Chest

Chest

Volume 120, Issue 2, August 2001, Pages 402-408
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Clinical Investigations
Dyspnea
Perception of Dyspnea in Patients With Neuromuscular Disease

https://doi.org/10.1378/chest.120.2.402Get rights and content

Background

The perception of dyspnea is not a prominent complaint of resting patients with neuromuscular disease (NMD). To our knowledge, no study has been addressed at evaluating the interrelationships among lung mechanics, respiratory motor output, and the perception of dyspnea in patients with NMD receiving ventilatory stimulation.

Material

Eleven patients with NMD (mean ± SD age, 44 ± 11.8 years; 5 men) of different etiology and a group of normal subjects matched for age and sex (control subjects).

Methods

While patients were breathing room air, lung volumes, arterial blood gases, the pattern of breathing (minute ventilation [ V˙e], tidal volume[Vt], respiratory frequency, inspiratory time), and maximal (less negative) esophageal pressure during a sniff maneuver (Pessn), as an index of inspiratory muscle strength, were measured. Then we evaluated the response to hypercapnic-hyperoxic stimulation (hypercapnic-hyperoxic rebreathing test [RT]) in terms of breathing pattern, inspiratory swing of pleural pressure (Pessw), and inspiratory effort (Pessw[%Pessn]). During the RT, dyspnea was assessed every 30 s using a modified Borg scale (0 to 10).

Results

Pulmonary volumes were reduced in seven patients, and Pco2 was out of proportion to V˙e in four patients. Group Pessn was 42.8 ± 23.6 cm H2O in patients and 107 ± 20.4 cm H2O in control subjects (p < 0.001). Dynamic elastance (Eldyn)[p = 0.0016] and Pessw(%Pessn) [p < 0.0005] were higher in patients. During the RT, Borg/CO2, Pessw(%Pessn)/CO2, and Borg/Pessw(%Pessn) were similar in the two groups, while V˙e/CO2 and Vt/CO2 were lower in patients (p < 0.0002 for both). As a consequence, for unit change in Vt (percentage of predicted vital capacity [%VC]), greater changes in Pessw(%Pessn) were associated with greater Borg scores in patients. Baseline Eldyn related to Pessw(%Pessn)/Vt(%VC) during hypercapnia (r2 = 0.85), an index of neuroventilatory coupling of the ventilatory pump (NVC). NVC predicted a good amount of the variability in Borg/ V˙e (r2 = 0.46, p < 0.02).

Conclusions

In this subset of NMD patients during hypercapnic stimulation, a normal inspiratory motor output per unit change in Pco2 results in a shallow breathing pattern. The consequent impairment of NVC underlies the higher scoring of dyspnea in these patients.

Section snippets

Patients

Eleven consecutive patients (5 men) aged 44.7 ± 11.8 years (range, 23 to 72 years), including 7 patients with limb-girdle dystrophy, 2 patients with Duchenne muscular dystrophy, and 2 patients with amyotrophic lateral sclerosis and no respiratory complaints, were studied. Patients were ambulatory and wheelchair bound. The standard criteria were used to select patients.1213

None of the patients had a scoliosis or any abnormalities shown on chest radiography or obvious abnormalities in diaphragm

Results

Anthropometric and functional characteristics of the subjects are depicted in Table 1. Seven patients exhibited a mild-to-moderate restrictive pattern, and in four of these seven patients, Pco2 was out of proportion to V˙e. Group Pessn was lower while inspiratory effort (Pessw[%Pessn]) and Eldyn were significantly greater in patients compared to control subjects (Table 2). During the RT, Borg/Pco2, Pessw(%Pessn)/Pco2, and both slope and intercept of the relationship between changes in Borg

Discussion

In this subset of patients with NMD, a worse-than-normal neuroventilatory coupling of the respiratory pump (NVC) was found to be associated with a greater perception of dyspnea during CO2-stimulated breathing. Changes in NVC with hypercapnia reflected the mechanical abnormalities of the respiratory system at rest. A normal central motor output did not appear to be a major determinant of the increased dyspnea.

First of all, we decided to give patients a global definition of the sensation of

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    This study was supported by a grant from Fondazione Don C. Gnocchi, ONLUS, Pozzolatico (Firenze), and from the Ministero dell'Università e della Ricerca Scientifica e Tecnologica of Italy.

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    Copyright © 2001 The American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.