Sustainable inspiratory pressures over varying flows, volumes, and duty cycles

T. L. Clanton, B. T. Ameredes, D. B. Thomson, M. W. Julian

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


This study identifies the influence of flow (0.5-2.0 l/s), duty cycle (0.29-0.57), and tidal volume (1.08-2.16 liters) on sustainable inspiratory muscle pressure (Pmus) and transdiaphragmatic pressure (Pdi) development. Six normal humans performed endurance tests using an isoflow method, which allowed for measurements of maximum dynamic Pmus and Pdi, with controlled lung inflation. The subjects repeated maximum dynamic voluntary inspirations for 10 min. Pressures dropped exponentially from initial measurements at rest (Pmus(i) or Pdi(i)) to sustainable values (Pmus(s) or Pdi(s)). As flow and tidal volume increased, maximum initial and sustainable pressures decreased significantly. However, at a constant duty cycle, the sustainable dynamic pressures remained predictable fractions of initial dynamic pressures (i.e., Pmus(s)/Pmus(i) or Pdi(s)/Pdi(i)), regardless of changes in flow and tidal volume. In contrast, as duty cycle increased, the sustainable fractions significantly decreased for both Pdi and Pmus. For example, at a duty cycle of 0.29, Pmus(s)/Pmus(i) was ~0.71, and at a duty cycle of 0.57, Pmus(s)/Pmus(i) was ~0.62. Calculated sustainable pressure-time indexes varied significantly between 0.16 to 0.32 for Pmus and 0.11 to 0.22 for Pdi over the breathing patterns studied. We conclude that 1) the maximum dynamic pressure that can be sustained at a given duty cycle is a predictable fraction of the maximum dynamic pressure that can be generated at rest when measured under the same conditions of inspiration and 2) the sustainable fraction of initial dynamic pressure significantly decreases with increasing duty cycle.

Original languageEnglish (US)
Pages (from-to)1875-1882
Number of pages8
JournalJournal of Applied Physiology
Issue number5
StatePublished - 1990
Externally publishedYes


  • breathing pattern
  • chest wall mechanics
  • diaphragm
  • endurance
  • force-velocity-length
  • inductance plethysmography
  • muscle energetics
  • pressure-flow-volume relationship
  • respiratory muscle fatigue
  • respiratory muscles
  • tension-time index
  • thoracoabdominal configuration
  • work of breathing

ASJC Scopus subject areas

  • General Medicine


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