**4. Results**

**Table 1** shows the demographic, general and clinical characteristics of the population under study. Of the 549 participants, 41 (7.5%) had ISH as measured by conventional means (ISHC). This figure is similar to those obtained for the ambulatory sub-types of ISH, namely 24-hour, Night-time and Daytime ISH which had 39 (7.1%), 42 (7.7%) and 41 (7.5%) participants respectively. Systolic-diastolic hypertension was observed in 161 (29%) of the participants. The mean age of the population was 45.3 ± 18.5 years and the ISHC group was significantly older (65.3 ± 13.5 years) than both normotensives (39.7 ± 17.6 years) and hypertensives (52.1 ± 15.5 years). There were slight reductions in average age within the other ISH subtypes, with ISH24 at 57.8 ± 20.1 years, ISHN at 55.4 ± 24.6 years and ISHD at 53.7 ± 20.9 years. We observed that all the ISH subgroups had greater proportions of female participants than the normotensive or hypertensive groups [51]. Anthropometry revealed significantly higher waist circumference in the ISHC group than in the normotensives, this was also true for all the other ISH subgroups albeit of no known significance. In addition to this, the overall population was overweight with a BMI of 29.1 ± 7.8 kg/m2 . Both ISHC and hypertensives were obese (BMI of 31.4 ± 7.5 kg/m2 and 30.9 ± 7.5 kg/m<sup>2</sup> respectively), the former group having a significantly higher BMI than the normotensives (BMI = 28.0 ± 7.7 kg/m<sup>2</sup> ). The average SBPC of the ISHC group (153.1 ± 11.7 mm Hg) was higher than that of the hypertensive group (149.6 ± 20.3 mm Hg), and significantly higher than that of the normotensives (129.7 ± 21.4 mm Hg). Overall, the SBPC values for all ISH sub-types were high. Conventional ISH had an average DBPC of 83.5 ± 4.8 mm Hg, significantly higher than that of normotensives (77.6 ± 7.2 mm Hg) and significantly lower than that of hypertensives (98.6 ± 8.4 mm Hg). Similarly, 24-hour, night-time and daytime ISH all had conventional diastolic blood pressures below those of hypertensives but above those of normotensives. All sub-types of ISH had higher pulse pressure values than both normotensives and hypertensive groups, significantly so for those participants with ISHC (PP = 69.7 ± 12.3 mm Hg).

**Tables 2** and **3** show the ROC curve analysis of the relationships between the sub-types of ISH and cardiovascular target organ changes. All subtypes of ISH were significantly associated with increased PWV and LVMI. Conventional ISH strongly predicts arterial stiffness and left ventricular hypertrophy, with area under the curve (AUC) values of 0.88 ± 0.03 (CI: 0.83 to 0.93) and 0.86 ± 0.03 (CI: 0.88 to 0.92), respectively. Daytime ISH was shown to be a strong predictor of both (PWV and LVMI) with all the values exceeding 0.8. all three organ changes under study



**Table 1.**

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*Ambulatory Isolated Systolic Hypertension and Cardiovascular Target Organ Damage in People…*

ISH subtype AUC CI ISHC 0.88±0.03 0.83 to 0.93 ISH24 0.77±0.04 0.68 to 0.86 ISHN 0.78±0.04 0.70 to 0.85 ISHD 0.83±0.05 0.74 to 60.92 *AUC, area under the curve; CI, confidence intervals; ISHC, conventional isolated systolic hypertension; ISH24, 24 hour Isolated systolic hypertension; ISHN, Night-time isolated systolic hypertension; ISHD, Daytime isolated systolic hypertension P < 0.05 for all associations. Adjustments were made for age, gender, BMI, the use of antihypertensive* 

ISH subtype AUC CI ISHC 0.86±0.03 0.88 to 0.92 ISH24 0.76±0.03 0.67 to 0.86 ISHN 0.71±0.05 0.62 to 0.80 ISHD 0.80±0.06 0.68 to 0.09 *AUC, area under the curve; CI, confidence intervals; ISHC, conventional isolated systolic hypertension; ISH24, 24 hour Isolated systolic hypertension; ISHN, Night-time isolated systolic hypertension; ISHD, Daytime isolated systolic hypertension. P < 0.05 for all associations. Adjustments were made for age, gender, BMI, the use of antihypertensive* 

(AUC values all exceeding 0.8). The pattern of association and the significance was

*Comparison of PWV of ISH subgroups, the hypertensives and the normotensives. This figure shows data of PWV expressed as adjusted means ± SD. The differences between the means was calculated using the general linear model and adjustments were made for the following covariates; age, gender, BMI, alcohol intake and cigarette smoking. There was no significant difference in the PWV of the different ISH subtypes and none of the ISH subtypes was significantly different from the hypertensives. However, the PWV of all the ISH subtypes and* 

**Figures 1** and **2** shows data of PWV and LVMI respectively expressed as adjusted means ± SD. For both PWV and LVMI, there was no significant difference in the PWV of the different ISH subtypes and none of the ISH subtypes was

maintained even after adjusting for confounding variables.

*hypertensives was significantly higher than that of the normotensives. \* = p value <0.05.*

*DOI: http://dx.doi.org/10.5772/intechopen.96521*

*medication, smoking and alcohol consumption.*

*medication, smoking and alcohol consumption.*

*ROC curve analysis of the relationship between ISH and PWV.*

*ROC curve analysis of the relationship between ISH and LVMI.*

**Table 2.**

**Table 3.**

**Figure 1.**

*Demographic and clinical characteristics of participants according to blood pressure status.*

*Ambulatory Isolated Systolic Hypertension and Cardiovascular Target Organ Damage in People… DOI: http://dx.doi.org/10.5772/intechopen.96521*


*AUC, area under the curve; CI, confidence intervals; ISHC, conventional isolated systolic hypertension; ISH24, 24 hour Isolated systolic hypertension; ISHN, Night-time isolated systolic hypertension; ISHD, Daytime isolated systolic hypertension P < 0.05 for all associations. Adjustments were made for age, gender, BMI, the use of antihypertensive medication, smoking and alcohol consumption.*

#### **Table 2.**

*ROC curve analysis of the relationship between ISH and PWV.*


*AUC, area under the curve; CI, confidence intervals; ISHC, conventional isolated systolic hypertension; ISH24, 24 hour Isolated systolic hypertension; ISHN, Night-time isolated systolic hypertension; ISHD, Daytime isolated systolic hypertension. P < 0.05 for all associations. Adjustments were made for age, gender, BMI, the use of antihypertensive medication, smoking and alcohol consumption.*

#### **Table 3.**

*ROC curve analysis of the relationship between ISH and LVMI.*

#### **Figure 1.**

*Comparison of PWV of ISH subgroups, the hypertensives and the normotensives. This figure shows data of PWV expressed as adjusted means ± SD. The differences between the means was calculated using the general linear model and adjustments were made for the following covariates; age, gender, BMI, alcohol intake and cigarette smoking. There was no significant difference in the PWV of the different ISH subtypes and none of the ISH subtypes was significantly different from the hypertensives. However, the PWV of all the ISH subtypes and hypertensives was significantly higher than that of the normotensives. \* = p value <0.05.*

(AUC values all exceeding 0.8). The pattern of association and the significance was maintained even after adjusting for confounding variables.

**Figures 1** and **2** shows data of PWV and LVMI respectively expressed as adjusted means ± SD. For both PWV and LVMI, there was no significant difference in the PWV of the different ISH subtypes and none of the ISH subtypes was

#### **Figure 2.**

*Comparison of the LVMI of the ISH subtypes, the normotensives and the hypertensives. This figure shows data of LVMI expressed as adjusted means ± SD. The differences between the means was calculated using the general linear model and adjustments were made for age, gender, BMI, alcohol intake, cigarette smoking and presence of diabetes. There was no significant difference in the LVMI of the different ISH subtypes and none of the ISH subtypes was significantly different from the hypertensives. However, the LVMI of all the ISH subtypes and hypertensives was significantly higher than that of the normotensives. \* = p value <0.05.*

significantly different from the hypertensives. However, the PWV and LVMI of all the ISH subtypes were significantly higher than that of the normotensives.

### **5. Discussion**

In the present study, we determined the general characteristics of ISH and went on to divide it into four subtypes namely Conventional ISH, 24-hour ISH, Night-time ISH and Daytime ISH. We proceeded to investigate the associations between each of these subtypes with PWV and LVM. We further investigated the extent to which each of the ISH subtypes predicted the target organ changes mentioned. The results of the present study show that 7.5% of the cohort had ISHC and the same percentage had Daytime ISH. Night-time ISH was found in 7.7% of the population, while 7.1% of the participants had 24-hour ISH. Furthermore, our findings show that all subtypes of ISH are significantly associated with increased PWV and LVMI in measures comparable to general hypertension, The percentage of participants with ISHC in our study is consistent with the work of Gupta *et al.,* [52] who found a similar (7.78%) prevalence of the condition following their study of office workers in a North Indian town. Huang *et al.,* [53] also found a similar prevalence of ISH (7.6%) in a Chinese study. However, all these studies used only conventional BP measurements to determine the prevalence of ISH. Hence our study is the first to identify the three ISH subtypes identified by ambulatory BP monitoring.

#### **5.1 Determinants of ISH**

#### *5.1.1 Socio-economic status*

Our and other studies indicate that the prevalence of isolated systolic hypertension averages around 8% across populations whether measured by conventional or ambulatory BP techniques. However, Ntuli, et al. [54] investigated a population ethnically similar to our study cohort and their study revealed a much higher

**87**

latter would raise PP.

*Ambulatory Isolated Systolic Hypertension and Cardiovascular Target Organ Damage in People…*

prevalence of ISHC (21%). The most likely explanation for this is the socioeconomic difference between their sample population and ours. The study by Ntuli et al. [54] was conducted in rural Limpopo (Dikgale), where unemployment and poverty is high and there is limited access to adequate healthcare [54–56]. Ntuli's study indicates that socio-economic factors could play a role in the prevalence of ISH. Socioeconomic factors have been implicated in contributing to the high prevalence of hypertension in developing countries [57, 58], and it would not be surprising that

The mean age of participants in the present study (45.3 years) was similar to that of subjects in the study by Ntuli et al. [54] (44.2 years). Gupta et al. [52] did not report a mean age for their population which was limited to the working age-group under 58 years, while Huang et al. [53] carried out their investigation on participants in the 35–74 age group [52, 53]. The bulk of studies on ISHC have been focused on specific age groups, usually the young (under 35 years of age) or the old (over 50 years old) [27, 49, 59, 60] unlike our population which included all consenting persons over the age of 18. While several studies in recent years have shown that the condition is not at all restricted to the older population [25–27], the relatively high average age associated with ISH (especially the conventional subtype) in our study is consistent with the findings of a number of researchers and with the widely accepted notion that ISH is predominant and naturally occurring in the elderly population [1, 16, 18, 30, 61]. A study by Huang et al. [53] also showed

Martins et al. [62] observed an increase in PP and SBP from the age of 45 upward in their analysis of data from the NHANES. Indeed, the most commonly described pathophysiological mechanism for ISH involves changes occurring to the large arteries owing to ageing [13]. With age progression, elastin in the media decreases, leading to a fragmented media [13, 18] which is susceptible to calcium and lipid accumulation. Along with this media calcification occurs the accumulation of smooth muscle cells within the intima, collagen cross linking occurs and all this leads to the thickening and fibrosis of the arterial wall [13, 18, 43]. These changes culminate in arterial stiffness, an increased wall-to-lumen ratio and a reduced cross-sectional area of the lumen of the greater arteries [13, 37, 63]. Due to poor compliance, the large arteries fail to expand and subsequently recoil effectively in systole and diastole of the cardiac cycle, respectively. There is a resultant increase in aortic PP and PWV. Consequently, the reflected wave which would normally return during diastole, returns during late systole and augments systolic pressure; SBP increases while the DBP decreases [43, 63]. In line with this, we observed higher values of average SBPC in the ISH groups than in the normotensive group, and these were comparable to that of hypertensive participants. This was coupled with relatively low DBPC for all ISH sub-types when compared to the hypertensive group. By definition, PP is the difference between SBP and DBP, thus its normal value is approximately 40 mm Hg [64]. Pulse Pressure values exceeding 60 mm Hg are associated with target organ damage which may or may not be asymptomatic [3]. In the present study, PP was markedly increased in participants with ISHC, with an average of 69.7 mm Hg. Wallace et al. [65] also observed similar elevated SBP and PP (67 mm Hg) in their ISHC group. This finding was as expected based on the definition and underlying physiology of the condition [16, 18, 61] since PP is the difference between systolic and diastolic BPs; and an increase in the former and/or decrease in the

*DOI: http://dx.doi.org/10.5772/intechopen.96521*

ISHC would follow the trend.

an increase in ISHC with age.

*5.1.2 Age*

#### *Ambulatory Isolated Systolic Hypertension and Cardiovascular Target Organ Damage in People… DOI: http://dx.doi.org/10.5772/intechopen.96521*

prevalence of ISHC (21%). The most likely explanation for this is the socioeconomic difference between their sample population and ours. The study by Ntuli et al. [54] was conducted in rural Limpopo (Dikgale), where unemployment and poverty is high and there is limited access to adequate healthcare [54–56]. Ntuli's study indicates that socio-economic factors could play a role in the prevalence of ISH. Socioeconomic factors have been implicated in contributing to the high prevalence of hypertension in developing countries [57, 58], and it would not be surprising that ISHC would follow the trend.
