Respiratory Physiology and Exercise

Breathing and Carbon Dioxide Regulation

• During high-intensity exercise, respiratory rate increases due to the body's need to expel carbon dioxide (CO₂) rather than just to take in more oxygen (O₂).

• Elevated CO₂ levels stimulate chemoreceptors located in the carotid body and lung tissue, driving the respiratory response.

  • Chemoreceptors detect changes in CO₂ concentration and blood pH.

  • The Herring-Breuer reflex protects from overstretching the lungs during deep breaths.

Pulmonary Ventilation

• Pulmonary Ventilation (PE): The total volume of air moved in and out of the lungs per minute.

  • Calculated as: PE = Tidal ext{ Volume} imes Respiratory ext{ Rate}

• Tidal Volume (TV): Amount of air inhaled or exhaled during normal breathing.

Phases of Pulmonary Ventilation during Exercise

1. Phase 1: Immediate increase due to body movement rather than need for O₂ or CO₂ removal.

2. Phase 2: As exercise continues, increased need for O₂ and removal of CO₂ alters ventilation levels.

   • Respiratory depth and frequency increase to maintain O₂ saturation and regulate pH levels.

3. Post-Exercise: Elevated respiratory rate persists for a while to recover balance in O₂ and CO₂ levels.

Ventilatory Equivalent Ratio

• The Ventilatory Equivalent compares pulmonary ventilation to the amount of O₂ being utilized at the tissue level, calculated as:
  Ventilatory ext{ Equivalent} = rac{PE}{VO₂}

• Remains constant at lower exercise intensities but increases at high intensities due to excess CO₂ production.

Anaerobic Threshold and Metabolism

• The Ventilatory Threshold marks the transition from aerobic to anaerobic metabolism during exercise, leading to lactate accumulation.

  • This is where the demand for energy exceeds the O₂ supply, triggering anaerobic metabolism and increased CO₂ production, affecting pH balance.

• Trained individuals can typically maintain aerobic metabolism longer than untrained individuals.

Implications of Breathing Under Stress

• During hypoxic conditions, respiratory demand increases due to a lower partial pressure of O₂, leading to a need for faster and deeper breaths.

  • For example, at high altitudes, despite the same O₂ percentage in the air, the reduced atmospheric pressure results in decreased partial pressures, making breathing feel harder.

Physiological Responses to High Altitude

• Reduced O₂ saturation in the air leads to the body producing less O₂ in the arterioles, affecting aerobic metabolism and causing hypoxia.

• Training at altitude can induce adaptations such as increased erythropoietin (EPO) production, leading to an increase in red blood cells and hemoglobin.

• Recommended training strategies involve living at altitude (for adaptation) but training at lower altitudes (for performance efficiency).

Hyperventilation and Oxygen Loading

• Hyperventilation can temporarily decrease CO₂ levels in the body (hypocapnia), allowing an increased breath-holding capacity but does not enable more O₂ loading on hemoglobin since saturation levels are already high.

• The Bohr Effect explains how increased CO₂ and lowered pH can promote O₂ dissociation from hemoglobin, allowing greater O₂ availability in metabolically active tissues during exercise.

Breathing Irregularities

• Dyspnea: Labored breathing; often a symptom of over-exertion or lung disease.

• Hyperventilation: An abnormally high respiratory rate (over 20 breaths/min), often caused by stress or anxiety, leading to hypocapnia.

Conclusion

• Understanding the respiratory responses and adaptations during exercise can inform training methods and improve performance while considering the effects of altitude considerations. Maintaining efficient gas exchange is critical for maximizing athletic potential.