La presencia del vampiro en el cine y la literatura a) El vampiro en el cine

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YES 139 (18.6%) 12 (16.2%) 151 (18.3%) 0.874 0.510 - 1.499 Key: For the purpose of this analysis, pupils whose parents didn’t know their blood pressure status or BP status of other first degree relative(s) where applicable were excluded.

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prevalence rates from other Nigerian studies might be attributable to urbanization and life style changes that might have taken place over the years as there has been a period of > 20 years in between those studies and the present one. These factors have been reported to predispose both lower and higher social classes to cardiovascular disease risk factors; the former due to socio-economic stressors, limited access to health care and poor diet, the latter to obesity, excess food, and lack of exercise. ¹²³ Differences in methodology may also be contributory as the previous Nigerian studies have defined hypertension as BP ≥ mean + 2 SD for age and sex, ^{7, 16, 41} while this study defined hypertension as values ≥ 95^th percentile for age, sex and height. The former definition of mean + 2 SD tends to under estimate the prevalence because the 95^th percentile is mean + 1.645 SD according to the NHBPEP charts.³⁸

The prevalence rate of 4.7% for systolic hypertension obtained in this study was lower than the 9.8% obtained by Akor et al ²⁴ from Jos, Nigeria. The prevalence rate of 5.0% for diastolic hypertension obtained in this study is however, comparable with the 5.4% obtained by Akor et al

24 in that same study, using the same criteria of SBP and / DBP values at or above the 95^th percentile for age, sex and height for the population.³⁸ Body size alone could not account for the difference in prevalence of systolic hypertension, when the lower prevalence obtained in the heavier and taller subjects in this study was compared with the higher prevalence obtained by Akor et al²⁴ in their lighter and shorter subjects. A possible postulation for the higher prevalence of systolic hypertension in the study by Akor et al ²⁴ may be attributable to the fact that blood pressure levels in some population may be influenced by other factors like place of abode and environment, like altitude,since Jos is at a higher altitude than Abuja. ¹¹⁶ As it has been shown that blood pressure and systemic vascular resistance rises over time at high altitude as a result of increasing sympathetic activity and reduced tissue hypoxia with acclimatization.¹²⁴

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The overall prevalence of hypertension which was 9.1% obtained from this study using similar definition as SBP and/ DBP ≥ 95^th percentile for age, sex and height is higher than that reported by Sorof et al ⁷⁸ and McNiece et al ⁸⁰ from USA, Thakor et al ⁷⁹ and Taksande et al ⁸² from India and Subhi⁸³ from Iraq, who got 4.7%⁷⁸, 3.2%⁸⁰, 2.3%⁷⁹, 5.75%⁸² and 1.7%⁸³ respectively.

Conversely, the prevalence of hypertension from this study is lower than that reported by Urrutia-Rojas et al, ⁷⁵ Mahyar et al, ⁸¹Moura et al ⁸⁴ and Jafar et al ⁸⁸ who got 20.6%⁷⁵, 12.8%⁸¹ , 9.4%⁸⁴, and 12.2%⁸⁸ from USA, Iran, Brazil and Pakistan respectively.

The differences in prevalence rates between this study and those from the other parts of the world may be attributable to differences in the age distribution of the various populations, as some of the authors have included subjects older than the subjects in the present study. 75, 78, 79-84, 88 For example, Urrutia-Rojas et al, ⁷⁵ Moura et al ⁸⁴ andJafar et al ⁸⁸ from the USA, Brazil and Pakistan, studied children that were 8 to 13, 7 to 17, and 5 to 14 years respectively.

The higher prevalence of obesity in some of the other populations may also be another reason, as studies have shown the prevalence of hypertension to increase progressively with increasing BMI.³⁸ For example Urrutia-Rojas et al⁷⁵ reported a prevalence rate of obesity in their study population to be as high as 31.9%. This study has similarly reported significantly higher mean SBP in overweight/obese subjects in comparison to subjects with normal BMI, and further corroborates previous reports that excess fat mass is associated with elevated SBP, regardless of age. Also, the degree of elevation in blood pressure with weight gain in children is similar to that in adults and is said to likely be a function of an increased heart rate and cardiac output rather than a rise in systemic vascular resistance.¹²⁵ The risk of developing hypertension was also found to be higher in overweight or obese subjects (OR = 2.304, 95% CI = 1.675 – 3.169). This is

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similar to previous report by Stray-Pederson et al, ¹⁰⁴ who found obesity to be strongly associated with hypertension in the groups of adolescents studied from Argentina and Norway.

Differences in distinct reference criteria, may also contribute to the differences in the prevalence rates,⁸⁴ hence this underscores the need to adopt standardized criteria for BP measurement so that results could be comparable, no matter what country or place the study was conducted.

There was a progressive increase in BP with increasing age, from 94.5 mm Hg at 6 years to 101.0 mm Hg at 12 years for SBP and from 61.5 mm Hg at 6 years to 65.3 mm Hg at 12 years for DBP. This finding of increasing BP with age has been documented in various other studies. ^7,

10-13, 17, 19-25. The increase in BP with age could be attributable to the corresponding increase in weight and height with age, since body size is a strong determinant of BP.^{3, 38} The rate of increase in the present study which was 1.08 mm Hg/year and 0.64 mm Hg/year for SBP and DBP respectively is comparable with the rate of 1 mm Hg/year and 0.5-1 mm Hg/year for SBP and DBP respectively as obtained by de Swiet et al in children from Kent England in the Brompton study¹¹ but was however lower than that reported by Taksande et al⁸² who reported an increase of 2 mm Hg/year for SBP and 1 mm Hg/year for DBP in Indian children of similar age group.

When compared to a similar study by Obidike ⁴⁷ from South Eastern part of Nigeria, this study reported a lower value for both the mean SBP and DBP for similar age groups. The lower mean DPB in the study subjects compared to that reported by Obidike⁴⁷ could be attributable to differences in methodology such as the use of the 4^th Korotkoff for DBP in that study. The reason for the lower SBP may also be attributable to differences in methodology, as the present

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study used an average of 3 readings on each occasion while Obidike ⁴⁷ used an average of 2 readings.

Both mean SBP and DBP for the different ages from this study were significantly higher than that reported by Antia-Obong et al ⁴¹ for children from Oyo state Nigeria and Wang et al ¹²⁶ in Chinese children of similar age groups. These differences may be attributable to the fact that the subjects in this study were taller and heavier than the subjects in those studies.

These variations in blood pressure levels observed between the study population and other populations was not an isolated finding, as other authors have previously reported variations in blood pressure levels amongst different populations of children. 79, 81, 127 This they attributed to differences in the ages of the populations, and also racial, geographical, dietary, cultural and lifestyle variations which may come into play in various populations and act in concert with body size to influence blood pressure. Further evaluation of these factors is outside the scope of this study.

Differences in methodology may also account for the inter-population variations, such as use of 4^th versus 5^th Korotkoff for DBP since it is well known that the 4^th Korotkoff sound is higher than the 5^th by at least 10 mm Hg. ³⁷ The number of readings per visit is also important as studies have shown 3 readings per visit to give a better accuracy, ³⁷ as BP levels tend to fall on subsequent measurement as a result of an accommodation effect and regression to the mean. ^{37, 38} Another reason may be the degree of accuracy in reporting the SBP and DBP, which has been shown to vary among researchers. ³⁷

The 50^th percentile DBP values obtained in this study were significantly higher than the normatic reference values established in American children of similar age from the NHBPEP charts.³⁸

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Similarly the 90^th percentile SBP value for the 12 year old children in this study which was 113 mm Hg and 112 mm Hg for males and females respectively is lower than the 120 mm Hg obtained by Taksande et al⁸² in Indian children of similar age. Also, the 90^th percentile DBP obtained in this study for the 12 year old children which was 76 mm Hg for both males and females, was lower than that the 80 mm Hg obtained by Taksande et al⁸² in Indian children of similar age. The reason for these differences was not apparent when the heavier and taller 12 year old children in this study had lower 90^th percentile values in comparison to the lighter and shorter 12 year old children from the study by Taksande et al.⁸² However, some possible explanation to this findings may be as a result of differences in the impact of maturational factors on BP, where there are both inter and intra population variability.³⁶ It has been shown that the ages at which pubertal growth spurts occur when maximum effects on BP levels are recorded vary from one population to another.^{36, 126} Such inter-population differences may emphasize the need for the development of percentile charts for individual populations. This will help in the identification of children with blood pressure levels at or above the pre-hypertensive range for proper monitoring and intervention.

In this study, significantly higher mean SBP in girls was demonstrated in ages 8- <9 and 11- <12 respectively. Other studies have also previously reported gender differences in blood pressure levels of their subjects, for example Obidike, ¹⁹ Bugaje et al, ²¹ Sebanjo and Oshikoya²⁵ found significantly higher DBP level for girls in the age groups studied. Leccaio et al, ¹⁰⁷ from Italy however, reported significantly higher SBP in males. Mahya et al⁸¹ found significant differences in mean DBP levels in age groups 7, 8, and 11 year old children from Iran. Conversely, some authors like Eferakeya, ⁷ Ejike et al, ²² Antia-Obong et al, ⁴¹ Hamidu et al, ⁴⁶Agyemang et al, ¹⁵

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Ngandu et al ¹⁰³ and others, 42, 49, 106 have reported no gender differences in blood pressures of the children they studied.

Weight and height differences could not account for the gender differences in mean SBP in age group 8 - <9 years as there was no significant gender difference in their anthropometry. In the age group 11 - <12 years however, the females were significantly taller, heavier and they had significantly higher BMI than their male counterpart and this may account for the significant difference in mean SBP for this group.

The significant rise noticed in mean SBP for females between 10 - <11 years and 11 - <12 years, corresponded to a significant increase in weight between the two age groups. It is similar to the findings of Akor et al, ²⁴ as this may be due to earlier onset of puberty in females which might also be accompanied by rapid physical growth, increase in body mass, hormonal changes and concomitant rise in BP. ^{24, 79}

The relationship between BP and body size has been a subject of various studies and reports ^{9, 38,}

127 andhas further been corroborated by the significant positive correlation between both SBP and DBP with weight, height, BMI and age. In comparison to this study, Akor et al ²⁴ from Jos, Nigeria, also found a significant positive correlation between both SBP and DBP with age(r = 1.22, 0.60), weight (r = 0.74, 0.66) and height (r = 0.26, 0.30). The correlations between both SBP and DBP with age and weight from the study by Akor et al²⁴ were however stronger than the correlations between both SBP and DBP with age and weight from this study. The significant albeit low correlations between both SBP and DBP with height from the study by Akor et al were comparable with the low values of correlation between both SBP and DBP with height as obtained from this study. Obidike ⁴⁸ also found a significant positive correlation between SBP

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with weight and height in both genders (r = 0.3205, p < 0.05; r = 0.2585, p < 0.05 for boys and r

= 0.4249, p < 0.05; r = 0.3972, p < 0.05 for girls respectively). He also found a significant positive correlation between DBP with weight and height in both genders (r =0.1785, p < 0.05; r

= 0.1504, p <0.05 for boys and r = 0.1656, p < 0.05; r = 0.1667, p < 0.05 for girls respectively).

The low albeit significant positive correlation between both SBP and DBP with weight and height from the study by Obidike⁴⁸ is similar to that obtained in children of similar age group from the present study. Antia-Obong et al ⁴¹ also documented significant positive correlation between SBP and DBP with height and weight. The correlation between BMI with SBP and DBP from that study was however, poor.⁴¹ These findings show that anthropometry has varying effect on the blood pressure levels of children from different populations.

Multiple linear regressions of variables that significantly correlated with BP in this study further showed that age was the independent predictor of SBP while the independent predictors of DBP were age, height and BMI. Bugaje et al ²¹ from Nigeria found weight and pulse rate to be the predictors of SBP and DBP, while Agyemang et al ¹⁵ from Ghana found BMI and locality to be the independent predictors of both systolic and diastolic BP. Wang et al ¹²⁶ from China found weight to be the independent predictor of diastolic and systolic BP in the populations studied.

These findings further buttress the fact that different factors play some role to varying degrees to determine the blood pressures of different populations. This may show the need for various populations to develop their normograms based on locality, race, environment etc amongst other factors like anthropometry. ^{4, 89} It is therefore important to take such factors into consideration and control for them where possible.

The findings of age as being the predictor of SBP, and age, height, and BMI as being the predictors of DBP and also the significant association between SBP and gender, support the basis

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of taking body size, age and gender into strong consideration in developing BP reference values for various populations.^{38, 127} This is to avoid misclassifying children who are very short or very tall.^{38, 127}

The non-significant relation of BP to parental socio-economic class (SEC) in this study is similar to the findings of Eferakeya ⁷ and Balogun et al ⁴³ in Nigerian children from Benin and Ile-Ife respectively and contrasts with the findings of Longo et al ¹¹² from Kinshasa and Akingkugbe et al ⁶, Ogunkunle et al ⁴⁹ and Ansa et al ¹¹³from the Southern parts of Nigeria who reported children and adolescents from lower SEC to have higher BP. Akor et al ²⁴ from Jos however reported significantly higher BP in 6-12 year old children from private schools who were mainly from upper and middle SEC. This was attributed to variations in environment, lifestyle and diet.

The findings of no significant relationship between BP and SEC in this study could be that factors peculiar to a particular social class level may not have had sufficient time to exert a significant effect on BP in the age group of pupils studied.⁹⁵ For example, Akinkugbe et al, ⁶ and Ansa et al ¹¹³ studied adolescents, who are likely to have been exposed to the socio-economic environment in which they were, for a longer period of time by virtue of their age, for it to have an effect on their BP.

The relationship between family history of hypertension and CVD risk factors in children like high blood pressure amongst others, have been investigated by different authors. 8, 98, 110, 128, 129

This study found no significant association between BP of the subjects with family history of hypertension, and children with positive family history of hypertension were not at higher risk of developing hypertension. This is similar to that reported by Ogunkunle et al ⁴⁹ from Ibadan Nigeria, and Fesharak Nia et al ¹²⁸ from Iran. It however contrasts with the findings of

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Soudarssanane et al, ⁹⁸ Verma et al¹²⁹ and Kuschnir et al¹¹⁰ from India and Brazil respectively who found a strong association between family history of hypertension and BP of the subjects.

Inaccuracies associated with self-reported family history and the fact that some risk factors associated with family history which may not be fully apparent in the age group of subjects studied ²⁸ may explain the non-significant association between BP of subjects and family history of hypertension in the present study.

The lack of association of place of residence and the BP of the subjects in this study may mean that place of residence may not have a strong influence on the BP levels in the group of children studied. This is however not the case for the group of 8 to 16 year old Ghanaian children studied by Agyemang et al¹⁵ from Ghana who reported place of abode to be one of the predictors of their subjects’ blood pressure levels.

The prevalence rate of 9.1% for hypertension from this study shows that hypertension is not an uncommon finding in children. Since studies have shown that hypertension may start in childhood, epidemiological surveys for childhood hypertension, its risk factors and determinants should be encouraged, as childhood blood pressure level is a strong predictor of adult blood pressure level and helps in planning primordial preventive strategies.^{27, 37}

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