Respiratory 6 Flashcards
If perfusion remains constant and hypoxia is not caused by hypoventilation or alterations in atmospheric PO2 then what causes the problem
Issue with gas exchange between the alveoli and blood
- issue at exchange barrier with diffusion
What causes an issue with gas exchange
Alterations in a layer
Water layer, or interstitial space
What are the layers between alveoli and capillary
Alveolar air - water layer - interstitial space - alveolar type 1 epithelial cell - interstitial space with matrix - blood plasma - cytoplasm of RBC
What happens to oxygen once diffuse into cytoplasm of RBC
Attaches to hemoglobin
Diffusion
Random movement of molecules from a region of high concentration to a region of low concentration
What are 4 things that will affect the random movement of gas molecules between the alveoli and capillaries
- Concentration gradient
- Surface area
- Barrier permeability
- solubility of gas - Diffusion distance
What is the only thing that changes in healthy individuals to affect diffusion
Concentration gradient
What is directly proportional to diffusion
Surface area, concentration gradient, barrier permeability
What is inversely proportional to rate of diffusion
Distance
What is constant under normal conditions in relation to diffusion
Surface area, diffusion distance and barrier permeability
What is the main determinant of diffusion
Concentration grradien
Emphysema
PO2 normal or low
- destruction of alveoli
- decreased surface area
What diseases cause hypoxia
Emphysema, fibrotic lung disease, pulmonary edema, asthma
Pulmonary fibrosis
- PO2 normal or low
- thickened fibrous connective tissue slows gas exchange
- loss of lung compliance
- decreased barrier permeability
Restrictive
Pulmonary edema
Fluid in interstitial space increases diffusion distance
- PO2 normal
Asthma
Increased airway resistance, bronchioles constrict
- PO2 low
- decreased concentration gradient
What is alveolar gas exchange influenced by
O2 reaching alveoli and gas diffusion between the alveoli and blood
What is O2 reaching alveoli determined by
Composition of inspired air
Alveolar ventilation
What is alveolar ventilation determined by
Rate and depth of breathing, airway resistance, lung compliance
What is gas diffusion between alveoli and blood determined by
Surface area and diffusion distance/permeability
What is diffusion distance/permeability determined by
Barrier thickness, amount of fluid
Why must respiratory gases be soluble in liquids
Alveoli lined with liquid, space between alveoli and capillaries liquid and plasma is liquid
What is the movement of gas molecules form air to liquid directly proportional to
- Pressure gradient of the gas
- Solubility of gas in liquid
- Temperature- relatively constant
Why do we need hemoglobin to carry O2
O2 not very soluble in liquid
What is equilibrium
Gas moving in =gas moving out
PO2 matched
CO2 solubility
Very soluble
Increased diffusion distance (pulmonary edema) doesn’t affect PCO2
What happens to 02 and CO2during pulmonary edema
Fluid in interstial space decreased diffusion because O2 not very soluble in liquid
PCO2 is normal because higher solubility
What is mass flow
Movement of X per minute
Measurement of movement of substance into, out of, or within body
What is mass balance
Any substance in body must remain constant
What shows mass flow and mass balance in body
Oxygen transport in circulation and oxygen consumption by tissues
Equation for mass flow
O2 transport = cardiac output (L blood/min) x O2 concentration (mL O2/L blood)
Equation for mass balance
Arterial O2 transport - venous O2 transport = QO2
Fick equation (mass flow and mass balance)
CO x (arterial O2 - venous O2) = QO2
O2 consumption by systemic tissues
Arterial O2 transport
200 ml O2/L blood and CO is 5L/min
ML O2/min to cells= 200ml 02/L blood x 5L blood/min
= 1000 ml O2/min delivered to tissues
Venous O2 transport
Venous blood 150ml O2/L blood, CO 5L/min
ML O2 taken away from cells= 150 ml blood x 5L blood/min
= 750 ml O2 taken away
Fick equation
CO= 5L
Arterial O2 200ml
Venous O2 150ml
5L/min (200ml - 150ml)
=250 ml O2/min
How much O2 is bound to hemoglobin
More than 98%
How much O2 is dissolved in plasma
Less than 2%
How many Hb molecules in one RBC and how much O2 carried
~250 million Hb in one RBC = 1 billion O2
What is the process of O2 moving from alveoli to cells
- O2 diffuses into plasma where <2% dissolves
- O2 diffuses into RBC, binds to Hb
- Transport to cells
- Process reverses and HbO2 broken down
- O2 dissolves in plasma and into cells
Oxygen binding obeys what law
Law of mass action
What is law of mass action
When PO2 high Hb will bind to O2
When PO2 low Hb will start to release O2
Binding is reversible
What does oxygen binding to Hb produce
HbO2
How long does RBC spend in pulmonary capillary at rest and how long for it to become saturated
~0.75 sec and ~.40 secs
What is the transfer of O2
Alveolar air to plasma to RBCs onto hemoglobin
What happens when deoxygenated blood reaches lungs
Amount of O2 around Hb increases so Hb will start to bind O2
Where type of tissues does blood travel to
Low PO2 tissues
- draws O2 out of plasma, which disrupts the equilibrium and causes Hb to release its O2 into plasma
- O2 can diffuse into tissues
When is equilibrium reached
When P02 is matched in alveoli, plasma and cytoplasm and Hb no longer capable of taking up anymore o2
For any given PO2 what happens
Certain number of Hb binding sites will be saturated
Why does O2 diffuse from alveoli to plasma
Alveoli 100mmHg
Plasma 40 mmHg
When plasma starts to increase PO2 until 100mmHg
Start binding to Hb
How does Hb ensure the partial pressure gradient continues
O2 bound to Hb no longer contribute to partial pressure gradient
02 will continue to move across until equilibrium reached
At rest how much oxygen is consumed
250 ml O2/min
What is the O2 content of plasma and total O2 carrying capacity
3mL O2/L blood
3 mL x 5L blood/min = 15 ml O2/min
What is total O2 carrying capacity with RBC
O2 content of RBC= 197 ml O2/L blood
200 ml O2/L blood
200 ml x 5 L blood/min = 1000 ml O2/min
