Chronic hypertension blood pressure measurement

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Assistant Editor-In-Chief: Taylor Palmieri

Overview

In daily practice, the frequently adopted technique for BP measurement is the sphygmomanometer. Devices can be electronic, commonly used for better home BP measurement, aneroid, or mercury, with the latter being the gold standard. Hypertension (HTN) is generally defined as an elevated systolic blood pressure (SBP) ≥ 140 mmHg and/or diastolic blood pressure (DBP) ≥ 90 mmHg at each of two or more visits.(Ref: 16512265). However, target BP values are set at a lower threshold in specific populations, such as diabetics and subjects with significant proteinuria.

Blood Pressure Measurement

1- Sphygmomanometer

• BP measurement using the sphygmomanometer yields two values that assess the pressure exerted by the blood on the walls of the arteries at two points in time:
  • Systole: The maximum exerted pressure during a ventricular contraction and during expulsion of blood from the heart chambers into the aorta and corresponding arteries. The corresponding value measured by the sphygmomanometer is the SBP.
  • Diastole: The minimum exerted pressure directly before the next heartbeat. The corresponding value measured by the sphygmomanometer is the DBP.

Conventionally, BP is frequently denoted as systolic and diastolic pressures and expressed in mmHg. Another way to denote BP is using the mean BP, calculated by: [(SBP + 2DBP)/3].

• Nonetheless, blood pressure is a continuously fluctuating hemodynamic parameter with various factors leading to such fluctuations other than the cardiac cycle. Those include the respiration, the baroreceptor loop, hormones, in addition to others. Therefore, experts do not rely solely on static BP parameters but also on dynamic ones, such as pulse pressure, defined as the pressure difference in systolic and diastolic BP, in the evaluation of BP curve.
• Hence, accurate, precise, and reproducible measurements are pre-requisites for the evaluation of blood pressure. The level of blood pressure plays a major role in the diagnostic, therapeutic, and prognostic decision-making processes of various disease states (See: Blood pressure measurement).

Blood Pressure Measurement Technique

According to “Practice Guidelines of the European Society of Hypertension for Clinic, Ambulatory, and Self Blood Pressure Measurement” (Ref: 15775768) and JNC 7 (Ref: 16512265), the optimal procedure to measure blood pressure is the following:

Selecting an Accurate Device

List of devices, protocol for use, and details of validation status can be obtained on www.dableducational.org.

Cuff and Bladder Choice

Cuff bladder must enfold ≥ 80% of the measured arm circumference. Miscuffing is a common error during blood pressure measurement. The cuff and the bladder should be chosen according to the size of the arm circumference, as usually detailed by the device protocol. Commonly, such errors target obese patients where cuff size is too small for arm circumference, leading to a phenomenon called “Cuff Hypertension”. =====Patient Profile=====Special populations require special attention while measuring blood pressure. This includes children, elderly, obese individuals, patients with arrhythmias, and pregnant women. In the latter group, Korotkoff sounds may be heard down to zero mmHg, in which the fourth phase or muffling of sounds should be used to assess diastolic blood pressure. =====Explanation to the Patient=====This attempts to eliminate patient’s fear that might contribute to a phenomenon called “White Coat Effect”, whereby patients’ blood pressure values are elevated only in the clinic setting. Ambulatory BP measurement helps in identifying the white coat effect (WCE) and white coat hypertension (WCHT).

Comfortable Positioning

Patients should relax silently for a few minutes before blood pressure is measured. Individuals should sit with the back supported, legs uncrossed and cuffed arm positioned at heart level. Likewise, the person conducting the measurement should also be seated comfortably to prevent rapid deflation of the cuff that might underestimate and overestimate systolic and diastolic blood pressures, respectively.

Arm Choice

On the first consultation, patient’s blood pressure must be measured in both arms. Consecutive readings showing differences of > 20 mmHg or > 10 mmHg for systolic and diastolic pressures respectively might suggest an underlying arterial disease that should be ruled out, such as subclavian stenosis. Further BP measurements should be conducted in the arm with the highest values at first assessment if the difference between right and left readings was within normal limits. =====Assessment of Postural Hypotension=====Due to increasing prevalence, postural hypotension must be assessed by measuring blood pressure when the patient assumes an erect position (Ref: 18327095). Postural hypotension is defined as a systolic BP drop of ≥ 20 mmHg or diastolic BP decrease of ≥ 10 mmHg when the patient stands from a seated position (Ref: 7726701). The presence of postural hypotension suggests in most of the cases impairment in the baroreceptor (firing of afferent nerves and consequential dysfunction of the initiation of autonomic cardiovascular reflex) (Ref: 2231190). It is most commonly present in diabetics and elderly. According to the Honolulu Heart Program in 1998, it carries a prognostic value with 64% increase in age-adjusted mortality compared to control population (Ref: 9826316). Intensive BP control then might be compromised due to the presence of orthostatic hypotension, making control of hypertension a bigger challenge in such patients(Ref: 16512265).

Common Sources of Error

Technical sources of error include, but are not limited to:

• Misconfigured sphygmomanometer
• Use of low quality or unclean or non-fitting stethoscope
• Inappropriate positioning of the arm
• Inappropriate cuff size for the arm or cuff placed too tight over the arm
• Too rapid deflation of the cuff
• Observer error, digit preference, prejudice, or bias

2- Ambulatory Blood Pressure Measurement (ABPM)

• Usually 24-hour blood pressure measurement that allows repetitive BP measurement at specified intervals.
• Diagnosis of hypertension is based on average SBP ≥ 130 mmHg and/or DBP > 85 mmHg.
• Can identify hidden phenomena like white-coat hypertension (elevated BP only during patient’s visit to clinic) or masked hypertension (normal blood pressure only during patient’s visit to clinic).
• Considered superior to all other techniques in its association with hypertension complications such as target organ damage.
• Most expensive, but still cost-effective.
• Requires interpretation by skilled medical personnel.(Ref: 18362225)

3- Self Blood Pressure Measurement (SBPM)

• Normally, two measurements should be obtained each morning and evening for seven consecutive days. First day measurements are to be eliminated. Remaining 24 blood pressure measurements averaged to obtain mean arterial blood pressure
• Diagnosis of hypertension is done based on average SBP ≥ 135 mmHg and/or DBP > 85 mmHg
• Can identify hidden phenomena like white-coat hypertension or masked hypertension
• Superior only to OBPM in assessing hypertension complications, such as target organ damage
• More expensive than OBPM but less expensive than ABPM(Ref: 18362225)

Medical personnel assistance used to be recommended; however with currently available accurate and validated electronic devices, BP measurement became feasible, easy, and dependent only on patient education.