My Notes (Bootcamp)

Equal Pressure Point (EPP): Location in the airways where pleural pressure equals airway pressure.
- In normal healthy lungs, this point is located just past the cartilaginous bronchi, preventing airway collapse.
- Emphysema: Results in destruction of elastic tissue in the lungs.
  - Loss of elastic recoil leads to little elastic recoil, causing the collapsibility pressure to be low.
  - Consequently, the pleural space is not super expanded and pleural pressure is not extremely negative.
  - The formula for transpulmonary pressure (TPP) during end inspiration is:
    $TPP = 0 - (-3)$
  - During forced expiration, the pleural pressure achieves a range of -3 cm H₂O to +3 cm H₂O.
  - The peak transpulmonary pressure can be defined as:
    $A = +33$
- The lower EPP shifts the collapsing pressure closer to the alveoli, resulting in airway obstruction due to collapse.

Tidal Volume (TV): Amount of air inhaled or exhaled during normal resting breathing.
Inspiratory Reserve Volume (IRV): Amount of air breathed in after a normal tidal breath, representing maximum value.
Expiratory Reserve Volume (ERV): Maximum volume of air that can be forcefully exhaled.
Residual Volume (RV): Volume of air remaining in the lungs that cannot be expired.
- Clinical Note: RV increases in obstructive lung disease and with aging.
Formulas:
- Inspiratory Capacity (IC):
  $IC = TV + IRV$
- Vital Capacity (VC):
  $VC = IRV + TV + ERV$
- Functional Residual Capacity (FRC):
  $FRC = ERV + RV$
- Total Lung Capacity (TLC):
  $TLC = TV + RV + ERV + IRV$

At Functional Residual Capacity (FRC):
- The lung's collapsing force equals the expanding force, leading to zero net force. Although the pleural pressure remains negative, the opposing forces result in lung stability.

Anatomical Dead Space: Volume of air that is in the conducting zones where no gas exchange occurs.
- Consists of airway epithelium (pseudostratified columnar with goblet cells) and is important for warming and humidifying air.
Alveolar Dead Space: Occurs when there is no perfusion to areas of the lungs.
Physiological Dead Space: Total volume of anatomical and alveolar dead space.
- Bohr's Equation:
 $VD = rac{VT imes (P{aCO₂} - P{eCO₂})}{P_{aCO₂}}$
- Where:
- $V_D$ = physiologic dead space volume
- $V_T$ = tidal volume
- $P_{aCO₂}$ = arterial Partial Pressure of CO₂
- $P_{eCO₂}$ = expired Partial Pressure of CO₂

Minute Ventilation (VE): Total air entering the lungs per minute, given by:
$VE = V_T imes RR$
Alveolar Ventilation ($VA$): Air reaching the alveoli per minute: $VA = (VT - VD) imes RR$
- Noteworthy Reference: The anatomical dead space is approximately 150 mL.

Surfactant: A lipid-protein substance produced by Type II pneumocytes.
- Reduces surface tension in alveoli, preventing collapse.
- Surfactant has both hydrophilic and hydrophobic properties, which result in decreased collapsing force by reducing the air-water interface.
- Surfactant's presence is crucial for maintaining lung compliance and elasticity.

The phenomenon where the pressure-volume curve differs between inflation and deflation phases of lung mechanics.
- Surfactant deficiency leads to an increase in surface tension and a risk of lung collapse, particularly observed in conditions like Neonatal Respiratory Distress Syndrome (NRDS) and Acute Respiratory Distress Syndrome (ARDS).

Flow-Volume Loop Analysis:
- Passive respiration (tidal breathing) displays a characteristic loop shape.
- In obstructive lung disease, the curve shifts to the left, indicating breath occurs at high lung volumes with early airway collapse due to diminished elastic recoil from tissue destruction.
- The shape indicates greater resistance during expiration.
Key Notes:
- Tidal Breathing: Approximately 500 mL of air is inspired at rest.
- Residual Volume (RV): Reflects air trapped due to obstructive conditions, causing hyperinflation in lungs.

Compliance (C): Reflects the ease or difficulty of lung expansion.
- Mathematical representation:
  $C = rac{ΔV}{ΔP}$
- High compliance indicates ease of expansion (e.g., a grocery bag), whereas low compliance indicates difficulty (e.g., a balloon that is hard to inflate).

High Compliance Conditions:
- Emphysema results in decreased elastic recoil making lungs easy to inflate but hard to maintain shape due to compromised structures.
Low Compliance Conditions:
- Pulmonary fibrosis and respiratory distress affect lung structure leading to lower compliance, causing increased work to expand.

Resistance is highest in medium-sized bronchi.
Conditions leading to increased resistance include:
1. Obstructive Lung Diseases: (e.g., COPD, asthma) lead to greater airflow obstruction.
2. Mucus Plug Formation: chronic bronchitis causes airways to collapse due to increased mucus and irritation.

Composed of thick epithelium, including:
- Trachea and bronchi that warm, humidify, and filter air, preventing foreign particle entry.
- Terminal bronchioles transition from epithelium to alveoli where gas exchange occurs via thin-walled Type I pneumocytes.

Low oxygen levels in the alveoli trigger hypoxic pulmonary vasoconstriction, allowing blood to divert to better-ventilated areas.
- Clinical Implication: Opposite response to hypoxia compared to systemic circulation, ensuring efficient oxygenation in lungs.

Refers to the difference between alveolar and arterial blood partial pressures of O₂.
- Normal gradient exists to facilitate gas transfer during respiration but can become impaired in diseased states.

Primary Causes of Hypoxemia:
1. High altitude: Reduced ambient O₂ partial pressure.
2. Hypoventilation: Reduced O₂ intake.
3. R/L shunting: Obstruction leading to deoxygenated blood returning to circulation.
4. Diffusion defects: Pathologies such as pulmonary fibrosis affecting gas transfer.

Hypoxia: Insufficient O₂ delivery to organs.
Ischemia: Inadequate blood flow resulting in lack of O₂ transport.
- Conditions such as anemia and CO poisoning affect oxygen content despite normal blood flow rates.

Asthma: Characterized by episodic bronchoconstriction typically triggered by allergens, exercise, or stress, featuring wheezing and coughing.
- Types include atopic (allergic) and non-atopic (intrinsic) asthma, with specific treatments targeted at airway inflammation.
COPD: Encompasses both chronic bronchitis and emphysema:
1. Chronic Bronchitis: Irreversible obstruction with mucus hypersecretion leading to productive cough, often referred to as “blue bloaters.”
2. Emphysema: Progressive destruction of alveoli leads to difficulty expelling air, termed “pink puffers.”

Understanding the mechanics of lung function, including pressures, volumes, compliance, and resistance, is vital in diagnosing and managing respiratory diseases.