Respiratory Physiology 1 Flashcards
In the lateral position, which lung has greater perfusion?
The dependent lung
In the lateral position, which lung has less ventilation?
The uppermost lung
In the lateral position, where is V/Q higher?
Ventilation and perfusion are higher in the lower (dependent) lung although perfusion is slightly better than ventilation so V/Q <1
In the lateral position, which lung has the lower PO2?
The dependent lung.
V/Q < 1 (degree of shunt)
In areas of shunt the alvelolar mixed gas tends toward mixed venous so PO2 is low and PCO2 slightly raised.
In the lateral position, which lung has the higher PCO2?
Dependent lung.
In the non-dependent lung V/Q >1 (ie degree of dead space)
Alveolar gas now tends towards inspired gas and so PO2 is raised but PCO2 is also low.
What lung volumes can spirometry NOT measure?
All except
- FRC
- residual volume
- TLC
What methods can measure FRC?
- body plethysmography
- nitrogen wash out
- helium wash in
Where on deoxyHb does 2,3 DPG bind?
The beta chains
What is 2,3, DPG formed from?
Product of glycolysis from phosphoglyceraldehyde in RBCs
How does 2,3 DPG affect oxygen utilisation by cells?
2,3 DPG shifts the O2 dissociation curve to the right.
Reduces O2 binding to Hb and therefore increasing O2 availibility for tissue utilization.
How do thyroid hormones affect 2,3 DPG?
They increase 2,3 DPG concentration in red cells
(as does growth hormone and androgens)
Can 2,3 DPG bind to fetal Hb?
No because fetal Hb doesn’t have beta chains
Where are peripheral chemoreceptors found?
Carotid and aortic BODIES
NOT carotid sinus
What do central chemoreceptors in the medulla respond to?
A rise in PaCO2 and CSF pH
**predominant ventilation control is central chemoreceptors in medulla**
Are peripheral chemoreceptors downregulated in the presence of chronic lung disease?
No
Does elevated levels of carboxyHb stimulate peripheral chemoreceptors?
No
Where is hypoxia sensed?
The carotid body
(This will give rise to increased afferent signals when PaO2 falls below 13kPa)
Can CO2 freely cross the BBB?
Yes but H+ and HCO3- cannot.
How is CO2 mainly transported in blood?
As bicarbonate.
Only 5% is transported unchanged.
Does CO2 change the pH of blood or CSF more?
CSF because it lacks buffers
What does the haldane effect do?
The transport of CO2 by Hb is inhibited by rising O2 sats
Does CO2 have direct sympathomimetic activity?
No but does increase activation of the sympathetic system
What is the normal mean arterial pressure of pulmonary blood?
15 mmHg
When does blood flow occur mainly in West zone 1?
During systole because in this zone:
pA >pa >pv
What does a minute ventilation of 4L/min with pulmonary blood flow of 6L/min suggest?
Perfusion is significantly greater than ventilation => shunt
Which West zone has the best pulmonary blood flow?
Zone 3
What are the characteristic spirometry findings in restrictive lung disease? What arterial PO2 would you expect and why?
- decreased FEV1
- decreased FVC
- normal FEV1/FVC ratio
- fall in vital capacity and FRC
- no CO2 retention
- fall in arterial PO2 due to alveolar collapse (reduced FRC) and resultant shunt
During IPPV, what happens to right ventricular filling?
It falls compared to spontaneous ventilation, which reduces cardiac output
Can PEEP reinflate collapsed alveoli?
No - it can prevent collapse but isn’t normally high enough to re-inflate collapsed lung
How does IPPV increased right ventricular workload?
PVR may rise during IPPV due to hyperinflation/alveolar collapse (PVR is lowest at FRC and rises above or below this)
How does IPPV reduce LV workload?
By decreasing LV cavity size and transluminal wall tension
What does hyperventilation produce?
- muscle spasm (due to decreased proportion of ionised calcium in alkalosis - causes tetany)
- raised pH
- decreased cerebral blood flow
- vasoconstriction due to hypocarbia
- reduced cardiac output (hypercarbia causes increased CO due to increased sympathetic activity)
