Official reprint from UpToDate®
www.uptodate.com ©2015 UpToDate®

Tests of respiratory muscle strength

John Moxham, MD
Section Editor
James K Stoller, MD, MS
Deputy Editor
Geraldine Finlay, MD


Respiratory muscle strength can be assessed by measuring the maximal inspiratory pressure (MIP, PImax, or negative inspiratory force [NIF]) and the maximal expiratory pressure (MEP or PEmax). The MIP reflects the strength of the diaphragm and other inspiratory muscles, while the MEP reflects the strength of the abdominal muscles and other expiratory muscles. An alternative or additional test of inspiratory muscles strength is maximal sniff nasal inspiratory pressure (SNIP) (discussed below). Common indications for measurement of the MIP, SNIP, and MEP include:

  • Respiratory muscle weakness is suspected, such as a patient with dyspnea, weak cough, and known neuromuscular disease
  • Spirometry detected a pattern of restriction: reduced forced expiratory volume in one second (FEV1), reduced forced vital capacity (FVC), normal FEV1/FVC ratio, and reduced total lung capacity (TLC) and respiratory muscle weakness is in the differential diagnosis
  • Spirometry detected a low vital capacity (VC) of unknown etiology and respiratory muscle weakness is in the differential diagnosis
  • Spirometry detected a low maximal voluntary ventilation (MVV) maneuver of unknown etiology and respiratory muscle weakness is in the differential diagnosis
  • Evaluation of whether known respiratory muscle weakness has improved, remained stable, or worsened
  • To determine whether there is an increased risk of incident mobility disability in older individuals, hospitalizations and death in patients with COPD, mortality in patients with heart failure [1-4]

Measurement, interpretation, quality assurance, and clinical applications of the MIP and MEP are discussed in this topic review. Alternative tests of respiratory muscle strength, particularly SNIP, are also mentioned. Assessments of other aspects of respiratory function (eg, airflow, lung volumes, gas exchange) are described separately. (See "Overview of pulmonary function testing in adults" and "Diffusing capacity for carbon monoxide" and "Reference values for pulmonary function testing" and "Flow-volume loops" and "Office spirometry".)


Measurement of the MIP and MEP can be made with a mechanical pressure gauge that is connected to a mouthpiece (picture 1). However, electronic devices are widely available, which may be hand-held or connected to a computer (figure 1) [5-7]. The device should contain a small hole (1 mm diameter and 20 to 30 mm in length), which allows an air leak. This prevents the patient from generating pressure by using their cheek muscles [8].

Maximal inspiratory pressure (MIP) — Place a rubber mouthpiece with flanges on the device. Instruct the patient to seal his or her lips firmly around the mouthpiece, exhale slowly and completely, and then "pull in hard, like you are trying to suck up a thick milkshake." Demonstrate the maneuver and have the patient repeat it. The patient should maintain inspiratory pressure for at least 1.5 seconds and the largest negative pressure sustained for at least 1 second (not a transient spike) should be recorded [9]. These durations are estimated by the individual supervising the test. Allow the patient to rest for about one minute and then repeat the maneuver five times. Provide verbal or visual feedback after each maneuver. The goal is for the variability among measurements to be less than 10 cm H2O [10]. Measurements should be rounded to the nearest 5 cm H2O.


Subscribers log in here

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information or to purchase a personal subscription, click below on the option that best describes you:
Literature review current through: Jun 2015. | This topic last updated: Jun 5, 2013.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2015 UpToDate, Inc.
  1. Buchman AS, Boyle PA, Leurgans SE, et al. Pulmonary function, muscle strength, and incident mobility disability in elders. Proc Am Thorac Soc 2009; 6:581.
  2. Frankenstein L, Nelles M, Meyer FJ, et al. Validity, prognostic value and optimal cutoff of respiratory muscle strength in patients with chronic heart failure changes with beta-blocker treatment. Eur J Cardiovasc Prev Rehabil 2009; 16:424.
  3. Vilaró J, Ramirez-Sarmiento A, Martínez-Llorens JM, et al. Global muscle dysfunction as a risk factor of readmission to hospital due to COPD exacerbations. Respir Med 2010; 104:1896.
  4. Moore AJ, Soler RS, Cetti EJ, et al. Sniff nasal inspiratory pressure versus IC/TLC ratio as predictors of mortality in COPD. Respir Med 2010; 104:1319.
  5. Hamnegård CH, Wragg S, Kyroussis D, et al. Portable measurement of maximum mouth pressures. Eur Respir J 1994; 7:398.
  6. Watson, L. A method for measuring sniff nasal inspiratory pressure using the PK Morgan Pm meter. Inspire, the Official J Assoc Respir Technicians Physiologists 1997; 1:14.
  7. Enright PL, Kronmal RA, Manolio TA, et al. Respiratory muscle strength in the elderly. Correlates and reference values. Cardiovascular Health Study Research Group. Am J Respir Crit Care Med 1994; 149:430.
  8. Evans JA, Whitelaw WA. The assessment of maximal respiratory mouth pressures in adults. Respir Care 2009; 54:1348.
  9. American Thoracic Society/European Respiratory Society. ATS/ERS Statement on respiratory muscle testing. Am J Respir Crit Care Med 2002; 166:518.
  10. Wen AS, Woo MS, Keens TG. How many maneuvers are required to measure maximal inspiratory pressure accurately. Chest 1997; 111:802.
  11. Fiz JA, Carreres A, Rosell A, et al. Measurement of maximal expiratory pressure: effect of holding the lips. Thorax 1992; 47:961.
  12. Sachs MC, Enright PL, Hinckley Stukovsky KD, et al. Performance of maximum inspiratory pressure tests and maximum inspiratory pressure reference equations for 4 race/ethnic groups. Respir Care 2009; 54:1321.
  13. Harik-Khan RI, Wise RA, Fozard JL. Determinants of maximal inspiratory pressure. The Baltimore Longitudinal Study of Aging. Am J Respir Crit Care Med 1998; 158:1459.
  14. Gaultier C, Zinman R. Maximal static pressures in healthy children. Respir Physiol 1983; 51:45.
  15. Leech JA, Ghezzo H, Stevens D, Becklake MR. Respiratory pressures and function in young adults. Am Rev Respir Dis 1983; 128:17.
  16. Polkey MI, Green M, Moxham J. Measurement of respiratory muscle strength. Thorax 1995; 50:1131.
  17. Rochester DF. Tests of respiratory muscle function. Clin Chest Med 1988; 9:249.
  18. Orozco-Levi M. Structure and function of the respiratory muscles in patients with COPD: impairment or adaptation? Eur Respir J Suppl 2003; 46:41s.
  19. Morrison NJ, Richardson J, Dunn L, Pardy RL. Respiratory muscle performance in normal elderly subjects and patients with COPD. Chest 1989; 95:90.
  20. Steier J, Kaul S, Seymour J, et al. The value of multiple tests of respiratory muscle strength. Thorax 2007; 62:975.
  21. Moxham J. Lung function tests: physiological principles and clinical applications. In: Respiratory Muscles, Hughes JB, Pride NB, Saunders WB (Eds), London 1999.
  22. Aldrich TK, Spiro P. Maximal inspiratory pressure: does reproducibility indicate full effort? Thorax 1995; 50:40.
  23. Hughes PD, Polkey MI, Kyroussis D, et al. Measurement of sniff nasal and diaphragm twitch mouth pressure in patients. Thorax 1998; 53:96.
  24. Fauroux B, Aubertin G, Cohen E, et al. Sniff nasal inspiratory pressure in children with muscular, chest wall or lung disease. Eur Respir J 2009; 33:113.
  25. Celli BR. Clinical and physiologic evaluation of respiratory muscle function. Clin Chest Med 1989; 10:199.
  26. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1:307.
  27. Maillard JO, Burdet L, van Melle G, Fitting JW. Reproducibility of twitch mouth pressure, sniff nasal inspiratory pressure, and maximal inspiratory pressure. Eur Respir J 1998; 11:901.
  28. Keenan SP, Alexander D, Road JD, et al. Ventilatory muscle strength and endurance in myasthenia gravis. Eur Respir J 1995; 8:1130.
  29. Goswami R, Guleria R, Gupta AK, et al. Prevalence of diaphragmatic muscle weakness and dyspnoea in Graves' disease and their reversibility with carbimazole therapy. Eur J Endocrinol 2002; 147:299.
  30. Nava S, Crotti P, Gurrieri G, et al. Effect of a beta 2-agonist (broxaterol) on respiratory muscle strength and endurance in patients with COPD with irreversible airway obstruction. Chest 1992; 101:133.
  31. Larson JL, Covey MK, Vitalo CA, et al. Maximal inspiratory pressure. Learning effect and test-retest reliability in patients with chronic obstructive pulmonary disease. Chest 1993; 104:448.
  32. American Thoracic Society. Pulmonary Function Laboratory Management and Procedure Manual, Wanger J, Crapo RO, Irvin CG (Eds), 2005.
  33. Koulouris N, Mulvey DA, Laroche CM, et al. Comparison of two different mouthpieces for the measurement of Pimax and Pemax in normal and weak subjects. Eur Respir J 1988; 1:863.
  34. Wohlgemuth M, van der Kooi EL, Hendriks JC, et al. Face mask spirometry and respiratory pressures in normal subjects. Eur Respir J 2003; 22:1001.
  35. Carpenter MA, Tockman MS, Hutchinson RG, et al. Demographic and anthropometric correlates of maximum inspiratory pressure: The Atherosclerosis Risk in Communities Study. Am J Respir Crit Care Med 1999; 159:415.
  36. Lyall RA, Donaldson N, Polkey MI, et al. Respiratory muscle strength and ventilatory failure in amyotrophic lateral sclerosis. Brain 2001; 124:2000.
  37. Lechtzin N, Wiener CM, Shade DM, et al. Spirometry in the supine position improves the detection of diaphragmatic weakness in patients with amyotrophic lateral sclerosis. Chest 2002; 121:436.
  38. Polkey MI, Lyall RA, Green M, et al. Expiratory muscle function in amyotrophic lateral sclerosis. Am J Respir Crit Care Med 1998; 158:734.
  39. Teixeira A, Cherin P, Demoule A, et al. Diaphragmatic dysfunction in patients with idiopathic inflammatory myopathies. Neuromuscul Disord 2005; 15:32.
  40. Hughes PD, Polkey MI, Harrus ML, et al. Diaphragm strength in chronic heart failure. Am J Respir Crit Care Med 1999; 160:529.
  41. Ker JA, Schultz CM, Ker J. Respiratory muscle endurance in heart failure--the effect of clinical severity. S Afr Med J 1998; 88 Suppl 1:C20.
  42. Polkey MI, Kyroussis D, Hamnegard CH, et al. Diaphragm strength in chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1996; 154:1310.
  43. Lemos A, de Souza AI, Figueiroa JN, et al. Respiratory muscle strength in pregnancy. Respir Med 2010; 104:1638.
  44. Chetta A, Harris ML, Lyall RA, et al. Whistle mouth pressure as test of expiratory muscle strength. Eur Respir J 2001; 17:688.
  45. Man WD, Kyroussis D, Fleming TA, et al. Cough gastric pressure and maximum expiratory mouth pressure in humans. Am J Respir Crit Care Med 2003; 168:714.
  46. Szeinberg A, Tabachnik E, Rashed N, et al. Cough capacity in patients with muscular dystrophy. Chest 1988; 94:1232.
  47. van der Palen J, Rea TD, Manolio TA, et al. Respiratory muscle strength and the risk of incident cardiovascular events. Thorax 2004; 59:1063.
  48. Mier A. Respiratory muscle weakness. Respir Med 1990; 84:351.
  49. Jackson CE, Rosenfeld J, Moore DH, et al. A preliminary evaluation of a prospective study of pulmonary function studies and symptoms of hypoventilation in ALS/MND patients. J Neurol Sci 2001; 191:75.
  50. Mier-Jedrzejowicz A, Brophy C, Moxham J, Green M. Assessment of diaphragm weakness. Am Rev Respir Dis 1988; 137:877.
  51. Héritier F, Rahm F, Pasche P, Fitting JW. Sniff nasal inspiratory pressure. A noninvasive assessment of inspiratory muscle strength. Am J Respir Crit Care Med 1994; 150:1678.
  52. Uldry C, Janssens JP, de Muralt B, Fitting JW. Sniff nasal inspiratory pressure in patients with chronic obstructive pulmonary disease. Eur Respir J 1997; 10:1292.
  53. Rafferty GF, Leech S, Knight L, et al. Sniff nasal inspiratory pressure in children. Pediatr Pulmonol 2000; 29:468.
  54. Rieder P, Louis M, Jolliet P, Chevrolet JC. The repeated measurement of vital capacity is a poor predictor of the need for mechanical ventilation in myasthenia gravis. Intensive Care Med 1995; 21:663.
  55. Morgan RK, McNally S, Alexander M, et al. Use of Sniff nasal-inspiratory force to predict survival in amyotrophic lateral sclerosis. Am J Respir Crit Care Med 2005; 171:269.
  56. Kamide N, Ogino M, Yamashina N, Fukuda M. Sniff nasal inspiratory pressure in healthy Japanese subjects: mean values and lower limits of normal. Respiration 2009; 77:58.
  57. Laroche CM, Mier AK, Moxham J, Green M. The value of sniff esophageal pressures in the assessment of global inspiratory muscle strength. Am Rev Respir Dis 1988; 138:598.
  58. Miller JM, Moxham J, Green M. The maximal sniff in the assessment of diaphragm function in man. Clin Sci (Lond) 1985; 69:91.
  59. Mills GH, Kyroussis D, Hamnegard CH, et al. Unilateral magnetic stimulation of the phrenic nerve. Thorax 1995; 50:1162.
  60. Mills GH, Kyroussis D, Hamnegard CH, et al. Bilateral magnetic stimulation of the phrenic nerves from an anterolateral approach. Am J Respir Crit Care Med 1996; 154:1099.
  61. Watson AC, Hughes PD, Louise Harris M, et al. Measurement of twitch transdiaphragmatic, esophageal, and endotracheal tube pressure with bilateral anterolateral magnetic phrenic nerve stimulation in patients in the intensive care unit. Crit Care Med 2001; 29:1325.
  62. Hopkinson NS, Dayer MJ, Moxham J, Polkey MI. Abdominal muscle fatigue following exercise in chronic obstructive pulmonary disease. Respir Res 2010; 11:15.
  63. Luo YM, Moxham J, Polkey MI. Diaphragm electromyography using an oesophageal catheter: current concepts. Clin Sci (Lond) 2008; 115:233.