B2 Physiology of Respiration Flashcards
What is the term for the extent of elastic recoil during respiration (i.e. volume at expiration depending on what it was at inspiration)?
Hysteresis
What is hysteresis?
The idea that the volume that the lungs decrease by at expiration depends on how much they increased on inspiration
What three factors does lung stiffness depend on?
- Elasticity of lung tissue
- Surface Tension
- Role of Surfactant
What are the problems with having high surface tension in the alveoli?
a) high stiffness (low compliance)
b) alveolar instability, with small alveoli emptying into large alveoli; can cause atelectasis
c) movement of interstitial fluid into the alveoli (life threatening!)
What is the relationship between surface tension and surfactant?
Surfactant reduces alveolar surface tension
What is atelectasis?
Alveolar collapse
How is ventilation measured?
Litres/ Minute
What is tidal volume?
The volume of each breath
What is vital capacity?
Volume of maximum expiration following maximum inspiration
What is residual volume?
Air remaining in lungs after maximal expiration
What is inspiratory reserve volume?
Vital capacity - expiratory reserve volume
What is expiratory reserve volume?
Vital capacity - inspiratory reserve volume
True or false? residual volume can be measured by spirometry?
False
True or false? functional residual capacity can be measured by spirometry?
False
How is residual volume measured?
Helium dilution method
What does PEFR stand for?
Peak expiratory flow rate
How is PEFR measured
Mini peak flow meters
What is PEFR
The maximum flow at the outset of forced expiration
Why is PEFR measured in asthma and COPD patients?
Forced expiration would be reduced in proportion to the severity of airway obstuction; can monitor effects of drugs
How is carbon dioxide carried in the blood?
7% dissolved
70% HCO3
23% As carbamino compounds
What is the Haldane effect?
CO2 reacts more with deoxygenated Hb than oxygenated Hb
Deoxygenated Hb is less acidic so accepts more H+
This means that deoxygenation increases the CO2 carrying power of blood
Does the Haldane effect occur in the lungs?
No, the reverse reaction occurs
Oxygenation will decrease the CO2 carrying ability of blood, releasing it
What effect does expiring CO2 have on pH?
Decreases H+ -Increasing pH
What effect does inspiring CO2 have on pH?
Increases H+- Decreases pH
True or false? Ventilation is sensitive to PO2?
False. It’s sensitive to PCO2
What does hyperventilation cause?
Alkalosis
What is hyperventilation usually a result of?
Acidosis
Why does hyperventilation cause alkalosis?
Lungs lose excess CO2
HCO3 falls so pH rises
Kidney compensates by retaining H+ and excreting HCO3
pH is closer to normal but you’ve lost CO2 and HCO3
What do low partial pressures of oxygen cause?
Hypoxic sensitive ventilation
Why does hypoventilation cause acidosis?
Lungs keep the CO2
HCO3 rises so pH falls
Kidney compensates by keeping HCO3 and getting rid of H+
pH is closer to normal but CO2 and HCO3 are high
What is a metabolic cause of alkalosis?
Vomiting
What are metabolic causes of acidosis?
DKA and Renal failure
What are the body’s responses to pH changes?
Buffering - HCO3 - rapid but limited
Changes in ventilation - rapid but impossible if the cause is respiratory
Kidney compensation - Slow but limited if the problem is kidney failure
Are dead space and residual volume the same?
No
What is dead space?
The volume of the lung that isn’t available for gas exchange
What is anatomical dead space?
The conducting respiratory system that don’t take part in gas exchange anyway (about 150ml)
What is physiological dead space?
Anatomical, plus the alveoli that will get air but don’t have enough of a blood supply (about 150ml)
What type of V/Q ratio will alveoli with an insufficient blood supply have?
Increased/ >1
What is P50?
PO2 at 50% saturation of Hb (Normally about 27mm Hg)
