Spirometry in healthy subjects: do technical details of the test procedure affect the results?

Spirometry should follow strict quality criteria. The American Thoracic Society (ATS) recommends the use of a noseclip; however there are controversies about its need. ATS also indicates that tests should be done in the sitting position, but there are no recommendations neither about position of the upper limbs and lower limbs nor about who should hold the mouthpiece while performing the maneuvers: evaluated subject or evaluator. To compare noseclip use or not, different upper and lower limbs positions and who holds the mouthpiece, verifying if these technical details affect spirometric results in healthy adults. One hundred and three healthy individuals (41 men; age: 47 [33-58] years; normal lung function: FEV₁/FVC = 83±5, FEV₁ = 94 [88-104]%predicted, FVC = 92 [84-102]%predicted) underwent a protocol consisting of four spirometric comparative analysis in the sitting position: 1) maximum voluntary ventilation (MVV) with vs without noseclip; 2) FVC performed with vs without upper limbs support; 3) FVC performed with lower limbs crossed vs lower limbs in neutral position; 4) FVC, slow vital capacity and MVV comparing the evaluated subject holding the mouthpiece vs evaluator holding it. Different spirometric variables presented statistically significant difference (p