Journal of cardiac failure
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Editorial Comment
Consecutive screening and enrollment in clinical trials.
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Although the work of the respiratory muscles is markedly increased during exercise in patients with chronic heart failure, the role of this abnormality in exercise intolerance is still controversial. This issue may be clarified directly by dead space challenge, as this technique increases minute ventilation. Therefore, in this study, the effects of an external dead space on exercise ventilation, gas exchange data, and exercise capacity in patients with chronic heart failure were examined. ⋯ Dead space challenge appears to be a unique technique that characteristically increases the work of respiratory muscles during exercise in patients with chronic heart failure. By use of this technique, it was demonstrated that an increase in respiratory muscle work is not important in reducing exercise capacity of patients with chronic heart failure.
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The aim of this study was to evaluate whether abnormalities in heart rate variability (HRV) could act as markers of ventricular tachycardia and prognosis in patients with advanced, chronic heart failure. Fifty patients with chronic heart failure (45 men; mean age, 59 +/- 9 years; New York Heart Association [NYHA] class II-III; left ventricular ejection fraction [LVEF], 19 +/- 9% and peak oxygen consumption, 16.6 +/- 5.4 mL/kg/min) caused by idiopathic dilated cardiomyopathy (n = 12) and ischemic heart disease (n = 38) were included in the study. Heart rate variability measures derived from 24-hour electrocardiographic (ECG) monitoring (Marquette 8500 recorder, Marquette Electronics, Milwaukee, WI) were calculated in the time domain and frequency domain. ⋯ In patients with moderate to severe chronic heart failure, depressed indices of HRV on 24-hour ambulatory ECG monitoring could be related to higher risk of ventricular tachycardia and death, suggesting that analysis of HRV could be usefully applied to risk stratification in chronic heart failure patients.
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Obstructive and central sleep apnea are common in patients with congestive heart failure (CHF). These sleep-related breathing disorders are characterized by two pathophysiologic features that could have important implications for disease progression in CHF: sympathetic nervous system activation, and adverse changes in cardiac loading conditions. In patients with obstructive sleep apnea, blood pressure is frequently elevated as a result of excessive sympathetic nervous system activity elicited by the combination of apnea, hypoxia, and arousals from sleep. ⋯ Recent medium-term trials involving small numbers of patients have demonstrated that nocturnally applied continuous positive airway pressure in patients with CHF and central sleep apnea alleviates central sleep apnea, improves left ventricular function, reduces sympathetic nervous system activity and improves symptoms of CHF. These studies emphasize the importance of considering obstructive and central sleep apnea in the differential diagnosis of conditions that could contribute to the development or progression of CHF. They also suggest that continuous positive airway pressure is a promising nonpharmacologic adjunctive therapy for patients with CHF and coexisting sleep-related breathing disturbances that warrants further investigation.