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NIF or PImax in PFTs

last modified on: Mon, 12/11/2023 - 12:49

return to: Spirometry PIF Peak Inspiratory Flow

PImax = maximum inspiratory mouth pressure (also termed NIF = negative inspiratory force) - see video above

  • Is an index of inspiratory muscle strength (Black 1969)
  • Is a routine procedure in many pulmonary function laboratories
  • Hautmann et al in 2000 published the mean PImax (kPA)
    • for men (N=248) to be 9.95 kPa
    • for women (N=256) to be 7.43 kPa
  • "strongly dependent on the skill of the technician" (may account for 5%- 12% variation) and "the motivation of the patient"
  • strongest correlation in results were for sex and age, but also height/weight/BMI and different lung function parameters


Hautmann H, Hefele S, Schotten K, Huber RM: Maximal inspiratory mouth pressures (PIMAX) in Healthy Subjectes – what is the lower limit of normal. Respir Med. 2000 Jul; 94(7):689-93

Black LF, Hyatt RE. Maximal respiratory pressures: normal values and relationship to age and sex. Am Rev Respir Dis 1969;99:696-702