Respiratory Alfred Flashcards
What does central chemoreceptors respond to?
What are peripheral chemoreceptors respond to?
Central - CO2, pH
Peripheral - O2, CO2, pH (smaller effect)
Where do inspiratory neurons get stimulated?
Dorsal respiratory group in the medulla - diaphragm
What is activated at the end of inspiration to termination inspiration and start expiration?
Vagus nerve which negatively feeds back to the central respiratory controls
Where are central chemoreceptors located?
Ventral surface of medulla
Responds to changes in H+ (mediated by CO2) in the CSF (which is not regulated by HCO3 buffers in the blood)
Where is the lowest level of transection of the brainstem that would terminate respiration
Below medulla
How does arterial baroreceptors modulate breathing?
Responds to blood pressure
Hypertension causes hypoventilation
What is the volume of dead space? And how many generations of airways?
150mL
16 generations (terminal bronchioles)
Which way does the diaphgarm move during inspiration?
Moves down normally, but paradoxically moves up if the diaphgram is paralysed
What happen with lung compliance with:
- age
- atelectasis
- pulmonary oedema
- age - increases
- atelectasis - decreases
- pulmonary oedema - decreases
What produces pulmonary surfactant?
Type II alveolar epithelial cells
Which part of the lung has more ventilation in normal respiration??
Base because it is closer to the linear section of the intrapleural pressure and volume
However, at residual volume, there is more ventilation at the top of the lungs because the section on the curve changes
Where is equal pressure point normally?
Respiratory bronchioles
In COPD and asthma, there is earlier obstruction.
The asthma patient has increased resistance in the airways so the fall in pressure is very quick. In COPD patients, the airways is floppy so the airways will collapse at a lower pressure difference
Where is the party of the airways with the most airway resistance?
Medium-sized bromchi (up to generation 7)
Particularly affected in asthma
What is the shape of the pulmonary vascular resistance - lung volume curve and when is the pulmonary vascular resistance the lowest?
U shaped
Lowest at the functional residual capacity
This is because at the high lung volumes, the capillaries are stretches. In small lung volumes, the capillaries are squished and constricted
What is the change of VQ ratio throughout the lung
Top of the lung = high V/Q
Bottom of the lung = low V/Q
THis is because the change of perfusion throughout the lung is a lot more than the change in perfusion (even though both ventilation and perfusion is greater at the bottom)
Type A vs Type B VQ mismatch
Type A - emphysema - lots of dead space - normal CO2 but hypoxia
Type B - chronic bronchitis - shunting - mild hypoxia but increased CO2
Most COPD is on the spectrum
High paCO2 is due to MORE SHUNTING
Why does bronchodilation create an initial V/Q mismatch (especially IV administration) in asthma?
Initially bronchodilation in the vessels occur before the lungs, creathing more V/Q mismatch
What is the most common cause of hypoxia?
V/Q mismatch
What happens to lung volumes in elderly normal
Slightly increased FRC due to increased RV
Obstruction of lung function tests
<0.7 in FEV1/FVC (the ratio, not the percentage compared to normal)
What is differences in lung volumes between restrictive diseases due to intrinsic lung disease vs extrinsic chest wall?
Intrinsic lung disease - equal reduction in RV/TLC
Extrinsic - more reduction in TLC than RV
Best indication of gas trapping in COPD in lung volumes
Functional residual capacity or residual volume
How does smoking affect DLCO?
Decreases DLCO because it creates back pressure of carbon monoxide.
Hence, patients are supposed to not smoke for 12 hours prior pulmonary function tests
How to calculate amount of shunting
Ideal PO2 on 100% oxygen is 670 mmHg
every 20 mmHg below is a 1% shunt
What is the most common cause of hypercapnia
Hypoventilation
Then severe V/Q mismatch
Motor neuron disease lung volumes
Everything decreases
Does HbF and metHb have a higher or lower affinity for oxygen? (compared with normal adult Hb)
HbF and metHb have a higher affinity
PaO2, SaO2 and CaO2 in altitude
all reduced
Why is the haematocrit more in venous blood compared with arterial blood
The exit of HCO3- causes entrance of Cl-, which is always coupled with Na+, which draws water into the RBC, causing them to be slightly bigger
Which way does carbon monoxide cause the Hb-O2 curve shift?
Left
How does P50 (in the Hb-O2 curve) change with left and right shift of the curve?
lower P50 is left shift (corresponds with PaO2 with 50% of haemoglobn saturation)
Stepwise approach to ABGs
- pH - determines acidosis vs alkalosis
- Look at pCO2 and HCO3
- pCO2 <35mmHg is resp alkalosis, >45 resp acidosis
- HCO3 <22 is met acidosis, >30 met alkalosis
Amount of compensation of HCO3 in respiratory acidosis
Acute compensation:
- HCO3 increases by 1-1.5 for each 10mmHg increase in pCO2
Chronic compensation:
- HCO2 increases by 3-4 mEq/L for each 10 mmHg increase in pCO2
What abnormality causes no response to 100% FiO2
Shunt
ABG in carbon monoxide poisoning
normal PaO2
normal SaO2 (unless you specifically ask for CO)
lactic acidosis causing metabolic acidosis
hepatopulmonary syndrome cause of hypoxia
shunt
What happens to the Respiratory quotient during exercise
Resp quotient is VCO2/VO2
The CO2 output increases during exercise so the R quotient increases from around 0.8 -> 2
What causes the hypocapnia in extreme exercise?
Normal exercise has normocapnia.
In extreme exercise, the lactic acidosis causes hypocapnia
What is the cause of hyperventilation in acclimatisation to high altitude?
Hypoxic stimulation of the peripheral chemoreceptors
acclimatisation is limited by the time it takes for the kidneys to respond to the alkalosis from hyperventilation
What happens to the O2 Hb curve at high altitude
moderate altitude = right shift
high altitude = left shift
Treatment for acute mountain sickness complications - high altitude cerebral oedema, high altitude pulmonary oedema
- Oxygen
- Pressurisation
- Acetazolamide (but mainy used prophylacticly)
- Dex (for cerebral oedema)
Don’t use diuretics
What is MetHb?
The normal HbFe2+ loses an electron to the O2 making
HbFe3+ and O2-
met Hb reductase is able to reverse the reaction
Fe3+ haemes are unable to bind O2
O2 dissociation curve is left-shifted
MetHb is absorbing both waves lengths in the pulse oximetry (used normally to measure oxy and de-oxyhaemoglobin
Treatment of Met Hb
<20% no therapy - stop offending agent
>20% use methylene blue (cannot use for G6PD deficiency)
cyanosis and normal PaO2 with normal or low sats
MetHb
Absorbs waves of both the oxy and deoxyHb wavelengths
Lung volume changes in pregnancy
TLC only slight reduction
More significant reductions (20%) in FRC, ERV, RV after 2nd trimester
What is the sniff test and what does it show
The diaphragm goes up instead of down. Indicates diaphragmatic paralysis
