This phenomenon also frequently occurs in elderly subjects due to the age-related loss of lung elastic recoil, and is a common feature of patients with chronic obstructive pulmonary disease, not only during exercise but also at rest in the most severe cases. In fact, in highly fit endurance athletes the pressure produced by inspiratory muscles can approach the maximum and expiratory pressures are increased to levels at which dynamic compression of the airways determines expiratory flow limitation. However, this is only true for healthy subjects not those who are trained athletes. At maximal exercise, the oxygen consumed by the respiratory muscles to breathe is only ∼10% of the total. The mechanics of the breathing pattern is regulated so precisely that the work performed by the respiratory muscles is minimised.Īt higher levels of exercise up to maximal exercise, the pressures produced by the respiratory muscles are well below their maximum. How do respiratory muscles undertake the increased ventilatory demands of exercise?Īt moderate levels of exercise, metabolic requirements increase in parallel with alveolar ventilation, arterial blood–gas tensions and acid-base balance are maintained close to their levels at rest. Tidal volume occurs in the most compliant part of the respiratory system the diaphragm is lengthened and thus works near its optimal length at each breath part of the required inspiratory work is previously stored in the form of elastic energy during the previous expiration. As a result, end-expiratory lung volume is decreased during exercise ( figure 1) and the mechanics of breathing is optimised for several reasons.
MUSCLES OF INSPIRATION GENERATOR
This mechanism has several effects: 1) it prevents rib cage distortion 2) the diaphragm is unloaded and can act as a flow generator and 3) the volume of the abdomen is decreased below resting levels. During inspiration, while the rib cage muscles contract, the abdominal muscles gradually relax, and vice versa during expiration. Within each single breath their action is highly coordinated with that of the inspiratory rib cage muscles. ĭifferently than rest, during exercise the expiratory muscles play an active role in breathing. develop the pressures required to move the rib cage and abdomen, respectively. Conversely, rib cage and abdominal muscles are primarily “pressure generators”, i.e. This means that its mechanical power is mainly expressed as velocity of shortening rather than pressure. Muscle power is equal to velocity of shortening multiplied by pressure.ĭifferently than rest, during exercise the diaphragm is primarily a “flow generator”. This determines an increased mechanical power developed by the muscles. How does the ventilatory pump work during exercise?ĭuring exercise the increased ventilatory demands determine an increased neural drive to the respiratory muscles. During breathing at rest, this is accomplished by the coordinated activity of the diaphragm and inspiratory rib cage muscles. A highly coordinated recruitment of two or three muscle groups is required to avoid these effects. When each muscle group contracts alone or the contraction is predominant compared to the other groups, undesirable effects (such as “paradoxical” inward or outward motion during inspiration and expiration, respectively) occur on at least one of the compartments. The abdominal muscles act on the abdomen and the abdominal rib cage and are expiratory.
The rib cage muscles, including the intercostals, the parasternals, the scalene and the neck muscles, mostly act on the upper part of the rib cage (pulmonary rib cage) and are both inspiratory and expiratory.
Contraction of the diaphragm expands the abdomen and the lower part of the rib cage (abdominal rib cage). the lung-apposed rib cage, the diaphragm-apposed rib cage and the abdomen. Each group acts on the chest wall and its compartments, i.e. From a functional point of view, there are three groups of respiratory muscles: the diaphragm, the rib cage muscles and the abdominal muscles.
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