Respiratory - FA p646-656 Flashcards
Formula to find O2 content of blood?
(1.34 × Hb × Sao2) + (0.003 × Pao2)
Formula for minute ventilation
Total volume of gas entering lungs per minute
VE = VT × RR
How does O2 sat and PAO2 change with dec Hgb?
There is no change in either one, the only change is with normal O2 content in arterial blood (PaO2).
Hb decreased
PaO2 is normal
Alveolar ventilation
Volume of gas that reaches alveoli each minute
VA = (VT − VD) × RR
What disease cause an increase in total O2 content?
Polycythemia
In which disease will there be dec O2 sat’n but normal Hgb?
CO poisoning
Diffusion equation
Diffusion:
V˙ gas = A × Dk × [(P1 – P2)/T]
A = area,
T = alveolar wall thickness,
Dk(P1 – P2) ≈ difference in partial pressures:
When is area decreased? when is alveolar wall thickness inc?
Emphysema, Pulm fibrosis
At ___, inward pull of lung is balanced by outward pull of chest wall, and system pressure is _________.
At FRC, inward pull of lung is balanced by outward pull of chest wall, and system pressure is atmospheric.
Dec in paO2 causes what in lung a/v?
VC (diff from systemic circ)
PVR formula (pulm vas resistance)
PVR =( Ppulm artery – P L atrium)/Cardiac Output
T or F Both ventilation and perfusion are greater at the base of the lung than at the apex of the lung.
True
How does ventilation and perfusion change with exercise?
With exercise (INC cardiac output), there is vasodilation of apical capillaries –> V˙/Q˙ ratio approaches 1.
Respiratory rate (RR)
12–20 breaths/min
Tidal volume
500 mL/breath
Physiological dead space
150 mL/breath
Formula to determine dead space, define dead space
.VD = physiologic dead space = anatomic dead space of conducting airways plus alveolar dead space; apex of healthy lung is largest contributor of alveolar dead space. Volume of inspired air that does not take part in gas exchange. VT = tidal volume. Paco2 = arterial Pco2. Peco2 = expired air Pco2
Cl−, H+, CO2, 2,3-BPG, and temperature cause what change in Hgb and O2?
favor taut form over relaxed form (shifts dissociation curve right O2 unloading).
T or F Myoglobin has higher affinity for O2 > Hgb
True
MoA of Cyanide/CO poisoning
Both inhibit aerobic metabolism via inhibition of complex IV (cytochrome c oxidase) –> hypoxia unresponsive to supplemental O2 and inc anaerobic metabolism
Treatment of CN poisoning?
Hydroxocobalamin (forms cyanocobalamin) or induced methemoglobinemia with nitrites and sodium thiosulfate.
Cyanide is found in ?
synthetic product combustion, ingestion of amygdalin (cyanogenic glucoside found in apricot seed)
Presentation of CO poisoning?
headaches, dizziness, and cherry red skin.
Treatment for CO poisoning?
100% O2, Hyperbaric O2
What CNS lesion is seen with CO poisoning?
Classically associated with bilateral globus pallidus lesions on MR
What is methemoglobin?
Oxidized form of Hb (ferric, Fe3+) that does not bind O2 as readily, but has inc affinity for cyanide.
Methemoglobinemia - presentation and Tx?
Methemoglobinemia may present with cyanosis and chocolate-colored blood
methylene blue and vitamin C.
R shift of O2 curve - what does it mean? causes?
dec Hb affinity for O2 (facilitates unloading of O2 to tissue)
R shift = get Rid of O2
Inc H+ ( dec pH, Acid)
Inc PCO₂
Inc 2,3–BPG
Exercise
High Altitude
Inc Temperature
L shift of O2 curve means? Causes?
dec unloading into tissues
inc pH
dec PCO2
dec temp
dec 2,3 BPG
Inc CO, Met Hb, HbF
How does the body compensate for left shift?
dec O2 unloading –> renal hypoxia –> inc EPO synthesis –> erythrocytosis
Dec of PAO2 causes what?
DEC in PAO2 causes a hypoxic vasoconstriction that shifts blood away from poorly ventilated regions of lung to well-ventilated regions of lung.
Which gases are perfusion limited and which are diffusion limited?
Perfusion - O2 (normally), CO2, N2 - exchange can only inc if blood flow inc
Diffusion limited - O2 (emphysema, fibrosis, exercise) & CO
Why does fetal Hgb shift the curve L?
Fetal Hb has higher affinity for O2 than adult Hb (due to low affinity for 2,3-BPG), so its dissociation curve is shifted left.
Increased parameters in elderly
Lung compliance (loss of elastic recoil)
RV
V ˙/Q ˙ mismatch
A-a gradient
Decreased parameters in the elderly
Chest wall compliance (inc chest wall stiffness)
FVC and FEV1
Respiratory muscle strength (can impair cough)
ventilatory response to hypoxia/hypercapnia
How does CN/CO affect the O2 Sat curve?
CN - Curve normal; oxygen saturation may appear normal initially.
CO - inc oxygen-binding capacity with left shift in curve, dec O2 unloading in tissues. ( Binds competitively to Hb with 200× greater affinity than O2 to form carboxyhemoglobin. )
When is A-a gradient normal / Inc?
Normal A-a gradient = 10-15 nmHg
A-a gradient may occur in hypoxemia; causes include R–> L shunting, V˙/Q˙ mismatch, fibrosis (impairs diffusion)
Causes of Hypoxia
DEC cardiac output
Hypoxemia
Anemia
CO poisoning
Causes of Hypoxemia (DEC PaO2)
Normal A-a gradient
High altitude
Hypoventilation (eg, opioid use)
INC A-a gradient
V˙/Q˙ mismatch
Diffusion limitation (eg, fibrosis)
Right-to-left shunt
Ischemia (loss of blood flow)
Impeded arterial flow
dec venous drainage
CO2 is transported from tissues to lungs in what forms?
HCO3− (90%). Carbaminohemoglobin or HbCO2 (5%). CO2 bound to Hb at N-terminus of globin (not heme). CO2 binding favors taut form (O2 unloaded). Dissolved CO2 (5%).
Bohr Effect?
In peripheral tissue, inc H+ from tissue metabolism shifts curve to right, unloading O2 (Bohr effect).
haldane effect?
In lungs, oxygenation of Hb promotes dissociation of H+ from Hb. This shifts equilibrium toward CO2 formation; therefore, CO2 is released from RBCs
Majority of blood CO2 is carried as _____ in the plasma.
Majority of blood CO2 is carried as HCO3− in the plasma.
Initial Body response to high altitude - what metabolic disturbance
dec atmospheric oxygen DEC (PiO2) –> dec PaO2 –> INC ventilation –> PaCO2 –> respiratory alkalosis –> altitude sickness.
Other body responses to high altitude What two things do we produce more of? What happens in the kidney? on a cellular level?
- Inc erythropoietin –> Inc hematocrit and Hb (chronic hypoxia).
- Inc 2,3-BPG (binds to Hb so that Hb releases more O2).
- Cellular changes ( Inc mitochondria).
- Inc renal excretion of HCO3− to compensate for respiratory alkalosis (can augment with acetazolamide).
- Chronic hypoxic pulmonary vasoconstriction results in pulmonary hypertension and RVH.
Response to Exercise
INC CO2 production.
INC O2 consumption.
INC ventilation rate to meet O2 demand.
V ̇/Q ̇ ratio from apex to base becomes more uniform.
INC pulmonary blood flow due to INC cardiac output.
What happens to pH in exercise?
Dec due to lactic acid
How do gas values change in exercise? (PaO2, PaCO2, v CO2/o2 content)
No change in paO2, and PaCO2, but INC venous CO2, and dec venous O2
