Flashcards in Control of breathing, Hypoxia, Resp Failure Deck (69):
What is hypoxia?
• A fall in alveolar, thus arterial pO2
What is hypercapnia?
• A rise in alveolar, thus arterial CO2
What is hypocapnia?
• A fall in alveolar, thus arterial CO2
What is hyperventilation?
• Ventilation increases with no change in metabolism• (breathing more than you actually have to)
What is hypoventilation?
• Ventilation decreases with no change in metabolism• (breathing less than you have to)
How does hyperventilation affect plasma pH?
• pCO2 down• pH increases
How does hypoventilation affect CO2 and plasma pH?
• pCO2 up • pH down
What is the normal metabolic pH?
What is the body's normal pH range?
• 7.38 - 7.42
What happens if plasma pH falls below 7.0?
• Plasma k+ rises to dangerous levels and enzymes are lethally denatured• Function of heart affected
What happens if plasma pH rises above 7.6?
• Free calcium concentration falls enough to produce fatal tetany• Calcium salts soluble in acid conditions - In alkalosis, calcium forms complexes. Nerves become excitable, causing tetany
Give two events which will occur when hypoventilation occurs?
• Hypercapnia• Respiratory acidosis• pH falls below 7.0• Enzymes become lethally denatured
Give two events which will occur when hyperventilation occurs?
• Hypo capnia and respiratory alkalosis• pH rises above 7.6 • Free calcium concentration falls enough to produce fatal tetany ○ Ca2+ is only soluble in acid, so pH rises Ca2+ cannot stay in blood. Nerves become hyperexcitable.
What is respiratory acidosis?
• CO2 produced more rapidly than it is removed by the lungs (hypoventilation). • pCO2 rises, so (dissolved CO2) rises more than HCO3-, producing a fall in plasma pH
What is compensated respiratory acidosis?
• Respiratory acidosis persists, and the kidneys responsd to low pH by reducing excretion of HCO3-, thus restoring ratio of (dissolved CO2) to (HCO2-), producing a rise in pH
How long does compensation take?
• 2-3 days
What is respiratory alkalosis?
• CO2 is removed from alveoli more rapidly than it is produced (hyperventilation)• Alveolar pCO2 decreases, changing the ratio of (dissolved CO2) to (HCO3-) producing an increase in plasma pH
What is compensated respiratory alkalosis?
• Respiratory Alkalosis persists, and the kidneys respond to the high pH by excreting HCO3-, thus restoring the ratio of [Dissolved CO2] to [HCO3-], and therefore the pH.
What is metabolic acidosis?
• HCO3- displaced by metabolically produced acids• Blood pH form
How can metabolic acidosis be compensated for?
• Ratio of (dissolved CO2) to (HCO3-) may be restored to near normal by increasing ventilation rate to decrease pCO2
What does acidosis mean?
• Reduction in HCO3- • NOT PH
What is metabolic alkalosis?
• Plasma HCO3- rises, causing the pH of blood to rise (after vomiting?)• Stomach produces HCO3- when acid generated• If acid removed from stomach, gastrin released which produces more acid• HCO3- produced in excess as a result of this increased production
How can metabolic alkalosis be compensated for?
• Ratio of dissolved CO2 to HCO3- may be restored to near normal by raising pCO2• Lungs decrease ventilation to correct pH• Dangerous
What is the control of our breathing moderated by?
• pH• Oxygen requirements are secondary
Give three variables which affect breathing?
• pH• Decrease O2• Increased CO2
What occurs when there is falling inspired pO2?
• Detected by peripheral chemoreceptors located in carotid and aortic bodies• Increase the tidal volume and rate of respiration• Changes in circulation direction more blood to the brain and kidney• Increased pumping of blood by the heart
What occurs when there is an increase in inspired pCO2
• Central chemoreceptors in medulla more sensitive than peripheral• Small rise in pCO2 -> Increase ventilation• Small decrease in pCO2 -> Decrease ventilation• Basis of negative feedback control of breathing
What is low O2 detected by?
• Peripheral chemoreceptors
Where are peripheral chemoreceptors found?
• Carotid bodies• Aortic bodies
Why do peripheral chemoreceptors only respond to large changes in O2?
• High blood flow in carotid and aorta• Lots of O2, usually
What are peripheral chemoreceptors stimulated by?
• Low O2• High CO2 (minor function)
Give three ways in which chemoreceptors response to a decrease in O2
• Increase tidal volume and rate of respiration• changes in circulation directing blood to the brain and kidney• Increased pumping of blood by the heart
What is a central chemoreceptor and where is it found?
• Found in medulla of the brain• Much more sensitive, altering breathing on a second to second basis
What do the central chemoreceptors do in response to arterial pCO2?
• Small rise in pCO2 -> Increase ventilation• Small fall in pCO2 -> Decrease ventilation
What do central chemoreceptors respond to?
• Changes in the pH of cerebro-spinal fluid (CSF)• CSF separated from blood by the blood-brain barrier
What is CSH (HCO3-) controlled by?
• Choroid plexus cells
What out of HCO3-, CO2 and H+ can cross the BBB
• CO2 only
What is the pH of the CSF governed by?
• The ratio of HCO2- to pCO2
How is regulation of brain pH different to that of the rest of the body?
• Occurs within hours
Apart from pCO2 and pO2, what do the central chemoreceptors respond to?
• Changes in pH of CSF
How is the CSF separated from the blood?
• By the blood brain barrier
What is the CO2 of the CSF determined by?
• Arterial pCO2• HCO3- and H+ cannot cross
What is CSF (HCO3-) controlled by?
• Choroid plexus cells
What is the pH of CSF determined by?
• The ratio of HCO3- to pCO2 • In the short term HCO3- is fixed, so falls in pCO2 -> increase in pH• Rise in pCO2 -> lower pH • Persisting changes compensated for by choroid plexus cells altering CSF
What is the oxygen transport chain?
• Air -> Airways -> Alveolar gas -> alveolar membrane -> Arterial blood -> Regional arteries -> Capillary blood -> Tissues
• A fall in alveolar, thus arterial pO2
Give conditions which cause diffusion impairments
• Fibrotic lung disease ○ Thickened alveolar membrane slows gas exchange• Pulmonary oedema ○ Fluid in interstitial space increases diffusion distance• Emphysema ○ Destruction of alveoli reduces surface area for gas exchange
What is respiratory failure?
• Not enough oxygen enters the blood• Not enough CO2 leaves the blood
What is type 1 respiratory failure?
• Arterial hypoxia (pO2 below 8kPa), accompanied by normal or low pCO2• Breathlessness, Exercise intolerance, central cyanosis
What alveoli can t1 respiratory failure effect?
• Some or all alveoli
Give three symptoms of T1 Respiratory failure
• Breathlessness• Exercise intolerance• Central cyanosis
Can ventilation perfusion matching bring lungs to 100% capacity
Give four possible causes of T1 respiratory failure can be caused by conditions affecting some alveoli
• Pulmonary embolism• Pneumonia• Consolidation• Early stages of acute asthma
Give two possible causes of T1 respiratory failure which can be caused by conditions affecting most alveoli
• Pulmonary oedema• Fibrosis ○ Pneumoconiosis ○ Asbestosis ○ Extrinsic allergic alveolitis
What is type 2 respiratory failure?
• Arterial hypoxia, accompanied by an elevated pCO2• (Arterial hypoxia = 8kPa)
How is O2 saturation measured?
• Pule oximeter• Blood gas analysis
Give three causes of T2 respiratory failure
• Poor respiratory effort ○ Narcotics ○ Muscle weakness (upper and lower motoneurone)• Chest wall problems ○ Scoliosis/Kyphosis ○ Trauma ○ Pneumothorax• Hard to ventilate lungs ○ High airway resistance ○ COPD ○ Asthma
What is emphysema?
• Destruction of lung tissue ( lack of a1-antitrypsin)• Changes in compliance• Ventilation perfusion mismatch• Affects O2 supply• Initally T1 failure, then T2
What happens in the body to solve chronic hypoxia?
• There is a renal correction of acid base balance• Increase in ventilation
Outline the acute effects of Type 2 respiratory failure
• pCO2 rises• Central chemoreceptors detects• Breathlessness ○ Some compensation ○ Poor ventialtion prevents full compensation
What happens in chronic type 2 respiratory failure
• CSF acidity corrected by choroid plexus• Central chemoreceptors rest to high CO2 level• Persisting hypoxia• Reduction of respiratory drive, which is now driven by hypoxia
What happens if you give O2 to someone with COPD (T2 respiratory failure)
• They may stop breathing
What effect does T2 respiratory failure have on pulmonary circulation?
• Effects of hypoxia on pulmonary arterioles ○ Pulmonary hypertension ○ Right heart failure ○ Cor pulmonale• Increased O2 transport capacity• Hb increased• 2,3 BPG
Give five factors necessary to maintain arterial pO2, problems with which will cause hypoxia
• Low pO2 in inspired air• Hypoventilation• Diffusion impairment • Ventilation perfusion mismatch• abnormal right to left cardiac shunts
What causes low pO2 in inspired air?
• Everything is normal, air has low pO2
What is hypoventilation often associated with?
• Increased pCO2 (type 2 respiratory failure)
What are neuromuscular causes of hypoventilation?
• Respiratory depression due to opiate overdose • Head injury• Muscle weakness (NMJ/Nerve/Muscle diseases)
What are some Chest wall problems (Mechanical) of hypoventilation
• Scoliosis/kyphosis• Morbid obesity• Trauma• Pneumothorax