CARDIOVASCULAR JOURNAL OF AFRICA • Volume 34, No 4, September/October 2023 AFRICA 227 The ambulatory blood pressure-monitoring parameters and blood pressure variability were compared among the three groups. Significant differences were found in 24-hour heart rate, daytime systolic and diastolic blood pressure, night-time systolic and diastolic blood pressure, 24-hour mean systolic and diastolic blood pressure, daytime systolic and diastolic standard pressure deviation, night-time systolic standard pressure deviation, 24-hour systolic pressure standard deviation, and daytime systolic and diastolic blood pressure coefficient of variation (p < 0.05). No significant differences were detected in night-time diastolic pressure standard deviation, 24-hour diastolic pressure standard deviation, 24-hour systolic and diastolic blood pressure coefficient of variation, and night-time systolic and diastolic blood pressure coefficient of variation among the groups (p > 0.05) (Table 3). According to Spearman rank correlation analysis, salt sensitivity of essential hypertension patients was positively correlated with night-time systolic standard deviation, 24-hour systolic standard deviation and 24-hour systolic blood pressure coefficient of variation (r = 0.827, 0.734 and 0.658, p < 0.05), but it had no significant correlations with other parameters (p > 0.05) (Table 4). During the one-year follow up, major cardiovascular events occurred in 105 patients. With the incidence of cardiovascular events as dependent variables, and age, family history of cardiovascular diseases, salt-sensitivity risk stratification, low-density lipoprotein cholesterol, standard deviation of sequential five-minute normal-to-normal interval, 24-hour heart rate, night-time systolic standard deviation, 24-hour systolic standard deviation and 24-hour systolic blood pressure coefficient of variation as independent variables, Cox multivariate linear regression analysis was performed. The results revealed that age ≥ 55 years, family history of cardiovascular diseases, a high risk of salt sensitivity, night-time systolic standard deviation ≥ 14 mmHg, 24-hour systolic standard deviation ≥ 20 mmHg and 24-hour systolic blood pressure coefficient of variation ≥ 13.5% were all independent risk factors for cardiovascular diseases (p < 0.05) (Table 5). ROC curve analysis was conducted on the predicted results of the regression model for cardiovascular events and the actual results. The area under the ROC curve, sensitivity, specificity and Youden index were 0.837, 0.743, 0.899 and 0.859, respectively (Fig. 1). Discussion Hypertension is the first risk factor for cerebral–cardiovascular Table 2. Clinical indices of groups with different grades of salt-sensitivity risk Clinical indices Low-risk group (n = 141) Medium-risk group (n = 410) High-risk group (n = 179) Fasting blood glucose (mmol/l) 6.02 ± 1.06 6.13 ± 1.78 6.07 ± 1.35 Total cholesterol (mmol/l) 4.75 ± 1.17 4.86 ± 1.06 4.78 ± 1.28 Triglyceride (mmol/l) 1.63 ± 1.04 1.94 ± 1.01 1.89 ± 1.32 High-density lipoprotein cholesterol (mmol/l) 1.25 ± 0.37 1.29 ± 0.46 1.36 ± 0.52 Low-density lipoprotein cholesterol (mmol/l) 2.87 ± 1.05 3.12 ± 1.43a 3.54 ± 1.79a,b Uric acid (μmol/l) 327.65 ± 83.14 349.28 ± 91.36 346.81 ± 87.25 Serum creatinine (μmol/l) 64.58 ± 19.27 69.13 ± 22.75 65.59 ± 20.16 Standard deviation of the normal-to-normal intervals (ms) 132.92 ± 41.68 133.54 ± 38.21 135.02 ± 36.31 Standard deviation of sequential 5-min normal-to-normal interval (ms) 72.15 ± 101.34 64.82 ± 73.60a 43.26 ± 60.39a,b ap < 0.05 vs low-risk group, bp < 0.05 vs medium-risk group. Table 3. Ambulatory blood pressure monitoring parameters of groups with different grades of salt-sensitivity risk Parameters Low-risk group (n = 141) Medium-risk group (n = 410) High-risk group (n = 179) 24-h heart rate (beat/min) 62.33 ± 4.56 69.71 ± 6.15a 76.18 ± 7.34a,b Daytime systolic blood pressure (mmHg) 122.37 ± 9.15 136.89 ± 10.52a 144.96 ± 13.78a,b Daytime diastolic blood pressure (mmHg) 74.23 ± 6.71 83.12 ± 11.68a 87.45 ± 8.96a,b Night-time systolic blood pressure (mmHg) 110.34 ± 7.58 129.67 ± 10.37a 142.17 ± 13.02a,b Night-time diastolic blood pressure (mmHg) 66.07 ± 8.36 76.91 ± 10.19a 89.85 ± 11.23a, b 24-h mean systolic blood pressure (mmHg) 117.62 ± 8.59 132.57 ± 9.32a 143.01 ± 11.67a,b 24-h mean diastolic blood pressure (mmHg) 73.28 ± 6.71 82.64 ± 7.33a 87.19 ± 9.06a,b Daytime systolic standard deviation (mmHg) 12.53 ± 3.16 13.92 ± 4.51a 15.19 ± 4.72a,b Daytime diastolic pressure standard deviation (mmHg) 11.74 ± 3.29 12.33 ± 3.37a 14.50 ± 3.42a,b Night-time systolic standard deviation (mmHg) 11.67 ± 3.28 13.55 ± 5.64a 14.95 ± 3.67a,b Night-time diastolic pressure standard deviation (mmHg) 9.08 ± 3.41 9.65 ± 4.12 10.33 ± 6.07 24-h systolic standard deviation (mmHg) 15.27 ± 4.96 19.36 ± 4.15a 23.69 ± 5.02a,b 24-h diastolic pressure standard deviation (mmHg) 15.32 ± 4.50 16.54 ± 4.87 18.96 ± 4.23 24-h systolic blood pressure coefficient of variation (%) 12.14 ± 3.02 13.17 ± 2.05 14.19 ± 3.74 24-h diastolic blood pressure coefficient of variation (%) 17.11 ± 4.03 18.15 ± 6.02 19.18 ± 5.01 Daytime systolic blood pressure coefficient of variation (%) 11.76 ± 3.29 13.68 ± 4.15a 14.32 ± 4.58a,b Daytime diastolic blood pressure coefficient of variation (%) 17.65 ± 5.34 18.19 ± 7.22a 19.75 ± 6.08a,b Night-time systolic blood pressure coefficient of variation (%) 11.25 ± 4.37 10.76 ± 4.12 11.58 ± 4.62 Night-time diastolic blood pressure coefficient of variation (%) 14.58 ± 6.35 14.86 ± 5.99 15.02 ± 6.92 ap < 0.05 vs low-risk group, bp < 0.05 vs medium-risk group. Table 4. Association between salt sensitivity and blood pressure variability Variables r p-value Daytime systolic standard deviation 0.053 0.142 Daytime diastolic pressure standard deviation 0.00 0.253 Night-time systolic standard deviation 0.827 0.019 Night-time diastolic pressure standard deviation 0.012 0.307 24-h systolic standard deviation 0.734 0.026 24-h diastolic pressure standard deviation 0.036 0.285 24-h systolic blood pressure coefficient of variation 0.658 0.045 24-h diastolic blood pressure coefficient of variation 0.047 0.192 Daytime systolic blood pressure coefficient of variation 0.004 0.791 Daytime diastolic blood pressure coefficient of variation 0.047 0.208 Night-time systolic blood pressure coefficient of variation 0.010 0.341 Night-time diastolic blood pressure coefficient of variation 0.002 0.892
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