Phrenic motoneuron discharge during sustained  inspiratory resistive loading

Iscoe, Steve

doi:10.1152/jappl.1996.81.5.2260

Cited by 5 publications

(6 citation statements)

References 25 publications

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“…Phrenic motoneuron firing rates, along with our previous results, now strongly suggest that during IRL peripheral fatigue occurs, but drive to the diaphragm remains high. A similar finding has been reported for decerebrate cats, in which integrated phrenic activity and phrenic motoneuron firing rates remained high even when Pdi declined during severe IRL (17). In these cats, there was greater phrenic motor activity during IRL than during CO 2 rebreathing, when compared at equal values of end-tidal CO 2 , suggesting to Iscoe (17) that there was a source of respiratory drive in addition to high Pa CO 2 , for example from afferents in the lungs or respiratory muscles.…”

Section: Discussionsupporting

confidence: 87%

“…This finding raises questions about the intensity of diaphragmatic activation during prolonged loading. The only previous study of phrenic motoneuron firing rates during potentially fatiguing contractions (17) found no drop in rates during IRL, but only one recording session lasted beyond 22 min. In the present study, we recorded from single motor units during severe IRL for 30 min while also measuring inspiratory pressures.…”

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confidence: 80%

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Phrenic motoneuron firing rates before, during, and after prolonged inspiratory resistive loading

Road

Cairns

1997

Journal of Applied Physiology

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Phrenic motoneuron firing rates during brief inspiratory resistive loading (IRL) are high, and nearly all the motoneurons are recruited. Diaphragmatic fatigue has been difficult to demonstrate during IRL. Furthermore, evidence from studies in limb muscles has shown variable motoneuron responses to prolonged high-intensity loads. We studied phrenic motoneuron firing rates before, during, and after prolonged IRL in anesthetized rabbits. Of 117 phrenic axons, only 2 axons were not recruited; 41 axons were silent during unloaded breathing but were recruited at higher loads. Silent axons showed a more rapid increase in firing rate as the load increased. Phrenic motoneuron firing rates increased throughout the period of loading, whereas airway pressure swings did not. After prolonged IRL, higher motoneuron firing rates were needed during brief loads to produce the same airway pressure. No evidence of a decline in motoneuron firing rates was seen at any point. We conclude that the respiratory muscles can be shown to demonstrate physiological responses consistent with fatigue during prolonged IRL, and activation rates are high and remain so throughout this prolonged loading.

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Section: Discussionsupporting

confidence: 87%

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confidence: 80%

Phrenic motoneuron firing rates before, during, and after prolonged inspiratory resistive loading

Road

Cairns

1997

Journal of Applied Physiology

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“…increased drive necessary to maintain the same pressure generation) is not. Our results are similar to those of previous work in cats on IRL (Iscoe, 1996) and in rabbits subjected to brief loads after prolonged IRL (Road & Cairns, 1997). They are also consistent with an earlier report in man of rapid recovery of pressuregenerating capacity following progressive inspiratory threshold loading to failure coexisting with reduced twitch amplitudes in response to phrenic nerve stimulation (Eastwood et al 1994).…”

Section: Failure Fatigue Injury and Recoverysupporting

confidence: 92%

“…Imposition of the same contractile regimen on motor units with different contractile characteristics may therefore injure and fatigue fibre types, with consequent effects on sTnI release, in a manner very different from that under ‘normal’ circumstances. Indeed, under conditions of increased chemical drive, as elicited here by IRL, motor units are recruited in a stereotyped pattern, from slow oxidative to fast fatiguable (Sieck & Fournier, 1989), in which compensation for injured diaphragmatic motor units can be accomplished by recruiting other motor units in the diaphragm and, possibly, synergistic muscles, and by generating more force with doublets at the onset of discharge (Burke et al 1970; Iscoe, 1996).…”

Section: Discussionmentioning

confidence: 99%

Respiratory muscle injury, fatigue and serum skeletal troponin I in rat

Simpson

Eyk

Iscoe

2004

The Journal of Physiology

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To evaluate injury to respiratory muscles of rats breathing against an inspiratory resistive load, we measured the release into blood of a myofilament protein, skeletal troponin I (sTnI), and related this release to the time course of changes in arterial blood gases, respiratory drive (phrenic activity), and pressure generation. After ∼1.5 h of loading, hypercapnic ventilatory failure occurred, coincident with a decrease in the ratio of transdiaphragmatic pressure to integrated phrenic activity (P di / Phr) during sighs. This was followed at ∼1.9 h by a decrease in the P di / Phr ratio during normal loaded breaths (diaphragmatic fatigue). Loading was terminated at pump failure (a decline of P di to half of steady-state loaded values), ∼2.4 h after load onset. During 30 s occlusions post loading, rats generated pressure profiles similar to those during occlusions before loading, with comparable blood gases, but at a higher neural drive. In a second series of rats, we tested for sTnI release using Western blot-direct serum analysis of blood samples taken before and during loading to pump failure. We detected only the fast isoform of sTnI, release beginning midway through loading. Differential detection with various monoclonal antibodies indicated the presence of modified forms of fast sTnI. The release of fast sTnI is consistent with load-induced injury of fast glycolytic fibres of inspiratory muscles, probably the diaphragm. Characterization of released fast sTnI may provide insights into the molecular basis of respiratory muscle dysfunction; fast sTnI may also prove useful as a marker of impending respiratory muscle fatigue.

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“…For example, the phrenic nerve is the major neural pathway for electrical impulses to the diaphragm. Increases in phrenic motoneuron activation have been observed during and after inspiratory resistance training (21,22). Activation of phrenic motoneurons and recruitment of phrenic nerve axons may have contributed to the increases in respiratory muscle strength observed in this study.…”

Section: Discussionsupporting

confidence: 50%

Effects of Respiratory Resistance Training With a Concurrent Flow Device on Wheelchair Athletes

Litchke

Russian

Lloyd

et al. 2008

The Journal of Spinal Cord Medicine

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Background/Objective: To determine the effect of respiratory resistance training (RRT) with a concurrent flow respiratory (CFR) device on respiratory function and aerobic power in wheelchair athletes. Methods: Ten male wheelchair athletes (8 with spinal cord injuries, 1 with a neurological disorder, and 1 with postpolio syndrome), were matched by lesion level and/or track rating before random assignment to either a RRT group (n ¼ 5) or a control group (CON, n ¼ 5). The RRT group performed 1 set of breathing exercises using Expand-a-Lung, a CFR device, 2 to 3 times daily for 10 weeks. Pre/posttesting included measurement of maximum voluntary ventilation (MVV), maximum inspiratory pressure (MIP), and peak oxygen consumption (V O 2 peak). Results: Repeated measures ANOVA revealed a significant group difference in change for MIP from pre-to posttest (P , 0.05). The RRT group improved by 33.0 cm H 2 O, while the CON group improved by 0.6 cm H 2 O. Although not significant, the MVV increased for the RRT group and decreased for the CON group. There was no significant group difference betweenV O 2 peak for pre/posttesting. Due to small sample sizes in both groups and violations of some parametric statistical assumptions, nonparametric tests were also conducted as a crosscheck of the findings. The results of the nonparametric tests concurred with the parametric results. Conclusions: These data demonstrate that 10 weeks of RRT training with a CFR device can effectively improve MIP in wheelchair athletes. Further research and a larger sample size are warranted to further characterize the impact of Expand-a-Lung on performance and other cardiorespiratory variables in wheelchair athletes.

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Phrenic motoneuron discharge during sustained inspiratory resistive loading

Cited by 5 publications

References 25 publications

Phrenic motoneuron firing rates before, during, and after prolonged inspiratory resistive loading

Phrenic motoneuron firing rates before, during, and after prolonged inspiratory resistive loading

Respiratory muscle injury, fatigue and serum skeletal troponin I in rat

Effects of Respiratory Resistance Training With a Concurrent Flow Device on Wheelchair Athletes

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