16) Pulmonary ventilation Flashcards
1
Q
What does tachypnoeic, tachycardic and hypoxemic mean?
A
- Tachypnoeic: Elevated breathing rate
- Tachycardic: Elevated heart rate
- Hypoxemic: Lower than normal levels of oxygen
2
Q
What is Total Lung Capacity (TLC)?
A
- The total amount of air the lungs can accommodate
3
Q
What is tidal volume?
A
- The volume of air being breathed in and out
4
Q
What is Inspiratory Reserve Volume (IRV)?
A
- It is the amount of air a person can forcefully inhale
5
Q
What is Expiratory Reserve Volume?
A
- It is the amount of air a person can forcefully exhale
6
Q
What is the Residual Volume (RV)?
A
- The amount of air remaining in a person’s lungs after fully exhaling
7
Q
What is Functional Residual Capacity (FRC)?
A
- The volume of air remaining in the lungs after passive exhalation
8
Q
What is Vital Capacity (VC)?
A
- The maximum amount of air a person can inhale after maximum exhalation
9
Q
What can lung volume and capacity depend on?
A
- Age
- Sex
- Height
- Lung properties (e.g. obstruction/damage due to disease)
10
Q
Do we use our total lung capacity all the time when breathing?
A
- No. At rest our tidal volume is much smaller than our total lung capacity
11
Q
What is pulmonary ventilation?
A
- The movement of air from the atmosphere to gas exchange surfaces within the lungs
12
Q
Why is pulmonary ventilation important?
A
- It maintains the O2 and CO2 gradients between air in the alveoli and the arterial blood
- This allows a sufficient level of gas exchange to occur which ensure adequate O2 supply to respiring tissues and CO2 removal from respiring tissues from the blood
13
Q
Describe the movement of oxygen from the atmosphere to respiring tissues.
A
- First oxygen is taken in from the atmosphere into the alveoli in our lungs in the airways through pulmonary ventilation
- In the alveoli gas exchange occurs and oxygen diffuses into the blood and is now in pulmonary circulation.
- Through blood flow it travels to the heart, then enters systemic circulation and finally reaches respiring tissues
14
Q
Describe the concentrations of oxygen and carbon dioxide in the atmosphere, alveoli and in the capilliaries.
A
- In atmospheric air (which we inhale) there is a very high conc. of oxygen and a very low conc. of CO2
- In the alveoli (site of gas exchange in the lungs) we find high levels of O2 and low levels of CO2
- In the capillaries we find low levels of O2 and high levels of CO2
15
Q
Describe the pressure gradient across the alveoli.
A
- At the venous end we find lower partial pressures of O2 and higher partial pressures of CO2 in the blood than in the alveoli
- As we get towards the arterial end the partial pressures level off and are equal in the blood and in the alveoli
16
Q
How does the level of ventilation affect levels of gas exchange?
A
- Higher levels of ventilation means there is a steeper partial pressure gradient between the alveoli and blood
- This steeper gradient means there is more gas exchange that occurs
17
Q
How does the level of ventilation affect partial pressure of O2 in the alveoli?
A
- As ventilation increases the level of oxygen in the alveoli increases
- As we decrease ventilation the level of oxygen in the alveoli decreases as the oxygen is being pulled out of the alveoli at a faster rate than it is being replenished
- However at a certain limit levels of the partial pressure starts to plateau as ventilation increases
- This is because at this point the partial pressure of oxygen in the atmosphere is the same as the partial pressure of oxygen in the alveoli
18
Q
How does the level of ventilation affect partial pressures of CO2?
A
- As ventilation increases partial pressure of CO2 decreases as more gas excchange occurs so more CO2 is being exhaled
- However as ventilation decreases partial pressure of CO2 increases. This is because it will just build up in the alveoli
19
Q
What is the formula for total ventilation?
A
- V = Vt x f
- V: minute volume (the total volume of air inhaled in all breaths over one minute)
- Vt: tidal volume (volume of air inhaled in each breathe)
- f: frequency (number of breaths per minute)
20
Q
What does air within the lungs consist of ?
A
- The air in the lungs consist of “stale” air and “fresh air”
- Stale air is air that has remained from the last breathe
- Fresh air is air that has just been inhaled
- Therefore the alveolar air is not the same as the inspired air
21
Q
Why do we have stale air?
A
- The respiratory system is a two-way system in which air enters and leaves via the airways
- The airways is known as anatomic dead space as no gas exchange takes place in this area (only in the alveoli)
- This means at the end of each expiration there is a residual volume of air which remains in the airways and never takes part in gas exchange
- When we inhale again the fresh air then mixes with this stale air
22
Q
What is the formula of alveolar ventilation?
A
- Va= (Vt - Vd) * f
- Va: Alveolar minute volume (the total volume of fresh air entering the alveoli across all breathes in a minute)
- (Vt - Vd): volume of fresh air entering the alveoli in each breathe
- Vt: Tidal volume (volume of air being inhaled/exhaled)
- Vd: Dead space volume (volume of air remaining in the respiratory system at the end of expiration)
- f: Frequency
23
Q
How does gas naturally move?
A
- From areas of higher pressure to areas of lower pressure
24
Q
What is Boyle’s law and how is it derrived?
A
- P ∝ n/v
- P: Pressure (the number of gas molecules in a given volume)
- n: No. moles
- V: Volume
- If n is constant then as volume increases pressure decreases
- It is derived from the ideal gas equation: PV=nRT
- R: gas constant
- T: Temperature
25
Q
What are pleura?
A
- These are serous membranes that surround each lung which line the chest wall
26
Q
What is the pleural cavity?
A
- A fluid filled space between the pleura (membranes which line the chest wall and the lungs)
- It helps reduces friction between lungs and chest
27
Q
What is the effect of the pleural cavity on volume?
A
- The properties of the pleural cavity (i.e. sealed, fluid-filled) means they resist changes in volume
- Hence changes in volume of the thoracic cavity (due to respiring muscle activity) results in changes in lung volume
28
Q
How is the pleural cavity put under “negative pressure”?
A
- The opposing elastic recoil of the chest wall (outward) and lungs (inward) results in the pressure within the pleural cavity being sub-atmospheric (or under negative pressure)
29
Q
What is negative and positive pressure?
A
- Differences in pressure between neighbouring spaces are unstable.
- In the absence of sufficient opposing forces, equilibrium will be re-established either through the movement of liquid/gases or the collapse/expansion of a volume.
- Negative pressure: Lower number of molecules per volume (compared to surroundings) and so generates a collapsing force which pulls surfaces together
- Positive pressure: Increased number of molecules per volume (compared to surroundings) and so generates an expanding force which pushes the surfaces apart.
30
Q
How is air flow in the lungs generated during inspiration
A
- During inspiration the diaphragm contracts and the thoracic cavity expands. This causes an increase in thoracic cavity volume.
- Intrapleural pressure becomes more negative so the lungs expand and increase lung volume
- Alveolar pressure decreases below atmospheric pressure
- This change in pressure sets up a pressure gradient between the alveoli and the atmosphere and the air flows from the atmosphere (high pressure) into the alveoli (low pressure)
31
Q
How is air flow out of the lungs generated during expiration
A
- During expiration the diaphragm relaxes and the lung recoils due to elastic fibres.
- This causes the thoracic (lung) volume to decrease (so compresses the air) and intrapleural pressure increases
- The lungs become compressed (only during forced expiration) and the volume decreases
- This causes an increase in alveolar pressure above the atmospheric pressure
- This change in pressure sets up another pressure gradient between the alveoli and the atmosphere and so the air flows from the alveoli (high pressure) to the atmosphere (low pressure)
- The lungs deflate
32
Q
What is pneumothorax?
A
- Pneumothorax is a collapsed lung
- It occurs when air enters into the pleural cavity
33
Q
What happens if either of the pleura is ruptured?
A
- If there is a rupture, the pleura cavity is no longer sealed and provides a passage way for the air to move from one compartment to another
- Due to the pressure gradient between the pleural cavity and the surrounding, air will enter (pneumothorax) until the intrapleural pressure is the same as atmospheric pressure.
- Air will enter causing pleural cavity volume to increase.
- The lung tissue then recoils and expansion of chest (during inspiration) can draw more air into the pleural space
