Reliability and acceptability of measuring sniff nasal inspiratory pressure (SNIP) and peak inspiratory flow (PIF) to assess respiratory muscle strength in older adults: a preliminary study

Abstract

Sniff nasal inspiratory pressure (SNIP) and peak oral inspiratory flow (PIF) are portable, relatively new methods for indirect measurement of respiratory muscle strength. The reliability and acceptability of these measures were investigated in older adults. The study included 21 self-reported healthy adults, aged 65-84years (mean 73.5; SD 6.4years). Participants were tested in a sitting position on two occasions, 1week apart. The best of three attempts for PIF measured through the mouth, and five for each nostril for SNIP were recorded. Reliability was tested using intra-class correlation coefficient (ICC), standard error of measurement, minimal detectable change (MDC) and Bland and Altman analysis. Feedback on the measures in relation to ease of completion and preference was obtained using a semi-structured interview. Between-day reliability of SNIP and PIF were ICC3,1 0.76 (95% CI 0.49-0.9) and 0.92 (0.81-0.97), respectively. Standard error of measurement for SNIP (11.94cmH2O) and MDC (33.10cmH2O) were at the least 61% higher than for PIF. The participants reported difficulties in performing SNIP, rating it as being less easy and uncomfortable to perform than PIF, with a higher rate of missing data for SNIP due to participants' dislike of the test. The wide range of SNIP readings, lower ICC value and negative user feedback are suggestive of a less robust and unacceptable clinical measure. PIF showed excellent reliability and acceptability and is therefore recommended for assessing inspiratory muscle strength in older people without known obstructive lung disease.