BLOOD PRESSURE

Definition

• Blood pressure is the force exerted on the walls of the arteries when the blood is pumped from the heart into the blood vessels.

Blood Pressure Readings

The Normal Blood Pressure is 120/80 mmHg

• Systolic Blood Pressure: When the left Ventricle  of the heart ejects the blood into the aorta the maximal aortic pressure exerted by the ejection of blood is termed as Systolic Blood Pressure

The Normal Systolic Pressure is 120mmHg.

• Diastolic Blood Pressure: As the left ventricle is relaxing and refilling, the pressure in the aorta falls. The lowest pressure in the aorta, which occurs just before the ventricle ejects blood into the aorta, is termed the diastolic pressure

The Normal Diastolic Pressure is 80mmHg.

Physiology of Blood Pressure

Blood Pressure physiology depends on the following factors:

• Stroke Volume & Cardiac Output
• Compliance of Blood Vessels
• Blood Volume
• Blood Viscosity
• Blood Vessel Length & Diameter

Regulation of Blood Pressure

• Baroreceptors and neuronal Regulation
• Renin-Angiotensin Aldosterone System (RAAS)
• Anti-Diuretic Hormone
• Atrial Natriuretic Peptide
• Prostaglandins

Baroreceptors

Changes in blood pressure are detected by baroreceptors. These are located in the arch of the aorta and the carotid sinus. Baroreceptors regulate blood pressure only for short term because the mechanism of triggering baroreceptors takes place only when an adequate blood pressure is restored.

Sympathetic Stimulation

•  Decreased arterial pressure is detected by baroreceptors, which then trigger a sympathetic response. This stimulates an increase in heart rate and cardiac contractility leading to an increased blood pressure.

Para Sympathetic Stimulation

• Increased arterial pressure stretches the wall of the blood vessel, triggering the baroreceptors. These baroreceptors stimulate the autonomic Nervous System to reduce the heart rate and cardiac contractility via the efferent parasympathetic fibres (vagus nerve) thus reducing blood pressure.

Renin-Angiotensin Aldosterone System (RAAS)

• Renin is a peptide hormone released by the granular cells of the juxtaglomerular apparatus in the kidney.

It is released in response to:

• Sympathetic stimulation.
• Reduced sodium-chloride going to the distal convoluted tubule.
• Decreased blood flow to the kidney.

Anti Diuretic Hormone

• Blood pressure is regulated is release of Anti Diuretic Hormone (ADH) from the hypothalamus in response to thirst or an increased plasma osmolarity.
• ADH acts to increase the permeability of the collecting duct to water in the apical membrane.
• It also stimulates sodium reabsorption from the thick ascending limb of the loop of Henle. This increases water reabsorption thus increasing plasma volume & Increases Blood Pressure.

Atrial natriuretic peptide (ANP)

• Atrial natriuretic peptide (ANP) is synthesised and stored in cardiac myocytes. It is released when the atria are stretched, in high blood pressure.
• ANP acts to promote sodium excretion. It dilates the afferent arteriole of the glomerulus, increasing blood flow (GFR). Moreover, ANP inhibits sodium reabsorption along the nephron.
•  On the other hand, ANP secretion is low when blood pressure is low.

Prostaglandins

• Prostaglandins act as local vasodilators to increase Glomerular Filtration rate and reduce sodium reabsorption. They also act to prevent excessive vasoconstriction triggered by the sympathetic nervous and renin-angiotensin-aldosterone systems and therefore maintain Blood Pressure.

Factors Affecting Blood Pressure

• Age:  As age Increases the Blood pressure also Increases due to structural changes in the arteries and especially with large artery stiffness.
• Gender: Women tend to have a slightly lower Blood pressure than men until menopause due to the presence of estrogen which naturally decreases BP.
• Body Mass and Obesity:  Increased Body mass is associated with Increased Blood Pressure due to Increased length of blood vessels & Increased vascular tone.
• Emotional states: In emotional States like Stress & Anxiety, cortisol is released that increases the heart rate & BP.
• Exercise: Exercise lowers blood pressure by reducing blood vessel stiffness and increasing the blood flow.
• Life style: Sedentary lifestyle & urbanization can result in overweight that can lead to Increased Blood pressure due to formation of fatty deposits on the walls of the arteries that decreases the diameter of the blood vessels causing Increased BP.
• Habits: Habits like smoking, alcohol & drug Abuse can cause vasoconstriction which can lead to Increased BP.
• Hereditary: Person with a family history of Increased BP is also at risk of developing Increased BP.
• Medications: Drugs like NSAIDs & decongestants can Increase BP by causing vasoconstriction of the arteries. Drugs like Anti-hypertensives can decrease the BP.
• Diet: Diet high in Sodium & Vitamin-D can cause Increased BP by Increasing the Blood volume & Peripheral Vascular Resistance. Diet high in Potassium can decrease BP by causing relaxation of smooth muscles of blood vessels.
• Climate: Blood pressure generally is higher in the winter and lower in the summer. In low temperatures blood vessels constrict — which increases blood pressure because more pressure is needed to force blood through your narrowed veins and arteries.
• Diurnal Variation: Blood Pressure rapidly rises on wakening in the early morning, reaches a plateau during the morning, falls slightly in the early afternoon and rises again in the early evening.
• Fever: Fever can Increased the blood pressure due to dehydration that Increases the workload of the heart & Kidneys which in turn Increases BP
• Fluid Intake: Excess Fluid Intake can Increase the congestion within the blood vessels and therefore Increases the BP