Lung Mechanisms

Question 1

what the forces for pulmonary ventilation

Answer 1

interrelationships among pressures inside and outside the lungs are important in ventilation

Question 2

what are the 3 different pressure considerations important in ventilation

Answer 2

• atmospheric
• intra-alveolar
• intrapleural

Question 3

what is Patm at sea level

Answer 3

760 mmHg

Question 4

when does Patm decrease

Answer 4

as altitude increases

Question 5

what is intra-alveolar pressure

Answer 5

pressure of air in alveoli
open system

Question 6

what happens to intra-alveolar pressure during respiration

Answer 6

inspiration - negative (less than atm)
expiration - positive (more than atm)

Question 7

what drives ventilation

Answer 7

difference between Palv and Patm

Question 8

what are the factors determining intra-alveolar pressure

Answer 8

quantity of air in alveoli
volume of alveoli

Question 9

what happens to Palv during inspiration

Answer 9

lungs expand -> volume increases + pressure decreases -> air into lungs
quantity of air in alveoli rises -> pressure increases

Question 10

what happens to Palv during expiration

Answer 10

lungs recoil -> volume decreases + pressure increases -> air out of the lungs
quantity of air in alveoli falls -> pressure decreases

Question 11

what is intra-pleural pressure

Answer 11

pressure inside the pleural sac
closed system

Question 12

what is Pip at rest

Answer 12

756 mm Hg = -4

Question 13

what is Pip compared to Palv

Answer 13

always less

Question 14

what Pip at normal conditions

Answer 14

always negative

Question 15

what is Pip negative pressure due to

Answer 15

elasticity in lungs and chest wall
- lungs recoil inwards
- chest wall recoils outwards
- opposing pulls on intrapleural space
- surface tension of intrapleural fluid hold wall and lungs together
- sub-atmospheric p - due to vacuum in the pleural cavity

Question 16

what affects pulmonary ventilation

Answer 16

lung compliance
airway resistance

Question 17

what is lung compliance

Answer 17

ease at which lungs can be stretched

Question 18

the less compliant the lungs are …

Answer 18

the more work is required to produce a given degree of inflation

Question 19

what is lung compliance affected by

Answer 19

elasticity (elastic recoil)
surface tension of lungs - type II cells produce surfactant to decrease surface tension

Question 20

what is airway resistance affected by

Answer 20

passive forces
contractile activity of smooth muscle
mucous secretion

Question 21

what is FRC

Answer 21

functional residual capacity
volume of air in lungs between breaths (at rest)

Question 22

what is flow

Answer 22

flow = Patm - Palv/R

Question 23

what is boyle’s law

Answer 23

pressure is inversely related to volume in an airtight container

Question 24

what are the mechanics of breathing

Answer 24

• Flow = Patm - Palv / R
• atmospheric pressure constant (during breathing cycle)
• therefore, changes in alveolar pressure create/change gradients
• Boyles Law: pressure is inversely related to volume in an airtight container (closed system)
• thus - can change alveolar pressure by changing it’s volume
• R = resistance to air flow
  
  • resistance related to radius of airways and mucus

Question 25

what muscles are at work during inspiration

Answer 25

diaphragm external intercostal

Question 26

what happens to the diaphragm during inspiration and what is the outcome

Answer 26

lowering of the diaphragm on contraction increases vertical dimension of thoracic cavity

Question 27

what happens to the external intercostals during inspiration and what is the outcome

Answer 27

contraction of external intercostal muscles causes elevation of ribs which increases side-to-side dimension of thoracic cavity

Question 28

what happens to the bones during inspiration and what is the outcome

Answer 28

elevation of ribs causes the sternum to move upward and outward, which increases front-to-back dimension of thoracic cavity

Question 29

what muscles are involved in expiration

Answer 29

diaphragm internal intercostal muscles abdominal muscles

Question 30

what happens to the diaphragm during expiration and what is the outcome

Answer 30

return of diaphragm to resting position on relaxation of inspiratory muscles restores thoracic cavity to preinspiratory size

Question 31

what happens to the bones during expiration and what is the outcome

Answer 31

return of ribs and sternum to resting position on relaxation of inspiratory muscles restores thoracic cavity to preinspiratory size

Question 32

what happens to the internal intercostal muscles during expiration and what is the outcome

Answer 32

contraction of the intercostal muscles flattens ribs and sternum, further reducing side-to-side and front-to-back dimensions of the thoracic cavity

Question 33

what happens to the abdominal muscles during expiration and what is the outcome

Answer 33

contraction of abdominal muscles causes diaphragm to be pushed upward, further reducing vertical dimension of thoracic cavity

Question 34

when is the work of breathing increased

Answer 34

- when pulmonary compliance is decreased - when airway resistance is increased - when elastic recoil is decreased when there is a need for increased ventilation (COPD)

Question 35

what is TV

Answer 35

tidal volume - the amount of air that moves in and out of the lungs with each respiratory cycle - approx 500ml

Question 36

what is IRV

Answer 36

inspiratory reserve volume - the maximal amount of air that can be inspired after a normal quiet breath - approx 3000ml

Question 37

what is IC

Answer 37

inspiratory capacity - the maximal volume of air that can be inspired at the end of a resting respiration - IC = TV + IRV - approx 3500ml

Question 38

what is ERV

Answer 38

expiratory reserve volume - the maximal amount of air that can be expired after a normal expiration - approx 1000ml

Question 39

what is RV

Answer 39

residual volume - the amount of air that remains in the lungs constantly and cannot be expired - approx 1200ml

Question 40

what is FRC

Answer 40

functional residual capacity - the amount of air that remains in the lungs after a tidal expiration - the volume of air in the lungs at rest between breathes - FRC = ERV + RV - approx 2200ml

Question 41

what is VC

Answer 41

vital capacity - the maximal volume of air that can be expired after a maximum inspiration - VC = TV + IRV + ERV - approx 4500ml

Question 42

what is TLC

Answer 42

total lung capacity - TLC = TV + IRV + ERV + RV - approx 5700ml