Lecture 2 - Mechanics of breathing

Question 1

definition of breathing

Answer 1

bodily function that leads to ventilation of the lungs

also known as external respiration

Question 2

Ventilation definition

Answer 2

Process of moving gases in - inspiration and out (expiration) of the lungs

Question 3

Mechanics of breathing involves…

Answer 3

describes the structural and physiological bases of ventilation

Question 4

in what 2 ways do diseases affect ventilation

Answer 4

obstructive conditions: asthma, COPD, lung cancer
Restrictive:
Intrinsic : pulmobary fibrosis
extrinsic: pneumothorax, disorders of thoracic skeleton

Question 5

How will gas flow?

Answer 5

through patent airways according to the pressure gradient between atmosphere (barometric pressure) and alveoli

Question 6

Pressure during inspiration

Answer 6

Pb (atmospheric pressure) is greater than alveolar pressure

Question 7

Pressure during expiration

Answer 7

Aloveolar pressure (variable - Pa) is greater than the atmospheric pressure

Question 8

Why does airway obstruction have a major effect on flow? describe in terms of the equation

Answer 8

flow = (k x delta PX r^4)/ (L)

As flow depends on the radius, airway obstruction would majorly affect it.

Question 9

How is generation of Delta P brought about

Answer 9

atmospheric pressure is constant

therefore difference in pressure generation is dependent on the pressure changes in the chest

Question 10

How does alveolar pressure changes related to thoracic volume

Answer 10

Change in pressure is inversely proportional to thoracic volume. The pressure is higher when the volume is low and vice versa

Question 11

What are inspiratory muscles used in quiet breathing and when there is an increasing effort

Answer 11

quiet breathing: diaphragm
external intercostals stabilise rib cage

Increasing effort:
diaphragm
, external intercostals lift and expand rib cage, accessory muscles, neck muscles, shoulder girdle muscles

Question 12

Expiratory muscles during quiet breathing and increasing effort

Answer 12

quiet breathing: elastic recoil of tissues

increasing effort: internal intercostals, abdominal wall muscles

Question 13

what physical changes happen in inspiration

Answer 13

increased vertical diameter
increase A-P diameter
elevated rib cage
external intercostals contracted
internal intercostals relaxed
neck muscles contract

Question 14

Expiration: physical changes

Answer 14

abdominals contracted

Question 15

Innervation of diaphragm and intercostals

Answer 15

phrenic nerve - C3,4,5

Intercostals: segmental thoracic nerves

Question 16

What can a spinal cord injury cause

Answer 16

ventricular muscle paralysis

Question 17

What are the pleura responsible in doing

Answer 17

transmitting thoracic cage expansion into lung volume expansion
thoracic cage expansion exerts an increasing negative pressure on the intrapleural space

Question 18

What does a spirometer measure

Answer 18

Volume of air moving in and out of the lungs

Question 19

What is tidal volume

Answer 19

the volume of air moved in or out of the lungs during normal breathing. 
at rest - 6-7 ml/kg
during exercise - 15 ml/Kg
Volumes dependent on age, sex and height
typical value of an adult male is 500 ml

Question 20

Inspiratory reserve volume

Answer 20

after normal expiration, take as deep a breath as possible

typical value for 70 kg male - 3000 ml

Question 21

Expiratory reserve volume

Answer 21

after normal inspiration, breath out as deeply as possible

1,500 ml for 70 kg male

Question 22

What is residual volume

Answer 22

even after maximal expiration, air remains in the lungs. this is because of rigid nature of thorax and pleural attachments of the lungs to the chest wall that prevent complete emptying.

this volume left is residual volume
cannot be measured by spirometry
typical value is 1000 ml

Question 23

Lung capacities

Answer 23

combinations of lung volumes

Question 24

Total lung capacity

Answer 24

TV+IRV+ERV+RV

Question 25

Vital capacity

Answer 25

TV+IRV+ERV

Question 26

Functional residual capacity

Answer 26

ERV+RV

Question 27

What is vital capacity

Answer 27

after a maximal inspiration, make a maximal expiration

typical value - 5,000 ml

Question 28

Examples of chest diseases affecting lung volumes and capactities

Answer 28

Restrictive lung diseases - pulmonary fibrosis - reduced Residual volume, FRC, VC, TLV
Obstructive - asthma, copd, emphysema,
increased RV, TLC may be reduced or increased
FRC increased in emphysema

Question 29

what is measured clincally using a vitalograph spirometer

Answer 29

forced expiratory measurements

FVC, Forced expiratory volume in 1 second (FEV1)

Question 30

What is a peak flow meter used to measure

Answer 30

peak expiratory flow rate

Question 31

How do you distinguish between obstructive and restrictive clinically?

Answer 31

FEV1/FVC ratio
ratio below 0.7 - obstructive
ratio above 0.7 - restrictive

Question 32

Peak expiratory flow rate

Answer 32

convenient way of measuring airways obstruction, not as good as spirometry for airflow limitation
can use it at home to monitor asthma or copd
wide diurnal variations - highest in the evenings and lowest in early hours
PEFR - less depenent on effort than FEV1

Question 33

Reversibility of airflow limitation

Answer 33

In asthma, the airway constriction is reversible so that FEV1 and PEFR would be restored to normal after salbutamol.

Question 34

when is airways constriction irreversible?

Answer 34

COPD

Question 35

what provides additional information about pulmonary disease

Answer 35

flow-volume loops

Question 36

What is FEV1?

Answer 36

The fraction of the vital capacity expired during the first second of forced respiration.

Question 37

When can it be reduced even when vital capacity is normal?

Answer 37

in diseases like asthma when airway resistance is increased because of bronchial constriction.