Respiratory Gas Exchange and Transport Flashcards
Once O2 enters the lungs how does it get to the tissues?
- O2 diffuses across alveoli membrane - enters pulmonary capillaries - returns to heart via pulmonary vein - distributed around the body
How is CO2 removed from pulmonary capillaries?
- diffuses across capillary membrane and into lungs - down concentration gradient - expired out of lungs
What is the interstitium?
- small space between alveolar and capillaries
What are the cells of the capillaries and alveolar?
- capillaries = simple squamous epithelial cells - alveoli = squamous (type 1) and cuboidal (type 2) epithelial cells
Roughly how big is normal interstitium space?
- aprox 0.5um
What are the 2 types of cells in the alveolar?
- type 1 cells = squamous - type 2 cells = cuboidal
What is partial pressure?
- in a mixture of gases - individual gases exert a pressure - this is called partial pressure
What is the total pressure in relation to partial pressures?
- the sum of all the partial pressures added together
Instead of referring to concentration gradients, what should we refer to when talking about gas exchange?
- partial pressure = concentrations
Instead of referring to high and low concentration gradients gradients, what should we refer to when talking about gas exchange?
- high and low diffusion gradients
Does gas move up of down diffusion gradients?
- partial pressures always move down pressure gradients
What does O2 saturation, also referred to as SATs mean?
- level of O2 bound to haemoglobin in red blood cells - measured as SaO2 % (% of O2 bound to haemoglobin)
What is the normal range for haemoglobin in the body for males and females?
- male = 13.8 - 17.2 g/dL - female = 12.1 - 15.1 g/dL
What are a few things that can affect the amount of haemoglobin in the body?
- age - gender - ethnicity
What are normal O2 saturation levels?
- 94-99%
What are normal O2 saturation levels in COPD patients?
- 88-92%
What O2 saturation level would be classified as hypoxic?
- <88%
What does SpO2 mean?
- amount of O2 bound to haemoglobin - relative to the haemoglobin not carrying oxygen - measured by blood gas analysis
What does SaO2 mean?
- amount of O2 bound to haemoglobin - relative to the haemoglobin not carrying oxygen - measured by pulse oximetry
What does the Oxygen Dissociation curve SpO2 tell us?
- shows tight relationship between O2 partial pressure and O2 saturation of haemoglobin
What shape is the curve in the Oxygen Dissociation curve SpO2?
- sigmoid shape
- like and S curve
Where the Oxygen Dissociation curve plateaus, would an increase in O2 partial pressure (PaO2) change oxyhemoglobin saturation?
- no
- already around 98% so no real change
At 50% partial pressure on the Oxygen Dissociation curve, would a change in O2 partial pressure (PaO2) change oxyhemoglobin saturation?
- yes
- small changes in PaO2 have a large effect on oxyhemoglobin saturation
Would PaO2 (O2 partial pressure) be highest in the arterial or venous blood flow?
- arterial
- delivering O2 to tissues
- venous is left over or reserve
When might we expect to see the Oxygen Dissociation curve shift to the left?
- at the lungs
- at lower PaO2 would still ⬆️ oxyhemoglobin saturation
- O2 affinity for haemoglobin is highest at the lungs
When might we expect to see the Oxygen Dissociation curve shift to the right?
- at the tissues during exercise
- O2 affinity is low to increase diffusion into tissues
What would a shift in Oxygen Dissociation curve shift to the right do to pH, temperature, CO2 levels and O2 affinity?
- temperature = ⬆️
- CO2 = ⬆️
- pH = ⬆️
- O2 affinity = ⬇️
What would a shift in Oxygen Dissociation curve shift to the right do to pH, temperature, CO2 levels and O2 affinity?
- temperature = ⬆️
- CO2 = ⬆️
- pH = ⬇️
- O2 affinity = ⬇️
What are the 4 main things that can affect the Oxygen Dissociation curve?
- pH
- temperature
- 2,3 BPG (reduces O2 affinity) (also known as DPG)
- PCO2
What does oxyhemoglobin mean?
- O2 bound to haemoglobin
What is the diffusing capacity for carbon monoxide (DLCO) test used for?
- assess lung function - specifically ability how much air gets to erythrocytes - overall function of capillary membrane
Does carbon monoxide or O2 have a higher affinity for haemoglobin?
- carbon monoxide - aprox 213 times more affinity and soluble in blood
What is the normal process for DLCO?
1 - inhale gas including O2, helium and 0.3% CO 2 - breath hold for up to 10 seconds 3 - breathe out and discard first 1 litre 4 measure air after 1st litre
What is the measurement of the DLCO?
- CO able to diffuse per minute
What is a severe impairment in lung function measured by DLCO?
- <40%
Patients with emphysema are likely to have an impaired DLCO, why?
- alveolar are damaged
- ⬇️ alveolar membrane surface
- ⬇️ area for diffusion
Patients with pulmonary fibrosis are likely to have an impaired DLCO, why?
- interstitium becomes scarred, causing thickening
- ⬆️ interstitium thickness causes ⬇️ diffusion
Patients with pulmonary hypertension are likely to have an impaired DLCO, why?
- blood vessels to alveoli are compressed reducing blood flow
- ⬇️ blood flow means ⬇️ diffusion
Patients with anaemia are likely to have an impaired DLCO, why?
- less haemoglobin bound to blood - ⬇️ haemoglobin to bind with blood - ⬇️ diffusion
What is the respirator quotient (RQ)?
- ratio between CO2 and O2 absorbed
What can the respirator quotient (RQ) tell us about fuel source?
- RQ number indicates main substrate for energy - 1 = carbohydrates - 0.7 = fats - 0.8 = proteins
What is the main role of CO2 in the blood?
- maintain pH
What is the formula for converting CO2 in H+ through carbonic anhydrase?
- CO2 + H2O = carbonic acid = HCO3- + H+ - all facilitated by carbonic anhydrase
What does CO2 and H+ do to blood pH?
- reduces blood pH
What is a common cause of alkalosis?
- hyperventilation
- increased CO2 removed from body
- imbalance between HCO3- and CO2
What is a common cause of acidosis?
- obesity or asthma
What is carboxyhemoglobin?
- when carbon monoxide (CO) is bound to haemoglobin - COHb - able to bind with iron on haemoglobin
What can concentrations of carbon monoxide as low as 0.1% do to SaO2 in the blood?
- ⬇️ SaO2 - ⬇️ oxyhemoglobin - 50% of haemoglobin convert to carboxyhemoglobin
Inhaling concentrations of carbon monoxide as low as 0.1% can cause symptoms, how quickly can this happen??
- <1 hour
Inhaling concentrations of carbon monoxide as high as 0.2% can cause death, how quickly can this happen??
- <2 hours
What is methaemoglobin?
- when iron on haemoglobin becomes oxidised
- becomes Fe3+ instead of Fe2 (this normally happens whjen O2 binds
- Fe3+ called ferric state
- O2 unable to bind to heme
What can high levels of methaemoglobin cause?
- ⬇️ O2 binding to haemoglobin - ⬇️ SaO2 - ⬇️ in respiratory function
In patient with methaemoglobin, what colour is their skin and blood?
- brown blood - blue skin due to lack of O2
What is the main cause of methaemoglobin from birth?
- congenital birth defects - causes deficiency in coenzyme factor 1
What is the main cause of methaemoglobin from inheritance?
- autosomal recessive congenital - 2 forms of defective gene
Can methaemoglobin be acquired?
- yes - due to chemical exposure, antibiotics, dapsones, chloroquine or nitrates
How is Diffusing Capacity for Carbon Monoxide (DLCO) calculated?
- measured in ml/min/mmHg
- measured as a % of normal age matched ml/min/mmHg
