Physiology Of Gas And Fluid Exchange In The Lungs

Question 1

Three interacting process for gas exchange within the lungs

Answer 1

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)

Question 2

Bulk flow

Answer 2

Mass movement or convection of gases through conducting airways

Movement is caused by differences in total pressure gradients.

Question 3

How are oxygen and carbon dioxide most commonly transported?

Answer 3

Oxyhemoglobin for oxygen (98%)

Bicarbonate for carbon dioxide (70%)
- other 30% is blood dissolved

Question 4

Diffusion

Answer 4

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)

Question 5

Daltons law

Answer 5

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

Question 6

Causes of hypoventilation

Answer 6

Decreased CNS activity

Altered neural and neuromuscular transmission

Muscle abnormalities

Chest wall and pleural abnormalities

Lung and airway distress

Sepsis/circulatory shock

Question 7

Most common cause of hyperventilation

Answer 7

Panic attacks And Anxiety

Others include:

• bleeding
• COPD
• Asthma
• Heart attacks
• diabetic keto acidosis

Question 8

Minute ventilation

Answer 8

Is the product of the volume of each breath and the frequency of breathing

Question 9

Henrys law

Answer 9

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*

Question 10

How does partial pressures of gases change with hypoventilation and hyperventilation?

Answer 10

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

Question 11

Flicks law

Answer 11

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

Question 12

Lung diffusion capacity

Answer 12

Measure of the lungs ability to transfer gases

- is also the sum of all individual membrane diffusing capacity’s in series

Question 13

Cystic fibrosis

Answer 13

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

Question 14

Amount of time it takes RBCs to get through capillaries and to achieve oxygen equillibration

Answer 14

0. 25 sec = equilibration
1. 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*

Question 15

Difference between perfusion limited vs diffusion limited gas exchange

Answer 15

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

Question 16

General important solubility coefficients (S)

Answer 16

Oxygen 0.024

CO2 = 0.57

Carbon monoxide = 0.018

Nitrogen = 0.012

Helium = 0.008

Question 17

Hydrostatic edema vs permeability edema

Answer 17

Both are types of pulmonary edema that affect the flow rate or fluids and ions via starling forces

Hydrostatic:

• often tied to cardiogenic issues
• abnormality is an increase in pressure differences (with capillary getting larger)
• seen in left heart failure and others
• treatment = get rid of fluid excess (diuretic)

Permeability edema

• often tied to non-cardiogenic issues
• abnormality is endothelium injury which increases permeability coefficient/ factor
• seen in trauma and chronic infections
• treatment = fix underlying problem

Question 18

Pulmonary wedge pressure

Answer 18

Measurement that determines the pressure difference form the pulmonary capillaries to the left atrium

• increases indicate increased preload on left ventricle and pulmonary edema
• often seen in mitral stenosis as well

elevation from normal is a sign of cardiogenic edema NOT non-cardiogenic edema