Emerging concepts in the evaluation of ventilatory limitation during exercise - The exercise tidal flow-volume loop

Traditionally ventilatory limitation (constraint) during exercise has been determined by measuring the ventilatory reserve or how close the minute ven tilation ((V) over dot E ) achieved during exercise (ie, ventilatory demand ) approaches the maximal voluntary ventilation (MVV) or some estimate of th e MVV (ie, ventilatory capacity), More recently, it has become clear that r arely is the MVV breathing pattern adopted during exercise and that the (V) over dot E/MVV relationship tells little about the specific reason(s) for ventilatory constraint, Although it is not a new concept, by measuring the tidal exercise flow-volume (FV) loops (estFVLs) obtained during exercise an d plotting them according to a measured end-expiratory lung volume (EELV) w ithin the maximal FV envelope (MFVL), more specific information is provided on the sources (and degree) of ventilatory constraint, This includes the e xtent of expiratory now limitation, inspiratory flow reserve, alterations i n the regulation of EELV (dynamic hyperinflation), end-inspiratory lung vol ume relative to total lung capacity (or tidal volume/inspiratory capacity), and a proposed estimate of ventilatory capacity based on the shape of the MFVL and the breathing pattern adopted during exercise, By assessing these types of changes, the degree of ventilatory constraint can be quantified an d a more thorough interpretation of the cardiopulmonary exercise response i s possible. This review will focus on the potential role of plotting the ex tFVL within the MFVL for determination of ventilatory constraint during exe rcise in the clinical setting. Important physiologic concepts, measurements , and limitations obtained from this type of analysis will be defined and d iscussed.