Arterial Blood Pressure PDF

Arterial Blood Pressure Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Define blood pressure and contrast systolic and diastolic blood pressure. Explain how gravity, vascular compliance, blood viscosity, and blood inertia contribute to blood pressure...

Arterial Blood Pressure Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Define blood pressure and contrast systolic and diastolic blood pressure. Explain how gravity, vascular compliance, blood viscosity, and blood inertia contribute to blood pressure. Explain how cardiac output, systemic vascular resistance, and blood volume interact to regulate blood pressure. Blood Pressure Blood pressure is the amount of force exerted by the blood against the walls of the blood vessels. Arterial pressure The pressure exerted by blood on the arterial walls. Higher than venous pressure Venous pressure The pressure exerted by blood in the veins. Lower than arterial pressure Blood Pressure Each blood vessel has a blood pressure value – e.g. arterial blood pressure 120 mm Hg systolic. Capillary blood pressure averages 25 mm Hg. The pressures in the pulmonary system are much lower (8-20mmHg) than systemic circulation. Blood flows from an area of high to an area of low blood pressure - there must be a difference in pressure for the blood to flow. Arterial Blood Pressure Systolic pressure. Pressure generated during ventricular contraction (systole).  SBP ∝ CO (Cardiac Output) Diastolic pressure Pressure during cardiac relaxation (diastole). DBP ∝ TPR (Peripheral resistance or systemic vascular resistance) ABP= Systolic BP/diastolic BP Normal level: 120/80 mmHg High: ≥ 140/90 mmHg (Hypertension) low : below 90/60 mmHg (Hypotension) Pulse pressure = systolic BP – diastolic BP. Measurement of ABP by Sphygmomanometer Mean Arterial Pressure (MAP) The mean arterial pressure is the average of the arterial pressures for one cardiac cycle MAP is the average of systolic + diastolic/2 ??? True or False. False, because a greater fraction of the cardiac cycle is spent in diastole (0.5 sec) than in systole (0.3sec) Mean arterial pressure (MAP) = Diastolic + 1/3 pulse pressure Normal range: 70 to 100 mmHg Function of The Arterial Blood Pressure 1. it maintains tissue perfusion. 2. It produces the capillary hydrostatic pressure, which is the main force that determine the filtration pressure that affects tissue fluid formation. 3. Function of the diastolic blood pressure Maintain blood flow during diastole → continuous and non intermittent blood flow to the tissues. Essential for normal coronary blood flow. Prevent blood stasis in the arteries. Physiological Variations of ABP  Age: BP increases with age.    At birth (70/50 mmHg). At 20 (120/80) At 60 (140/90)  Sex: high in males than in female.  Body built: higher in obese.  Diurnal variation: Lowest during the sleep due to decrease of sympathetic tone and highest in the mornings after waking up  Exercise & Emotions : increase ABP.  Temperature:  cold weather causes vasoconstriction → increase ABP.  Hot weather causes vasodilation → decrease ABP. Physiological Variations of ABP Respiratory movement: ABP shows rhythmic fluctuation during respiration called Trabue –Hering waves. ABP increases during Late Inspiration. ABP decreases during Late Expiration  Gravity: Supine position → No change in ABP  on standing the force of gravity increase the mean arterial pressure and venous pressure below reference point (right atrium, tricuspid valve) and decrease them above this level by about 0.77mmHg /cm.  N.B At the right atrium the pressure is 0 mmHg Factors that determines and maintains ABP Cardiac output Total Peripheral resistance Elasticity of the aorta (compliance) Blood volume Cardiac output ABP = Cardiac output X Resistance. ABP is directedly proportionate to the C.O. C.O = Stroke volume X Heart rate ABP is directedly proportionate to Stroke volume : with constant H.R, Increase S.V. → increase systolic blood pressure. ABP is directedly proportionate to Heart Rate: with constant S.V., Increase H.R → increase diastolic blood pressure. Total Peripheral resistance (TPR) or systemic vascular resistance ABP is directedly proportionate to the TPR. Peripheral resistance is essential for maintenance of ABP particularly Diastolic blood pressure. TPR is produced in the arteriole. According to Poiseuille’s law, R = 8Lη / πr4 TPR is determined by 1. Radius (diameter) of the vessel(most important factor), inversely proportionate. Vasoconstriction of arteriole causing small radius → ↑TPR → ↑diastolic blood pressure. 2. Blood viscosity (directedly proportionate). 3. The length of the vessel (directedly proportionate). Total Peripheral resistance (TPR) or systemic vascular resistance Vasoconstriction → ↑ TPR → ↑ ABP Vasodilation → ↓ TPR → ↓ ABP Elasticity of the aorta (compliance) Compliance is the stretch built into blood vessels, and it helps maintain the blood pressure. Stretch of the blood vessel maintains a more constant flow of blood. Compliant vessel prevent the increase in ABP. Atherosclerosis: accompanied by Hypertension. Blood volume Normally there is about 4.7-5.5 L of blood in an average human body. Increase blood volume → increase systemic filling pressure (Psf) → increase ABP. Low blood volume as in haemorrhage → low blood pressure (hypotension) Review Questions A 23-year-old man is brought into the emergency department with a gunshot wound to the abdomen. An emergency medical technician (EMT) is applying pressure to the wound, and it is not currently bleeding. The patient’s vitals are immediately taken: his blood pressure is 100/80 mmHg and pulse 150/min. He is confused and appears very pale. What is the next best step in helping this patient? A. B. C. D. E. Give diuretic medications to cause renal salt and water loss Give intravenous fluids Give medications to decrease heart rate Give medications to decrease the cardiac stroke volume Give medications to decrease the systemic vascular resistance Summary Define blood pressure and contrast systolic and diastolic blood pressure. Explain how gravity, vascular compliance, blood viscosity, and blood inertia contribute to blood pressure. Explain how cardiac output, systemic vascular resistance, and blood volume interact to regulate blood pressure.