Exercise hyperventilation, dyspnea sensation, and ergoreflex activation in lone atrial fibrillation

Abstract

Lone atrial fibrillation may be associated with daily life disability and exercise limitation. The extracardiac pathophysiology of these effects is poorly explored. In 35 subjects with lone atrial fibrillation (mean age 67 Ϯ 7 yr), we investigated pulmonary function, symptom-limited cardiopulmonary exercise performance, muscle ergoreflex (handgrip exercise) contribution to ventilation, and brachial artery flow-mediated dilation (as a measure of endothelial function) before and after (average interval 20 Ϯ 5 days) restoring sinus rhythm with external cardioversion. Respiratory volumes and lung diffusing capacity at rest were within normal limits during both atrial fibrillation and after restoring sinus rhythm. Cardioversion was associated with the following changes: a decrease of the slope of exercise ventilation vs. CO2 production (from 35 Ϯ 5 to 29 Ϯ 3; P Ͻ 0.01) and of dyspnea sensation (Borg score from 4 to 2) and an increase of peak oxygen uptake (V O2; from 16 Ϯ 4 to 20 Ϯ 5 ml⅐ min Ϫ1 ⅐ kg Ϫ1 ; P Ͻ 0.01), V O2 at anaerobic threshold (from 11 Ϯ 2 to 13 Ϯ 2 ml⅐ min Ϫ1 ⅐ kg Ϫ1 ; P Ͻ 0.05), and O2 pulse (from 8 Ϯ 3 to 11 Ϯ 3 ml/beat; P Ͻ 0.01). After cardioversion, the observed improvement in ventilatory efficiency was accompanied by a significant peak end-tidal CO2 increase (from 33 Ϯ 2 to 37 Ϯ 2 mmHg; P Ͻ 0.01) and no changes in dead space-to-tidal volume ratio (from 0.23 Ϯ 0.03 to 0.23 Ϯ 0.02; P ϭ not significant). In addition, the ergoreflex contribution to ventilation was remarkably attenuated, and the brachial artery flow-mediated dilatation was significantly augmented (from 0.32 Ϯ 0.07 to 0.42 Ϯ 0.08 mm; P Ͻ 0.01). Ten patients had atrial fibrillation relapse and, compared with values after restoration of regular sinus rhythm, invariably showed worsening of endothelial function, exercise ventilatory efficiency, and muscle ergoreflex contribution to ventilation. In subjects with lone atrial fibrillation, an impairment in ventilatory efficiency appears to be involved in the pathophysiology of exercise limitation, and to be primarily related with a demodulated peripheral control of ventilation. lone atrial fibrillation; exercise; ventilation; dyspnea LONE ATRIAL FIBRILLATION is the most common sustained arrhythmia encountered in clinical practice (11,39). A reduced maximal exercise oxygen uptake (V O 2 ; see Refs. 12, 21, and 23) is a frequent finding, and exercise intolerance is not an uncommon daily life disability factor (19,22). As to the pathophysiological bases of physical limitation, previous studies have extensively investigated the putative role of hemodynamic abnormalities associated with atrial fibrillation (3,8,10,36). Exercise performance, however, not only depends on the cardiovascular system function but on any organ system involved in O 2 transport, including the respiratory system, skeletal muscles, hormonal and neural feedback control system for breathing, cardiac output, blood pressure, and blood volume. A contribution of peripheral changes resulting from this arrhythmia to the pathogenes...

Endothelial dysfunction and exercise performance in lone atrial fibrillation or associated with hypertension or diabetes: different results with cardioversion

“…Exercise correlates of these dysfunctions are underperfusion of working muscle, hyperventilation, and breathlessness (10). These findings are consistent with the concept that, during exercise, an endothelium-mediated vasodilation modulates neurogenic vasoconstriction, increases arterial conductance, and upregulates muscle perfusion (6,12,16).…”

“…These findings are consistent with the concept that, during exercise, an endothelium-mediated vasodilation modulates neurogenic vasoconstriction, increases arterial conductance, and upregulates muscle perfusion (6,12,16). Conversion to sinus rhythm [i.e., cardioversion (CV)] is beneficial in this respect (10). Irregular pulsatile blood flow in AF may impair the endothelial responsiveness to vascular shear stress, and loss of the cyclic stretch of atrial endocardial cells may decrease expression of NO synthase (3).…”

“…AF interferes with endothelial function (10,27) and exercise capacity (9,18,19,24), and a pathophysiological link seems to exist between the two variables (10). Our results have provided evidence that sinus rhythm conversion restores endothelial function in patients with lone AF and is partially effective (hypertension) or ineffective (diabetes) in those with comorbidities that cause endothelial dysfunction.…”

“…arrhythmias; endothelium; exercise ATRIAL FIBRILLATION (AF) impairs endothelial function and downregulates nitric oxide (NO) production (3,10,27). Exercise correlates of these dysfunctions are underperfusion of working muscle, hyperventilation, and breathlessness (10).…”

Increased Peripheral Chemoreceptors Sensitivity and Exercise Ventilation in Heart Transplant Recipients

“…First, we estimated PaCO 2 in HTRs and control subjects using the following formula: PaCO 2 ϭ5.5ϩ(0.9ϫPetCO 2 )Ϫ(0.0021ϫVT), as suggested by Jones et al 19 This method of PaCO 2 estimation is used in clinical studies on heart failure patients when only end-tidal PetCO 2 is measured. 35 Afterward, we recalculated VD/VT using PaCO 2 in the Bohr equation. Although we observed a small difference between VD/VT in the patients and control subjects at rest, we still could not find a significant difference between the 2 groups at peak exercise (Pϭ0.84).…”