Peripheral and Central Ventilatory Responses in Central Sleep Apnea with and without Congestive Heart Failure

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Abstract
Given that the apnea-ventilation cycle length during central sleep apnea (CSA) with congestive heart failure (CHF) is approximately 70 s, we hypothesized that rapidly responsive peripheral CO(2) ventilatory responses would be raised in CHF-CSA and would correlate with the severity of CSA. Sleep studies and single breath and rebreathe hypercapnic ventilatory responses (HCVR) were measured as markers of peripheral and central CO(2) ventilatory responses, respectively, in 51 subjects: 12 CHF with no apnea (CHF-N), 8 CHF with obstructive sleep apnea (CHF-OSA), 12 CHF-CSA, 11 CSA without CHF ("idiopathic" CSA; ICSA), and 8 normal subjects. Single breath HCVR was equally elevated in CHF-CSA and ICSA groups compared with CHF-N, CHF-OSA, and normal groups (0.58 +/- 0.09 [mean +/- SE] and 0. 58 +/- 0.07 versus 0.23 +/- 0.06, 0.25 +/- 0.04, and 0.27 +/- 0.02 L/min/PET(CO(2)) mm Hg, respectively, p < 0.001). Similarly, rebreathe HCVR was elevated in both CHF-CSA and ICSA groups compared with CHF-N, CHF-OSA, and normal groups (5.80 +/- 1.12 and 3.53 +/- 0. 29 versus 2.00 +/- 0.25, 1.44 +/- 0.16, and 2.14 +/- 0.22 L/min/PET(CO(2)) mm Hg, respectively, p < 0.001). Furthermore, in the entire CHF group, single breath HCVR correlated with central apnea-hypopnea index (AHI) (r = 0.63, p < 0.001) and percentage central/total apneas (r = 0.52, p = 0.022). Rebreathe HCVR correlated with awake Pa(CO(2)) (r = -0.61, p < 0.001), but not with central AHI or percentage central/total apneas independent of its relationship with single breath HCVR. In conclusion, in subjects with CHF, raised central CO(2) ventilatory response predisposes to CSA promoting background hypocapnia and exposing the apnea threshold to fluctuations in ventilation, whereas raised and faster-acting peripheral CO(2) ventilatory response determines the periodicity and severity of CSA.