2008 Use of Exercise Tidal Flow-Volume Loop to assess Ventilatory Constraint— Experience in Local Chronic Obstructive Pulmonary Disease patients
Dr Wong Chun Man
Department of Medicine, North District Hospital
Background
Patients with chronic obstructive pulmonary disease (COPD) have variable degree of exercise intolerance which limits their activities of daily living. Ventilatory constraint is an important factor that causes exercise limitation. Ventilatory constraint can be quantified by breathing reserve index, as well as obtaining various ventilatory constraint parameters using exercise tidal flow-volume loop (extFVL) method on cardiopulmonary exercise testing (CPET).
Methods
COPD patients in North District Hospital who underwent pulmonary rehabilitation program had CPET and extFVL performed from January 2005 to April 2007. The extFVL at peak exercise were retrieved for analysis. Ventilatory constraint indexes including expiratory flow limitation (Vfl/Vt%), dynamic hyperinflation (as quantified by the decrease in inspiratory capacity from at rest to peak exercise, ΔIC), inspiratory flow reserve % capacity, and minute ventilation divided by ventilatory capacity (Ve/VeCAP) were measured on the extFVL.
Results
Twenty-three patients (21 male; mean ± SD age, 68 ± 8 years old; post bronchodilator FEV1/FVC 44 ± 12%; post bronchodilator FEV1, 1.10 ± 0.41 Liters (L); post bronchodilator FEV1 % predicted, 46 ± 18 %; GOLD stages II-IV) were included. Expiratory flow limitation and dynamic hyperinflation were present in all of the patients. Increased Ve/VeCAP was seen in 22 (96%) patients. After excluding 7 patients with flattening of inspiratory limb of the maximal flow-volume loop (MFVL) performed at rest, inspiratory flow reserve % capacity was elevated in 11 (69%) patients. When the degree of ventilatory constraint is concerned, our patients as a group had severe expiratory flow limitation (Vfl/Vt%, 84 ± 12%), severe dynamic hyperinflation (ΔIC 0.36 ± 0.19), mild inspiratory flow limitation (inspiratory flow reserve % capacity 80 ± 23%), and severe overall ventilatory constraint (Ve/VeCAP 157 ± 94%). FEV1 and FEV1% predicted negatively correlated with Vfl/Vt% (Pearson’s correlation coefficient (R) of -0.53 (P=0.010) and -0.63 (P=0.001) respectively). In addition, FEV1 and FEV1% predicted were also negatively correlated with Ve/VeCAP (Pearson’s correlation coefficient (R) of -0.42 (P=0.046) and -0.45 (P=0.030) respectively). Using raised Ve/VeCAP as “gold standard” to identify overall ventilatory constraint, the conventional breathing reserve index failed to identify ventilatory limitation in 15 (65%) patients.
Conclusions
ExtFVL ventilatory constraint parameters (expiratory flow limitation (Vfl/Vt%), dynamic hyperinflation, inspiratory flow reserve % capacity, and Ve/VeCAP) showed all of our COPD patients had ventilatory constraint on exercise. The degree of expiratory flow limitation, dynamic hyperinflation and Ve/VeCAP was severe on extFVL analysis. Our patients also exhibited the presence of mild inspiratory flow limitation at peak exercise. FEV1 and FEV1% predicted negatively correlated with expiratory flow limitation and Ve/VeCAP. The conventional breathing reserve index failed to identify ventilatory limitation in a significant proportion of the patients when compared with Ve/VeCAP. ExtFVL study improves our ability to detect ventilatory constraint, and our understanding on the components of ventilatory constraint in COPD patients. Quantitative measurements of extFVL parameters can be carried out using no additional commercial equipments.
