Elevated blood pressure (BP) over its entire range is known to be a major cause of heart disease in adults with disease and death because of heart disease in them related to a known level of BP. Although high BP (or hypertension) and heart disease often present during adult life the origins of these problems commence during childhood. To reduce the chances of having these health issues later in life, it is important to identify the seeds of high BP and heart disease as early as possible during childhood.
Blood pressure readings have two numbers, the upper number and the lower number and is measured in millimetres of mercury, as ‘mmHg’. The upper number is the systolic blood pressure and is the highest level of pressure that is reached following a heartbeat and helps to move the blood around the body. The lower number is the diastolic blood pressure and is the lowest level of pressure reached when the heart is relaxing between two heart beats. For example a BP value of 110/70 mmHg, denotes systolic BP of 110 and diastolic BP of 70 mmHg. As BP levels change with activity and stress it is important that blood pressure is measured in a specific manner, using the correct BP measurement device and if raised, confirmed on at least three separate occasions. Blood pressure is considered elevated, if either the upper or the lower number is above the BP value decided by the doctor.
Defining raised blood pressure as ‘high’ blood pressure or hypertension during childhood though is arbitrary and based on the normal distribution of BP levels in children and adolescents. Higher BP levels are seen with increasing age and height throughout childhood; generally, boys have higher BP values than girls. This distribution of blood pressure means that the tallest and oldest adolescent boys have the highest BP values amongst all children.
Children and adolescents younger than 16 years are considered to have high blood pressure or hypertension if their BP values are in the upper range of the distribution of BP values (≥ 95th percentile). Blood pressure at this or higher value is considered a risk to health with serious concerns for BP values that are very high.
Blood pressure considered to be just higher than what it should be is called ‘high-normal’ BP and are in the higher range of the distribution of BP values (≥90th to <95th percentile). This does not mean that the risks to health are the same as high blood pressure but that the child could go on to develop hypertension later during childhood or as a young adult. Blood pressure is considered to be ‘normal’ at the lower levels of normal distribution (<90th percentile) and mean that the risks to health are considerably lower (than at higher BP levels) and maintaining BP in this range will improve health.
It remains difficult to decide, when BP levels in a teenager should be considered similar to an adult. This decision would imply that changes that influence BP levels during adolescence in boys and girls become irrelevant. Although this is not known precisely, it is considered that in those aged 16 years or older, levels defining high, high-normal and normal blood pressure should be similar to adults and carry the same risk implications.
Prof. Manish Sinha, Department of Nephrology, Evelina London Children’s Hospital, London, United Kingdom.
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