Respiratory physiology Flashcards
Inspiratory reserve volume
air that can still be breathed in during normal inspiration;
Tidal volume
air that moves into lung with each quiet inspiration, typically 500 cc
Expir reserve volume
volume that can still be expired after a normal expiration
how to remember lung volumes
LITER; lung, inspir reserve volume, tidal volume, expir reserve volume, residual volume
residual volme
the air left in the lung after you have already expired as much air as you can
inspiratory capacity
IRV + TV
functional residual capacity
RV + ERV; volume of gas in lung after normal expiration
Vital capacity
TV+IRV+ERV; max volume of gas that can be expired after max inspiration
total lung capacity
just like it sounds
Physiologic dead space
the space in the lung where you don’t have gas exchange; this includes the conducting airways plus the alveolar dead space; apex of healthy lung is the largest contributer of alveolar dead space because you don’t have blood flow up there; VDead=(VT x PaCO2 -PECO2)/PaCO2
Minute ventilation
VE= VT x RR
Alveolar ventilation
VA= (VT-VD) x RR; volume of gas per unit time that acutally reaches the alveoli
Compliance of lung
decreased in pulmonary fibrosis, pneumonia, pulm edema; increaed in emphysema, normal aging
Hemoglobin molecule
Composed of 4 polypeptide subunits (2 alpha, 2 beta) and exist in 2 forms: T (taut, deoxygenated and also has low affinity for oxygen) and R (relaxed, oxygenated);
Which conditions favor the taut (deoxygenated) form of the hemoglobin?
increased chloride, increased H+ (low pH), CO2, 2,3-BPG, and temperature; these all shift the dissociation curve to the right and lead to increaed oxygn unloading
Fetal hemoglobin
2 alpha and 2 gamma subunits; has lower affinitiy for 2,3 BPG than adult hemoglobin, which means more affinity for oxygen
2 types of hemoglobin modifications that lead to tissue hypoxia from decrease o2 sat and decreased o2 content
methemoglobin and carboxyhemoglobin
methemaglobin
oxidized form of Hb (Fe3+) that does not bind oxygen as readily (normal has Fe2+) but has increased affinity for cyanide; may present wth cyanosis and chocolate colored blood; induced methemoglobinemia may be used to treat cyanide poisoning
carboxyhemoglobin
form of Hb bound to CO in place of oxygen; caues decreased oxygen binding capacity with left shif in curve; decreased O2 binding in the tissues; CO binds to Hb with affinitity 200 x greater than o2
What causes a right shift in the oxygen dissoc curve?
gives the Hb less affinity for oxygen; almost everything shift the curve right: acid, CO2, exercise, 2,3BPG, altitude, temperature
oxygen content of blood
oxygen binding capacity x % saturation + dissolved O2
A-a gradient
alveolar PO2 minus arterial PO2
Causes of increased A-a gradient
shunting, V/Q mismatch, fibrosis (impairs diffusion)
Hypoxemia versus hypoxia versus ischemia
hypoxemia is low oxygen in the blood; hypoxia is decreased ox delivery to the tissue; ischemia is loss of blood flow
Hypoxemia with normal A-a gradient
altitude, decreased ventilation (opioid use)
Hypoxemia with increased A-a gradient
V/Q mismatch, diffusion limitation, right to left shunt
Hypoxia
Decreased cardiac output, hypoxemia, anemia, CO poisoning
Ischemia
Impeded arterial flow, decreased venous drainage
V/Q at the apex versus base of the lung
At the apex, it is much greater than 1; at the base, it is much less than 1; ideal is 1
Both ventilation and perfusion are greater at the base of the lung
But proportionally, there is more perfusion than ventilation at the bottom and more ventilation than perfusion at the apex
With increased exercise
vasodilation at the apex, so V/Q approaches 1 at the apex
CO2 is transported from tissues to lungs in 3 forms
HCO3- (90%), carbaminohemoglobin or HbCO2 (5%), dissolved CO2 (5%)
What is the Haldane effect?
In the lungs, oxygenation of Hb promotes dissociation of H+ from Hb; this shift equilibriu toward CO2 formation, and CO2 is released from RBCs
What is the Bohr effect?
In peripheral tissue, increased H+ from tissue metabolism shifts curve to right, unloading O2
Response to high altitude
Decreased PO2 leads to increased ventilation; EPO increases; 2,3 BPG increases (more Oxygen released); cellular changes (increase mitochondria); increased renal excretion of bicarb to compensate for resp alkalosis (can augment with acetazolamide); chronic hypoxia pulm vasoconstriction results in RVH
Response to exercise
Increased CO2 production; increased oxygen consumption; increased ventilation rate to mee ox demand; V/Q ratio apex to base becomes more uniform; increased pulm blood flow due to increased CO; decreased pH during strenuous exercise (2/2 lactic acidosis); no chnage in PaO2 and PaCO2 but increased in venous CO2 content and decreased in venous O2 content
