Introduction
Neuromuscular disease (NMD) is a broad spectrum of progressive diseases affecting the functioning of the muscles. When the respiratory muscles are involved in the long run, the vital capacity of the lung is reduced whereas the alternation of mechanical properties of the lung leads to the cough ineffectiveness. Particularly, patients with peak cough flow (PCF) less than 270 L/min are prone to develop respiratory tract infection due to ineffective cough. While PCF offers an overall evaluation of cough efficacy, suspected respiratory muscle weakness is not quantitatively assessed. Therefore, other respiratory muscles performance parameters are required to provide additional information regarding the coughing efficiency of the patient such that early intervention can be provided to avoid sputum retention.
Objectives
To quantitatively evaluate the coughing effort of NMD patients by exploring the relationship between PCF and maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP) and sniff nasal inspiratory pressure (SNIP).
Methodology
This was a cross-sectional study in collaboration with the Department of Medicine, Queen Elizabeth Hospital (QEH). Since September 2017, NMD patients who attended the NMD clinic of QEH underwent detailed comprehensive cough assessment including measurements on PCF, MIP, MEP and SNIP conducted by experienced physiotherapists. Spearman’s rank correlation coefficient was used to quantify the relationship between different respiratory parameters. The correlation coefficient (r) above 0.5 was considered having moderate to good relationship. Receiver Operating Characteristic (ROC) curves were used to estimate the cut-off scores of MIP, MEP and SNIP.
Results & Outcome
From September 2017 to November 2018, 16 patients of NMD clinic were referred for cough assessment. 62.5% were male patients. The mean age was 59.4±12.7 years old. A significant positive correlation of PCF to MIP (r=0.606, p=0.013), MEP (r=0.531, p=0.034) and SNIP (r=0.555, p=0.026) was demonstrated. In identifying an effective cough (PCF ≥ 270L/min), the cut-off scores of MIP, MEP and SNIP were 22.0 cmH₂O, 49.5 cmH₂O and 27.5 cmH₂O respectively. The result of this pilot study showed that there is significant correlation between PCF and other respiratory muscles performance parameters. Following the identification of ineffective cough, individualized intervention could be provided to the NMD patients including manual assisted cough, air stacking, mechanical insufflation-exsufflation and nasopharyngeal suctioning. With the comprehensive cough assessment, NMD patients with ineffective cough could be early intervened before the development of pulmonary complication and hence to relieve the burden to both patients and healthcare providers.
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