Pulmonary ventilation Flashcards
What is the primary function of the respiratory system?
To supply respiring tissues with oxygen and remove excess carbon dioxide by ensuring sufficient levels of gas exchange take place within the lungs.
What does gas exchange rely on?
On the partial pressure gradients (the gas equivalent of concentration gradients) between alveolar air and blood, the respiratory system functions to maintain gradients of oxygen and carbon dioxide by ventilating gas exchange surfaces.
Where does air move to?
This involves moving air from the atmosphere to the alveoli and then out again, ensuring that fresh oxygen is supplied to alveoli and carbon dioxide does not accumulate.
What are the partial pressures inside the alveoli and capillaries?
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What is Hypoventilation and hyperventilation?
Hypoventilation and hyperventilation are defined as insufficient/excessive levels of breathing relative to that required to meet the metabolic demands of the body, and can be identified by the level of CO2 present within the blood .
Hypoventilation results in excessive levels of CO2 within arterial blood (PaCO2 > 6.0 kPa)
Hypoventilation reduces alveolar oxygen pressure and increases carbon dioxide pressure.
Hyperventilation results in reduced levels of CO2 within arterial blood (PaCO2 < 4.9 kPa).
Hyperventilation increases alveolar oxygen pressure and reduces carbon dioxide pressure.
What does increasing and decreasing the rate of ventilation do?
Increasing the rate of ventilation increases alveolar oxygen partial pressure (PAO2), and decreases alveolar carbon dioxide partial pressure (PACO2). Decreasing the rate of ventilation has the opposite effects.
What does lung volume depend on?
Height, sex, age and extent of respiratory diseases
What is the total lung capacity?
The maximum volume of air that can fill the lungs
What is vital capacity?
The total volume of air an individual is able to breath in, going from a max forced expiration to a max forced inspiration
What is residual volume?
The volume of air remaining in the lungs after a maximum forced expiration
What is expiratory reserve volume?
he additional volume of air that can be expired at the end of a resting/quiet expiration
What is functional residual capacity?
The volume of air within the lungs at the end of a resting/quiet expiration
What is inspiratory reserve volume?
The inspiratory reserve volume (IRV) is the additional amount of air that can be inhaled after a normal inspiration (tidal volume).
What is the equation for the total volume of air inhaled in all breathes over a minute (minute volume)
V = Vt x f
Vt = = tidal volume (mL), the volume of air in each breathe
f = frequency min^-1, the number of breaths per minute
What is the term for the air that resides in the lungs even after forced expiration
dead space that does not contribute towards gas exchange
What is the purpose of residual air?
Ensure the lungs do not collapse
How do we calculate the volume of air reaching respiratory surfaces (alveolar ventilation)
We need to account for the volume of air that does not reach the alveoli
Va = (Vt - Vd) x f
Va = Alveolar minute volume (mL), the total volume of fresh air entering the alveoli across all breaths over a minute
Vt = tidal volume
Vd = Dead space volume (mL), then the volume of air remaining in the respiratory system at the end of expiration
f = frequency (min^-1)
Vt - Vd = the volume of fresh air entering the alveoli in each breath
What does Boyles Law state?
This describes the relationship between pressure, volume and molar quantity
What is required to move air into the lungs
Alveolar pressure must fall below must fall below atmospheric pressure, so air moves down pressure gradient
What is required to move air out of the lungs?
Alveolar pressure must rise above atmospheric pressure
How are changes in pressure achieved?
These pressure changes are achieved by contraction/relaxation of respiratory muscles. This alters the volume of the thoracic cavity (with the opposite effect on alveolar pressure).
Describe the changes in pressure and volume during inspiration and expiration
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What are the lungs and the chest cavity separated by?
Membranes known as pleurae
Where does the (inner) visceral pleura line?
Each lung
Where does the (outer) parietal pleura line?
Thoracic cavity, surrounding the chest, diaphragmatic and mediastinum (contains the heart)
What is between the pleurae?
Fluid-filled cavity
What causes the pressure between the pleura to become sub-atmospheric?
The tissues attached to each pleura recoil in opposite directions due to their elastic properties (i.e. the lungs recoil inwards, the chest wall recoils outwards), stretching the sealed pleural cavity between them very slightly and resulting in the pressure within the cavity being naturally sub-atmospheric (approximately -0.5kPa at the beginning of inspiration).
Describe the steps in inspiration?
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Describe the steps in expiration?
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how are lung volume, intrapleural pressure, alveolar pressure and airflow all related?
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What is Pneumothorax?
What are the 2 effects of this?
If either of the either of the pleural membranes is ruptured (e.g. due to trauma, bleb formation, or disease), the pressure gradient between the pleural cavity and the atmosphere (or lungs, depending on the particular injury) will cause air to enter the pleural space (‘pneumothorax’).
Entry of air into the pleural cavity results in its volume increasing, at the expense of the lung. Furthermore, recoil of the lungs and expansion of the chest wall during breathing will potentially draw additional air into the cavity, further decreasing lung volume.
Describe the the effects of rupturing the pleural membrane and entry of air into the pleural cavity (pneumothorax) on intrapleural pressure and lung volume.
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