Cardiorespiratory effects of added dead space in patients with heart failure and central sleep apnea

Background: Inhaled CO₂ has been shown to stabilize the breathing pattern of patients with central sleep apnea (CSA) with and without congestive heart failure (CHF). Added dead space (DS) as a form of supplemental CO₂ was effective in eliminating idiopathic CSA. The efficacy and safety of DS has not yet been evaluated in patients with CHF and CSA. Methods: We examined the respiratory and cardiovascular effects of added DS in eight patients with CHF and CSA. The DS consisted of a facemask attached to a cylinder of adjustable volume. During wakefulness, the cardiorespiratory response to 200 to 600 mL of DS was tested. Cardiac output and stroke volume were measured using echocardiography with and without DS. During the nocturnal study, patients slept with and without DS, alternating at approximately 1-h intervals. Results: Values are expressed as the mean ± SE. The wakefulness study revealed a plateau in the partial pressure of end-tidal CO₂ (PETCO₂) and the partial pressure of end-tidal O₂ between DS amounts of 400 and 600 mL. The mean stroke volume index (33±7 vs 34 ± 7 mL/m², respectively) and the mean cardiac index (1.9 ± 0.3 vs 1.9 ± 0.4 L/min/m², respectively) were not affected by DS. Neither heart rate nor BP showed a significant change in response to DS of ≤ 600 mL. During sleep, DS increased the PETCO₂ (40.7 ± 2.7 vs 38.9 ± 2.6 mm Hg, respectively; p < 0.05), reduced apnea (1 ± 1 vs 29 ± 7 episodes per hour, respectively; p < 0.01) and arousal (21 ± 8 vs 30 ± 8 arousals per hour, respectively; p < 0.05), increased the mean arterial oxygen saturation (Sao₂) [94.4 ± 1.0% vs 93.5 ± 1.1%, respectively; p < 0.01), and reduced Sao₂ oscillations (ΔSao₂ from maximum to minimum, 1.8 ± 0.4% vs 5.5 ± 0.9%, respectively; p < 0.01). Conclusion: DS stabilized CSA and improved sleep quality in patients with CHF without significant acute adverse effects on the cardiovascular function.