Ventilation and Compliance Flashcards
Describe what it means by tidal volume?
TV - Tidal Volume. The volume of air breathed in or out of the lungs at each breath.
500ml
Describe what it means by expiatory reserve volume?
ERV - Expiratory Reserve Volume. The maximum volume of air which can be expelled
1100ml
Describe what it means by inspiratory reserve volume?
IRV - Inspiratory Reserve Volume. The maximum volume of air which can be drawn
3000ml
Describe what it means by residual volume?
RV - Residual Volume. The volume of gas in the lungs at the end of a maximal expiration.
1200ml
Describe what it means by vital capacity?
VC - Vital Capacity = tidal volume + inspiratory reserve volume + expiratory reserve volume.
Describe what it means by total lung capacity?
TLC - Total Lung Capacity = vital capacity + the residual volume.
Describe what it means by inspiratory capacity?
IC - Inspiratory Capacity = tidal volume + inspiratory reserve volume.
Describe what it means by function residual capacity?
FRC - Functional Residual Capacity = expiratory reserve volume + residual volume.
Describe what it means by FEV1?
FEV1 = Forced Expired Volume in 1 second
Describe what it means by FEV1:FVC?
Fraction of Forced Vital Capacity expired in 1 second.
What does it mean by anatomical dead space and what is the value for this?
Anatomical dead space volume is ~150 mL and is the volume of gas occupied by the conducting airways that cannot undergo gas exchange.
What does ventilation refer to?
Ventilation refers to the movement of air in and out of the lungs (breathing).
What are the two types of ventilation and describe each one
Pulmonary (minute) ventilation – total air movement in and out of the lungs
Alveolar ventilation – fresh air (with high O2 content) getting to the alveoli and therefore available for gas exchange.
What does hypoventilation mean?
Hypoventilation is when our alveolar ventilation is low.
What does hyperventilation mean?
Hyperventilation is when our alveolar ventilation is high.
How can alveolar ventilation be calculated?
Alveolar ventilation (mL/min) can be calculated by the respiratory rate (breathes per minute) and the air to alveoli (mL/min).
What does partial pressure mean and what unit is it expressed by?
The partial pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole mixture.
Pressure is common expressed in mmHg or kPa units (normally use mmHg)
T/F All gas molecules exert same pressure, so partial pressure increases with increasing [gas]mixture
TRUE
What are the normal values for alveolar PO2 and CO2
PO2 = 100mmHg (13.3 kPa)
PCO2 =40mmHg (5.3 kPa)
What happens to the PO2 and PCO2 during hyperventilation?
PO2 increases to 120mmHg
PCO2 falls to 20mmHg
What happens to the PO2 and PCO2 during hypoventilation?
PO2 falls to 30mmHg
PCO2 increases to 100mmHg
What cells are the alveolar walls made of?
Type I -thin walled
- cells which permit gas exchange
Type II - cells which secrete surfactant fluid
What is surfactant and describe its function
Surfactant is a detergent-like fluid produced by type II alveolar cells. This reduces the surface tension on alveolar surface membrane thus reducing the tendency for alveoli to collapse.
Why is it important to reduce surface tension?
Surface tension is the attraction of one water molecule to the other molecules. Since the alveoli is lined with fluid that is largely water-based with the water molecules arranged in a sphere around the alveoli, the attraction between these molecules causes a force that leads to the alveoli to collapse.
Why is surfactant more effective in smaller alveoli?
The molecules of the surfactant are closer together therefore more concentrated
What law determined the pressure required to keep an alveoli open and stop from collapsing?
The law of LaPlace
P=2Tr
P-pressure
T-surface tension
r-radius
Describe the surfactant production in a fetus
Surfactant production starts at week 25 of gestation and is complete at abut week 36 (40 weeks = full term). Stimulated by the thyroid hormone and cortisol which increases towards the end of pregnancy. Premature babies surfer Infant Respiratory Distress Syndrome (IRDS).
What is the definition of compliance
Compliance is the change in volume relative to the change in pressure so essentially how much does volume change for any given change in pressure.
(represents the stretchability of the lung not the elasticity
Define high-compliance
large increase in lung volume for a small decrease in inter-plueral (ip) pressure.
Define low-compliance
small increase in lung volume for large decrease in ip pressure
Why does it require a greater change in pressure from FRC to reach a particular lung volume during inspiration than to maintain that pressure during expiration?
This is because inspiration requires work to overcome the tissue inertia and also to drive air into the lungs.
Expiration requires less work due to the elastic recoil of the lungs.
What can affect compliance?
Emphysema - causes expiration to be difficult leading to either same or increased compliance
Fibrosis - causes inspiration to require more effort thus decreasing compliance
What is the difference between static or dynamic spirometry?
Static – where the only consideration made is the volume exhaled
Dynamic – where the time taken to exhale a certain volume is what is being measured
What factors are being measured in spirometry
FEV1= forced expiratory volume in 1 second (fit, healthy males: 4.0L)
FVC= forced vital capacity (fit, healthy males: 5.0L)
FEV1/FVC= 80% in a healthy individual.
What does Dalton’s law state?
the total pressure of a gas mixture is the sum of the pressures of the individual gases. (partial pressure)
What is FEF?
Forced expiratory flow (FEF25%-75%). Average expiratory flow over the middle of an FVC. Correlates with FEV1, but changes are generally more striking, however “normal” range is greater.
