Task failure from inspiratory resistive loaded breathing: a role for inspiratory muscle fatigue?

Abstract

The use of non-invasive resistive breathing to task failure to assess inspiratory muscle performance remains a matter of debate. CO2 retention rather than diaphragmatic fatigue was suggested to limit endurance during inspiratory resistive breathing. Cervical magnetic stimulation (CMS) allows discrimination between diaphragmatic and rib cage muscle fatigue. We tested a new protocol with respect to the extent and the partitioning of inspiratory muscle fatigue at task failure. Nine healthy subjects performed two runs of inspiratory resistive breathing at 67 (12)% of their maximal inspiratory mouth pressure, respiratory rate (fR), paced at 18 min(-1), with a 15-min pause between runs. Diaphragm and rib cage muscle contractility were assessed from CMS-induced esophageal (P(es,tw)), gastric (P(ga,tw)), and transdiaphragmatic (P(di,tw)) twitch pressures. Average endurance times of the first and second runs were similar [9.1 (6.7) and 8.4 (3.5) min]. P(di,tw) significantly decreased from 33.1 to 25.9 cmH2O in the first run, partially recovered (27.6 cmH2O), and decreased further in the second run (23.4 cmH2O). P(es,tw) also decreased significantly (-5.1 and -2.4 cmH2O), while P(ga,tw) did not change significantly (-2.0 and -1.9 cmH2O), indicating more pronounced rib cage rather than diaphragmatic fatigue. End-tidal partial pressure of CO2 ( PETCO2) rose from 37.2 to 44.0 and 45.3 mmHg, and arterial oxygen saturation (SaO2) decreased in both runs from 98% to 94%. Thus, task failure in mouth-pressure-targeted, inspiratory resistive breathing is associated with both diaphragmatic and rib cage muscle fatigue. Similar endurance times despite different degrees of muscle fatigue at the start of the runs indicate that other factors, e.g. increases in PETCO2, and/or decreases in SaO2, probably contributed to task-failure.

Gender Differences in the Fatigability of the Inspiratory Muscles

“…Inspiratory muscle fatigue at task failure was observed in all subjects in the present study. The level of inspiratory muscle fatigue induced in the present study (15-20%) is close to that reported by other studies utilizing a target resistive breathing task (23). However, the present study provides new information in that gender differences in inspiratory muscle fatigue were found following resistive breathing.…”

“…However, the results of a recent study by Rohrbach et al (23) indicated that both diaphragmatic and intercostal muscle fatigue occurred during constantload resistive breathing to task failure. It is generally thought that the inspiratory muscles do not generate the same tension with each breath during loaded breathing, and that the recruitment of inspiratory muscles may be coordinated in such a way that they protect the diaphragm against fatigue.…”

“…Respiratory muscle fatigue has been reported to occur during voluntary hyperpnea (19), high-intensity cycling (16), treadmill exercise (1), inspiratory resistive breathing (8,23), and repeated generation of transdiaphragmatic pressures (2). Resistive breathing has been used extensively as a noninvasive tool for assessment of respiratory muscle performance (8,23), and is generally held as an effective method to elicit inspiratory muscle fatigue. The task requires breathing against an inspiratory load until task failure, which is often defined as the inability to generate sufficient inspiratory pressure to open the inlet-breathing valve.…”

Expiratory muscle fatigue impairs exercise performance

“…However, recent studies have shown that muscle performance is enhanced rather than impaired by higher lactate concentrations (Nielsen et al 2001;Pedersen et al 2004). Moreover, in a previous study we did not observe a signiWcant increase in blood lactate concentration as a result of inspiratory resistive breathing at 70% PI max to exhaustion (Rohrbach et al 2003). Hence, it is unlikely that the decreased performance during EMF-EX was caused by increased blood lactate concentration resulting from expiratory resistive breathing.…”

Increased fatigue resistance of respiratory muscles during exercise after respiratory muscle endurance training

“…Due to the large amount of stimulations needed when testing twitch pressures during increasing stimulator output, the time associated with this procedure, and the ensuing discomfort for the subjects, supramaximal stimulation was confirmed only for one stimulation site per subject, i.e., 10 subjects were tested during cervical stimulation and the other 11 subjects during thoracic stimulation. Although supramaximal stimulation was tested only for one stimulation site per subject, previous results from our laboratory using the same method (36,46), as well as confirmation of supramaximal stimulation on the sites tested, suggest that most, if not all, stimulations were supramaximal.…”