Respiratory Responses to Exercise

Question 1

Pulmonary respiration

Answer 1

◦ Ventilation

◦ Exchange of O2 and CO2 in the lungs

Question 2

Cellular respiration

Answer 2

O2 utilization and CO2 production by the tissues

Question 3

Purposes of the respiratory system during exercise

Answer 3

Gas exchange between the environment and the body

◦ Regulation of acid-base balance during exercise

Question 4

Do respiratory muscles fatigue during exercise?

Answer 4

Current evidence suggests that respiratory muscles do fatigue during exercise
◦ Prolonged (>120 minutes)
◦ High-intensity (90–100% VO2 max)

Question 5

Do respiratory muscle adapt to training?

Answer 5

Increased oxidative capacity improves respiratory muscle endurance
◦ Reduced work of breathing

Question 6

Pulmonary Ventilation

Answer 6

The amount of air moved in or out of the lungs per minute (V)

V = VT x f
V = VA + VD

Question 7

Tidal volume (VT)

Answer 7

Amount of air moved per breath

Question 8

Breathing frequency (f)

Answer 8

Number of breaths per minute

Question 9

Alveolar ventilation (VA)

Answer 9

Volume of air that reaches the respiratory zone

Question 10

Dead-space ventilation (VD)

Answer 10

Volume of air remaining in conducting airways

Question 11

Pulmonary circuit

Answer 11

Same rate of flow as systemic circuit ◦Lower pressure

Question 12

When standing, most of the blood flow is to

Answer 12

the base of the lung

Due to gravitational force

Question 13

During exercise, blood flow to

Answer 13

to apex

Question 14

Ventilation Perfusion Relationships

Answer 14

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)

Question 15

Ventilation-Perfusion Relationships: During Exercise

Answer 15

Light exercise improves V/Q ratio

◦ Heavy exercise results in V/Q inequality

Question 16

O2 Transport in the Blood

Answer 16

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

Question 17

Oxygen Content of Blood for males and females

Answer 17

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

Question 18

Oxyhemoglobin Dissociation Curve

Answer 18

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)

Question 19

pH effect on O2- Hb Dissociation Curve

Answer 19

Decreased pH lowers Hb-O2 affinity
Results in rightward shift of curve
Favors offloading of O2 to tissues

Question 20

Temperature effect on O2- Hb Dissociation Curve

Answer 20

Increased blood temperature lowers Hb-O2 affinity

Results in rightward shift of the curve

Question 21

2-3 DPG effect on O2- Hb Dissociation Curve

Answer 21

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

Question 22

O2 Transport in Muscle

Answer 22

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

Question 23

CO2 transport in blood

Answer 23

Dissolved in plasma (10%)
Bound to hB (20%)
Bicarbonate (70%)

Question 24

CO2 transport in blood at tissue

Answer 24

H+ binds to Hb
◦ HCO3– diffuses out of RBC into plasma
◦ Cl– diffuses into RBC (chloride shift)

Question 25

CO2 transport in blood at lung

Answer 25

At the lung: ◦ O2 binds to Hb (drives off H+) ◦ Reaction reverses to release CO2

Question 26

Pulmonary ventilation removes H+ from blood by the HCO3– reaction: What is the reaction

Answer 26

CO2 + H2O (Carbonic anhydrase)-> H2CO3 -> H + HCO3

Question 27

Ventilation and CO2

Answer 27

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)

Question 28

At the onset of constant-load submaximal exercise:

Answer 28

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

Question 29

Incremental Exercise-Untrained Subject

Answer 29

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

Question 30

Incremental Exercise-Elite Athlete

Answer 30

``` 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 ```

Question 31

Input to the Respiratory Control Center: Humoral (blood borne) chemoreceptors

Answer 31

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

Question 32

Input to the Respiratory Control Center: Neural input

Answer 32

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

Question 33

Ventilatory Control During Exercise: Submaximal Exercise

Answer 33

``` Primary drive: ◦ Higher brain centers (central command) ◦ “Fine tuned” by: ◦ Humoral chemoreceptors ◦ Neural feedback from muscle ```

Question 34

Ventilatory Control During Exercise: Heavy Exercise

Answer 34

◦ Alinear rise in VE ◦ Increasing blood H+ (from lactic acid) stimulates carotid bodies ◦ Also K+, body temperature, and blood catecholamines may contribute

Question 35

How training reduces the ventilatory response to exercise

Answer 35

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

Question 36

Mechanisms for improving exercise ventilation

Answer 36

Changes in aerobic capacity of locomotor muscles ◦ Result in less production of H+ ◦ Less afferent feedback from muscle to stimulate breathing

Question 37

Does the Pulmonary System Limit Exercise Performance? Low-to-moderate intensity exercise

Answer 37

Pulmonary system does not limit exercise tolerance

Question 38

Does the Pulmonary System Limit Exercise Performance? High intensity exercise

Answer 38

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