Lecture 17 resp physiology work of breathing / lung volumes

Question 1

Work of Breathing

Answer 1

1. Expand chest / lungs

2. Overcome airways resistance

Question 2

what do you need to overcome to expand chest / lungs?

Answer 2

Stiffness / elasticity of lung/chest wall - Compliance

AND

Surface tension
(How hard is it to expand lungs?)

Question 3

what is compliance lung stiffness?

Answer 3

measure of how easy it is to change lung volume

increase pressure = increase lung volume

Question 4

Fibrosis

Answer 4

Low compliance = “stiff lungs”

Need to do more work to expand

increase pressure

Question 5

Fluid lining alveoli

Answer 5

exerts surface tension which causes them to contract / resist expansion
-> need to overcome this force to expand lung

Question 6

Surface tension reduced by

Answer 6

SURFACTANT

Question 7

Surfactant

Answer 7

reduces surface tension in alveoli

i.e makes them easier to expand

Question 8

Lack of surfactant/failure

Answer 8

results in stiff lungs

fibrosis

Question 9

Surfactant

where produced?

Answer 9

by alveolar type II pneumocytes.

Major constituent is phospholipids

Lowers surface tension.

Question 10

surfactant

why do you lower surface tension?

Answer 10

Reduces attractive forces between fluid molecules lining alveoli.

Easier to increase lung size i.e. increased compliance

Question 11

what does Lack of surfactant/failure to produce

adequate surfactant result in?

Answer 11

stiff lungs

Question 12

Surfactant is absent in premature infants what syndrome does it result in?

Answer 12

development of respiratory distress syndrome (RDS)

Question 13

what air flow is during quiet breathing?

Answer 13

laminar flow

Question 14

what determines resistance to flow?

Answer 14

Poiseuille’s Law

Question 15

Poiseuille’s Law

Answer 15

R = 8nl / πr4

R=resistance;
n = viscosity;
l = length;
r = radius

R inversely proportional to r4

Question 16

R inversely proportional to r4

what does 1/2 r =?
what does 2r =?

Answer 16

16 x R

1 / 16 x R

Question 17

what are some important elements in airways resistance (e.g. asthma)?

Answer 17

Bronchoconstriction /Bronchodilation

Question 18

Bronchi

Answer 18

Main area airway resistance

Question 19

where does most of the resistance to airflow rise?

Answer 19

in upper airways and the first 6 generations of the lower airway

Question 20

do small airways contribute a lot or very little to airway resistance and why?

Answer 20

Very little

due to high CSA

Question 21

Ventilation → Pressure gradient →

Answer 21

Airflow

Question 22

Need to do work to generate a big enough pressure gradient to:

(also = work of breathing?

Answer 22

Expand lung - overcome lung stiffness

Move air - overcome airways resistance

Question 23

How big a breath can you take?

Answer 23

Measurement of Lung Function

Spirometry

Question 24

what are some Measurement of Lung Function tests?

Answer 24

Pulmonary Function tests, Lung Function tests

Question 25

Spirometry

Answer 25

1. Lung volumes – How much? | 2. Air flow rates – How fast?

Question 26

Pulmonary Function Tests (Spirometry)

Answer 26

Mechanical / Digital Common, simple test Can measure how much and how fast Test response to therapy

Question 27

Explain what Pulmonary Function Tests (Spirometry) Mechanical / Digital is?

Answer 27

Breathe into/out of a hollow bell inverted over water – measures volume inspired / exhaled

Question 28

Spirometry: How Much? Divide the air in lungs into four volumes: what are they?

Answer 28

Tidal volume Inspiratory reserve volume Expiratory reserve volume Residual volume

Question 29

whats Tidal volume?

Answer 29

``` 500 ml (VT). Volume of air moved in and out during normal quiet breath ```

Question 30

whats Inspiratory reserve volume?

Answer 30

3300ml (IRV). | Extra volume that can be inspired with maximal inhalation - external intercostal muscles

Question 31

whats Expiratory reserve volume?

Answer 31

1000ml (ERV). | Extra volume that can be exhaled with maximal effort - internal intercostal and ab muscles

Question 32

whats Residual volume?

Answer 32

1200ml (RV). | Volume remaining in lungs after maximal exhalation.

Question 33

Lung capacities These volumes can then be grouped into capacities: what are they?

Answer 33

Vital capacity Total lung capacity Inspiratory capacity Functional residual capacity

Question 34

whats Vital capacity?

Answer 34

~4800ml. | Maximal breath in to maximal out – volume of air you can shift in/out of lungs

Question 35

whats Total lung capacity?

Answer 35

~6000ml. | Total volume in lungs when maximally full = VC + RV

Question 36

whats Inspiratory capacity?

Answer 36

Tidal volume + IRV

Question 37

whats Functional residual capacity?

Answer 37

~2200ml. Volume at end of normal breath out (Equilibrium point for thorax / lungs)

Question 38

Spirometry: how fast? Forced measurements give info about flow. what are they?

Answer 38

Forced Vital capacity (FVC) Forced expiratory volume in one second FEV1

Question 39

whats Forced Vital capacity (FVC)?

Answer 39

maximum breath into maximum breath out (VC) - forced out as hard as possible

Question 40

whats Forced expiratory volume in one second FEV1?

Answer 40

How much of FVC comes out in first second Reduced with diseases causing resistance to airflow (airways obstruction e.g. asthma) or small lungs

Question 41

what diseases causes resistance to airflow?

Answer 41

airways obstruction e.g. asthma or small lungs reduce FEV1

Question 42

whats FEV1/FVC ratio?

Answer 42

Normal ~ 80% | < 0.70 indicates airways obstruction

Question 43

what can Spirometry identify?

Answer 43

Obstruction and restriction airflow diseases

Question 44

whats an Obstructive disease?

Answer 44

Increase Resistance to airflow Asthma Chronic obstructive lung disease (Chronic bronchitis and Emphysema)

Question 45

whats a restrictive disease?

Answer 45

decrease lung volume (reduced lung capacity) Fibrosis (reduced lung compliance) Chest wall abnormalities Respiratory muscle disease

Question 46

how much do we breathe in / out?

Answer 46

Volume of single breath = Tidal Volume = VT = 500 ml (0.5L) Respiratory rate = Frequency (f) = 10 – 12 / minute Total (mouth) ventilation (Respiratory minute volume - VE) = Frequency x Tidal volume

Question 47

Respiratory minute volume (VE)

Answer 47

= frequency (f) x Tidal Volume (VT)

Question 48

VE = Frequency (f) x VT units

Answer 48

``` VE = ml / min f = breaths / min VT = ml / breath ```

Question 49

whats DEAD SPACE (VD)?

Answer 49

150ml Some of the inhaled air never gets to the alveoli so cannot gas exchange About 150 ml of each breath just fills upper airways and is of no use for gas exchange

Question 50

What’s really important is the amount of air that gets into the alveoli. whats this called?

Answer 50

....Alveolar Ventilation VA

Question 51

whats Alveolar Ventilation VA?

Answer 51

measures the flow of fresh gases into and out of the alveoli– VA = f x (VT - VD)

Question 52

Hypoventilation

Answer 52

Low VA

Question 53

Hyperventilation

Answer 53

High VA

Question 54

whats the equation for pulmonary ventilation?

Answer 54

Pulmonary ventilation VE = frequency x tidal volume

Question 55

whats the equation for Alveolar Ventilation?

Answer 55

Alveolar ventilation VA = frequency x (tidal volume – dead space)