Physiology

Question 1

What is the equation for velocity of blood flow?

Answer 1

V=Q/A

• *V**= velocity in cm/s
• *Q **= cardiac output/flow in mL/min
• *A **= cross sectional area of vessel

Question 2

What is the equation for CO/ blood flow?

Answer 2

Q = ΔP/R

“Ohm’s law” I = ΔV/R

• *Q **= flow/CO in mL/min
• *ΔP **= pressure in mmHg
• *R **= total peripheral resistance in mmHg/mL/min

Question 3

What is the Law of Laplace?

Answer 3

τ = Pr/2H

• *τ** = tension in vessel wall (or wall stress in ventricles)
• *P** = transmural pressure
• *r** = radius of vessel (or cavity for ventricle)
• *H** = wall thickness (negligble for capillaries)

Question 4

When can you apply the Law of Laplace? What is its clinical relevance?

Answer 4

Can be applied to vessels or ventricles

This law explains why LV thickens in response to high BP to decrease wall stress

Question 5

What is Poiseuille’s equation?

Answer 5

R = 8ηℓ/πr⁴

R = resistance
η = viscosity of blood
ℓ = length of blood vessel
r = radius of blood vessel

Question 6

What is the total resistance for a series arrangement?

Answer 6

R_T = R₁ + R₂ + R₃ …

Question 7

What is the total resistance for a parallel arrangement?

Answer 7

1/R_T = 1/R₁ + 1/R₂ + 1/R₃ …

Question 8

What is the difference between laminar flow and turbulent flow?

Answer 8

Laminar flow = streamlined, parallel to vessel

Turbulent flow = in axial/radial directions; it’s audible

Question 9

What is Reynbold’s number?

Answer 9

N_R = ρdv/η

• *N_R** = Reynold’s number
• *ρ** = density of blood
• *d** = diameter of blood vessel
• *v** = velocity of blood flow
• *η** = viscosity of blood

If <2000, blood flow usually laminar
If >3000, blood flow usually turbulent

Question 10

Why does decreasing the diameter of a blood vessel cause an increase in Reynold’s number?

Answer 10

It’s puzzling bc diameter is on top in Reynold’s number equation

But rememer that v = Q/A = Q/πr^2. This shows that velocity increases as radius decreases, which takes over because r is to the second power here. Therefore this effect is greater nd since v is also on top in the Reynold’s equation, as radius decreases, Reynold’s number increases.

Question 11

What is capitance?

Answer 11

C = V/P

C=capitance/compliance mL/mmHg
V=volume mL
P=pressure mmHg

Question 12

What is the meaning of capitance/compliance?

What is the result of changes in compliance?

Answer 12

Capitance describes the volume of blood that a vessel can hold at a given pressure… veins are more compliant bc they are less stressed: can hold more volume at lower pressure

Changes in compliance (i.e. due to vasoconstriction) cause redistribution of blood

Also loss of elasticity in arteries due to aging means that compliance decreases: at a given pressure, arteries hold less blood. So to hold the same volume of blood, bp must increase…this is how you get hypertension

Question 13

What is the relationship between CO, MAP, RAP, and TPR?

Answer 13

CO = (MAP - RAP)/TPR

• *CO** = cardiac output
• *MAP** = mean arterial pressure
• *RAP** = right atrial pressure
• *TPR** = total peripheral resistance

*Multiply by 80 to convert from mmHg min/L to dyne sec/cm⁵

Question 14

What is the Fick equation?

Answer 14

CO = O₂ consumption/([O₂]_PV - [O₂]_PA)

• *O₂ consumption** = O₂ use by body in mL O₂/min
• *[O₂]_PV** = O₂ content in pulmonary vein (mL O₂/mL blood)
  
  • *[O₂]_PA** = O₂ content in pulmonary artery (mL O2/mL blood)

Question 15

How do you calculate MAP? 3 equations

Answer 15

MAP = (SBP+2DPB)/3

MAP = DBP + (1/3)PP

MAP = DBP + (1/3)(SBP - DBP)

Question 16

What is the equation for pulmonary vascular resistance?

Answer 16

PVR= (MPAP-PCWP)/CO in L/min

Question 17

What is the Frank-Starling law?

Answer 17

SV increases in response to an increase in preload volume

Up to a point– bc when you overwhelm the system, pulmonary venous pressure increases & fluid leaks out of the capillaries –> impaired gas exchange

Question 18

Preload

Answer 18

Load on ventricle at end of diastole

Measures include: end diastolic volume, end diastolic pressure, end diastolic wall stress, venous return

Question 19

Afterload

Answer 19

Load on ventricle during ejection– determined by arterial system: force that LV must generate to eject blood

Measures: aortic pressure, total peripheral resistance, ejection wall stress

Question 20

Stroke volume

Answer 20

SV=EDV-ESV

EDV=end diastolic volume

ESV=end systolic volume

Question 21

Ejection Fraction=

Answer 21

EF= SV/EDV

Question 22

Pressure Volume Loop: ID the following:

SV, EDV, ESV, aortic valve open/close, mitral valve open/close, EDPVR, ESPVR, end systole, end diastole

Answer 22

A= ventricle fills until end diastolic volume (when P in LV>LA –> mitral valve closure) = S1

A–>B=isovolumic contraction

B= aortic valve opens when P LV>P aorta

B –> C = ejection phase

C= end of systole, when P in LV

C –> D = isovolumic reduction

D = diastole, ventricle starts to fill. When P LV < LA, mitral valve opens & ventricle starts to fill

Question 24

What happens to the PV-loop when you increase preload? Afterload? Contractility?

Answer 24

Question 25

What’s an inotrope?

What is the effect of inotropes on the ESPVR?

Answer 25

Inotropes alter the force of contraction by altering Ca release, affinity of myofilaments for Ca, or number of myofilaments available

Positive inotropes make the relationship steeper

Negative inotropes make the relationship less steep

This is an index of contractility– if you change contractility, the ESPVR changes