Physiology Of Gas And Fluid Exchange In The Lungs Flashcards
Three interacting process for gas exchange within the lungs
Ventilation: brings oxygen from the air into the alveoli
- bidirectional from inspiration -> expiration and vice versa
Diffusion: process by which Oxygen in alveoli passes across the alveolar wall into the pulmonary capillaries
- does not require energy and is passive
Perfusion: moves the blood through the pulmonary circulation and allows continuous flow of RBCs to take on oxygen
- unidirectional from right ventricle (pulmonary system) to left atrium (systemic system)
Bulk flow
Mass movement or convection of gases through conducting airways
Movement is caused by differences in total pressure gradients.
How are oxygen and carbon dioxide most commonly transported?
Oxyhemoglobin for oxygen (98%)
Bicarbonate for carbon dioxide (70%)
- other 30% is blood dissolved
Diffusion
Movement of individual gases and molecules based on their own individual partial pressure gradients
Occurs due to random molecular movements and is dependent on temperatures changes (increases as temperatures get higher)
Daltons law
The sum of the partial pressures of gases in a mixture is equal to the total pressure
(760mmHg) always in standard atmospheric air
- 21% is oxygen
- 79% is nitrogen
Note when measuring humidified air, take 760 And -47 from it. Then calculate
Causes of hypoventilation
Decreased CNS activity
Altered neural and neuromuscular transmission
Muscle abnormalities
Chest wall and pleural abnormalities
Lung and airway distress
Sepsis/circulatory shock
Most common cause of hyperventilation
Panic attacks And Anxiety
Others include:
- bleeding
- COPD
- Asthma
- Heart attacks
- diabetic keto acidosis
Minute ventilation
Is the product of the volume of each breath and the frequency of breathing
Henrys law
Gas dissolved = ((s) x (partial Pressure of dissolved gas))
S = Determines the amount of gas dissolved in a liquid at any given temperature (inversely related to the temperature)
- is proportional to the partial pressure and unique solubility of the gas talked about.
Partial pressure is determined by ((concentration of dissolved gas)/ (solubility coefficient))
- accounts only for gases that are physically dissolved and cannot do for chemically combined gases*
- flow is also directly proportional to the pressure gradient*
How does partial pressures of gases change with hypoventilation and hyperventilation?
Hypoventilation (<5L/min)
- increases partial pressures of CO2
- decreases partial pressures of Oxygen
Hyperventilation (>5L/min)
- increases partial pressures of oxygen
- decreases partial pressures of CO2
Flicks law
Diffusion of gas = ((area) x (diffusion content) x (Pressure changes) / (tissue thickness))
Determines the relationship between area, diffusion, pressure changes and tissue thickness as it pertains to gas diffusion
Thickness is inversely proportional to gas dissolved
Lung diffusion capacity
Measure of the lungs ability to transfer gases
- is also the sum of all individual membrane diffusing capacity’s in series
Cystic fibrosis
Recessive genetic disease affecting children and young adults
Caused by mutations in CFTR proteins
results in:
- reduced chloride secretion
- increased sodium absorption
- insufficient airway luminal fluid
- improper mucocillary transport
- bacterial infections
Most common bacterial agents are pseudomonas aeruginosa and staph aureus
Amount of time it takes RBCs to get through capillaries and to achieve oxygen equillibration
- 25 sec = equilibration
- 75 sec = time spent in capillaries
* when exercising, it is hard for the RBCs to reach equilibration for oxygen (since time in capillaries is reduced to 0.4 sec), an effect called hypoxemia*
Difference between perfusion limited vs diffusion limited gas exchange
Diffusion limited
- seen at rest and pulmonary blood flow determines oxygen transfer
- partial pressure gradient is not maintained
- increasing gas transport = increase blood flow
Perfusion limited
- amount of gas transported is affected by the diffusion coefficient of each gas as well as partial pressures
- partial pressure gradient is maintained to allow continues diffusion
- increasing gas transport = increase partial pressure gradient