Pediatric Pulmonology 40:181–182 (2005)

Commentary

Pump Action: Effect of Maturation on RespiratoryMuscle Endurance

Key words: respiratory muscle endurance; puberty.

Respiratory muscle endurance is important. A recentAmerican Thoracic Society/European Respiratory Socie-ty statement defined endurance as the ability to sustain aspecific muscular task over time, and a lack of endurancecould be a cause of breathlessness and, in the extreme,could result inventilatory failure.1Although a reduction inrespiratorymuscle strength does not necessarily indicate areduction in endurance, and vice versa, there is no doubtthat endurance and strength are integrally linked. Conse-quently, as strength and endurance of the respiratorymuscles are so important to maintain effective ventilation,the measurement of these variables can provide an in-depth understanding of both physiological and pathologi-cal processes.

Over the years, pulmonary scientists have been insearch of a holy grail. Their goal is to develop a robust testof respiratorymuscle endurance that provides data on boththe endurance of an individual or group of subjects, andalso provides data on the pulmonary mechanics ofinspiratory loading. There are a number of ways to loadthe respiratory muscles, with either resistive, elastic, orthreshold loads, all of which can be applied with either afixed or an unconstrained breathing pattern.At first glance,this wide variety seems attractive. However, it has resultedin the publication of a variety of endurance tests withdiffering results. Nevertheless, more recent advancesfavor the use of inspiratory threshold loading as the mostsatisfactory technique, because it provides a relativelyflow-independent method of loading, and avoids some ofthe problems of other loading techniques. In adults, a re-producible endurance test has been described that employsinspiratory threshold loading with an unconstrainedbreathing pattern and a sophisticated method for dataanalysis, but thismethod requires the insertion of a ballooncatheter for measuring esophageal pressure.2,3 Althoughinsertion of these catheters is not impossible in children,even with disease,4,5 this technique would be difficult toapply to a pediatric population. However, a much simpler,less invasive test has been established that can be

successfully applied to healthy children and children withdisease.6

A natural progression in the field of endurance mea-surement in healthy children is to investigate the effect ofpuberty and maturation on respiratory muscle endurance.In this issue of Pediatric Pulmonology, Koechlin et al.7 doexactly this. Their basic hypothesis behind the currentstudy was that endurance would be lower in prepubertaland peripubertal children than in children near the end ofthe pubertal process, based on physical changes occurringaround puberty. Using an inspiratory threshold loadingmethod, subjects were exposed to an inspiratory load of50% of their maximum inspiratory pressure. Althoughrespiratory muscle strength was similar between the twogroups, the time that the submaximal load was sustained,i.e., the endurance time or time limit (Tlim), was reducedin the prepubertal and peripubertal groups compared withthe group nearer the end of puberty. This difference in Tlim

between children at the start and end of puberty reflects areduction in respiratory muscle endurance. Furthermore,this observational study acknowledged that the time limita specific submaximal task can be sustained is an over-simplification of the much more complex task of res-piratory muscle endurance. This study also demonstratedthat the load applied to the respiratory muscles duringinspiration was the same in the pre- and peripubertalchildren as in the children near the end of puberty.Therefore, the pressure and timing of contraction duringinspiration are similar for both groups, based on thepressure applied to the system, duty cycle, and mean

*Correspondence to: Nicholas Hart, Lane Fox Unit, Guy’s and St. Thomas’

NHS Foundation Trust, St. Thomas’ Hospital, London, SE1 7EH UK.

E-mail: nicholas.hart@gstt.nhs.uk

Received 3 April 2005; Accepted 13 April 2005.

DOI 10.1002/ppul.20270

Published online 13 July 2005 in Wiley InterScience

(www.interscience.wiley.com).

� 2005 Wiley-Liss, Inc.

inspiratory flow rate, and thus the difference in endurancetime between the two groups is not explained by anydifferences in breathing strategy.Although this study does not provide the answer to the

cause of the difference in respiratory muscle endurancebetween these children at differing stages of puberty, it doesidentify that it is not as a result of differences in breathingstrategy, and thus we can obviously speculate as to thephysiological cause. Is it a consequence of intrinsicdifferences in the muscle itself, or a result of differencesin pulmonary mechanics? As always, we require furtherstudies to be performed, but Koechlin et al.7 show thatalthough there is a close relationship between strength andendurance, the link is not directly proportional, and endu-rance properties could have a greater bearing on the abilityof a patient to cope with a prolonged respiratory load.

—NICHOLAS HART, MRCP, PhD*Lane Fox Unit

Guy’s and St. Thomas’ NHS Foundation TrustSt. Thomas’ Hospital

London, UK

REFERENCES

1. American Thoracic Society/European Respiratory Society. State-

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2. Hart N, Hawkins P, Hamnegard C-H, Green M, Moxham J, Polkey

MI. A novel clinical test of respiratory muscle endurance. Eur

Respir J 2002;19:232–239.

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disease severity in children and young adults with cystic fibrosis.

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