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dr. S. Wulandari, M.Sc
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HemodynamicsDescribes the physical factors governing blood flow within the circulatory system Pressure Flow Resistance
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Blood Velocity
Q = VA
V = Q/A
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Blood FlowBlood flow : the quantity of blood that passes a given point in the circulation in a given period of time ml/mnt, L/mntDetermined by :Pressure gradientForce that pushes the blood through the vesselVascular resistanceThe impediment to blood flow through the vessel as a result of friction between the flowing blood and the intravascular endothelium all along the inside of the vesselOrgans blood flow is determined by changes in resistance
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Ohms Law
Q = P R
Q : Blood Flow P : Pressure Difference (P1 P2)R : Resistance
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Blood flow in the total circulation Cardiac output (CO)CO : the amount of blood pumped into the aorta by the heart each minuteBlood flow within each organ changes with body activities
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Laminar Blood FlowStreamline Each layer remaining the same distance from vessel wallParabolic velocity Most portion of the blood stays in the centre of the vessel
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Turbulen Blood FlowCauses :High velocityObstructionSharp turnRough surfaceDisorderlyGreater resistance
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Reynolds numberRe : reynolds numberv : mean velocity (cm/s)d : diameter (cm) : density : viscosity (poise) the measure of the tendency for turbulence to occur
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POISEUILLEs LAW Q = debit / flow rate (m/s) = blood viscosity (Poiseuille/Pa.s) r = radius of the vessel(m)P1/P2 = pressure (N/m = Pa) L = length of the vessel (m) Applied only to single vessel
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Resistance to Blood FlowFlow Rate = Pressure ResistancePressure = Flow Rate x Resistance
Pressure = Q
Flow Rate =
Resistance =
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Total Peripheral Vascular Resistance & Total Pulmonary Vascular ResistanceCirculatory Blood Flow rate ~ CO ( 100 ml/s)Total Peripheral Resistance : the resistance of the entire systemic circulation 1 PRUTotal Pulmonary Resistance : 1/7 systemic circulationvasodilation resistance decreasesvasoconstriction resistance increases
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Series & Parallel VesselsSeries Vessels Arteries, arterioles, cappilaries, venules & vein are collectively arranged in seriesFlow through each vessel is the sameThe total resistance to blood flow is equal to the sum of the resistances of each vesselParallel vesselPermits each tissue to regulate its own blood flowthe total resistance is far less than the resistance of any single blood vessel
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The total parallel resistance is less than single lowest resistanceChanging the resistance of a small number of parallel vessel will have little effect on total resistance
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Blood ConductanceConductance is a measure of the blood flow through a vessel for a given pressure difference.
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Blood Viscosity & HematocritThe greater the viscosity, the less the flow in a vesselWater viscosity= 10-3 Pa s (20)Blood viscosity= 3-4 x 10-3 Pa sHematocrit >>> Blood viscosity >>>Temperature >Flow >
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Polisitemia vera
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Vessels DiameterThe most important factor determining resistance to flowQ ~ r4
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Blood PressurePressure >>> Flow >>>an increase in arterial pressure not only increases the force that pushes blood through the vessels but also distends the vessels at the same time, which decreases vascular resistance.
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= QTekanan Darah :- Berbanding lurus dengan V (curah jantung)- Berbanding lurus dengan tahanan (perifer) dipengaruhi oleh tonus dan elastisitas arteri - Berbanding lurus (viskositas darah) dipengaruhi oleh volume darah - Berbanding lurus dengan L (panjang pembuluh) - Berbanding terbalik dengan r (jari-jari/ diameter pembuluh)
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METODE PENGUKURAN TEKANAN DARAHDiukur dengan SphygmomanometerSpygmomanometer terdiri dari : 1. Manometer 2. Pressure cuffTipe Spygmomanometer : 1. Manometer air raksa tekanan = tinggi kolom air raksa 2. Manometer aneroid tekanan menyebabkan jarum bergerak ke angka
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TEKANAN ZAT CAIR PA PB = g ( hA hB ) hA & hB (+) jika diukur ke bawah PA = PA + PO PB = PB + PO PA & PB = tekanan mutlak zat cair PO = tekanan atmosfer PA & PB = selisih tekanan mutlak & tekanan atmosfer Metode Pengukuran Tekanan : Menentukan tinggi kolom cairan yang memproduksi tekanan yang setara dengan tekanan yang diukur Manometer (tabung bentuk U yang terisi cairan, biasanya air raksa/air)
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Arteries and blood pressurePressure reservoirArterial walls are able to expand and recoil because of the pressure of elastic fibers in the arterial wallSystolic pressure: maximum pressure occurring during systoleDiastolic pressure: pressure during diastole
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Figure 14.8Arterial blood pressure
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Blood pressure values: what do they mean?Pulse pressure: PP = SP-DP
Mean arterial blood pressure = MAP
MAP = Pdias 1/3 (Psys Pdias)
MAP = (CO x SVR) + CVP
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LAJU ENDAP DARAH (LED) v = kecepatan endap/sedimentasi r = jari-jari benda = viskositas g = percepatan gravitasi = massa jenis benda 0 = massa jenis zat cair
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ReferensiGuyton, A.C., John E. Hall., 2006. Textbook of Medical Physiology.11th ed. Elsevier Inc.Philadelphia, Pennsylvania.Klabunde, R.E. 2011. Cardiovascular physiology concepts. 2nd ed. Lippincott Wiliams & Wilkins.Cameron, John R., 2006. Fisika Tubuh Manusia; Alih bahasa, Brahm U. Pendit. Ed.2-Jakarta. EGC. Gabriel J.F. 1996. Fisika Kedokteran. 7th ed. Jakarta. Penerbit Buku Kedokteran EGC.
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.......Terima Kasih
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