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Perception of Dyspnea in Patients With Neuromuscular Disease^*

^* From the Fondazione Don C. Gnocchi, ONLUS, Pozzolatico (Firenze), Italy.

Correspondence to: Giorgio Scano MD, FCCP, Section of Respiratory Disease, Fondazione Don C. Gnocchi, ONLUS, Pozzolatico, Via Imprunetana, Pozzolatico (Firenze) 50020 Italy; e-mail: g.scano{at}dfc.unifi.it

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 [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 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 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/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.

Key Words: breathing pattern • dyspnea • neuromuscular coupling • neuromuscular disease • respiratory drive • respiratory muscles

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				N Ambrosino and M Serradori Determining the cause of dyspnoea: linguistic and biological descriptors Chronic Respiratory Disease, July 1, 2006; 3(3): 117 - 122. [PDF]

				G. Scano, L. Stendardi, and M. Grazzini Understanding dyspnoea by its language Eur. Respir. J., February 1, 2005; 25(2): 380 - 385. [Abstract] [Full Text] [PDF]