title: A method for estimating respiratory muscle efficiency using an automated metabolic cart.
abstract: We measured respiratory muscle efficiency (RME) in twelve healthy human subjects by dividing the added energy cost of breathing against a threshold resistance load by the associated increase in caloric expenditure. Caloric expenditure was calculated using steady-state measurements of oxygen consumption and carbon dioxide production during loaded and unloaded breathing. Calculated RME ranged from 1.7% to 5.5% (mean 3.5%). The coefficient of variation in six subjects averaged 13%. We compared these calculations with a previously described oxygen consumption-based method that did not incorporate carbon dioxide production measurements. We found that changes in the respiratory quotient during resistive breathing could cause significant errors in oxygen consumption-based calculations of RME. Limits of agreement of 95% suggest that the oxygen-consumption-based calculations could potentially overestimate efficiency by as much as 5.0% or underestimate by up to 3.4%. We recommend that carbon dioxide production be measured when this technique for estimation of RME is used. This can be easily accomplished through the use of an automated metabolic cart.
authors.affiliation: Department of Medicine, Allegheny University Hospitals-Center City, MCP Hahnemann School of Medicine, Philadelphia, PA 19102-1192, USA.
authors.forename: M
authors.initials: M
authors.lastname: Sherman
authors.forename: A
authors.initials: A
authors.lastname: Matityahu
authors.forename: D
authors.initials: D
authors.lastname: Campbell
mesh_terms: D000328:Adult; D001331:Automation; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D008297:Male; D010101:Oxygen Consumption; D010827:Physiology / Q000295:instrumentation* / Q000379:methods*; D012132:Respiratory Muscles / Q000378:metabolism / Q000502:physiology*; D014939:Work of Breathing