ventilation perfusion relationship Flashcards
partial pressure
exerted by a single gas within a mixture of gases
daltons law of partial pressure
Total pressure equals the sum of the partial pressures of the individual gases in a mixture of gases.
atmospheric pressure
Pressure exerted by the weight of air molecules above a given subject
components of air
N2, O2, CO2, Ar
partial pressure and percentage of atmospheric O2 at sea level
159 mmHg
20.84%
what is the gas composition of O2 of humidified air at sea level
149.3 mmHg
19.67 %
factors that play a role in partial pressure of alveolar gas?
Fraction of inspired O2 (FiO2)
Barometric pressure (PB)
Vapor pressure of H2O (PH2O)
Partial pressure of expired CO2 (PaCO2)
Respiratory quotient
what is the respiratory quotient
The ratio between carbon dioxide production and oxygen consumption.
gas composition of alveolar air at sea level
100
gas exchange in lungs is determined by
Ventilation/perfusion (V/Q) ratio of a lung unit
Absolute amounts of V/Q ratios of multiple lung units
Ventilation/perfusion = What determines the concentration of O2 in the alveolar compartment and, therefore, in the effluent blood?
-Rate at which O2 is added (ventilation)
-Rate at which blood (with O2) is pumped (blood flow–perfusion)
-Concentration of O2 is determined by the ratio of these rates
areas of lungs that are well ventilated will have
poor perfusion
areas of lungs that are well perfused will have
poor ventilation
t/f ventilation and perfusion vary from top to bottom in the lungs
true
at the base of the lung there is
higher perfusion than ventilation
effect of V/Q inequality on overall gas exchange
is not able to adequately transfer O2 and CO2
hypoxemia = lower than normal PaO2
Hypercapnia (higher than normal PaCO2)
When V/Q is lower than normal
“physiologic (intrapulmonary) shunt”
When V/Q is greater than normal
“physiologic dead space”
The greater the physiologic shunt
the greater the amount of blood that fails to be oxygenated as it passes through the lungs
t/f there is a higher partial pressure of O2 in the alveolus than in arterial blood
true
why is there a difference in partial pressure In alveolus and arterial blood?
Diffusion can occur due to pressure gradient
causes of hypoxemia
Hypoventilation
Diffusion limitation
Ventilation-perfusion mismatch
Right-to-left anatomical shunts
define hypoxemia
partial pressure of O2 lower than normal in arterial blood
hypoventilation is determined by the alveolus, 2 factors affected It
Rate of removal of O2 by blood
Rate of replenishment of O2 by alveolar ventilation
with hypoventilation there will be an increase of
CO2 in alveolus and arterial blood
causes of hypoventilation
Drugs
Opioids, sedatives, barbiturates and other anesthetics
Paralysis of respiratory muscles and nerves
Trauma to the chest wall
Tracheal and airway obstruction
treatment for hypoventilation
O2 saturation
increase ventilationn
what causes diffusion limitation
Decreased capillary transit time of red blood cells= Strenuous exercise at high altitude
Thickening of the blood-gas barrier = Rate of rise of PO2 in the red cells is slow, so the PO2 may not reach that of the alveolar gas before red cell leaves the pulmonary capillary
shunt perfusion are usually caused by
atelectasis
obstructive
Mucus plugs
Upper airway foreign bodies
Tumors
non obstructive
Pneumothorax
Diaphragmatic hernia
Increased intraabdominal pressure (e.g., laparoscopy, gastrointestinal distention)
Recumbency under general anesthesia
dead space ventilation is usually caused by
pulmonary embolism
cardiogenic shock
what causes increased physiological dead space
Anything that decreases pulmonary blood flow
Hypotension
Hypovolemia
Decreased cardiac output
Shock
Pulmonary thromboembolism
causes of right to left anatomical shunt
Reverse patent ductus arteriosus (PDA)
Tetralogy of Fallot
how do you fix a right to left anatomical shunt?
correct the anatomical defects
