Regulation of end-expiratory lung volume during exercise

Abstract

We determined the effects of exercise on active expiration and end-expiratory lung volume (EELV) during steady-state exercise in 13 healthy subjects. We also addressed the questions of what affects active expiration during exercise. Exercise effects on EELV were determined by a He-dilution technique and verified by changes in end-expiratory esophageal pressure. We also used abdominal pressure-volume loops to determine active expiration. EELV was reduced with increasing exercise intensity. EELV was reduced significantly during even mild steady-state exercise and during heavy exercise decreased an average of 0.71 +/- 0.3 liter. Dynamic lung compliance was reduced 30-50%; EELV remained greater than closing volume. Changing the resistance to airflow (via SF6-O2 or He-O2 breathing) during steady-state exercise changed the peak gastric and esophageal pressure generation during expiration but did not alter EELV; breathing through the mouthpiece produced similar effects during exercise. EELV was significantly reduced in the supine position. With supine exercise active expiration was not elicited, and EELV remained the same as in supine rest. With CO2-driven hyperpnea (7-70 l/min), EELV remained unchanged from resting levels, whereas during exercise, at similar minute ventilation (VE) values EELV was consistently decreased. At the same VE, treadmill running caused an increase in tonic gastric pressure and greater reductions in EELV than either walking or cycling. We conclude that both the exercise stimulus and the resultant hyperpnea stimulate active expiration and a reduced FRC. This new EELV is preserved in the face of moderate changes in mechanical time constants of the lung. This reduced EELV during exercise aids inspiration by optimizing diaphragmatic length and permitting elastic recoil of the chest wall.

Expiratory muscle fatigue impairs exercise performance

“…Hyperpnoea, however, also requires active expiration in addition to increased inspiratory muscle activity (Abraham et al 2002;Henke et al 1988;Strohl et al 1981). Active expiration not only contributes to a higher breathing frequency by increasing expiratory Xow rates, but also facilitates inspiration by decreasing the endexpiratory lung volume.…”

“…On the one hand, a smaller endexpiratory lung volume (below functional residual volume) increases the proportion of "passive" inspiration due to elastic recoil of the chest wall. On the other hand, it extends the diaphragm, thereby optimizing its ability to generate inspiratory Xow (Henke et al 1988;Martin and De Troyer 1982;Verges et al 2006a). …”

Relationship between Respiratory Muscle Strength and Exercise Tolerance

“…Expiratory muscles have a lower oxidative capacity and thus are known to be more prone to fatigue than inspiratory muscles 11,12) . It has also been shown Mean ± SD that expiratory muscle activity during exercise not only increases respiratory frequency but also reduces end expiratory lung volume, thereby increasing respiratory efficiency during inspiration, and that increased expiratory muscle activity causes the diaphragm to be pushed further upward, promoting contraction of the diaphragm 2,13,14) . The abdominal muscle group, a major expiratory muscle, functions to maintain stable posture and control ventilation.…”

“…During exercise, breathing is hyperventilatory and requires expiratory muscle activity as well as an increase in inspiratory muscle activity [1][2][3] . Respiratory muscle activity plays an important role in ventilation control and is especially essential for respiratory response during exercise.…”

The The abdominal muscles – a functional review

“…Increases in blood CO 2 concentrations (Abe et al 1996), end expiratory lung volume (Henke et al 1988, Bishop 1974) and increased expiratory flow resistance (Baker et al 1979) potently activate the abdominal muscles.…”