02. Supporting Metabolism

• the cardiorespiratory system adjusts depending on energetic requirements of the body
• the energetic cost of aerobically sustainable activities is estimated by rate of O2 consumption and CO2 production
• the concentration of exhaled gases is affected by:

  • metabolic demand of tissues
  • flow of respiratory medium over respiratory surface
• measuring composition and volume of exhaled gases leads to estimation of metabolic rate
• the respiratory exchange ratio is the ratio between the rate of O2 consumption and CO2 production

  • values under 1 = aerobic
  • values over 1 = anaerobic
• the respiratory exchange ratio consumed by cells each minute = the respiratory the quotient

  • depends on substrate
• at rest an adult produces 250mls/min O2 and consumes 200mls/min of CO2
• an ECG records the electrical activity of the heart
• a pulse transducer senses the pressure wave coming down an artery
• a spirometer measures pulmonary function
• gas analysis measures changes in composition of expired gases
• average tidal volume = 500mls
• average respiratory frequency = 15
• slope of spirometer = rate of O2 consumption