The importance of maintaining the same order of performance of lung function and SNIP tests in patients with amyotrophic lateral sclerosis

Abstract

Objective: Sniff nasal inspiratory pressure (SNIP), a useful tool for the assessment of diaphragm function in patients with Amyotrophic Lateral Sclerosis (ALS), is usually performed together with lung function tests. The aim of this study was to evaluate whether SNIP results are influenced by the order of performance of the tests. Methods: 103 consecutive patients (65% males, 80% spinal onset) were recruited. The highest value of up to 10 sniffs, was recorded before (SNIPT0) and after (SNIPT1) the assessment of lung function, peak cough (PCF), and peak expiratory flow (PEF). Results: Mean and median values were respectively 31.10 and 26.00 cm H₂O for SNIPT0 and 28.93 and 25.00 cm H₂O for SNIPT1 (p < 0.001). The median value of (SNIPT1 − SNIPT0)/SNIPT0% was −7.10. Patients showing post lung function SNIP values above the median were included in Group 1 (51%), the others in group 2 (49%). Group 2 showed more severe baseline ventilatory restriction and reduction in PCF than Group 1. Positive direct relationships were found between SNIPT0 and SNIPT1 (coefficient β = 0.95, p < 0.001), and forced vital capacity and forced expiratory volume at one second. Conclusions: 50/103(49%) patients with ALS show a significant reduction in SNIP when assessed shortly after the performance of lung function tests. These patients suffer from more severe ventilatory restriction than patients not showing the reduction. Our findings suggest standardizing the order of respiratory tests during the follow up in order to avoid to misestimate the real strength of inspiratory muscles.

Keywords:

• Amyotrophic lateral sclerosis
• respiratory muscle
• motoneuron disease
• neuromuscular disease
• lung function tests

Aknowledgments

The authors would like to thank Prof. Fiorito for the English revision.

Declaration of Interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.