Abstract
PurposeTo investigate the changes of cough sensitivity in patients with metabolic syndrome and its possible mechanisms.MethodA total of 29 metabolic syndrome (MetS) patients with OSAHS (group-1), 22 MetS patients without OSAHS (group-2), and 25 healthy controls (group-3) were included. All participants underwent a routine physical examination and completed the gastroesophageal reflux disease questionnaire (GerdQ), and the inflammatory mediator profile were determined. The cough threshold for capsaicin, induced sputum cell count and cell classification, and inflammatory mediators in induced sputum supernatants were compared. The correlation between capsaicin cough sensitivity and various indicators in the MetS population was analyzed.ResultsThe minimum concentration of inhaled capsaicin needed to induce ≥ 5 coughs (C5) was significantly different among three groups (H = 14.393, P = 0.001) and lower for group-1 and group-2 than it for group-3 (P = 0.002, P = 0.005). The percentage of neutrophils in induced sputum and the concentrations of calcitonin gene-related peptide (CGRP), substance P (SP), and interleukin 8 (IL-8) in the sputum supernatant of group-1 and group-2 were significantly higher than those of group-3. Besides, the pepsin concentrations were significantly different among the 3 groups (F = 129.362, P < 0.001), which significantly was highest in group-1 (P < 0.001) and lowest in group-3 (P < 0.001). Triglycerides, AHI, pepsin concentration and BMI were risk factors of increased capsaicin cough sensitivity.ConclusionIncreased capsaicin cough sensitivity in MetS patients is closely related to sleep apnea and gastroesophageal reflux. For patients in MetS patients without OSAHS, gastroesophageal reflux is an important factor for increased capsaicin cough sensitivity. Airway inflammation, especially airway neurogenic inflammation, may also play a role in the pathogenesis of increased capsaicin cough sensitivity.Trial registration The protocol was registered in the Chinese Clinical Trials Register (http://www.chictr.org.cn/) (ChiCTR1800014768). Written informed consent was obtained from all participants before enrollment.
Highlights
Chronic cough is defined as cough ≥ 8 weeks with normal chest X-ray or CT scan
The pepsin concentrations were significantly different among the 3 groups (F = 129.362, P < 0.001), which significantly was highest in group-1 (P < 0.001) and lowest in group-3 (P < 0.001)
For patients in metabolic syndrome (MetS) patients without Obstructive sleep apnea–hypopnea syndrome (OSAHS), gastroesophageal reflux is an important factor for increased capsaicin cough sensitivity
Summary
Chronic cough is defined as cough ≥ 8 weeks with normal chest X-ray or CT scan. Upper airway cough syndrome, eosinophilic bronchitis, and gastroesophageal reflux-induced cough are common etiologies of chronic cough [1, 2]. Obstructive sleep apnea–hypopnea syndrome (OSAHS) has recently been considered as a possible disease that can lead to chronic cough [3]. Most cough could be controlled or relieved after treatments according to the diagnosis and treatment procedures [4]. 10–42% of chronic cough patients cannot clarify the etiology or receive effective treatment measures [5], causing refractory or persistent cough. Rare etiologies must be continuously identified, which can effectively reduce the proportion of patients with refractory cough
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