Question

Describe the ventilatory response to incremental (graded) exercise. Include in your discussion factors that contribute to the alinear rise in ventilation at work rates > 50% VO2max, the location and function of chemoreceptors and mechanoreceptors that contribute to the regulation of breathing.

Answer 1

Ventilatory response to increased exercise are ask follow :

1) Increased pulmonary Ventilaton

2) Increased oxygen uptake.

Increased Pulmonary Ventilaton :

• Pulmonary Ventilaton Increases linearly with Increased intensity of exercises.
• Increse in RR at begining of Respiration is abrupt, called as exercise hyperpnea. It is due to psychic stimuli & afferent stimuli from proprioreceptors in muscle, tendon & joints.
• During exercise even though the arteial pH, pCO2 and pO2 remain same, there is Increased Respiratory drive due to increased K+ in plasma due to exercising muscle --> stimulation of peripheral Chemoreceptors.
• Increase in temperature also lead to increased Ventilaton.
• Incresed sensitivity of neurons to CO2 also responsible for increase in Ventilaton.

Chemoreceptors of Respiration :

1) Peripheral Chemoreceptors - Located in the carotid body and aortic body. Located at carotid bifurcation and aortic bodies at arch of aorta.

These are stimulated mainly by Hypoxis & Hypercarbia. Also fo increased pH, Increased plasma K+ etc.

2) Central Chemoreceptors : They are present in the brain. More sensitive to arterial pCO2 but not to PO2 of blood.

Mechanoreceptors in Respiration :

1) J receptors - these are receptors located very close to pulmonary capillary hence Juxtaxalillary receptors. These consist of slowly conducting unmylinated vagal C fibers.

J receptor stimulated in response to - Pulmonary Congetion, hyperinflation, Increased interstial fluid volume.

2) Respiratory reflex from muscle, tendos & joints.

- Muscle spindle and Golgi tendon organ located in Respiratory muscle.

- Proprioreceptors of joints in exercise causes hyperpnea.

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Oxygen Consumption in Exercise: VO2max
- When exercise intensity increases, oxygen consumption
increases till maximal O2 consumption is
reached (VO2max).
- VO2max- point at which there is no further increase in oxygen uptake even after further increases in workload.
- When workload exceeds the VO2max, the energy for increased workload provided by nonaerobic processes, which results in a rapid buildup of lactic acid.

- With increased acid, the increases in ventilation but CO2 production remain proportional, so CO2 change relatively litle (isocapnic bufering).

- With more accumulation of lactic acid, the
increase in ventilation outweigh CO2 production and
alveolar PCo2 & arterial pCO2 fall. While pO2 of arterial blood remain constant or slightly increased duringsevere exercise.