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Blood Pressure

Blood Pressure is the force exerted by blood on the walls of blood vessels. Blood vessels are a network of pipes inside the body that transports blood throughout the human body. When the heart contracts or beats, it pumps blood. The resulting pressure of the blood against the blood vessel wall is called Systolic. When the heart is relaxed and rests between beats, the pressure is called Diastolic [1]. Together, Systolic and Diastolic Pressures constitute Blood Pressure and is represented in "mm Hg" units with Systolic shown first followed by Diastolic. For example, if the Systolic blood pressure is 118 mm Hg and Diastolic blood pressure is 70 mm Hg, the Blood Pressure is shown as 118/70 mm Hg.

See the TED video below to learn more about how blood pressure works.

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High Blood Pressure (Hypertension)

Blood pressure normally rises and falls throughout the day, but it can damage your heart and cause health problems if it stays high for a long time [3]. The classification of a patient being hypertensive depends on guidelines and the doctor (see below section on classification), but typically goals are set for a systolic blood pressure of less than 140 mmHg (130mmHg for patients who are diabetic or have kidney disease) and a diastolic blood pressure of less than 90 mmHg [4, 7, 10].

Hypertension is a major contributor of risk for Cardiovascular diseases. 54% of stroke and 47% of ischemic heart diseases are attributable to hypertension [7]. In some age groups, the risk of cardiovascular disease doubles for each increment of 20/10 mmHg of blood pressure. In addition to coronary heart diseases and stroke, complications of raised blood pressure include heart failure, peripheral vascular disease, renal impairment, retinal hemorrhage and visual impairment. Widening of pulse pressure (difference between systolic and diastolic pressure) is an indicator of cardiovascular risk - atherosclerosis (plaques build up of fatty material on the inner walls of arteries) and arteriosclerosis (thickening and hardening of walls of arteries). Treating blood pressure is associated with a reduction in cardiovascular complications [6].

Symptoms of High Blood Pressure

Worldwide, raised blood pressure is estimated to cause 7.5 million deaths, about 12.8% of the total of all deaths [6]. 1 in 2 US adults have Hypertension (some reports suggest 1 in 3 US adults but they are based on older classification guidelines) [5, 10]. Hypertension is also known as the "Silent Killer" as many people who have high blood pressure don’t even know that they have it as there are no obvious symptoms [2, 12].  Symptoms of high blood pressure may not show until significant damage is already done. Therefore, it is very important to regularly monitor blood pressure during health checkups or at home. Only about 1 in 4 US adults (24%) with hypertension have their condition under control [3, 10]. Some signs of high blood pressure may include headaches, shortness of breath and nosebleeds. But the stage when these signs of high blood pressure start showing may be severe or life threatening [21].

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What is normal blood pressure?

Depending on the country or region, guidelines have been established for blood pressure ranges to classify individuals for hypertension. Two of the commonly used guidelines are:

1. 2017 ACC/AHA (American College of Cardiology, American Heart Association) [14]
2. 2018 ESC/ESH (European Society of Cardiology, European Society of Hypertension) [15]

Classifications are mainly intended as guidelines and not a mandate. Therefore, limits for classification have to be set based on discussing with a doctor who better understands the individual's medical condition.

2017 ACC/AHA for United States

2018 ESC/ESH for Europe

Causes of High Blood Pressure

The 3 main mechanisms

Excess Sodium: Over the past 100 years, daily salt consumption in developed countries has significantly increased to a magnitude of 10-12g per day which overwhelms the capacity of the kidney to remove the excess sodium from the body. The build up of excess sodium triggers several auto-regulatory responses from the body that leads to increase in blood pressure. Most of the excess sodium in diet does not come from adding salt to food but from processed foods [7]. Excess sodium contributes to hypertension in almost half or more of patients with hypertension [4].

Neurohormonal: The Renin-Angiotensin System (RAS) helps ensure that blood pressure does not fall too low. When blood pressure falls low, the kidneys sense it and help bring back blood pressure by secreting the hormone renin. If the RAS system is stimulated when blood pressure is normal, it can lead to high blood pressure [4, 7]. In addition, the release of the hormone adrenaline due to a "fight or flight" situation will lead to increase in blood pressure. Physical or emotional stimuli can both cause release of hormones that signal the body to increase blood pressure [4, 7]. Emotional and physical stress can over activate neural systems that increase blood pressure [7].

‍Vascular conditions: Alterations in the structure and functions of arteries can lead to hypertension [7].

Other factors that are associated with Hypertension

Age: The chance of hypertension increases with age [7, 13]. Typically, after the age of 50, the systolic blood pressure continues to rise with age while the diastolic pressure reduces which indicates aortic stiffness [7]. Framingham Heart Study investigators indicate that hypertension can vary by age where systolic hypertension is seen in young adults (age 17 to 25 years), diastolic hypertension is seen in middle aged (age 30 to 50 years) and isolated systolic hypertension in older adults (55 years or older) [7].

Racial Disparity: Within the United States, hypertension is more prevalent in African Americans (40%) compared to other races, including Hispanics (28%) even with the high incidence of obesity and type-2 diabetes amongst Hispanics [3, 7]. Amongst US African Americans, hypertension is not only more prevalent but also starts at a younger age compared to other races. However, it is not certain that the high rate of hypertension amongst US African Americans is due to genes or socioeconomic disadvantages. Also, hypertension is more prevalent in several predominantly white European countries than US African Americans and is relatively less common in some African countries that have predominantly black population [7].

Gender, Income and Geographic Disparity: Hypertension is more prevalent in men than women. In 2015, 1 in 4 men and 1 in 5 women had hypertension worldwide [1]. In addition, the prevalence of hypertension was highest in Africa, where it was 46% for both sexes combined. The lowest prevalence of raised blood pressure was in the Americas at 35% for both sexes [6, 8]. Across the income groups of countries, the prevalence of raised blood pressure was consistently high, with low, lower middle and upper middle countries all having rates of around 40%. The prevalence in high income countries was lower, at 35% [6]. Overall, 80% of hypertension burden occurs in low and middle income economies [7].

‍Tobacco: A leading cause of preventable death in the United States and globally, it was estimated that tobacco use accounted for 7.1 million deaths worldwide in 2016 [5]. Each cigarette raises blood pressure by 7/4 mm Hg on average but twice as much on some patients. Cigars and smokeless tobacco also raises blood pressure but nicotine replacement therapy has shown not to raise blood pressure [7]. Types of nicotine replacement therapy include nicotine patches, gum, lozenge, inhaler, nasal spray and prescription medicine [11].

Obesity: Weight gain increases the incidence of hypertension. An average rise of systolic blood pressure of 4.5 mm Hg is seen for every 10 lb increase in weight. There is a positive correlation in average BMI vs. percent hypertension across populations [7]. Physical activity has shown to reduce stress and obesity which can help reduce incidence of hypertension. According to NHANES (National Health and Nutrition Examination Survey) in 2015-16, 39.6% of US adults and 18.5% of youths were obese, and 7.7% of adults and 5.6% of youth had severe obesity.

Diabetes: Hypertension and Diabetes frequently coexist [7].

High Cholesterol: There is some evidence that individuals with high cholesterol also develop hypertension.

Birth Control Pills: Can elevate blood pressure, sometimes severely through overstimulation of the RAS system [4].

Family History: Hypertension runs in families. Large studies of adopted and biological siblings showed that 60% of familial association of hypertension is caused by shared genes and 40% by shared environment [7].

Caffeine: Coffee can acutely raise blood pressure from 3/4 to 15/13 mm Hg [7].

High Uric Acid: Consuming food with more meat, fructose and high calories [7].

Alcohol: The relation of blood pressure to alcohol intake is shown as a "J" shape relation where teetotalers have slightly higher blood pressure compared to moderate drinkers (1 to 2 drinks a day) but progressively increases for alcohol intake above moderate to heavy binge drinking [7].

Other Environmental factors: Low temperature, high altitude, vitamin D deficiency (lack of sunlight), exposure to lead, air pollution and dietary deficiency (Potassium, Magnesium, Calcium, Phosphorous and Citrate) are all factors that shave shown rise in blood pressure [7].

Risks of Hypertension

Over a period of time, high blood pressure can result in serious health conditions due to damage to arteries, heart and kidneys which may even result in death. The damage done by blood pressure over period of time can result in the following medical conditions [16].

Stroke: High blood pressure can damage blood vessels that can either rupture or form clots. A stroke can occur when the the blood vessel to the brain is clogged due to the clot (ischemic stroke) or bursts rupture blood vessel near the brain (hemorrhagic stroke). When a stroke occurs, part of the brain is no longer getting the blood and oxygen it needs due to the clogged blockage, which could lead to the part of the brain dying, vegetative state, permanent disability or even death.

Heart Failure: High blood pressure over a period of time leads to narrowing of arteries. Narrow arteries are less elastic which makes it more difficult for the blood to travel smoothly throughout the body. This causes the heart to work harder. In order to meet the increased demand, the heart enlarges and becomes less efficient at pumping blood and it is unable to deliver blood, that carries oxygen and vital nutrients, to the rest of the body.

Heart Attack: Hypertension can damage blood vessels that supply blood to the heart. Narrowing of these blood vessels (coronary arteries) due to build up of fat, cholesterol and other substances, can cause blockage of blood supply to the heart which leads to a heart attack.

Vision Loss: Hypertension can cause damage to blood vessels which can lead to reduced or lack of blood flow to the retina (retinopathy), fluid build up under the retina (choroidopathy) and optic nerve damage (optic neuropathy). All these conditions can result in temporary and permanent vision loss.

Kidney Disease or Failure: Kidneys help filter waste and other fluids from the blood. To perform its function of filtering blood, kidneys themselves need high volume of blood to perform its task. High blood pressure over period of time can damage the blood vessels that deliver blood to the kidneys. The blood vessel damage results in poor blood supply which impairs the function of the kidney as it needs the oxygen, nutrients and other biochemicals, found in the supplied blood, to perform. Damaged kidneys can also fail to regulate aldosterone, a hormone which is important in regulating blood pressure in the mechanism that manages excess sodium.

Sexual Dysfunction: Insufficient blood supply due to damaged blood vessels caused by high blood pressure can result in erectile dysfunction and loss of libido or interest due to fatigue.

Low Blood Pressure (Hypotension)

According to Mayo Clinic, for some people, low blood pressure does not cause problems. However, for many people, abnormally low blood pressure (Hypotension) where a blood pressure of 90 (systolic)/60 (diastolic) mmHg or lower can cause life-threatening conditions, especially if there is a sudden drop of blood pressure of 20mmHg or more. Low blood pressure symptoms include dizziness and fainting. Conditions that cause Hypotension include pregnancy, heart problems, endocrine problems, dehydration, blood loss, severe infection, severe allergic reaction and lack of nutrients in diet [17].

What causes low blood pressure?

Blood pressure medications (Diuretics. Alpha-blockers, Beta-blockers), drugs for erectile dysfunction when taken with heart medications, drugs for antidepressants and Parkinson's disease can all lead to low blood pressure conditions [17]. Drop in blood pressure when standing from a sitting or lying down position (orthostatic hypotension) or after eating (postprandial hypotension) occurs primarily in adults older than 65. Neurally mediated hypotension, where there is signal miscommunication between the heart and brain, primarily affects children and younger adults [17].

Monitoring Blood Pressure

Measurement error leads to over estimation of blood pressure which leads to over treatment. On one hand over using medication or dosage is not a good idea as these drugs can cause side effects and unnecessarily increase the cost burden [4] and on the other hand, the accuracy of the monitor is also important to ensure that false low results do not mislead patients into believing their blood pressure is normal. In addition to the dangers of incorrect results from blood pressure monitors that are not clinically proven, lately patients are misled by apps that claim to measure blood pressure using a phone camera. There is no app that is approved by regulatory agencies such as FDA, EU MDR, etc. that has clinically proven to measure blood pressure using a phone camera. There has been some research on pulse wave transit time (PTT) where blood pressure changes are detected after a calibration procedure with a regular oscillometric blood pressure monitor. The time between the ECG and pulse wave is used to model and correlate to determine the blood pressure, but the technology comes with disadvantages of needing additional ECG sensors, frequent calibration to a reference blood pressure sphygmomanometer, noisy signal and low accuracy which leads to inconsistent correlation between PTT and blood pressure [20]. Although there aren't any successful clinically proven products in the market due to the disadvantages discussed, with new sensors such as ECG and pulse detection embedded in wearables, like Apple Watch, in the future there could be a wearable that can accurately detect blood pressure without an inflatable blood pressure cuff.

A typical system used in both the clinic and home to measure blood pressure is a noninvasive indirect method, where an inflatable blood pressure cuff fully occludes a blood vessel in the upper arm, which is typically a pressure of few mmHg higher than the systolic pressure. When the systolic pressure exerts a pressure higher than the occlusive pressure from the blood pressure cuff, blood spurts and flows out of the blood vessel and creates a sound (Korotkoff sound). The pressure when the first sound is heard is the systolic pressure. As the pressure in the blood pressure cuff decreases, the period of muffling to silence brackets the diastolic pressure [19]. In the hospital, a clinician is trained to hear these sounds through the stethoscope and record the blood pressure [18, 19]. For home blood pressure monitors, the sound oscillometric vibrations are recorded through digital sensors. A microprocessor regulates an air pump that inflates the blood pressure cuff and processes the signal from the sensors to calculate the systolic, diastolic and pulse automatically. The measurements are displayed on the screen of the blood pressure monitor or sent wirelessly to a mobile device app to display the measurements.

Home Monitoring

In a clinic or hospital, many people have shown elevated blood pressure than if the measurement was taken elsewhere. This phenomenon is also known as "White Coat Hypertension" which may or may not be due to anxiety and experience with the doctor [4]. White coat hypertension may lead to overestimation of blood pressure which further leads to unnecessary over medication. Another phenomenon called "Masked Hypertension" may show an individual's blood pressure as normal in the clinic but may actually be high [4]. Therefore, patients are asked by their doctors to also monitor their blood pressure at home.

As mentioned above, it is very important to use a reliable, accurate blood pressure monitor that is clinically validated and certified by the FDA, EU MDR, AAMI, British Hypertension Society or European Hypertension Society. The dabl education trust provides independent evaluations of accuracy of blood pressure monitors from a number of manufacturers for upper arm and wrist. However, note that studies have consistently show that wrist and finger blood pressure monitors are not as accurate as upper arm blood pressure monitors. It is highly recommended to refer the dabl recommended list tables to determine if your blood pressure monitor is a reliable model [4]. Another great resource is American Medical Association's (AMA) US Blood Pressure Validated Device Listing website [22]. In some cases, while the brand name is reliable, accuracy of some models from the "reliable brands" are questionable. One simple test that can be done is take your blood pressure monitor to the clinic and check if both the clinic's blood pressure monitor and your device are giving the same results. Of course, this assumes that the clinic blood pressure monitor is accurate, which may or may not be true.

Measuring blood pressure correctly

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Other important factors of measuring blood pressure at home

Blood Pressure Cuff Size: Choose a blood pressure cuff size that is right for you. If you have a large arm, use a large cuff [4].

Measurement Location: Check your blood pressure in one arm and not both. Narrowing of arteries can cause blood pressure to be different between arms and may indicate atherosclerosis but this test is typically done in the clinic or hospital by your doctor and you need not do this at home as the measurements maybe off because of the hassle of changing the blood pressure cuffs to different arms. Again, it is recommended to measure blood pressure on upper arm and not wrist or finger [4].

Settling Time: After putting on the blood pressure cuff, sit for a few minutes and settle down before measuring blood pressure [4].

Number of Measurements: Take 3 measurements, one or two minutes apart and either take the average of second and third measurement because the first may be higher than your actual blood pressure [4] or the average of all three measurements. Discuss with your doctor on what is the number of measurements you need to take and which ones need to be averaged.

Measurement Time during AM/PM: Discuss with your doctor on when should you take your measurements. Blood pressure is changing throughout the day.

Blood Pressure Medications

It is very important to find the right medication and dosage to treat hypertension. Patients may or may not be taking their medications regularly or may not be on the right medication as different people need different medications, doses and combinations. On average, for a population, every drug lowers blood pressure but at the individual level, certain drugs lower blood pressure much more than others. Therefore, it is important to first understand the underlying cause for hypertension and which mechanism should the drug target to control blood pressure.

Medications for hypertension are mainly prescribed based on whether the excess sodium, neurohormonal or vascular mechanisms need to be targeted. For more information, I highly recommend the book by Dr. Samuel J. Mann - Hypertension and You - Old Drugs, New Drugs and The Right Drugs for your High Blood Pressure. It's a great and easy read with useful information on types of drugs. The book serves as a guide for patients to work with their doctors to find the right medication.

Sodium Volume

‍If there is reduced kidney function to remove excess sodium or the arteries fail to relax, due to the excess sodium and volume blood pressure increases. Individuals with "volume mediated hypertension" are usually treated with Diuretics or Calcium Channel Blocker (CCB) [4].

The 3 main types of Diuretics are:

• Thiazide Diuretics
• Loop Diuretics
• Potassium sparing Diuretics

The 2 main types of CCBs are:

• Dihydropyridine
• Nondihydropyridine

Common side effects of CCBs [4]:

• Edema (fluid retention in legs)
• Constipation
• Frequent urination in the night

Renin-Angiotensin System (RAS)

The RAS hormonal system helps keep the body's blood pressure from falling too low [4,7]. The four main categories of drugs that can block the RAS system from being overstimulated are:

• Angiotensin converting enzyme inhibitors (ACEI)
• Angiotensin receptor blockers (ARB)
• Direct renin inhibitor (DRI)
• Beta Adrenergic Receptor Blocker (beta blocker)

Common side effects of ACEI [4]:

• Cough
• Swelling of face, mouth, throat and elsewhere
• Frequent urination in the night

Although well tolerated, both ACEI and ARB could excessively lower blood pressure in the first dose (particularly in patients who are also taking a diuretic) [4].

Sympathetic Nervous System (SNS)

The SNS monitors our blood pressure and sends signals to increase or decrease blood pressure when needed. Overactivity when not needed can result in high blood pressure. This may also include emotion and stress. Drugs most widely used for addressing SNS mediated hypertension are:

• Beta Adrenergic Receptor Blocker (beta blocker)
• Alpha Adrenergic Receptor Blocker (alpha blocker)
• Central Alpha-Agonists

Common side effects [4]:

Beta-blockers:

• Fatigue
• Mental, emotional dullness, depression
• Asthma
• Weight gain
• Increased chance of diabetes
• Erectile dysfunction
• Hair loss
• Cold extremities
• Withdrawal syndrome from beta-blockers

Alpha-blockers:

• Sharp drop in blood pressure
• Edema (fluid retention in legs)

Central Alpha-Agonists:

• Fatigue
• Sexual dysfunction
• Dry mouth
• Withdrawal syndrome

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References

[1] World Health Organization (WHO) - Hypertension

[2] American Heart Association (AHA) Facts about Blood Pressure

[3] Center for Disease Control (CDC) Facts about Hypertension

[4] "Hypertension and You" - Samuel J Mann

[5] Heart Disease and Stroke Statistics—2019 Update: A Report From the American Heart Association

[6] WHO Global Health Observatory Data

[7] "Clinical Hypertension" - Norman M. Kaplan, Ronald G. Victor

[8] Worldwide trends in blood pressure from 1975 to 2015: a pooled analysis of 1479 population-based measurement studies with 19·1 million participants, Zhou, Bin et al. The Lancet, Volume 389, Issue 10064, 37 - 55 NCD Risk Factor Collaboration

[9] CDC : National Center for Health Statistics - Hypertension

[10] Hypertension Cascade: Hypertension Prevalence, Treatment and Control Estimates Among US Adults Aged 18 Years and Older Applying the Criteria From the American College of Cardiology and American Heart Association’s 2017 Hypertension Guideline

[11] Mayo Clinic - Quit Smoking Products

[12] AHA - High Blood Pressure Symptoms

[13] National Institute of Aging - High Blood Pressure

[14] 2017 ACC/AHA Guideline for the Prevention,Detection, Evaluation, and Management of High Blood Pressure in Adults

[15] 2018 ESC/ESH Guidelines for the management of arterial hypertension: The Task Force for the management of arterial hypertension of the European Society of Cardiology (ESC) and the European Society of Hypertension (ESH), European Heart Journal, Volume 39, Issue 33, 01 September 2018, Pages 3021–3104

[16] American Heart Association (AHA) - Health Threats from High Blood Pressure

[17] Mayo Clinic - Hypotension

[18] Sphygmomanometer - How to use

[19] Medical Instrumentation - Application and Design, John G. Webster

[20] M. Forouzanfar, H. R. Dajani, V. Z. Groza, M. Bolic, S. Rajan and I. Batkin, "Oscillometric Blood Pressure Estimation: Past, Present, and Future," in IEEE Reviews in Biomedical Engineering, vol. 8, pp. 44-63, 2015, doi: 10.1109/RBME.2015.2434215.

[21] High Blood Pressure - Mayo Clinic

[22] American Medical Association's (AMA) US Blood Pressure Validated Device Listing