Ventilation and gas exhange Flashcards
What is hyperventilation?
Excessive ventilation of the lungs atop of metabolic demand (results in reduced PCO2 - alkalosis)
How to calculate minute ventilation? ( L/min )
Typical range?
Tidal Volume L x breathing frequency min
6 L/min
How to calculate Alveolar ventilation ( L/min )
Gas entering and leaving the alveoli
( Tidal volume - Dead space ) x Breathing frequency
What factors affect lung volume and capacities?
Body size - height
Sex
Disease
Age
Fitness
What is the conductive zone?
Equivalent to anatomical dead space
150 mL in adults at FRC
16 generations
Gas exchange doesn’t occur here, e.g. bronchi, trachea, larynx etc
In comparison to respiration zone
What is the non-perfused parenchyma?
Alveolar dead space
Alveoli with no blood supply
No gas exchange
0 mL in adults
Parenchyma: should be functional not supportive tissue, in this case it is alveoli which is not functioning ( non-perfused )
How to increase volume of dead space?
Anaesthethic circuit snorkelling
intubation
How to decrease volume of dead space?
Tracheostomy
Cricothyroctomy
The chest wall has a tendency to ( a ) , and the lung has a tendency to ( b ) inwards
a - spring outwards
b - recoil inwards
What is the FRC?
Functional residual capacity which is the neutral position of the intact chest
- FRC also represents the point of the breathing cycle where the lung tissue elastic recoil and chest wall outward expansion are balanced and equal.
Inspiratory muscle effort + chest recoil > lung recoil ?
INSPIRATION
Chest recoil < lung recoil + expiratory muscle effort ?
EXPIRATION
Describe the basic chest wall anatomy?
The lungs are surrounded by a visceral pleural membrane
The inner surface of the chest wall is covered by a parietal pleural membrane
The pleural cavity (the gap between pleural membranes) is a fixed volume and contains protein-rich pleural fluid
What diseases affecting lung anatomy can cause issues with ventilation ?
Haemothorax - intrapleural bleeding
Pneumothoriax - performated chest wall / lung
What is negative pressure breathing?
Pressure alv is reduced below Pressure atm
- normal healthy breathing
What is positive pressure breathing?
Pressure atm increased above P alv
- recusitation
Describe the three compartment model?
Transmural pressures
(Pinside – Poutside)
A negative transrespiratory pressure will lead to inspiration
A positive transmural pressure leads to expiration
What is Dalton’s Law?
Pressure of a gas mixture is equal to the sum (Σ) of the partial pressures (P) of gases in that mixture
What is Fick’s Law
Molecules diffuse from regions of high concentration to low concentration at a rate proportional to the concentration gradient (P1-P2), the exchange surface area (A) and the diffusion capacity (D) of the gas, and inversely proportional to the thickness of the exchange surface (T)
What is Henry’s Law?
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
What is Boyle’s Law?
At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas
What is Charle’s law?
At a constant pressure, the volume of a gas is proportional to the temperature of that gas
What ‘type’ of air could a patient be breathing?
Room air
Oxygen therapy: + O2
Smoke: -O2 +CO2 +CO
High altitude: Same proportion as room air but all increased
How is Inspired air modified in airways?
warmed, humid, slower going down
Dry air outside:
PO2 = 21.3 kPa
PCO2 = 0 kPa
PH2O = 0 kPa
Conducting airways:
PO2 = 20 kPa
PCO2 = 0 kPa
PH2O = 6.3 kPa
Respiratory airways
PO2 = 13.5 kPa
PCO2 = 5.3 kPa
PH2O = 6.3 kPa
