VQ mismatch and shunt

What would occur to the PO2 and PCO2 if there was an issue with the alveoli

PO2 would drop significantly from 100 to 40 mmHg and PCO2 increase from 40 to 45; compensation = alveolar CONSTRICTION

What would happen to PO2 and PCO2 if there was a problem with the blood vessels

PO2 will increase to match the outside (from 100 to 159) and PCO2 will drop from 40 to 0.3; compensation is bronchial CONSTRICTION

What can cause V/Q mismatch

Shunt (low VQ) and dead space (high VQ)

What happens in shunt

Low V/Q; when there is low ventilation but normal perfusion → Leads to hypoxemia

What conditions commonly cause shunting

Pneumonia and pulmonary edema

What happens in dead space

Normal ventilation with low perfusion; leads to shortness of breath and low O2

What conditions cause dead space

Pulmonary embolism, emphysema, bronchiectasis

How is ventilation different in the upper and lower lung

Upper: Larger less compliant alveoli, less ventilation, more negative pressure

How is perfusion different in upper and lower lung

Upper: Higher resistance, less blood flow, less recruitment

What describes the order of highest to lowest pressure in Zone 1 (Zones of West)

Pressure alveoli > Pressure PA > Pressure PV

What describes the order of highest to lowest pressure in Zone 2 (Zones of West)

Pressure PA > Pressure alveoli > Pressure PV

What describes the order of highest to lowest pressure in Zone 3 (Zones of West)

Pressure PA > Pressure PV > Pressure alveoli

What is the characteristic of zone 1

Highest V/Q, lowest ventilation and perfusion; Highest PaO2, lowest PaCO2

What is the characteristic of zone 2

V/Q = 1; ventilation and perfusion equal

What is the characteristic of zone 3

Lowest V/Q;  Highest PaCO2, lowest PaO2

What is the pattern of O2 pressure as it moves from outside to tissue

Starts as 159mmHg in atmosphere → Decreases to 100 in lung → 95 in blood vessel → 50 in tissue 

What is diffusion limitation 

PO2 difference between alveolar gas and capillary blood is very small 

What situations can increase difference in diffusion limitation

Exercise, thicker blood gas barrier, low O2 mixture is inhaled

In PE what would be the pressure values in both alveoli and blood

No arterial PaCO2 and PaO2 (blockage): high PAO2 (150) and PACO2 of 0

In airway obstruction what are the pressure values in both alveoli and blood

PaO2 decreases to 40 mmHg, PaCO2 increases to 46 mmHg; no PA values (no ventilation) 

What is the anatomical shunt 

Bronchial artery and coronary artery feed the bronchiole and myocardium 

What is the physiological shunt

Coronary artery shunt → Thebesian shunt in myocardium; 2% of blood bypass pulmonary capillary

You administer 100% oxygen to a hypoxic patient. Their arterial oxygen levels do not improve significantly (refractory hypoxemia). Which of the following is the most likely cause?

Intrapulmonary shunt → Blood flowing through parts of body with no air

In a healthy person standing upright, which region of the lung receives the most blood flow (perfusion) due to gravity?

Base (bottom) of lung

A child inhales a peanut, completely blocking the airway to the right lower lobe. Blood continues to flow to that lobe initially. What is the approximate V/Q ratio of this specific lung unit?

V/Q = 0; airway obstruction = ventilation is zero → 0/Q = 0 

A patient suffers a Pulmonary Embolism (PE), where a clot blocks blood flow to a segment of the lung, but airflow continues. This creates an area of High V/Q. What is the clinical term for this?

Alveolar dead space 

When a specific area of the lung becomes hypoxic (low oxygen), the small arteries in that area constrict to redirect blood flow to healthier areas. What is this protective reflex called?

Hypoxic pulmonary vasoconstriction