Date Published: January 31, 2013
Publisher: Public Library of Science
Author(s): Nadim Srour, Carole LeBlanc, Judy King, Douglas A. McKim, Mauricio Rojas. http://doi.org/10.1371/journal.pone.0056676
Pulmonary function abnormalities have been described in multiple sclerosis including reductions in forced vital capacity (FVC) and cough but the time course of this impairment is unknown. Peak cough flow (PCF) is an important parameter for patients with respiratory muscle weakness and a reduced PCF has a direct impact on airway clearance and may therefore increase the risk of respiratory tract infections. Lung volume recruitment is a technique that improves PCF by inflating the lungs to their maximal insufflation capacity.
Our goals were to describe the rate of decline of pulmonary function and PCF in patients with multiple sclerosis and describe the use of lung volume recruitment in this population.
We reviewed all patients with multiple sclerosis referred to a respiratory neuromuscular rehabilitation clinic from February 1999 until December 2010. Lung volume recruitment was attempted in patients with FVC <80% predicted. Regular twice daily lung volume recruitment was prescribed if it resulted in a significant improvement in the laboratory. There were 79 patients included, 35 of whom were seen more than once. A baseline FVC <80% predicted was present in 82% of patients and 80% of patients had a PCF insufficient for airway clearance. There was a significant decline in FVC (122.6 mL/y, 95% CI 54.9–190.3) and PCF (192 mL/s/y, 95% 72–311) over a median follow-up time of 13.4 months. Lung volume recruitment was associated with a slower decline in FVC (p<0.0001) and PCF (p = 0.042). Pulmonary function and cough decline significantly over time in selected patients with multiple sclerosis and lung volume recruitment is associated with a slower rate of decline in lung function and peak cough flow. Given design limitations, additional studies are needed to assess the role of lung volume recruitment in patients with multiple sclerosis.
Multiple sclerosis (MS) is an inflammatory disease of the central nervous system, leading to neuron demyelination and muscle weakness. Respiratory problems in patients with MS can be due to respiratory muscle weakness, bulbar dysfunction or abnormalities of breathing control.  Reduced muscle strength and spasticity result in lower lung volumes and, with progression, stiffness of the lung and chest wall due to a diminished range of motion.  With the reduction in mobility, loose connective tissue within muscles is converted to dense connective tissue with an increase in elastance. The result is an increased work of breathing for a muscle system which is already weakened. Furthermore, loss of lung volume and resulting atelectasis diminishes alveolar surfactant, the most important element preventing alveolar collapse. Alveolar stretch is the most potent stimulus for the production of surfactant, thereby maintaining lung compliance and gas exchange. .
We collected data retrospectively from all patients with multiple sclerosis seen in the CANVent clinic (Canadian Alternatives in Non-invasive Ventilation) at the Ottawa Hospital Rehabilitation Centre from February 1999 until December 2010. Multiple sclerosis was diagnosed by the treating neurologist and patients were referred from the physiatry clinic in our institution or from other clinics for inability to manage secretions, sleep-disordered breathing, low voice volume, when they were wheelchair-assisted or for any other respiratory symptoms. This study was approved by the Ottawa Hospital Research Ethics Board, which did not require that informed consent be obtained.
There were 79 patients included in the cohort (Table 1), 35 (44.3%) of whom were seen more than once. Among patients seen more than once, the median number of visits was 2 (IQR 2-4) with a median follow-up of 13.4 months (IQR 4.4–58.9). No patient was on invasive ventilation during the follow-up period. One patient was on non-invasive ventilation for about 5 of 10 years of follow-up. Kyphoscoliosis was present in 27/73 patients (37.0%). Patients were significantly disabled with a mean EDSS of 7.33 (95% CI 6.97–7.70). Few were on disease-modifying therapy, which included glatiramer acetate and interferon β-1a. No patient was on chronic corticosteroid therapy. Fifty patients (67.6%) were on medication for spasticity. Overall, 64 patients (82%) had a baseline FVC <80% of predicted and 63 patients (80%) had a baseline PCF <270 L/min (4.5 L/s). Measurements following lung volume recruitment were obtained in 39 patients with an FVC <80% of predicted and, at their request, in 2 patients with an FVC of 81.4% and 87.6% of predicted respectively. While impairment of respiratory function has been described in multiple sclerosis, this is, to our knowledge, the first description of the decline of respiratory function over time in this population, as well as the first description of the use of lung volume recruitment in this population. We found that the FVC decreased significantly over time, more than can be expected in healthy individuals.  The PCF also decreased significantly over time in our selected population. Furthermore, our results suggest that individuals who demonstrate an improvement in PCF after lung volume recruitment have a lower rate of decline of both FVC and PCF compared to individuals who do not demonstrate an improvement in PCF after lung volume recruitment, despite taking into account the lower baseline values. Source: http://doi.org/10.1371/journal.pone.0056676