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Respir Care. 2015 Apr;60(4):533-9. doi: 10.4187/respcare.03367. Epub 2015 Jan 13.

Muscle impairment in neuromuscular disease using an expiratory/inspiratory pressure ratio.

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Physical Therapy Department of Universidade Federal do Rio Grande do Norte, Natal, Brazil
Physical Therapy Department of Universidade Federal do Rio Grande do Norte, Natal, Brazil.
Physical Therapy Department of Universidade Federal de Pernambuco, Recife, Brazil.
Dipartimento di Elettronica, Informazione e Bioingegneria-Politecnico di Milano, Milan, Italy.
Hospital Universitário Onofre Lopes-Universidade Federal do Rio Grande do Norte, Natal, Brazil.
Physical Therapy Department of Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.



Neuromuscular diseases (NMDs) lead to different weakness patterns, and most patients with NMDs develop respiratory failure. Inspiratory and expiratory muscle strength can be measured by maximum static inspiratory pressure (PImax) and maximum static expiratory pressure (PEmax), and the relationship between them has not been well described in healthy subjects and subjects with NMDs. Our aim was to assess expiratory/inspiratory muscle strength in NMDs and healthy subjects and calculate PEmax/PImax ratio for these groups.


Seventy (35 males) subjects with NMDs (amyotrophic lateral sclerosis, myasthenia gravis, and myotonic dystrophy), and 93 (47 males) healthy individuals 20-80 y of age were evaluated for anthropometry, pulmonary function, PImax, and PEmax, respectively.


Healthy individuals showed greater values for PImax and PEmax when compared with subjects with NMDs. PEmax/PImax ratio for healthy subjects was 1.31 ± 0.26, and PEmax%/PImax% was 1.04 ± 0.05; for subjects with NMDs, PEmax/PImax ratio was 1.45 ± 0.65, and PEmax%/PImax% ratio was 1.42 ± 0.67. We found that PEmax%/PImax% for myotonic dystrophy was 0.93 ± 0.24, for myasthenia gravis 1.94 ± 0.6, and for amyotrophic lateral sclerosis 1.33 ± 0.62 when we analyzed them separately. All healthy individuals showed higher PEmax compared with PImax. For subjects with NMDs, the impairment of PEmax and PImax is different among the 3 pathologies studied (P < .001).


Healthy individuals and subjects with NMDs showed higher PEmax in comparison to PImax regarding the PEmax/PImax ratio. Based on the ratio, it is possible to state that NMDs show different patterns of respiratory muscle strength loss. PEmax/PImax ratio is a useful parameter to assess the impairment of respiratory muscles in a patient and to customize rehabilitation and treatment.


PEmax/PImax ratio; neuromuscular diseases; respiratory muscle imbalance; respiratory muscle strength; respiratory therapy

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