5) Darcy in Clinical, Energy, & Power

describe darcy’s law when applied to the cardiovascular system

CO = (MAP - CVP) / SVR

each organ’s blood supply is arranged in ________ thru capillary bed

parallel

overall resistance to blood flow of entire cardiovascular system is ________

additive

arteriolar/bronchiole resistances are in ________

parallel

what’s the organ with its portion of blood flow in series?

liver via portal vein

what’s an example of laminar flow in the body?

RBCs bc they align themselves in center of blood vessel

what’s an example of turbulent flow in the body?

aorta, ventricles due to large diameter, narrowing portions, sharp turns, angles, and high velocity

laminar flow

turbulent flow

critical RE exceeded

when does blood flow turn from laminar to bolus flow?

capillaries → single file

as heart does ________ work to pump blood thru vasculature, network ________ is overcome

mechanical, resistance

________ energy is converted into ________ energy of flowing blood

metabolic, kinetic

the right and left side CO is ________

equal

compare the work of the right and left ventricles

RV does 1/5 of work of LV

event at 1

mitral valve closes and full heart begins to contract

event at 2

aortic valve opens

event at 3

aortic valve closes

event at 4

mitral valve opens

ΔV from 2 to 3

stroke volume = ejection

point 4 to 1

filling

point 1 to 2

isovolumetric contraction

point 3 to 4

isovolumetric relaxation

in the cardiac pressure-volume loop, what is represented by the area within the loop

stroke work

what does this pressure-volume loop show?

increased preload (increased volume or pressure before blood gets to heart)

what does this pressure-volume loop show?

increased afterload (increased resistance due to high BP or aortic stenosis)

what does this pressure-volume loop show?

increased contractility (ex: exercise, CHF)

2 types of resistance in lungs

airway resistance and tissue resistance of lungs and chest wall

airway resistance is caused by…

friction between gas molecules and airway wall

pulmonary tissue resistance is caused by…

friction encountered in lungs as tissues move against each other during expansion

what % of total lung resistance is due to tissue resistance?

20%

what % of total lung resistance is due to airway resistance?

80%

what structures cause upper airway resistance?

how much of the total resistance does it take up?

nose, turbinates, nasopharynx, oropharynx, larynx

25-40%

what structure causes lower airway resistance?

tracheobronchial tree

what are the major factors determining airway resistance?

small and medium size airways

upon inhalation, airway resistance ________ because the tethering effect causes radius to ________

decreases, increase

define tethering effect

mechanical outward pulling force exerted by the alveolar walls and elastic fibers on the outer walls of small airways

upon exhalation, airway resistance ________ because the tethering effect causes radius to ________

increases, decrease

what keeps airways from collapsing?

elastic recoil (traction from connective tissue)

what keeps alveoli open?

pressure gradient (peep)

what does PEEP stand for?

positive end expiratory pressure

in medium size airways., what influences cross sectional area?

smooth muscle tone

what alters smooth muscle tone?

autonomic nervous system

when PEEP is too low, ____ pressure will be needed to re-expand alveoli

more

how is resistance in the airway overcome?

pressure

how does rapid breathing cause hypoxia?

rapid breathing = more turbulence = more power to maintain flow rate = increased energy consumption by respiration muscles = higher O2 demands that can surpass O2 supply

what conditions can cause alterations to airway resistance?

bronchiole dilation/constriction, lung disease (COPD), pleural effusions, pulmonary edema

conditions that change airway resistance have a significant effect on…

work of breathing and ability to distribute gas throughout the lungs

a majority of airway resistance is due to…

changes in airway radii

major site of resistance in tracheobronchial tree is in…

1st six generations

disease involving central airways has ________ impact on total resistance of lung

greatest

in terms of reynold’s number equation, turbulent flow occurs when…

high velocity, high density, large radius, low viscoity

during exhalation, velocity of airway through the trachea is ________ when compared to bronchioles and alveoli

greater

because airways are in parallel, total resistance is ____ than the sum of individual' airways’ resistances

less

why is He-O₂ used clinically?

decreased density = decreased resistance = decreased likelihood of turbulent flow

opposite of compliance is…

elastance

compliance equation

C = change in volume / change in pressure

define compliance

tendency of blood vessels, airways, or the breathing circuit to become distended by an inflating force (pressure)

what does the slope of the line represent?

compliance

the _________ the slope, the more compliant

steeper

how much is system compliance in mL?

6.667mL/cmH2O

how do you calculate compliance lost to the system?

multiple system compliance and peak pressure (at end of inspiration)

how to calculate how much Vt a patient receives?

Vt delivered - compliance lost by system

why do you not have to worry about calculating compliance lost to the system?

new machines compensate for it

what happens in phase 1 of filling the 3L breathing bag?

3L capacity achieved

what happens in phase 2 of filling the 3L breathing bag?

pressure peaks

what happens in phase 3 of filling the 3L breathing bag?

pressure plateaus or decreases despite increasing volume

why is phase 3 of filling the 3L breathing bag beneficial?

ceiling effect provides minimal protection against high airway pressures in the patient’s lungs if APL left closed with FGF on

why is too high of pulmonary compliance a bad thing?

elastic coil is diminished so exhalation muscles do more work

why is too low of pulmonary compliance a bad thing?

work done to inhale is increased

patients with emphysema have too ____ of compliance and too ____ elastance

high, low

low compliance requires ________ pressure to achieve same volume

higher

examples of low compliance states

atelectasis, fibrosis, edema, pneumonia, surfactant deficiency

define the time constant of lung filling and what it is normally

time necessary to inflate a particular lung region to 63% of its capacity. 0.2 sec

how to calculate time constant for how well gas is moved in and out of alveoli

multiply resistance and compliance

because alveoli are all different, it takes different time for each one to fill and they have ________ time constants

unequal

work equation

W = force x distance

units of work

newton meters or joules (electrically)

define thermal energy

energy of vibrating molecules

define sound energy

energy transferred by mechanical vibration of air molecules in a wave manner

what is extracorporeal shockwave lithotripsy (ESWL)?

using ultrasound shock waves to crush urinary stones for easier elimination

define elastic energy

potential energy stored in deformed or stretched material

efficiency equation

Efficiency = (energy output / energy input) x 100%

define power

the rate at which work is done or energy is transferred

power equation

P = work / change in time where work = change in pressure x change in volume

where is CVP transduced?

junction of superior vena cava and right atrium

MAP equation

MAP = (2 x DBP + SBP) / 3

highest resistance in the airway is at level of ________

arterioles

what percent of metabolic energy is converted to mechanical energy by the heart and where does the rest go?

10%, the rest is lost as heat

what’s mechanical output of the heart at rest?

1.3W

how much energy does the heart need to power it at rest?

13W

during quiet breathing, flow is ________ in trachea and ________ in small peripheral airways

turbulent, laminar

why is turbulent flow better at purging contents of a tube?

its pressure front is a square not a cone