Ventilation and Compliance 3,4/ Surfactant, Compliance and lung function tests

Question 1

which cells produce surfactant?

Answer 1

Type 2 alveolar cells (pneumocytes)

Question 2

what does surfactant do to surface tension?

Answer 2

reduces it, thus reducing tendency for alveoli to collapse

Question 3

what is surface tension?

Answer 3

where there is an air-water interface, and refers to the attraction between water molecules

Question 4

what does surfactant physically do to the lung?

Answer 4

increases lung compliance (distensibility), reduces lung’s tendency to recoil (makes breathing easier)

Question 5

in which alveoli are surfactant molecules more effective ?

Answer 5

is small alveoli because it is more concentrated (larger alveoli don’t need to have their surface tension reduced by as much to prevent collapse because they have a bigger radius, and pressure is proportional to 2T/r with T= surface tension and r= radius)

Question 6

when does surfactant production start and end?

Answer 6

starts at about 25 weeks gestation and ends at about 36 weeks gestation

Question 7

which hormones stimulate surfactant production?

Answer 7

thyroid hormones and cortisol

Question 8

how does the production of these hormones vary throughout pregnancy?

Answer 8

they increase at the end of pregnancy

Question 9

what do premature babies therefore suffer from?

Answer 9

Infant Respiratory Distress Syndrome (IRDS)

Question 10

why are lungs not inflated with air in utero?

Answer 10

to prevent an air-water interface (no surface tension), so the lung can inflate while requiring less pressure (no need to overcome surface tension)

Question 11

what is compliance?

Answer 11

change in volume relative to change in pressure (how much does volume change for any given change in pressure), represents the stretchability (not elasticity, which refers to capability to return to original shape)

“the pressure required to inflate the lungs must overcome the airway resistance and expand the elastic elements of the chests as measured by compliance/ determined by elastic forces, surface tension at the alveolar air-liquid interface and by airway resistance”

Question 12

what does a high compliance refer to in terms of variation of lung volume per variation in ip (intrapleural?) pressure

Answer 12

large increase in lung volume for small decrease in ip (intrapleural?) pressure

Question 13

what does a low compliance refer to in terms of variation of lung volume per variation in ip (intrapleural?) pressure

Answer 13

small increase in lung volume for large decrease in ip (intrapleural?) pressure

Question 14

what factors affect compliance?

Answer 14

disease states and age

Question 15

which required greater change in pressure (= greater effort)? inspiration (reaching a particular lung volume) or expiration (maintaining that volume)

Answer 15

it requires a greater change in pressure (from FRC) to reach a particular lung volume during inspiration than to maintain that volume during expiration

Question 16

expiration/ inspiration- which requires most effort in a healthy person?

Answer 16

effort (work) of inspiration is recovered as elastic recoil during expiration and in a healthy person, expiration is passive (no effort)

Question 17

what do you call the loss of elastic tissue in ventilation mechanism? what is the consequence of this?

Answer 17

emphysema means expiration requires effort

Question 18

what consequences does fibrosis have on fibrous tissue? on ventilation?

Answer 18

inert fibrous tissue means effort of inspiration increases (decreased compliance)

Question 19

where is alveolar ventilation greatest? how does it vary throughout the lung?

Answer 19

alveolar ventilation declines with height from base to apex (greater at base)

Question 20

where is compliance greatest? how does it vary throughout the lung?

Answer 20

compliance declines with height from base to apex (greater at base)

Question 21

what does the anatomy of alveoli have to do with compliance at the base of the lung?

Answer 21

at the base the alveoli are compressed between the weight of the lung above and the diaphragm below and hence more compliant on inspiration

Question 22

what does the anatomy of alveoli have to do with compliance at the apex of the lung?

Answer 22

at the apex, the alveoli are more inflated at FRC

Question 23

what are the characteristics of an obstructive lung disorder?

Answer 23

obstruction of air flow, especially on expiration

Question 24

what are the characteristics of a restrictive lung disorder?

Answer 24

restriction of lung expansion

Question 25

is asthma an obstructive or restrictive lung disorder?

Answer 25

obstructed lung disorder, because increased airway resistance

Question 26

are COPD obstructive or restrictive lung disorders?

Answer 26

COPD = chronic obstructive pulmonary disease (obstructive)

Question 27

give examples of COPDs and their main characteristics

Answer 27

chronic bronchitis (inflammation of the bronchi), emphysema (destruction of the alveoli, loss of elasticity)

Question 28

what is the prevalence for COPD? how does it vary with age?

Answer 28

80 000 000 people worldwide have moderate to severe COPD, its prevalence increases with age

Question 29

is loss of lung compliance an obstructive or restrictive lung disorder?

Answer 29

restrictive lung disorder because associated with lung stiffness and incomplete lung expansion

Question 30

is fibrosis an obstructive or restrictive lung disorder?

Answer 30

(fibrosis = formation or development of excess fibrous connective tissue) restrictive lung disorder

Question 31

is fibrosis an obstructive or restrictive lung disorder?

Answer 31

restrictive

Question 32

is oedema an obstructive or restrictive lung disorder?

Answer 32

restrictive

Question 33

is pneumothorax an obstructive or restrictive lung disorder?

Answer 33

restrictive

Question 34

what is taken into account in static measurements of lung function (static spirometry)?

Answer 34

only the volume exhaled

Question 35

what is taken into account in dynamic measurements of lung function (dynamic spirometry)?

Answer 35

the time take to exhale a certain volume (so the volume and the time are taken into account)

Question 36

which volumes can by measured by spirometry?

Answer 36

tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), inspiratory capacity (IC), vital capacity (VC) (NOTE: only residual volume cannot be measured, so functional residual capacity cannot be either)

Question 37

what is the value of forced expiratory volume in 1 second (FEV1) in fit, healthy males?

Answer 37

4.0L

Question 38

what is the forced vital capacity (FVC) in fit, healthy males?

Answer 38

5.0L

Question 39

what is the value of FEV1/FVC in fit, healthy males?

Answer 39

80%

Question 40

how does FEV1/FVC vary with an obstructive disorder?

Answer 40

both FEV and FVC fall but FEV more so, ratio is reduced

the rate at which air is exhaled is much slower, the FVC is also reduced (FRC may be increased), major effect is on the airways and so FEV is reduced to a greater extent than FVC, the ratio is also reduced)

Question 41

how does FEV1/FVC vary with an restrictive disorder?

Answer 41

both FEV and FVC fall so ratio remains same

the absolute rate of airflow is reduced, total volume is reduced due to limitations to lung expansion, ratio remains constant or can increase as a large proportion of volume can be exhaled in the first second (no need to increase breathing rate)

Question 42

is a normal FEV1/FVC ratio always indicative of health?

Answer 42

No, because constant FEV1/FVC in restrictive disorders despite sever compromise of function

Question 43

what is the Forced Expiratory Flow (FEF25-75)

Answer 43

average expired flow over the middle of an FVC, correlates with FEV1 but changes are generally more striking
“normal” range is greater
(EN GROS: variations de la FEV1/FVC dans l’intervalle FVC)