PROF ASHRAF HUSAIN

RESPIRATORY CHANGES DURING EXERCISE

According to muscular contraction

1. Isotonic2. Isometric3. Mixed

OXYGEN DEBT

The two major components of oxygen recovery are:

• Alactacid oxygen debit (fast component) – the portion of oxygen

required to synthesise and restore muscle phosphagen stores (ATP and PC)

• Lactacid oxygen debit (slow component)

• the portion of oxygen required to remove lactic acid from the muscle cells and blood

The replenishment of muscle myoglobin with oxygen is normally completed within the time required to recover the Alactacid oxygen debit component.

The replenishment of muscle and liver glycogen stores depends on the type of exercise: short distance, high intensity exercise (e.g. 800 metres) may take up to 2 or 3 hours and long endurance activities (e.g. marathon) may take several days. Replenishment of glycogen stores is most rapid during the first few hours following training and then can take several days to complete. Complete restoration of glycogen stores is accelerated with a high carbohydrate diet

Physiological changes seen in response to exercise depends on

1. Frequency 2. Duration3. Intensity4. Age5. Fitness6. Training7. Environment

Respiratory response

Increase minute Ventilation (VE) normal = 5-6L/min. Exercise = 150 L/min. Due to increased respiratory rate and tidal volume.

VE = Respiratory rate X VT

Respiratory rate is the major contributor to minute volume in non athlete where as the tidal volume is major contributor in athlete

Slight decrease in total lung capacity due to an increase in the pulmonary blood flow.

Increase in tidal volume occurs at the expense of inspratory reserve volume.

During moderate exercise the inspiratory time remains constant, but the expiratory time decreases.

Increase in respiratory rate mainly due to fast expiration.

Diffusion capacity(DLCo) of oxygen and carbon dioxide increases during exercise.

O2 diffusion capacity at rest is 20ml/min/mm of Hg. And during exercise it may go up to 80 ml/min/mm of Hg. This change is due to the greater no. of capillaries opening in the lung, increase gas diffusion gradients and large increase in pul. capillary blood volume.

Airway resistance is reduced due to switching of breathing from nose to mouth.

A very little change in alveolar and arterial co2 is seen due to isocapnic buffering During exercise large amount of lactic acid is

produced which is buffered by bicarbonate and during this process CO2 is produced which stimulates respiratory center causing increase ventilation leading to co2 washout.

VO2max (definition)= the maximal oxygen uptake or the maximum volume of oxygen that can be utilized by the human body in one minute during maximal exercise. It is measured as milliliters of oxygen used in one minute per kilogram of body weight (ml/kg/min). VO2max and is usually ranged from 20-40 ml/kg/min (in unfit and ordinary subjects) and up to 80-90 ml/mg/min (in elite endurance athletes). Physiologically, it is the most significant parameter that predict long-term endurance and performance

in athletes.VO2 is the product of maximum cardiac out put

and maximum O2 extraction by the tissue.

Respiratory exchange ratio is a ratio of carbon dioxide produced with oxygen consumption, normal ratio is 0.8.

Respiratory exchange ratio =200/250 = 0.8During exercise it may go up to 1.Note: old terminology of respiratory exchange

ratio used to be mentioned as RQ(respiratory quotient)