Study objectives: Sleep apnea is common in patients with congestive heart failure, and may contribute to the progression of underlying heart disease. Cardiovascular and metabolic complications of sleep apnea have been attributed to intermittent hypoxia. Elevated free fatty acids (FFA) are also associated with the progression of metabolic, vascular, and cardiac dysfunction. The objective of this study was to determine the effect of intermittent hypoxia on FFA levels during sleep in patients with heart failure.
Design and interventions: During sleep, frequent blood samples were examined for FFA in patients with stable heart failure (ejection fraction < 40%). In patients with severe sleep apnea (apnea-hypopnea index = 65.5 ± 9.1 events/h; average low SpO₂ = 88.9%), FFA levels were compared to controls with milder sleep apnea (apnea-hypopnea index = 15.4 ± 3.7 events/h; average low SpO₂ = 93.6%). In patients with severe sleep apnea, supplemental oxygen at 2-4 liters/min was administered on a subsequent night to eliminate hypoxemia.
Measurements and results: Prior to sleep onset, controls and patients with severe apnea exhibited a similar FFA level. After sleep onset, patients with severe sleep apnea exhibited a marked and rapid increase in FFA relative to control subjects. This increase persisted throughout NREM and REM sleep exceeding serum FFA levels in control subjects by 0.134 mmol/L (P = 0.0038). Supplemental oxygen normalized the FFA profile without affecting sleep architecture or respiratory arousal frequency.
Conclusion: In patients with heart failure, severe sleep apnea causes surges in nocturnal FFA that may contribute to the accelerated progression of underlying heart disease. Supplemental oxygen prevents the FFA elevation.
Keywords: Intermittent hypoxia; apnea; free fatty acids; heart failure; sleep.