respiratory mechanics

Question 1

chest wall relationship with lung

Answer 1

chest wall has tendency to spring outwards while lung recoils inwards

Question 2

when are forces in equilibrium

Answer 2

end-tidal respiration (neutral position of intact chest)

Question 3

inspiration: relationship with muscle effort and chest recoil vs lung recoil

Answer 3

inspiratory muscle effort + chest recoil out > lung recoil in

Question 4

expiration: relationship with muscle effort and lung recoil vs chest recoil

Answer 4

expiratory muscle effort + lung recoil in > chest recoil out

Question 5

what pleura are lungs surrounded by

Answer 5

visceral pleura

Question 6

what pleura is chest wall covered in

Answer 6

parietal pleura

Question 7

what is in between the two pleuras

Answer 7

pleural cavity and fixed-volume fluid, with a double-folded layer to allow both surfaces to work together. meaning 2 pressure gradients (pleura and alveoli, which affects size of alveoli, and alveoli and atmosphere, which affects direction and rate of flow)

Question 8

mechanics of ventilation: inspiration

Answer 8

diaphragm contracts to flatten, while ribs move upwards and outwards → parietal pleura pulled away from visceral → wider space so lower intrapleural pressure → pressure gradient between alveoli and plerual space widens, so alveoli inflate → intralveolar pressure drops → air flow into alveoli from atmosphere

Question 9

Palv, Patm and Ppl at rest (cmH2O)

Answer 9

0, 0, -5

Question 10

P[TT; intrapleural space - transthoracic atmospheric], P[TP; intra-alveolar - intrapleural] and P[RS; intra-alveolar - respiratory atmosphere] at rest (cmH2O)

Answer 10

-5, 5, 0

Question 11

pressure/volume relationships (sigmoid-shaped graph)

Answer 11

at no external pressure from intercostals and diaphragm, small change in pressure causes large change in volume; at extremes, a large change in pressure required to effect a change in volume

Question 12

forced exhalation pleural pressure

Answer 12

increase in pleural pressure to -2 cmH2O, due to inward muscle force being larger than outward recoil force

Question 13

forced inhalation pleural pressure

Answer 13

increase in negative pressure (becomes more negative) to -8 cmH2O, due to outward muscle force being larger than inward recoil force, leading to pulling apart of the pleura

Question 14

effect of restrictive respiratory disease on pressure/volume relationships (sigmoid-shaped graph)

Answer 14

squashed reduced vital capacity so lower on graph; stretched with shallower curve because more effort to move air in; chest wall:lung interface less compliant

Question 15

effect of obstructive respiratory disease on pressure/volume relationships (sigmoid-shaped graph)

Answer 15

operates at higher volumes so higher on graph; smaller vital capacity as tissue is more compliant, so squashed with steeper curve

Question 16

mechanical forces involved in tidal breathing

Answer 16

75% due to diaphragm contraction and 25% external intercostals with passive recoil

Question 17

mechanical forces involved in maximal ventilation

Answer 17

accessory muscles and internal intercostals affect much larger change in volume, and hence gas exchange

Question 18

mechanical forces involved in fluid-filled lungs (surfactant)

Answer 18

fluid-water interface increases compliance (surface tension), so fluid-filled lungs expand under greater pressure

Question 19

mechanical forces involved in air-filled lungs

Answer 19

lack of fluid-water interface decreases compliance (no surface tension), so much larger change in pressure needed to inflate lungs

Question 20

mechanics of ventilation: expiration

Answer 20

diaphragm relaxes, while ribs move downwards and inwards → parietal pleura rejoins visceral → narrower space so higher intrapleural pressure → pressure gradient between alveoli and plerual space narrows, so alveoli deflate → intralveolar pressure increases → air flow out of alveoli into atmosphere