Peak oxygen uptake and breathing pattern in COPD patients--a four-year longitudinal study

Obstructive sleep apnea reduces functional capacity and impairs cardiac autonomic modulation during submaximal exercise in patients with chronic obstructive pulmonary disease: A follow-up study

BACKGROUND

Functional capacity and heart rate variability (HRV) are important prognostic markers in chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea syndrome (OSA). However, the impact of the overlap of these diseases and the one-year clinical follow-up has not yet been evaluated.

OBJECTIVES

To assess whether the presence of OSA can impair functional performance and cardiac autonomic control during exercise in patients with COPD; and to verify whether the overlap of these diseases could lead to worse clinical outcomes during the one-year follow-up.

METHODS

Thirty-four patients underwent pulmonary function tests, echocardiography and polysomnography for diagnostic confirmation, disease staging, exclusion of any cardiac changes, and allocation between groups. The patients underwent the six-minute walk test (6MWT) to assess functional capacity and HRV during exercise. Subsequently, patients were followed up for 12 months to record outcomes such as exacerbation, hospitalization, and deaths. At the end of this period, the patients were revaluated to verify the hypotheses of the study.

RESULTS

The OSA-COPD group showed greater functional impairment when compared to the COPD group (p=0.003) and showed worse cardiac autonomic responses during the 6MWT with greater parasympathetic activation (p=0.03) and less complexity of the autonomic nervous system, in addition to being more likely to exacerbate (p=0.03) during one year of follow-up.

CONCLUSION

OSA-COPD produces deleterious effects on functional performance and a greater autonomic imbalance that impairs clinical outcomes.

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

AIM

To identify better predictors of early death in patients with chronic obstructive pulmonary disease (COPD) using potential predictors derived from key measures obtained from cardiopulmonary exercise testing (CPET).

METHODS

This is a prospective, cohort study with 42-month follow-up in 126 COPD patients. Every patient completed the clinical evaluation, followed by a pulmonary function test and CPET. CPET was performed on a cycle ergometer with electromagnetic braking and ventilatory expired analysis was measured breath-by-breath using a computer-based system. Peak oxygen consumption (V̇O_2, mlO_2. kg^-1_. min^-1), minute ventilation/carbon dioxide production and the, minute ventilation (V̇_E, L/min), and the V̇_E/carbon dioxide production (V̇_E/V̇CO₂) slope were obtained from CPET.

RESULTS

48 (38%) patients died during the 42-month follow-up. Kaplan Meier analysis revealed a V̇_E/V̇CO₂ slope ≥30, peak V̇_E ≤ 25.7L/min and peak V̇O₂ ≤ 13.8 mlO_2. kg^-1_. min^-1were strong predictors of mortality in COPD patients. Cox regression revealed that the V̇O₂ peak ≤13.8 mlO_2. kg^-1_. min^-1 (CI 95% 0.08-0.93), V̇_E/V̇CO₂ slope ≥30 (CI 95% 0.07-0.94), V̇_E peak ≤25.7 L/min (CI 95% 0.01-0.15), Sex (CI 95% 0.04-0.55) and Age (CI 95% 1.03-1.2) were the main predictors of mortality risk.

CONCLUSION

Diminished exercise capacity and peak ventilation as well as ventilatory inefficiency are independent prognostic markers. Similar to patients with heart failure, CPET may be a valuable clinical assessment in the COPD population.

Breathing patterns in people with exercise-induced laryngeal obstruction

Exercise-induced laryngeal obstruction (EILO) is common, but we lack readily available diagnostic tools. The larynx represents an important point of resistance in the airways, and we therefore hypothesized that EILO is associated with characteristic breathing patterns possible to record from a standard incremental ergospirometry test. We studied 24 individuals with moderate/severe EILO and 20 individuals with no-EILO, mean (SD) age 17 (6.1) and 24 (6.4) years, respectively. EILO versus no-EILO was verified from maximal continuous laryngoscopy treadmill exercise (CLE) tests, which also included ergospirometry. We described the relationships between minute ventilation ( V ˙ E ) versus tidal volume (VT ) and V ˙ E versus carbon dioxide output ( V ˙ CO 2 ), using respectively quadratic and linear equations, and applied adjusted regression models to compare ergospirometry data and curve parameters. Compared to the no-EILO group, the group with EILO had prolonged inspiratory time (Tin ), lower breathing frequency (Bf ), lower V ˙ E , and lower inspiratory flow rate ( V ˙ in ) at peak exercise. Mathematical modeling of the breathing pattern relationships was feasible in both groups, with similar coefficients of variation. For V ˙ E versus VT , the mathematical curve parameters were similar. For V ˙ E versus V ˙ CO 2 , the slope was similar but the intercept was lower in the EILO group. EILO was associated with prolonged Tin , lower Bf , V ˙ E , and V ˙ E . The relationship between V ˙ E versus VT was similar, whereas for V ˙ E versus V ˙ CO 2 , the slope was almost parallel but shifted downward for the EILO group. Most ergospirometry data overlapped, except V ˙ in which discriminated between EILO and no-EILO in a promising way.

The correlation between quadriceps muscle strength and endurance and exercise performance in patients with COPD

To determine the association between quadriceps muscle strength (QMS) and endurance (QME) and exercise capacity in patients with COPD after stratification for sex and resting lung function (LF). Data were collected from 3,246 patients with COPD (60% men, 64 ± 9 yr), including measures of exercise capacity [peak aerobic capacity (peakV̇o₂), 6-min walk distance (6MWD)] and isokinetic QMS and QME. Patients were stratified for sex, forced expiratory volume in 1 s (>50/≤50% predicted), single breath carbon monoxide diffusing capacity (>50/≤50% predicted), and residual volume (>140/≤140% predicted). After stratification for resting LF, QMS and QME were significantly associated with peakV̇o₂ (r range: 0.47-0.61 and 0.49-0.65 for men and 0.53-0.66 and 0.48-0.67 for women, respectively) and 6MWD (r range: 0.29-0.42 and 0.44-0.55 for men and 0.25-0.54 and 0.34-0.55 for women, respectively) (P < 0.001). Regression models demonstrated that QMS and QME were significant determinants of peakV̇o₂ (explained variance R² range: 35.6%-48.8% for men and 36.8%-49.0% for women) and 6MWD (R² range: 24.3%-43.3% for men and 28.4%-40.3% for women), independent of age and fat-free mass. Quadriceps muscle function was significantly associated with peakV̇o₂ and 6MWD in male and female patients with COPD after stratification for resting LF, in which QME appear to be a more important determinant than QMS. This underlines the importance of systematically evaluating both quadriceps muscle strength and endurance in in all patients with COPD.NEW & NOTEWORTHY Our findings identified quadriceps muscle function as an important determinant of exercise capacity across a wide spectrum of lung function. Quadriceps muscle endurance appears to be a more important determinant than quadriceps muscle strength, underlining the importance of including both the measurement of quadriceps muscle strength and endurance in routine assessment for all patient with COPD.

Intercept of minute ventilation versus carbon dioxide output relationship as an index of ventilatory inefficiency in chronic obstructive pulmonary disease

Background

Ventilatory inefficiency contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). The intercept of the minute ventilation (V^˙_E) vs. carbon dioxide output (V^˙ CO₂) plot is a key ventilatory inefficiency parameter. However, its relationships with lung hyperinflation (LH) and airflow limitation are not known. This study aimed to evaluate correlations between the V^˙_E/V^˙ CO₂ intercept and LH and airflow limitation to determine its physiological interpretation as an index of functional impairment in COPD.

Methods

We conducted a retrospective analysis of data from 53 COPD patients and 14 healthy controls who performed incremental cardiopulmonary exercise tests (CPETs) and resting pulmonary function assessment. Ventilatory inefficiency was represented by parameters reflecting the V^˙_E/V^˙ CO₂ nadir and slope (linear region) and the intercept of V^˙_E/V^˙ CO₂ plot. Their correlations with measures of LH and airflow limitation were evaluated.

Results

Compared to control, the slope (30.58±3.62, P<0.001) and intercept (4.85±1.11 L/min, P<0.05) were higher in COPD_stages1-2, leading to a higher nadir (31.47±4.47, P<0.01). Despite an even higher intercept in COPD_stages3-4 (7.16±1.41, P<0.001), the slope diminished with disease progression (from 30.58±3.62 in COPD_stages1-2 to 26.84±4.96 in COPD_stages3-4, P<0.01). There was no difference in nadir among COPD groups and higher intercepts across all stages. The intercept was correlated with peak V^˙_E/maximal voluntary ventilation (MVV) (r=0.489, P<0.001) and peak V^˙ O₂/Watt (r=0.354, P=0.003). The intercept was positively correlated with residual volume (RV) % predicted (r=0.571, P<0.001), RV/total lung capacity (TLC) (r=0.588, P<0.001), peak tidal volume (V_T)/FEV₁ (r=0.482, P<0.001) and negatively correlated with rest inspiratory capacity (IC)/TLC (r=−0.574, P<0.001), peak V_T/TLC (r=−0.585, P<0.001), airflow limitation forced expiratory volume in 1 s (FEV₁) % predicted (r=−0.606, P<0.001), and FEV₁/forced vital capacity (FVC) (r=−0.629, P<0.001).

Conclusions

V^˙_E/V^˙ CO₂ intercept was consistently correlated with worsening static and dynamic LH, pulmonary gas exchange, and airflow limitation in COPD. The V^˙_E/V^˙ CO₂ intercept emerged as a useful index of ventilatory inefficiency in COPD patients.

Six years progression of exercise capacity in subjects with mild to moderate airflow obstruction, smoking and never smoking controls

BACKGROUND

Exercise capacity is an important feature in patients with COPD. Its impairment drives disability and dependency for daily activities performance. This study evaluated the six years change in exercise capacity in subjects with airflow obstruction and compared this to subjects without airflow obstruction, with and without a smoking history.

METHODS

Cardiopulmonary exercise tests (CPET) were repeatedly performed during a six years follow up period. Peak oxygen uptake (VO2peak), work rate (WRpeak), heart rate (HRpeak), minute ventilation (VEpeak), respiratory exchange ratio (RERpeak) and ventilatory reserve (VE/MVV) were collected as effort dependent outcomes. The slopes of oxygen uptake, ventilatory and mechanical efficiency (OUES, ΔVE/ΔVCO2 and ΔVO2/ΔWR) were collected as effort independent outcomes.

RESULTS

One hundred and thirty-eight subjects were included. Thirty-eight presented airflow obstruction (63±6 years, 74% men, FEV1 90±15%pred), 44 had a smoking history but no airflow obstruction (61±5 years, 61% men, FEV1 105±15%pred) and 56 had never smoked (61±7 years, 57% men, FEV1 117±18%pred). At baseline, the airflow obstruction group had slightly worse exercise capacity in comparison to the never smoking control group, in absolute terms and expressed as percentage of the predicted value (VO2peak = 27±5 versus 32±8 ml/min/kg, p<0.01; 112±29 versus 130±33%pred, p = 0.04). Most exercise variables showed a statistically significant yearly deterioration, with exception of VE/MVV, ΔVE/ΔVCO2 and ΔVO2/ΔWR. The yearly decline in VO2peak and OUES was not faster in subjects with airflow obstruction than in smoking and never smoking controls (VO2peak -67 (9) versus -76 (9) ml/min, p = 0.44 and versus -58 (9), p = 0.47; OUES -32 (11) versus -68 (10), p = 0.03 and versus -68 (13), p = 0.03).

CONCLUSIONS

With exception of VO2peak, effort dependent variables deteriorated faster in subjects with airflow obstruction compared to never smoking controls. The deterioration of effort independent variables, however, was not accelerated in the airflow obstruction group compared to controls.

COPD assessment test and FEV1: do they predict oxygen uptake in COPD?

Background

Chronic obstructive pulmonary disease (COPD) manifests itself in complex ways, with local and systemic effects; because of this, a multifactorial approach is needed for disease evaluation, in order to understand its severity and impact on each individual. Thus, our objective was to study the correlation between easily accessible variables, usually available in clinical practice, and maximum aerobic capacity, and to determine models for peak oxygen uptake (VO₂peak) estimation in COPD patients.

Subjects and methods

Individuals with COPD were selected for the study. At the first visit, clinical evaluation was performed. During the second visit, the volunteers were subjected to the cardiopulmonary exercise test. To determine the correlation coefficient of VO₂peak with forced expiratory volume in 1 second (FEV₁) (% pred.) and the COPD Assessment Test score (CATs), Pearson or Spearman tests were performed. VO₂ at the peak of the exercise was estimated from the clinical variables by simple and multiple linear regression analyses.

Results

A total of 249 subjects were selected, 27 of whom were included after screening (gender: 21M/5F; age: 65.0±7.3 years; body mass index: 26.6±5.0 kg/m²; FEV₁ (% pred.): 56.4±15.7, CAT: 12.4±7.4). Mean VO₂ peak was 12.8±3.0 mL⋅kg⁻¹⋅min⁻¹ and VO₂peak (% pred.) was 62.1%±14.9%. VO₂peak presented a strong positive correlation with FEV₁ (% pred.), r: 0.70, and a moderate negative correlation with the CATs, r: -0.54. In the VO₂peak estimation model based on the CAT (estimated VO₂peak =15.148− [0.185× CATs]), the index explained 20% of the variance, with estimated error of 2.826 mL⋅kg⁻¹⋅min⁻¹. In the VO₂peak estimation model based on FEV₁ (estimated VO₂peak =6.490+ [0.113× FEV₁]), the variable explained 50% of the variance, with an estimated error of 2.231 mL⋅kg⁻¹⋅min⁻¹. In the VO₂peak estimation model based on CATs and FEV₁ (estimated VO₂peak =8.441− [0.0999× CAT] + [0.1000× FEV₁]), the variables explained 55% of the variance, with an estimated error of 2.156 mL⋅kg⁻¹⋅min⁻¹.

Conclusion

COPD patients’ maximum aerobic capacity has a significant correlation with easily accessible and widely used clinical variables, such as the CATs and FEV₁, which can be used to estimate peak VO₂.

Role of inspiratory capacity on dyspnea evaluation in COPD with or without emphysematous lesions: a pilot study

Background

Since forced expiratory volume in 1 second (FEV₁) shows a weak correlation with patients’ symptoms in COPD, some volume parameters may better reflect the change in dyspnea symptoms after treatment. In this article, we investigated the role of inspiratory capacity (IC) on dyspnea evaluation among COPD patients with or without emphysematous lesions.

Methods

In this prospective study, 124 patients with stable COPD were recruited. During the baseline visit, patients performed pulmonary function tests and dyspnea evaluation using the modified Medical Research Council (mMRC) scale. Partial patients underwent quantitative computerized tomography scans under physicians’ recommendations, and emphysematous changes were assessed using the emphysema index (EI; low attenuation area [LAA]% −950). These subjects were then divided into the emphysema-predominant group (LAA% −950≥9.9%) and the non-emphysema-predominant group (LAA% −950<9.9%). After treatment for ~1 month, subjects returned for reevaluation of both pulmonary function parameters and dyspnea severity. Correlation analysis between the change in IC (ΔIC) and dyspnea (ΔmMRC) was performed.

Results

Correlation analysis revealed that ΔIC was negatively correlated with ΔmMRC (correlation coefficient [cc], −0.490, P<0.001) in the total study population, which was stronger than that between ΔFEV₁ and ΔmMRC (cc, −0.305, P=0.001). Patients with absolute ΔmMRC >1 were more likely to exhibit a marked increase in IC (≥300 mL) than those with absolute ΔmMRC ≤1 (74.36% versus 35.29%; odds ratio [OR], 5.317; P<0.001). In the emphysema-predominant group, only ΔIC strongly correlated with ΔmMRC (cc, −0.459, P=0.005), while ΔFEV₁ did not (P>0.05).

Conclusion

IC could serve as an effective complement to FEV₁ in COPD patients undergoing dyspnea evaluation after treatment. For COPD patients with predominant emphysematous lesions, an increase in IC is particularly more suitable for explaining dyspnea relief than FEV₁.