Abstract
Objective
To examine the subgroup characteristics of seasonal blood pressure (BP) fluctuations in maintenance hemodialysis (MHD) patients and to evaluate their association with cardiovascular and cerebrovascular events (CCVE).
Methods
A total of 154 eligible MHD patients treated at our center between May 2018 and October 2021 were retrospectively enrolled with informed consent. Systolic (SBP) and diastolic (DBP) BP values were collected and analyzed across different seasons, stratified by sex, age, and primary disease. The seasonal distribution of intradialytic hypertension, intradialytic hypotension, CCVE incidence, and mortality was further assessed. The interaction between season, age, and gender on BP was analyzed after using a multi-factor nonlinear mixed effects model, to correct for antihypertensive drug prescription, ultrafiltration rate, and dry body weight fluctuations.
Results
BP demonstrated significant seasonal variation (P < 0.05), with the lowest SBP and DBP observed in summer and the highest in winter, while spring and autumn showed intermediate values. Across all seasons, BP rose progressively with age: SBP and DBP were significantly higher in the 45–60 year group compared with < 45 years (P < 0.05), and highest in patients > 60 years (P < 0.05). Male patients consistently exhibited higher SBP and DBP than females in both warm (spring-summer) and cold (autumn-winter) seasons (P < 0.05). Compared with spring-summer, autumn-winter was associated with a higher proportion of intradialytic hypertension (37.66% vs. 20.78%, P < 0.01), a lower proportion of intradialytic hypotension (13.64% vs. 29.22%, P < 0.001), and increased CCVE incidence (22.73% vs. 11.69%) and mortality (7.79% vs. 3.25%, both P < 0.05). The amplitude of seasonal SBP fluctuation was greatest in patients > 60 years (19.72 ± 6.13 mmHg) compared with 45–60 years (14.13 ± 4.92 mmHg) and < 45 years (8.52 ± 3.21 mmHg, all P < 0.05). Male patients also showed larger SBP fluctuations than females (16.82 ± 5.73 mmHg vs. 11.53 ± 4.82 mmHg, P < 0.001), while no significant differences were observed among subgroups stratified by primary disease (P > 0.05). After multi-factor model correction, the interaction between season and age (P = 0.018) and season and gender (P = 0.025) remained significant, indicating that the seasonal increase in BP in elderly and male patients was independent effect of antihypertensive medication adjustment, ultrafiltration rate, and dry body weight fluctuations.
Conclusion
BP in MHD patients was jointly influenced by season, age, and sex. The highest values and greatest fluctuations occurred in autumn-winter, in males, and in patients > 60 years. These subgroups represented high-risk populations for adverse cardiovascular and cerebrovascular outcomes during colder months. Targeted, season- and subgroup-specific BP management strategies might have helped mitigate CCVE risk and improve survival in MHD patients.
Keywords: Hemodialysis, Blood pressure, Seasonal fluctuations, Cardiovascular events
Introduction
Chronic renal failure (CRF), the terminal stage of chronic kidney disease, is characterized by a glomerular filtration rate (GFR) below 15 mL/min/1.73 m². At this stage, uremic toxins such as guanidinosuccinic acid and benzoic acid cannot be adequately excreted, leading to endothelial dysfunction, increased thrombogenicity, and higher mortality [1].
Accumulating evidence has demonstrated that blood pressure (BP) in the general population undergoes seasonal variation, typically rising in colder months and declining in warmer ones [2–4]. Physiologically, cold exposure induces vasoconstriction, increases peripheral resistance, and enhances the secretion of pressor substances such as catecholamines, thereby elevating BP. Epidemiological studies have confirmed a negative correlation between ambient temperature and BP [5]. Moreover, seasonal lifestyle modifications-including reduced outdoor activity, increased intake of high-salt and high-calorie foods, and circadian rhythm disruption caused by shorter daylight hours-further contribute to BP variability.
These influences are particularly pronounced in patients undergoing maintenance hemodialysis (MHD). Because of impaired renal function, their ability to regulate water-salt balance is diminished, rendering BP more susceptible to seasonal factors [6–7]. Prior research has shown that MHD patients may experience greater seasonal BP fluctuations than the general population [8–9]. Intradialytic BP instability-whether hypertensive or hypotensive-not only compromises treatment efficacy but also increases the risk of cardiovascular and cerebrovascular events (CCVE) and mortality [10]. Fujishima et al. [11] found in the Japanese multi-center hemodialysis initiation cohort (n = 1396) that patients initiating hemodialysis in autumn had a significantly higher risk of cardiac events within 3 years compared to those initiating in summer (adjusted HR = 1.50), suggesting that the season of initiation itself is a potential predictor of cardiac prognosis. This indicates that the seasonal fluctuations in BP among the hemodialysis population may begin at the initiation stage of hemodialysis treatment and have a continuous impact on long-term prognosis. Takahashi et al. [12] confirmed that the systolic BP before hemodialysis showed a seasonal variation with the highest level in winter and the lowest in summer. Moreover, the seasonal variation range of systolic BP was significantly correlated with major adverse cardiovascular events (MACE) and the risk of all-cause hospitalization, indicating that the seasonal fluctuation range of BP in hemodialysis patients itself serves as an independent adverse prognostic factor, separate from average BP levels. This suggests that the seasonal fluctuation of BP is an independent risk factors for adverse outcomes. Additionally, the value of home BP monitoring in identifying seasonal BP variations and guiding individualized treatment is increasingly recognized. The remote BP monitoring project conducted by Obi et al. [13] confirmed that there was a significant difference between home BP and BP measured at the hemodialysis center, suggesting that self-monitoring can provide important supplementary information for precise seasonal BP management.
Although seasonal fluctuations in BP are widely recognized as a clinical phenomenon, and the basic influence of age and gender on the annual rhythm of BP is also clear, existing research is limited to describe the average trend of the overall population, and some studies have small sample sizes. There is insufficient exploration of the sensitivity differences and underlying mechanisms of BP to seasonal fluctuation in different patients, especially the lack of quantitative differences in seasonal fluctuations between different gender and age subgroups in maintenance hemodialysis patients. Also, there is a lack of a systematic comparison in abnormal BP events and the risk of cardiovascular and cerebrovascular endpoints during hemodialysis. As a result, the existing seasonal BP management recommendations are general and difficult to meet the needs of individualized precision medicine. Clarifying the specific fluctuation patterns of these subgroups is the prerequisite for formulating individualized and seasonally adjusted precise management strategies. Based on this, this study aims to explore the heterogeneity of BP fluctuation patterns in different clinical subgroups, with the expectation of providing guidance for clinical treatment.
Materials and methods
Study design and patient population
This retrospective cohort study included 154 patients who underwent maintenance hemodialysis at our hospital’s hemodialysis unit between May 2018 and October 2021. All participants met the eligibility criteria and provided informed consent. The cohort comprised 80 men and 74 women, aged 37–79 years (mean ± SD: 52.84 ± 10.35 years), with a mean dialysis duration of 24.17 ± 6.29 months. The primary etiologies of end-stage renal disease were primary renal disease (n = 65), hypertensive nephropathy (n = 26), and diabetic nephropathy (n = 63).
Inclusion and exclusion criteria
Inclusion criteria: (1) Diagnosis of CRF in accordance with established guidelines [14]. (2) First initiation of maintenance hemodialysis, with treatment duration ≥ 3 months. (3) Stable mental status and vital signs during the study period.
Exclusion criteria: (1) Concurrent infectious diseases, malignant tumors, or autoimmune disorders. (2) Coexisting hematological diseases. (3) Severe dysfunction of major organs (e.g., heart, brain) unrelated to CRF. (4) Incomplete clinical data or subsequent kidney transplantation during follow-up.
Continuous hemodialysis data for each patient were recorded for 12 consecutive months, covering the four complete seasons of spring, summer, autumn and winter. Each patient’s data included at least one full annual cycle of BP and clinical parameter records. The flowchart of patient enrollment was illustrated in figure 1.
Fig. 1.
Patient Enrollment Flowchart
Data collection
This study utilized the hospital hemodialysis unit’s electronic management system to collect BP data from patients undergoing maintenance hemodialysis, using the single dialysis session as the unit of analysis. Data collection included:
Measurement time points: prior to dialysis initiation (supine position, brachial artery of the non-fistula arm), during dialysis (once every hour, supine position, brachial artery of the non-fistula arm, with a minimum of four measurements per session), and at dialysis termination (supine position, brachial artery of the non-fistula arm). The initial BP measurement for each patient before the first hemodialysis after enrollment was a single measurement. The BP measurement was completed immediately after hemodialysis (within 1 min).
Data quality control: to ensure reliability, invalid readings (e.g., due to patient movement or inappropriate cuff size) were excluded. The proportion of valid readings was required to be no less than 70% of all collected measurements. The mean of all valid readings within a single dialysis session was calculated and used as the representative BP value for that session in subsequent analyses.
Standardized recording protocol: all BP measurements were performed by hemodialysis staff who had received uniform training, using standardized electronic sphygmomanometers. Procedures strictly adhered to the Chinese Guidelines for Blood Pressure Measurement to minimize operator-related variability.
Collect the following parameters synchronously to calibrate the statistical model: (1) Prescription of antihypertensive drugs: record the type, dosage and adjustment plan of antihypertensive drugs for each patient in different seasons; (2) Ultrafiltration rate: the ratio of ultrafiltration volume (L) per hemodialysis to hemodialysis time (h), and calculate the seasonal average ultrafiltration rate; (3) Fluctuation of dry body weight (DBW): the dry body weight value was evaluated each month, and the fluctuation in dry body weight (ΔDBW) between adjacent seasons was calculated.
Observation indicators
Core BP indicators
Seasonal (spring, summer, autumn, winter) levels of systolic BP (SBP) and diastolic BP (DBP) to examine temporal trends.
Subgroup stratification indicators
BP levels were compared across sex (male/female), age (< 45 years, 45–60 years, > 60 years), and primary etiology (primary renal disease, hypertensive nephropathy, diabetic nephropathy), with seasonal differences assessed between warm (spring/summer) and cold (autumn/winter) periods.
Intradialytic BP abnormalities
Intradialytic hypertension: defined as an increase in mean arterial pressure (MAP) > 15 mmHg compared with pre-dialysis.
Intradialytic hypotension: defined as SBP < 90 mmHg, DBP < 60 mmHg, or a reduction in MAP > 30 mmHg compared with pre-dialysis.
Seasonal incidence rates of these events were calculated to assess associations with temperature variation.
Clinical outcomes
The incidence of cardiovascular and cerebrovascular events (myocardial infarction, ischemic stroke, hemorrhagic stroke, heart failure, etc.) and mortality were recorded across different seasons.
Seasonal BP fluctuation amplitude
For each patient, the mean winter systolic BP (SBP_W), mean winter diastolic BP (DBP_W), mean summer systolic BP (SBP_S), and mean summer diastolic BP (DBP_S) were calculated. Seasonal fluctuation amplitudes were then derived as ΔSBP = SBP_W - SBP_S and ΔDBP = DBP_W - DBP_S. Subgroup analyses (by sex, age, and primary disease) were conducted to evaluate differences in fluctuation magnitude.
Statistical analysis
All analyses were conducted using SPSS version 25.0 (IBM Corp., Armonk, NY, USA). Categorical variables were expressed as n (%) and compared using the χ² test. Continuous variables with normal distribution were expressed as mean ± standard deviation (SD). Group comparisons were performed with independent-samples t-tests for two groups and one-way analysis of variance (ANOVA) for three or more groups, followed by least significant difference (LSD) post-hoc tests. Two-way ANOVA or generalized linear models (GLM) were used to evaluate the interaction between season and subgroup factors (sex, age, primary disease) on BP levels, intradialytic hypertension/hypotension incidence, CCVE occurrence, and mortality. To correct for confounding factors, a multi-factor nonlinear mixed-effects model was used to analyze the effects of season and subgroup factors (gender, age group, primary disease) on BP levels, the incidence of hypertension/hypotension during hemodialysis, the incidence of cardiovascular and cerebrovascular events, and mortality. The following covariates were included in the model: antihypertensive medication prescriptions (types, dose changes), ultrafiltration rate (continuous variable), and dry body weight fluctuation (ΔDBW, continuous variable), and the interaction between these variables and seasons was considered. Due to the possible non-linear relationship between BP, ultrafiltration rate, and dry body weight fluctuation, quadratic terms or spline functions were introduced in the model for fitting. A two-sided P < 0.05 was considered statistically significant.
Results
Seasonal variations in BP among maintenance hemodialysis patients
Seasonal differences in BP among maintenance hemodialysis patients were statistically significant (P < 0.05). Compared with summer, systolic BP (SBP) and diastolic BP (DBP) were significantly higher in spring, autumn, and winter (all P < 0.05). Compared with spring, SBP and DBP were significantly higher in winter (P < 0.05), SBP was higher in autumn (P < 0.05), and both SBP and DBP level were lower in summer (P < 0.05). Compared with autumn, SBP and DBP were significantly higher in winter (P < 0.05) but lower in summer (P < 0.05). Detailed values were presented in Table 1; Fig. 2.
Table 1.
Comparison of Blood Pressure Changes in Maintenance Hemodialysis Patients in Different Seasons (mean ± SD)
| Season | Number of cases | SBP | DBP |
|---|---|---|---|
| Spring | 154 | 135.62 ± 12.83 | 78.21 ± 8.54 |
| Summer | 154 | 128.34 ± 11.52* | 72.53 ± 7.91* |
| Autumn | 154 | 138.91 ± 13.24# | 80.12 ± 9.23# |
| Winter | 154 | 142.53 ± 14.12*#△ | 83.64 ± 9.72*#△ |
| F | — | 33.44 | 42.16 |
| P | — | < 0.001 | < 0.001 |
*P < 0.05 compared with spring; #P < 0.05 compared with summer; △P < 0.05 compared with autumn
Fig. 2.
Seasonal Variations in Blood Pressure among Maintenance Hemodialysis Patients. (A) Seasonal comparisons of systolic BP (SBP). (B) Seasonal comparisons of diastolic BP (DBP).*Note: Compared with spring, *P < 0.05; compared with summer, #P < 0.05; compared with autumn, △P < 0.05.
Overall, BP exhibited a consistent seasonal pattern, with the highest levels in winter, the lowest in summer, and intermediate values in spring and autumn. To further investigate differences in BP and adverse event risk between cold and warm periods, subsequent analyses consolidated the four seasons into two groups: spring-summer (warm) and autumn-winter (cold). This grouping not only reflects common research practice in season-related clinical studies but also more clearly demonstrates the association between BP variation and cardiovascular/cerebrovascular risk.
Subgroup analysis by sex, age, and primary disease
Men demonstrated higher SBP and DBP than women during both spring-summer and autumn-winter (P < 0.05). Across all seasons, BP increased progressively with age: SBP and DBP in the 45–60 year group were significantly higher than in the < 45 year group (P < 0.05), while SBP and DBP in the > 60 year group were significantly higher than in both the < 45 year group (aP < 0.05) and the 45–60 year group (P < 0.05). No significant seasonal differences in SBP or DBP were observed across patients with different primary renal diseases (P > 0.05, Table 2).
Table 2.
Blood Pressure Variations Stratified by Sex, Age, and Primary Disease (mean ± SD, mmHg)
| Group | Number of cases | Spring Summer | Autumn and Winter | ||
|---|---|---|---|---|---|
| SBP | DBP | SBP | DBP | ||
| Gender | 80 | ||||
| Male | 74 | 136.21 ± 13.12 | 79.53 ± 8.82 | 140.82 ± 14.31 | 82.34 ± 9.52 |
| Female | — | 130.53 ± 11.72 | 75.12 ± 7.63 | 135.21 ± 12.93 | 78.62 ± 8.91 |
| t | — | 2.825 | 3.306 | 2.546 | 2.4498 |
| P | 0.005 | 0.001 | 0.012 | 0.014 | |
| Age (years) | 30 | ||||
| <45 | 80 | 125.32 ± 10.21 | 70.12 ± 6.83 | 129.83 ± 11.52 | 73.52 ± 7.21 |
| 45 ~ 60 | 44 | 134.62 ± 12.53a | 77.82 ± 8.21a | 138.53 ± 13.22a | 80.21 ± 8.72a |
| >60 | — | 142.13 ± 14.32ab | 83.21 ± 9.12ab | 146.72 ± 15.13ab | 85.93 ± 9.82ab |
| F | — | 15.76 | 22.51 | 14.16 | 17.90 |
| P | <0.001 | <0.001 | <0.001 | <0.001 | |
| Primary Disease | 65 | ||||
| Primary kidney disease | 26 | 133.21 ± 12.42 | 77.32 ± 8.31 | 137.53 ± 13.62 | 80.12 ± 9.02 |
| Hypertensive nephropathy | 63 | 132.82 ± 11.93 | 76.93 ± 7.82 | 136.92 ± 12.83 | 79.73 ± 8.52 |
| Diabetic nephropathy | — | 133.53 ± 12.12 | 77.52 ± 8.13 | 137.82 ± 13.23 | 80.32 ± 8.83 |
| F | — | 0.03 | 0.05 | 0.04 | 0.04 |
| P | 0.968 | 0.953 | 0.959 | 0.960 |
aP<0.05 compared to under 45 years old; bP<0.05 compared with 45 ~ 60 years old
Seasonal variations in intradialytic hypertension and hypotension in maintenance hemodialysis patients
Compared with spring-summer, the proportion of intradialytic hypertension was significantly higher in autumn-winter (37.66% vs. 20.78%, P < 0.001), while the proportion of intradialytic hypotension was significantly lower (13.64% vs. 29.22%, P < 0.001). Details were shown in Table 3; Fig. 3.
Table 3.
Seasonal variations in intradialytic hypertension and hypotension among maintenance hemodialysis patients [n (%)]
| Grouping | Number of cases | Intradialytic Hypertension | Hypotension during dialysis |
|---|---|---|---|
| Spring Summer | 154 | 32(20.78) | 45(29.22) |
| Autumn and Winter | 154 | 58(37.66) | 21(13.64) |
| χ² | — | 10.612 | 11.107 |
| P | — | 0.001 | 0.001 |
Fig. 3.
Seasonal variations in intradialytic hypertension and hypotension among maintenance hemodialysis patients
Comparison of cardiovascular events and mortality across seasons
The incidence of cardiovascular events and mortality was significantly higher in autumn-winter compared with spring-summer (P < 0.05, Table 4).
Table 4.
Comparison of cardiovascular events and mortality rates among maintenance hemodialysis patients across different seasons [n (%)]
| Grouping | Number of cases | Cardiovascular and cerebrovascular events | Mortality rate |
|---|---|---|---|
| Spring Summer | 154 | 18(11.69) | 5(3.25) |
| Autumn and Winter | 154 | 35(22.73) | 14(9.09) |
| χ 2 | 6.586 | 4.543 | |
| P | 0.010 | 0.033 |
Comparison of winter-summer bp differences among subgroups
Across all subgroups stratified by gender, age, and primary disease, BP in winter was significantly higher than in summer (P < 0.001). Among age-stratified groups, the magnitude of BP fluctuations was increased progressively with age: the winter-summer difference in SBP and DBP was significantly greater in the 45-60-year group compared with the < 45-year group (P < 0.05), and markedly higher in the > 60-year group compared with both the < 45-year (P < 0.05) and 45-60-year groups (P < 0.05). The winter-summer elevation in SBP and DBP was markedly higher in males than in females (P < 0.001). No significant differences in BP fluctuation magnitude were observed among patients with different primary diseases (P > 0.05, Table 5).
Table 5.
Comparison of winter-summer blood pressure differences among patient subgroups
| Grouping | Number of cases | ΔSBP (Winter - Summer) | ΔDBP (Winter - Summer) |
|---|---|---|---|
| Overall | 154 | 14.20 ± 5.32 | 11.12 ± 4.83 |
| Gender | |||
| Male | 80 | 16.82 ± 5.73* | 13.21 ± 5.12* |
| Female | 74 | 11.53 ± 4.82 | 8.92 ± 4.21 |
| t | — | 6.174 | 5.653 |
| P | — | < 0.001 | < 0.001 |
| Age (years) | |||
| < 45 | 30 | 8.52 ± 3.21 | 6.23 ± 2.92 |
| 45 ~ 60 | 80 | 14.13 ± 4.92a | 10.82 ± 4.31a |
| > 60 | 44 | 19.72 ± 6.13ab | 15.32 ± 5.52ab |
| F | — | 32.65 | 30.17 |
| P | — | < 0.001 | < 0.001 |
| Primary disease | |||
| Primary kidney disease | 65 | 14.02 ± 5.21 | 11.03 ± 4.72 |
| Hypertensive nephropathy | 26 | 13.83 ± 5.02 | 10.92 ± 4.53 |
| Diabetic nephropathy | 63 | 14.52 ± 5.43 | 11.32 ± 4.92 |
| F | — | 0.21 | 0.18 |
| P | — | 0.81 | 0.83 |
*P < 0.05 compared with females; a P < 0.05 compared with < 45 years; bP < 0.05 compared with 45–60 years
Multi-factor analysis after adjusting for covariates such as antihypertensive drugs
Using a multi-factor nonlinear mixed-effects model, the prescription of antihypertensive drugs (types, dose changes), ultrafiltration rate, and dry body weight fluctuation (ΔDBW) were included as covariates, and the interaction terms of season, age, and gender were also incorporated. A correction analysis was conducted to address the seasonal variations in BP. The results showed that after controlling for the use of antihypertensive drugs, ultrafiltration rate, and fluctuation in dry body weight, SBP and DBP in winter were still significantly higher than those in summer (P < 0.05). The interaction between season and age was significant (P < 0.05), meaning that the amplitude of BP elevation in elderly patients during winter was still greater than that in younger patients after correction. The interaction between season and gender was also significant (P < 0.05), with males experiencing a greater increase in BP during winter than females. There was a certain correlation between the adjustment of antihypertensive drug prescriptions and seasons (the proportion of increased antihypertensive drug dosage or type in autumn and winter was higher than that in spring and summer), however, after including the model, it did not change the main effect direction of season on BP or the significance of subgroup differences. The estimated mean values of SBP and DBP in each season after correction and the comparison results among subgroups were shown in Tables 6 and 7.
Table 6.
Estimated mean values of SBP (mmHg) for different seasons and subgroups after adjusting for covariates
| Factor | Spring SBP | Summer SBP |
Autumn SBP | Winter SBP | Seasonal P-value |
|---|---|---|---|---|---|
| Overall corrected mean | 134.82 ± 2.31 | 127.53 ± 2.28 | 138.12 ± 2.35 | 141.94 ± 2.40 | < 0.001 |
| Age stratification (years) | Interaction P = 0.018 | ||||
| <45 | 124.91 ± 3.52 | 120.32 ± 3.41 | 128.21 ± 3.60 | 130.52 ± 3.72 | |
| 45 ~ 60 | 134.12 ± 2.81 | 127.43 ± 2.75 | 137.22 ± 2.85 | 140.81 ± 2.93 | |
| >60 | 141.53 ± 3.12 | 132.14 ± 3.05 | 143.82 ± 3.22 | 147.63 ± 3.38 | |
| Gender stratification | Interaction P = 0.025 | ||||
| Male | 136.12 ± 2.62 | 128.61 ± 2.52 | 139.41 ± 2.71 | 143.22 ± 2.82 | |
| Female | 133.22 ± 2.53 | 126.33 ± 2.45 | 136.52 ± 2.58 | 140.41 ± 2.65 |
Table 7.
Estimated mean values of DBP (mmHg) for different seasons and subgroups after adjusting for covariates
| Factor | Spring DBP | Summer DBP |
Autumn DBP | Winter DBP | Seasonal P-value |
|
|---|---|---|---|---|---|---|
| Overall corrected mean | 77.62 ± 1.82 | 71.93 ± 1.78 | 79.52 ± 1.85 | 83.12 ± 1.92 | < 0.001 | |
| Age stratification (years) | Interaction P = 0.031 | |||||
| <45 | 69.71 ± 2.43 | 65.22 ± 2.38 | 72.81 ± 2.51 | 74.83 ± 2.60 | ||
| 45 ~ 60 | 77.31 ± 2.12 | 71.62 ± 2.08 | 79.42 ± 2.18 | 82.73 ± 2.25 | ||
| >60 | 82.83 ± 2.52 | 76.41 ± 2.45 | 84.53 ± 2.58 | 87.91 ± 2.70 | ||
| Gender stratification | Interaction P = 0.042 | |||||
| Male | 79.12 ± 2.02 | 73.21 ± 1.98 | 81.11 ± 2.08 | 84.62 ± 2.18 | ||
| Female | 76.02 ± 1.95 | 70.53 ± 1.90 | 77.82 ± 1.98 | 81.41 ± 2.05 | ||
Discussion
Hemodialysis is the most widely used renal replacement therapy worldwide, accounting for over 80% of all dialysis treatments and substantially prolonging survival in patients with end-stage renal disease [15]. It has been repeatedly confirmed that the BP of ordinary people and those undergoing hemodialysis shows a seasonal pattern of being higher in winter and lower in summer. This study, confirming this overall trend, further revealed the significant heterogeneity in the fluctuation amplitude among different subgroups: elderly and male patients not only had higher absolute BP levels, but also had a greater increase in BP elevation in winter. Moreover, this subgroup had a significantly higher incidence of hypertension and cardiovascular and cerebrovascular events during hemodialysis in cold seasons. This result suggested that applying “seasonal adjustment” in a generalized manner to all patients may not effectively capture the true needs of high-risk groups. Subgroup stratification based on gender and age is expected to achieve more precise seasonal BP control.
Previous studies have demonstrated seasonal variation in BP among patients with primary hypertension, with higher values observed in winter compared to summer. This has been attributed to increased sympathetic nervous system activity and a greater renal sodium excretion load in cold weather [16]. Meteorological factors such as ambient temperature, indoor temperature, cloud cover, and relative humidity may also influence BP potentially through effects on thermoregulation, cardiovascular autoregulation, and blood viscosity [17–18]. Hypertension is also a frequent comorbidity in maintenance hemodialysis patients, yet only a minority achieve adequate control. In our cohort, SBP and DBP were significantly lower in summer and significantly higher in winter than in spring, summer, and autumn, indicating a clear seasonal pattern in BP among dialysis patients. Possible mechanisms include reduced physical activity and cold-induced vascular smooth muscle contraction, leading to increased blood volume. These findings suggest that attending physicians should adjust antihypertensive therapy in response to seasonal variation. For example, in summer, higher temperatures, vasodilation, and greater perspiration may justify reducing antihypertensive dosages or selecting long-acting agents, whereas in winter, colder temperatures and vasoconstriction may require dose escalation or additional agents. Body Mass Index (BMI) increases during dialysis should also be controlled to within 3% of baseline values. Furthermore, strengthening patient education and promoting self-monitoring of BP are essential for the timely detection and management of abnormalities. After correcting for the effects of antihypertensive drug prescriptions, ultrafiltration rate, and fluctuations in dry body weight using a multi-factor nonlinear mixed-effects model, the main effect of season on BP and the interaction with age and gender still existed. This indicated that the seasonal fluctuations in BP of hemodialysis patients were not solely caused by the seasonal variations of the clinically adjustable factors mentioned above. This further supported the necessity of implementing predictive and proactive seasonal BP management strategies for the elderly and high-risk male subgroups. Even if the antihypertensive drugs and dry body weight have been adjusted accordingly, these populations still require more intensive monitoring and intervention.
Our subgroup analysis revealed that men had consistently higher SBP and DBP than women across both seasonal periods, and BP increased progressively with age. No significant differences were observed among patients with different primary diseases. These findings suggest that sex and age contribute to seasonal BP variation in hemodialysis patients. And these subgroup differences remained statistically significant even after adjusting for antihypertensive drugs, ultrafiltration rate, and fluctuation in dry body weight. This excluded the main confounding effects of treatment regimens or seasonal variations in volume status on the heterogeneity of the subgroups. The higher prevalence of smoking, alcohol consumption, and sedentary behavior among men, together with lower health awareness, may contribute to their higher BP levels. In older patients, the accumulation of comorbidities and age-related decline in autonomic function may heighten sensitivity to temperature changes. Sympathetic activation and vasoconstriction during cold exposure may thus exert a stronger hypertensive effect in the elderly [19–20]. Prior epidemiological studies also demonstrate sex differences in hypertension: among adults over 30 years, men have a higher prevalence than women (31.1% vs. 22.8%), but after age 60, men achieve better control rates (66% vs. 51%) [21].
Taken together, these findings highlight the importance of sex- and age-specific approaches to hypertension management in hemodialysis. For men, interventions should emphasize lifestyle modification, physical activity, early monitoring, and adherence to treatment. For women, particularly postmenopausal patients who are more likely to be salt-sensitive, strategies should prioritize sodium restriction, fluid control, and prevention of water-sodium retention. Furthermore, self-BP monitoring (SBPM) plays a significant role in BP control for hemodialysis patients. The review by Mulè et al. [22] indicated that SBPM can enhance patients’ cognitive level of their own BP status and enhance their sense of treatment participation through daily regular measurements. At the same time, the SBPM data provides a basis for physicians to adjust the antihypertensive treatment plan, which is helpful in improving treatment compliance. Home monitoring can also identify hidden hypertension (such as inter-dialysis period hypertension) beyond the BP in the clinic, thereby achieving more precise personalized treatment. For hemodialysis patients, the management of BP variability during hemodialysis is particularly important. SBPM provides a convenient and feasible technical means for this purpose. Therefore, it is recommended that patients increase the frequency of home BP monitoring during the autumn and winter seasons (when BP is more likely to be high), record the BP values at waking up, before going to bed, and before and after hemodialysis. Patients may regularly feedback the monitoring results to the hemodialysis center, to facilitate timely adjustment of the target dry body weight and BP control plan.
Abnormal BP represents a major clinical challenge in maintenance hemodialysis, with intradialytic hypotension being one of the most frequent complications. This condition is associated with end-organ ischemic injury and may elevate the risk of myocardial infarction, heart failure, and cognitive decline [23–24]. Hypertension is likewise prevalent in chronic renal failure patients on maintenance hemodialysis, affecting more than 90% of cases. Notably, 13%-23% may develop intradialytic hypertension, which compromises dialysis adequacy in approximately 22% of patients and is linked to an increased incidence of cardiovascular disease and mortality [25–26]. Our results demonstrate that the prevalence of intradialytic hypertension, cardiovascular events, and mortality was significantly higher in autumn and winter compared with spring and summer. This phenomenon may be attributable to pre-dialysis fluid overload and sodium retention caused by impaired renal function. Although dialysis partially corrects fluid overload, it can induce rapid shifts in plasma osmolarity, leading to pronounced short-term BP fluctuations that adversely affect prognosis [27]. To promote hemodynamic stability and mitigate adverse outcomes during dialysis, clinicians should closely monitor vital signs, reinforce nursing care, adhere strictly to aseptic techniques, and enhance patient awareness of treatment importance to foster adherence.
This study further quantified the seasonal amplitude of BP variation, revealing that winter increases were particularly pronounced in elderly and male patients. These subgroups therefore constitute high-risk populations for seasonal BP fluctuations and should be prioritized in clinical management. The findings also confirm that greater variability in BP (male sex, advanced age) coincides with heightened vulnerability to adverse events during cold seasons, underscoring the urgency of seasonal BP control. Consequently, management strategies should focus especially on the high-risk triad of winter, male sex, and advanced age. Preemptive interventions-initiated before the onset of autumn and winter-should include strict dietary sodium restriction, thermal protection, and regular monitoring, together with proactive adjustments to dry weight targets and antihypertensive regimens, as well as intensified intradialytic monitoring, in order to minimize risks related to seasonal BP shifts [28–29].
In conclusion, BP in hemodialysis patients was influenced by season, age, and sex. The peak of seasonal elevations was detected in autumn and winter; age-related increases were most pronounced in patients over 60 years; and men consistently exhibited higher BP than women. Autumn and winter thus represented high-risk periods, with elderly male patients constituting the most vulnerable subgroup. These findings highlight the importance of implementing proactive seasonal management strategies to mitigate BP fluctuations during dialysis, thereby reducing adverse events and improving survival and quality of life. Nonetheless, as an observational study, these results may be subject to residual confounding. Furthermore, reliance on limited outcome indicators constrains generalizability to other geographical or healthcare settings. Future prospective or multi-center studies with larger sample sizes are warranted to validate these findings.
Acknowledgements
Not applicable.
Author contributions
Shan Lan: Study design, quality assessment, data extraction, statistical analysis, drafting and revision of the manuscript, and data interpretation. Zhibin Wu: Selection of eligible articles, data collection and critical revision of the manuscript. All authors reviewed the draft and approved the final version of the manuscript.
Funding
This study was funded by Fujian Medical University Qihang Fund Project (No. 2021QH1269).
Data availability
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
This study was approved by The Ethics Committee of Zhangzhou Affiliated Hospital of Fujian Medical University.
Consent for publication
Not Applicable.
Clinical trial number
Not Applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.