Lecture 13: Mechanics of Ventilation 2

Question 1

what mechanical factors can limit an animals ability to maximise its tidal volume?

Answer 1

airway resistance
compliance
elasticity

Question 2

what equation describes the influences on the rate of airflow?

Answer 2

F = DP/R

F = Airflow rate
DP = pressure gradient/change in pressure
R = airway resistance

Question 3

is the combined cross sectional area of smaller bronchi greater or less than that of larger airways? what does this mean

Answer 3

greater than that of larger airways

==> lower resistance in small than large airways

Question 4

what is the narrowest part of the upper airway?

Answer 4

the larynx

Question 5

the tendency of the upper airways such as the trachea and larynx to collapse during inspiration is rested how?

Answer 5

cartilaginous support
muscular action: flaring of the nostrils, tensor muscles of pharyngeal walls, abduction of arytenoid cartilages, tracheal cartilages

Question 6

what are some pathological disorders restricting airflow?

Answer 6

• facial nerve paralysis
• displacement of soft palate - horses
• elongated soft palate - brachiocephalic dogs
• laryngeal hemiplasia (horse, dog)
• collapsing trachea (dog)

Question 7

what implications does obstruction of the upper airways have?

Answer 7

obstruction of upper airway = increased respiratory effort on inspiration and expiration = greater DP to gain O2 and expel enough CO2

• usually okay at rest (large reserve capacity of the lung) but issue at exercise
• • anaesthetised patient may not be able to maintain patency

Question 8

in health how is airway size and thus resistance to flow maintained within the lower airways?

Answer 8

ANS

• bronchoconstriction by parasymp
• bronchodilation by sympathetic

Question 9

what may cause increased resistance within the lower airways?

Answer 9

bronchoconstriction
excessive production of mucus
oedema of bronchial walls

Question 10

bronchiolar walls are not supported by cartilage, how do they prevent collapse?

Answer 10

maintenance of transmural pressure gradient –> lower pressure maintained in pleural cavity

Question 11

how does air become trapped in alveoli during exercise?

Answer 11

intrapleural pressure may rise above intraluminal pressure of the small airways => collapse of small airways at end of expiration = air trapped in alveoli

Question 12

how does air become trapped in alveoli in obstructive airway disease?

Answer 12

intrapleral pressure may rise above intraluminal pressure at the beginning of expiration –> premature collapse and reduced O2 transfer with atmosphere

Question 13

what is pulmonary compliance?

Answer 13

a measure of the distensibility of the lungs and thorax

less compliant lung = more work required to inflate it

Question 14

how is pulmonary compliance reduced?

Answer 14

reduced by disease (fibrosis) or increased alveolar fluid surface tension

Question 15

what is surface tension? in what circumstance/interface are molecules strongly attracted to each other?

Answer 15

results from attracting forces between atoms or molecules
at air water interface water molecules more strongly attracted to eachotehr than to air = resist forces that increase surface area

Question 16

what is a surfactant?

Answer 16

surface-active substance for which water molecules have less attraction, reducing surface tension

Question 17

what is a pulmonary surfactant

Answer 17

reduces tendency of alveoli to collapse, increases pulmonary compliance
keeps lungs dry

Question 18

what is an example of a pulmonary surfactant?

Answer 18

phospholipoprotien

Question 19

what is Laplaces law describe collapse of a small bubble?

Answer 19

P = 2T/R
P = collapsing pressure
T = surface tension
R = radius

Question 20

is a smaller or larger alveolus more likely to collapse

Answer 20

small alveolus should have greater tendency to collapse over large alveolus with same surface tension
HOWEVER, surfactant decreases surface tension of small alveoli, more than that of large alveolus.

Question 21

when does deficiency of pulmonary surfactant occur? what are the consequence of this?

Answer 21

can occur in newborn animals (horse and pig) and premature humans
more work is required to overcome greater alveolar surface tension, O2 rich environment helps by reducing amount of ventilation

Question 22

what is tidal volume?

Answer 22

the amount of air that enters the lung during normal inhalation at rest = 500mL

Question 23

what is residual volume

Answer 23

the amount of air that remains in a persons lungs after fully exhaling - 1.2L

Question 24

what is inspiratory reserve volume?

Answer 24

additional volume of air that can be inspired above resting tidal volume = 3L

Question 25

what is expiratory reserve volume?

Answer 25

extra volume of air that be actively expired beyond that normally passively expired - 1 L

Question 26

what is inspiratory capacity

Answer 26

maximum volume of air that can be inspired after a normal quiet expiration IC = IRV + TV = 3.5 L

Question 27

what is functional residual capacity?

Answer 27

volume of air in lungs at end of normal passive expiration = ERV + RV = 2.2 L

Question 28

what is vital capacity?

Answer 28

maximum volume that can be expired following maximal inspiration = IRV + TV + ERV = 4.5 L

Question 29

what is total lung capacity?

Answer 29

VC + RV = 5.7 L

Question 30

what is forced expiratory volume?

Answer 30

maximum volume of air that can be expired during first second after maximal inspiration, usually 80% of VC

Question 31

how does obstructive airway disease influence RV and VC

Answer 31

premature collapse => trapping of air at end of maximal expiration = increased Residual Volume, Reduced Vital Capacity

Question 32

restrictive lung disease causes loss of lung compliance, what does restrictive lung disease impact?

Answer 32

total lung capacity