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4. Physiology and pathophysiology > Laws and relationships > Flashcards

Laws and relationships Flashcards

1
Q

What is Frank Starling law

A

Relationship btwn the EDV and cardiac performance
* Length-tension relationship
* incr volume of blood before contraction => more vigorous contraction force
o Beat to beat adjustment of SV to preload

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2
Q

Explain physiologic mechanism of Frank Starling law

A

↑ venous return → ↑ ventricular filling → ↑ preload → myocyte stretch prior to contraction → ↑ sarcomere length → ↑ inotropy → ↑ SV
* ↑ active tension of muscle fibers → more cross bridge are cycling
o Titin = length sensor
 When stretched radial forces pull myosin toward actin
o ↑ velocity of fiber shortening (Vcf) for given afterload/inotropic state
* ↑ sarcomere length
o incr Troponin C sensitivity to Ca2+ => incr rate of cross bridge cycling
o  availability of Ca2+ to intiate cycling
* More stretched myofibrils => more powerful contract => incr ES pressure

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3
Q

Explain graphic display of Frank Starling

A
  • Y axis: parameter of systolic function
    o CO, SV
    o LV Pressure
  • X axis: preload
  • Ascending limb: as EDV incr, generated pressure incr
  • Descending limb: beyond certain point => generated pressure decr with further incr in EDV
    o Diastolic ventricular interactions: dilated RV compress LV and impair its fct
    o Titin play a role => progressively detach from myosin filament if stretched too much
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4
Q

Effect of changes in venous return on frank Starling curve

A

incr venous return => incr preload => incr initial stretching
o Move up and down a single curve
o Slope defined by afterload and inotropic state

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5
Q

Effect of changes in contractility and afterload on frank Starling curve

A

change the slope of the curve
o incr afterload or decr contractility: shift down and R
 For given EDP = decr SV
o decr afterload or incr contractility: shift upward and L
 For given EDP = incr SV

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6
Q

Equation of blood flow

A

Blood flow (Q) = change in pressure/Resistance

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7
Q

What is the primary determinant of blood pressure in vascular system

A

Resistance to blood flow

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8
Q

What determines resistance to blood flow

A

Physical properties of system
o Radius, Blood viscosity, Length

Concentrated in microcirculation (arterioles)
R is inversely ∝ to body size
All animals have same # of large vessels
Small vessels w // connections incr in larger animals to accommodate > blood flow
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9
Q

Equation of SVR

A

BP/CO

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10
Q

Equation of resistance to blood flow

A

flow must be laminar, steady, cylindrical conduit, Newtonian viscosity
o Major variable: radius
 Regulated by balance of vasodilatory and vasoconstrictive effects
o Length is stable
o Blood viscosity not important variable

R = 8nL/pi *r4

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11
Q

Units of vascular resistance

A

1 dyne sec/m5 = 80 mmHg/L/min
o dyne sec/m5
o mmHg/L/min (Wood’s unit)

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12
Q

Coronary vascular resistance

A
  • Ao pressure/coronary flow
  • 2 major types of arterial vessels
    o Small resistance arterioles => major resistance to flow
    o Large conductance arteries => govern qty of blood arriving to resistance vessels
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13
Q

Peripheral resistance units

A
  • Peripheral resistance units (PRU)
    o Normal arteriovenous pressure difference = 100mmHg
    o Normal CO in Hu = 100ml/sec
    o TPR = 100/100 = 1PRU
     Vasodilation → ↓ pressure difference → ↓ TPR = 0.2PRU
     Vasoconstriction → ↑ pressure difference → ↑ TPR = 4 PRU
  • Pulmonary vascular resistance = PAP-LAP/CO
    o Normal arteriovenous pressure difference = 14mmHg
    o Normal CO in Hu = 100ml/sec
    o PVR = 14/100 = 0.14 PRU
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14
Q

Def conductance

A
  • Measure of blood through a vessel for given pressure difference
    o mL/sec/mmHg
    o Reciprocal of resistance
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15
Q

Determinants of conductance

A

o Vessel diameter: ↑ diameter → markedly ↑ conductance
 Larger vessels allow more rapid flow (laminar flow in center → ↑ velocity)
 2/3 of total systemic resistance from small arterioles

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16
Q

Arrangement of systemic circulation vs resistance

A
  • Series: arteries → arterioles → capillaries
    o Total resistance = R1 + R2 + R3…
  • Parallel: blood supply to organs
    o Total resistance = 1/R1 + 1/R2 + 1/R3…
    o Each tissue regulates its own blood flow independently
    o ↓ total resistance: higher amount of blood will flow vs single vessel
     Each vessel provides pathway = ↑ conductance
17
Q

Control of peripheral vascular resistance

A
  • Integrated control
    o Sympathetic outflow
     If ↓ → decr renin release => decr Ang II mediated vasoconstriction
    o Baroreflex activation
     Vasoconstrictive A1 adrenergic R
    o Low renal artery pressures + A1 adrenergic effect => stimulation of renin release by kidneys
    o Excessive incr in BP:
     Baroreflex inhibition of adrenergic system
     Endothelial regulation
  • Normal endothelium: vascular shear force stimulates NO release
  • Damaged endothelium: stimulate endothelin release  vasoconstriction
  • Diameter of arterioles control SVR
18
Q

Major mechanism of control of peripheral vascular resistance

A

o Vasoconstrictor R: 3 major vascular R
 incr intra¢ Ca2+ => arteriolar vasoconstriction
 Respond to neurogenic, neurohumoral or endothelial agonists
* A1 adrenergic vasoconstrictor system: NE from terminal neuron w adrenergic stimulation
* RAAS: Ang II is end product of renin release
* Endothelin: released from damaged endothelium
o Cyclic nucleotide vasodilatory system
 Inhibition of contraction w cGMP and cAMP: inhibit myosin light chain kinase that activate vascular contraction
 B adrenergic vasodilation:  cAMP
 NO: synthetized by endothelium   cGMP
o Endothelial control
 Endothelin
 ETB: vasodilation by NO release
 ETA: vasoconstriction

19
Q

Poiseuille’s law

A

Ratio of driving pressure to blood flow
* Motion of blood in tube depends on:
o Force applied (pression) at either side of the vessel
o Radius → MAJOR EFFECT
o Length
o Blood viscosity
* Applies for special conditions: steady laminar flow in cylindrical tube

Q = pir4PG/8nL

20
Q

Law of Laplace

A

Calculate force producing a stretch
* Amount of sarcomere stretch: also determined by
o Compliance of chamber
o Orientation of sarcomere p/r to the force
o # sarcomeres in series

21
Q

Which component has greatest effect on flow and resistance

A

 Internal diameter of arterioles (radius)

22
Q

Wall stress equation/units

A

develops when tension is applied to a CSA
Units: force/unit area
End diastolic wall stress (σ)
Pressure (P)
Radius (r)
Wall thickness (WT)

Sigma = P end diastolic * r end diastolic/2* wall thick end diastolic

23
Q

Particularities of pulsatile flow

A
  • Resistance is the primary but not the only factor determining flow
  • Impedance contributes to 15% of interference to flow
    o Factors: blood density, viscosity, Ao diameter, compliance, reflectance
  • SVR contribute to 85%
24
Q

Def impedance

A

Sum of external factors opposing LV ejection (closely related to afterload)

Frequency dependent resistance
* Closely related to afterload
o Ao impedance is an index of afterload
 = Ao pressure/Ao flow
 Varies continuously during ejection

  • Ao impedance: index of afterload
25
Q

Factor determining impedance

A
  • Determined by physical properties of arterial wall and blood:
    o Blood density/viscosity
    o Ao diameter
    o Ao wall viscoelasticity
    o Reflected flow
    o Pressures in distal aterial system
26
Q

Def compliance and equation

A
  • Elastic behavior of vessel/chamber
  • Changes in volume in response to transmural pressure
    C = change volume/change pressure
  • Reciprocal to stiffness
27
Q

Determinants of compliance

A

elasticity of constituents
Elastic: elastic fibers + smooth muscle ¢
Non elastic: collagen

Mechanical behavior: influenced by interconnections of constituents
Simple elastical substance: force ∝ to distension
Blood vessels: become stiffer as they distend => 2nd to stiffness of collagen
28
Q

Def inertance

A
  • Force required to initiate mvt of blood => inertia
29
Q

Def reflectance

A
  • Backward reflection of pressure and flow waveforms
    o From branching sites of vasculature => abrupt change in vessels diameter
     From decr diameter of Ao
    o > force against which ventricle eject
  • Wave observed at any point: sum of forward + retrograde wave
30
Q

What is Bernoulli equation

A

Used to calculate transvalvular pressure gradient
* Constant volume of blood moved through orifice/vessel => pressure incr proximal to obstruction => proportional incr in blood flow velocity
o incr in kinetic energy, decr potential energy
* Pressure gradient = convective acceleration + flow acceleration + viscous friction
o Forces of viscous friction and flow acceleration are negligible
o Value of 1/2(p) = mass density of blood = 4
* Greatest application to measure severity of valvular stenosis

31
Q

modified Bernoulli equation

A

overestimate to a small degree when compared to cardiac KT gradients

Calculates instantaneous PG
* Peak to peak PG determined by calculating the difference btwn:
o Max LV pressure vs max Ao pressure
o Not at the same time
o Anesthesia: decr PG by 40-50%
* Doppler PG: calculate instantaneous pressure difference btwn Ao and LV pressure
o 30-40% higher vs invasive measurement
* More severe the stenosis: closer peak to peak and instantaneous pressure
o Highest LV pressures occur later in systole.

32
Q

Limitations of Bernoulli

A
  • Blood volume: will affect flow velocity
    o PG calculation inaccurate if high flow state => creates a high proximal velocity (V1)
    o Regurgitation through valve or stenotic region
     AI, AS, shunt, anemia, sepsis
  • HR, blood pressure and contractility can also affect
    o Sympathetic stimulation can incr PG
  • Tunnel lesions: overestimate PG => friction no longer insignificant
  • Blood viscosity: decr blood viscosity overestimate, incr blood viscosity underestimate PG
    o Not accurate when:
     Large intercept angle
     V1 is not negligible: high flow state or small PG
  • Simplified may be more accurate
33
Q

Reynold’s # equation

A

= 2rvp/n

describe relationship of cardiac murmurs to vessel size, flow velocity, blood viscosity.
 = radius x velocity x density/viscosity
 Critical number: 2300

34
Q

Define laminar flow

A

all fluid layers move in longitudinal direction
* Central velocity: most rapid motion
* Progressively decr toward tube’s walls
* Velocity profile => parabolic

35
Q

Def turbulent flow

A

disturbed laminar flow
* Can occur at sharp bends or obstructions

36
Q

Factors incr blood flow turbulence

A

o incr blood flow velocity
o decr viscosity
o Abrupt incr radius

37
Q

Turbulent flow causes

A

HM

38
Q
A

4. Physiology and pathophysiology (18 decks)

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