Abstract
ObjectiveTo evaluate sensitivity/specificity of the maximum relaxation rate (MRR) of inspiratory muscles, amplitude of electromyographic activity of the sternocleidomastoid (SCM), scalene (SCA), parasternal (2ndIS) and rectus abdominis (RA) muscles; lung function and respiratory muscle strength in subjects with Myotonic dystrophy type 1 (DM1) compared with healthy subjects.Design and methodsQuasi-experimental observational study with control group. MRR of inspiratory muscles, lung function and amplitude of the electromyographic activity of SCM, SCA, 2ndIS and RA muscles during maximum inspiratory pressure (PImax), maximum expiratory pressure (PEmax) and sniff nasal inspiratory pressure (SNIP) tests were assessed in eighteen DM1 subjects and eleven healthy.ResultsMRR was lower in DM1 group compared to healthy (P = 0.001) and was considered sensitive and specific to identify disease in DM1 and discard it in controls, as well as SNIP% (P = 0.0026), PImax% (P = 0.0077) and PEmax% (P = 0.0002). Contraction time of SCM and SCA was higher in DM1 compared to controls, respectively, during PImax (P = 0.023 and P = 0.017) and SNIP (P = 0.015 and P = .0004). The DM1 group showed lower PImax (P = .0006), PEmax (P = 0.0002), SNIP (P = 0.0014), and higher electromyographic activity of the SCM (P = 0.002) and SCA (P = 0.004) at rest; of 2ndIS (P = 0.003) during PEmax and of SCM (P = 0.02) and SCA (P = 0.03) during SNIP test.ConclusionsMD1 subjects presented restrictive pattern, reduced respiratory muscle strength, muscular electrical activity and MRR when compared to higher compared to controls. In addition, the lower MRR found in MD1 subjects showed to be reliable to sensitivity and specificity in identifying the delayed relaxation of respiratory muscles.
Highlights
Myotonic dystrophy type 1 (MD1), or Steinert’s disease, is the most common form of dystrophy in adolescents and adults, and the second most common neuromuscular disease [1,2,3]
The funders had no role in study design, data collection and maximum relaxation rate (MRR) was lower in DM1 group compared to healthy (P = 0.001) and was considered sensitive and specific to identify disease in DM1 and discard it in controls, as well as sniff nasal inspiratory pressure (SNIP)% (P = 0.0026), Maximum inspiratory pressure (PImax)% (P = 0.0077) and Maximum expiratory pressure (PEmax)% (P = 0.0002)
Contraction time of SCM and SCA was higher in DM1 compared to controls, respectively, during PImax (P = 0.023 and P = 0.017) and SNIP (P = 0.015 and P = .0004)
Summary
Myotonic dystrophy type 1 (MD1), or Steinert’s disease, is the most common form of dystrophy in adolescents and adults, and the second most common neuromuscular disease [1,2,3]. The classic form of MD1 is characterized by weakness and atrophy in skeletal muscles, myotonia, cardiac conduction abnormalities, cognitive impairment and myocardial changes. The respiratory impairment in MD1, is rather complex because progressive muscle weakness is associated to different degrees of central respiratory control abnormalities causing alveolar hypoventilation[9]. CO2 insensitivity occur in MD1 independently of lung function impairment and respiratory muscle weakness [10]. In addition the participation of myotonia in DM1 respiratory restriction is not fully clarified
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