1. CIRCULATION Dr. FarazBokhari Assistant Professor SKZMDC

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: ∆P* Resistance 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

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

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 Capillaries Capacitance Vessels Veins 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)

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