Lung mechanics 1

Question 1

Inspiratory muscles

Answer 1

Obligate: diaphragm, external intercostal, scalenes, parasternal intercostal
Accessory inspiratory muscles: neck muscles e.g. sternocleidomastoid

Question 2

Expiratory muscles

Answer 2

Internal intercostal, rectus abdominis, external oblique, internal oblique, transversus abdominis

Question 3

Why pressure in the pleural cavity negative even before inspiration and after expiration

Answer 3

elastic recoil of lungs

Question 4

Transmural pressure derivation

Answer 4

PL(transpulmonary pressure/distending pressure that inflates lung)=PA-PPL
Prs(transtotal pressure)=PA-PB
PW(trans chest wall pressure)=Ppl-PB

Question 5

Intrapleural pressure

Answer 5

negative during inspiration. Opposes elastic recoil of heart

Question 6

Transpulmmonary pressure

Answer 6

Pressure difference between intrapleural and alveolar pressure. High PL makes inspiration difficult. Holds lungs opem

Question 7

What lung volume can’t be measured directly by spirometry?

Answer 7

TLC, FRC, RV

Question 8

Define IRV, ERV, IC, TLC, FRC, RV

Answer 8

IRV-amount extra you can breathe in after normal breath in
ERV-amount extra you can breathe out after normal breath out
IC-max amount you can breathe in after tidal volume exhalation
TLC–from 0 air to max inhalation
FRC–amount you have left after tidal volume exhalation
RV-amount you can’t breathe out even after max exhalation

Question 9

dead space

Answer 9

airway volume with no gas exchange

Question 10

Physiologic dead space equaion

Answer 10

Physiologic=Alveoli (all except anatomic and respiratory bronchioles)+alveolar

Question 11

Flow equation

Answer 11

Flow=change in pressure/resistance

Question 12

Minute ventilation equation

Answer 12

Minute ventilation=tidal volxFrequency

Question 13

Dead space ventilation equation

Answer 13

Anatomic dead spacexfrequency

Question 14

Alveolar ventilation equation

Answer 14

Alveolar ventilation=minute ventilation-dead space ventilation

Question 15

Obstruction to inspiration

Answer 15

elastic resistance. Lung compliance (stretchiness)=change in lung vol/change in transmural gradient
Airway resistance=(alveolar pressure-mouth pressure)/airflow at mouth). Determined by turbulence

Question 16

How to apply poiseulle’s law for airway narrowing

Answer 16

Flow=change in pressure/Resistance

Resistance=8VL/pir^4. If radius halved, resistance increases 16 foldds and flow reduced to 1/16

Question 17

Why small distal airways have low resistance

Answer 17

individually higher resistance but large number in parallel decreases resistance

Question 18

What effects airway flow

Answer 18

Factors within airways e.g. smooth muscle tone (CO2 relaxes, NANC relax), inflammation
Pressure across airway wall

Question 19

Draw a breathing cycle with numbers for each compartment

Answer 19

ref. notes

Question 20

What does intrapleural pressure do in forced expiration

Answer 20

dynamic compression of airways around bronchi generation 3/4