Clinical studies
Muscle sympathetic nerve activity and ventilation during exercise in subjects with and without chronic heart failureActivité du nerf sympathique musculaire et ventilation durant l’effort chez des sujets souffrant ou non d’insuffisance cardiaque chronique

https://doi.org/10.1016/S0828-282X(08)70176-4Get rights and content

Background

Changes within skeletal muscle, including augmentation of its capacity to elicit reflex increases in both efferent muscle sympathetic nerve activity (MSNA) and ventilation during work, contribute significantly to exercise intolerance in heart failure (HF). Previously, we demonstrated that peak oxygen uptake (pVO2) in HF relates inversely to MSNA at rest and during exercise.

Objective

To test the hypothesis that there is an independent positive relationship between resting MSNA and the ratio of ventilation to carbon dioxide output during exercise (VE/VCO2) that is augmented in HF.

Methods

MSNA at rest and VE/VCO2 during stationary cycling were measured in 30 patients (27 men) with HF (mean ± SD ejection fraction 20 ± 6%) and in 31 age-matched controls (29 men).

Results

MSNA was higher in HF patients than in controls (51.5 ± 14.3 bursts/min versus 33.0 ± 11.1 bursts/min; P < 0.0001). The VE/VCO2 slope was also higher in HF patients than in controls (33.7 ± 5.7 versus 26.0 ± 3.5; P < 0.0001), whereas pVO2 was lower in HF patients than in controls (18.6 ± 6.6 versus 31.4 ± 8.4 mL/kg/min; P < 0.0001). There were significant relationships between MSNA and VE/VCO2 in both HF (r=0.50; P=0.005) and control subjects (r=0.36; P=0.046). The slope of this regression equation was steeper in HF (0.20 versus 0.11 × MSNA; P=0.001). An analysis of covariance for main effects, including age and pVO2, identified a significant independent relationship between MSNA burst frequency and VE/VCO2 (P=0.013) that differed between HF and controls (P < 0.01).

Conclusions

The magnitude of resting sympathetic activity correlates positively with the VE/VCO2 slope. Augmentation of this relationship in HF patients is consistent with the concept that enhanced mechanoreceptor reflex activity exaggerates their ventilatory response to exercise.

Historique

Les changements affectant les muscles squelettiques, y compris l’augmentation de la capacité du réflexe thoracique lors de l’activité des nerfs sympathiques musculaires (ANSM) efférents et de la ventilation à l’effort, contribuent significativement à l’intolérance à l’effort en présence d’insuffisance cardiaque (IC). Nous avons déjà démontré que la consommation maximum d’oxygène (pVO2) de l’Hb dans l’IC est inversement proportionnelle à l’ANSM au repos et à l’effort durant l’exercice.

Objectif

Vérifier l’hypothèse selon laquelle il y a un lien positif indépendant entre l’ANSM au repos et le rapport ventilation:rejet de dioxyde de carbone à l’effort (VE/VCO2), accru en présence d’IC.

Méthodes

L’ANSM au repos et le VE/VCO2 durant l’exercice sur bicyclette stationnaire ont été mesurée chez 30 patients (27 hommes) atteints d’IC (fraction d’éjection, 20 ± 6% [moyenne ± É.-T.]) et chez 31 témoins assortis selon l’âge (29 hommes).

Résultats

L’ANSM a été plus élevée chez les patients atteints d’IC que chez les témoins (51,5 ± 14,3 salves/minute, contre 33,0 ± 11,1 salves/ minute; p < 0,0001). La courbe VE/VCO2 a aussi été plus élevée chez les patients atteints d’IC que chez les témoins (33,7 ± 5,7, contre 26,0 ± 3,5; p < 0,0001), tandis que la pVO2 a été plus faible chez les patients atteints d’IC que chez les témoins (18,6 ± 6,6 contre 31,4 ± 8,4 mL/kg/minute; p < 0,0001). On a noté des liens significatifs entre l’ANSM et le VE/VCO2 tant chez les sujets atteints d’IC (r = 0,50, p = 0,005) que chez les témoins (r = 0,36, p = 0,046). La courbe de cette équation de régression a été plus abrupte chez les sujets atteints d’IC (0,20, contre 0,11 × ANSM, p = 0,001). Une analyse de la covariance pour les effets principaux, y compris l’âge et la pVO2 a fait ressortir un lien indépendant et significatif entre la fréquence des salves d’ANSM et le VE/VCO2 (p = 0,013) qui différait entre les sujets atteints d’IC et les témoins (p < 0,01).

Conclusions

L’ampleur de l’activité sympathique au repos est en corrélation positive avec la courbe VE/VCO2. L’augmentation de ce lien chez les patients atteints d’IC concorde avec la notion selon laquelle une activité réflexe mécanoréceptrice accrue accentue la réponse ventilatoire à l’exercice.

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