J, Chen C-H, Buranakitjaroen P, Chia Y-C, Divinagracia R, Nailes J, Hoshide S, Siddique S, Sison J, et al. Expert panel consensus recommendations for ambulatory blood pressure monitoring in Asia: the HOPE Asia network. J Clin Hypertens. 2019;21(9):1250–5. doi:10.1111/jch.13652. PubMed PMID: 31532913.
- Parati G, Ochoa JE, Lombardi C, Bilo G. Assessment and management of blood-pressure variability. Nat Rev Cardiol. 2013;10(3):143–55. doi:10.1038/nrcardio.2013.1. PubMed PMID: 23399972.
- Grassi G, Bombelli M, Seravalle G, Dell’oro R, Quarti-Trevano F. Diurnal blood pressure variation and sympathetic activity. Hypertens Res. 2010;33(5):381–85. doi:10.1038/hr.2010.26. PubMed PMID: 20203684.
- Rhoads MK, Balagee V, Thomas SJ. Circadian regulation of blood pressure: of mice and men. Curr Hypertens Rep. 2020;22(6):40. doi:10.1007/s11906-020-01043-3. PubMed PMID: 32440958.
- Smolensky MH, Hermida RC, Portaluppi F. Circadian mechanisms of 24-hour blood pressure regulation and patterning. Sleep Med Rev. 2017; 33. doi:10.1016/j.smrv.2016.02.003. PubMed PMID: 27076261.
- Yang W-Y, Melgarejo JD, Thijs L, Zhang Z-Y, Boggia J, Wei F-F, Hansen TW, Asayama K, Ohkubo T, Jeppesen J, et al. Association of office and ambulatory blood pressure with mortality and cardiovascular outcomes. JAMA. 2019;322(5):409–20. doi:10.1001/jama.2019.9811. PubMed PMID: 31386134.
- Boggia J, Li Y, Thijs L, Hansen TW, Kikuya M, Björklund-Bodegård K, Richart T, Ohkubo T, Kuznetsova T, Torp-Pedersen C, et al. Prognostic accuracy of day versus night ambulatory blood pressure: a cohort study. Lancet. 2007;370(9594):1219–29. doi:10.1016/S0140-6736(07)61538-4. PubMed PMID: 17920917.
- Narita K, Hoshide S, Kario K. Seasonal variation in blood pressure: current evidence and recommendations for hypertension management. Hypertens Res. 2021;44(11):1363–72. doi:10.1038/s41440-021-00732-z. PubMed PMID: 34489592.
- Stergiou GS, Palatini P, Parati G, O’Brien E, Januszewicz A, Lurbe E, Persu A, Mancia G, Kreutz R. 2021 European society of hypertension practice guidelines for office and out-of-office blood pressure measurement. J Hypertens. 2021;39(7):1293–302. PubMed PMID: 33710173. doi:10.1097/HJH.0000000000002843.
- Chinese hypertension league guidelines on ambulatory blood pressure monitoring Chinese circulation. Journal. 2021, 36 (4), 313–28. doi:10.3969/j.issn.1000-3614.2021.04.001.
- Kario K, Pickering TG, Matsuo T, Hoshide S, Schwartz JE, Shimada K. Stroke prognosis and abnormal nocturnal blood pressure falls in older hypertensives. Hypertens. 2001;38(4):852–57. doi:10.1161/hy1001.092640. Epub 2001/10/20 PubMed PMID: 11641298.
- Madden JM, O’Flynn AM, Fitzgerald AP, Kearney PM. Correlation between short-term blood pressure variability and left-ventricular mass index: a meta-analysis. Hypertens Res. 2016;39(3):171–77. doi:10.1038/hr.2015.126. PubMed PMID: 26581775.
- Manousopoulos K, Koroboki E, Barlas G, Lykka A, Tsoutsoura N, Flessa K, Kanakakis I, Paraskevaidis I, Zakopoulos N, Manios E, et al. Association of home and ambulatory blood pressure variability with left ventricular mass index in chronic kidney disease patients. Hypertens Res. 2021;44(1):55–62. doi:10.1038/s41440-020-0512-3. PubMed PMID: 32678320.
- Karadag B, Ozyigit T, Serindag Z, Ilhan A, Ozben B. Blood pressure profile is associated with microalbuminuria and retinopathy in hypertensive nondiabetic patients. Wien Klin Wochenschr. 2018;130(5):204–10. doi:10.1007/s00508-017-1270-3.
- Ozdemir E, Yildirimturk O, Cengiz B, Yurdakul S, Aytekin S. Evaluation of carotid intima-media thickness and aortic elasticity in patients with nondipper hypertension. Echocardiography (MountKisco NY). 2014;31(5):663–68. Epub 2013/11/14 PubMed PMID: 24219389. doi:10.1111/echo.12444.
- Kario K, Schwartz JE. Disruption of diurnal rhythm in the elderly. Lancet. 1999;354(9175):339. PubMed PMID: 10440339. doi:10.1016/S0140-6736(05)75247-8.
- Cui HW, Zhang ZX, Gao MT, Liu Y, Su AH, Wang MY. Circadian rhythm of melatonin and blood pressure changes in patients with essential hypertension. Chin J Cardiol. 2008;36(1):20–23. doi:10.3321/j.issn:0253-3758.2008.01.006.