Normal Respiratory Physiology Flashcards
What is PaO2 at rest?
98mmHg
What is PaCO2 at rest?
40mmHg
What is PvO2 at rest?
40mmHg
What is PvCO2 at rest?
46mmHg
What is PAO2 at rest?
100mmHg
What is PACO2 at rest?
40mmHg
What is PiO2 at rest?
150mmHg
What is PiCO2 at rest?
0mmHg
What is arterial pH at rest?
7.38-7.42
How much oxygen is supplied to the body per minute at rest?
250mLs
How much carbon dioxide is removed from the body per minute at rest?
200mLs
How much oxygen is supplied to the body per minute during exercise?
More than 4000mLs
How much carbon dioxide is removed from the body per minute during exercise?
More than 4000mLs
What is the difference between ventilation and gas exchange?
Ventilation is the air in and the air out, gas exchange is movement of gasses across the alveolar/capillary membrane
What is the role of ventilation?
To maintain PAO2 and PACO2
Are inspiration and expiration passive or active?
Inspiration is always active, expiration is passive at rest and active during exercise
What is the role of the inspiratory muscles?
To generate a negative intrapleural pressure
What are the inspiratory muscles?
diaphragm, external intercostals, sternocleidomastoids
What are the expiratory muscles?
internal intercostals, abdominal muscles
What is the tidal volume at rest?
500mLs
What is the tidal volume during exercise?
Half of the VC
What is the minute ventilation at rest?
7-8L/min
What is the minute ventilation during exercise?
100L/min
What is the total lung capacity?
The volume of air in the lungs at maximum inhalation - 5700mLs
What is the residual volume?
The volume of air in the lungs at maximum exhalation - 1200mLs
What is the vital capacity?
The difference between TLC and RV - 4500mLs
What is the FEV1?
The forced expiratory volume in 1 second - approximately 80% of forced vital capacity
What is the functional residual capacity?
The volume remaining after passive exhalation - 2200mLs
What two forces must be overcome in inspiration?
Resistive (airflow through bronchi) and elastic (expansion of lungs and chest wall)
What drives diffusion?
The difference in partial pressures of gasses on either side of the A-C membrane
What determines the rate of diffusion?
Ficks law - where rate is directly proportional to the surface area and the difference in partial pressures and inversely proportional to the thickness of the membrane
Why do carbon dioxide and oxygen have a different diffusion rate?
Because they have a different solubility and molecular weight so have a different constant in Ficks equation
What is the difference in diffusion rate between carbon dioxide and oxygen?
The diffusion rate of carbon dioxide is 20 times that of oxygen
How long does blood spend going past the alveoli at rest?
.75 seconds
How long does diffusion of oxygen take at rest?
0.25 seconds
What limits transfer of oxygen - diffusion or perfusion?
Perfusion (the amount of blood which goes past the alveoli)
When does diffusion limit the transfer of oxygen?
If the A-C membrane is grossly abnormal - in disease states
What is critical to efficient gas exchange?
Matching of ventilation and perfusion - most efficient when V/Q=1
What happens if there is a low V/Q?
There is not enough ventilation for the rate of perfusion - will lead to hypoxia
Where are the central chemoreceptors and what do they respond to?
Located on the ventrolateral medullary surface and respond to changes in H+ ions and CO2
Where are the peripheral chemoreceptors and what do they respond to?
Located in the aortic arch and carotid bodies and respond to changes in H+, CO2 and O2
Which has more effect on ventilation, carbon dioxide or oxygen partial pressures?
carbon dioxide
What is the neural control of breathing?
Neurons in the dorsal respiratory group and ventral respiratory group in the medulla. The DRG communicates the input from receptors to the VRG. The VRG has inspiratory and expiratory parts. The inspiratory part sends signals along the phrenic and intercostal nerves to initiate contraction. The expiratory part stops the signal to allow for passive relaxation. There is also the pontine respiratory centre which modifies the VRG.
What factors influence breathing?
Higher brain centres (voluntary control over breathing), pain and emotional stimuli acting through the hypothalamus, peripheral chemoreceptors, central chemoreceptors, stretch receptors in lung, irritant receptors in lung, receptors in muscles and joints
Does haemoglobin use the same binding site for oxygen and carbon dioxide?
No - different receptors
What are the three ways that carbon dioxide is carried in the blood?
Dissolved (10%), attached to proteins such as haemoglobin as carbamino compounds (30%), and as bicarbonate (60%) formed in RBCs by carbonic anhydrase
How is blood pH maintained?
Through a buffer system through this equation –
What happens when blood pH rises?
The respiratory centre is depressed so decreases ventilation so CO2 accumulates and the equation is pushed to the right
What happens when blood pH drops?
The respiratory centre is activated so increases ventilation so CO2 drops and the equation is pushed to the left
What is metabolic alkalosis?
When the blood pH is high and the respiratory system can’t compensate
What is metabolic acidosis?
When the blood pH is low and the respiratory system can’t compensate
What is respiratory acidosis?
Hypoventilation - when there is not enough ventilation so CO2 builds up and causes a decrease in blood pH
What is respiratory alkalosis?
Hyperventilation - when there is too much ventilation so not enough CO2 which causes a high blood pH
