Blood-pressure-buX.ppt
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Part-I Blood pressure Human physiology (BCH201) Difference between systole and diastole Formula to calculate blood pressure Role of baroreceptor in generating blood pressure Role of several hormones in controlling blood pressure Blood pressure A constant flow of blood is necessary to...
Part-I Blood pressure Human physiology (BCH201) Difference between systole and diastole Formula to calculate blood pressure Role of baroreceptor in generating blood pressure Role of several hormones in controlling blood pressure Blood pressure A constant flow of blood is necessary to transport oxygen to the cells of the body The arteries maintain an average blood pressure of around 90 mmHg This helps push the blood from the arteries into the capillaries In the capillaries, oxygen transfers from the blood to the cells The arteries fluctuate between a state of systole and diastole In systole, the pressure in the arteries increases as the heart pumps blood into the arterial system As the pressure increases, the elastic walls of the arteries stretch This can be felt as a pulse in certain arteries In diastole, the recoil of the elastic arteries forces blood out of the arterial system into the capillaries The pressure in the arteries falls as blood leaves the system Minimum diastolic pressure is typically 70-80 mmHg Maximum systolic pressure is typically 110-120 mmHg Note that there is always pressure in the arteries, never much below 70 – 80 mmHg Blood pressure depends on cardiac output (CO) and systemic vascular resistance (SVR) BP = CO x SVR* Cardiac output depends on heart rate and stroke volume CO = HR x SV* *SVR = total resistance of arterioles to flow of blood *SV = the amount of blood pumped by the heart each cycle The body responds quickly to falls in arterial pressure This immediate response is to increase cardiac output (CO) and systemic vascular resistance (SVR) Sympathetic activity causes vasoconstriction. This increases SVR Sympathetic activity causes an increase in both heart rate and stroke volume These both increase cardiac output CO = HR x SV Both SVR and CO have now increased so BP will increase BP = CO x SVR How does the body know that there has been a fall in blood pressure? Baroreceptors on the aorta and carotid artery respond to falls in BP They send signals to the cardiovascular centre in the brain stem medulla The medulla sends signals along the sympathetic nerves to the arterioles and heart, increasing SVR and cardiac output A drop in blood pressure causes a response that increases SVR and cardiac output Remember the formula for BP…? BP = CO x SVR An increase in SVR and cardiac output together increase BP Thank you very much Part-II Mechanism of action of antihypertensive drugs Human physiology (BCH201) Mechanism of action of different antihypertensive drugs 90% of cases of hypertension are of unknown origin. Idiopathic hypertension is also known as primary or essential hypertension. Hypertension is defined as having a systolic pressure of over 140 mm Hg and diastolic pressure over 90 mm Hg. Mild hypertension, between 140 – 159 mm Hg may initially be treated by changes in lifestyle More aggressive treatment is warranted as the problem gets worse. Prolonged high blood pressure can damage organs, especially the brain, kidneys and cardiovascular system and may result in haemorrhagic stroke, renal failure and myocardial infarction (heart attack). Atherosclerosis, a disease where fatty deposits accumulate and damage blood vessels is accelerated in people with high blood pressure, especially if they are also diabetic. All antihypertensive drugs act on the familiar formula… BP = SVR x CO (HR v SV) They act by 1. Reducing SVR.. or by... 2. Reducing cardiac output …by… 3. Reducing heart rate …or by… 4. Reducing stroke volume BP Renin Angiotensinogen Angiotensin I Angiotensin Converting Enzyme Angiotensin II ADH- Angiotensin II vasopressin Vasoconstriction Thirst Aldosterone Blood Pressure Sodium retention Beta-blockers are beta-adrenoceptor antagonists. They bind to and block 1 receptors on the heart so reducing its responsiveness to sympathetic activity These drugs are used to treat essential hypertension and some are also used for heart failure. This group includes candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan and valsartan. Angiotensin-II is a potent vasoconstrictor that causes an increase in SVR Angiotensin-II receptor blockers bind to and block the AT1 receptor and therefore reduce the vasoconstrictive effect of angiotensin-II Calcium-channel blockers (CCBs) exert their effects by different mechanisms. Drugs in this group licensed for the treatment of hypertension include, amlodipine, diltiazem, felodipine, isradipine, lacidipine, lercanidipine, nicardipine, nifedipine, nisoldipine and verapamil. Calcium channel blockers act on the heart’s conduction tissue to reduce heart rate, the myocardium to reduce stroke volume and the smooth muscles of the arterioles to reduce systemic vascular resistance. Stimulation of muscle cells causes contraction and vasoconstriction Thank you very much Part-III Electrocardiogram (ECG) Electrocardiogram (ECG) and its use Part-III Electrocardiogram (ECG) Electrocardiogram (ECG) and its use When the cardiac impulse passes through the heart, electrical current also spreads from the heart into the adjacent tissues surrounding the heart. A small portion of the current spreads all the way to the surface of the body. If electrodes are placed on the skin on opposite sides of the heart, electrical potentials generated by the current can be recorded; the recording is known as an electrocardiogram. A normal electrocardiogram for two beats of the heart The normal electrocardiogram is composed of a P wave, a QRS complex, and a T wave. The QRS complex is often, but not always, three separate waves: the Q wave, the R wave, and the S wave.The P wave is caused by electrical potentials generated when the atria depolarize before atrial contraction begins. The QRS complex is caused by potentials generated when the ventricles depolarize before contraction. In the Figure A depolarization, demonstrated by red positive charges inside and red negative charges outside, is traveling from left to right. In Figure B, depolarization has extended over the entire muscle fiber, and the recording to the righ has returned to the zero baseline because both electrodesare now in areas of equal negativity. Figure C shows halfway repolarization of the same muscle fiber, In Figure D, the muscle fiber has completely repolarized, and both electrodes are now in areas of positivity, Displays the overall electrical activities of the myocardial cells ◦ Heart rate & dysrhythmias ◦ Myocardial ischaemia ◦ Pacemaker function ◦ Electrolyte abnormalities ◦ Drug toxicity Does NOT indicate mechanical performance of the heart: ◦ Cardiac output ◦ Tissue perfusion Thank you very much