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  • *need oxygen supply…O2 diffuses to cells….hence distance from O2 source becomes imp….average distance from O2 source is about 100 micrometer…this optimal distance is cuz of CVS
  • rhoedes
  • *Fluid cannot move through a system unless some energy is applied to it. In fluid dynamics, this energy is in the form of a difference in pressure, or pressure gradient, between two points in the system. Pressure is expressed as units of force, or weight, per unit area. A familiar example of this is in the pounds per square inch (psi) recommendation stamped on the side of tires. The psi indicates the pressure to which a tire should be inflated with air above atmospheric pressure. Inflating a tire to 32 psi signifies that 32 more pounds press against every square inch of the inner tire surface than against the outside of the tire.The pressure exerted at any level within a column of fluid reflects the collective weight of all the fluid above that level as it is pulled down by the acceleration of gravity. It is defined aswhere P = pressure, ρ = the density of the fluid, g = the acceleration of gravity, and h = the height of the column of fluid above the layer where pressure is being measured. The force represented by pressure in a fluid system is often described as the force that is able to push a column of fluid in a tube straight up against gravity. In this way the magnitude of the force resulting from fluid pressure can be measured by how high the column of fluid rises in the tube In physiological systems, this manner of expressing pressure is designated as centimeters H2O, or the more convenient mm Hg, because mercury is much denser than water and therefore will not be pushed upward as far by typical pressures seen within the cardiovascular system.Without going into mechanistic details at this time, arterial pressure peaks shortly after the heart contracts and pumps blood into the aorta and falls to a lower value when the heart relaxes between beats and is therefore not pumping blood into the aorta. The peak pressure during contraction of the heart is called the systolic pressure and is typically about 120 mm Hg in humans, whereas the minimum arterial pressure value during relaxation of the heart is called the diastolic pressure and is about 80 mm Hg. Thus, if one end of a tube were to be inserted into the aorta with the other end connected to a column of mercury sitting perpendicular to the ground at the level of the heart, that column of mercury would rise 120 mm during systole and fall to 80 mm during diastole. In clinical practice, human arterial pressure is reported as systolic over diastolic pressure or, in this example, 120/80. (Our mean arterial pressure is not the arithmetic mean of systolic and diastolic pressure but is instead about 93 mm Hg, because the time the heart spends relaxing is longer than the time it spends contracting and ejecting blood into the aorta.)
  • Compliance, therefore, is related to the ease by which a given change in pressure causes a change in volume.In biological tissues, the relationship between DV and DP is not linear. As shown in Figure 1, compliance (which is the slope of the line relating volume and pressure) de-creases at higher volumes and pressures.Another way to view this is that the “stiffness” of a cardiac chamber or vessel wall increases at higher volumes and pressures.
  • *Systolic & Diastolic P are peak/lowest arterial pressuresIn reality arterial pressures vary around average values from heartbeat to heart beat & minute to minuteFor complex reasons, compliance (TPR) does not significantly influence MAP. So e.g. In arteriosclerosis, pulse P raises a lot, not MAP!!
  • *means increases or decreases in CO have proportionate effects on MAP
  • Transcript

      Dr. FarazBokhari
      Assistant Professor
    • 2. Cardiovascular System
      Multicellular organisms need CVS*
    • 3. General Principles
      Output of the Right and Left Heart Are Interdependent Because Their Chambers Are Connected in Series
      2-bucket example
    • 4. General Principles
      Blood Flow to Individual Organs Can Be Controlled Primarily Independently Because Circulations to Individual Organs Are Arranged in parallel
      Liver is an exception – own arterial supply + splanchnic circulation
      Hence tissue need dictates its own blood flow
    • 5. General Principles
      Lumen diameter of all Arteries & Veins can be actively changed by contraction or relaxation of the circular layers of SM within their walls
      Scores of normal physiological, pathological, and pharmacological agents that can alter vessel lumen
    • 6. General Principles
      Cardiac output – controlled – sum of all local tissue flows
      Arterial pressure – controlled – independently
    • 7. HemodynamicsBlood flow, Pressure & Resistance
      Blood flow through a vessel:
      F= ∆P/R (Ohm’s Law)
      Laminar Vs turbulent flow
      Eddie currents – more turbulence
      Tendency for turbulence – measured by Reynold’s number (Re)
      (Re= v.d.p/ŋ)
      Re >2000 – significant turbulence
      Blood pressure is the ‘force exerted by blood against any unit area of vessel wall’
    • 8. Blood flow, Pressure & Resistance
      Resistance is impediment to blood flow in a vessel
      If ∆P = 1 mm hg
      And if, Flow = 1 ml/sec
      Then, R = 1PRU
      Total peripheral resistance
      Strong sympathetic ++ : R=4 PRU
    • 9. Vessel Conductance
      Diameter – conductance relationship
      4-fold increase in d caused 256-fold increase in flow
      Hence, conductance of a vessel increases in proportion to the fourth power of diameter
      conductance ∞ diameter4
      Poiseuille’s Law – factors that change resistance of blood vessel (or conductance
      F = π∆P.r4 / 8ŋ.l
    • 10. Derivations of Poiseuille’s Law
      • F = ∆Pπr4/ 8ŋl or
      • 11. Q = ∆Pπr4 / 8ŋl
      • 12. ∆P = Q.8ŋl / πr4 where8ŋl / πr4= R
      • 13. ∆P = Q.R
      • 14. R= ∆P/Q
      • 15. mm Hg/mL per minute or PRU
      • 16. Q = ∆P/R (Ohm’s Law)
      • 17. Flow is proportional to pressure difference b/w entrance and exit points of a tube
      • 18. And inversely proportional to resistance
    • Vascular Compliance
      Vascular compliance
      Increase in V/increase in P
      Related to the ease by which a given change in pressure causes a change in volume
      Compliance of a systemic vein is about 24 times that of its corresponding artery
      Since it is about 8 times as distensible, and
      Has a volume about 3 times as great
      8 x 3 = 24
      Delayed compliance
      Increase in V – increase in P pressure normalizes (vasodilation)
      Vice versa
    • 19. Vessel Types
      Windkessel Vessels
      Elastic reservoir vessels
      Large arteries
      Highly distensible
      Serve to damp large pressure fluctuations
      Pulsatile flow converted to constant blood flow
      Resistance Vessels
      Arterioles, metaarterioles and pre-capillary sphincters
      Arterioles has extensive ANS innervation
      Alpha receptors – arterioles of skin, splanchnic, renal
      Beta receptors – arterioles of skeletal muscle
      Exchange Vessels
      Capacitance Vessels
      Shunt Vessels
      Present in skin and other areas
      Temperature regulation
    • 20. Arterial Pressures
      Systolic pressure
      In vascular system is the peak pressure reached during systole
      Diastolic pressure
      Lowest pressure during diastole
      Mean arterial pressure (MAP)
      Pulse pressure
    • 21. Arterial Pressure Pulsations
      Each heart beat
      Not only moves the blood in the vessels forward but also sets up a pressure wave
      This wave travels along the arteries
      It expands the arterial walls as it travels, and the expansion is palpable as the pulse
      Rate at which the wave travels is independent of and much higher than the velocity of blood flow!
    • 22. Pulse Pressure
      Pulse pressure = systolic P – diastolic P
      Depends on:
      Stroke Volume (SV)
      Arterial compliance
      Examples of variance in pulses
      Weak ("thready") in shock
      Strong in exercise / after administration of histamine
      Aortic insufficiency: collapsing, Corrigan, or water-hammer pulse
    • 23. Abnormal Aortic Pressure Pulses
    • 24. Transmission of Arterial Pulsations
      Arterial pressure pulsations
      Continuous blood flow Vs pulsatile blood flow
      Windkessel effect
    • 25. Mean arterial pressure (MAP)*
      Average of the arterial pressures measured millisecond by millisecond over a period of time
      Not an arithmetic mean, is closer to diastolic pressure than systolic
      Diastolic P + 1/3 Pulse P
      Depends on:
      Mean blood volume in arterial system (C.O.)
      Arterial compliance (TPR)
      BP = C.O. x TPR
      Systolic BP is mainly controlled by CO
      Diastolic BP is mainly controlled by TPR (BP ∞ TPR, Increase TPR – increase BP)
    • 26. SV, HR& TPR affect MAP, Pulse P
      MAP = CO x TPR
      Where CO = SV x HR
      CO influence on MAP is independent!*
      CO influence on Pulse P depends on whether:
      CO has increased due to change in SV or
      CO has increased due to change in HR
    • 27. Scenario 1:
      HR increases, SV decreases
      CO = constant; MAP = constant
      But, Pulse P decreases (since SV has decreased)
      Systolic P decreases
      Diastolic P increases (decreased runoff due to lower SV)
      Scenario 2:
      HR decreases, SV increases (atheletes @ rest)
      CO = constant; MAP = constant
      But, Pulse P increases (since SV increased)
      Systolic P increases
      Diastolic P decreases (increased runoff due to higher SV)
    • 28.
    • 29. Overview: MAP
    • 30. Variations in ArterialBP
      Physiological variations in BP
      Diurnal: lowest – early morning; highest – afternoon
      Gender: females tend to have < BP
      BP rises with age, BMI and mental stress
      BP decreases with sleep and food intake
      Exercise: moderate – only systolic increases; severe – both rise
      Posture: standing upright first decreases BP (decrease VR); SNS activation restores BP