Introduction A brisk ventilatory response to carbon dioxide (CO2) is integral to the development of central sleep disordered breathing (SDB) in heart failure (HF) patients. Modern treatments for HF enhance cardiac function and many improve central SDB. The role of hypercapnic ventilatory responses (HCVR) in central SDB in HF patients managed according to modern guidelines is unclear. For example, adaptive servoventilation (ASV), used to treat central SDB, both improves cardiac function and reduces hypercapnic ventilatory responses (HCVR), suggesting that heightened chemosensitivity in HF may relate to cardiac impairment.
Objective To test the hypothesis that there would be no difference in HCVR between optimally treated patients with HF and central SDB (HF-CSA), and those with HF alone (HF-noSDB).
Method Measurements of resting expired CO2 (awake) and evening and morning HCVR, using the Read rebreathe technique, were undertaken in patients optimally treated for HF. Patients also underwent overnight polysomnography. Sample size calculations (using data from Javaheri, NEJM 1999) showed 10 patients were needed in each group. Statistical analyses were undertaken using SPSS. The study received ethical approval.
Results Twenty-six HF patients were studied (11 with HF-CSA: median (IQR) age 68 (58–78) and 15 with HF-noSDB: age 72 (67–78)years). Left ventricular ejection fraction was: HF-CSA 32 (20–40)% and HF-noSDB 40 (27–47)%. The apnoea hypopnoea index was: HF-CSA 14.6 (12.9–37.1)/hr and HF-noSDB 5.0 (3.2–6.0)/hr. The HF-CSA group had lower median resting expired CO2 than the HF-noSDB group (end tidal CO2: 30.6 (28.6–37.3) vs. 36.2 (35.2–40.4)mmHg, p = 0.02). There was no significant difference between the HF-CSA and HF-noSDB in evening HCVR (2.15 (1.70–2.74) vs. 1.99 (1.60–3.33)L/min/mmHg ETCO2, p = 0.53) or morning HCVR (2.71 (1.43–4.88) vs. 2.20 (1.00–3.00)L/min/mmHg ETCO2, p = 0.23). Resting expired CO2 in the total study population correlated negatively with morning, but not evening, HCVR.
Conclusion The results of this small study suggest that modern HF management may have an effect on ventilatory stability via changes in HCVR. The timing of the HCVR tests may be a factor. We speculate that overnight disturbances in breathing may promote ventilatory instability in the morning, rather than the evening.
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