Design and population

Between 2015 and 2016, an observational cross-sectional study was conducted. The recruitment was done through open invitation to the people who were accompanying patients of the outpatient care department of our institution by convenience. These subjects were asked to fill out a survey and undergo an electrocardiogram to rule out any cardiovascular disease. Those with a history of hypertension, diabetes mellitus, smoking, alcoholism, ischemic heart disease, peripheral vascular disease, and electrocardiographic data of hypertensive heart disease were excluded from the study. A clinical questionnaire was applied and anthropometric measurements of weight in kilograms and height in meters were made to calculate the BMI. Subjects were classified according to their BMI values: underweight (< 18.5), normal (18.5-24.9), overweight (25-29.9), obesity Grade 1 (30-34.9), obesity Grade 2 (35-39.9), and obesity Grade 3 (≥ 40).

Measurement of CBP

An Arteriograph (TensioMed) device with oscillometric technique was used for its evaluation³; the CBP measurements of the subjects were carried out between 9:00 a.m. and 11:00 a.m., on a single occasion, all records were obtained in a quiet environment, after resting in supine position for 5 min and later analyzed with software (version 3.0.0.4.), which reported CBP, cPP, systolic brachial pressure (SBP), brachial pulse pressure (bPP), PWVAo, and Aix.

Statistical analysis

The numerical variables are summarized as mean and standard deviation or median and quartiles 25 and 75, according to their distribution. The categorical variables are summarized in frequency and percentage. We performed bivaried analysis of two independent groups with t-test or Mann–Whitney U-test for numerical variables and Chi-square test for categorical variables. When there are more than two groups to be compared, the ANOVA, Kruskal–Wallis, and Chi-square linear trend tests were used, depending on the case. Bivaried correlations were performed (Pearson or Spearman, according to distribution). Multivariate analysis was performed with logistic regression to predict CBP > 140 mmHg, PWVAo > 9 m/s, and Aix > 33% using the Statistical Package for the Social Sciences 22.0, a two-tailed p < 0.05 was considered statistically significant.

Analysis by sex

Table 1 shows the results divided by sex. There were no differences in age, BMI, or brachial systolic blood pressure. However, women had higher levels of CBP and cPP, with higher proportions with CBP above the expected limit, without statistical significance (> 140 mmHg, 29% vs. 23%, p = 0.056). At the same time, women had significantly higher values of PWVAo and Aix. Similarly, the calculated arterial age was higher for women, despite similar chronological ages. When taking the CBP cutoff points ≥ 140 mmHg and cPP ≥ 50 mmHg for the diagnosis of high blood pressure, a higher proportion of new diagnoses was observed in women, without observing important changes in men or when using brachial measurements (Fig. 1).

Figure 1 New diagnoses of high blood pressure. Red bar represents female. Blue bars represent male. With SBP, similar proportion of new high blood pressure diagnosis was made. With CBP, a higher proportion of high blood pressure new diagnosis in female was observed. The proportion is higher with cPP. SBP: systolic brachial blood pressure; CBP: central blood pressure; cPP: central pulse pressure. 

Analysis by age

Table 2 shows the measurements obtained by age group. We observed a moderate direct association between age and SBP (rho = 0.34, p < 0.001), which improves for CBP (r = 0.47, p < 0.0001) and cPP (r = 0.49, p < 0.0001). Two other phenomena were observed: the first, in subjects younger than 40 years, a significant gradient between SBP and CBP is observed, after this age, the pressures are similar (Fig. 2). Second, women under 40 years have lower values of CBP; however, when this age is exceeded, CBP exceeds men (Fig. 3). Regarding the parameters of vascular rigidity, both have moderate direct association with age (r = 0.52, p < 0.001 for PWVAo and r = 0.57, p < 0.001 for Aix). Regardless of age, women have higher Aix values.

Figure 2 Gradient between CBP and SBP by age. Black circles represent SBP. Red circles represent CBP. There is a significant gradient CBP-SBP before 40 years. After this age, CBP and SBP are similar. SBP: systolic brachial blood pressure (black circles); CBP: central blood pressure (red circles). 

Figure 3 CBP by age and sex. The blue box plots represent CBP in females. The green box plots represent CBP in males. Notice similar values between females and males before 40 years. After 40 years, CBP is higher in female subjects. CBP: central blood pressure. 

BMI analysis

Table 3 shows the measurements by weight category. Weak direct associations were observed between BMI, SBP (rho = 0.24, p < 0.001), and CBP (rho = 0.19, p < 0.001); however, the values of these last two increase to a greater degree of obesity in a significant way. When analyzing vascular rigidity parameters, no association with BMI is observed.

Logistic regressions

Table 4 shows logistic regressions. Independent predictors for CBP > 140 mmHg are age and BMI and for PWVAo > 9 m/s and Aix > 33% are age and sex, without showing effect by the BMI on these parameters related to vascular stiffness.

CBP and gender

Regarding the relationship between CBP and sex, a statistically significant difference was observed between men and women, however, with a delta of only 3 mmHg. Studies with a large number of patients in China and Europe showed similar results⁷,⁸. It is noteworthy that, after 40 years of age, the CBP is equal and even, when over 60 years old, the gradient is reversed and becomes greater for women than men.

Notably, the use of CBP and its measurements increased the proportion of women with a new diagnosis of hypertension, but not with the use of SBP. According to data from ENSANUT 2016, the prevalence in Mexico of hypertension is 25.5%, and 40% do not know its diagnosis⁹. The greater proportion of new diagnoses in women is due to the effect of the use of CBP, despite the fact that SBP values were similar.

When comparing the reference values of our population with European and Asian results, higher values were found⁷,⁸. These results are relevant because they may be associated with a higher baseline cardiovascular risk in Hispanics, according to previously reported¹⁰.

Regarding the cPP and Aix, women presented higher statistically significant values, however, directly influenced by the height, a finding already described previously¹¹. However, the PWVAo (which is not modified by the height) is elevated in women, probably in relation to greater vascular rigidity. Although our results cannot be conclusive in this regard, we believe that they support the hypothesis that women may present different risk and pathophysiology, so they may also need special considerations in treatment.

CBP and age

The increase in age leads to an increase in CBP and vascular rigidity parameters. This association has been reproduced by various publications⁷,⁸,¹², which is reflected in the higher prevalence of hypertension as the age advances¹³.

Of relevance, a statistically significant gradient of central-brachial pressure was observed in patients under 40 years of age. After this age, the significance is lost and both pressures present similar measurements. Our results show CBP values of 109 (103-118) and 114 (107-128) mmHg in < 30 and 30-40 years, respectively, and a central-brachial gradient of 11 and 7 mmHg was observed and may consider normal.

The significance of the loss of this gradient or the presence of higher CBP values in this age group and its relationship with an increased risk of arterial hypertension remains to be clarified. Saladini et al.¹⁴ recruited 305 patients with an age of 37 ± 10 years and performed measurements of SBP and CBP, finding this central-brachial gradient; at follow-up, subjects with a lower gradient had a higher incidence of high blood pressure. Therefore, the measurement of CBP could have a potential impact on the early diagnosis of high blood pressure in subjects less than 40 years.

CBP and BMI

Regarding the BMI, it was found that the greater the degree of obesity, there is an increase in the CBP and the brachial measurements, data observed in previous publications¹⁵,¹⁶. However, the parameters of vascular rigidity did not show differences between the degrees of obesity. Other authors have reported this finding¹⁵-¹⁷, suggesting that different physiopathological mechanisms are present in the patient with obesity. Messerli et al.¹⁸ conducted a study to assess the hemodynamic differences associated with hypertension and obesity, reporting that the total blood volume is significantly increased in obese hypertensive patients and found no differences in peripheral resistance or plasma renin activity. The same author later published that obese subjects had lower values of circulating catecholamines when compared with subjects of normal weight¹⁹. These data suggest that, at least partially, a cause of arterial hypertension in obese patients is the increase in blood volume and not an effect of vascular rigidity or catecholamines so that treatments should possibly be aimed at this objective.

Limitations

The main limitations of our study are the sample size, although, to our current knowledge, it could be the largest Hispanic population included in this issue. On the other hand, the lack of follow-up and hard outcomes makes it difficult to relate our findings to risk, so additional studies are needed to clarify the role of CBP and the parameters of vascular rigidity in the stratification and diagnosis of hypertension in Hispanics. Our study included a greater proportion of female sex because socially in our environment is this gender the natural companion of patients to their medical consultations; this could have an impact on the generalization of the results, mainly in the differences by gender.