Exertional dyspnoea in COPD: the clinical utility of cardiopulmonary exercise testing

The effect of carotid chemoreceptor inhibition on exercise tolerance in chronic obstructive pulmonary disease: A randomized-controlled crossover trial

BACKGROUND

Patients with chronic obstructive pulmonary disease (COPD) have an exaggerated ventilatory response to exercise, contributing to exertional dyspnea and exercise intolerance. We recently demonstrated enhanced activity and sensitivity of the carotid chemoreceptor (CC) in COPD which may alter ventilatory and cardiovascular regulation and negatively affect exercise tolerance. We sought to determine whether CC inhibition improves ventilatory and cardiovascular regulation, dyspnea and exercise tolerance in COPD.

METHODS

Twelve mild-moderate COPD patients (FEV₁ 83 ± 15 %predicted) and twelve age- and sex-matched healthy controls completed two time-to-symptom limitation (T_LIM) constant load exercise tests at 75% peak power output with either intravenous saline or low-dose dopamine (2 μg·kg^-1·min^-1, order randomized) to inhibit the CC. Ventilatory responses were evaluated using expired gas data and dyspnea was evaluated using a modified Borg scale. Inspiratory capacity maneuvers were performed to determine operating lung volumes. Cardiac output was estimated using impedance cardiography and vascular conductance was calculated as cardiac output/mean arterial pressure (MAP).

RESULTS

At a standardized exercise time of 4-min and at T_LIM; ventilation, operating volumes and dyspnea were unaffected by dopamine in COPD patients and controls. In COPD, dopamine decreased MAP and increased vascular conductance at all time points. In controls, dopamine increased vascular conductance at T_LIM, while MAP was unaffected.

CONCLUSION

There was no change in time to exhaustion in either group with dopamine. These data suggest that the CC plays a role in cardiovascular regulation during exercise in COPD; however, ventilation, dyspnea and exercise tolerance were unaffected by CC inhibition in COPD patients.

Ventilation efficiency to exercise in patients with cystic fibrosis

INTRODUCTION

Exercise ventilation efficiency index in cardiopulmonary exercise testing (CPET) is elevated in patients with heart failure providing useful information on disease progression and prognosis. Few data, however, exist for ventilation efficiency index among cystic fibrosis (CF) patients.

AIMS

To assess ventilation efficiency index (ΔVE/ΔVCO₂ or V'E/V'CO₂ slope) and intercept of ventilation (VE-intercept) in CF patients with mild, moderate, and severe cystic fibrosis (CF) lung disease. To assess possible correlations with ventilation inhomogeneity and structural damages as seen on high resolution computed tomography (HRCT).

METHODS

CF patients with mild (FEV₁  > 80%, n = 47), moderate (60% < FEV₁  < 80%, n = 21), and severe (FEV₁  < 60%, n = 9) lung disease, mean age 14.9 years participated. Peak oxygen uptake (VO₂ peak), pulmonary ventilation at peak exercise (VE), respiratory equivalent ratios for oxygen and carbon dioxide at peak exercise (VE/VO₂ , VE/VCO₂ ), end-tidal CO₂ (PetCO₂ ), and ΔVE/ΔVCO₂ , ΔVE/ΔVO₂ in a maximal CPET along with spirometry and multiple breath washout indices were examined. HRCT scans were performed and scored using Bhalla score.

RESULTS

Mean ΔVE/ΔVCO₂ showed no significant differences among the three groups (P = .503). Mean VE_int discriminated significantly among the different groups (p ² < 0.001). Ventilation efficiency index did not correlate either with LCI or Bhalla score. However, VE together with ΔVE/ΔVCO₂ slope could predict Bhalla score (r ²  = 0.869, P = .006).

CONCLUSION

No significant differences were found regarding ΔVE/ΔVCO₂ slope levels between the three groups. Ventilation intercept (VE_int ) was elevated significantly as disease progresses reflecting increased dead space ventilation. CF patients retain their ventilation efficiency to exercise even as lung function deteriorates by adopting a higher respiratory rate along with increased dead space ventilation.

Low resting diffusion capacity, dyspnea, and exercise intolerance in chronic obstructive pulmonary disease

The mechanisms linking reduced diffusing capacity of the lung for carbon monoxide (DlCO) to dyspnea and exercise intolerance across the chronic obstructive pulmonary disease (COPD) continuum are poorly understood. COPD progression generally involves both DlCO decline and worsening respiratory mechanics, and their relative contribution to dyspnea has not been determined. In a retrospective analysis of 300 COPD patients who completed symptom-limited incremental cardiopulmonary exercise tests, we tested the association between peak oxygen-uptake (V̇o2), DlCO, and other resting physiological measures. Then, we stratified the sample into tertiles of forced expiratory volume in 1 s (FEV1) and inspiratory capacity (IC) and compared dyspnea ratings, pulmonary gas exchange, and respiratory mechanics during exercise in groups with normal and low DlCO [i.e., <lower limit of normal (LLN)] using Global Lung Function Initiative reference values. DlCO was associated with peak V̇o2 ( P = 0.006), peak work-rate ( P = 0.005), and dyspnea/V̇o2 slope ( P < 0.001) after adjustment for other independent variables (airway obstruction and hyperinflation). Within FEV1 and IC tertiles, peak V̇o2 and work rate were lower ( P < 0.05) in low versus normal DlCO groups. Across all tertiles, low DlCO groups had higher dyspnea ratings, greater ventilatory inefficiency and arterial oxygen desaturation, and showed greater mechanical volume constraints at a lower ventilation during exercise than the normal DlCO group (all P < 0.05). After accounting for baseline resting respiratory mechanical abnormalities, DlCO<LLN was consistently associated with greater dyspnea and poorer exercise performance compared with preserved DlCO. The higher dyspnea ratings and earlier exercise termination in low DlCO groups were linked to significantly greater pulmonary gas exchange abnormalities, higher ventilatory demand, and associated accelerated dynamic mechanical constraints.

NEW & NOTEWORTHY Our study demonstrated that chronic obstructive pulmonary disease patients with diffusing capacity of the lung for carbon monoxide (DlCO) less than the lower limit of normal had greater pulmonary gas exchange abnormalities, which resulted in higher ventilatory demand and greater dynamic mechanical constraints at lower ventilation during exercise. This, in turn, led to greater exertional dyspnea and exercise intolerance compared with patients with normal DlCO.

Ventilatory inefficiency adversely affects outcomes and longer-term survival after planned colorectal cancer surgery

BACKGROUND

Impaired cardiorespiratory reserve is an accepted risk factor for patients having major surgery. Ventilatory inefficiency, defined by an elevated ratio of minute ventilation to carbon dioxide excretion (VE/VCO₂), and measured by cardiopulmonary exercise testing (CPET), is a pathophysiological characteristic of patients with cardiorespiratory disease. We set out to evaluate the prevalence of ventilatory inefficiency in a colorectal cancer surgical population, and its influence on surgical outcomes and long-term cancer survival.

METHODS

In this retrospective study of 1375 patients who had undergone preoperative CPET followed by colorectal cancer surgery, we used receiver operating characteristic curve analysis to identify an optimal value of VE/VCO₂ associated with 90-day mortality. Binary logistic regression was used to evaluate whether this degree of ventilatory inefficiency was independently associated with decreased survival, both after surgery and in the longer term.

RESULTS

We identified an optimal VE/VCO₂ >39 cut-off for predicting 90-day mortality; 245 patients (17.8%) had VE/VCO₂ >39, of which 138 (10% of total cohort) had no known cardiorespiratory risk factors. Ventilatory inefficiency was independently associated with death at 90-days (8.2% mortality vs 1.9%; adjusted odds ratio [OR], 4.04; 95% confidence interval [CI], 2.09-7.84), with death after unplanned critical care admission (OR=4.45; 95% CI, 1.37-14.46) and with decreased survival at 2 yr (OR=2.21; 95%, 1.49-3.28) and 5 yr (OR=2.87; 95% CI, 1.54-5.37) after surgery.

CONCLUSIONS

A significant proportion of patients having colorectal cancer surgery have ventilatory inefficiency observed on CPET, the majority of whom have no history of cardiorespiratory risk factors. This group of patients has significantly decreased survival both after surgery and in the long-term, irrespective of cancer stage. Survival might be improved by formal medical evaluation and intervention in this group.

Current challenges in managing comorbid heart failure and COPD

INTRODUCTION

Heart failure (HF) with reduced ejection fraction and chronic obstructive pulmonary disease (COPD) frequently coexist, particularly in the elderly. Given their rising prevalence and the contemporary trend to longer life expectancy, overlapping HF-COPD will become a major cause of morbidity and mortality in the next decade. Areas covered: Drawing on current clinical and physiological constructs, the consequences of negative cardiopulmonary interactions on the interpretation of pulmonary function and cardiopulmonary exercise tests in HF-COPD are discussed. Although those interactions may create challenges for the diagnosis and assessment of disease stability, they provide a valuable conceptual framework to rationalize HF-COPD treatment. The impact of COPD or HF on the pharmacological treatment of HF or COPD, respectively, is then comprehensively discussed. Authors finalize by outlining how the non-pharmacological treatment (i.e. rehabilitation and exercise reconditioning) can be tailored to the specific needs of patients with HF-COPD. Expert commentary: Randomized clinical trials testing the efficacy and safety of new medications for HF or COPD should include a sizeable fraction of patients with these coexistent pathologies. Multidisciplinary clinics involving cardiologists and respirologists trained in both diseases (with access to unified cardiorespiratory rehabilitation programs) are paramount to decrease the humanitarian and social burden of HF-COPD.

Pathophysiological mechanisms of exertional breathlessness in chronic obstructive pulmonary disease and interstitial lung disease

PURPOSE OF REVIEW

Breathlessness is a common and distressing symptom in patients with chronic obstructive pulmonary disease (COPD) and fibrotic interstitial lung disease (ILD), particularly during exercise. Effective medical management of exertional breathlessness in people living with COPD and fibrotic ILD is challenging for healthcare providers and requires an understanding of its mechanisms. Thus, in this brief review we summarize recent advances in our understanding of the pathophysiological mechanisms of exertional breathlessness in COPD and fibrotic ILD.

RECENT FINDINGS

The collective results of recent physiological and clinical trials suggest that higher intensity ratings of exertional breathlessness in both COPD and fibrotic ILD compared to healthy control individuals is mechanistically linked to the awareness of greater neural respiratory drive (quantified using inspiratory muscle electromyography) needed to compensate for pathophysiological abnormalities in respiratory mechanics and pulmonary gas exchange efficiency.

SUMMARY

Any therapeutic intervention capable of decreasing intrinsic mechanical loading of the respiratory system and/or increasing pulmonary gas exchange efficiency has the potential to decrease the prevalence and severity of activity-related breathlessness and improve related clinical and patient-reported outcomes (e.g., exercise tolerance and health-related quality of life) by decreasing neural respiratory drive in people with COPD and fibrotic ILD.

Nitrogen single-breath washout test for evaluating exercise tolerance and quality of life in patients with chronic obstructive pulmonary disease

Pulmonary function tests (PFTs) traditionally used in clinical practice do not accurately predict exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to assess whether the nitrogen single-breath washout (N₂SBW) test explains exercise intolerance and poor quality of life in stable COPD patients. This cross-sectional study included 31 patients with COPD subjected to PFTs (including the N₂SBW test) and a cardiopulmonary exercise test (CPET). Patients were also evaluated using the following questionnaires: the COPD assessment test (CAT), the 36-Item Short Form Health Survey (SF36) and St. George's Respiratory Questionnaire (SGRQ). Peak oxygen uptake (peak VO₂) was negatively correlated with the phase III slope of the N₂SBW (SIII_N2) (r=-0.681, P<0.0001) and positively correlated with forced expiratory volume in one second (FEV₁; r=0.441, P=0.013). Breathing reserve was negatively correlated with SIII_N2, closing volume/vital capacity, and residual volume (RV) (r=-0.799, P<0.0001; r=-0.471, P=0.007; r=-0.401, P=0.025, respectively) and positively correlated with FEV₁, forced vital capacity (FVC) and FEV₁/FVC (r=0.721; P<0.0001; r=0.592, P=0.0004; r=0.670, P<0.0001, respectively). SIII_N2 and CAT were independently predictive of VO₂ and breathing reserve at peak exercise. RV, FVC, and FEV₁ were independently predictive of the SF36-physical component summary, SF36-mental component summary, and breathing reserve, respectively. The SGRQ did not present any independent variables that could explain the model. In stable COPD patients, inhomogeneity of ventilation explains a large degree of exercise intolerance assessed by CPETs and, to a lesser extent, poor quality of life.

Cardiopulmonary exercise test and PaO2 in evaluation of pulmonary hypertension in COPD

Background

Exercise tolerance decreases as COPD progresses. Pulmonary hypertension (PH) is common in COPD and may reduce performance further. COPD patients with and without PH could potentially be identified by cardiopulmonary exercise test (CPET). However, results from previous studies are diverging, and a unified conclusion is missing. We hypothesized that CPET combined with arterial blood gases is useful to discriminate between COPD outpatients with and without PH.

Methods

In total, 93 COPD patients were prospectively included. Pulmonary function tests, right heart catheterization, and CPET with blood gases were performed. The patients were divided, by mean pulmonary artery pressure, into COPD-noPH (<25 mmHg) and COPD-PH (≥25 mmHg) groups. Linear mixed models (LMMs) were fitted to estimate differences when repeated measurements during the course of exercise were considered and adjusted for gender, age, and airway obstruction.

Results

Ventilatory and/or hypoxemic limitation was the dominant cause of exercise termination. In LMM analyses, significant differences between COPD-noPH and COPD-PH were observed for PaO₂, SaO₂, PaCO₂, ventilation, respiratory frequency, and heart rate. PaO₂ <61 mmHg (8.1 kPa) during unloaded pedaling, the only load level achieved by all the patients, predicted PH with a sensitivity of 86% and a specificity of 78%.

Conclusion

During CPET, low exercise performance and PaO₂ strongly indicated PH in COPD patients.

Exertional dyspnoea in cardiorespiratory disorders: the clinical use of cardiopulmonary exercise testing

Is dyspnoea worth documenting and accurately assessing? The answer is undoubtedly yes, for at least the following reasons. 1) Activity-related dyspnoea is usually the earliest and most troublesome complaint for which patients with cardiopulmonary diseases seek medical attention. 2) This symptom progresses relentlessly as the underlying disease advances, leading invariably to avoidance of activity with consequent skeletal muscle deconditioning and an impoverished quality of life. 3) It is estimated that up to a quarter of the general population and half of severely ill patients are affected by it. 4) Dyspnoea is also an important predictor of quality of life, exercise tolerance and mortality in various conditions. In patients with chronic obstructive pulmonary disease (COPD), it has been shown to be a better predictor of mortality than forced expiratory volume in 1 s. In patients with heart disease referred for clinical exercise testing, it is a better predictor of mortality than angina. 5) Dyspnoea is also associated with decreased functional status and worse psychological health in older individuals living at home. 6) It is also a factor in the low adherence to exercise training programmes in sedentary adults and in patients with COPD. 7) The effective management of exertional dyspnoea remains a major challenge for caregivers and modern treatment strategies that are based on attempts to reverse the underlying chronic condition are only partially successful [1–7].

A series of articles on exertional dyspnoea in cardiorespiratory disorders begins in the European Respiratory Reviewhttp://ow.ly/fLT0300uHgw

Physiological and clinical relevance of exercise ventilatory efficiency in COPD

Exercise ventilation (V'_E) relative to carbon dioxide output (V'_CO2 ) is particularly relevant to patients limited by the respiratory system, e.g. those with chronic obstructive pulmonary disease (COPD). High V'_E-V'_CO2 (poor ventilatory efficiency) has been found to be a key physiological abnormality in symptomatic patients with largely preserved forced expiratory volume in 1 s (FEV₁). Establishing an association between high V'_E-V'_CO2 and exertional dyspnoea in mild COPD provides evidence that exercise intolerance is not a mere consequence of detraining. As the disease evolves, poor ventilatory efficiency might help explaining "out-of-proportion" breathlessness (to FEV₁ impairment). Regardless, disease severity, cardiocirculatory co-morbidities such as heart failure and pulmonary hypertension have been found to increase V'_E-V'_CO2 In fact, a high V'_E-V'_CO2 has been found to be a powerful predictor of poor outcome in lung resection surgery. Moreover, a high V'_E-V'_CO2 has added value to resting lung hyperinflation in predicting all-cause and respiratory mortality across the spectrum of COPD severity. Documenting improved ventilatory efficiency after lung transplantation and lung volume reduction surgery provides objective evidence of treatment efficacy. Considering the usefulness of exercise ventilatory efficiency in different clinical scenarios, the V'_E-V'_CO2 relationship should be valued in the interpretation of cardiopulmonary exercise tests in patients with mild-to-end-stage COPD.