2. mechanics underlying ventilation of the lung

Question 1

what is ventilation?

Answer 1

Ventilation is the process of inspiration and expiration

The physical action of breathing and moving air into and out of the lung

Question 2

what is respiration?

Answer 2

Respiration is the exchange of oxygen and carbon dioxide across a membrane either in the lungs or at the cellular level

Question 3

what is tidal volume?

Answer 3

the amount of air moved during quiet inspiration and expiration

Question 4

how is breathing routinely regulated?

Answer 4

Neurones in respiratory centre of brain automatically generate impulses to inspiratory muscles making breathing rhythmic and involuntary

Question 5

what is boyles law?

Answer 5

inverse relationship between pressure of a gas and volume it occupies

Question 6

what are the lung mechanics of quiet inspiration?

Answer 6

Requires active expansion of the thoracic cavity, which in turn expands the lungs – increase in volume causes decrease in pressure relative to atmosphere - Air is drawn into the airways

Question 7

what is the pressure inside the lungs called?

Answer 7

the intrapulmonary pressure

Question 8

what is the lung mechanics in quiet expiration?

Answer 8

Air expelled from the airways passively, by relaxing muscles used in inspiration. This reduces volume of thoracic cavity and also reduces volume of lungs, this increases pressure inside lungs relative to atmosphere and air expelled

Question 9

lungs have a tendency to want to collapse in. Why is this?

Answer 9

as the lungs have a natural elastic recoil, especially with increased stretch

Question 10

what keeps the lungs adherent to the thoracic wall during inspiration?

Answer 10

Pleural fluid found between visceral and parietal pleura (in intrapleural ‘space’) forms
seal between lung and thoracic wall because of surface tension, making the lungs expand as the thoracic cavity expands

Question 11

What do we call the state when we have just expired and before we start inspiring?

Answer 11

resting expiratory level (during quiet expiration)

Question 12

what is the volume of the lungs at the resting expiratory level called?

Answer 12

functional residual capacity

Question 13

what does the resting expiratory level represent?

Answer 13

Represents equilibrium (balance) between elastic recoil chest outwards
and elastic recoil lungs inwards

Question 14

what is the active period of normal respiration

Answer 14

Inspiration (breathing in) is active - Muscles contract to allow the chest wall and diaphragm to overcome inward pull of the lung recoil

Question 15

what is the passive period of normal ventilation

Answer 15

Expiration (breathing out) is passive - Muscles stop contracting. Chest wall &diaphragm no longer
overcome inward pull of lung recoil. Return to resting expiratory level

Question 16

what is intrapulmonary pressure compared against?

Answer 16

atmospheric pressure

Question 17

what is the pressure within the intrapleural space?

Answer 17

Pressure in this space is negative throughout expiration and inspiration
(relative to atmospheric pressure) due to elastic recoil of lung pulling visceral pleura inward and chest wall pulling parietal pleura outward

Question 18

what holds the visceral and parietal pleura together?

Answer 18

the pleural seal - surface tension created in the pleural space by a small amount of serous fluid

Question 19

what happens if the pleural seal is broken?

Answer 19

atelectasis - lung collapse

Question 20

what are the accessory muscles of inspiration?

Answer 20

sternocleidomastoid muscles
scalene muscles
serrates anterior
pectoralis major

Question 21

what are the accessory muscles of expiration

Answer 21

internal intercostals

abdominal wall muscles

Question 22

when are accessory muscles of respiration used?

Answer 22

during exercise

during diseases that affect the lung

Question 23

how do we visualise mechanical function of the lungs?

Answer 23

spirometry

Question 24

what is spirometry?

Answer 24

Spirometry is a common office test used to assess how well your lungs work by measuring how much air you inhale, how much you exhale and how quickly you exhale. Spirometry is used to diagnose asthma, chronic obstructive pulmonary disease (COPD) and other conditions that affect breathing.

Question 25

what lung volumes cannot be calculated during spirometry?

Answer 25

functional residual capacity
residual volume
total lung capacity
each of these volumes includes the residual volume which cannot be breathed out and therefore cannot be measured

Question 26

what does tidal volume represent?

Answer 26

represents the volume of air entering and leaving the lungs in a single breath (during quiet inspiration and expiration)

Question 27

what is the inspiratory reserve volume?

Answer 27

the amount above the normal inspiratory tidal volume that is achieved in maximal inhalation

Question 28

what is the inspiratory capacity?

Answer 28

the total volume of air inhaled during maximum effort from exhaled tidal volume (resting expiratory level)
composed of the inspiratory reserve volume and the tidal volume

Question 29

what is the expiratory reserve volume?

Answer 29

the volume of air exhaled on maximal effort from resting expiratory level

Question 30

what is inspiratory capacity?

Answer 30

the maximal volume of air inhaled from resting expiratory level

Question 31

what is vital capacity?

Answer 31

the difference in volume between maximal inspiration and maximal expiration

Question 32

what is total lung capacity?

Answer 32

vital capacity + residual volume

Question 33

what limits the expansion of the alveoli?

Answer 33

Alveoli Surface Lined by Fluid, this fluid Creates Surface Tension That Limits Their Expansion
Decreases compliance making it difficult for alveoli (and therefore lungs) to expand

Question 34

what secretes surfactant?

Answer 34

type II pneumocytes

Question 35

what is the function of surfactant?

Answer 35

has detergent like properties that reduces the surface tension produced by fluid lining the alveoli.
Acts to disrupt interaction between fluid molecules on alveolus surface reducing surface tension and stopping the alveoli from collapsing

Question 36

what is the function of pneumocytes?

Answer 36

type 1 = gas exchange

type 2 = secrete surfactant

Question 37

what factor affects the functioning of the surfactant?

Answer 37

Surfactant is more effective at disrupting surface tension when its molecules are closer together.
smaller alveoli: molecules are closer together, more effective reduction in surface tension. Prevents the pressure from rising inside the alveoli as a result of smaller volume
larger alveoli : surfactant molecules spread further apart, less disruption of surface tension, more pressure in alveolus.

Question 38

why is inhalation progressively harder as we inhale?

Answer 38

as we inhale the size of the alveoli expand. This disperses the molecules of surfactant, making them less effective at disrupting the surface tension and decreases the compliance of the alveoli

Question 39

what mechanism prevents small alveoli from collapsing into big alveoli?

Answer 39

as big alveoli have more volume you would expect them to have lower intraalveolar pressure. This is not the case because of the surfactant being diluted. the diluted surfactant means that larger alveoli have greater surface tension. Thus pressure does not drop in larger alveoli and is consistent with that of smaller alveoli, and small alveoli do not collapse into big alveoli

Question 40

when is surfactant present in the fetus?

Answer 40

after 25 weeks

Question 41

what is respiratory distress syndrome?

Answer 41

a condition that can be seen in premature babies, due to lack of surfactant

Question 42

what is poiseuilles law?

Answer 42

tubes of small diameter have higher resistance to flow.

Question 43

how does ventilation overcome small airways increased resistance?

Answer 43

numerous small airways running in parallel creates effective massive diameter and hence low resistance