Modules #3: Respiratory Function Flashcards
What drives gas exchange in the body?
driven by pressure gradients in both pulmonary capillaries and systemic capillaries
What is the PaO2 in the lungs?
PaO2 = 103 mmHg in the lungs
What is the PaO2 in blood returning from tissue?
as low as 40 mmHg
What is the PaO2 in blood leaving the pulmonary capillaries?
PaO2 = ~ 100 mmHg
What is the PaCO2 in the lungs?
PaCO2 = 40 mmHg
What is the PaCO2 in blood returning from tissue?
PaCO2 = 45 mmHg
What is the PaCO2 of blood leaving the pulmonary capillaries?
PaCO2 = ~ 40 mmHg
What is the PaO2 of tissues?
depending on metabolic demand, can be as low as 20 mmHg
What is the PaCO2 of tissues
depending on metabolic demand can be as high as 46 mmHg
What is pulmonary perfusion?
it is pulmonary circulation (blood flow)
How much is resting cardiac output (CO)?
5 L/min
How much is exercise cardiac output (CO)?
can increase up to 25 L/min
Describe the alveoli at the base of the lung
alveoli are smaller (and therefore have a reduced surface tension) which makes them easer to inflate
What are the alveoli @ the base responsible for?
normal tidal volume ventilation
Describe the alveoli at the apex of the lung
They’re larger (b/c they contain larger amount of residual air) which means they have an increased amount of surface tension = harder to inflate
What are the alveoli @ the apex responsible for?
ventilation during exercise
What is the pulmonary perfusion distribution dependent on?
Gravity
Does the base or apex have a greater amount of blood flow?
The base has a larger amount of blood flow
What happens when alveolar gas pressure exceeds capillary pressure?
the capillary collapses or is compressed
perfusion slows or stops
What happens as far as ventilation and perfusion at the 3 zones in upright lungs?
Zone I: alveolar pressure > arterial capillary pressure > venous capillary pressure –> perfusion is STOPPED by alveolar pressure
Zone II: arterial capillary pressure > alveolar pressure > venous capillary pressure –> perfusion = SLOWED DOWN by alveolar pressure
Zone III: arterial capillary pressure > venous capillary pressure > alveolar pressure –> perfusion is NOT EFFECTED by alveolar pressure
what is the V/Q ratio?
ratio of ventilation/perfusion
compares amount of air that enters alveoli/min w/ the amount of blood that travels through pulmonary capillaries/minute (Cardiac Output)
What is the V/Q ratio in the apex of the lung?
ventilation exceeds perfusion
this is a very small portion of the lung
What is the V/Q ratio in the base of the lung?
perfusion exceeds ventilation
What does V/Q measure clinically?
sum of V/Q from all zones
What is normal V/Q at rest?
.8
Ventilation is lightly less than perfusion
See outline for explanation of calculation
What is the V/Q during moderate exercise?
still @ .8
ventilation and respiration increase proportionately
What is the V/Q during very intense exercise?
V/Q increases 5/1: ventilation = 100 L/min cardiac outut = 20 L/min
Ventilation increases way more than perfusion, meaning lungs aren’t limiting factor in exercise
What happens to V/Q when blood flow is obstructed (i.e. pulmonary embolism?
V/Q will increase infinitely
What happens to V/Q when ventilation is obstructed (i.e. COPD)
V/Q decreases
What drives O2 transport across capillary membrane?
Drive by pressure gradients
At rest how much time does it take RBC to travel through pulmonary capillary?
.75 seconds
At rest how long does it take for for O2 to bind to hemoglobin (Hb)
.25 seconds
What is the purpose of the oxyhemoglobin dissociation curve?
demonstrates oxygen saturation amounts @ different pressures
What does the “flat” top portion of the oxyhemoglobin dissociation curve represent ?
buffer zone - 60 mmHg - 100 mmHg
increased O2 binding to Hb is maintained in this region
What is happening at the “steep” portion of the oxyhemoglobin dissociation curve?
O2 doesn’t bind as well and will dissociate from hemoglobin
What is happening with oxygen and hemoglobin in tissues?
Tissues are generally hypoxic (low PaO2) and will promote the release of O2 from hemoglobin so it can diffuse from blood stream into tissue
Explain what is happening when the oxyhemoglobin dissociation curve has a “right shift” and what causes it.
there is a decreased affinity between hemoglobin and O2
elevated levels H+ (acidosis)
elevated levels of CO2 (hypercapnia)
Explain what is happening when the oxyhemoglobin dissociation curve has a “left shift” and what causes it.
there is an increased affinity between hemoglobin and O2
low levels of H+ (alkalosis)
decreased CO2 levels (hypocapnia)
What are the other 2 factors (besides H+ and CO2) that alters the oxyhemoglobin dissociation curve?
Body temperature
2,3 DPG levels
What is the saturation of hemoglobin if PaO2 is 100 mmHg (like in the lung)?
Hb should be 98% saturated w/ O2
What is the saturation of hemoglobin if PaO2 is 60 mmHg (right on the cusp of the flat portion of the curve?)
Hb should be 90% saturated w/ O2
What is the saturation of hemoglobin If PaO2 is 40 mmHg (like what is typical of blood leaving exercising muscle)?
Hb should be 75% saturated w/ O2
What does a pulse oximeter measure?
O2 saturation of arterial blood
What is the normal pulse-ox values for healthy individuals?
95-97% saturated
What is an acceptable pulse-ox values for pts suffering from pulmonary is eases like COPD?
90-90% saturated
What is the threshold for “abnormal” pulse-ox values?
90%
Whats the difference between the pressure gradient of CO2 and O2?
CO2 pressure gradient is much smaller
alveoli PaCO2 = 39-40 mmHg and pulmonary arteries/capillaries PaCO2 = 46 mmHg
Name the 3 ways CO2 is transported throughout the body
dissolved in blood plasma
bound to hemoglobin (Hb)
transported in RBCs as bicaronate (HCO3-)
How much of CO2 is dissolved in blood plasma?
5-10%
How much of CO2 is bound to hemoglobin?
5-30%
How much of CO2 is in bicarbonate form?
60-90%
Describe the process of how CO2 forms bicarbonate
CO2 enters RBC
combines w/ H2O –> carbonic acid (H2CO3)
carbonic acid dissociated to form H+ + HCO3-
bicarbonate dissolves into blood plasma and RBCs buffer the H+
What is the Bohr effect?
right shift of oxyhemoglobin dissociation curve
elevated CO2 decreases Hb - O2 affinity and promotes Hb - CO2 affinity
seen in tissues
What is the Haladane effect?
left shift of oxyhemoglobin dissociation curve
elevated O2 values decreases Hb - CO2 affinity and promotes Hb - O2 affinity
seen in lungs
