pulm Flashcards
formula for physiologic dead space?
VD = VT * (PaCO2 - PECO2) / (PaCO2)
PaCO2 = alveolar PCO2 PECO2 = expired air PCO2
** Taco, Paco, Peco, Paco!
formula for minute ventilation?
VE = VT * RR
formula for alveolar ventilation?
VA = (VT - VD) * RR
lung/chest wall dynamics at FRC?
inward lung pull = outward chest wall pull
systemic P = atmospheric
lung pressures at FRC?
airway and alveolar P = 0
intrapleural P < 0 (~ -5) –> prevents PTX
dz that increase/decrease compliance?
increase: emphysema, aging
decrease: fibrosis, PNA, edema
taut form of Hb?
deoxygenated
low affinity for O2
favored by increased Cl, H, CO2, 2,3BPG
relaxed form of Hb?
oxygenated
positive cooperativity and negative allostery
fetal Hb affinity for 2,3 BPG?
lower affinity for 2,3 BPG –> higher affinity for O2 (LEFT shift in dissociation curve)
oxidized form of Hb, decreased affinity for O2, increased affinity for cyanide?
methemoglobin - ferric (Fe 3+)
cyanosis and chocolate colored blood?
methemoglobinemia
- tx with methylene blue
- can be induced with nitrites/thiosulfate and benzocaine –> treat cyanide poisoning
Hb bound to CO?
carboxyhemoglobin
CO causes what shift in Hb-O2 dissociation curve?
LEFT shift = decreased O2 unloading in tissues
** CO has 200x greater affinity for Hb than O2
what causes right shift in Hb-O2 curve?
Acid CO2 exercise 2,3 BPG altitude temperature
formula for O2 content of blood?
O2 content = (O2 binding capacity * % saturation) + dissolved O2
how much O2 can 1g of Hb bind?
1.34 mL O2
when do you see cyanosis?
deoxygenated Hb > 5 g/dL
what is approx O2 binding capacity?
20 mL O2/dL
how does CO poisoning affect blood O2 parameters?
decreased Hb O2 saturation, decreased total O2
normal [Hb] and normal PaO2
how does anemia affect blood O2 parameters?
decreased [Hb] and decreased total O2
normal Hb O2 saturation and PaO2
how does polycythemia affect blood O2 parameters?
increased [Hb] and increased total O2
normal Hb O2 saturation and PaO2
which gases are perfusion limited?
O2 (in normal lung)
CO2
N2O
which gases are diffusion limited?
O2 (in emphysema, fibrosis)
CO
formula for diffusion of gas?
Vgas = A/T * (difference in partial P) A = area T = alveolar wall thickness
- emphysema causes decreased A
- fibrosis causes increased T
alveolar gas equation?
PAO2 = PIO2 - (PaCO2/R)
** at sea level, room air PAO2 = 150 mmHg - (PaCO2/0.8)
causes of hypoxemia with normal A-a gradient?
high altitude
hypoventilation
causes of hypoxemia with increased A-a gradent?
V/Q mismatch
diffusion limitation
R-to-L shunt
causes of hypoxia?
decreased CO
hypoxemia
anemia
CO poisoning
V/Q at lung apex vs base?
apex: V/Q = 3 (ventilation > perfusion)
base: V/Q = 0.6 (perfusion > ventilation)
V, Q largest at bases or apices of lung?
both largest at base
perfusion has larger difference between base and apex
how does exercise affect V/Q distribution?
vasodilation of apical capillaries –> increased perfusion –> V/Q at apex approaches 1
forms of CO2 in blood?
HCO3 = 90%
HbCO2 = 5% (CO2 binds at N-terminus of globin –> favors taut form)
dissolved CO2 = 5%
Haldane effect?
Hb oxygenation in lungs –> H+ dissociation from Hb –> CO2 formation –> CO2 release from RBCs
Bohr effect?
increased H+ from tissue metabolism –> favors O2 unloading
changes in response to high altitude?
increase in: ventilation, EPO, 2,3BPG, mitochondria
increase in renal HCO3 excretion to compensate for respiratory alkalosis
** chronic hypoxic pulmonary vasoconstriction –> RVH
changes in response to exercise?
increase in: CO2 prod, O2 consumption, ventilation rate, pulm blood flow
decrease in pH
V/Q ratio more uniform b/w apices and bases
- PaO2 and PaCO2 STAY THE SAME
- increase in venous CO2 and decrease in venous O2
