Exertional ventilation/carbon dioxide output relationship in COPD: from physiological mechanisms to clinical applications

Abstract

There is well established evidence that the minute ventilation (V′E)/carbon dioxide output (V′CO2) relationship is relevant to a number of patient-related outcomes in COPD. In most circumstances, an increased V′E/V′CO2 reflects an enlarged physiological dead space (“wasted” ventilation), although alveolar hyperventilation (largely due to increased chemosensitivity) may play an adjunct role, particularly in patients with coexistent cardiovascular disease. The V′E/V′CO2 nadir, in particular, has been found to be an important predictor of dyspnoea and poor exercise tolerance, even in patients with largely preserved forced expiratory volume in 1 s. As the disease progresses, a high nadir might help to unravel the cause of disproportionate breathlessness. When analysed in association with measurements of dynamic inspiratory constraints, a high V′E/V′CO2 is valuable to ascertain a role for the “lungs” in limiting dyspnoeic patients. Regardless of disease severity, cardiocirculatory (heart failure and pulmonary hypertension) and respiratory (lung fibrosis) comorbidities can further increase V′E/V′CO2. A high V′E/V′CO2 is a predictor of poor outcome in lung resection surgery, adding value to resting lung hyperinflation in predicting all-cause and respiratory mortality across the spectrum of disease severity. Considering its potential usefulness, the V′E/V′CO2 should be valued in the clinical management of patients with COPD.

Prognostic value of key variables from cardiopulmonary exercise testing in patients with COPD: 42-month follow-up

“…In our study, an increased V ̇ E/V ̇ CO2 slope (i.e., ≥30), which is an indicator of ventilation/perfusion mismatch and overall worsening cardiopulmonary pathophysiology [22,23], was a predictor of mortality in the 42-month period in patients with COPD. There is evidence that the V ̇ E/V ̇ CO2 slope is relevant for a number of patient-related outcomes in COPD, as an increase in the V ̇ E/V ̇ CO2 slope reflects an increased physiological dead space [24]. Torchio et al [23] found that a V ̇ E/V ̇ CO2 slope ≥34 was related to a mortality risk of 5.5% and highlighted this variable for screening COPD patients who are candidates for pulmonary resection for potential ventilatory (Clinician's guide to cardiopulmonary exercise testing in adults: A scientific statement from the American heart association)failure.…”

Molecular Mechanisms of Obesity-Induced Development of Insulin Resistance and Promotion of Amyloid-β Accumulation: Dietary Therapy Using Weak Organic Acids via Improvement of Lowered Interstitial Fluid pH

“…Thus, COPD patients are at high risk of developing insulin resistance via a TNF-α-mediated pathway [52,54]. However, it should also be considered that the interstitial fluid acidity due to elevated CO 2 level in COPD patients [55][56][57][58] would cause insulin resistance [12].…”

Exercise Physiology and Cardiopulmonary Exercise Testing

“…Ventilatory efficiency (V̇ E /V̇CO 2 nadir and ΔV̇ E /ΔV̇CO 2 slope) : the relationship of V̇ E to V̇CO 2 has emerged as an important CPET outcome, reflecting disease severity, gas exchange inefficiency, and prognosis in both pulmonary 110 and cardiovascular 111 diseases. It is characterized either as the absolute ratio V̇ E /V̇CO 2 at its nadir shortly after GET ( Fig.…”