Respiratory Physiology and Exercise
Functions of the Respiratory System
- Deliver oxygen (O₂) and remove carbon dioxide (CO₂) from tissues
- Gas exchange to maintain pH balance in the body
- Cellular Respiration: Bioenergetics process of converting food into usable energy
Main Processes in the Respiratory System
- Ventilation: Mechanical movement of air in and out of the lungs
- Diffusion: Movement of molecules, O₂ into the blood, and CO₂ out of the blood
Gradients
- Concentration Gradient: Movement from high to low concentration
- Pressure Gradient: Key for both ventilation and diffusion
conducting and respiratory zones
- Conducting Zone: Filters and humidifies air
- Respiratory Zone: Location of alveoli where the gas exchange occurs
- Surface area of alveoli = 60-80 m² (size of a tennis court)
- Alveolar walls are very thin (similar to the thickness of red blood cells
- Diffusion occurs rapidly due to very short distance.
Mechanics of Breathing
- Inspiration: Active process requiring muscle contraction
- Involves(diaphragm and intercostal muscles)
- Increases thoracic cavity size, dropping pressure and drawing air in
- Expiration: Passive process at rest, active during heavy exercise
- Diaphragm and intercostal muscles relax, reducing thoracic cavity size and forcing air out
Muscles Involved
- Inspiration Muscles: Diaphragm, Intercostals; accessory muscles activated during heavy exercise (scalenes, sternocleidomastoid)
- Expiration Muscles: Relaxation of inspiratory muscles, intercostals, and abdominal muscles
Inspiration Vs Expiration
- Inspiration- Diaphragm most important muscle of inspiration.
- Expiration- passive at rest (no muscle activation) using
•Rectus abdominis & internal oblique
•Push the diaphragm upwards and pull ribs downward and inward.
•Results in increased intrathoracic pressure, forcing expiration
Pulmonary Diffusion
- Gas exchange (O₂ and CO₂) between lungs and blood
- Requires a concentration gradient
Respiratory Terminology
- Minute Ventilation (Vₑ): Amount of gas exchanged per minute
- Dead Space: Air that doesn’t participate in gas exchange (anatomical and alveolar)
Respiratory Membrane and Gas Exchange
- Alveoli: Balloon-like sacs where gas exchange occurs
- Surrounded by capillaries for rapid diffusion
- Partial Pressures: Individual gas pressures summing to the total atmospheric pressure (Dalton’s Law)
- **Important Formulas: Dalton’s Law and Fick’s Law of Diffusion
- Volume of gas diffused ∝ Surface Area (A) and Pressure Gradient (P₁ - P₂), inversely ∝ Membrane Thickness (T)
Gas Transport
- Oxygen: Primarily bound to hemoglobin (98%); dissolved in plasma (2%)
- Carbon Dioxide: Transported as bicarbonate ions (60-70%), bound to hemoglobin (20-33%), dissolved in plasma (7-10%)
Oxygen-Hemoglobin Dissociation Curve
- Bohr Effect: Right shift due to increased temperature, CO₂, or decreased pH (during exercise)
Control of Breathing
- Voluntary Control: Cerebral cortex signals respiratory centers
- Chemoreceptors: Located in aortic arch and carotid arteries, respond to chemical changes (pH, CO₂, O₂)
- Lung Receptors: Stretch (prevents overinflation) and irritant receptors (trigger sneezing/coughing)
Phases of Ventilation During Exercise
- Phase 1: Immediate increase due to body movement
- Phase 2: Increase due to temperature and chemical changes
- Post-Exercise: Elevated ventilation to restore equilibrium (pH, temperature, CO₂)
Pulmonary Volumes and Capacities
- Tidal Volume (TV): Air moved per breath
- Vital Capacity (VC): Max air exhaled after max inhalation
- Residual Volume (RV): Air remaining in lungs after max exhalation
- Total Lung Capacity (TLC): VC + RV
Metabolic Equivalents (METS)
- 1 MET = 3.5 ml O₂/kg/min
- Used to express exercise intensity relative to resting metabolism
- Rest = 1 MET, Moderate Intensity = 3-6 METs, Vigorous Intensity > 6 METs
Example Calculation
- Converting METs to Oxygen Cost: (10 METs x 3.5 ml O₂/kg/min) = 35 ml O₂/kg/min
- Absolute Vₒ₂: Convert ml/kg/min to liters/min
- Energy Expenditure: L/min multiplied by 5 kcal
Exercise Effects on Respiratory System:
- Increased breathing frequency and depth
- Maintains O₂ supply, removes CO₂, maintains pH
Special Conditions
- Hyperventilation: Rapid breathing, reduces CO₂ (hypocapnia)
- Valsalva Maneuver: Holding breath, increases intra-abdominal pressure, not recommended for heavy lifting
- Breathing Irregularities: Dyspnea (shortness of breath), commonly due to unconditioned respiratory muscles
Common Respiratory Issues
- Examples include COPD, asthma—can limit physical performance in severe cases.
Recommendations: Apply pressure, bend forward, take deep breaths to relieve 'side stitches' during exercise.