Question

an adverse effect of COPD is: increased work of breathing resulting in decreased energy expenditure

true or false ?

does the increased work of breathing results and leads to decreased energy expenditure ?

Answer 1

• The statement increased work of breathing resulting in decreased energy expenditure is false.

Patients with COPD have an increased total daily energy expenditure, but resting energy expenditure is normal. Since there appears to be no difference in postprandial thermogenesis, the increase must be due to the physical activity component.

Gas exchange requires expenditure of energy, by the respiratory muscles to affect alveolar ventilation; by the right ventricle to pump mixed venous blood through the pulmonary capillaries; and, to a much lesser degree, by the arteriolar and bronchiolar smooth muscle to cause proper distribution of blood and gas within the lungs.

The factors which influence the amount of energy output by the respiratory muscles and heart are

• The mechanical properties of the lung, which include the resistance of the airways and lung tissue and the distensibility of the lung, which in turn depends on the elasticity of the tissues and the surface forces in the alveoli
• The mechanical properties of the chest wall and its musculature, the chest tissue resistance, and compliance
• The efficiency of the respiratory muscles, the condition of these muscles, and the shape and integrity of the chest wall
• Respiratory dead space
• Ventilation perfusion coordination
• Transfer of gases across alveolar membranes by diffusion
• The efficiency of the chemical processes in the blood
• The rate and volume of respiration.

Even in the healthy individual the effort necessary to get a given amount of gas exchange varies with the rate of gas exchange required. When disease deranges the system, the energy required for any level of gas exchange is increased.