Respiratory physiology I: Lung Mechanics

Question 1

Describe breathing and ventilation

Answer 1

this is the flow in and out of the respiratory system

Question 2

what is the movement of air into the body due to

Answer 2

the movement of air in and out of the lungs occurs due to pressure differences

Question 3

how are pressure differences created

Answer 3

• Pressure differences are created by changes in lung volume because air flows from a region of a high pressure to a region of low pressure

Question 4

describe what drives inhalation

Answer 4

• driven by diaphragm which contracts and flattens leading to an increase in lung size and consequently air moves into the lungs

Question 5

what drives exhalation

Answer 5

– diaphragm relaxes which leads to a decrease in lung size and therefore pressure increases and air moves out of the lungs

Question 6

How do we measure lung function

Answer 6

spirometry

Question 7

define tidal volume

Answer 7

amount of air you move into and out of your lungs during rest, not the sum of the two

Question 8

define inspiratory capacity

Answer 8

total volume of air that you can breathe in at maximum lung capacity at rest

Question 9

define expiratory capacity

Answer 9

total volume of air that you can breath out of the lungs at maximum lung capacity at rest

Question 10

define forced vital capacity

Answer 10

maximum volume of air into and out of the lungs in a single respiratory cycle

Question 11

define residual volume

Answer 11

volume of air that remains in the lungs even after maximal exhalation

Question 12

How do you calculate the forced vital capacity

Answer 12

• Inspiratory reserve capacity+ tidal volume + expiratory reserve volume = forced vital capacity

Question 13

what is FEV1/FVC

Answer 13

• FEVI/FVC is a ratio of Forced Expiratory Volume in 1 sec & Forced Vital Capacity

Question 14

what is the normal FEV1/FVC ratio

Answer 14

values above 70-80% = normal. Age/gender adjusted

Question 15

what causes the decrease of the FEV1/FVC

Answer 15

• Airflow limitation (e.g. Asthma)

Question 16

what generates the pressure differences for breathing

Answer 16

it is the respiratory muscles that generate the pressure differences for breathing

Question 17

what happens during inspiration of quiet breathing

Answer 17

• inspiration: active part of passive breathing

- Diaphragm and external intercostal muscles

Question 18

what happens during inspiration in forced breathing

Answer 18

• Inspiration: diaphragm, external intercostal muscles and accessory muscles such as pectoralis major and minor and serratus anterior

Question 19

what is the diaphragm innervated by

Answer 19

• it is innervated by the phrenic nerve

Question 20

describe measurements of the diaphragm

Answer 20

• rest – 1-2cm

- forced breathing < 10cm

Question 21

what are the two muscles that the external intercostal muscles do

Answer 21

• pump handle movements; anterior end of each rib is elevated
• bucket handle movements; dimeter of chest increases

Question 22

what happens during expiration in quiet breathing

Answer 22

• expiration; largely passive as a result of elastic recoil of the lungs

Question 23

what happen during expiration in forced breathing

Answer 23

• active
• involves accessory respiratory muscles
• E.g. Anterior abdominal muscles & quadratus lumborum

Question 24

define alveolar ventilation

Answer 24

• Defined by portion of the total ventilation that reaches the alveoli and participates in gas exchange

Question 25

How do gasses move between air and blood

Answer 25

move between air and blood by passive diffusion

- movement of gases is defined by partial pressure gradients

Question 26

what is hypoventilation or hyperventilation a sign of

Answer 26

lung diseases

Question 27

what decreases as you descend the airways

Answer 27

airway ventilation and perfusion decrease

Question 28

what is dead space

Answer 28

• Volume of air in the mouth, pharynx, trachea and bronchi up to the terminal bronchioles
it is the volume of air that does not exchange in gas

Question 29

how large is the anatomical dead space

Answer 29

150 ml does not exchange gas

Question 30

what is the anatomical dead space made out of which structures

Answer 30

made up of upper respiratory tract, trachea, bronchi, bronchioles, terminal bronchioles

Question 31

what is alveolar dead space

Answer 31

alveoli that have insufficient blood supply to act as effective respiratory membranes therefore do not take part in gas exchange

Question 32

How do you work out physiological dead space

Answer 32

anatomical dead space and alveolar dead space

Question 33

how do you work out the rate at which new air reaches the alveoli

Answer 33

(tidal volume - dead space) x respiratory rate

Question 34

describe the example of how you work out the rate at which new air reaches the alveoli

Answer 34

tidal volume – dead space) x respiratory rate

• Tidal volume=500 mL
• Anatomic dead space=150 mL
• Fresh air entering the lungs=350 mL
• Respiratory rate=12 breaths/min
• Alveolar ventilation (ml/min)
• 12X350=4200 mL/min (4.2L/min)
• This is the effective ventilation that brings about the exchange of O2 and CO2.

Question 35

describe alveolar ventilation and respiratory exchange

Answer 35

Room = Almost zero CO2 & alveolar gas = 5.5% giving an output of:
4.2 X (5.5-0/100)=0.231 L/min or 231 mL/min
Oxygen forms 21% of atmospheric air and alveolar gas contains about 14% giving an uptake of:
4.2 X (21-14/100)=0.294 L/min or 294 mL/min

Question 36

How do you see the spirometers restyles

Answer 36

• look at flow volume loops on the graph, where the Y axis is and X axis is
• after the starting point the curve rapidly mounts to a peak (peak expiratory flow)
• after the PEF the curve descends = the flow decreases as more air is expired, a normal non pathological F/V loop will descend into a straight or a convex line form top PEF to bottom FVC