Pulmonary Function During Exercise

The Respiratory System Provides gas exchange between the environment and the body Regulates of acid-base balance during exercise

Ventilation

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

Mechanics of Breathing Ventilation –Movement of air into and out of the lungs via bulk flow Inspiration –Diaphragm pushes downward, lowering intrapulmonary pressure

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

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

Respiration

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

Partial Pressure of Gases Each gas in a mixture exerts a portion of the total pressure of the gas The partial pressure of oxygen (PO 2 ) –Air is 20.93% oxygen Expressed as a fraction:

Partial Pressure of Gases Each gas in a mixture exerts a portion of the total pressure of the gas The partial pressure of oxygen (PO 2 ) –Air is 20.93% oxygen Expressed as a fraction: –Total pressure of air = 760 mmHg PO 2 = x 760 = 159 mmHg

Partial Pressure and Gas Exchange

O 2 Transport in the Blood O 2 is bound to hemoglobin (Hb) for transport in the blood –Oxyhemoglobin: O 2 bound to Hb Carrying capacity –201 ml O 2 /L blood in males 150 g Hb/L blood x 1.34 mlO 2 /g Hb

O 2 Transport in the Blood O 2 is bound to hemoglobin (Hb) for transport in the blood –Oxyhemoglobin: O 2 bound to Hb Carrying capacity –201 ml O 2 /L blood in males 150 g Hb/L blood x 1.34 mlO 2 /g Hb –174 ml O 2 /L blood in females 130 g Hb/L blood x 1.34 mlO 2 /g Hb

Oxyhemoglobin Dissociation Curve

O 2 -Hb Dissociation Curve: Effect of pH Blood pH declines during heavy exercise

O 2 -Hb Dissociation Curve: Effect of pH Blood pH declines during heavy exercise Results in a “rightward” shift of the curve

O 2 -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 O 2 to the tissues

O 2 -Hb Dissociation Curve: Effect of pH Oxygen Content (ml O 2 / 100 ml blood) Amount of O 2 unloaded

O 2 -Hb Dissociation Curve: Effect of Temperature Increased blood temperature results in a weaker Hb-O 2 bond Rightward shift of curve –Easier “offloading” of O 2 at tissues

O 2 -Hb Dissociation Curve: Effect of Temperature Amount offloaded Oxygen Content (ml O 2 / 100 ml blood)

O 2 Transport in Muscle Myoglobin (Mb) shuttles O 2 from the cell membrane to the mitochondria Higher affinity for O 2 than hemoglobin –Even at low PO 2 –Allows Mb to store O 2

Dissociation Curves for Myoglobin and Hemoglobin

Carbon Dioxide Transport

CO 2 Transport in Blood Dissolved in plasma (10%) Bound to Hb (20%)

CO 2 Transport in Blood Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%) CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 - Muscle Intense Exercise binds to Hb Carbonic Acid Bicarbonate

CO 2 Transport in Blood Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%) CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 - Lung Ventilation O 2 replaces on Hb

CO 2 Transport in Blood Dissolved in plasma (10%) Bound to Hb (20%) Bicarbonate (70%) CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 - –Also important for buffering H + Muscle Lung Intense Exercise Ventilation

Release of CO 2 From Blood

Effect of Respiratory Gases on Ventilation

Control of Ventilation Respiratory control center in the brainstem

Control of Ventilation Respiratory control center in the brainstem –Regulates respiratory rate

Control of Ventilation Respiratory control center in the brainstem –Regulates respiratory rate –Receives neural and humoral input Feedback from muscles PO 2, PCO 2, H +, and K + in blood PCO 2 and H + concentration in cerebrospinal fluid

Effect of Arterial PO 2 on Ventilation

Effect of Arterial PCO 2 on Ventilation

Ventilation and Acid-Base Balance Blood pH is regulated in part by ventilation

Ventilation and Acid-Base Balance Blood pH is regulated in part by ventilation An increase in ventilation causes exhalation of additional CO 2

Ventilation and Acid-Base Balance Blood pH is regulated in part by ventilation An increase in ventilation causes exhalation of additional CO 2 –Reduces blood PCO 2 –Lowers H + concentration H + + HCO 3 -  H 2 CO 3  CO 2 + H 2 O

Ventilatory Control During Submaximal Exercise

Incremental Exercise Linear increase in ventilation –Up to ~50-75% VO 2max.

Incremental Exercise Linear increase in ventilation –Up to ~50-75% VO 2max Exponential increase beyond this point.

Incremental Exercise Linear increase in ventilation –Up to ~50-75% VO 2max Exponential increase beyond this point Ventilatory threshold (T vent ) –Inflection point where V E increases exponentially..

Ventilatory Response to Exercise: Tvent

Effect of Training on Ventilation Ventilation is lower at same work rate following training

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

Effects of Endurance Training on Ventilation During Exercise

Ventilatory Response to Exercise: Trained vs. Untrained In the trained runner –Decrease in arterial PO 2 near exhaustion –pH maintained at a higher work rate –T vent occurs at a higher work rate

Ventilatory Response to Exercise: Trained vs. Untrained

Do the Lungs Limit Exercise Performance? Submaximal exercise –Pulmonary system not seen as a limitation

Do the Lungs Limit Exercise Performance? Submaximal exercise –Pulmonary system not seen as a limitation Maximal exercise –Not thought to be a limitation in healthy individuals at sea level

Do the Lungs Limit Exercise Performance? Submaximal 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