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VET 408: Cardio/Respiratory > Pulmonary Mechanics > Flashcards

Pulmonary Mechanics Flashcards

1
Q

total lung capacity (TLC)

A

sum of all lung volumes

MAXIMUM volume - after forced inspiration

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2
Q

tidal volume

A

volume moved in a normal breathing cycle

resting breath - NOT forced

small amount of TLC

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3
Q

residual volume (RV)

A

smallest volume possible in the lung inside of an intact chest

MINIMUM volume - after forced expiration

maintained by coupling of lung to chest wall

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4
Q

minimum volume (MV)

A

smallest volume possible in the lung of an open chest

absolute minimum value - requires uncoupling of lung to chest wall

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5
Q

inspiratory reserve volume (IRV)

A

the volume that can be moved during a forced inspiration up to total capacity

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6
Q

expiratory reserve volume (ERV)

A

volume that can be moved during a forced expiration down to residual volume

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7
Q

functional residual capacity (FRC)

A

volume left in the lungs at the end of a passive respiration

normal resting lung volume

maintained by equilibrium between inward lung recoil and outward chest wall recoil pressures (creates negative pressure)

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8
Q

what is the purpose of functional residual capacity

A

acts as a buffer of oxygen for gas exchange - prevents immediate hypoxia if you stop breathing

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9
Q

TLC equation

A

TLC = RV + ERV + VT + IRV

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9
Q

vital capacity (VC)

A

sum of all volumes in the lung that can be moved

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10
Q

IRV equation

A

IRV = TLC - VT

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11
Q

ERV equation

A

ERV = VT - RV

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12
Q

FRC equation

A

FRC = RV + ERV

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13
Q

VC equation

A

VC = VT + ERV + IRV

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14
Q

what drives air movement

A

pressure gradients (moves from high to low)

generated by the contraction/relaxation of inspiratory muscles

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15
Q

what are the inspiratory muscles

A

diaphragm and external intercostal muscles

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16
Q

inspiration

A

active process initiated by. the contraction of inspiratory muscles

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17
Q

steps of inspiration

A
  1. diaphragm and intercostal muscles contract, which increases the volume in the thoracic cavity
  2. increasing volume causes pressure inside thoracic cavity to drop, which decreases pressure in the pleural space and alveoli
  3. air moves from outside (high PB) to inside alveoli (low PA)
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18
Q

expiration

A

passive process initiated by the relaxation of inspiratory muscles

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19
Q

steps of expiration

A
  1. diaphragm and intercostal muscles relax, causing volume to decrease in thoracic cavity
  2. decreasing volume causes pressure to increase inside pleural space and alveoli
  3. air moves from inside (high PA) to outside (low PB)
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20
Q

how does expiration differ in horses

A

horses have ACTIVE end-expiration (contraction of expiratory muscles) during normal breaths

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21
Q

artificial ventilation

A

use of an external ventilator to generate positive pressure to force air into the lungs, causing an increase in pleural/alveolar pressure during inspiration

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22
Q

how does artificial ventilation differ from normal ventilation

A

pressure gradient is generated by an outside machine NOT by contraction of inspiratory muscles

causes pressure to increase in pleural space/alveoli during inspiration

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23
Q

what are the two mechanical properties of the airways and lungs

A
  1. elastic (compliance)
  2. resistance
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24
Q

compliance

A

the ease by which the elastic structures of the respiratory system stretch

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25
Q

what two components of the respiratory system determine compliance

A

chest wall
lungs

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26
Q

compliance equation

A

C = deltaV / deltaP

delta P: the pressure difference from beginning to end of breath

if C is high –> low pressure required to expand lungs
if C is low –> high pressure required to expand lungs

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27
Q

resistance

A

obstructions to air movement

USUALLY related to airway diameter

high resistance = more pressure required to inflate lungs

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28
Q

what two components of the respiratory system determine resistance

A

airways
tissues

29
Q

elastic properties of the lungs

A

strong inward recoil caused by:
1. elastic composition (elastin + collagen)
2. alveolar surface tension

30
Q

elastic properties of the chest wall

A

outward recoil due to relaxation at rest

31
Q

why do the lungs and chest wall have opposing elastic properties

A

coupling of the chest wall and the lungs generates a positive pressure gradient across the alveoli, which keeps the alveoli open

32
Q

what happens if the lung and chest wall become uncoupled

A

lung retracts/collapses, chest wall expands

causes a loss of the pressure gradient leading to inability to breath

33
Q

atelectasis

A

collapse of alveoli that causes a decrease in the amount of tissue available for gas exchange

34
Q

LaPlace’s law

A

P = 2T / r
(T = tension; constant
r = alveoli radius)

THEORY that low radius (small) alveoli should be higher pressure than high radius (large) alveoli, causing air to flow from small to large alveoli, which collapses the small and overinflation of the large alveoli

does NOT happen in normal lungs due to coupling of lungs to chest wall and production of surfactant

35
Q

surface tension

A

the tendency of fluid-lined surfaces to “contract” due to the greater attraction of liquid molecules to each other than to air molecules

present at all fluid-gas interfaces

THEORY - should cause alveoli to collapse, but does not happen due to surfactant production

36
Q

surfactant

A

phospholipid-protein-CHO complex that covers alveolar walls to reduce surface tension

acts as a detergent that lowers surface tension and minimizes the effects of La Place’s law by creating equal pressures in large and small alveoli

37
Q

is surfactant more effective at high or low lung volumes

A

lower lung volumes

38
Q

what would happen without surfactant

A
  • alveolar collapse
  • decreased compliance
  • pulmonary edema

requires external ventilation

39
Q

pressure-volume (PV) curves

A

graphs the pressure required to generate a certain amount of volume into the lung

40
Q

what is slope on a PV curve

A

compliance (C = deltaV / deltaP)

steep slope = higher compliance

shallow slope = lower compliance

41
Q

hysteresis

A

the difference between the inspiratory and expiratory path on the PV curve

caused by greater surfactant efficacy at lower lung volumes

42
Q

function of PV curves

A

asses changes in compliance

if slope is low: low compliance; more pressure needed to achieve normal lung volumes

if slope is high: high compliance; less pressure needed to achieve normal lung volumes

43
Q

what is total airway resistance determined by

A
  1. airway resistance
  2. tissue resistance
44
Q

where does the majority of airway resistance come from

A

upper airways; especially medium sized bronchi

small bronchioles have smaller radius BUT larger total cross sectional area, so less resistance

45
Q

in what scenario does tissue resistance affect the lungs

A

lung disease - makes the lungs heavier and more resistant to air flow

46
Q

what are the three airflow patterns

A
  1. laminar
  2. turbulent
  3. transitional
47
Q

laminar flow

A
  • normal, straight flow
  • LOW resistance
  • inner air is faster than outer air
48
Q

turbulent flow

A
  • disorganized flow
  • present in LARGE, HIGH VELOCITY airways and bifurcations/bends
  • HIGH resistance
49
Q

transitional flow

A

combination of laminar and turbulent flow

common in airways due to bifurcations

50
Q

ohm’s law

A

R = deltaP / Q

calculates resistance as a function of pressure gradient and volume

51
Q

poiseuille’s law

A

Q = (deltaP x pi x r^4) / 8nL

calculates flow as a function of pressure gradient, radius, viscosity, and airway length

52
Q

what is the main determinant of air flow

A

RADIUS (airway diameter)

53
Q

Reynold’s number

A

Re = 2rvd / n

determines when flow changes from laminar to transitional to turbulent

54
Q

what causes an increase in reynolds number

A

increases in radius, velocity and density

more likely to become TURBULENT

55
Q

what causes a decrease in reynolds number

A

increases in viscosity

less likely to become turbulent

56
Q

how does the ANS affect airflow

A

controls airway radius by innervating bronchial smooth muscle

SNS: B2 receptors –> bronchodilation (dec. resistance)

PNS: muscarinic receptors –> bronchoconstriction (inc. resistance)

57
Q

how does lung volume affect airflow

A

increases in lung volume = expands lungs = opens/dilates airways = decreases resistance = increases flow

58
Q

what are the 5 factors affecting resistive properties

A
  1. radius of airways and gas viscosity
  2. artificial airway radius (ET tube size)
  3. flow pattern - turbulent vs laminar (reynolds number)
  4. lung volume
  5. ANS innervation
59
Q

dynamic airway obstruction

A

obstructions to airflow that change based on inspiration or expiration

ex. collapsing trachea

60
Q

what part of respiration is affected by an extra thoracic collapsed trachea

A

inspiration

61
Q

what part of respiration is affected by an intra thoracic collapsed trachea

A

expiration

62
Q

pressure gradients throughout respiratory cycle

A
  1. pre-inspiration (FRC): negative pressure in pleural space, 0 pressure in airways - POSITIVE PRESSURE GRADIENT
  2. inspiration: air flow follows positive pressure gradient from airways –> alveoli
  3. forced expiration: contraction of expiratory muscles increases pleural pressure (positive pleural pressure > airway pressure), leads to a normal decrease in airway diameter
63
Q

total work of breathing

A

elastic work + resistive work

increased WOB = high elastic work (low compliance) + high resistance

64
Q

what is elastic work

A

compliance

influenced by LUNG VOLUME
(high vol = high elastic work = dec. compliance)

65
Q

examples of states with decreased compliance (increased elastic work)

A

obestiy
pneumonia

66
Q

what is restrictive work

A

airway resistance

influenced by RESPIRATORY RATE - tries to decrease total WOB

(high RR = high RW = high resistance)

67
Q

breathing at resting state

A

animal breathes at the rate and volume that results in the lowest WOB

68
Q

breathing in states of increased elastic work (decreased compliance)

A

animal will increase RR and decrease lung volume to achieve the lowest total WOB

69
Q

breathing in states of increased resistive work (increased resistance)

A

animal will decrease RR and increase lung volume to achieve the lowest total WOB

(ex. lower airway disease)

VET 408: Cardio/Respiratory (38 decks)

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