Ventilation-Perfusion Relationships Flashcards
What are the issues with the alveolar lung?
Gas and Blood don’t flow past each other
Convective gas flow to a blind ended sack
Inspired air mixes with existing gas in lung
Arterial PO2 equilibrates to the PO2 of the alveolus
Much less efficient and thus consequences for V/Q Matching
Why is insect tracheal gas exchange better?
highly efficient and supports highest aerobic metabolic rates
O2 delivery is carrier free
Why is the fish gill exchange better?
Efficient gas/blood barrier
Involves counter-current gas exchange to efficiently oxygenate blood to environmental PO2
Why is the bird parabronchial system better?
Constant uni-directional convective gas flow
perpendicular arrangement of air tubes and vasculature enables cross-current gas exchange
Venous blood oxygenates to within 90% of inspired PO2
Greater efficiency of oxygen uptake - allows flight at high altitude
How does the ECMO machine take advantage of the design?
counter current gas exchange
all flow
no convection
inspired PO2 can be above atmospheric and above 21%
What is ventilation?
the amount of O2 consumed
What is perfusion?
the rate of O2 transfer from alveolus to blood
What is the effect on V/Q as body size decreases?
there becomes a larger mismatch
How does the shrew compensate for the mis-match?
higher HR and breathing rate - limit of heart and lung performance
What causes a pulmonary embolism?
a high demand for oxygen placing high transmural pressure over blood gas barrier
What does increased minute ventilation do?
increase pulmonary artery pressure and decreases alveolar pressure causing rupture as transmural pressure increases
What does grunting do?
increases the air flow out of the lung during exhalation
What is the equation used to measure pAO2?
pAO2 = FlO2(pATM-SVP)-paCO2(flO2 + 1-FlO2/RQ)
What is FlO2(pATM-SVP)?
the proportion of oxygen in inhaled gas
What is FlO2 +1-FlO2/RQ?
rate of O2 consumption by metabolism
What is the standard vapour pressure of water?
SVP = 47mmHg
What is the typical respiratory quotient?
0.8
What is alveolar PO2 significantly affected by?
atmospheric PO2 and arterial carbon dioxide
What happens if PCO2 increases?
alveolar PO2 decreases
What happens if RQ increases?
alveolar PO2 increases
How might you increase RQ?
eating high carbohydrate diet
At high altitude how might you adapt to conserve pAO2?
increasing breathing frequency to decrease paCO2
high carbohydrate diet - RQ=1
climb when barometric pressure is high
What are the adaptive breathing responses to hypoxia?
increase breathing depth and frequency
increasing blood flow rate through the lung by vasoconstriction
What is the maximum O2 delivery set by/
tidal volume
breathing frequency
airway smooth muscle constriction
What is the maximum O2 loadning into blood set by?
O2 in alveolus pulmonary artery blood pressure vascular smooth muscle tone blood flow (All alveolar-arterial pressure gradient)
What are the effects of raising pulmonary artery blood pressure through constriction?
redirects blood flow to alveoli
speeds up transit time of blood through lung
What are the problems of raising pulmonary artery blood pressure through constriction?
greater resistance for blood to enter lung vascular tree
rapid transit time through alveolus reduces time for gas exchange
What does increase breathing depth and frequency do?
raises alveolar PO2 which increases drive to blood
What does the right shift in the oxy-hemoglobin curve do?
favour off-loading to tissues
What else can be done to increase oxygen availability?
increase no of RBCs
increase no. of peripheral vessels
increase capacity for tissue anaerobic metabolism
What does hypoxia do to the alveolar-arterial oxygen partial pressure gradient?
increases the gradient due to low venous return to the lung
What would happen without the HPV response?
arterial pO2 would wall and p[A-a] collapses resulting in death
What does HPV response do?
increases RBCs to increase O2 carrying capacity
increased breathing brings pAO2 closer to atmospheric
What happens with poor ventilation and large blood flow?
need to reduce perfusion - so hypoxia constricts pulmonary arterioles - redirects blood to well ventilated areas
What happens with good ventilation and poor blood flow?
need to reduce ventilation - low CO2 constricts bronchioles - redirects air to better vascularised areas
