Pulmonary Mechanics: Dynamics of Breathing

Question 1

which direction is flow during inspiration and how does this reflect alveolar pressure?

Answer 1

it is negative and has the same shape of the curve as the alveolar pressure

Question 2

during eupnea how much time is spent during inspiration and expiration?

Answer 2

inspiration 1/3 of time and expiration 2/3

Question 3

what is the tidal volume of the lungs? what is the functional residual capacity?

Answer 3

0. 5 L

2. 5L

Question 4

what pressure drives the airflow and what pressure sets the lung volume?

Answer 4

alveolar pressure-airflow

pleural pressure-volume

Question 5

what is the value of Palv at the beginning and end of inspiration and expiration? what is the flow?

Answer 5

both are 0

Question 6

how much does the alveolar pressure change to get to max inspiration? what percentage of total pressure is that?

Answer 6

1 cm H2O

0.1% change from atmospheric

Question 7

what is the lung pressure?

Answer 7

the transmural pressure across the lung

P alv-P pl

Question 8

what does contraction of the diaphragm do to the pleural pressure and the lung pressure?

Answer 8

it makes the pleural pressure more negative and increases the transmural lung pressure

Question 9

why is the pleural pressure curved and not a straight line during breathing?

Answer 9

because there is a need for extra pressure to overcome frictional tissue and airway resistance

Question 10

when is frictional tissue and airway resistance a consideration?

Answer 10

only when air is flowing

Question 11

what can happen to the intrapleural pressure during exercise expiration that does not happen during eupnea?

Answer 11

it can become positive

Question 12

what is the mechanical equilibrium position of the respiratory apparatus compared to the vital capacity?

Answer 12

it occurs at 36% of the vital capacity

Question 13

at functional residual capacity, how do chest pressure and lung pressure compare?

Answer 13

chest pressure is equal to the negative of lung pressure

Question 14

what does the compliance of the lung depend on?

Answer 14

the degree of inflation

Question 15

what is the difference between total compliance and lung compliance?

Answer 15

total compliance includes the pressure volume curve for the lung plus the chest wall (two compliances in series)

Question 16

what is total compliance near the resting position of the lung?

Answer 16

it is about 0.1 L/cm H2O

Question 17

how do the pressures recorded during the measurement of compliance compare to the pressures during breathing?

Answer 17

they are not the same- it becomes positive during the test

Question 18

what is the dynamic lung compliance?

Answer 18

the compliance obtained from measurements of change in volume and intrapleural pressure at end inspiration and expiration during breathing

Question 19

what happens to the dynamic lung compliance if there is abnormally increased resistance? what disease may cause this?

Answer 19

the C dyn will be less than static compliance
less flow for a given pressure change
small airway disease

Question 20

does the dynamic compliance change with altered breathing rates?

Answer 20

no

Question 21

in small airway disease, when is the tidal volume decreased? why?

Answer 21

at an increased respiratory rate because of increased airway resistance

Question 22

when is the flow of air laminar and when is it turbulent in the bronchial tree?

Answer 22

it is laminar in the trachea but turbulent at each bifurcation

Question 23

what does turbulent flow in the lungs produce?

Answer 23

the sound of quiet respiration and surface roughness in the conductive zone

Question 24

what type of flows are seen in at bifurcations and the glottis?

Answer 24

eddy flow at bifurcations and orifice flow at the glottis

Question 25

describe orifice flow

Answer 25

there is turbulence after the stenosis of the flow reopens

Question 26

what is the equation for reynold's number? when does flow become turbulent?

Answer 26

Re= (density x velocity x diameter of tube)/ viscosity of air becomes turbulent at Re>3000

Question 27

what is reynold's number in the trachea? what creates the noise of flow in this part of the airway?

Answer 27

1800 | geometrical irregularities account for the sound

Question 28

how does bronchitis change the sound of breathing?

Answer 28

it increases surface roughness due to the altered geometry

Question 29

what percentage of resistance to breathing is due to tissue resistance and which is due to airway resistance?

Answer 29

20% due to tissue and 80% due to airway

Question 30

where is airway resistance highest? where is it lowest?

Answer 30

highest in the nose or mouth | lowest in the bronchioles

Question 31

when can the bronchioles become a site of airway resistance?

Answer 31

in bronchitis

Question 32

what is tissue resistance and airway resistance? what causes them?

Answer 32

resistance from the motion of tissues (chest wall) resistance from the motion of the air both caused by viscous flow of either tissue or air

Question 33

when is tissue resistance increased?

Answer 33

in fibrotic disease

Question 34

how does replacing nitrogen gas with helium affect breathing?

Answer 34

helium has a slightly higher viscosity than nitrogen and a much lower density so it decreases turbulence and therefore work required for breathing

Question 35

what is the relationship of airway resistance as you move through the bronchial tree?

Answer 35

resistance increases for the first three bifurcations because the cross sectional area decreases. it then decreases as cross sectional area increases

Question 36

how does airway resistance compare to lung volume?

Answer 36

as lung volume increases, airway resistance falls

Question 37

why do inhaled particles settle out in small airways?

Answer 37

because the velocity of air moving through these areas is low

Question 38

why does it take considerable small airway disease before the measurement of total airway resistance would detect a problem?

Answer 38

because it affects the bronchioles where there is a large cross sectional area and therefore low resistance

Question 39

what receptors does epinephrine bind to in the smooth muscle of the airway?

Answer 39

high affinity beta 2 receptors

Question 40

what intracellular cascade causes epinephrine to decrease airway resistance?

Answer 40

increase of cAMP and stimulation of PKA | PKA phosphorylates MLCK and decreases its sensitivity for calmodulin

Question 41

what is the effect of decreasing the sensitivity of MLCK for calmodulin and how does it effect breathing?

Answer 41

it inhibits the activation of myosin to form cross bridges and contract the smooth muscle, relaxing it and opening the airway

Question 42

what is the typical value for airway resistance and what is its normal range?

Answer 42

typical value: 1.2 cm H20 sec/L | normal range: 0.5-1.5

Question 43

what factors reflexively cause constriction of the airway?

Answer 43

smoke particles, noxious gases and extreme cold

Question 44

how does the parasympathetic nervous system cause airway constriction?

Answer 44

the vagus nerve interacts with muscarinic receptors

Question 45

what effects does histamine have on the bronchi and blood vessels? what receptor mediates these effects?

Answer 45

it is a bronchoconstrictor but a vasodilator | H1 receptor

Question 46

how does airway resistance change in asthma?

Answer 46

inflammatory swelling of bronchial mucosa increases the airway resistance

Question 47

what does the positive end expiratory pressure do in patients on respirators?

Answer 47

decreases the airway resistance

Question 48

does breathing through the nose or mouth have greater resistance?

Answer 48

the nose

Question 49

how are isovolume pressure flow curves constructed?

Answer 49

by measuring flow rate, lung volume and alveolar pressure during a series of forced expirations of increasing vigor

Question 50

what do isovolume pressure flow curves demonstrate?

Answer 50

the dependence of flow on pressure at constant lung volume

Question 51

what is the trend of IVPF curves?

Answer 51

at low lung volumes, increasing driving pressure leads to a maximal flow rate and it increases with decreasing lung volumes

Question 52

when the flow is maximal what does V equal? how does it change with changing pressure?

Answer 52

change in pressure/resistance | it does not change with changing pressure so R and delta P must change in direct proportion

Question 53

what causes the increase in resistance with increasing alveolar pressure?

Answer 53

dynamic compression of the airways

Question 54

when is there deviation from Ohm's law during expiration?

Answer 54

when there is greater expiratory efforts, especially when there are low lung volumes

Question 55

where on the IVPF curve is there a plateau and where is there not?

Answer 55

there is not a plateau for inspiration but there is for expiration

Question 56

what is the equal pressure point?

Answer 56

the point between the alveolus and the mouth where the pressure inside the airway increases the intrapleural pressure

Question 57

what is the pressure downstream of the EPP (towards the mouth)? what occurs in this area?

Answer 57

downstream, airway pressure is less than intrapleural pressure. this is where dynamic compression occurs (partially collapsed airway)

Question 58

when is dynamic compression more pronounced and why?

Answer 58

low lung volumes because the lung is more compliant at low volumes

Question 59

what is the result of increased compliance on dynamic compression? what occurs when this person tries to forcibly exhale?

Answer 59

more of the airway will close during expiration, creating difficulty in exhaling if there is forced exhalation, the EPP will be closer to the alveoli and more of the airways will be compressed

Question 60

how can the alveolar pressure be maintained and compression prevented during expiration with low compliance lungs?

Answer 60

pursed lips breathing