Abstract
Cardiopulmonary exercise testing (CPET) is an established method for evaluating dyspnea and ventilatory abnormalities. Ventilatory reserve is typically assessed as the ratio of peak exercise ventilation to maximal voluntary ventilation. Unfortunately, this crude assessment provides limited data on the factors that limit the normal ventilatory response to exercise. Additional measurements can provide a more comprehensive evaluation of respiratory mechanical constraints during CPET (e.g., expiratory flow limitation and operating lung volumes). These measurements are directly dependent on an accurate assessment of inspiratory capacity (IC) throughout rest and exercise. Despite the valuable insight that the IC provides, there are no established recommendations on how to perform the maneuver during exercise and how to analyze and interpret the data. Accordingly, the purpose of this manuscript is to comprehensively examine a number of methodological issues related to the measurement, analysis, and interpretation of the IC. We will also briefly discuss IC responses to exercise in health and disease and will consider how various therapeutic interventions influence the IC, particularly in patients with chronic obstructive pulmonary disease. Our main conclusion is that IC measurements are both reproducible and responsive to therapy and provide important information on the mechanisms of dyspnea and exercise limitation during CPET.
Highlights
Cardiopulmonary exercise testing (CPET) is increasingly recognized as an important clinical diagnostic tool for assessing exercise intolerance and exertional symptoms, and for objectively determining functional capacity and impairment [1]
These authors demonstrated consistent peak esophageal pressures throughout exercise despite changes in inspiratory capacity (IC). They concluded that total lung capacity (TLC) did not change and that the IC was reliable for assessing changes in EELV during exercise
This VT inflection, or plateau, which occurs at an IRV of 0.5–1.0 L below TLC (Figure 4), is an important mechanical event during exercise in chronic obstructive pulmonary disease (COPD)
Summary
Cardiopulmonary exercise testing (CPET) is increasingly recognized as an important clinical diagnostic tool for assessing exercise intolerance and exertional symptoms, and for objectively determining functional capacity and impairment [1]. It is important to consider the potential confounding effects of thoracic gas compression and bronchodilation when using this technique [4] Another refinement in the assessment of mechanical volume constraints is the portrayal of changes in operating lung volumes (VT, end-expiratory lung volume (EELV), endinspiratory lung volume (EILV), and inspiratory reserve volume (IRV)) as a function of time, VE, work rate or oxygen uptake (VO2 ) during exercise (Figure 1(b)). This analysis of operating lung volumes, in conjunction with breathing pattern and dyspnea intensity ratings, allows a comprehensive evaluation of ventilatory abnormalities during exercise and their contribution to exercise limitation in the individual patient Both of these approaches are critically dependent on an accurate measurement of inspiratory capacity (IC) to track changes in EELV.
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