VII: Ventilation-Perfusion Relationships Flashcards
How does the ventilation-perfusion ratio change in the vertical lung?
At the apex (top) of the lung, the ratio is the highest. At the base (bottom) of the lung, the ratio is the lowest. This is because perfusion (Q) increases to a much greater degree than ventilation (Vdot) from apex to base due to gravity, which is why the ratio is so low at the base of the lungs.
Is the partial pressure of carbon dioxide high or low at the apex of the lung? Why?
It is LOW because there’s more ventilation than perfusion at the apex. If an area is ventilated faster than it is perfused, CO2 is blown off and does not have time to accumulate.
Is the partial pressure of oxygen high or low at the apex of the lung?
It is actually the lowest in the base because there is more perfusion than ventilation, so all of the oxygen that is coming in from the alveoli is being eaten up quickly by the high perfusion rate.
The lungs pump air at what volume and frequency compared to the heart pumping blood?
lungs pump air at high volume and low frequency; heart pumps blood at low volume, high frequency
Does a high ventilation/perfusion ratio improve oxygenation?
no, but it DOES decrease carbon dioxide levels
Define hypoxemia.
Lowered oxygen levels in the ARTERIAL blood, which may indicate either lowered oxygen content and/or lowered oxygen partial pressure.
What are the 3 basic alveolar types distinguished by?
ventilation to perfusion ratios
List the 3 basic alveolar types.
- dead space alveoli: VA/Q>1
- shunt alveoli: VA/Q<1
- ideal alveoli: VA/Q=1
In which part of the lung does hypoxic vasoconstriction occur?
It occurs in the base of the lung to redirect blood from the shunt alveoli, thereby increasing the low ventilation/perfusion rations up toward 1.
In which part of the lung does hypocapnic bronchoconstriction occur?
It occurs in the apex of the lung to redirect ventilation to dead space alveoli and decrease high ventilation/perfusion ratios toward 1.
What is the cure for High Altitude Pulmonary Edema (HAPE)?
getting the patient down to a lower altitude immediately while administering 100% oxygen
Why does hypoxic vasoconstriction occur in response to low oxygen partial pressures?
This is to help re-direct blood flow from poorly-ventilated lung regions to well-ventilated lung regions in order to distribute blood flow regionally and increase the overall efficiency of gas exchange. This helps to better maintain ventilation/perfusion matching.
Why does hypocapnia result in bronchoconstriction?
This is to decrease ventilation in order to even out the ratio of pO2 and pCO2. More ventilation further reduces pCO2, which we don’t want since pCO2 is already low in hypocapnia.
