Gas Exchange Flashcards
What is optimal V/Q
0.8-1
1 = maximal efficient pulmonary function
What is hypoxic pulmonary ventilation
Blood flow directed away from poorly ventilated alveoli to well ventilated areas
Small arteries constrict to redirect blood flow away from poorly ventilated areas
Define ventilation rate (V)
Volume of gas inhaled and exhaled by the lungs in a given time period (usually 1 minute)
What is the average V
6L/min
What does the V/Q ratio depend on
Which part of the lung is concerned
Ventilation exceeds perfusion towards the apex
Perfusion exceeds ventilation towards the base
Ratio is different in areas due to the heart
- areas of the lung below the heart have increased perfusion relative to ventilation
What can V/Q be caused by
- Reduced ventilation to part of the lung
- Reduced perfusion
Describe the 3 west zones
Zone 1 = top of lungs = very little perfusion
Zone 2 = middle - more arterial increases during systole but not diastole
Zone 3 = Both bigger
Describe shunting
Blood is going through the lung but not taking part in any gas exchange
V/Q = slightly reduced
Describe hypoxic pulmonary vasoconstriction
High altitudes arteries narrow to try and maintain V/Q mis match
Moves to areas where ventilating - reduces blood flow to areas where not
Local hypoxia - e.g. peanuts
Generalised hypoxia = e.g. altitude
Describe a ventilation/perfusion scan
Breath in radioactive gas, inject albumin with technetium attached to it
Good for patients with allergies to issues with kidney function
Describe oxygen dissociation curve - co-operativity
Each haemoglobin unit can bind to a single oxygen molecule = each haemoglobin molecule can associate with oxygen = 4 oxygen molecules at one time
When oxygen binds to the haeme group causes conformational change
One change = change in all other subunits
1 oxygen binding to 1 haemoglobin increases subunits affinity for oxygen
Oxygenated haemoglobin = R state allowing oxygen to bind more easily
Deoxygenated haemoglobin = T state low affinity for oxygen
Results in sigmoid shape
What are the influences on haemoglobin-oxygen binding
2,3 diphosphoglyceric acid
H+
Temperature
CO2
What happens to the curve at low pH
Reduces affinity for oxygen binding
RIGHT
More oxygen is offloaded to metabolically active tissues
Describe the Bohr Effect
Reduction of oxygen affinity at a low pH
What direction does low pH shift the curve
Right
What direction does high pH shift the curve
Left
What is the middle pH of the curve
7.4
Describe the role of temperature on the curve
Increase in temperature = decrease in haemoglobin affinity
Important effect in exercise when temperature increases so offloading is important
What direction does high temperature have
Right
What direction does low temperature have
Left
What does a shift to the right promote
Offloading
What does a shift to the left promote
Binding
What effect does high DPG have
Right
What effect does low DPG have
Left
What is DPG
Intermediate of glycolysis
More DPG = more glycolysis
More oxygen needed so more = more offloading
What effect does CO2 have on the curve
CO2 reduced haemoglobins affinity for oxygen
What does high CO2 shift the curve to
Right
What does low CO2 shift the curve to
Left
What shifts the curve to the right
Low pH
High
- Temp
- DPG
- CO2
What shifts the curve to the left
High pH
Low
- temp
- DPG
- CO2
Describe Poiseuille’s Law
Resistance is related to
- length
- viscosity
R to the power of 4
What is Poiseuille’s Equation
(8 x L x viscosity) / pie x r to the power of 4
What does many smaller airways running in parallel do
Reduces total resistance to airflow
Where is the highest total resistance
Trachea and larger bronchioles
