Postural breathing pattern changes in patients with myotonic dystrophy

We recorded by pneumotachography the breathing in nine patients with myoton ic dystrophy (MD), both seated and supine and with eyes open in both positi ons. Irregular breathing (coefficient of variation > 20% for VT and TTOT) w as observed in six of the patients, two of whom showed irregularity in both positions whilst the remaining four had irregular breathing only when supi ne. In addition, in this latter group, irregularities first appeared in VT and only after a few minutes in TTOT. Whereas in the group exhibiting irreg ular breathing in both seated and supine positions, irregularities were obs erved throughout the recording. However, no significant difference in any v entilatory variable was observed as between the two postures. Rib cage (RC) and abdomen (AB) motions were recorded by uncalibrated respiratory inducta nce plethysmography. Although for MD patients the mean values of the RC/AB ratio lay within the normal range the relative decrease in value as between seated (0.78 +/- 0.52) and supine (0.31 +/- 0.13) position was less than i n healthy subjects. These observations suggest that MD may cause deficienci es in several mechanisms. Analyses of the respiratory pattern in each patie nt may provide information leading to the identification of the impaired re spiratory mechanisms. (C) 2000 Elsevier Science B.V. All rights reserved.