Elevated exercise ventilation in mild COPD is not linked to enhanced central chemosensitivity.

BACKGROUND: The purpose of this study was to determine if altered central chemoreceptor characteristics contributed to the elevated ventilation relative to carbon dioxide production (V̇E/V̇CO2) response during exercise in mild chronic obstructive pulmonary disease (COPD). METHODS: Twenty-nine mild COPD and 19 healthy age-matched control participants undertook lung function testing followed by symptom-limited incremental cardiopulmonary exercise testing . On a separate day, basal (non-chemoreflex) ventilation (V̇EB), the central chemoreflex ventilatory recruitment threshold for CO2 (VRTCO2), and central chemoreflex sensitivity (V̇ES) were assessed using the modified Duffin's CO2 rebreathing method. Resting arterialized blood gas data were also obtained. RESULTS: At standardized exercise intensities, absolute V̇E and V̇E/V̇CO2 were consistently elevated and the end-tidal partial pressure of CO2 was relatively decreased in mild COPD versus controls (all p < 0.05). There were no between-group differences in resting arterialized blood gas parameters, basal V̇E, VRTCO2, or V̇ES (all p > 0.05). CONCLUSION: These data have established that excessive exercise ventilation in mild COPD is not explained by altered central chemosensitivity.

Impact of pulmonary rehabilitation on the major dimensions of dyspnea in COPD.

The evaluation of dyspnea and its responsiveness to therapy in COPD should consider the multidimensional nature of this symptom in each of its sensory-perceptual (intensity, quality), affective and impact domains. To gain new insights into mechanisms of dyspnea relief following pulmonary rehabilitation (PR), we examined effects on the major domains of dyspnea and their interaction with physiological training effects. This randomized, controlled study was conducted in 48 subjects with COPD. Subjects received either 8-weeks of PR or usual care (CTRL). Pre- and post-intervention assessments included: sensory-perceptual (i.e., exertional dyspnea intensity, dyspnea descriptors at end-exercise), affective (i.e., intensity of breathing-related anxiety during exercise, COPD self-efficacy, walking self-efficacy) and impact (i.e., activity-related dyspnea measured by the Baseline/Transition Dyspnea Index, Chronic Respiratory Questionnaire dyspnea component, St. George's Respiratory Disease Questionnaire activity component) domains of dyspnea; functional performance (i.e., 6-minute walk, endurance shuttle walk); pulmonary function; and physiological measurements during constant work rate cycle exercise at 75% of the peak incremental work rate. Forty-one subjects completed the study: PR (n = 17) and CTRL (n = 24) groups were well matched for age, sex, body size and pulmonary function. There were no significant between-group differences in pre- to post-intervention changes in pulmonary function or physiological parameters during exercise. After PR versus CTRL, significant improvements were found in the affective and impact domains but not in the sensory-perceptual domain of dyspnea. In conclusion, clinically meaningful improvements in the affective and impact domains of dyspnea occurred in response to PR in the absence of consistent physiological training effects.

Effect of adjunct fluticasone propionate on airway physiology during rest and exercise in COPD.

RATIONALE: Combination therapy with corticosteroid and long-acting ß(2)-agonists (LABA) in a single inhaler is associated with superior effects on airway function and exercise performance in COPD compared with LABA monotherapy. The physiological effects of adding inhaled corticosteroid monotherapy to maintenance bronchodilator therapy (long-acting anticholinergics and LABA singly or in combination) in COPD are unknown. METHODS: This was a randomized, double-blind, placebo-controlled, crossover study (NCT00387036) to compare the effects of inhaled fluticasone propionate 500 µg (FP500) twice-daily and placebo (PLA) on airway function during rest and exercise, measured during constant work rate cycle exercise at 75% of maximum incremental cycle work rate, in 17 patients with COPD (FEV(1) ≤ 70% predicted). RESULTS: After treatment with FP500 compared to PLA, there were significant increases in post-dose measurements of FEV(1) (+115 mL, P = 0.006) and the FEV(1)/FVC ratio (+2.5%, P = 0.017), along with decreases in plethysmographic residual volume (-0.32L; P = 0.031), functional residual capacity (-0.30L, P = 0.033), and total lung capacity (-0.30L, P = 0.027) but no changes in vital capacity or inspiratory capacity (IC). Post-treatment comparisons demonstrated a significant improvement in endurance time by 188 ± 362 s with FP500 (P = 0.047) with no concomitant increase in dyspnea intensity. End-inspiratory and end-expiratory lung volumes were reduced at rest and throughout exercise with FP500 compared with PLA (P < 0.05). CONCLUSION: Inhaled FP500 monotherapy was associated with consistent and clinically important improvements in FEV(1), static lung volumes, dynamic operating lung volumes, and exercise endurance when added to established maintenance long-acting bronchodilator therapy in patients with moderate to severe COPD.

Effect of menopause on the chemical control of breathing and its relationship with acid-base status.

This study examined the role of alterations in the chemoreflex control of breathing, acid-base balance, and their interaction in postmenopausal ventilatory adaptations. A modified iso-oxic hyperoxic and hypoxic CO(2)-rebreathing procedure was employed to evaluate central and peripheral chemoreflex drives to breathe, respectively, in 15 healthy postmenopausal and 20 premenopausal women of similar age. Arterialized venous blood samples were collected at rest for the estimation of arterial Pco(2) (Pa(CO(2))) and H(+) concentration ([H(+)]), plasma strong ion difference ([SID]) and total weak acid ([A](tot)) concentrations, and serum progesterone ([P(4)]) and 17beta-estradiol ([E(2)]) concentrations. In post- compared with premenopausal women, Pa(CO(2)), [SID], and the central chemoreflex ventilatory recruitment threshold for Pco(2) (VRTco(2)) were higher, whereas [P(4)] and [E(2)] were lower (all P < 0.05), with no significant change in central or peripheral chemoreflex sensitivity, peripheral chemoreflex VRTco(2), and [A](tot). The acidifying effect of an increased Pa(CO(2)) was offset by the alkalizing effect of an increased [SID], such that [H(+)] was preserved in post- compared with premenopausal women. Pa(CO(2)) correlated positively with the central chemoreflex VRTco(2) (r = 0.67, P < 0.01), which in turn correlated positively with [SID] (r = 0.53, P < 0.01) within the pooled data. In conclusion, the relative alveolar hypoventilation and attendant arterial hypercapnia in healthy post- compared with premenopausal women could be explained, in part, by the interaction of 1) reduced central, but not peripheral, chemoreflex VRTco(2), 2) increased [SID], and 3) reduced circulating female sex steroid hormone concentrations.