Resp 6 - Control of breathing Flashcards
Define hypoxia:
Deficiency in amount of oxygen reaching the tissues
O2 saturation < 94%
Define hypercapnia:
Abnormally high concentration of CO2 in the blood
Define Hypocapnia:
Abnormally low concentration of CO2 in the blood
Define hyperventilation:
How does it affect plasma pH?
Abnormally fast or deep breathing
Increases plasma pH, as causes loss of CO2 from the blood
Define hypoventilation:
How does it affect plasma pH?
Abnormally slow breathing
Decreases plasma pH, as less CO2 removed from the blood
Where are the peripheral chemoreceptors located?
- Carotid bodies (carotid sinus)
- Aortic bodies (Aortic arch)
What is detected by peripheral chemoreceptors?
How do they respond?
Large drops in PO2, or large rise in PCO2
- ^ respiratory rate
- Change heart rate
- Change blood flow distribution
Where are the central chemoreceptors located?
Ventral surface of Medulla (exposed to CSF)
What is detected by the central chemoreceptors?
Small changes (~ 0.3 kPa) in PCO2 (via H+ from the CSF)
How does the body compensate for persisting hypoxia, to avoid brain damage (ie COPD)?
- Initially, detected by peripheral chemoreceptors = ^ ventilation rate (but PCO2 falls = alkalosis)
- Choroid plexus cells compensate for altered PCO2 by adding H+ to the CSF
= central chemoreceptors accept new PCO2 as normal level - Increased renal production of erythropoetin
= Increased production of RBC = increased carrying capacity of blood for O2
How does the body compensate for persisting hypercapnia, to avoid brain damage?
- Peripheral and central chemoreceptors detect drop in plasma pH = ^ ventilation rate
- Choroid plexus cells compensate for altered PCO2 by adding HCO3- to CSF to protect neurones
= central chemoreceptors accept new PCO2 as normal level
What is the choroid plexus, and what is its main functions?
- Vascular structure of pia mater located in ventricles of the brain
- Acts as barrier between capillaries and CSF (one of the blood-brain-barriers)
- Makes ~ 500 ml of CSF per day
- Can selectively pump H+ or HCO3- into CSF to maintain suitable pH for neurones (contains Carbonic Anhydrase)
Name the cells/structures which produce CSF:
- Choroid plexus
- Eppendymal cells
What is the normal volume of CSF?
~ 140 - 270 ml
Give the main 4 constituents of CSF:
1) Water
2) Glucose
3) NaCl
4) Protein
Which 2 cell types can be found in CSF normally?
- Monocytes/macrophages
- Lymphocytes
List some molecules that can cross the blood-brain-barrier easily:
- O2
- CO2
- H2O
- Ethanol
- Nicotine
- Glucose
Which of the following can easily cross the blood-brain-barrier?
O2 Glycine Catecholamines Ethanol H2O Nicotine H+ HCO3-
O2
Ethanol
H2O
Nicotine
What are the 4 types of hypoxia?
1) Hypoxaemic
2) Anaemic
3) Ischaemic
4) Histiotoxic
What type of hypoxia is caused by high altitude?
Hypoxaemic
What type of hypoxia is caused by iron deficiency?
Anaemic
What type of hypoxia is caused by a myocardial infarction?
Ischaemic
What type of hypoxia is caused by cyanide?
Histiotoxic
How does cyanide cause hypoxia?
Cyanide inhibits cytochrome c oxidase (the last electron acceptor in the ETC - complex IV)
= no ATP = inhibits anaerobic respiration
= Histiotoxic hypoxia
What is the normal range of O2 saturation?
94 - 98%
Define Type I Respiratory Failure:
PO2 < 8 kPa
O2 saturation < 90%
Normal or low PCO2
Define Type II Respiratory Failure:
PO2 < 8 kPa
O2 saturation < 90%
HIGH CO2 > 6.7 kPa
What is the ideal ventilation:perfusion ratio?
Ideal V/Q = 1
~ 5 L/min
What happens to alveolar PO2 and PCO2 if the V/Q ratio < 1?
PO2 decreases
PCO2 increases
How does ventilation perfusion mismatch cause Type I Respiratory failure?
- Alveolar PO2 decreases, and PCO2 increases
- Chemoreceptors cause hyperventilation, normalising PCO2 levels
= Type I Respiratory failure
What may cause a ventilation perfusion mismatch?
Reduced ventilation of part of lung:
- Pneumonia (alveoli filled with exudate)
- Respiratory distress syndrome (collapsed alveoli)
- Acute Asthma/COPD (narrowed airways)
Reduced perfusion of part of lung:
- Pulmonary embolism
In diseases causing diffusion impairment (ie Fibrosis/Emphysema), why is O2 diffusion affected, but not CO2 diffusion? Therefore what type of respiratory failure is caused?
CO2 is 20x more soluble than O2, so diffusion is unaffected
Type I Respiratory failure
List some causes of hypoventilation:
Opiates/brain stem injury Trauma to spinal cord Guillan-Barre syndrome Myasthenia Gravis Myopathy/Motor neurone disease Severe obesity Kyphoscoliosis Flail segment Pneumothorax Pleural effusion Newborn respiratory distress syndrome Lung fibrosis Upper airway obstruction Acute asthma Late COPD
Name the commonest cause of type II respiratory failure:
Late COPD
What is the treatment for type I respiratory failure?
- Oxygen therapy
- Treat underlying cause
What are the signs/symptoms of hypoxia?
- Exercise intolerance
- Tachypnoea
- Confusion
- Central cyanosis (+ peripheral cyanosis)
Central cyanosis is a sign that SaO2 is below what value?
SaO2 < 85%
What is polycythaemia, and why is it caused by chronic hypoxia?
Abnormally high haemoglobin in the blood
Increases O2 delivery to tissues
What are the signs/symptoms of chronic hypercapnia?
- Warm hands
- Bounding pulse
- Flapping tremors
