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MP - Lecture 32

Pulmonary Pathophyysiology

Medical Physiology – Lecture 32 Pulmonary Pathophysiology
A-a PCO2 gradient difference is: Insignificant (~0)
PCO2 of inspired air is: ~0 mmHg
Largest PCO2 difference is between: Inspired air and alveoli
Hypoventilation always increases: Alveolar, arterial, and venous PCO2
Hypercapnia Elevated PCO2
Respiratory acidosis is caused by: CO2 backup all the way to venous/tissues
Respiratory alkalosis is caused by: Rapid CO2 expiration (Hyperventilation)
Alveolar ventilation is ___ proportional to alveolar PCO2 at constant CO2 production. Inversely (VA decrease = alveolar PCO2 increase)
Causes of CO2 retention: Hypoventilation and decreased blood flow relative to VCO2
Causes of hypoventilation: Increased airway resistance, reduced lung/thorax compliance, depressed respiratory center, or muscle dysfunction
If alveolar PCO2 is 60 to 75 mmHg: Severe dyspnea
If alveolar PCO2 is 80 to 100 mmHg: Lethargy, possible coma
If alveolar PCO2 is greater than 100 mmHg: Depressed ventilation, increased PCO2, decreased PO2, and death
Difference between inspired PO2 and alveolar PO2 is increased by: Hypoventilation
Diffusion impairment (low VA/Q) caused by: Absolute shunt, physiological shunt, and pulmonary embolism
Effect of VA/Q mismatch on alveolar PCO2 is: Minimal
Pneumonia creates a: An absolute right to left shunt
Saturation of blood if one long is completely consolidated but still equal flow is: (98 + 60) /2 = 79%
Saturation of shunted blood is: Equal to mixed venous blood (~60%)
If 100% O2 is given to lungs with one side completely consolidated: Minimal effect, unsaturated shunted blood outweighs small gain by good lung
Atelectasis causes: Absolute right to left shunt
Hypoxia and decreased volume in collapsed lung causes: Increased vascular resistance and blood flow less than half of cardiac output
Pulmonary Embolism Venous thrombus from lower extremity or pelvis travels through right heart and lodges in pulmonary artery
Large pulmonary embolism causes: severe VA/Q mismatch resulting in increased physiological dead space and wasted ventilation
Increased arterial to venous PO2 difference caused by: Low flow, left shifted Hb, anemia, and CO poisoning
CO compared to O2: Same size but more polarized
CO binds Hb: 200x stronger than O2
CO bound Hb increases: affinity for O2 (left shift)
CO poisoning causes: Decreased arterial O2 content and increased O2 affinity (decreased unloading)
In the placenta, O2 transfer is from: Blood to blood
How does fetal blood pick up O2 in placenta: Lower p50 with more hematocrit than maternal Hb and double Bohr effect
Double Bohr Effect Bohr effect in maternal blood helps O2 unloading and in fetal blood helps O2 loading
Effect of CO in fetal O2 delivery Maternal HbCO lowers arterial O2 content and p50, lowering PO2 in maternal side of placenta which lowers fetal arterial PO2, CO also bound to Hbf increases affinity
Effect of cyanide (CN-) Competes with O2 and inhibits cytochrome oxidase
Venous PO2 in cyanide poisoning is: Increased because O2 consumption reduced (Fick)
Forced expiration test measures: Forced vital capacity (FVC)
FEV1 is: Volume forcefully expired in 1 second, ~80% of FVC
Flow-volume curve shows: max flow at each volume
Maximum flow for each volume caused by: Dynamic airway collapse
Dynamic Airway Collapse During forced expiration pressure surrounding airway becomes larger than inside pressure and causes airway collapse
Restrictive flow-volume curve has: Decreased compliance and lower max volume, but normal slope for max flow because normal airway resistance
Obstructive flow-volume curve has: Higher initial volume, but decreased overall volume with decreasing curve due to increased resistance
Hazards of O2 therapy CO2 retention in COPD, retrolental fibroplasia in infants, damage to alveolar endothelium leading to edema, hyperbaric PO2 causing CNS convulsions, and absorption atelectasis
Absorption Atelectasis Obstructed alveoli eventually collapses after absorbing gases into venous blood, N2 slows atelectasis because of slow diffusion rate
Created by: emyang



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