Respiratory Physiology Flashcards
What are the axis on the oxygen dissociation curve and what does it look like
X axis - partial pressure of oxygen
Y axis - oxygen saturation of Haemoglobin
Sigmoidal shape, higher partial pressures of oxygen lead to higher haemoglobin saturations
What does a left shift mean and what can cause it
Hb has increased affinity for oxygen Reduced PCO2 Alkalosis Cold Reduced 2,3DPG CO poisoning
What does a right shift mean and what can cause it
Hb has reduced affinity for oxygen Raised PCO2 Acidosis Hot Raised 2,3DPG Exercise
Why do we used 92% saturations as a cut off
At this point the curve starts to drop off
Does myoglobin have a higher or reduced affinity for oxygen compared to Hb and what does this mean
Much higher affinity meaning it will hold on to its oxygen until partial pressures are very low. This means there is delayed onset anaerobic respiration and lactic acid production
How is CO2 transported
Bound to Hb
Dissolved in water and transported as a solution
Diffused into erythrocytes (Co2 + H2O = HCO3 + H+)
Describe the location and function of central chemoreceptors
In the medulla near the floor of the 4th ventricle
They detect the pH of CSF therefore indirectly measuring PCO2
Describe the location and function of peripheral chemoreceptors
Carotid and aortic bodies
They detect plasma O2
Why can arterial PaO2 drop extremely low before being detects in cases of anaemia or CO poisoning
Peripheral chemoreceptors actually detect plasma pO2 not arterial blood
What would the effect of haemorrhage be on peripheral chemoreceptors
Localised stagnant hypoxia due to reduced blood flow stimulates them leading to a sympathetic drive
What are the stretch receptors (respiration control) and where are they found
Pulmonary - airway smooth muscle they inhibit inspiration and increase expiration when distended (Hering Breuer reflex)
J - alveoli walls they cause rapid shallow breathing
Golgi tendon organs - intercostal muscles they inhibit inspiration when the chest wall is distended
What is the role of irritant receptors
Bronchoconstriction and apnoea to stop you breathing in any more of the irritant
How is alveolar ventilation calculated
(Tidal volume - physiological deadspace volume) x RR
What is the oxygen delivery equation
Oxygen delivery = CO x arterial oxygen content (which is determined by Hb, arterial O2 saturation and amount of O2 dissolved in blood)
What is pre-oxygenation and what is its role
100% O2 given for 3 minutes to fill the functional residual capacity therefore increasing oxygen stores
Why is there a reduced PaO2 in anaesthesia
Hypoventilation (anaesthetic agents, opioids, sedatives)
Raised metabolic rate increases oxygen demand
Inhibition of the normal response to hypoxia
Loss of tone of respiratory muscles
Hypoxic-pulmonary vasoconstriction inhibited
What is the normal response to hypoxia
Carotid and aortic bodies stimulate the sympathetics leading to hyperventilation and increased CO
What is diffusion hypoxia and what needs to be done to prevent it
This describes reduced alveoli PaO2 when nitrogen (if patient allowed to breath air) and nitrous oxide (which diffuses out of the blood to the alveoli when discontinued at the end of anaesthesia) mix
Need to give 100% O2 when stopping anaesthesia
What is the oxygen cascade
Stepwise reduction in PaO2 as O2 passes from the environment to tissues
Why is there a drop in PO2 between
A) air to alveoli
B) alveoli to pulmonary capillaries
A) addition of water vapour and mixing with CO2
B) either there is a V/Q mismatch or due to diffusion across the alveolar-capillary membrane
What are the 2 types of V/Q mismatch
Deadspace - ventilated but not perfused - VQ»1
Shunt - perfused but not ventilated - VQ«1
What happens if alveoli pressure >pulmonary artery pressure and when could this happen?
Pressure collapses the blood vessels leading to dead space
Seen in haemorrhage (reduced artery pressure), PE and +ve pressure ventilation (increases alveoli pressure)
In a pneumothorax should you put the affected lung up or down and why
Bad lung up so that good lung is getting better perfusion (gravity)
Why can the body not compensate very well for a pulmonary shunt
Well ventilated alveoli can’t compensate because of the capacity of Hb to carry oxygen
What are some lung pathologies that exacerbate a shunt
Atelectasis, consolidation, pulmonary oedema
What is hypoxic pulmonary vasoconstriction
Minimises pulmonary shunting
Blood vessels vasoconstrict to hypoxia meaning blood flow is redirected to well ventilated areas of the lung
Compare the upper and lower zones in terms of their V, Q and VQ ratio
Lower zone is better perfused (gravity) and ventilated (sits right next to diaphragm so increased compliance)
Upper zone is relatively more ventilated than perfused so has a much higher V/Q ratio
What are the 4 types of hypoxia and give some examples
Hypoxic (PO2 too low to saturate Hb)- altitude, hypoventilation
Anaemic (not enough functioning Hb) - anaemia, CO, methemogobinaemia
Hystotoxic (tissue can’t use available O2) - cyanide
Stagnant (poor flow to tissues) - HF, shock
What is the role of nitrogen
Stop the alveoli collapsing when O2 is extracted
What is positive end expiratory pressure
The pressure left in the lungs at the end of expiration which enables the alveoli to stay open. This increases their compliance (blowing up a balloon)
When is positive end expiratory pressure raised
Hyperventilation
Obstructed or narrow airway
CPAP
Pursed lip breathing
What pathologies lead to increased compliance
Emphysema
Elderly
What can lead to decreased compliance
Tension pneumothorax
Fibrosis
Obesity
Supine position
Define tidal volume, inspiratory and expiratory reserve volume, residual volume
A) Volume of air inhaled and exhaled during one respiratory cycle
B) Volume of air that can be forcibly inhaled/exhaled after a normal tidal volume
C) Volume of air remaining in the lungs after maximal exhalation
Define inspiratory capacity, functional residual capacity, vital capacity, total lung capacity
A) Volume of air than can be inhaled from a resting state
B) Volume of air left in the lung following a tidal expiration
C) Volume of air that can be exhaled after maximal inhalation
D) Maximum volume of air the lungs can accommodate
What is the role of increasing atmospheric pressure (hyperbaric chambers)
This increases the concentration of oxygen dissolved in the blood
What is the role of the dorsal respiratory group (located in medulla)
Initiates inspiration
Receives and integrates information
What is the role of the ventral respiratory group
Expiratory aspect of breathing
Rhythm generation
?Inactive during restful breathing
What is the role of the pneumotaxic centre (Pons)
Inhibits the apneustic centre to limit inspiration
What is the role of the apneustic centre (Pons)
Controls the depth of breathing by prolonging inspiration
In short what are the roles of the medulla and pons in central respiratory control
Medulla = rhythm Pons = depth
What is lung compliance
Change in volume of the lung per unit force
What is the role of surfactant and where is it produced
Type 2 pneumocytes
Decreases the surface tension of alveoli meaning they don’t collapse as easily
Which nerve innervates the carotid body chemoreceptors
Glossopharyngeal
What nerve innervates peripheral chemoreceptors in aortic bodies
Vagus
