Ujvala Jupalli '25

An Introduction to Blood Pressure

BY UJVALA JUPALLI '25

Cover Image: Blood pressure should be checked more regularly as the one gets older. It is crucial to maintain a blood pressure of 120/80 mmHg by eating a wellbalanced diet and exercising daily. Image Source: Wikimedia Commons

Overview and Trends of Blood Pressure

Blood pressure is the force of one’s circulating blood against the walls of arteries and veins. Most of this pressure comes from the heart pumping blood through the circulatory system to the rest of the body. Blood pressure, also known as arterial pressure, is determined by the volume of blood ejected by the heart into the arteries, the elasticity of artery walls, and the rate of blood flow out of those arteries (Magder, 2018). There are two different types of blood pressure: systolic pressure and diastolic pressure. Systolic pressure is generated by cardiac contraction and is critical for pumping blood against gravity, up to the brain, and out to the rest of the body through arteries and capillaries. Diastolic pressure is the pressure in the arteries during cardiac relaxation that ensures continuous blood flow while the heart receives oxygen. According to the Center for Disease Control, a healthy and active adult should have a systolic blood pressure of less than 120 mmHg and a diastolic pressure of less than 80 mmHg. High blood pressure is a leading cause of cardiovascular disease, chronic kidney disease, dementia, and more. In 2015, high systolic blood pressure was associated with the death of over 8.5 million people (Zhou et al., 2021). However, problems with blood pressure are not spread out evenly across low and high income regions. High blood pressure is more prevalent in lower- and middle- class countries rather than in highincome regions. This is evidenced by the decline of the mean systolic and diastolic blood pressures among high income regions and the increased mean blood pressure among women and men in East Asia, South Asia, and sub-Saharan Africa (Zhou et al., 2021).

Determinants of Blood Pressure

There are two main determinants of blood pressure. The strength of cardiac contraction determines systolic pressure since the pumping of the heart determines how much blood is in the arteries. Vessel resistance determines diastolic pressure as diastolic pressure depends on the speed of the blood flow back to the heart. This is also why blood pressure increases during physical exertion: the heart pumps stronger and faster to get more oxygen to the organs and muscles that are working. The volume of blood in the vascular space also plays a major role in determining blood pressure since more blood increases pressure (Magder, 2018).

Environmental factors such as ambient temperature and altitude have also been shown to

have an impact on blood pressure. Temperature tends to have an inverse relationship with blood pressure. This means that when temperature decreases, many individuals tend to have a higher blood pressure. The reason for this could be further explained by changes in diet, lower vitamin D levels, and reduced physical activity (Brook et al., 2011). On the other hand, there is a direct relationship between altitude and blood pressure. Increases in blood pressure due to higher altitudes are most likely explained by the lower temperatures and fewer oxygen molecules in the air. With less oxygen available, individuals will have to exert more physical effort to get the same amount of oxygen as in lower altitudes. It is important to note that the amount of time spent in these higher altitudes also plays a role- many individuals will acclimate to higher altitudes over time, and their blood pressures will neutralize to how they were in lower altitudes in a couple weeks (Brook et al., 2011).

How is Blood Pressure Maintained?

Blood pressure is maintained in the human body with the help of the endocrine system, a messenger system composed of glands and hormones. If one’s blood pressure drops due to blood loss or dehydration, their kidneys can sense it in their juxtaglomerular apparatus (JG apparatus). The JG apparatus will then release an enzyme known as renin, which in turn creates a hormone called angiotensin II (Li et al., 2018). This hormone will then cause the arterioles to constrict, therefore narrowing the vascular space and increasing the pressure of blood against the walls of those arteries and veins. Angiotensin II will also cause the adrenal glands to secrete aldosterone, which instructs the kidneys to retain sodium. When this happens, the kidneys will produce less urine, and as a result blood volume will increase and cause blood pressure to go back up (Li et al., 2018). Alternatively, when blood pressure rises, the human body reacts in the opposite way, causing the arterioles to expand and the kidneys to produce more urine. These Another way the human body controls blood pressure is through blood pressure sensors called arterial baroreceptors which are located in the carotid sinus near the carotid artery and the aortic arch (Hirschl & Kundi, 2014). These baroreceptors inform the autonomic nervous system of any changes in the blood pressure by detecting the tension of arterial walls. For instance, if blood pressure suddenly fell after a person stood up, the baroreceptors would sense it and decrease their firing rate. This leads to an increase in sympathetic outflow including hormones like epinephrine (also known as adrenaline) and norepinephrine which accelerate the heart rate, thereby increasing blood pressure. On the other hand, when blood pressure rises, the baroreceptors would increase their firing rate which leads to an increase in parasympathetic activity (Hirschl & Kundi, 2014). This includes the hormone acetylcholine which slows down the heart rate and dilates blood vessels, thereby decreasing blood pressure. A combination of these processes keeps blood pressure stable on a daily basis.

Hypotension

Hypotension, or low blood pressure, occurs when there is an inadequate amount of pressure in the bloodstream for the blood to make it to the brain, organs, and tissues. The blood is not able to maintain the supply of nutrients and oxygen. When low blood pressure prevails, shock can occur causing organ failure and other major problems later on (Biaggioni 2016). There are three major causes of hypotension: loss of blood volume (due to a major hemorrhage or severe dehydration), low cardiac output, and loss of peripheral vessel resistance (commonly due to a bacterial infection called sepsis). A major hemorrhage occurs when there is a rupture in a blood vessel that causes blood to be released inside or outside the body. Similarly, dehydration leads to a decreased amount of fluid circulating in one’s blood vessels. Low cardiac output results when the heart cannot pump enough blood to other organs in the body. This leads not only to low blood pressure, but also to other issues including lightheadedness, low urine output, and fatigue since the heart isn’t pumping enough oxygen to the brain and other organs. Lastly, when peripheral resistance is lost, arteries dilate and blood flows at a faster rate. This leads to organ malfunction and even shock.

Image 1: Systolic pressure is determined by the heart’s ability to pump out blood to other organs and diastolic pressure makes sure that there is still blood flow while the heart is refilled with oxygen. Image Source: Wikimedia Commons

"There are three major causes of hypotension: los of blood volume...,low cardiac output, and loss of peripheral vessel resistance..."

Image 2: Foods like fries and hamburgers contain high levels of sodium and fat. Consistently eating high sodium foods can increase blood pressure and lead to heart complications. Source: Wikimedia Commons

"High blood pressure... puts the indiviudal at a higher risk for a heart attack, stroke, or heart disease."

Hypertension

Hypertension occurs when blood pressure exceeds the 140/90 systolic to diastolic range and is classified as extreme when it exceeds 180/120. When an individual has high blood pressure, their heart must work harder to pump blood to organs and muscles. This has a negative effect on the heart and can cause the left ventricle to thicken, which puts the individual at a higher risk for a heart attack, stroke, or heart disease. Hypertension can also damage arteries by decreasing their elasticity which affects the flow of oxygen and blood to the heart as well as the other organs. Hypertension can be caused by various reasons. A diet that contains high levels of fat, sodium, or cholesterol and a lack of physical activity can lead to obesity and cause blood pressure to increase. Genes and family history also have a role in one’s blood pressure, but genes alone do not cause hypertension. Furthermore, high stress levels are known to play a role in increasing blood pressure (Ayada et al., 2015). Lastly, underlying health conditions such as diabetes, kidney diseases, and other long-term kidney infections can cause hypertension.

Treatments for Controlling Blood Pressure

Blood pressure can be controlled using medications or through a balanced and healthy lifestyle. A low-calorie diet with low levels of sodium as well as daily exercise can allow individuals to maintain a healthy blood pressure. It is crucial to control body weight and to make sure one is within the recommended BMI range. There are also medications that are taken daily that help control blood pressure. One type of medication called Losartan inhibits the formation of angiotensin II by blocking the interaction between angiotensin II and its receptor (Siegl et al., 1995). Another type of medication called beta blockers blocks the actions of epinephrine. Thus, the individual will not have arterial constriction and/or lower cardiac output. Diuretics cause the kidney to get rid of sodium through urine, lowering the blood volume. Lastly, another drug category, called vasodilators, forces arterioles to relax (Hariri and Patel, 2022). A combination of some of these drugs along with a change in a diet can allow an individual to control their blood pressure.

Conclusion

All in all, blood pressure is an important factor in life that must be controlled through a healthy diet and exercise. High blood pressure is when one has a systolic pressure above 140 and a diastolic pressure above 90. Chronic high blood pressure or hypertension can lead to damaged arteries and increased risk of a heart attack or stroke. Low blood pressure or hypotension can also occur due to dehydration or blood loss. This can result in dizziness or cause one to faint since the brain isn’t able to get enough blood. There are, however, a variety of medications that can be used to keep one’s blood pressure stable along with a change in diet.

References

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Biaggioni, I. (2016). The Pharmacology of Autonomic Failure: From Hypotension to Hypertension. In S. W. Watts (Ed.), Pharmacological Reviews (Vol. 69, Issue 1, pp. 53–62). American Society for Pharmacology & Experimental Therapeutics (ASPET). https://doi. org/10.1124/pr.115.012161

Brook, R. D., Weder, A. B., & Rajagopalan, S. (2011). “Environmental Hypertensionology” The Effects of Environmental Factors on Blood Pressure in Clinical Practice and Research. In The Journal of Clinical Hypertension (Vol. 13, Issue 11, pp. 836–842). Wiley. https://doi.org/10.1111/ j.1751-7176.2011.00543.x

Hariri L, Patel JB. Vasodilators. [Updated 2022 Feb 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/ NBK554423/

Hirschl, M., Kundi, M. Carotid interventions and blood pressure. Wien Med Wochenschr 164, 503–507 (2014). https://doi.org/10.1007/s10354014-0327-4

Li, X. C., Zhu, D., Zheng, X., Zhang, J., & Zhuo, J. L. (2018). Intratubular and intracellular reninangiotensin system in the kidney: a unifying perspective in blood pressure control. Clinical

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Siegl, P. K., Kivlighn, S. D., & Broten, T. P. (1995). Pharmacology of losartan, an angiotensin II receptor antagonist, in animal models of hypertension. Journal of hypertension. Supplement : official journal of the International Society of Hypertension, 13(1), S15–S21. https:// doi.org/10.1097/00004872-199507001-00002

Zhou, B., Perel, P., Mensah, G.A. et al. Global epidemiology, health burden and effective interventions for elevated blood pressure and hypertension. Nat Rev Cardiol 18, 785–802 (2021). https://doi.org/10.1038/s41569-02100559-8