Respiratory Responses to Exercise Flashcards
Pulmonary respiration
◦ Ventilation
◦ Exchange of O2 and CO2 in the lungs
Cellular respiration
O2 utilization and CO2 production by the tissues
Purposes of the respiratory system during exercise
Gas exchange between the environment and the body
◦ Regulation of acid-base balance during exercise
Do respiratory muscles fatigue during exercise?
Current evidence suggests that respiratory muscles do fatigue during exercise
◦ Prolonged (>120 minutes)
◦ High-intensity (90–100% VO2 max)
Do respiratory muscle adapt to training?
Increased oxidative capacity improves respiratory muscle endurance
◦ Reduced work of breathing
Pulmonary Ventilation
The amount of air moved in or out of the lungs per minute (V)
V = VT x f V = VA + VD
Tidal volume (VT)
Amount of air moved per breath
Breathing frequency (f)
Number of breaths per minute
Alveolar ventilation (VA)
Volume of air that reaches the respiratory zone
Dead-space ventilation (VD)
Volume of air remaining in conducting airways
Pulmonary circuit
Same rate of flow as systemic circuit ◦Lower pressure
When standing, most of the blood flow is to
the base of the lung
Due to gravitational force
During exercise, blood flow to
to apex
Ventilation Perfusion Relationships
Ventilation/Perfusion ration (V/Q)
Indicates matching of blood flow to ventilation
Ideal: 1.0
Apex of lung: underperfused (ratio <1.0)
Base of lung: Overperfused (ratio >1.0)
Ventilation-Perfusion Relationships: During Exercise
Light exercise improves V/Q ratio
◦ Heavy exercise results in V/Q inequality
O2 Transport in the Blood
99% of O2 is transported bound to hemoglobin (Hb)
◦ Oxyhemoglobin: Hb bound to O2
◦ Deoxyhemoglobin: Hb not bound to O2
Amount of O2 that can be transported per unit volume of blood is dependent on the Hb concentration
◦ Each gram of Hb can transport 1.34 ml O2
Oxygen Content of Blood for males and females
Oxygen content of blood (100% Hb saturation)
◦ Males:
150 g Hb/L blood x 1.34 ml O2/g Hb = 200 ml O2/L blood
◦ Females:
130 g Hb/L blood x 1.34 ml O2/g Hb = 174 ml O2/L blood
Oxyhemoglobin Dissociation Curve
Reaction= Deoxyhemoglobin + O2 -> Oxyhemoglobin
Direction of reaction depends on: PO2 of blood and affinity between Hb and O2
At lung= high PO2 (formation of oxyhemoglbin
At tissues = Low PO2 (release of O2 to tissues)
pH effect on O2- Hb Dissociation Curve
Decreased pH lowers Hb-O2 affinity
Results in rightward shift of curve
Favors offloading of O2 to tissues
Temperature effect on O2- Hb Dissociation Curve
Increased blood temperature lowers Hb-O2 affinity
Results in rightward shift of the curve
2-3 DPG effect on O2- Hb Dissociation Curve
Byproduct of RBC glycolysis
May result in a rightward shift of the curve
Can happen during altitude exposure but not major cause of rightward shift
O2 Transport in Muscle
Myoglobin (Mb)
◦ Shuttles O2 from the cell membrane to the mitochondria
Mb has a higher affinity for O2 than hemoglobin
◦Even at low PO2
◦Allows Mb to store O2
◦ O2 reserve for muscle
◦ Buffers O2 needs at onset of exercise until cardiopulmonary system increases O2 delivery
CO2 transport in blood
Dissolved in plasma (10%)
Bound to hB (20%)
Bicarbonate (70%)
CO2 transport in blood at tissue
H+ binds to Hb
◦ HCO3– diffuses out of RBC into plasma
◦ Cl– diffuses into RBC (chloride shift)
CO2 transport in blood at lung
At the lung:
◦ O2 binds to Hb (drives off H+)
◦ Reaction reverses to release CO2
Pulmonary ventilation removes H+ from blood by the HCO3– reaction: What is the reaction
CO2 + H2O (Carbonic anhydrase)-> H2CO3 -> H + HCO3
Ventilation and CO2
Increased ventilation results in CO2 exhalation
◦ Reduces PCO2 and H+ concentration (pH increase)
◦ Decreased ventilation results in buildup of CO2 ◦ Increases PCO2 and H+ concentration (pH decrease)
At the onset of constant-load submaximal exercise:
Initially, ventilation increases rapidly
◦ Then, a slower rise toward steady state
◦PO2 and PCO2 are relatively unchanged
◦ Slight decrease in PO2 and increase in PCO2
◦ Suggests that increase in alveolar ventilation is slower than increased metabolism
Incremental Exercise-Untrained Subject
Ventilation
◦ Linear increase up to ~50–75% VO2 max
◦ Exponential increase beyond this point
◦ Ventilatory threshold (Tvent)
◦ Inflection point where VE increases exponentially
PO2
◦ Maintained within 10–12 mmHg of resting value
Incremental Exercise-Elite Athlete
Ventilation ◦ Tvent occurs at higher % VO2 max PO2 ◦ Decrease of 30–40 mmHg at near-maximal work ◦ Hypoxemia ◦Due to: ◦ Ventilation/perfusion mismatch ◦ Short RBC transit time in pulmonary capillary due to high cardiac output
Input to the Respiratory Control Center: Humoral (blood borne) chemoreceptors
Central chemoreceptors
◦ Located in the medulla
◦ Sensitive to PCO2 and H+ concentration in cerebrospinal fluid
Peripheral chemoreceptors
◦ Aortic and carotid bodies
◦ Sensitive to PO2, PCO2, H+, and K+ in blood
Input to the Respiratory Control Center: Neural input
From motor cortex and skeletal muscle receptors
◦ Muscle mechanoreceptors: Muscle spindles, Golgi tendon organs, joint pressure receptors
◦ Muscle chemoreceptors: sensitive to K+ and H+ concentrations
◦ Important for regulating breathing during submaximal, steady-state exercise
Ventilatory Control During Exercise: Submaximal Exercise
Primary drive: ◦ Higher brain centers (central command) ◦ “Fine tuned” by: ◦ Humoral chemoreceptors ◦ Neural feedback from muscle
Ventilatory Control During Exercise: Heavy Exercise
◦ Alinear rise in VE
◦ Increasing blood H+ (from lactic acid) stimulates carotid bodies
◦ Also K+, body temperature, and blood catecholamines may contribute
How training reduces the ventilatory response to exercise
No effect on lung structure (which can be a limting factor for elite athletes)
Ventilation is lower during exercise following training
- Exercise ventilation is 20-30% lower at same submaximal work rate
Mechanisms for improving exercise ventilation
Changes in aerobic capacity of locomotor muscles
◦ Result in less production of H+
◦ Less afferent feedback from muscle to stimulate breathing
Does the Pulmonary System Limit Exercise Performance? Low-to-moderate intensity exercise
Pulmonary system does not limit exercise tolerance
Does the Pulmonary System Limit Exercise Performance? High intensity exercise
Not a limitation in healthy individuals at sea level at most exercise intensities
◦ However, evidence that respiratory muscle fatigue does occur during high intensity exercise (95-100% VO2 max)
◦ May be limiting in some elite endurance athletes ◦ 40–50% experience hypoxemia
