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VOLUME 8 , ISSUE 1 ( January-June, 2019 ) > List of Articles


Time Constant: What Do We Need to Know to Use It?

Madhuragauri S. Shevade

Keywords : Compliance, resistance, time constant

Citation Information : Shevade MS. Time Constant: What Do We Need to Know to Use It?. Indian J Respir Care 2019; 8 (1):4-7.

DOI: 10.4103/ijrc.ijrc_7_18

License: CC BY-NC-SA 4.0

Published Online: 05-12-2022

Copyright Statement:  Copyright © 2019; Indian Journal of Respiratory Care.


Mechanical ventilation is an important strategy to manage patients with respiratory ailments in the acute as well as chronic setups. To be able to do so, we need a good understanding of the physiology of the respiratory system and the disease pattern. Two major components of the lung physiology are compliance and resistance and these define time constants (TCs). Compliance is the measure of distensibility of lungs. It is the change in pressure by the change in volume. Resistance is the opposing force that is created when air flows in the airway. Compliance and resistance together produce an entity called TC. TC defines the amount of time taken in seconds for the lung unit to fill or empty. TCs normally vary within the lungs and do more so in the diseased lungs. This article gives an overview of TCs and its components for the better understanding of the reader.

  1. Global Burden of Disease. Available from: https://www.vizhub. [Last accessed on 2018 Feb 15].
  2. Ghoshal AG, Ravindran GD, Gangwal P, Rajadhyaksha G, Cho SH, Muttalif AR, et al. The burden of segregated respiratory diseases in India and the quality of care in these patients: Results from the Asia-Pacific burden of respiratory diseases study. Lung India 2016;33:611-9.
  3. West JB. Respiratory Physiology: The Essentials. 9th ed. Philadelphia: Lippincott Williams & Wilkins; 2012.
  4. Abernathy C, Harken AH, Moore EE. Abernathy's surgical secrets. In: Alden H. Harken EEM, editor. 6th ed. Mosby/Elsevier; 2009. p. 517. Available from: [Last cited on 2018 Mar 31].
  5. Carlo WA, Ambalavanan N. Conventional mechanical ventilation: Traditional and new strategies. Pediatr Rev 1999;20:e117-26.
  6. Kaminsky DA. What does airway resistance tell us about lung function? Respir Care 2012;57:85-96.
  7. Kackmarek R, Wilkins R, Stoller JK. Egan's Fundamentals of Respiratory Care. 9th ed. Philadelphia: Mosby/Elsevier; 2009.
  8. Beachey W. Respiratory Care Anatomy and Physiology. 2nd ed. Philadelphia: Mosby/Elsevier; 2007.
  9. Hess DR. Respiratory mechanics in mechanically ventilated patients. Respir Care 2014;59:1773-94.
  10. Fuhrman BP, Zimmerman JJ. Pediatric Critical Care E-Book. 5th ed. Philadelphia: Elsevier Health Sciences; 2011.
  11. Kamat SS. Practical Applications of Mechanical Ventilation. 2nd ed. New Delhi: Jaypee Brothers Medical Publishers Ltd.; 2015.
  12. Arnal JM. Bedside tip: How to Use the Expiratory Time Constant. Available from:˜2018-04-04˜Bedside-tip:-How-to-use-the-expiratorytime-constant˜a90bbb8e-6848-4854-ad6f-2f8e86e16f81˜.html. [Last accessed on 2018 Jun 03].
  13. Wiriyaporn D, Wang L, Aboussouan LS. Expiratory time constant and sleep apnea severity in the overlap syndrome. J Clin Sleep Med 2016;12:327-32.
  14. Guttmann J, Eberhard L, Fabry B, Bertschmann W, Zeravik J, Adolph M, et al. Time constant/volume relationship of passive expiration in mechanically ventilated ARDS patients. Eur Respir J 1995;8:114-20.
  15. Henderson WR. Expiratory Time Constant Heterogeneity in Experimental Acute Respiratory Distress Syndrome (dissettation). Vancouver: The University of British Columbia; 2016.
  16. Pilbeam SP, Cairo JM. Mechanical Ventilation: Physiological and Clinical Applications. 4th ed. Philadelphia: Mosby; 2006.
  17. Henderson WR, Dominelli PB, Molgat-Seon Y, Lipson R, Griesdale DE, Sekhon M, et al. Effect of tidal volume and positive end-expiratory pressure on expiratory time constants in experimental lung injury. Physiol Rep 2016;4. pii: e12737.
  18. Al-Rawas N, Banner MJ, Euliano NR, Tams CG, Brown J, Martin AD, et al. Expiratory time constant for determinations of plateau pressure, respiratory system compliance, and total resistance. Crit Care 2013;17:R23.
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