Module 4 - Sleep-Disordered Breathing Flashcards
What is the difference between breathing and respiration?
Breathing: act of pumping, inspiration and expiration
Respiration: metabolism of substrate (glucose with oxygen) in cells
What are the structures that air passes through during inspiration?
Nasal cavity
Oral cavity
Pharynx
Larynx
Esophagus
Trachea
Splits into bronchi -> continues to divide ~23x
Alveoli
Lung
Describe the trachea
A 1.5-2cm diameter scaffolding of cartiladge
What is the difference in size between nasal passage and alveoli?
~1.5-2cm at nasal region
Alveolar region is ~1-2x tennis courts
What are the features of the alveolar regions to promote gas exchange?
Lots of fine capillaries along alveoli.
Blood and air become very close, only separated by some cells. Allows for maximum gas exchange.
How does the diaphragm muscle work to promote breathing?
A pump.
When contracted, thorax becomes a cylinder and causes a vacuum around lungs -> area EXPANDS -> Inspiration
When relaxed, thorax relaxes and reduces vacuum around lungs -> area REDUCES -> expiration
What is the difference between pulmonary and systemic circulation in terms of pressure and oxygen?
Pulmonary -> lungs -> LOWER pressure
Systemic circulation -> rest of the body -> HIGHER pressure
What is the pathway of blood from the heart through the pulmonary circulation?
Right side of heart ->
both lungs ->
picks up O2 and eliminates CO2 ->
returns to left atrium ->
pumped to systemic circulation
Why is the blood pressure in pulmonary circulation lower than in systemic circulation?
Because you are bringing blood close to the atmosphere (single cell separating). The capillaries can’t tolerate increased pressure.
Why does the systemic circulation system have increased blood pressure?
So it can pump blood to the entire body.
What is the difference between the circulatory control and respiratory control systems?
Circulatory: contracts without innervation
Breathing: dependent on brain (brainstem)
How does the brain control respiration?
Diaphragm is in control from the brainstem, via nerves that innervate it.
What does the nasal airway do to the air?
Like an aircon
Increased temperature
Adds moisture
How do you measure the function of breathing?
Taking arterial gasses through blood which comes directly from left ventricle from lungs.
We measure the partial pressure of blood gases from that.
What are normal arterial blood gas measurements? (Oxygen, CO2, pH, base excess, bicarb)
PaO2: 95-100mmHg
PaCO2: 40mmHg
pH: 7.4
BE: 0
Bicarb: 26 Meq/L
How much air is inhaled per minute and what is the PaCO2 and PaO2 at this volume?
~7 Litres
PaCO2: 40mmHg
PaO2: 95-100mmHg
If arterial CO2 increases, what happens to alveolar ventilation?
Decreases breathing
What is alveolar ventilation?
Amount of air reaching surface of lungs that partake in gas exchange
If PaCO2 decreases, what happens to breathing?
Breathing increases
How is PaO2 related to ventilation?
Decreased PaO2, decreased ventilation
Increased PaO2, increased ventilation
What is the relationship between PaO2 and Oxygen saturation?
Sigmoid relationship
Across wide range of PaO2, it will carry close to 100% saturation, but once around 60mmHg, haemoglobin gives up O2.
What does oximetry measure?
SaO2. The colour of red cells as they change with differential pressures
What are the varying oxygen pressures between the atmosphere, at the alveoli, in plasma and in the red cells?
Atmosphere: 150mmHg
PAO2: 100mmHg
Then O2 diffuses across membrane into the plasma
PaO2: 100mmHg
Plasma: 0.3mL/100mL
Red Cells: 20mL/100mL unless PaO2 < 60mmHg in plasma
How does haemoglobin behave if PaO2 is between 60-100mmHg?
Rapidly uptakes O2
Is CO2 or O2 more diffusible?
CO2 as it’s carried by more than just red blood cells, also bicarbonate and others.
If alveolar ventilation increases, how does PAO2, SaO2, pH, PACO2
PAO2 increases from 100 -> 120mmHg
SaO2 stable
pH increases from 7.4-7.6
PACO2 decreases from 40 -> 20
If alveolar ventilation decreases, how does PAO2, SaO2, pH, PACO2
PAO2 decreases from 100 rapidly
SaO2 stable until around 3L/min
pH reduces from 7.4->7.2
PACO2 increases from 40 towards 80mmHg
What are the partial pressures of oxygen and carbon dioxide at the alveoli?
PAO2: 100mmHg
PACO2: 40mmHg
What is the partial pressure of oxygen in the atmosphere?
150mmHg
What are the partial pressures of oxygen and carbon dioxide in the blood before it reaches the tissues?
PaO2: 90mmHg
PaCO2: 40mmHg
What are the partial pressures of oxygen and carbon dioxide in the blood after it reaches the tissues?
PvenousO2: 40mmHg
PvenousCO2: 45mmHg
Where are the central chemoreceptors and what are their role?
Medulla & brainstem. Ventral surface.
CO2 detectors (+ maybe pH)
Where are the peripheral chemoreceptors and what are their role?
Carotid body in the main arteries to head and brain
Sensitive to SaO2 and CO2
What type of response to central and peripheral chemoreceptors have to changes in CO2 and O2?
Linear (in Central, even 1mmHg increase increases ventilation markedly)
Peripheral are not always linear response.
Negative feedback control system
What happens when someone stops breathing oxygen by breathing in a bag?
Tidal volume increases over time by increasing ventilation.
Slow but linear rise in CO2
Where is oximetry commonly measured?
Finger or earlobe.
Earlobe has best oxygenated blood as they haven’t gone through tissues yet.
Fingers have similar response to normal circulation.
What happens when you manipulate how much O2 someone can access but maintain CO2 in a sleep study? Which chemoreceptors are these driven by?
Early and rapid increase in ventilation for roughly 2 minutes.
Carotid. Normally only CO2 drives ventilation but in abnormal circumstances SaO2 (but not PaO2) will change ventilation.
Does CO2 or O2 drive ventilation changes?
CO2
In abnormal circumstances, SaO2 but not PaO2 will change ventilation. Such as in OSA.
Which stage of sleep has the lowest “ebb” of respiratory function?
NREM
When is breathing control best revealed?
When the system malfunctions
What changes in NREM sleep in relation to breathing?
Slight fall in ventilation
Slight rise in CO2 (1-2mmHg increase)
Breathing is clockwork regular
What changes in REM sleep in relation to breathing?
Variable ventilation
Irregular breathing patterns
Short central apneas
Breathing often represents what’s happening in dream
CO2 can change greatly
How does the control of breathing influence NREM sleep?
Brain is resting, so there’s reduced gain of chemo responses but effective arousal responses remain.
Control is from the brainstem.
What happens to the respiratory muscles in NREM sleep?
Loss of muscle tone especially in upper airway
Upper airway narrows, increasing load
How does the control of breathing influence REM sleep?
Brain is activated
Control inputs from behavioural activity that is associated with brain activation
What happens to the respiratory muscles in REM sleep?
Marked active inhibition of postural muscles, including accessory muscles (paralysed by brainstem)
Breathing is totally diaphragm dependent
Why is sleep often worse for disorders in REM sleep?
Zero muscle tone
True or false?
Arousal responses to respiratory stimuli are MORE important than the respiratory responses.
TRUE
What are the 3 key features of arousal responses in sleep?
Stimulus specific: upper airway vs chemoreceptor (diff thresholds)
Sleep-state specific: REM “depression” of chemoresponses
HIGHLY plastic: sleep fragmentation markedly reduces responses. Drugs and alcohol depress arousal response. Excessive arousability leads to apneas (M & C) and greater fragmentation
When will breathing stop in sleep?
If PaCO2 < 40mmHg
ONLY in sleep in normal people. NO threshold when awake.
This produces arousal and the cycle starts again
How can central apneas become apparent in sleep?
Reduced chemoresponsiveness and apnea threshold
What to the central chemoreceptors impact?
Central oscillator and cardiovascular controller