Chest
Volume 105, Issue 4, April 1994, Pages 1163-1170
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Control of Breathing and Respiratory Muscle Strength in Patients With Multiple Sclerosis

https://doi.org/10.1378/chest.105.4.1163Get rights and content

In 11 patients with moderately severe multiple sclerosis, lasting 11.2± 7.3 years, in stable condition, and in 10 age- and sex-matched control subjects, we investigated lung function, respiratory muscle strength, and ventilatory control system. Respiratory muscle strength was assessed by measuring maximal inspiratory and expiratory mouth pressures (Pimax and PEmax, respectively). Respiratory central drive was evaluated in terms of neuromuscular (P0.1) and ventilatory ( V˙e) output, breathing room air and during CO2 rebreathing. In the absence of any significant impairment of lung function, patients showed a reduction of Pimax and PEmax amounting to about 40 percent and 60 percent of the predicted value at functional residual capacity (FRC), respectively; a significant, inverse correlation was found between both Pimax and PEmax at FRC and the severity score of the disease. While at rest V˙e was similar to that of control subjects, baseline P0.1 was significantly higher in patients (1.97 ± 0.79 vs 0.97 ± 0.20 cm H2O, p<0.005). Compared with the control group, during CO2 rebreathing P0.1/PETCO2 slope, although less steep, was not dissimilar in patients (0.34 ± 0.13 vs 0.46± 0.19 cm H2O/mm Hg, NS); on the other hand, V˙e/PetCO2 slope was much lower in the patient group (1.93 ± 0.91 vs 3.27±1.11 L/min/mm Hg, p<0.01) and was significantly related to the functional stage of disease and to Pimax and PEmax values at FRC. These results indicate that in patients with clinically stable, moderately severe multiple sclerosis, the respiratory muscle function is abnormal. Moreover, the inspiratory drive at rest is increased and the drive response to CO2 appears normal, while the ventilatory response to CO2 is significantly impaired. Respiratory muscle weakness (and/or lack of coordination) could explain, at least in part, the lower ventilatory response in these patients, whereas the mechanism of increased rate of the initial inspiratory force generation remains unclear.

Section snippets

METHODS

Eleven patients, 10 of whom were female (mean age, 44.1±12.0 years) with stable MS, lasting 11.2±7.3 years, were studied when they were inpatients enrolled in a neuromuscular rehabilitation program, together with a group of 10 control subjects, age (36.8 ± 6.2 years) and sex matched. The neurologic impairment was scored from 0 to 10, according to the expanded disability status scale (EDSS)8 by the neurologists involved in the study. The mean EDSS was 6.7 ± 1.2, ranging from 5 to 9.5. In the

RESULTS

Lung volumes, usual parameters derived from the flow-volume curves, and maximal inspiratory and expiratory pressures are listed in Table 2 for each patient as individual data and for both patients and control subjects as percent predicted.

Results of lung function tests were essentially normal in the MS group. However, despite normal FRC (89 percent of predicted), patient 2 had greatly reduced VC (27 percent of predicted) and markedly increased RV (157 percent of predicted).

The MVV was on the

DISCUSSION

First of all, the results of this study indicate that patients with moderately severe MS (ambulatory with assistance and wheelchair bound), in stable condition, exhibit on average a 40 percent and 60 percent reduction of Pimax and PEmax, respectively. In these patients, however, this level of respiratory muscle dysfunction does not appear severe enough to induce significant restrictive changes in lung volumes.

In other neuromuscular diseases,5 the decline of Pimax and PEmax precedes changes in

ACKNOWLEDGMENTS

The authors wish to thank Rita Fraboni for her valuable technical assistance.

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