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Chapter 10 Pulmonary Function During Exercise The Respiratory System Provides gas exchange between the environment and the body Regulates of acid-base balance during exercise Ventilation Moving Air Conducting and Respiratory Zones Conducting zone Conducts air to respiratory zone Humidifies, warms, and filters air Components: – Trachea – Bronchial tree – Bronchioles Respiratory zone Exchange of gases between air and blood Components: – Respiratory bronchioles – Alveolar sacs Pathway of Air to Alveoli Mechanics of Breathing Ventilation – Movement of air into and out of the lungs via bulk flow Inspiration – Diaphragm pushes downward, lowering intrapulmonary pressure Expiration – Diaphragm relaxes, raising intrapulmonary pressure Resistance to airflow – Largely determined by airway diameter The Mechanics of Inspiration and Expiration Pulmonary Volumes and Capacities Measured by spirometry Vital capacity (VC) – Maximum amount of air that can be expired following a maximum inspiration Residual volume (RV) – Air remaining in the lungs after a maximum expiration Total lung capacity (TLC) – Sum of VC and RV Pulmonary Volumes and Capacities Inspiratory Reserve volume (IRV) – Maximum amount of air that can be inspired following a normal inspiration Expiratory reserve volume (ERV) – Air remaining in the lungs after a normal expiration A Spirogram Showing Pulmonary Volumes and Capacities Check measurements to find: Norms for body sizes Indications of healthy lung function Indications of diseases/conditions that affect ventilation – Asthma – Emphysema . Pulmonary Ventilation (VE) The amount of air moved in or out of the lungs per minute – Product of tidal volume (VT) and breathing frequency (FB) . – (looks similar to Q = SV x HR? ) . VE = VT x FB Respiration Movement of gasses Diffusion of Gases Gases diffuse from high low partial pressure – From lungs to blood and back to lungs – From blood to tissue and back to blood Partial Pressure of Gases Each gas in a mixture exerts a portion of the total pressure of the gas The partial pressure of oxygen (PO2) – Air is 20.93% oxygen • Expressed as a fraction: 0.2093 – If total pressure of air = 760 mmHg, then PO2 = 0.2093 x 760 = 159 mmHg Partial Pressure and Gas Exchange O2 Transport in the Blood O2 is bound to hemoglobin (Hb) for transport in the blood – Oxyhemoglobin: O2 bound to Hb Carrying capacity – 201 ml O2•L-1 blood in males • 150 g Hb•L blood-1 x 1.34 mlO2•g Hb-1 – 174 ml O2•L-1 blood in females • 130 g Hb•L blood-1 x 1.34 mlO2•g Hb-1 Oxyhemoglobin Dissociation Curve O2-Hb Dissociation Curve: Effect of pH Blood pH declines during heavy exercise Results in a “rightward” shift of the curve – Bohr effect – Favors “offloading” of O2 to the tissues O2-Hb Dissociation Curve: Effect of pH 10 8 6 4 2 Amount of O2 unloaded Oxygen Content (ml O2 / 100 ml blood) 20 18 16 14 12 O2-Hb Dissociation Curve: Effect of Temperature Increased blood temperature results in a weaker Hb-O2 bond Rightward shift of curve – Easier “offloading” of O2 at tissues O2-Hb Dissociation Curve: Effect of Temperature Oxygen Content (ml O2 / 100 ml blood) Amount offloaded O2 Transport in Muscle Myoglobin (Mb) shuttles O2 from the cell membrane to the mitochondria Higher affinity for O2 than hemoglobin – Even at low PO2 – Allows Mb to store O2 Dissociation Curves for Myoglobin and Hemoglobin Carbon Dioxide Transport Not identical to oxygen transport CO2 Transport in Blood Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%) Carbonic Acid binds to Hb CO2 + H2O H2CO3 H+ + HCO3Muscle Normal Metabolism Bicarbonate CO2 Transport in Blood Lung Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%) Ventilation CO2 + H2O H2CO3 H+ + HCO3- O2 replaces on Hb CO2 Transport in Blood Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%) Ventilation Lung CO2 + H2O H2CO3 H+ + HCO3Muscle Intense Exercise – Also important for buffering H+ Release of CO2 From Blood Effect of Respiratory Gases on Ventilation How do these gasses affect breathing? Control of Ventilation Respiratory control center in the brainstem – Regulates respiratory rate – Receives neural and humoral input • Feedback from muscles • PO2, PCO2, H+, and K+ in blood • PCO2 and H+ concentration in cerebrospinal fluid Effect of Arterial PO2 on Ventilation Effect of Arterial PCO2 on Ventilation Ventilation and Acid-Base Balance Blood pH is regulated in part by ventilation An increase in ventilation causes exhalation of additional CO2 – Reduces blood PCO2 – Lowers H+ concentration H+ + HCO3- H2CO3 H2O + CO2 Exhalation Ventilatory Control During Submaximal Exercise Incremental Exercise Linear increase in ventilation . – Up to ~50-75% VO2max Exponential increase beyond this point Ventilatory threshold (T ) vent . – Inflection point where VE increases exponentially Ventilatory Response to Exercise: Tvent Is This Trainable? Does an endurance trained person breathe less? Does an endurance trained person need less oxygen? Effect of Training on Ventilation Ventilation is lower at same work rate following training – May be due to lower blood lactic acid levels – Results in less feedback to stimulate breathing – Well trained produce less CO2 – stim. for breathing Effects of Endurance Training on Ventilation During Exercise Ventilatory Response to Exercise: Trained vs. Untrained In the trained runner – Decrease in arterial PO2 near exhaustion • more oxygen extracted – pH maintained at a higher work rate • less lactic acid produced – “aerobic metab.” – Tvent occurs at a higher work rate • lower relative intensity Ventilatory Response to Exercise: Trained vs. Untrained Do the Lungs Limit Exercise Performance? Sub maximal exercise – Pulmonary system not seen as a limitation Maximal exercise – Not thought to be a limitation in healthy individuals at sea level – May be limiting in elite endurance athletes Questions? End