Respiratory Anatomy & Physiology
Pulmonary Ventilation
| Parameter |
Definition |
Normal Value |
| Tidal volume (TV) |
Volume of each breath at rest |
500 mL |
| Inspiratory reserve volume (IRV) |
Maximal inspiratory effort |
3000 mL |
| Expiratory reserve volume (ERV) |
Maximal expiratory effort |
1200 mL |
| Residual volume (RV) |
Volume remaining after max expiration |
1200 mL |
| Total lung capacity (TLC) |
Maximal lung volume |
6000 mL |
| Vital capacity (VC) |
Maximal voluntary ventilation |
4800 mL |
Gas Exchange
Alveolar Gas Equation:
PAO₂ = FiO₂ × (Patm - PH₂O) - (PaCO₂ / RQ)
Where:
- FiO₂ = Fraction inspired O₂ (0.21 at sea level)
- Patm = Atmospheric pressure (760 mmHg at sea level)
- PH₂O = Water vapor pressure (47 mmHg at 37°C)
- RQ = Respiratory quotient (~0.8)
Normal PAO₂: ~100 mmHg
Normal PaO₂: 80-100 mmHg (declines with age)
Ventilation-Perfusion (V/Q) Matching
| Region |
V/Q Ratio |
Implication |
| Normal lung base |
~0.8 |
Optimal matching |
| Lung apex |
>3.0 |
Wasted ventilation (high V/Q) |
| Lung base |
<0.8 |
Wasted perfusion (low V/Q) |
| Shunt |
V/Q = 0 |
No gas exchange (e.g., ARDS) |
Pulmonary Function Testing
Spirometry
Flow-Volume Loop Interpretation:
Inspiratory ┌──────┐ ┌──────────┐
limb │ │ │ │
│ │ │ │
│ │ │ │
│ │ │ │
└──────┴───┘ │
└──────────────────────┘
Expiratory limb
Obstructive: Scooped ("festoons"), reduced FEV1/FVC
Restrictive: Tall/narrow, preserved FEV1/FVC, reduced volumes
| Parameter |
Obstructive |
Restrictive |
| FVC |
Normal or ↓ |
↓ Markedly |
| FEV₁ |
↓ Markedly |
↓ Proportionally |
| FEV₁/FVC |
↓ (<70%) |
Normal (>70%) |
| TLC |
Normal or ↑ |
↓ |
| RV |
Normal or ↑ |
↓ |
| DLCO |
Normal or ↓ |
Normal or ↓ |
Lung Volumes
| Volume |
Definition |
Clinical Significance |
| Functional residual capacity (FRC) |
RV + ERV |
Body pletysmography measures |
| Total lung capacity (TLC) |
All volumes |
Serial measurements track disease |
| Diffusing capacity (DLCO) |
Gas transfer |
Interstitial vs. obstructive |
Obstructive Lung Diseases
Chronic Obstructive Pulmonary Disease (COPD)
Definition: Progressive airflow limitation, not fully reversible, usually progressive, associated with enhanced inflammatory response to noxious particles/gases.
GOLD Classification
| GROUP |
Symptoms |
Spirometry |
FEV₁ (% predicted) |
| A |
Low risk, few symptoms |
FEV₁ ≥ 80% |
≥ 80 |
| B |
Low risk, more symptoms |
FEV₁ ≥ 50-79% |
50-79 |
| C |
High risk, few symptoms |
FEV₁ 30-49% |
30-49 |
| D |
High risk, more symptoms |
FEV₁ < 30% |
< 30 |
Pharmacologic Management
COPD_TREATMENT = {
"short-acting_bronchodilators": {
"SABA": ["albuterol", "salbutamol"],
"SAMA": ["ipratropium"],
"use": "Rescue therapy"
},
"long-acting_bronchodilators": {
"LABA": ["salmeterol", "formoterol", "indacaterol"],
"LAMA": ["tiotropium", "umeclidinium", "glycopyrronium"],
"use": "Maintenance therapy"
},
"inhaled_corticosteroids": {
"indications": ["History of ≥2 exacerbations/yr", "Elevated eosinophils"],
"examples": ["fluticasone", "budesonide"]
},
"triple_therapy": {
"components": ["LABA + LAMA + ICS"],
"indications": ["Group D COPD", "Frequent exacerbations"]
}
}
Asthma
Definition: Chronic inflammatory disorder of airways, reversible airflow obstruction, airway hyperresponsiveness.
Asthma Control Test (ACT)
| Score |
Control Level |
Action |
| 25 |
Well-controlled |
Maintain therapy |
| 20-24 |
Well-controlled |
May step down |
| 15-19 |
Not well-controlled |
Step up therapy |
| <15 |
Very poorly controlled |
Urgent action |
Stepwise Asthma Management
| Step |
Treatment |
Notes |
| 1 |
SABA PRN |
Low-dose ICS PRN as needed |
| 2 |
Low-dose ICS |
Or LTRA |
| 3 |
Medium-dose ICS + LABA |
Consider adding LAMA |
| 4 |
High-dose ICS + LABA |
Add LAMA |
| 5 |
Add oral montelukast |
Refer for OCS, consider biologics |
| 6 |
Add oral corticosteroids |
Biologic therapy |
Restrictive Lung Diseases
Interstitial Lung Diseases (ILD)
| Category |
Examples |
Key Features |
| Idiopathic pulmonary fibrosis (IPF) |
Usual interstitial pneumonia (UIP) |
Honeycombing, basilar |
| Sarcoidosis |
Non-caseating granulomas |
Lymphadenopathy, upper lobe |
| Hypersensitivity pneumonitis |
Bird fancier's lung |
Exposure history |
| Connective tissue disease-associated |
RA-ILD, SSc-ILD |
Underlying autoimmune disease |
| Drug-induced |
Bleomycin, methotrexate |
Medication history |
Pulmonary Function in Restriction
Pattern: ↓ TLC, ↓ FVC, ↓ FEV₁, Normal FEV₁/FVC ratio
Severity (TLC % predicted):
- Mild: 65-80%
- Moderate: 50-64%
- Severe: <50%
High-Resolution CT (HRCT) Patterns
| Pattern |
Characteristics |
Differential |
| UIP/IPF |
Honeycombing, reticulation, traction bronchiectasis |
Idiopathic pulmonary fibrosis |
| COP |
Cryptogenic organizing pneumonia |
Bilateral consolidations |
| NSIP |
Ground-glass, reticulation, relatively preserved |
Symmetric, lower lobe |
| LIP |
Lung cysts, ground-glass |
Diffuse, thin-walled cysts |
Respiratory Failure
Type I vs. Type II
| Type |
pO₂ |
pCO₂ |
Examples |
| I (hypoxemic) |
< 60 mmHg |
Normal or ↓ |
PE, ARDS, pneumonia, edema |
| II (hypercapnic) |
< 60 |
> 50 |
COPD exacerbation, obesity hypoventilation |
Acute Respiratory Distress Syndrome (ARDS)
Berlin Definition:
| P |
O₂ Requirement |
| Mild |
PaO₂/FiO₂ 200-300 mmHg with PEEP ≥ 5 |
| Moderate |
PaO₂/FiO₂ 100-200 mmHg with PEEP ≥ 5 |
| Severe |
PaO₂/FiO₂ < 100 mmHg with PEEP ≥ 5 |
Etiology:
- Direct: Pneumonia, aspiration, near-drowning, inhalation injury
- Indirect: Sepsis, transfusion, pancreatitis, trauma
Sleep-Related Breathing Disorders
Obstructive Sleep Apnea (OSA)
Diagnosis: AHI ≥ 5 events/hour with symptoms, or AHI ≥ 15 events/hour regardless of symptoms
| Event |
Type |
Definition |
| Apnea |
Cessation |
≥ 10 seconds |
| Hypopnea |
Decrease |
≥ 30% + 3% desaturation or arousal |
| RDI |
Apnea + hypopnea |
Events per hour |
Treatment Options
| Treatment |
Indication |
Notes |
| CPAP |
First-line OSA |
Standard pressure 5-20 cmH₂O |
| BiPAP |
Ventilatory failure |
CPAP failure, overlap syndrome |
| MAD |
Dental |
OAS mild-moderate |
| Surgery |
UPPP |
Palatal surgery |
| Weight loss |
All overweight |
5-10% improvement |
Pulmonary Imaging
Chest X-Ray Patterns
| Pattern |
Radiographic Appearance |
Clinical Correlation |
| Consolidation |
Airspace opacity, air bronchograms |
Pneumonia, edema, hemorrhage |
| Interstitial |
Reticular, nodular |
ILD, heart failure |
| Cavitation |
Central lucency |
Lung abscess, TB, tumor |
| Pleural effusion |
Blunted costophrenic angle |
Transudate vs. exudate |
| Pneumothorax |
Visceral pleural line, no lung markings |
Trauma, spontaneous |
CT Pulmonary Angiography (CTPA)
Indication: Suspected pulmonary embolism
| Finding |
Sensitivity |
Specificity |
| Central PE |
83-100% |
89-97% |
Common Errors to Avoid
- Confusing obstructive vs. restrictive patterns — Always look at FEV₁/FVC ratio and TLC
- Ignoring DLCO — Essential for differentiating emphysema vs. chronic bronchitis
- Missing hypoxemia triggers — Consider altitude, V/Q mismatch, shunt
- Inadequate rescue inhaler technique — Check technique at each visit
- Underestimating sleep apnea — Screen all snorers, especially with hypertension
- Delayed biopsy in ILD — Consider multidisciplinary discussion
- Oxygen prescription errors — Target SpO₂ 88-92% for COPD, 94-98% for others
- Ignoring vaccination status — Influenza annually, pneumococcal per guidelines
1---2name: pulmonology3description: Respiratory Anatomy & Physiology4---56## Respiratory Anatomy & Physiology78### Pulmonary Ventilation910|Parameter|Definition|Normal Value|11|---------|-----------|-------------|12|Tidal volume (TV)|Volume of each breath at rest|500 mL|13|Inspiratory reserve volume (IRV)|Maximal inspiratory effort|3000 mL|14|Expiratory reserve volume (ERV)|Maximal expiratory effort|1200 mL|15|Residual volume (RV)|Volume remaining after max expiration|1200 mL|16|Total lung capacity (TLC)|Maximal lung volume|6000 mL|17|Vital capacity (VC)|Maximal voluntary ventilation|4800 mL|1819### Gas Exchange2021```22Alveolar Gas Equation:23PAO₂ = FiO₂ × (Patm - PH₂O) - (PaCO₂ / RQ)2425Where:26- FiO₂ = Fraction inspired O₂ (0.21 at sea level)27- Patm = Atmospheric pressure (760 mmHg at sea level)28- PH₂O = Water vapor pressure (47 mmHg at 37°C)29- RQ = Respiratory quotient (~0.8)3031Normal PAO₂: ~100 mmHg32Normal PaO₂: 80-100 mmHg (declines with age)33```3435### Ventilation-Perfusion (V/Q) Matching3637|Region|V/Q Ratio|Implication|38|------|---------|-----------|39|Normal lung base|~0.8|Optimal matching|40|Lung apex|>3.0|Wasted ventilation (high V/Q)|41|Lung base|<0.8|Wasted perfusion (low V/Q)|42|Shunt|V/Q = 0|No gas exchange (e.g., ARDS)|4344---4546## Pulmonary Function Testing4748### Spirometry4950```51Flow-Volume Loop Interpretation:5253 Inspiratory ┌──────┐ ┌──────────┐54 limb │ │ │ │55 │ │ │ │56 │ │ │ │57 │ │ │ │58 └──────┴───┘ │59 └──────────────────────┘60 Expiratory limb6162Obstructive: Scooped ("festoons"), reduced FEV1/FVC63Restrictive: Tall/narrow, preserved FEV1/FVC, reduced volumes64```6566|Parameter|Obstructive|Restrictive|67|---------|------------|-----------|68|FVC|Normal or ↓|↓ Markedly|69|FEV₁|↓ Markedly|↓ Proportionally|70|FEV₁/FVC|↓ (<70%)|Normal (>70%)|71|TLC|Normal or ↑|↓|72|RV|Normal or ↑|↓|73|DLCO|Normal or ↓|Normal or ↓|7475### Lung Volumes7677|Volume|Definition|Clinical Significance|78|-------|-----------|---------------------|79|Functional residual capacity (FRC)|RV + ERV|Body pletysmography measures|80|Total lung capacity (TLC)|All volumes|Serial measurements track disease|81|Diffusing capacity (DLCO)|Gas transfer|Interstitial vs. obstructive|8283---8485## Obstructive Lung Diseases8687### Chronic Obstructive Pulmonary Disease (COPD)8889**Definition**: Progressive airflow limitation, not fully reversible, usually progressive, associated with enhanced inflammatory response to noxious particles/gases.9091#### GOLD Classification9293|GROUP|Symptoms|Spirometry|FEV₁ (% predicted)|94|-----|---------|----------|------------------|95|A|Low risk, few symptoms|FEV₁ ≥ 80%|≥ 80|96|B|Low risk, more symptoms|FEV₁ ≥ 50-79%|50-79|97|C|High risk, few symptoms|FEV₁ 30-49%|30-49|98|D|High risk, more symptoms|FEV₁ < 30%|< 30|99100#### Pharmacologic Management101102```python103COPD_TREATMENT = {104 "short-acting_bronchodilators": {105 "SABA": ["albuterol", "salbutamol"],106 "SAMA": ["ipratropium"],107 "use": "Rescue therapy"108 },109 "long-acting_bronchodilators": {110 "LABA": ["salmeterol", "formoterol", "indacaterol"],111 "LAMA": ["tiotropium", "umeclidinium", "glycopyrronium"],112 "use": "Maintenance therapy"113 },114 "inhaled_corticosteroids": {115 "indications": ["History of ≥2 exacerbations/yr", "Elevated eosinophils"],116 "examples": ["fluticasone", "budesonide"]117 },118 "triple_therapy": {119 "components": ["LABA + LAMA + ICS"],120 "indications": ["Group D COPD", "Frequent exacerbations"]121 }122}123```124125### Asthma126127**Definition**: Chronic inflammatory disorder of airways, reversible airflow obstruction, airway hyperresponsiveness.128129#### Asthma Control Test (ACT)130131|Score|Control Level|Action|132|-----|-------------|------|133|25|Well-controlled|Maintain therapy|134|20-24|Well-controlled|May step down|135|15-19|Not well-controlled|Step up therapy|136|<15|Very poorly controlled|Urgent action|137138#### Stepwise Asthma Management139140|Step|Treatment|Notes|141|-----|---------|-----|142|1|SABA PRN|Low-dose ICS PRN as needed|143|2|Low-dose ICS|Or LTRA|144|3|Medium-dose ICS + LABA|Consider adding LAMA|145|4|High-dose ICS + LABA|Add LAMA|146|5|Add oral montelukast|Refer for OCS, consider biologics|147|6|Add oral corticosteroids|Biologic therapy|148149---150151## Restrictive Lung Diseases152153### Interstitial Lung Diseases (ILD)154155|Category|Examples|Key Features|156|---------|--------|-------------|157|Idiopathic pulmonary fibrosis (IPF)|Usual interstitial pneumonia (UIP)|Honeycombing, basilar|158|Sarcoidosis|Non-caseating granulomas|Lymphadenopathy, upper lobe|159|Hypersensitivity pneumonitis|Bird fancier's lung|Exposure history|160|Connective tissue disease-associated|RA-ILD, SSc-ILD|Underlying autoimmune disease|161|Drug-induced|Bleomycin, methotrexate|Medication history|162163### Pulmonary Function in Restriction164165```166Pattern: ↓ TLC, ↓ FVC, ↓ FEV₁, Normal FEV₁/FVC ratio167168Severity (TLC % predicted):169- Mild: 65-80%170- Moderate: 50-64%171- Severe: <50%172```173174### High-Resolution CT (HRCT) Patterns175176|Pattern|Characteristics|Differential|177|-------|---------------|-----------|178|UIP/IPF|Honeycombing, reticulation, traction bronchiectasis|Idiopathic pulmonary fibrosis|179|COP|Cryptogenic organizing pneumonia|Bilateral consolidations|180|NSIP|Ground-glass, reticulation, relatively preserved|Symmetric, lower lobe|181|LIP|Lung cysts, ground-glass|Diffuse, thin-walled cysts|182183---184185## Respiratory Failure186187### Type I vs. Type II188189|Type|pO₂|pCO₂|Examples|190|----|----|-----|--------|191|I (hypoxemic)|< 60 mmHg|Normal or ↓|PE, ARDS, pneumonia, edema|192|II (hypercapnic)|< 60|> 50|COPD exacerbation, obesity hypoventilation|193194### Acute Respiratory Distress Syndrome (ARDS)195196**Berlin Definition**:197198|P|O₂ Requirement|199|---|---|200|Mild|PaO₂/FiO₂ 200-300 mmHg with PEEP ≥ 5|201|Moderate|PaO₂/FiO₂ 100-200 mmHg with PEEP ≥ 5|202|Severe|PaO₂/FiO₂ < 100 mmHg with PEEP ≥ 5|203204**Etiology**:205- Direct: Pneumonia, aspiration, near-drowning, inhalation injury206- Indirect: Sepsis, transfusion, pancreatitis, trauma207208---209210## Sleep-Related Breathing Disorders211212### Obstructive Sleep Apnea (OSA)213214**Diagnosis**: AHI ≥ 5 events/hour with symptoms, or AHI ≥ 15 events/hour regardless of symptoms215216|Event|Type|Definition|217|------|-----|----------|218|Apnea|Cessation|≥ 10 seconds|219|Hypopnea|Decrease|≥ 30% + 3% desaturation or arousal|220|RDI|Apnea + hypopnea|Events per hour|221222### Treatment Options223224|Treatment|Indication|Notes|225|---------|-----------|-----|226|CPAP|First-line OSA|Standard pressure 5-20 cmH₂O|227|BiPAP|Ventilatory failure|CPAP failure, overlap syndrome|228|MAD|Dental|OAS mild-moderate|229|Surgery|UPPP|Palatal surgery|230|Weight loss|All overweight|5-10% improvement|231232---233234## Pulmonary Imaging235236### Chest X-Ray Patterns237238|Pattern|Radiographic Appearance|Clinical Correlation|239|-------|------------------------|---------------------|240|Consolidation|Airspace opacity, air bronchograms|Pneumonia, edema, hemorrhage|241|Interstitial|Reticular, nodular|ILD, heart failure|242|Cavitation|Central lucency|Lung abscess, TB, tumor|243|Pleural effusion|Blunted costophrenic angle|Transudate vs. exudate|244|Pneumothorax|Visceral pleural line, no lung markings|Trauma, spontaneous|245246### CT Pulmonary Angiography (CTPA)247248**Indication**: Suspected pulmonary embolism249250|Finding|Sensitivity|Specificity|251|--------|------------|------------|252|Central PE|83-100%|89-97%|253254---255256## Common Errors to Avoid2572581. **Confusing obstructive vs. restrictive patterns** — Always look at FEV₁/FVC ratio and TLC2592. **Ignoring DLCO** — Essential for differentiating emphysema vs. chronic bronchitis2603. **Missing hypoxemia triggers** — Consider altitude, V/Q mismatch, shunt2614. **Inadequate rescue inhaler technique** — Check technique at each visit2625. **Underestimating sleep apnea** — Screen all snorers, especially with hypertension2636. **Delayed biopsy in ILD** — Consider multidisciplinary discussion2647. **Oxygen prescription errors** — Target SpO₂ 88-92% for COPD, 94-98% for others2658. **Ignoring vaccination status** — Influenza annually, pneumococcal per guidelines266
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