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Fog-induced Cough with Impaired Respiratory Sensation in Congenital Central Hypoventilation Syndrome

¹ Dipartimento di Area Critica Medico Chirurgica, ² Dipartimento di Scienze Fisiologiche, and ³ Dipartimento di Pediatria, Università degli Studi di Firenze, Florence, Italy; and ⁴ University of London, London, United Kingdom

Correspondence and requests for reprints should be addressed to Giovanni A. Fontana, M.D., Dipartimento di Area Critica Medico Chirurgica, Sezione di Medicina Respiratoria, Università degli Studi di Firenze, Viale G.B. Morgagni, 85-50134 Florence, Italy. E-mail: g.fontana{at}dac.unifi.it

Rationale: Congenital central hypoventilation syndrome (CCHS) is a genetic disorder mainly characterized by failure of automatic control of breathing, causing alveolar hypoventilation. Little is known regarding cough in CCHS. Parental reports indicate that patients cough normally during airway infections; however, previous studies have demonstrated no cough response to fog inhalation.

Objectives: To evaluate the sensory and motor components of cough, respiratory sensations, and changes in ventilation evoked by fog inhalation in children with CCHS and in sex- and age-matched control subjects.

Methods: Cough threshold was measured and cough intensity was indexed in terms of cough peak expiratory flow and integrated abdominal electromyographic activity. The pattern of breathing was recorded by inductive plethysmography. Respiratory sensations were also investigated.

Measurements and Main Results: All control subjects and six of seven patients coughed in response to fog inhalation. The seventh coughed with citric acid aerosol inhalation. Cough threshold values were similar in control subjects (range, 0.40–2.22 ml/min) and patients (range, 0.40–3.26 ml/min). Mean values of cough peak expiratory flow and of integrated abdominal electromyographic activity–related variables during coughing were also similar and corresponded to 80% of those recorded during maximum voluntary cough. Cough appearance was preceded by respiratory sensations and increases (P < 0.01) in ventilation in the control subjects but not in the patients.

Conclusions: Children with CCHS have normal cough threshold and motor responses to fog inhalation. However, the lack of respiratory sensations and the likely related ventilatory changes typically elicited by tussigenic fog concentrations suggest a neural sensory deficit that may increase the risk of respiratory disease in these patients.

Key Words: cough • respiratory sensations • control of breathing • central nervous system.

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Patients with congenital central hypoventilation syndrome (CCHS) may have an impaired cough reflex to fog inhalation, suggesting a deficit of substrates subserving cough in the disease. There is no information on the ventilatory adjustments and respiratory sensations associated with fog inhalation. What This Study Adds to the Field Voluntary and reflex cough in CCHS are normal, suggesting that the neural substrates subserving cough are also normal. Reduced awareness of airway irritation in CCHS suggests that these patients have a central neural sensory deficit.

 

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