Ventilation/Perfusion Flashcards
Respiration
Entire breathing process which includes both ventilation and oxygenation
Ventilation
Exchange of gases in the lungs on a molecular level caused by moving air in and out of the body
O2 in CO2 out
Oxygenation
Diffusion of oxygen from the air into the red blood cells where it is then delivered to the tissues
Perfusion
Blood flow, to the alveoli and the tissues
What drives ventilation?
High CO2
What is CO2
Waste product of energy production during the Kreb’s cycle
High levels of CO2 leads to formation of…
CO2 and water form carbonic acid, which is a weak acid that dissociates into bicarbonate and H+ ions
Increase of H+ leads to
Decrease in pH (More acidic)
Increase in CO2 leads to a/an _________ in pH
Decrease, more acidic from formation of H+ ions
Normal rage of pH
7.35 - 7.45
Chemoreceptors
Monitor the pH of the blood and can then trigger change in ventilation to alter amount of CO2 in the body which in turn can increase or decrease pH
Minute ventilation
Respiratory rate x tidal volume
RR x VT = MV
# of breaths x volume of each breath
Result of increase in tidal volume or RR
Increase amount of CO2 expelled, so decrease in amount of H+ ions and increase in pH (more basic)
Hypercapnia (hypercarbia)
CO2 retention
Elevation in PaCO2 (amount of CO2 in the blood) over 45 mmHg
Hypocapnia
A decrease in PaCO2 (CO2 in the blood) below 35 mmHg
Equation to determine acidity from CO2
Regulation of pH with respirations time
Seconds to minutes
Just breathing more or less to change CO2
Regulation of pH with kidneys time
Days to weeks
How respirations change the pH equation
Change the amount of CO2 by breathing more or less
Left side
How kidneys control pH equation
Right side of equation
Changing retention or excretion of bicarbonate and H+ into the urine
Hypoventilation
Less breathing, so retaining CO2, not increased production
Decreases acidity
Impact of chronic CO2 elevation
Down regulates chemoreceptors which makes it so they don’t respond to the consistent difference pH
Hypercapnia
Hypoxia becomes primary stimulus for ventilation
Hypoxemia
Decrease amount of O2 in the blood
PaO2 is low (under 75 mmHg)
Oxygen saturation
How much oxygen is currently bound to hemoglobin
Measured by pulse oximetry
Hypoxia
When the tissue oxygen level is impaired
(Tissues now have decreased O2 amount)
Anoxic
No oxygen delivery to a tissue
(Infarction, tissue death)
Most common cause of hypoxia
Due to low oxygen available in the blood
Hypoxemia without hypoxia
Means there is a decrease amount of O2 in the blood but not in the tissues
Increased delivery of O2 to compensate for low PaO2
(Increase in CO to maintain perfusion or hypothermia so tissues don’t need as much O2)
Hypoxia without hypoxemia
O2 is in the blood but there is insufficient oxygen supply at the tissue level
Tissues are unable to use O2 effectively
O2 delivery is impaired (MI)
V/Q mismatch used in cases of
Hypoxemia
So decrease amount of O2 in the blood
V/Q mismatch
Ventilation/perfusion mismatch occurs when the ratio of ventilation to perfusion is abnormal in one or more areas of the lung. This can lead to a decrease in oxygen delivery to the tissues and an increase in carbon dioxide retention. Ventilation/perfusion mismatch is diagnosed by measuring the ratio of ventilation to perfusion in different areas of the lung.
V/Q mismatch equation
1 = V divided by Q
V =
Alveolar ventilation
Air entering lungs into alveoli
Q =
Perfusion
Blood flow in capillaries past the alveoli
What is V/Q mismatch looking at
Hypoxemia can occur when ventilation and perfusion aren’t matched
Seeing which is the cause
Hypoxic pulmonary vasoconstriction
Try to maintain proper V/Q ratios by sensing areas of hypoxia and poor gas exchange and vasoconstricting flow to these poorly functioning areas
Healthy areas get the blood flow
Max out though when thinking about chronic disease issues
5 most common causes of hypoxemia (V/Q mismatch)
Asthma
COPD
Pulmonary embolism
Cystic fibrosis
Interstitial lung disease
Asthma V/Q mismatch
Bronchoconstriction = lower V (.75)
Blood flow is the same = Q of 1
.75 / 1 = .75
Low mismatch
Pulmonary embolism V/Q mismatch
Blood clot is decreasing blood flow in artery so Q is lower = .5
Ventilation is the same so V= 1
1/.5 = 2
High mismatch
Right to left shunt
When blood travels from the RV to the LA without ever being oxygenated
Extreme form of low ratio V/Q mismatch
Diffusion limitation
Difficulty in getting oxygen from the alveolus into the capillary
Often due to scaring/fibrosis of the alveolar - capillary membrane or of reduced surface tension in the alveoli
FiO2
Fraction of inspired oxygen
Room air is 21%
If less then less O2 for gas exchange leading to hypoxemia
Carbon monoxide and Hb
Has 250X greater binding affinity for Hb than O2
CO + O2 Hb
CO is a competitive antagonist
When CO binds it changes Hb shape to make it more difficult to unload oxygen into the tissues
