SNIF test has been described as a method to explore the diaphragmatic function. But there are no defined the reference values of this test in healthy population. The investigators' hypothesis is that there is a variation on SNIF values in Mediterranean population depending on gender, age and anthropometric variables such as height and weight.

The investigators will analyze 1000 SNIF test of healthy people. The investigators will divide in 5 groups of age (20-30, 30-40, 40-50, 50-60, 60-70) and in each group the investigators will study 100 men and 100 women.

All the subjects will perform a forced spirometry, maximal inspiratory pressure (MIP) and SNIF. If spirometry and MIP are correct the investigators will consider that person has a correct diaphragmatic function and strength. Then the investigators will measure the SNIF test. With all of these SNIF values the investigators will try to achieve the reference values of this test in the different groups of age in Mediterranean population. And the investigators will compare SNIF with MIP.

Cross multicentric study. Hospitals involved: Hospital de Bellvitge, Hospital del Mar, Hospital Parc Taulí, Hospital de la Santa Creu i Sant Pau (coordinator center) and Hospital de la Vall d'Hebrón.

Inclusion Criteria:

• Healthy people with spirometry and MIP values in the reference range
• Age between 20 and 70 years old
• Caucasian race

Exclusion Criteria:

• Rhinitis
• Nasal obstruction
• Frequent episodes of epistaxis
• Ongoing cold

Community sample