Pulmonary Ventilation Flashcards
Define lung volumes and capacities terms
IDK Lung volumes and capacities depend on factors like age, sex, height as well as lung properties (compliance, obstruction/damage due to disease) Total lung capacity Vital capacity Functional residual capacity Inspiratory reserve volume Tidal volume- the volume that we are breathing in and out Expiratory reserve volume Residual volume
Why do we need pulmonary ventilation?
Pulmonary ventilation is required to maintain adequate O2 supply to (and CO2 removal from) respiring tissues Pulmonary ventilation (movement of air from the atmosphere to gas exchange surfaces within the lung) is required to maintain O2 and CO2 gradients between alveolar air and arterial blood This enables a sufficient level of gas exchange to take place, ensuring adequate O2 supply/CO2 removal to/from respiring tissues (via blood)
What factors does adequate O2 transport depend on?
Adequate transport of O2 from atmosphere to respiring tissues depends on healthy levels of alveolar ventilation, gas exchange and cardiac output
How are pressure gradients maintained?
Pressure gradients between alveoli and blood are maintained by adequate ventilation
How do the partial pressures of Co2 and O2 change?
The partial pressure of O2 within alveoli increases as ventilation increases
The partial pressure of CO2 within alveoli decreases as ventilation increases
What is ventilation and how is it calculated?
Ventilation: what volume of fresh air reaches respiratory surfaces over a given time
Ventilation depends on volume (depth) and rate of breathing)
V= VT x f
V- minute volume (mL), the total volume of air inhaled in all breathes over one minute
VT- tidal volume (mL) the volume of air inhaled each breath
f- frequency (min^-1) the number of breaths per minute
What is the difference between alveolar and fresh air? (fresh and stale)
Alveolar ≠ inhaled air: the lungs contain a mixture of ‘fresh’ and ‘stale’ air
Gas exchange only takes place in alveoli, but air must first pass through the airways (airways= “anatomic dead space”)
The respiratory system is a two-way system; air enters and leaves via the same path
Also, a residual volume of air remains in the airway and lungs at the end of expiration
This means that the final is around 150mL (dead space volume) of each inspiration never reaches the alveoli or takes place in gas exchange
Fresh and stale air in this context refers to air that has just enters the respiratory system from the atmosphere, vs. air that entered the lungs during a previous breath and which has already participated in gas exchange, respectively
How does the respiratory system achieve movement of air?
Gases naturally move from (connected) areas is higher pressure to lower pressure, until an equilibrium is reestablished
Changes in lung volume induce changes in alveolar pressure, which generate pressure gradients between alveoli and atmosphere causing air to flow
Inspiration- diaphragm contracts and thoracic cavity expands
Alveolar pressure decreases
Expiration- diaphragm relaxes (and lung recoils)
Thoracic cavity volume
HOw does pressure affect gas exchange?
Changes in lung volume induce changes in alveolar pressure, which generate pressure gradients between alveoli and atmosphere, causing air to flow
Equal pressure- At the end of expiration, Palveoli= Patmosphere, therefore there is no movement of air
Higher pressure- The outer surfaces of the lung are pulled outwards (expansion)
↑volume = ↓alveolar pressure
Palveoli < Patmosphere
Air flows from high (atmosphere) to low (alveoli) pressure
Lower- Air within the lung is compressed
↓volume = ↑alveolar pressure
Palveoli > Patmosphere
Air flows from high (alveoli) to low (atmosphere) pressure
What is the pleural cavity and its function?
The lungs and chest wall are indirectly attached via the pleural cavity
Pleural cavity- fluid filled space between the membranes (pleura) that lines the chest wall and each lung- helps to reduce friction between lungs and chest
The properties of the pleural cavity (sealed, fluid-filled) mean that it resists changes in volume
Thus, changes in the volume of the thoracic cavity (due to resp. muscle activity) result in changes in lung volume
The opposing elastic recoil of the chest wall (outward) and lungs (inward) results in the pressure within the pleural cavity being sub-atmospheric (under “negative pressure”)
What is meant by negative pressure?
Differences in pressure between neighbouring spaces are unstable
In the absence of sufficient opposing force, equilibrium will be re-established via either movement of liquid/gas or collapse/expansion of volume (at the expense of surrounding structures)
Negative pressure- lower number of molecules per volume (relative to surroundings) -> generates collapsing force (pulls surfaces of contained space together)
Positive pressure- increased number of molecules per volume (relative to surroundings) -> generates expanding force (pushes surfaces of contained space apart)
What are the effect of positive and negative pressure?
As there is a lower pressure in the plural cavity this is negative pressure
What would happen is that this negative pressure will exert force on its neighbouring structures and pulls them together in order to try to reduce the volume, so the lungs will be expanded as a result
By expanding it decreases the volume and the pressure goes back to 0; the equilibrium
And vice versa for positive pressure, where the positive pressure wants to push structures apart
What happens during inspiration?
Movement of air into/out of the lungs chieved by changing the volume of the thoracic cavity
Inspiration:
1. Respiratory muscles (e.g. diaphragm) contract
2. Volume of thoracic cavity increases
3. Intrapleural pressure becomes more negative
4. Lungs expand, increasing volume
5. Palv (alveolar pressure) decreases below Patm (atmospheric pressure)
6. Air moves down pressure gradient, through airways into alveoli, expanding the lungs
What happens during expiration?
Expiration involves elastic recoil of the lungs and relaxation of respiratory muscles
Expiration
1. Respiratory muscles (e.g. diaphragm) relax, lungs recoil due to elastic fibres
2. Volume of thoracic cavity decreases
3. Intrapleural pressure increases
4. Lungs compressed* volume decreases
5. Palv increases above Patm
6. Air moves down pressure gradient into atmosphere, deflating lungs
Compression of the lungs due to increased intrapleural pressure only occurs during forced expiration
In quiet breathing, elastic recoil is sufficient to decrease lung volume
How does inspiration and expiration affect interpleural pressure (1), alveolar pressure (2), air flow (3), volume changes (4)
1) As lung volume increases during inspiration, intrapleural pressure becomes more negative due to the elastic properties of the lung generating increasing recoiling force.
2) As the lungs expand, the increase in volume decreases PAlv. As air enters the lungs, the pressure re-equilibrates once again as the increased concentration of gas molecules compensates for the increased volume (P = n/V) 3) When PAlv < PAtm the pressure gradient causes air to move into the lungs. Where PAlv > PAtm air moves out. The speed of airflow is dependent on the pressure gradient and level of airway resistance present. 4) Entry of air into the lungs due to (3) leads to inflation and increased volume, which is reversed during expiration.
