Ventilation and Lung Mechanics Flashcards
What is the normal pO2?
9.3-13.3 kPa
What is the normal pCO2?
4.7-6 kPA
What is the tidal volume?
Volume of air which enters and leaves the lungs with each breath
(Anatomical dead space + alveolar ventilation)
What is the anatomical dead space?
The total volume of the conducting airways from the nose or mouth down to the level of the terminal bronchioles (does not take part in gas exchange)
What is the physiological dead space?
Volume of air in alveoli which are not perfused or damaged that does not take part in gas exchange
What is the total dead space?
Anatomical + physiological dead space
Total air inhaled that does not take part in gas exchange
How would you calculate total pulmonary ventilation?
Tidal volume x respiratory rate
How would you calculate alveolar ventilation?
(Tidal volume - dead space) x respiratory rate
What is inspiratory reserve volume (IRV)?
The maximal amount of additional air that can be drawn into the lungs by determined effort after normal inspiration
What is expiratory reserve volume (ERV)?
The additional amount of air that can be expired from the lungs by determined effort after normal expiration
What is residual volume (RV)?
The amount of air that remains in a person’s lungs after fully exhaling
What is the vital capacity (VC)?
The greatest volume of air that can be expelled from the lungs after taking the deepest possible breath.
What is inspiratory capacity (IC)?
The volume of air that can be inspired after a normal expiration; it is the sum of the tidal volume and the inspiratory reserve volume.
What is the functional residual capacity (FRC)?
The volume of air present in the lungs at the end of passive expiration
What is functional residual capacity determined by?
The balance of elastic forces of the chest wall, favouring outward expansion, and the elasticity and surface tension of the lung, favouring a small lung volume
What is the link between the lungs and the chest wall?
Pleural membranes
What is present between the 2 pleural membranes?
Small amount of fluid
Describe the pressure within the pleural space at end-expiration
Slightly negative
chest wall wants to sprind out and lungs want to recoil in
What happens to the ipsilateral lung if the pleural seal is broken?
It would shrink down, regardless of breathing manoeuvres
What happens to pleural pressure upon inhalation?
Gets more negative
What are the accessory muscles of inspiration?
Sternocleidomastoid, scalene muscles, pectoralis major and minor, trapezius
What are the accessory muscles of expiration?
Internal intercostals and muscles of the abdominal wall
In the older adult, FRC is relatively higher than in the young person and the balance between the chest wall and lung has changed. Why is this?
Lungs are less elastic in older people
How do you calculate compliance?
Change in volume/change in pressure
In what situation would lungs have low compliance?
Fibrosis - lungs are stiffer
In what situation would lungs have high compliance?
Emphysema - slack lungs
What is the function of surfactant?
Decreases alveolar surface tension
- Allows the lung to inflate more easily (increased compliance)
- Prevents alveolar collapse
What secretes surfactant?
Alveolar cells
When does production of surfactant begin in the fetus?
Between 25 and 28 weeks
At what gestational age is surfactant adequate?
35
What things could cause increased airways resistance?
Increased mucus (chronic bronchitis)
Hypertrophy of smooth muscle/oedema (asthma)
Loss of radial traction (emphysema)
What is respiratory distress syndrome of the newborn caused by?
Lack of surfactant (usually in premature babies)
Without surfactant, the surface tension of the alveolar sacs is high - increased tendency of the alveoli to collapse
What are some signs of respiratory distress in babies?
Cyanosis, grunting, intercostal and subcostal recession
How do you calculate resistance of an airway?
Pressure/ rate of flow
Why is pleural pressure negative?
Its in between two opposing forces - outward expansion of chest wall and lungs wanting to recoil
- increased volume in space = smaller pressure
