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• Incostintencies in defining "Work of breathing"
  Paola Papoff
  Published on: 20 April 2016

• Published on: 20 April 2016

  Incostintencies in defining "Work of breathing"

  • Paola Papoff, researcher
  • Other Contributors:
    • Fabio Midolla,Francesco Montecchia

  We read with great interest the recent article by Shetty et al (Arch Dis Child Fetal Neonatal Ed 2016;0:F1-F4) who showed that continuous positive airway pressure (CPAP) and humidified high-flow nasal cannula (HHFNC) in infants with evolving or established bronchopulmonary dysplasia (BPD) have similar effects on work of breathing (WOB).1 Like many other articles in this field, Shetty's paper unfortunately suffers from in...

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  We read with great interest the recent article by Shetty et al (Arch Dis Child Fetal Neonatal Ed 2016;0:F1-F4) who showed that continuous positive airway pressure (CPAP) and humidified high-flow nasal cannula (HHFNC) in infants with evolving or established bronchopulmonary dysplasia (BPD) have similar effects on work of breathing (WOB).1 Like many other articles in this field, Shetty's paper unfortunately suffers from inconsistencies in defining WOB, which we wish to clarify. The definition "WOB" used throughout the paper, as a proxy for respiratory effort, seems misleading insofar Shetty et al actually assessed not WOB but the pressure time product (PTP) of the diaphragm (PTPdi). WOB and PTP, expressed either as esophageal pressure PTP or PTPdi, are two independent physical variables that address distinctly different features related to respiratory effort. In physics, the term "WOB" refers to the work done during each respiratory cycle and is mathematically expressed as WOB = ? Ppl x dVt. The Campbell diagram depicts the dynamic relationship between these two variables.2 In respiratory physiology, WOB describes the energy required as inspiratory flow begins to perform the task of ventilation. The term WOB might therefore be inaccurate to indicate the actual effort necessary for the patient to breathe, because it overlooks the energy expended during the isometric phase of respiration (muscle contraction without volume displacement). More properly, Shetty et al determined PTP, a variable that directly measures energy expenditure during the dynamic and isometric respiratory phases. PTP comprises the average inspiratory pressure starting from the onset of respiratory effort and the end of inspiration (Pavg): PTP = Pavg ? Ti.3 Because research into respiratory mechanics in spontaneously breathing infants is an exciting new field of study that increasingly attracts students, researchers, and physicians we need a concerted effort to clarify terminology that they might find confusing. Especially confusing is the tendency to use WOB as a proxy for respiratory effort when the variable measured is actually PTP. To prevent further confusion, we suggest defining respiratory effort in a consistent manner, keeping WOB and PTP as the variables for quantifying it physically. We hope that the research community will support this proposal and look forward to reading articles that put it into practice. Paola Papoff, MD Fabio Midulla, MD Francesco Montecchia, PhD References 1) Shetty S, Hickey A, Rafferty GF, et al. Work of breathing during CPAP and heated humidified high-flow nasal cannula. Arch Dis Child Fetal Neonatal Ed 2016; 0:F1-F4. 2) Cabello B, Mancebo J. Work of breathing. Intensive Care Med 2006;32:1311-4. 3) Grinnan DC1, Truwit JD. Clinical review: respiratory mechanics in spontaneous and assisted ventilation. Crit Care 2005;9:472-84.

  Conflict of Interest:

  None declared

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  Conflict of Interest:
  None declared.

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