Pulmonary Ventilation Flashcards
What is the primary function of the respiratory system
Supply respiring tissues with oxygen and remove excess carbon dioxide by ensuring sufficient levels of gas exchange take place within the lungs
What is hypo/hyperventilation
Insufficient/excessive levels of breathing to meet metabolic demands
How to calculate total level of ventilation
Depends on volume of air inspired, and the frequency of breathing
V = Vt x f
V = minute volume (mL), total volume of air inhaled in all breaths over one minute
Vt = Tidal volume (mL), volume of air inhaled in each breath
f = frequency (min-1), the number of breaths per minute
Why does total ventilation not perfectly reflect the volume of air reaching respiratory surfaces to take part in gas exchange
Gas exchange occurs in alveoli not airways. Residual air is always required to occupy airways (Dead-space not used in gas exchange), as well as in the lungs to prevent alveoli collapse
The final 150ml of air of each inspiration never reaches the alveoli, as it is first to leave the resp system in expiration
How to calculate volume of air reaching respiratory surfaces accounting for dead-space volume
Va = (Vt - Vd) x f
where Va = alveolar minute volume
Vt = tidal volume
Vd = dead space volume
f = frequency
Describe Boyle’s Law
Pressure is inversely proportional to volume, and directly proportional to moles
P () n / v
Describe how alveolar pressure changes regulate movement of air between atmosphere and lungs
Inspiration - Alveolar pressure must fall below atmospheric pressure (air flows in)
Expiration - Alveolar pressure must rise above atmospheric pressure (air out)
Describe the pleura
Inner pleura line each lung, outer pleura line the thoracic cavity. Between the two, the fluid-filled pleural cavity.
Pleura tissue recoil in opposite directions, stretching the cavity to decrease pressure within the pleural space (greater volume same mols)
Pressure within pleural space is negative.
What does negative pressure do
Generates a collapsing force, pulling the surfaces of the contained space together, whereas positive pressure generates an expanding force, pushing the surfaces of the contained space apart
Negative vs positive intrapleural pressure
Negative - Pulls pleura (lungs/chest wall) together
Positive - Pushes pleura away from each other
Describe what the elastic recoil of the chest wall does vs elastic recoil of the lungs
Elastic recoil of the chest wall (and inspiratory muscle contraction) acts to pull the chest wall outwards, expand thoracic cavity
Recoil of the lungs pulls the visceral pleural inwards, compresses the lung volume
Which 3 forces determine if lungs expand or compress at a given time
Elastic recoil of the chest wall and inspiratory respiratory muscle contraction
Elastic recoil of the lungs
Degree of negative intrapleural pressure
Describe inspiration
Contraction of respiratory muscles, generates force to pull parietal pleura outwards. Pleural cavity stretched, decreasing intrapleural pressure. As pressure becomes more negative, the two pleurae are pulled together.
When the force pulling the pleurae together is greater than the elastic recoil of the lung, the visceral pleura is pulled outwards, expanding the lung
Describe expiration
Relaxation of inspiratory respiratory muscles results in decreased outwards force acting on the parietal pleura. Intrapleural pressure increases, now lower than elastic recoil of the lung, so visceral pleura pulled inwards, decreasing lung volume
Describe forced expiration
Muscle contraction generates inward force on the parietal pleura, compressing the pleural cavity and lungs, faster and stronger decrease in lung volume
