ventilation Flashcards
Describe the difference between pulmonary and alveolar ventilation:
Pulmonary ventilation is the total air movement in and out of the lungs
- tidal x resp rate
Alveolar ventilation is the fresh air getting to alveoli and therefore available for gas exchange
- (tidal volume - dead space) x resp rate
what is the difference between obstructive and restrictive lung disease?
give example
Obstructive = obstruction of airflow, especially on expiration
Restrictive= restriction of lung expansion
Obstructive; Asthma, COPD, emphysema, Chronic Bronchitis
Restrictive; CF, Infant Resp Distress, Oedema, Pneumothorax
define patency and how it’s maintained:
Patency is the state of the airways being open.
It is maintained by the C-shaped rings of cartilage
bronchial smooth muscle alters resistance to airflow:
Contraction
decreases diameter = increases resistance
→ e.g. SNS (noradrenaline/adrenaline) acting on a1 receptors
Relaxation
increases diameter = decreases resistance
→ e.g. SNS (noradrenaline/adrenaline) acting on b2 receptors
the pressure changes (PA & Patmos & Pip) during inspiration:
As the diaphragm and external intercostals contract, thoracic volume increases, causing:
Pip - more negative/subatmospheric
PA - decreases inside the lungs compared to Patmos
the pressure changes (PA & Patmos & Pip) during expiration.
As the diaphragm and external intercostals relax, thoracic volume decreases (REST)
→ due to elastic recoil of chest walls and lungs
OR
As the internal intercostals and abdominal muscles contract, thoracic volume decreases (LOAD) causing:
Pip - more positive
PA increases inside the lungs compared to Patmos
Define the following types of pressure:
[1] Intra-thoracic (Alveolar) Pressure (PA)
[2] Intra-pleural Pressure (Pip)
[3] Transpulmonary pressure (PT)
[1] Intra-thoracic (Alveolar) Pressure (PA)
→ pressure inside the thoracic cavity, (essentially pressure inside the lungs).
- May be negative or positive compared to atmospheric pressure.
[2] Intra-pleural Pressure (Pip)
→ pressure inside the pleural cavity.
- Typically negative compared to atmospheric pressure (in healthy lungs at least!)
[3] Transpulmonary pressure (PT)
→ difference between alveolar pressure and intra-pleural pressure.
- Almost always positive because Pip is negative (in health).
hypoventilater has less alveolar ventilation compared to a hyperventilate:
Hypoventilation = shallow but rapid breathing
→ less tidal volume & higher respiratory rate = decreased alveolar ventilation
Hyperventilation = deep but slow breathing
→ more tidal volume & lower respiratory rate = increased alveolar ventilation
what is the impact of hyperventilation and hypoventilation on PO2 and PCO2?
hyperventilation (increased alveolar ventilation)
- PO2 rises to about 120 mmHg and PCO2 falls to about 20 mmHg.
hypoventilation (decreased alveolar ventilation)
- PO2 falls to 20 mmHg and PCO2 rises to 100 mmHg.
why does a small change in intrapleural pressure brings about a larger change in volume at the base of the lungs compared with the apex?
compliance is lower at the apex due to the alveoli being more inflated.
compliance is higher at the base because the diaphragm slightly compresses the lungs, causing the alveoli to be less inflated.
why is the depth of breathing more influential in determining alveolar ventilation than the rate of breathing?
consider the effect of anatomical dead space (ADS).
increased depth of breathing = higher tidal volume = more %air is effective after the addition of ADS = increased alveolar ventilation
increased rate of breathing = lower tidal volume = less %air is effective after the addition of ADS = decreased alveolar ventilation
factors that influence the diffusion of gases across the alveoli:
directly proportional to the:
- partial pressure gradient.
- gas solubility
- available surface area
inversely proportional to the thickness of the membrane
- most rapid over short distances.
state partial pressures of gases in the alveoli, systemic arteries, and veins:
PAO2 (alveolar) - 100mmHg / 13.3kPa
PACO2 (alveolar) - 40mmHg / 5.3kPa
PaO2 (arterial) - 100mmHg / 13.3kPa
PaCO2 (arterial) - 40mmHg / 5.3kPa
PvO2 (venous) - 40mmHg / 5.3kPa
PvCO2 (venous) - 46mmHg / 6.2kPa
why does CO2 diffuses rapidly (200ml/min) compared to O2 (250ml/min) when the PCO2 gradient between alveoli and pulmonary arterial blood is 10 times less than the PO2 gradient:
CO2 is more soluble
how does pulmonary oedema affect diffusion (not ventilation)?
the collection of fluid in interstitial space increases diffusion distance between alveoli and capillary.
harder for oxygen to get into capillaries (doesn’t dissolve well in water)
PACO2 - stays normal because CO2 dissolves well in water.
PAO2 - decreased
what is emphysema and how does it affect diffusion and cause expiration to become harder?
leads to the destruction of alveoli
- reduces the surface area for gas exchange.
caused by smoking which induces an enzyme called Elastin
breaks down elastic tissue and causes expiration/exhalation to become harder
decreased PAO2
increased PACO2
Emphysema → problem with diffusion & ventilation (especially expiration)
how does asthma directly infect ventilation and indirectly affect diffusion?
increases the airway resistance by constricting the airways
decreases airway ventilation (less oxygen gets to the alveoli, which leads to reduced PaO2)
define high elasticity for lungs:
they can passively constrict during rest through elastic recoil, without having to use the internal intercostals and abdominal muscles.
(emphysema requires using the muscles even at rest)
define FEV1/ FVC:
FEV1 (Forced expiratory volume in 1 second)
→ fit, healthy, young adult males: 4.0L
FVC (Forced vital capacity)
→ fit, healthy, young adult males: 5.0L
FEV1/FVC = 80% (normal ratio around 80% for all people)
FEV1:FVC → Fraction of forced vital capacity expired in 1 second.
Describe the FEV1/FVC in obstructive lung disease (COPD) and a restrictive lung disease (pulmonary fibrosis):
obstructive = air flow through airways is compromised
→ Exhalation of air is much slower
Both FEV1 & FVC are reduced, but FEV1 is reduced to a greater extent.
Therefore FEV1/FVC is less compared to a normal lung.
restrictive = lung expansion is compromised
→ absolute rate of airflow is reduced (bc. lung volume is reduced - less air to flow)
Both FEV1 & FVC are reduced, but FEV1 is reduced to a lesser extent.
Therefore FEV1/FVC remains normal or can increase.
why does it require more work during expiration in obstructive diseases e.g. emphysema?
loss of elastic tissue means expiration requires effort - bc. the elastic recoil of the energy harnessed during inspiration is not available.
why does it require more work during inspiration in restrictive diseases fibrosis?
inert fibrous tissue leads to loss of compliance (stretchability), which means the effort of inspiration increases.
Why is expiration, not inspiration, most affected in Asthma/Bronchitis?
during inspiration, airways are pulled open by physical forces of inspiration
(except in severe diseases)
during expiration, airways are compressed by physical forces of expiration with increased airway resistance due to reduced airway radius due to Asthma/Bronchitis.
describe spirometry:
used to measure lung function
[1] Static – measures expiration volume only
[2] Dynamic – measures the time taken to expire a certain volume
