Beachey: Respiratory Care Anatomy and Physiology, 2nd Edition

Answers to Concept Questions

Chapter 20: Cardiopulmonary Response to Exercise in Health and Disease

20-1	Because fat metabolism generates less carbon dioxide than carbohydrate metabolism to produce a mole of adenosine triphosphate (ATP), a high-fat diet requires less ventilation per unit of energy generated. This is theoretically advantageous in patients with chronic obstructive pulmonary disease with limited ventilatory capacity.

20-2	In severe shock the cardiovascular system does not supply enough oxygen to the tissues to adequately sustain aerobic metabolism. The resulting anaerobic metabolism generates pyruvic acid, which is immediately metabolized to lactic acid. Thus severe shock is associated with increased blood levels of lactic acid, producing metabolic acidosis.

20-3	Anaerobic metabolism produces lactic acid. Plasma bicarbonate ions buffer these lactic acid molecules, generating carbon dioxide in the process. This carbon dioxide is added to aerobically generated carbon dioxide, exposing the medullary chemoreceptors to an abrupt rise in PCO2 and thus a rise in [H+]; this stimulates an abrupt rise in alveolar ventilation.

20-4	These two people presumably have equal oxygen consumptions because each performs the same amount of work. A given amount of work requires the same number of oxygen molecules to produce the required adenosine triphosphate (ATP) molecules necessary to accomplish the work. Thus oxygen consumption is the same for a given work load, regardless of the person’s fitness level.

20-5	The sedentary person reaches the maximum heart rate relatively early during progressive exercise. This means the heart rate is high for a given oxygen consumption. Therefore the oxygen consumed per heartbeat (the O2 pulse) is low in sedentary people.

20-6	A major effect of physical conditioning is an increased stroke volume. Therefore a conditioned athlete can sustain the resting cardiac output at a lower heart rate than an unconditioned person can. This lowered resting heart rate is a hallmark of physical conditioning.