Question

Discuss the mechanisms responsible for the changes seen during incremental submaximal exercise (oxygen consumption, ventilation, blood pressure, heart rate). You will need to discuss the receptors and effectors that regulate these responses (300 words)

Answer 1

INCREASE IN VENTILATION

The major reapiratory change in exercise is increase in ventialtion.The increased ventilation matches the metabolic demand of exercise and ventilation may increase to about twenty fold.The ventilation increases almost linearly with increase in intensity of exercise until anaerobic threshold is reached.Anaerobic threshold is degree of exercise that produces the elevation of blood lactate levels that result from shift from aerobic to anaerobic metabolism.Lactic acidosis stimulates the ventilation further and therefore reaches rise in ventilation becomes supralinear.In athelets,lactate threshold occurs at higher level than non athlets.

Exact mechanism for increased vebtilation is still not clearly known.However effects are possibly meadiated by neural,chemical and thermal mechanisms.Ventilation increases abruptly at beginning of exercise,then followed by breif pause,again increases gradually to reach a steady state as exercise is continued.The initial rise is mediated via neural mechanism and gradual increase in later phase is mediated by chemical mechanism.

Neural mechanism:

It plays important role at beginning.It increases due to psychuc stimuli originating in limbic system.Also,impulses originating from proprioceptors contribute.

Chemival mechanism:

In later phase.The arterial po2,pco2,pH ,k+ play role in this process . It is suggested that accentuations of normal oscillations in po2 and pco2 ,synchronous with respiration stimulate in turn stimualte ventilation.

Thermogenic mechanism:

Exercising muscles generate heat and increase body tenparature.Increased tenparature in sustained exercise contributes to stimulation of ventilation.

INCREASE IN O2 UPTAKE

Hyperventilation in exercise increases oxygen uptake in lungs.This helps maintain arterial oxygentaion.Maximal O2 uptake may be about 20 times the resting O2 uptake.

Mechanisms:

Increased alveolar to arterial gradient of pO2

Increased perfusion of lungs

Increased diffusion capacity of alveolacapillary membrane

INCREASE IN HEART RATE

It is good index of Paradympathetic activity .Heart rate increases linearly with severity and duration of exercise. It takes time to return to normal.

Mechanisms:

Increased sympathetic discharge

Muscle heart re ex

Harmonal mechanisms

Thernogenic stimulation

BLOOD PRESSURE CHANGES

Systolic: it always increases in exercise proportionate to increase in cardiac output.This iccurs due to sympathetic induced cardio acceleration.

Diastolic: It depends on degree of exercise.Depends on peripheral resistance, which primarily depends on diameter of blood vessels. In mild to moderate, vasoconstriction induced by sympathetic activation increases diastolic pressure .In moderate to severe activity, vasodilatation decreases peripheral resistance which in turn decreases diastolic pressure

Mechanisms:

Sympathetic cholinergic vasodilation of skeletal blood vessels

Metabolic vasodilation

Thermogenic vasodilation