The acute effects of particulate matter air pollution on ambulatory blood pressure: A multicenter analysis at the hourly level
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Epidemiological evidence from ambulatory blood pressure monitoring is needed to clarify the associations of particulate air pollution with blood pressure and potential lag patterns. We examined the associations of fine and coarse particulate matter (PM2.5, PM2.5-10) with ambulatory blood pressure among 7108 non-hypertensive participants from 7 Chinese cities between April 2016 and November 2020. Hourly concentrations of PM2.5 and PM2.5-10 were obtained from the nearest monitoring stations. We measured four blood pressure indicators, including systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and pulse pressure (PP). Linear mixed-effect models combined with distributed lag models were applied to analyze the data. Generally, very short-term exposure to PM2.5 was significantly associated with elevated blood pressure. These effects occurred on the same hour of blood pressure measurement, attenuated gradually, and became insignificant approximately at lag 12 h. An interquartile range (IQR, 33 μg/m3) increase of PM2.5 was significantly associated with cumulative increments of 0.58 mmHg for SBP, 0.31 mmHg for DBP, 0.38 mmHg for MAP, and 0.33 mmHg for PP over lag 0 to 12 h. The exposure-response relationship curves were almost linear without thresholds, but tended to be flat at very high concentrations. No significant associations were observed for PM2.5-10. Our study provides independent and robust associations between transient PM2.5 exposure and elevated blood pressure within the first 12 h, and reinforces the evidence for a linear and non-threshold exposure-response relationship, which may have implications for blood pressure management and hypertension prevention in susceptible population.Keywords:
Interquartile range
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Ambulatory blood pressure (BP) monitoring is a technique associated with several operational characteristics that make its use in adult hypertension trials attractive. To extend its use effectively to hypertension trials in children, additional studies are needed to assess its performance in this population. It is likely that ambulatory monitoring will be important in this population for the study of drug efficacy and safety. In general, ambulatory monitoring has better short-term and long-term reproducibility than office BP. Some data suggest that this superiority of ambulatory over office BP is also true in children. This better reproducibility should allow a drug effect to be detected with a smaller sample size, especially in crossover studies. Ambulatory BP averages are also free from the office-induced increase in BP, making it is easier to include adults and children in trials who have ambulatory hypertension. Such a requisite for a trial has to be planned to include more patients in the recruitment and run-in phases as use of an ambulatory criterion for hypertension will lead to some patients with elevated office BP not qualifying based on ambulatory readings. Of additional major importance, ambulatory monitoring of BP correctly identifies the temporal effects of a drug and hence allows accurate calculation of its trough-to-peak ratio. Ambulatory monitoring promises to be a significant tool for the study of hypertension in children including pathophysiology and the efficacy of antihypertensive drugs.
Antihypertensive drug
Crossover study
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Ambulatory blood pressure (BP) monitoring provides a more precise measure of BP status than clinic BP and is currently recommended in the evaluation of high BP in children and adolescents. However, ambulatory BP monitoring may not always be available. Our aim was to determine the clinic BP percentile most likely to predict ambulatory hypertension. We evaluated clinic and ambulatory BP in 247 adolescents (median age, 15.7 years; 63% white; 54% male). Clinic BP percentile (based on the fourth report and the 2017 American Academy of Pediatrics clinical practice guidelines) and ambulatory BP status (normal versus hypertension) were determined by age-, sex-, and height-specific cut points. Sensitivity and specificity of different clinic BP percentiles and cutoffs to predict ambulatory hypertension were calculated. Forty (16%) and 67 (27%) patients had systolic hypertension based on the fourth report and the 2017 guidelines, respectively, whereas 38 (15%) had wake ambulatory systolic hypertension. The prevalence of ambulatory wake systolic hypertension increased across clinic systolic BP percentiles, from 3% when clinic systolic BP was <50th percentile to 41% when ≥95th percentile. The 2017 guidelines' 85th systolic percentile had similar sensitivity (86.8%) and better specificity (57.4% versus 48.1%) than elevated BP (≥90th percentile or ≥120 mm Hg) to diagnose ambulatory hypertension. When evaluating adolescents for hypertension, 2017 guidelines' clinic systolic 85th percentile may be the optimal threshold at which to perform ambulatory BP monitoring.
Prehypertension
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Ambulatory blood pressure (BP) monitoring has matured into a useful methodology that obtains automated measurements of brachial artery BP during a 24‐hour period. Cardiovascular outcomes in the treated patient with hypertension are often better predicted by ambulatory BP than by office pressures. Consensus guidelines have advocated lower goals of treated office BP in the majority of patients with hypertension; guidelines for the goal of ambulatory BP are needed as well. Recently, prospective cohort studies have shown that individuals whose clinic pressure is relatively normal but whose 24‐hour BP is elevated are more likely to have a cardiovascular event than individuals with both normal clinic BP and ambulatory BP. Along with the knowledge gained from analyses of higher‐risk hypertension patients, recommendations can now be made for how to use ambulatory BP monitoring in clinical practice. For example, ambulatory BP monitoring may be useful in verifying 24‐hour control in high‐risk patients whose office BP appears to be normal at rest or during the peak effect time of their antihypertensive agents. Evidence is mounting from studies that support the use of ambulatory BP monitoring in patients with resistant hypertension at the time of diagnosis and following clinically guided therapy.
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Home measurement and ambulatory 24-hour monitoring of blood pressure (BP) have many advantages over conventional office BP measurement and are increasingly used in clinical practice. However, their effect on the treatment of hypertension requires additional study. We assessed the hypothesis that the adjustment of antihypertensive treatment based on home BP instead of ambulatory BP would lead to equivalent BP control. After a 4-week wash-out period with placebo, a total of 110 patients whose daytime diastolic ambulatory BP averaged 85 mmHg or higher were randomized to either ambulatory BP or home BP groups. Antihypertensive treatment was then adjusted in a stepwise fashion at 6-week intervals according to the mean daytime ambulatory diastolic BP or the mean home diastolic BP during the preceding week, depending on the patient's randomization group. Both ambulatory BP monitoring and home BP measurement were performed on all patients during the study. If the diastolic BP guiding treatment was above 80 mmHg, a physician blinded to the randomization intensified hypertensive treatment; if equal to or below 80 mmHg the treatment was left unchanged. A total of 98 patients completed the study; 52 in the home BP group (age 54±1.4 y, 37% men) and 46 in the ambulatory BP group (age 54±1.0 y, 50% men). After a 24-week follow-up period BP was significantly reduced within both groups (p<0.01). The between-group differences in systolic and diastolic BP changes were statistically nonsignificant (p>0.05). An equal share of patients had progressed to multiple-drug treatment in the home and ambulatory BP groups (65.4% vs. 67.4%, p=0.83). We conclude that the adjustment of antihypertensive treatment based on home BP measurement instead of 24-hour ambulatory BP monitoring led to equally intensive drug treatment with preservation of BP control. (See Table) Changes in BPs After a 24-week Follow-up Values expressed as mean ± SEM. SBP, systolic blood pressure; DBP, diastolic blood pressure. Changes in BPs After a 24-week Follow-up Values expressed as mean ± SEM. SBP, systolic blood pressure; DBP, diastolic blood pressure.
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What is the role of ambulatory blood pressure monitoring in the management of hypertensive patients?
Noninvasive ambulatory blood pressure (BP) recording is now clinically available for the evaluation of hypertensive patients. It is well known that pressures measured in the office or clinic are unreliable and that repeated measurements are better at predicting outcome than are single measurements. Several studies have compared the correlation between target organ damage and different measures of BP, and in every instance ambulatory BP measurements have given better correlations than clinic readings. In one prospective study the ambulatory BP readings were more predictive of BP-related morbidity than were clinic readings. Data are now being obtained that will establish normal ranges of BP during ambulatory monitoring, against which values from patients being evaluated for hypertension can be compared. It is concluded that ambulatory BP monitoring is of clinical value for the evaluation of patients with mild hypertension.
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The Canadian Hypertension Society has developed guidelines for the use of ambulatory blood pressure (BP) monitoring in clinical practice. Published articles with the best available levels of evidence were used to support the following recommendations: Physicians should only use ambulatory BP monitoring devices that have been validated independently using established protocols. A decision to withhold drug therapy based upon the ambulatory BP should take into account normal values for 24-h and awake ambulatory BP. Based upon studies on prognosis and a clinical trial based upon BP control as an outcome, ambulatory BP monitoring should be considered for untreated patients whenever an office-induced increase in BP is suspected. Ambulatory BP monitoring should be considered for treated patients suspected of having an office-induced increase in BP, including individuals with apparent resistance to drug therapy, symptoms suggestive of hypotension, and fluctuating office BP readings. Based upon studies on prognosis, changes in nocturnal BP should be taken into account in any decision to withhold drug therapy based upon the ambulatory BP. Further studies are required to determine whether the clinical benefit of antihypertensive therapy is more closely related to ambulatory or office BP.
Antihypertensive drug
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The purpose of this study was to compare home and ambulatory blood pressure (BP) in the adjustment of antihypertensive treatment. After a 4-week washout period, patients whose untreated daytime diastolic ambulatory BP averaged ≥85 mm Hg were randomized to be treated according to their ambulatory or home BP. Antihypertensive treatment was adjusted at 6-week intervals according to the mean daytime ambulatory diastolic BP or the mean home diastolic BP, depending on the patient's randomization group. If the diastolic BP stayed above 80 mm Hg, the physician blinded to randomization intensified hypertensive treatment. Ninety-eight patients completed the study. During the 24-week follow-up period both systolic and diastolic BP decreased significantly within both groups (P < .001). At the end of the study, the systolic/diastolic differences between ambulatory (n = 46) and home (n = 52) BP groups in home, daytime ambulatory, night-time ambulatory, and 24-h ambulatory BP changes averaged 2.6/2.6 mm Hg, 0.6/1.7 mm Hg, 1.0/1.4 mm Hg, and 0.6/1.5 mm Hg, respectively (P range .06 to .75) A nonsignificant trend to more intensive drug therapy in the ambulatory BP group and a nonsignificant trend to larger share of patients reaching (57.7% v 43.5%, P = .16) the target pressure in the home BP group was observed due to the 3.8 mm Hg difference in ambulatory and home diastolic BP at randomization. The adjustment of antihypertensive treatment based on either ambulatory or home BP measurement led to good BP control. No significant between-group differences in BP changes were seen at the end of the study. Additional research is needed to provide more conclusive results.
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Home and ambulatory blood pressure (BP) measurements are recommended for the diagnosis of hypertension. However, the clinical characteristics of individuals showing a diagnostic disagreement between their home and ambulatory BP measurements are unclear. Of the 470 individuals who were not on antihypertensive drug treatment with a BP ≥140/90 mmHg at an outpatient clinic, 399 who had valid office, home, and ambulatory BP results were included. Hypertension was diagnosed based on an average home BP ≥135/85 mmHg and/or an average daytime ambulatory BP ≥135/85 mmHg. The participants were divided into three groups: Agree-NT (home and ambulatory BP normotension), Disagree (home BP normotension and ambulatory BP hypertension, or home BP normotension and ambulatory BP hypertension), and Agree-HT (home and ambulatory BP hypertension). Eighty-four individuals (21.1%) were classified as the Disagree group. The mean serum creatinine, triglycerides, and electrocardiogram voltage in the Disagree group were intermediate between those observed in the Agree-NT and the Agree-HT group. In the Disagree group, the mean levels of office and home diastolic BP, all of the components of ambulatory BP, the aortic systolic BP, and the BP variabilities were found to be intermediate between those of the Agree-NT and the Agree-HT groups. These results indicate that individuals showing a diagnostic disagreement between their home and ambulatory BP may have cardiovascular risks that are intermediate between those with sustained home and ambulatory normotension and hypertension.
Masked Hypertension
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