Review: What Actually is Blood Pressure?
Blood pressure is the pressure of circulating blood against the walls of blood vessels. It is the force of blood pushing against the arteries as the heart pumps blood through the circulatory system. Blood pressure is typically measured in millimeters of mercury (mmHg) and is expressed as two numbers: systolic pressure (the maximum pressure during one heartbeat) and diastolic pressure (the minimum pressure between two heartbeats). The difference between these two pressures is known as pulse pressure, while the average pressure during a cardiac cycle is known as mean arterial pressure[6][10].
What Physical Factors Adjust Blood Pressure?
The key physiological factors that determine blood pressure and how they influence it are:
1. Blood Volume: The total amount of blood in circulation affects blood pressure. Increased blood volume leads to higher pressure, while decreased blood volume results in lower pressure[13][15].
2. Cardiac Output: The amount of blood pumped by the heart per minute, determined by stroke volume and heart rate, directly impacts blood pressure. Increases in cardiac output raise both systolic and diastolic pressure[13][15].
3. Peripheral Resistance: The resistance to blood flow in the small blood vessels, especially arterioles, is a major determinant of blood pressure. Increased peripheral resistance leads to higher pressure, while decreased resistance lowers pressure[13][14][15].
4. Vessel Elasticity: The ability of blood vessels, particularly arteries, to expand and recoil affects blood pressure. Stiffer, less elastic vessels result in higher pressures, while more elastic vessels can better accommodate changes in blood flow[13][15].
5. Blood Viscosity: The thickness or resistance to flow of blood also influences blood pressure. Higher blood viscosity increases peripheral resistance and raises pressure[13][15].
6. Vessel Diameter: The diameter of blood vessels, especially arterioles, is a key factor. Narrower vessels increase peripheral resistance and blood pressure, while wider vessels decrease resistance and pressure[13][15].
Many factors influence the above physical determinants of blood pressure. This includes the Autonomic Nervous System: The sympathetic nervous system can constrict blood vessels through the release of vasoconstrictors like norepinephrine, increasing peripheral resistance and blood pressure. The parasympathetic system has the opposite effect[13][15].
Understanding Oxidative Stress and Its Impact on Red Blood Cells
Hypertension, or high blood pressure, is a significant health concern that can lead to various complications, including heart disease and stroke. Research has shown that oxidative stress plays a crucial role in the development and progression of hypertension. In this context, oxidative stress refers to the imbalance between the production of reactive oxygen species (ROS) and the body’s ability to neutralize them through antioxidants.
Oxidative stress can alter the zeta potential of particles by changing their surface charge. This occurs when reactive oxygen species (ROS) formed interact with the surface of particles such as red blood cells, leading to changes in their surface electrokinetic potential[16][17][18].
Reduced Zeta Potential in Red Blood Cells
One key finding is that hypertensive patients have significantly lower zeta potential (surface charge) on their red blood cells (RBCs) compared to healthy individuals. This reduction in zeta potential is even more pronounced in patients with myocardial infarction (heart attack). The zeta potential of RBCs is typically negative, which helps them move smoothly through blood vessels. However, when this potential is reduced, it can lead to various changes in RBC behavior.
Causes of Reduced Zeta Potential
The primary cause of the reduced zeta potential in hypertension is oxidative stress. ROS, which are highly reactive molecules, damage the RBC membranes through a process called lipid peroxidation. This damage makes the membranes more fragile and prone to further oxidation. As a result, the negative surface charge of the RBCs is reduced, leading to changes in their behavior.
Consequences of Reduced Zeta Potential
The reduced zeta potential of RBCs in hypertensive patients has several significant consequences:
1. Increased RBC Aggregation: With a lower surface charge, RBCs are more likely to stick together, increasing blood viscosity and peripheral resistance.
2. RBC Deformity: The reduced zeta potential also leads to changes in RBC shape, resulting in abnormal forms such as poikilocytes and anisocytes.
3. Reduced Deformability: The damaged RBC membranes become less flexible, making it harder for them to change shape and move through narrow blood vessels.
Antioxidant Deficiency
Oxidative stress not only damages RBC membranes but also reduces the levels of antioxidant enzymes such as superoxide dismutase and glutathione peroxidase. These enzymes play a crucial role in neutralizing ROS and protecting the body from oxidative damage. The deficiency of these enzymes further exacerbates the damage to RBC membranes and the reduction in zeta potential.
Normal Blood Pressure with Reduced Zeta Potential
Hypertension: Hypertensive patients have been found to have significantly reduced zeta potential compared to healthy individuals, but even individuals with normal blood pressure can have reduced zeta potential, which is associated with increased risk of cardiovascular disease. This is due to other factors which change the physical determinants of blood pressure.
Diabetes: Patients with diabetes have a progressive deterioration of the zeta potential of red blood cells, which can increase the potential for red blood cell clumping and aggregation, leading to increased cardiovascular risk. People with diabetes are twice as likely to have high blood pressure compared to those without diabetes. High blood pressure is less common, however, in people with type 1 (auto-immune) diabetes compared to those with type 2 (metabolic) diabetes[19]. The body’s ability to regulate blood sugar may be impaired, but the body’s ability to regulate blood pressure can be relatively preserved. While there is a significant correlation between the two, blood pressure (BP) is not always linked to blood sugar levels[20].
Oxidative Stress: Oxidative stress can cause changes in the electrodynamics of red blood cells, leading to a reduction in zeta potential and increased aggregation, which can contribute to cardiovascular risk.
Aging: The zeta potential of red blood cells has been observed to decrease with age, which can increase the risk of cardiovascular disease.
Other Factors: Other factors such as smoking, lipid disorders can also increase blood viscosity and reduce zeta potential, which can contribute to cardiovascular risk.
However, even where there is blood sugar dis-regulation, oxidative stress, aging, and other factors, the body may still successfully regulate blood pressure by compensating for all of the above changes through various physiological mechanisms[21][22]. The cardiovascular system engages in homeostatic regulation to maintain adequate blood flow and blood pressure through neural, endocrine, and autoregulatory mechanisms[23].
Review of Key Points
Oxidative stress is the primary cause for a reduction in the zeta potential (surface charge) of red blood cells (RBCs).
– Hypertensive patients in one study had significantly lower zeta potential of RBCs (-16.06 mV) compared to healthy individuals (-23.39 mV). Patients with myocardial infarction had even lower zeta potential (-9.94 mV).[1]
– The reduced zeta potential in hypertension is caused by oxidative stress and reactive oxygen species (ROS) damaging the RBC membranes.[1][3] ROS leads to lipid peroxidation and oxidation of the RBC membrane, making it more fragile.[1]
– The lowered negative zeta potential results in increased RBC aggregation, deformity (poikilocytes, anisocytes), and reduced deformability, which increases blood viscosity and peripheral resistance.[1][3]
Summary
In summary, the increased oxidative stress in hypertension generates excessive ROS that oxidize and damage RBC membranes, reducing their negative surface charge (zeta potential). This reduction in zeta potential leads to increased RBC aggregation, deformity, and reduced deformability, which contributes to the elevated peripheral resistance seen in hypertension[1][3]. Understanding the role of oxidative stress in hypertension can help in the development of effective treatments to manage this condition.
Citations
[1] https://www.intechopen.com/chapters/72171
[2] https://www.researchgate.net/publication/325561977_Alterations_in_Zeta_Potential_and_Osmotic_Fragility_of_Red_Blood_Cells_in_Hyperglycemic_Conditions
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4115353/
[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9952760/
[5] https://www.nature.com/articles/hr2010264
[6] https://en.wikipedia.org/wiki/Blood_pressure
[7] https://my.clevelandclinic.org/health/diagnostics/17649-blood-pressure
[8] https://www.cancer.gov/publications/dictionaries/cancer-terms/def/blood-pressure
[9] https://www.ncbi.nlm.nih.gov/books/NBK268/
[10] https://medlineplus.gov/highbloodpressure.html
[11] https://homework.study.com/explanation/what-physiological-factors-influence-blood-pressure.html
[12] https://byjus.com/biology/what-are-the-5-factors-that-affect-blood-pressure/
[13] https://www.slideshare.net/slideshow/pptx-261200126/261200126
[14] https://journals.sagepub.com/doi/pdf/10.1177/216507997802600101
[15] https://healthacademy-web.radboudumc.nl/coo/ipweb7/misc/assignmentfiles/cardiovascular/Fact_Aff_Blood_Pressure.pdf
[16] https://en.wikipedia.org/wiki/Zeta_potential
[17] https://pubmed.ncbi.nlm.nih.gov/38727304/
[18] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5551541/
[19] https://www.bloodpressureuk.org/your-blood-pressure/understanding-your-blood-pressure/why-is-high-blood-pressure-a-problem/diabetes-and-high-blood-pressure/
[20] https://pubmed.ncbi.nlm.nih.gov/8728301/
[21] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6208507/
[22] https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2014.00084/full
[23] https://courses.lumenlearning.com/suny-ap2/chapter/homeostatic-regulation-of-the-vascular-system/