Day 9 VQ Mismatch and RL Shunts

VQ ratio indicates how much airflow and blood flow converge on what?

same alveolus

Why doesn't all inspired air participate in gas exchange?

anatomic deadspace, alveolar deadspace, gasses w/poor solubility

What conditions lead to a change in the proportion of inspired air participating in gas exchange?

breathing pattern

Decreasing breathing frequency and increasing tidal volume will do what?

increase alveolar ventilation

Increasing breathing frequency and decreasing tidal volume will do what?

increase deadspace ventilation

Why doesn't all blood entering the pulmonary veins participate in gas exchange?

some blood flows past alveoli not ventilated

Why hasn't all blood entering the left heart participated in gas exchange?

some venous blood from bronchial circulation enters pulmonary veins returning to left heart (anatomic R-L shunt)

How does blood flow to pulmonary capillaries differ between rest and exercise?

some pulmonary capillaries not perfused at rest, creating an exercise reserve

VQ mismatch improves with what?

exercise

Which does gravity affect more, blood flow or airflow?

blood flow

What happens when ventilation is greater than perfusion?

high VQ ratios

What leads to high VQ regions?

anything that reduces blood perfusion (vasoconstriction, pulmonary thromboembolism, heartworm disease, hypertension, hypovolemia)

Do high VQ regions contribute to hypoxemia?

no

Why do high VQ regions not contribute to hypoxemia?

wasted ventilation due to obstruction of blood flow, reduced opportunity for oxygenation

What value is often WNl for high VQ ratios?

PaO2

What happens when ventilation is lower than perfusion?

low VQ ratios

What conditions lead to low VQ regions?

any peripheral, intrathoracic airway obstruction

What is the impact of low VQ regions on PaO2?

reduces overall PaO2 of blood leaving the lungs, hypoxemia

What is the direction of blood flow through cardiac septal defects in the absence of other abnormalities?

left to right

Does providing supplemental O2 to patients with hypoxemia caused by RL shunt result in a change of PaO2?

no

What can cause RL shunts?

anatomic shunt, intrapulmonary blood perfusing alveoli not ventilated

What is the VQ ratio for patients with RL shunts?

0

How do RL shunts limit SO2 values under normal conditions?

bronchial veins anastomose w/pulmonary veins, prevents SO2 values from reaching 100%

What are common ABG findings in cases of RL shunt?

low PaO2, low SO2, high AaDO2, does not respond to oxygen therapy

What are common ABG findings in cases of low VQ ratio?

low PaO2, low SO2, high AaDO2, responds well to oxygen therapy

What is the most common cause of hypoxemia?

low VQ ratio

Which mechanisms of hypoxemia are most difficult to distinguish?

diffusion impairment and low VQ mismatch