# Physiology - Cardiovascular Notes.docx

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Published on 15 Jun 2012
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Flow, Pressure, Resistance:
Flow = volume (mL or L) /time (min)
Cardiac output = 5 L/min
o Flow generated by left or right heart
Flow through a vessel = area (cm3) x mean velocity (sec)
o Velocity not the same at all points in cross section
Cross-sectional area of aorta few cm
o Velocity in aorta high pressure fluid moving quickly
o Average speed in big vessel like aorta: 30cm/sec
o Down arterial tree cross-sectional area increasing and velocity decreasing flow same
o Flow slowest in smallest vessels
Practical units: cm H2O or mmHg
Pressure (Pa) = force/area (mmHg) = pgh = height (cm H2O)
o Blood pressure: 120/80 mmHg
o Central venous pressure: 6cm H2O
o pgh density (can’t change) x gravity (can’t change) x height (can change)
pressure exerted by column 10cm high, is 10cm
o 1mmHg = 13.6 mm H2O = 1.36 cm H2O
o Atmospheric pressure = 0
o Not all pressure hydrostatic pressure decreases as fluid moves out of a bag and down tube
Measuring CVP (central venous pressure)
o Veins which come into the right atrium have approximately the same pressure as in the right atrium
CVP = pressure in RA
o Keep manometer at higher level than right atrium cause fluid to move out of manometer and into
RA through catheter until hydrostatic pressure = RA pressure (CVP)
o When the liquid in the manometer is at the same level as the RA, the Pin = Pout and the flow = 0
Measure the amount of liquid in the manometer at that time, and that will be your CVP
o CVP = 5-10 cm H20
Jugular vein distension
o Put is chest cavity = everything pushed to left = RA squeezed and pressure increases inside =
transmural pressure increases (pressure inside pressure outside) = CVP increases = jugular v.d.
o Treatment? tube through ribs to take fluid out
Perfusion pressure = arterial pressure
o Perfusion pressure drives flow through vessels
o Perfusion pressure = arterial pressure venous pressure
o Venous pressure negligible so perfusion pressure = arterial pressure
o Perfusion pressure = pressure flowing in pressure flowing out
Pin = Pout P = 0 flow = 0 (no perfusion pressure = no flow)
Flow = perfusion pressure / resistance
o Absolute pressure not important difference in pressures is important
o Increase in p.p. = increase in flow VS. increase in resistance = decrease in flow
o Resistance = PRU = (mmHg/ml) x sec
Laminar or parabolic flow
o Velocity drops from centre of vessel to edge of vessel (velocity at edge of vessel = 0)
Parabolic flow - explains viscosity as blood flow from
o Normal flow through vessels = laminar flow (smooth flow)
Poiseuille’s Law
o R = (8vL)/(r4)
o R proportional to: length and viscosity
o R inversely proportional to radius
Small changes in r = large changes in R smaller r = larger R = less flow
Resistance
o Resistance in series: R = R1 + R2 (R > R1 or R2)
Flow = P/ R1 + R2
Don’t want system in series because don’t want all organs getting same amount of flow
ex. exercise more flow to muscles at that time
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o Resistance in parallel: 1/R = 1/R1 + 1/R2 (R < R1 or R2)
Flow = P/R1 + P/R2
Want system in parallel so small arterial pressure to drive flow through vessels
Concentrate on controlling size of vessels, which will control R of each organ and that
controls flow through each organ
Anatomy
Flow of blood
o RA RV pulmonary trunk R and L pulmonary arteries (2) lungs 2 R pulmonary veins
and 2 L pulmonary veins LA LV aorta rest of body superior & inferior vena cava RA
Atria - chambers through which blood flows from veins to ventricles its contraction aids ventricular filling
but is NOT essential for it
Ventricles drives blood to pulmonary system to get oxygenated, and then blood to rest of body
Arteries low-resistance tubes conducting blood to the various organs with little loss in pressure also act
as pressure reservoir for maintaining blood flow during ventricular relaxation
Arterioles major site of resistance to flow smooth muscles relax and contract which controls individual
organs resistance by controlling cross-sectional area individual organs control flow of blood to
themselves
Veins
o Low-resistance blood flow back to heart
o Superior vena cava blood from top part of body
o Inferior vena cava blood from bottom part of body
Pulmonary vessels
o 4 pulmonary veins (2 from R lung and 2 from L lung)
o 2 pulmonary arteries (1 to R lung and 1 to L lung both from pulmonary trunk)
Septums
o Inter-atrial septum separates RA and LA
o Inter-ventricular septum separates RV and LV
o LV free wall thicker than RV free wall LV pumps to whole body
Pericardium sac around heart fat and connective tissue
Valves
o A-V valves blood flow between atriums and ventricles
Tricuspid valve (3 flaps) RA RV
Bicuspid valve (mitral valve 2 flap) LA LV
o Semilunar valves blood flow between ventricles and aorta and pulmonary arteries
Pulmonic valve RV 2 pulmonic arteries
Aortic valve LV aorta
o Valves sit in fibrous ring which is not made of cardiac tissue
o Chordae tendinae (connective tissue don’t stretch) attached to valves and papillary muscles
Ventricles develop increased pressure causes valve to close ventricles contract
papillary muscles contract pull on chordate tendinae pull on leaflets on valves so they
don’t ever into atrium
Make sure no regurgitation from ventricles to atriums
Regurgitation if chordae tendinae or papillary muscles weak or not working valve
replacement
Covering of heart
o Endocardium covering of ventricles and atriums
o Myocardium muscle outside ventricles and atriums
o Epicardium (sticks to muscle) Pericardial fluid Pericardium (outside - very tough)
o Pericardial fluid acts as lubricant so heart can move easily when it contracts
If it fills with too much fluid, ventricles compressed and can’t fill properly can’t pump
properly less blood flow decreased BP
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Electrical System of Heart
Cardiogenic control of beating of heart is in heart itself
Sinoatrial node (sinus node) natural pacemaker of heart in corner of RA
Activation sequence:
o SA node spontaneous generation of AP like wave of depolarization, into atrial muscle RA
LA AV node bundle of His (between atriums) L and R bundle branches which travel in
interventricular septum purkinje fibers (smaller fibers) in endocardial muscle epicardium
(ventricular muscle)
Fibrous connective tissue between atriums and ventricles which is not excitable and acts as insulator
between atria and ventricles
Purkinje fibre network
o Some floating in cavity and some in endocardial muscle (in) epicardial muscle (out)
Cardiac cells
o Long and thin - intercalated discs join cells
o Nexus or gap junction specialized area in intercalated discs where 2 cells join very close
Cells so close together and sometimes no interstitial space allows cells to talk to one
another and AP to travel from one cell to next
o Connexions or hemi-junctions in gap junctions
Have interstitial fluid in between
Hemi-junctions dock together and that acts as a channel anything small can get through
(ions)
Slows propagation because not one whole cell hole in each cell but needed for
propagation
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## Document Summary

Flow = volume (ml or l) /time (min) Cardiac output = 5 l/min: flow generated by left or right heart. Flow through a vessel = area (cm3) x mean velocity (sec: velocity not the same at all points in cross section. Pressure (pa) = force/area (mmhg) = pgh = height (cm h2o: blood pressure: 120/80 mmhg, central venous pressure: 6cm h2o, pgh density (can"t change) x gravity (can"t change) x height (can change) Measuring cvp (central venous pressure: veins which come into the right atrium have approximately the same pressure as in the right atrium. Cvp = pressure in ra: keep manometer at higher level than right atrium cause fluid to move out of manometer and into. Ra through catheter until hydrostatic pressure = ra pressure (cvp: when the liquid in the manometer is at the same level as the ra, the pin = pout and the flow = 0.