Airway obstruction, dynamic hyperinflation, and breathing pattern during incremental exercise in COPD patients

Ventilatory Efficiency in Children and Adolescents Born Extremely Preterm

Purpose: Children and adolescents born extremely preterm (EP) have lower dynamic lung volumes and gas transfer capacity than subjects born at term. Most studies also report lower aerobic capacity. We hypothesized that ventilatory efficiency was poorer and that breathing patterns differed in EP−born compared to term−born individuals.

Methods: Two area−based cohorts of participants born with gestational age ≤28 weeks or birth weight ≤1000 g in 1982−85 (n = 46) and 1991–92 (n = 35) were compared with individually matched controls born at term. Mean ages were 18 and 10 years, respectively. The participants performed an incremental treadmill exercise test to peak oxygen uptake with data averaged over 20 s intervals. For each participant, the relationship between exhaled minute ventilation (V˙_E) and carbon dioxide output (V˙CO₂) was described by a linear model, and the relationship between tidal volume (V_T) and V˙_E by a quadratic model. Multivariate regression analyses were done with curve parameters as dependent variables, and the categories EP vs. term−born, sex, age, height, weight and forced expiratory volume in 1 s (FEV₁) as independent variables.

Results: In adjusted analyses, the slope of the V˙_E−V˙CO₂ relationship was significantly steeper in the EP than the term-born group, whereas no group difference was observed for the breathing pattern, which was related to FEV₁ only.

Conclusion: EP-born participants breathed with higher V˙_E for any given CO₂ output, indicating lower ventilatory efficiency, possibly contributing to lower aerobic capacity. The breathing patterns did not differ between the EP and term−born groups when adjusted for FEV₁.

Reliability of the Determination of the Ventilatory Threshold in Patients with COPD

PURPOSE

The purpose of this study was to determine the interobserver reliability of the assessment of the ventilatory threshold (VT) using two methods in patients with chronic obstructive pulmonary disease (COPD) and in control subjects.

METHODS

VT was identified from incremental exercise testing graphs of 115 subjects (23 controls and 23 in each COPD Global initiative for chronic Obstructive Lung Disease class) by two human observers and a computer analysis using the V-slope method and the ventilatory equivalent method (VEM). Agreement between observers in identifying oxygen uptake at VT (VO 2VT) and HR at VT (HR VT) across disease severity groups was evaluated using intraclass correlation (for humans) and Passing-Bablok regression analysis (human vs computer).

RESULTS

For human observers, ICC (95% confidence interval) in determining VO 2VT were higher in controls (0.98 (0.97-0.99) both with V-slope and with VEM) than those in COPD patients (0.72 (0.60-0.81) with V-slope and 0.64 (0.50-0.74) with VEM). Passing-Bablok analysis showed that human and computerized determination of VO 2VT was interchangeable in controls but not in patients with COPD. Forced expiratory volume in one second and peak minute ventilation during exercise were the only variables independently associated with greater interobserver differences in VO 2VT. Interobserver differences in HRVT ranged from 2 ± 1 (controls) to 10 ± 3 bpm (GOLD 4).

CONCLUSIONS

In patients with COPD, the reliability of human estimation of VO 2VT is less than that in controls and not interchangeable with a computerized analysis. This should be taken into account when using VT for exercise prescription, as a tool to monitor responses to an intervention, as a surrogate measure of overall aerobic fitness, or as a prognostic marker in patients with COPD.

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

Background

Activities of daily living in patients with chronic obstructive pulmonary disease (COPD) are limited by exertional dyspnea and reduced exercise capacity. The aims of the study were to examine longitudinal changes in peak oxygen uptake (V̇O_2peak), peak minute ventilation (V̇_Epeak) and breathing pattern over four years in a group of COPD patients, and to examine potential explanatory variables of change.

Methods

This longitudinal study included 63 COPD patients, aged 44-75 years, with a mean forced expiratory volume in one second (FEV₁) at baseline of 51 % of predicted (SD = 14). The patients performed two cardiopulmonary exercise tests (CPETs) on treadmill 4.5 years apart. The relationship between changes in V̇O_2peak and V̇_Epeak and possible explanatory variables, including dynamic lung volumes and inspiratory capacity (IC), were analysed by multivariate linear regression analysis. The breathing pattern in terms of the relationship between minute ventilation (V̇_E) and tidal volume (V_T) was described by a quadratic equation, V_T = a + b∙V̇_E + c∙V̇_E², for each test. The V_Tmax was calculated from the individual quadratic relationships, and was the point where the first derivative of the quadratic equation was zero. The mean changes in the curve parameters (CPET2 minus CPET1) and V_Tmax were analysed by bivariate and multivariate linear regression analyses with age, sex, height, changes in weight, lung function, IC and inspiratory reserve volume as possible explanatory variables.

Results

Significant reductions in V̇O_2peak (p < 0.001) and V̇_Epeak (p < 0.001) were related to a decrease in resting IC and in FEV₁. Persistent smoking contributed to the reduction in V̇O_2peak. The breathing pattern changed towards a lower V_T at a given V̇_E and was related to the reduction in FEV₁.

Conclusion

Increasing static hyperinflation and increasing airway obstruction were related to a reduction in exercise capacity. The breathing pattern changed towards more shallow breathing, and was related to increasing airway obstruction.

Submissive hypercapnia: Why COPD patients are more prone to CO2 retention than heart failure patients

Patients with late-stage chronic obstructive pulmonary disease (COPD) are prone to CO2 retention, a condition which has been often attributed to increased ventilation-perfusion mismatch particularly during oxygen therapy. However, patients with mild-to-moderate COPD or chronic heart failure (CHF) also suffer similar ventilatory inefficiency but they remain near-normocapnic at rest and during exercise with an augmented respiratory effort to compensate for the wasted dead space ventilation. In severe COPD, the augmented exercise ventilation progressively reverses as the disease advances, resulting in hypercapnia at peak exercise as ventilatory limitation due to increasing expiratory flow limitation and dynamic lung hyperinflation sets in. Submissive hypercapnia is an emerging paradigm for understanding optimal ventilatory control and cost/benefit decision-making under prohibitive respiratory chemical-mechanical constraints, where the need to maintain normocapnia gives way to the mounting need to conserve the work of breathing. In severe/very severe COPD, submissive hypercapnia epitomizes the respiratory controller's 'can't breathe, so won't breathe' say-uncle policy when faced with insurmountable ventilatory limitation. Even in health, submissive hypercapnia ensues during CO2 breathing/rebreathing when the inhaled CO2 renders normocapnia difficult to restore even with maximal respiratory effort, hence the respiratory controller's 'ain't fresh, so won't breathe' modus operandi. This 'wisdom of the body' with a principled decision to tolerate hypercapnia when faced with prohibitive ventilatory or gas exchange limitations rather than striving for untenable normocapnia at all costs is analogous to the notion of permissive hypercapnia in critical care, a clinical strategy to minimize the risks of ventilator-induced lung injury in patients receiving mechanical ventilation.