Distinguishing cardiac versus pulmonary limitation in exercise performance

Identifying limitations to exercise with incremental cardiopulmonary exercise testing: a scoping review

Cardiopulmonary exercise testing (CPET) is a comprehensive and invaluable assessment used to identify the mechanisms that limit exercise capacity. However, its interpretation remains poorly standardised. This scoping review aims to investigate which limitations to exercise are differentiated by the use of incremental CPET in literature and which criteria are used to identify them. We performed a systematic, electronic literature search of PubMed, Embase, Cochrane CENTRAL, Web of Science and Scopus. All types of publications that reported identification criteria for at least one limitation to exercise based on clinical parameters and CPET variables were eligible for inclusion. 86 publications were included, of which 57 were primary literature and 29 were secondary literature. In general, at the level of the cardiovascular system, a distinction was often made between a normal physiological limitation and a pathological one. Within the respiratory system, ventilatory limitation, commonly identified by a low breathing reserve, and gas exchange limitation, mostly identified by a high minute ventilation/carbon dioxide production slope and/or oxygen desaturation, were often described. Multiple terms were used to describe a limitation in the peripheral muscle, but all variables used to identify this limitation lacked specificity. Deconditioning was a frequently mentioned exercise limiting factor, but there was no consensus on how to identify it through CPET. There is large heterogeneity in the terminology, the classification and the identification criteria of limitations to exercise that are distinguished using incremental CPET. Standardising the interpretation of CPET is essential to establish an objective and consistent framework.

Pulmonary function threshold for distinguishing ventilatory- and nonventilatory-limited patients with airflow obstruction

Patients with chronic obstructive pulmonary disease (COPD) may demonstrate great variability between results on the pulmonary function test (PFT) compared to those on the cardiopulmonary exercise test (CPXT). The purpose of this study was to correlate PFT and CPXT indices and to identify PFT threshold values for predicting exercise capacity in patients with airflow limitation. Fifty-seven patients (48 men and 9 women) of mean age 66.4 +/- 4.8 years with COPD and 40 age-matched control patients underwent PFT and CPXT. Based on the CPXT results, the patients were divided into ventilatory-limited (VL) and nonventilatory-limited (NVL), and the findings were correlated with the PFT indices. Linear regression analysis was used to determine the relationship between dyspnea index (VEmax/MVV) and forced expiratory volume in one second (FEV1). The cutoff value for VL was FEV1 < 38% and for NVL FEV1 > 68%. The prominent limiting symptom (61%) in the VL group was dyspnea sensation, with leg discomfort presenting in only 14%; corresponding rates in the NVL group were 38% and 31%. We conclude that the FEV1 is a reliable index for distinguishing VL from NVL COPD patients during CPXT at two extremes: below 38% of the predicted value (VL) and above 68% of the predicted value (NVL).

Diagnostic value of maximal exercise tidal volume

Though breathing pattern is frequently analyzed during clinical exercise testing, there is little information regarding its usefulness in the differential diagnosis of impaired exercise tolerance. This study tested the hypothesis that differences in peak tidal volume during exercise between patients with different cardiorespiratory diseases are related largely to differences in severity of respiratory mechanical impairment (vital capacity), not to differences in disease state. Patients with chronic obstructive pulmonary disease, restrictive lung disease, bronchial asthma, and heart disease (mitral valve disease or left ventricular dysfunction) were studied. Subjects selected had one and only one of the above diagnoses. All subjects performed maximal (symptom-limited) incremental exercise on a cycle ergometer. Multiple linear regression of all subjects (n = 30) in all four groups showed a significant correlation between VTmax and VC: VTmax = 0.55, VC -0.09 L (r = 0.827, p less than 0.0001). The VTmax/VC (x 100) was (mean +/- SD) 44 +/- 15, 54 +/- 11, 56 +/- 11, and 54 +/- 12 for the COPD, RLD, BA and HD patients respectively. There was no significant difference between any of the groups. We concluded that differences in VTmax between different patients are related largely to differences in VC (ie, differences in severity of respiratory mechanical impairment), not to differences in disease state. Measurement of VTmax or the VTmax/VC ratio has little value in the differential diagnosis of exertional dyspnea.

Exercise and chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease have abnormal respiratory mechanics, respiratory muscle function, gas exchange, and cardiovascular function during exercise. Their impaired exercise tolerance is at least partly due to altered respiratory mechanics, but factors that increase ventilation during exercise indirectly contribute to exercise limitation. Clinical exercise testing is a very important tool in the assessment of exercise capacity, assessment of factors that contribute to exercise limitation, and differential diagnosis of cardiopulmonary disease.