BCSE
Physiology
Respiratory Physiology – BCSE Study Guide
March 28, 2026
30 min read
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BCSE study guide for Respiratory Physiology. High-yield review with exam-focused content and practice questions.
| Volume |
Definition |
Clinical Significance |
| Tidal Volume (TV) |
Volume of air inhaled or exhaled during normal, quiet breathing (approximately 10-15 mL/kg) |
Monitored during anesthesia; decreased in restrictive disease |
| Inspiratory Reserve Volume (IRV) |
Additional air that can be forcibly inhaled after normal inspiration |
Reserve for increased oxygen demand during exercise |
| Expiratory Reserve Volume (ERV) |
Additional air that can be forcibly exhaled after normal expiration |
Reduced in obesity, ascites, pregnancy |
| Residual Volume (RV) |
Air remaining in lungs after maximal forced expiration; cannot be measured by spirometry |
Prevents alveolar collapse; increased in obstructive disease (air trapping) |
| Capacity |
Formula |
Clinical Use |
| Inspiratory Capacity (IC) |
TV + IRV |
Maximum inspiration from resting level |
| Functional Residual Capacity (FRC) |
ERV + RV |
Volume at end of normal expiration; equilibrium point of chest wall and lung recoil |
| Vital Capacity (VC) |
IRV + TV + ERV |
Maximum air that can be exhaled after maximum inspiration |
| Total Lung Capacity (TLC) |
IRV + TV + ERV + RV |
Total volume of lungs at maximum inspiration |
| Factor |
Effect on Diffusion |
Clinical Example |
| Surface Area |
Increased area = increased diffusion |
Emphysema, pneumonectomy decrease area |
| Membrane Thickness |
Thicker membrane = decreased diffusion |
Pulmonary fibrosis, edema increase thickness |
| Pressure Gradient |
Larger gradient = faster diffusion |
High altitude decreases O2 gradient |
| Gas Solubility |
More soluble = faster diffusion |
CO2 is 20x more soluble than O2 |
| RIGHT SHIFT (Decreased Affinity = More O2 Released) |
LEFT SHIFT (Increased Affinity = Less O2 Released) |
| Increased Temperature (fever, exercise) |
Decreased Temperature (hypothermia) |
| Increased PCO2 (Bohr Effect) |
Decreased PCO2 (hyperventilation) |
| Decreased pH (acidosis) |
Increased pH (alkalosis) |
| Increased 2,3-DPG |
Decreased 2,3-DPG (stored blood) |
| Higher P50 (curve shifts right) |
Fetal hemoglobin, Carbon monoxide, Methemoglobin |
| Form |
Percentage |
Mechanism |
| Bicarbonate (HCO3-) |
70% |
CO2 + H2O converts to H2CO3 converts to HCO3- + H+ (carbonic anhydrase in RBCs) |
| Carbaminohemoglobin |
23% |
CO2 binds directly to amino groups on hemoglobin (NOT the heme group) |
| Dissolved CO2 |
7% |
Dissolved in plasma; measured as PaCO2 |
| Feature |
Carotid Bodies |
Aortic Bodies |
| Location |
Bifurcation of common carotid arteries |
Aortic arch |
| Innervation |
Glossopharyngeal nerve (CN IX) |
Vagus nerve (CN X) |
| Primary Stimulus |
Decreased PaO2 (hypoxemia) |
Decreased PaO2 (hypoxemia) |
| Secondary Stimuli |
Increased PaCO2, Decreased pH |
Increased PaCO2, Decreased pH |
| Importance |
MORE important; primary O2 sensor |
Less important for respiration |
| Species |
Key Respiratory Characteristics |
| Horse |
Obligate nasal breathers. 1:1 stride-to-breath coupling during gallop. Exercise-induced hypoxemia is NORMAL. Relatively blunted CO2 response. Quiet expiration has passive then active phase. |
| Cattle |
Low 2,3-DPG levels (left-shifted curve). More sensitive to hypoxic pulmonary vasoconstriction than horses. Prone to high-altitude disease (brisket disease). |
| Dog |
P50 varies between breeds (25.8-35.8 mmHg). Higher 2,3-DPG levels. Panting is thermoregulatory, not pathological. Brachycephalic breeds have upper airway obstruction. |
| Cat |
Open-mouth breathing is ALWAYS pathological (not normal panting). Small airways prone to bronchoconstriction. Feline asthma common. |
| Birds |
Unidirectional airflow through parabronchi. Air sacs for ventilation (not gas exchange). NO diaphragm. Cross-current gas exchange (more efficient). |
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