respiratory: ventilation-perfusion relationships Flashcards
pulmonary blood flow value
5000ml/min
if ventilation= 4l/min, whats V/Q in a normal human
v/q if left bronchus is obstructed, and left pulmonary embolus. consequence
v/q if right bronchus is obstructed, left pulmonary embolism
- 8-> normal gas exchange
- 8-> partial gas exchange
- 8-> no gas exchange-> death
what happens in a normal right to left shunt
> 98% of blood passes through lungs
venous blood from bronchial veins + thebesian veins (drain the left ventricle) -> added to left-sided blood w/o undergoing gas exchange
what happens in an abnormal right to left shunt? causes
no ventilation-> pulmonary capillaries do not get oxygenated-> mixed with arterial blood supply
atelectasis (collapsed lung)/lobar pneumonia/congenital heart diseases
shunts caused in Atrial septal defect and ventricular septal defect
left side stronger than right -> left to right shunt initially
in vsd-> large pressure placed on pulmonary circulation-> pulmonary vascular remodelling-> right to left shunt
fallot’s tetralogy
overriding aorta
RV hypertrophy
pulmonary stenosis
VSD
what does a 20% shunt mean
20% of blood goes the wrong way; 80% goes the right way
how does a fall in co2 and o2 content affect pco2 and po2?
pco2 drops moderately, po2 drops alot
what are the effects of increased ventilation in a left to right shunt
at first, low pao2 and high paco2-> stimulates chemoreceptors-> increased ventilation-> more co2 is lost, little o2 is gained as hb is alr saturated
would breathing 100% o2 help right to left shunts
o2 does not reach shunted blood, ventilated regions alr near full saturation
what happens if there is chronic hypoventilation
acidosis compensated by kidneys
what does a high v/q mean ? what is it like
under-perfusion, normal ventilation-> like dead space
what does a low v/q mean? what is it like
poor ventilation, normal perfusion-> like right to left shunt
(basically blood from lungs is kinda deoxygenated)
do high v/q areas balance out low v/q areas
no…
low v/q areas have LARGE FLOW with low po2/o2 content/high pco2/high co2 content;
high v/q areas have SMALL flow with high po2/normal o2/lowpco2/low co2 content;
they combine to give-> low o2/low po2/high co2/highpco2-> chemoreceptors stimulated-> hyperventilation-> low po2/low o2 content/low co2 content/low pco2;
more blood tends to come from low v/q areas;
in high v/q areas, blood is alr saturated so oxygen content isnt affected much
how does v/q different throughout the upright lung?
gravity increases perfusion and ventilation at the botom of the lung
effect on perfusion>ventilation-> v/q higher at top than bottom
