Postprandial effects on twitch transdiaphragmatic pressure

Man, William D.-C.; Luo, Y-M; Mustfa, Naveed; Rafferty, Gerrard F.; Glerant, J C H; Polkey, Michael I.; Moxham, John

doi:10.1183/09031936.02.00302702

Cited by 29 publications

(16 citation statements)

References 13 publications

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“…Despite the expense and bulk of the additional equipment, BAMPS has a significant advantage over CMS and aMS in that it reliably produces a supramaximal Pdi,tw [6,54,55] that is closely similar to values obtained with optimal electrical stimulation. This is probably because BAMPS results in less co-activation of extradiaphragmatic muscles, demonstrated by the similar oesophageal and gastric pressure contributions to Pdi,tw observed with BAMPS and electrical stimulation [54].…”

Section: Unilateral/bilateral Anterolateral Magnetic Phrenic Nerve Stmentioning

confidence: 92%

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Magnetic stimulation for the measurement of respiratory and skeletal muscle function

Man¹

2004

European Respiratory Journal

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117

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Respiratory and skeletal muscle function is of interest in many areas of pulmonary and critical care medicine. The capacity of the respiratory muscle pump to respond to the load imposed by disease is the basis of an understanding of ventilatory failure. Over the last four decades, considerable progress has been made in quantifying the capacity of the respiratory muscles, in terms of strength, endurance and fatigue. With the development of magnetic stimulation, it has recently become possible to nonvolitionally assess the respiratory muscles in a clinically acceptable way. This is of particular interest in the investigation of patients receiving critical care, those with neuromuscular disease, and in children where volitional efforts are either not possible or likely to be sub-maximal. Furthermore, the adaptation of these techniques to quantify the strength of peripheral muscles, such as the quadriceps, has allowed the effects of muscle training or rehabilitation, uninfluenced by learning effect, to be assessed. This article focuses on the physiological basis of magnetic nerve stimulation, and reviews how the technique has been applied to measure muscle strength and fatigue, with particular emphasis upon the diaphragm. The translation of magnetic stimulation into a clinical tool is described, and how it may be of diagnostic, prognostic and therapeutic value in several areas of pulmonary medicine. In particular, the use of magnetic stimulation in neuromuscular disease, the intensive care setting, chronic obstructive pulmonary disease and paediatrics will be discussed. The nonvolitional assessment of skeletal musclesFor routine muscle strength measurements, the force generated from a maximum voluntary contraction (MVC) is often used. However volitional, effort-dependent manoeuvres for measuring strength are not always suitable for patients as the ability to perform a true MVC relies upon subject motivation and cooperation. This is particularly so in patients on intensive care units (ICU), children, patients with cognitive difficulties, and those patients prevented from performing a true MVC by pain (for example, following surgery). However, even in well-motivated subjects, sub-maximal muscle activation is common in routine clinical practice [1]. As volitional manoeuvres are influenced by a learning effect, the value of MVC is also limited in studies of training or rehabilitation. Consequently, there has been a need for nonvolitional methods to assess muscle strength. Skeletal muscle physiologySkeletal muscle is controlled by electrical impulses conducted by motor neurones that lead to the release of acetylcholine from the motor end plate, thus depolarising the muscle cell membrane. The force generated by muscle contraction is dependent upon a number of factors, including the number of muscle fibres stimulated, muscle length at the time of stimulation and the frequency of stimulation. The force-frequency curve of a muscle is of particular relevance in the understanding of nonvolitional techniques to asse...

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Section: Unilateral/bilateral Anterolateral Magnetic Phrenic Nerve Stmentioning

confidence: 92%

“…However, both abdominal binding and a recent meal increase Pdi,tw [55,63], presumably through a change in abdominal compliance. Studies in intensive care are best performed at least 1-2 h after nasogastric feeding has been stopped, whilst in the outpatient setting, subjects should be studied with the abdomen unbound (e.g.…”

Section: Confounding Factorsmentioning

confidence: 99%

Magnetic stimulation for the measurement of respiratory and skeletal muscle function

Man¹

2004

European Respiratory Journal

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117

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“…This can be established by observing a plateau in the stimulus-response curve. In this study, supramaximality of bilateral anterolateral magnetic phrenic nerve stimulation was not formally assessed in order to limit the number of stimulations administered; however, the authors have previously found the technique to be supramaximal or close to supramaximal [21,28]. The supramaximality of femoral nerve stimulation was formally confirmed in all patients on each occasion.…”

Section: Supramaximalitymentioning

confidence: 99%

Acute effect of oral steroids on muscle function in chronic obstructive pulmonary disease

Hopkinson

Man²,

Dayer³

et al. 2004

European Respiratory Journal

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Prospective data to support the hypothesis that corticosteroids are a significant cause of muscle weakness in patients with chronic obstructive pulmonary disease (COPD) are lacking.The authors studied respiratory and quadriceps muscle function, using both volitional techniques and magnetic nerve stimulation, as well as measuring metabolic parameters during incremental cycle ergometry, in 25 stable COPD patients. The forced expiratory volume in one second was 37.6¡21.4 % predicted, before and after a 2-week course of o.d. prednisolone 30 mg. Quadriceps strength was also assessed in 15 control patients on two occasions.Only two patients met the British Thoracic Society definition of steroid responsiveness. There was no change either in sniff transdiaphragmatic pressure (pre: 96.8¡19.7 cmH 2 O; post: 98.6¡22.4 cmH 2 O) or in twitch transdiaphragmatic pressure elicited by bilateral anterolateral magnetic phrenic-nerve stimulation (pre: 16.8¡9.1 cmH 2 O; post: 17.9¡10 cmH 2 O). Quadriceps twitch force did not change significantly either in the steroid group (pre: 9.5¡3.1 kg; post: 8.9¡3.7 kg) or in the control patients (pre: 8.1¡2.7 kg; post: 7.9¡2.2 kg). There were no changes in either peak or isotime ventilatory and metabolic parameters during exercise.In conclusion, in stable patients with chronic obstructive pulmonary disease, a 2-week course of 30 mg prednisolone daily does not cause significant skeletal muscle dysfunction or alter metabolic parameters during exercise.

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“…For the abdominal muscles, force output is estimated by measuring the gastric pressure response to magnetic stimulation of the thoracic nerve roots (61). For nerve stimulation to provide a valid measure of respiratory muscle fatigue it is important to carefully control for several potential sources of error, including supramaximal stimulation (20,128), isovolumic conditions (47,114), abdominal compliance (58,73), and postactivation potentiation (71,143).…”

Section: Exercise-induced Respiratory Muscle Fatiguementioning

confidence: 99%

Exercise-induced respiratory muscle fatigue: implications for performance

Romer

Polkey²

2008

Journal of Applied Physiology

256

212

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Romer LM, Polkey MI. Exercise-induced respiratory muscle fatigue: implications for performance. J Appl Physiol 104: 879 -888, 2008. First published December 20, 2007 doi:10.1152/japplphysiol.01157.2007.-It is commonly held that the respiratory system has ample capacity relative to the demand for maximal O 2 and CO2 transport in healthy humans exercising near sea level. However, this situation may not apply during heavy-intensity, sustained exercise where exercise may encroach on the capacity of the respiratory system. Nerve stimulation techniques have provided objective evidence that the diaphragm and abdominal muscles are susceptible to fatigue with heavy, sustained exercise. The fatigue appears to be due to elevated levels of respiratory muscle work combined with an increased competition for blood flow with limb locomotor muscles. When respiratory muscles are prefatigued using voluntary respiratory maneuvers, time to exhaustion during subsequent exercise is decreased. Partially unloading the respiratory muscles during heavy exercise using low-density gas mixtures or mechanical ventilation can prevent exercise-induced diaphragm fatigue and increase exercise time to exhaustion. Collectively, these findings suggest that respiratory muscle fatigue may be involved in limiting exercise tolerance or that other factors, including alterations in the sensation of dyspnea or mechanical load, may be important. The major consequence of respiratory muscle fatigue is an increased sympathetic vasoconstrictor outflow to working skeletal muscle through a respiratory muscle metaboreflex, thereby reducing limb blood flow and increasing the severity of exerciseinduced locomotor muscle fatigue. An increase in limb locomotor muscle fatigue may play a pivotal role in determining exercise tolerance through a direct effect on muscle force output and a feedback effect on effort perception, causing reduced motor output to the working limb muscles. respiratory muscles; exercise; diaphragm; abdominals; magnetic stimulation; metaboreflex THE PURPOSE OF THIS MINIREVIEW is to address the question of whether the respiratory demands of exercise contribute significantly toward exercise limitation, either directly through limitations of the respiratory muscle pump or indirectly through effects on limb blood flow and locomotor muscle fatigue. We describe the mechanical and metabolic costs of meeting the ventilatory requirements of exercise. We then ask whether the respiratory muscles fatigue with exercise, what factors contribute to any such fatigue, and what the implications of these factors are for exercise tolerance. Finally, we deal with the potential mechanisms by which respiratory muscle fatigue could compromise exercise tolerance and whether it is possible to overcome this potential respiratory limitation. Our review focuses on the healthy young adult exercising near sea level. However, we also consider special circumstances that determine the balance between metabolic demand and respiratory system capacity in the highly trained endurance ...

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Postprandial effects on twitch transdiaphragmatic pressure

Cited by 29 publications

References 13 publications

Magnetic stimulation for the measurement of respiratory and skeletal muscle function

Magnetic stimulation for the measurement of respiratory and skeletal muscle function

Acute effect of oral steroids on muscle function in chronic obstructive pulmonary disease

Exercise-induced respiratory muscle fatigue: implications for performance

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