Human respiratory muscle actions and control during exercise

Abstract

We measured pressures and power of diaphragm, rib cage, and abdominal muscles during quiet breathing (QB) and exercise at 0, 30, 50, and 70% maximum workload (Wmax) in five men. By three-dimensional tracking of 86 chest wall markers, we calculated the volumes of lung- and diaphragm-apposed rib cage compartments (Vrc,p and Vrc,a, respectively) and the abdomen (Vab). End-inspiratory lung volume increased with percentage of Wmax as a result of an increase in Vrc,p and Vrc,a. End-expiratory lung volume decreased as a result of a decrease in Vab. DeltaVrc,a/DeltaVab was constant and independent of Wmax. Thus we used DeltaVab/time as an index of diaphragm velocity of shortening. From QB to 70% Wmax, diaphragmatic pressure (Pdi) increased approximately 2-fold, diaphragm velocity of shortening 6.5-fold, and diaphragm workload 13-fold. Abdominal muscle pressure was approximately 0 during QB but was equal to and 180 degrees out of phase with rib cage muscle pressure at all percent Wmax. Rib cage muscle pressure and abdominal muscle pressure were greater than Pdi, but the ratios of these pressures were constant. There was a gradual inspiratory relaxation of abdominal muscles, causing abdominal pressure to fall, which minimized Pdi and decreased the expiratory action of the abdominal muscles on Vrc,a gradually, minimizing rib cage distortions. We conclude that from QB to 0% Wmax there is a switch in respiratory muscle control, with immediate recruitment of rib cage and abdominal muscles. Thereafter, a simple mechanism that increases drive equally to all three muscle groups, with drive to abdominal and rib cage muscles 180 degrees out of phase, allows the diaphragm to contract quasi-isotonically and act as a flow generator, while rib cage and abdominal muscles develop the pressures to displace the rib cage and abdomen, respectively. This acts to equalize the pressures acting on both rib cage compartments, minimizing rib cage distortion.

Exercise-induced respiratory muscle fatigue: implications for performance

“…Third, the reduced EELV allows for storage of elastic energy in the chest and abdominal walls during expiration that can be used to produce a portion of the work required during the ensuing inspiration (5, 35), although it is also possible that inspiration is aided in this situation by passive descent of the diaphragm (35). Importantly, accessory respiratory muscles are progressively recruited with increasing ventilatory demand during exercise, thereby sharing the load needed to support the exercise hyperpnea (6). The unique structural characteristics of respiratory muscles combined with the precise neural regulation of breathing mean that the capacity of these muscles for pressure generation usually exceeds the demands placed on them.…”

“…Exercise-induced diaphragmatic fatigue may affect performance by decreasing the relative contribution of the diaphragm to total ventilation over time with a requirement for accessory inspiratory and expiratory muscles to be recruited to deliver the progressive hyperventilatory response (6,12,13,52). The increasing use of accessory respiratory muscles as exercise continues may distort the chest wall (34,36), reduce the mechanical efficiency of breathing (23,42) and, hence, increase the metabolic and blood flow demands of these muscles (see EXERCISE DEMANDS ON THE RESPIRATORY MUSCLES).…”

Compartmental chest wall volume changes during volitional hyperpnoea with constant tidal volume in healthy individuals

“…This should be kept in mind when comparing the present results with findings in the literature. For example, with increasing exercise intensity or CO 2 -induced hyperpnoea and concomitantly increasing ventilation, a progressive increase in end-inspiratory volumes of rib cage compartments and a decrease in the end-expiratory volume of the abdominal compartment is observed (Aliverti et al, 1997;Sanna et al, 1999;Duranti et al, 2004;Romagnoli et al, 2004;Vogiatzis et al, 2005). In the current study, these changes were present right from the start of hyperpnoea where ventilation was already required to be high.…”

“…The present data suggest that this lowering of end-expiratory volume took place exclusively in RCp. Since inspiratory rib cage muscles are predominantly responsible for rib cage expanding forces while the diaphragm acts as the main flow generator (Aliverti et al, 1997), it seems intuitive to decrease end-expiratory V rc,p further in order to improve the pressure-generating capacity of the inspiratory rib cage muscles.…”

Impacto de fatores externos sobre a mecânica respiratória avaliada por um modelo fotogramétrico específico: biofotogrametria

“…Therefore, a plane at the level of the anterior axillary fold divided the thoracic compartment into upper and lower thoracic sub-compartments; the same occurred for the abdominal compartment, where a plane at the level of the lower angle of the 10 th rib cartilage delineated the upper and lower abdominal The areas measured using BAMER corroborated the following statements: the thoracic inspiratory areas were larger at the post-exercise with PEEP time point (p < 0.05) than at the time points without expiratory load, and this was accompanied by a reduction in the expiratory area of the abdominal compartment (p < 0.05), explained by the reduction in that of the lower abdominal sub-compartment. Healthy subjects who exercised on a stationary cycle ergometer with PEEP (19) had increased pulmonary end-inspiratory volume, mostly due to the thoracic expansion, accompanied by a reduction in abdominal end-inspiratory volume. Similarly, when compared with the inspiratory areas prior to and following the same tests, there was difference (p < 0.05) for the thoracic compartment in the test with PEEP, that is, between the time point 3 and time point 5, as well as between time point 4 and time point 5.…”