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Key Concepts in Respiratory Assessment

Humidity and Ventilation

• Relative Humidity: Measures the amount of humidity in the air.

• Ventilation and CO2: Arterial Blood Gas (ABG) assesses ventilation through carbon dioxide (CO2) levels.

• Acid-Base Balance: Evaluated with pH levels and partial pressure of oxygen (pAOT).

Alveolar Characteristics

• Smaller Alveoli:

  • Exhibit increased pressure due to smaller radius.

  • More difficult to expand compared to larger alveoli (e.g., filling a small water balloon vs. a large one).

• Surface Tension in Alveoli: Surfactant decreases surface tension allowing easier expansion of alveoli.

Gas Behavior and Laws

• Boyle's Law: Inverse relationship between gas pressure and volume; as pressure decreases, volume increases.

• Condensation and Evaporation:

  • Condensation is the process of gas turning to liquid (e.g., water droplets on a bottle).

  • Evaporation is the opposite, from liquid to gas.

Compliance and Elastance

• Compliance: The measure of the lung's ability to stretch and expand; low elastance and high compliance indicate ease in lung filling.

• Vital Capacity: The maximum amount of air an individual can inhale and exhale; differs from total lung capacity.

• Atelectasis: Condition causing decreased compliance and increased elasticity in pulmonary fibrosis patients.

Ventilation and Gas Exchange

• Alveolar Ventilation: The amount of gas exchange occurring in the alveoli during breathing, differentiated from overall minute ventilation.

• Dead Space: Refers to areas of the lungs with wasted ventilation and no gas exchange, typically occurring in the upper lung regions.

Respiratory Rates and Patterns

• Tachypnea: Fast breathing rate, typically over 20 breaths per minute.

• Bradycardia/Bradyapnea: Slow respiratory rates.

• Work of Breathing during Asthma: Increased minute ventilation and depth of breathing; often involves the use of accessory muscles.

Pressure Dynamics in Breathing

• Intrapulmonary Pressure: Refers to the pressure inside the lungs, while interpleural pressure is the pressure in the pleural space.

• Transrespiratory Pressure: The pressure gradient responsible for air movement in and out of the lungs.

Gas Laws and Breathing Mechanics

• Charles' Law: Warm air expands; as the temperature increases, the volume of the gas also increases at a constant pressure.

• Gay-Lussac's Law: Pressure of a gas increases with temperature when the volume is constant.

Airway Resistance Factors

• Factors affecting airway resistance include:

  • Pattern of gas flow (laminar vs. turbulent).

  • Diameter and length of airways.

  • Characteristics of the gas being breathed (e.g., density).

• Normal airway resistance ranges from 0.5 to 2.5 cm H2O/L/s; higher on mechanical ventilation.

Clinical Relevance

• Benevolent Deception: Withholding the truth from a patient for their benefit; need for trust in patient-provider relationships.

• Healthcare Liability: Health professionals need to ensure they have the correct medications and monitor for contraindications.