The role of facemask spirometry in motor neuron disease.

The role of facemask spirometry in motor neuron disease Respiratory failure is the most frequent cause of death in people with motor neuron disease (MND). Vital capacity and maximal inspiratory and expiratory mouth pressures are the methods most commonly used to assess respiratory muscle impairment. Forced vital capacity (FVC) at diagnosis , and the rate of decline, are predictors of survival. An FVC of <50% predicted is proposed by the National Institute of Clinical Excellence (NICE, UK) as an indication of the need for evaluation for non-invasive ventilation. 1 For many patients with MND who have facial or bulbar muscle weakness, standard spirometry with a mouthpiece or tube is inaccurate due to mouth leaks as they are unable to effectively seal their lips around the tube/mouthpiece. Sniff nasal inspiratory pressure (SNIP), and maximal inspiratory mouth pressure (PiMax) may be preferable, but are less widely available and not always successful. 2 Mask spirometry has been used but not validated in MND 2 and in healthy volunteers, tube spirometry gives greater Figure 1 (A) Bland–Altman plot showing that mask readings were higher in 36 cases, equal to the tube in one and lower in 17. The mask gave significantly greater values for FVC than the tube, the mean difference was 0.19 l (95% CI 0.07 to 0.31; p=0.0024, paired Student t test). In five subjects, the difference was >1 l (B) Linear regression fitted to predict mask results from tube results gives: Mask (litres)= 0.61+0.80 Tube (litres) (R 2 =90%). The equivalence line (intercept) is >0 and slope <1, that is estimated mask FVC is higher for low values and lower for high values (above approximately 3 l). (C) For patients with both FVC measurements, the mask value was higher or equal in 21/24 (88%) of cases with bulbar disease, and 15/30 (50%) with non-bulbar disease (Fisher's exact test 0.004). values than a mask. 3 We compared mask and tube interfaces for spirometry in subjects with MND. Consecutive patients were approached in our MND clinic. Exclusions included continuous ventilator dependence, trache-ostomy and standard contraindications for spirometry. Bulbar involvement was quantified using the first three questions of the revised Amyotrophic Lateral Sclerosis Functional Rating Scale (b ALSFRS r score) and a score <9/12 defined important bulbar symptoms. FVC was measured with a calibrated hand-held spirometer via a tube or a face mask (Leardal, child No.4) in randomised order. PiMax and SNIP were also …