Respiratory muscle dynamics and control during exercise with externally imposed expiratory flow limitation

Abstract

To determine how decreasing velocity of shortening (U) of expiratory muscles affects breathing during exercise, six normal men performed incremental exercise with externally imposed expiratory flow limitation (EFLe) at approximately 1 l/s. We measured volumes of chest wall, lung- and diaphragm-apposed rib cage (Vrc,p and Vrc,a, respectively), and abdomen (Vab) by optoelectronic plethysmography; esophageal, gastric, and transdiaphragmatic pressures (Pdi); and end-tidal CO2 concentration. From these, we calculated velocity of shortening and power (W) of diaphragm, rib cage, and abdominal muscles (di, rcm, ab, respectively). EFLe forced a decrease in Uab, which increased Pab and which lasted well into inspiration. This imposed a load, overcome by preinspiratory diaphragm contraction. Udi and inspiratory Urcm increased, reducing their ability to generate pressure. Pdi, Prcm, and Wab increased, indicating an increased central drive to all muscle groups secondary to hypercapnia, which developed in all subjects. These results suggest a vicious cycle in which EFLe decreases Uab, increasing Pab and exacerbating the hypercapnia, which increases central drive increasing Pab even more, leading to further CO2 retention, and so forth.

Chest wall volume regulation during exercise in COPD patients with GOLD stages II to IV

“…2b). In fact, this is the way normal subjects breathe during exercise [20,21]. In most cases, this strategy attenuates the progressive increase in EEVcw and the occurrence of dynamic chest wall hyperinflation during exercise.…”

“…Indeed, the greater reduction in end-expiratory abdominal volume in the healthy subjects compared with COPD patients during exercise ( fig. 2b, d, f and h) could be associated with increased diaphragm length, greater diaphragmatic power output and descent, and greater expansion of abdominal wall during inspiration [21], resulting in a higher end-inspiratory abdominal volume in healthy subjects than in COPD patients. Nevertheless, at the limit of tolerance, the IRVcw in stage II patients (530 mL), and in healthy subjects (570 mL) remained higher than the ''minimum'' inspiratory reserve volume (350 mL), which is commonly taken to represent the inability to further expand VT [2,5,7].…”

Effects of a multidisciplinary body weight reduction program on static and dynamic thoraco-abdominal volumes in obese adolescents

“…Fat mass was calculated as the difference between total body mass and fat-free mass. Thoraco-abdominal perimeters, areas, and volumes were measured by optoelectronic plethysmography (OEP) (Smart System BTS, Milan, Italy) (Aliverti et al 2002). Eight video cameras, 4 in front of the subject and 4 behind, tracked the movement of 89 retroreflective markers placed anteriorly and posteriorly over the trunk or chest wall, extending from clavicles to pubis, with the subject seated on the cycle ergometer.…”

“…The distribution of the latter into the different thoraco-abdominal compartments is determined by the action of different respiratory muscle groups (Aliverti et al , 2002 and can be noninvasively assessed by optoelectronic plethysmography (Cala et al 1996). Distinct altered patterns of chest wall operating volumes during exercise have been described in chronic obstructive pulmonary disease, pulmonary fibrosis, and cystic fibrosis (Aliverti et al 2004(Aliverti et al , 2009Vogiatzis et al 2005a;Georgiadou et al 2007;Wilkens et al 2010).…”

“…The main hypothesis was that the abdominal volume (mass) would affect the action of the diaphragm and abdominal muscles and consequently the regulation of the operating volumes of the 2 compartments influenced by these muscles, namely the abdominal rib cage and abdomen (Ward et al 1992;Kenyon et al 1997;Aliverti et al 2002Aliverti et al , 2003. In addition, it has been recently shown that the inclusion of respiratory muscle endurance training (RMET) in a multidisciplinary body weight reduction program (MBWRP) improves exercise performance in overweight and obese adults more than exercise and nutritional counseling alone (Frank et al 2011).…”