lab respiratory -2025-03-03

Breathing Mechanism

• Fundamental Concept: Breathing involves changes in volumes and pressures.

  • Gases flow down pressure gradients from high pressure to low pressure.

  • Volume is inversely proportional to pressure.

• Pressure Explained:

  • Pressure is the force exerted by gas within a given volume.

  • Increasing the volume of a container reduces pressure, while decreasing volume increases pressure.

Inhalation and Exhalation

• Inhalation Process:

  • Inhalation involves increasing the volume of the thoracic cavity.

  • To inhale, pressure inside the lungs must drop below atmospheric pressure (1 atmosphere = 760 mmHg).

• Diaphragm's Role:

  • The diaphragm contracts and flattens, increasing thoracic cavity volume, leading to decreased pressure and air flowing in.

• Exhalation Process:

  • The diaphragm relaxes, pressure inside the lungs increases above atmospheric pressure, and air flows out.

  • Normal exhalation is passive; internal intercostal muscles assist in forced exhalation.

  • External intercostal muscles aid in inhalation by lifting the ribs to increase cavity volume.

Lung Volumes and Capacities

• Spirometry:

  • Measures lung volumes and is vital for evaluating pulmonary function.

  • Four primary volumes measured:

    1. Tidal Volume (VT):

       • Normal air volume during quiet breathing (~500 ml).

    2. Inspiratory Reserve Volume (IRV):

       • Additional air volume inhaled after a normal breath.

    3. Expiratory Reserve Volume (ERV):

       • Additional air volume exhaled beyond normal expiration.

    4. Residual Volume (RV):

       • Air left in lungs after maximum exhalation.

• Lung Capacities Derived:

  • Inspiratory Capacity (IC): IRV + VT

  • Expiratory Capacity (EC): ERV + VT

  • Vital Capacity (VC): IRV + VT + ERV

  • Total Lung Capacity (TLC): VC + RV (approximately 6000 ml).

Clinical Relevance of Lung Measurements

• Importance: Understanding lung volumes aids in diagnosing pulmonary diseases (e.g., COPD, asthma).

  • COPD patients often have a lower inspiratory capacity and hyperinflated lungs.

  • Vital capacity and forced expiratory volume (FEV1) are crucial for assessing lung function.

• FEV1 Norm: Normal lungs can expel about 80% of air in the first second of forced exhalation. Lower percentages indicate issues.

Gas Transport and Blood Chemistry

• Oxygen Transport:

  • Oxygen diffuses across the respiratory membrane and binds to hemoglobin in red blood cells.

• Carbon Dioxide Transport:

  • About 70% of CO2 is transported in plasma as carbonic acid, dissociating into hydrogen ions (H+) and bicarbonate (HCO3-).

  • Increased CO2 concentration lowers pH (acidosis), affecting respiratory drive.

Regulation of Breathing

• Primary Factors Driving Respiration:

  1. CO2 Levels: Most critical for regulating breathing rate.

  2. pH Levels: Lower pH drives increased respiratory rate to expel CO2.

  3. Oxygen Levels: Less critical; significant drops in oxygen levels (hypoxia) are needed to stimulate breathing changes.

• Nurses and clinicians monitor these factors, especially during respiratory distress or conditions like sepsis or metabolic acidosis.

Summary of Key Concepts in Breathing Mechanics

• Normal breathing depends on pressure gradients facilitated by lung mechanics (diaphragm and intercostals).

• Understanding lung volumes and their clinical implications is crucial for assessing respiratory health.

• Gas exchange and transport dynamics highlight the importance of maintaining balanced CO2 and pH levels to ensure proper respiratory function.