10 - Ventilation Mechanics Flashcards
define ventilation
movement of air into and out of the lungs
involves anatomy and mechanics
define respiration
exchange of gasses (O2 and CO2)
happens at many levels
- external (b/w blood and lungs)
- internal (b/w tissue and blood)
What is boyles law
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)
How do the muscles inhale
- elevate ribs
- lower diaphragm
- enlarge thorax (AP and SI dimensions)
How do the muscles exhale
- depress ribs
- compress abdomen (elevates the diaphragm)
- compress thorax
What muscles are involved with respiration
accessory: sternocleidomastoid and scalenes
principal: external intercostals and diaphragm
internal intercostals
external oblique
internal oblique
transversus abdominus
rectus abdominus
Describe the pressure changes during pulmonary ventilation
- prior to inspiration:
- diaphragm relaxed
- alveolar pressure = atmospheric pressure
- no air flow - 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
- 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
what is the intercostal VAN
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
What is inspiratory reserve volume
The extra volume of air that can be inspired with maximal effort after reaching the end of a normal, quiet inspiration
what is tidal volume
1/2 volume of air
quiet breathing
What is expiratory reserve volume
The extra volume of air that can be expired with maximum effort beyond the level reached at the end of a normal, quiet expiration
What is vital capacity
life capacity
What is total lung capacity
total air in lungs
What is residual volume
the air trapped in our lungs
non collapsable airways (brachiales, bronchioles…) –> air stays
What is functional residual capacity
volume lungs obtain after exhalation in quiet breathing
no muscles are used
What is minute ventilation
What is the formula
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
What is alveolar ventilation
Is it more or less than minute ventilation
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
Factors that affect pulmonary ventilation
compliance/elastance & airway resistance
What is elastance
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
What is the effect of lung surfactant on lung compliance
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)
What is resistance
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)
How do changes in lung volume occur
when the muscles of ventilation move the chest wall and produce changes in plural pressure
PIP = intrapulmonary pressure
PPL = pleural pressure
What is positive pressure ventilation
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
What is normal ventilation
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
What happens to intrapulmonary pressure and intrapleural pressure during inspiration
decreases
intrapleural pressure almost always negative (subatmospheric)
intrapulmonary pressure fluctuates (+/-)
What happens to intrapulmonary pressure and intrapleural pressure during expiration
intrapulmonary pressure –> increases then decreases
intrapleural pressure –> increases
transpulmonary pressure increases
intrapleural pressure almost always negative (subatmospheric)
intrapulmonary pressure fluctuates (+/-)
