10 - Ventilation Mechanics

Question 1

define ventilation

Answer 1

movement of air into and out of the lungs
involves anatomy and mechanics

Question 2

define respiration

Answer 2

exchange of gasses (O2 and CO2)
happens at many levels
- external (b/w blood and lungs)
- internal (b/w tissue and blood)

Question 3

What is boyles law

Answer 3

ventilation of the lungs (alveoli):
Pressure (P) x Volume (V) = Constant (k)

increase in volume = decrease in pressure
decrease in volume = increase in pressure

differences in pressure drive the movement of air into and out of the lungs (ventilation)

Question 4

How do the muscles inhale

Answer 4

• elevate ribs
• lower diaphragm
• enlarge thorax (AP and SI dimensions)

Question 5

How do the muscles exhale

Answer 5

• depress ribs
• compress abdomen (elevates the diaphragm)
• compress thorax

Question 6

What muscles are involved with respiration

Answer 6

accessory: sternocleidomastoid and scalenes
principal: external intercostals and diaphragm
internal intercostals
external oblique
internal oblique
transversus abdominus
rectus abdominus

Question 7

Describe the pressure changes during pulmonary ventilation

Answer 7

1. prior to inspiration:
   - diaphragm relaxed
   - alveolar pressure = atmospheric pressure
   - no air flow
2. inhalation:
   - diaphragm contracts and external intercostals contract
   - chest cavity expands
   - alveolar pressure < atmospheric pressure
   - air enters the lungs

deep inhalations (forced inhalation) –> scalene and sternocleidomastoid muscles expand the chest further –> greater drop in alveolar pressure

3. exhalation:
   - diaphragm and external intercostals relax
   - chest and lungs recoil –> chest cavity decreases in size
   - alveolar pressure > atmospheric pressure
   - air exits lungs

forced exhalations –> internal intercostals and abdominal muscles contract –> reduces size of the thoracic cavity

Question 8

what is the intercostal VAN

Answer 8

intercostal vein
intercostal artery
intercostal nerve (mixed spinal and thoracic nerve)

supply the intercostal muscles that support ventilation

sits in the intercostal groove at the inferior border of each rib

Question 9

What is inspiratory reserve volume

Answer 9

The extra volume of air that can be inspired with maximal effort after reaching the end of a normal, quiet inspiration

Question 10

what is tidal volume

Answer 10

1/2 volume of air
quiet breathing

Question 11

What is expiratory reserve volume

Answer 11

The extra volume of air that can be expired with maximum effort beyond the level reached at the end of a normal, quiet expiration

Question 12

What is vital capacity

Answer 12

life capacity

Question 13

What is total lung capacity

Answer 13

total air in lungs

Question 14

What is residual volume

Answer 14

the air trapped in our lungs

non collapsable airways (brachiales, bronchioles…) –> air stays

Question 15

What is functional residual capacity

Answer 15

volume lungs obtain after exhalation in quiet breathing
no muscles are used

Question 16

What is minute ventilation
What is the formula

Answer 16

VE = rate that air moves in and out of the mouth (expiratory)

VE = breathing frequency (fb) x tidal volume (VT)
(air movement in and out)

at rest = 12breaths/min x 500 ml/breath = 6 L/min

Max exercise = 60 breaths/min x 3000 ml/breath = 180 L/min

Question 17

What is alveolar ventilation
Is it more or less than minute ventilation

Answer 17

VA = rate that fresh air moves in and out of alveoli

less than VE due to dead space volume of lungs (VD)
VD = 150 mL

Dead space: volume of air occupying the non-respiraoty segments of the airways (eg. nose, pharynx, laryng, trachea, bronchi, bronchioles, terminal bronchioles) and does not participate in gas exchange

Question 18

Factors that affect pulmonary ventilation

Answer 18

compliance/elastance & airway resistance

Question 19

What is elastance

Answer 19

Elastance: pressure required to inflate the lungs
- the measure of ‘stiffness’ of the lungs
- r/t the forces needed to blow up a balloon

lungs with low elastance –> compliant
lungs with high elastance –> stiff

complaince = 1/elastance

Question 20

What is the effect of lung surfactant on lung compliance

Answer 20

surfactant: phospholipid released by type II pneumocytes and reduces the surface tension of water
- reduces the effort needed to breathe
- produced continually after 27-28 weeks of gestation

elastic tissues of lungs of highly complaint (low elastance)

surface tension of water has low compliance compared to lung elastic tissue

water lining alveoli decreases lung compliance (increases lung elastance)

Question 21

What is resistance

Answer 21

related to the pressure needed to generate air flow
can be likened to ‘drag’ which opposes air flow

lungs with high resistance are obstructed
the factor with the biggest influence on resistance is airway diameter (caliber)

Question 22

How do changes in lung volume occur

Answer 22

when the muscles of ventilation move the chest wall and produce changes in plural pressure

PIP = intrapulmonary pressure
PPL = pleural pressure

Question 23

What is positive pressure ventilation

Answer 23

the lungs are inflated by increasing the pressure inside alveoli (intrapulmonary pressure)
- mechanical ventilation on patient or providing mouth to mouth resuscitation

• increase the pressure –> increase in lung volume

Question 24

What is normal ventilation

Answer 24

the lungs are expanded by reducing the pressure surrounding lungs to sub-atmospheric presures (bringing diaphram down)

• sub-atmospheric pressures are sometimes called negative pressures

Question 25

What happens to intrapulmonary pressure and intrapleural pressure during inspiration

Answer 25

decreases

intrapleural pressure almost always negative (subatmospheric)
intrapulmonary pressure fluctuates (+/-)

Question 26

What happens to intrapulmonary pressure and intrapleural pressure during expiration

Answer 26

intrapulmonary pressure –> increases then decreases
intrapleural pressure –> increases

transpulmonary pressure increases

intrapleural pressure almost always negative (subatmospheric)
intrapulmonary pressure fluctuates (+/-)