title: Overnight shift from obstructive to central apneas in patients with heart failure: role of PCO2 and circulatory delay.
abstract: BACKGROUND
  Obstructive (OSA) and central sleep apnea (CSA) can coexist in patients with congestive heart failure (CHF). However, the reason why OSA events occur at one time and CSA events at another has not been determined. We hypothesized that a change in PCO(2) would be associated with an alteration in apnea type: a decrease in PCO(2) should lead to CSA.
  
  
  RESULTS
  To test this hypothesis, we evaluated minute ventilation (V(I)), transcutaneous PCO(2) (PtcCO(2)), circulation time, and periodic breathing cycle length during overnight polysomnography in 12 patients with CHF and coexisting OSA and CSA. V(I) was significantly greater (mean+/-SEM, 9.4+/-1.3 versus 8.0+/-0.9 L/min; P:<0.05) and PtcCO(2) was lower (39.4+/-1.0 versus 41.9+/-1.1 mm Hg, P:<0.01) during episodes of CSA than of OSA. These changes were associated with significant lengthening of circulation time (23.6+/-3.7 versus 21.1+/-3.6 seconds, P:<0.01) and periodic breathing cycle length (53.7+/-3.5 versus 49.6+/-2.9 seconds, P:<0.01). In addition, the proportion of obstructive events decreased (from 68.5+/-11.4% to 22.5+/-7.2%, P:<0.001) and of CSA events increased (from 31.5+/-11.4% to 77.5+/-7.2%, P:<0.001) from the first to the last quarter of the night in association with a significant decrease in PtcCO(2) (from 42.6+/-0.9 to 40.8+/-0.9 mm Hg, P:<0.01).
  
  
  CONCLUSIONS
  In patients with CHF, the shift from OSA to CSA is associated with a reduction in PCO(2). This appears to be related to an overnight deterioration in cardiac function as suggested by the concurrent lengthening of circulation time. Therefore, in CHF patients, alterations in cardiac function may influence apnea type.
authors.affiliation: Sleep Research Laboratory of the Toronto Rehabilitation Institute and the Department of Medicine of the Toronto General Hospital/University Health Network, University of Toronto, Toronto, Ontario, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Tkacova
authors.forename: M
authors.initials: M
authors.lastname: Niroumand
authors.forename: G
authors.initials: G
authors.lastname: Lorenzi-Filho
authors.forename: T D
authors.initials: TD
authors.lastname: Bradley
mesh_terms: D001775:Blood Circulation; D002245:Carbon Dioxide; D002940:Circadian Rhythm; D005260:Female; D006333:Heart Failure / Q000150:complications*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010313:Partial Pressure; D017286:Polysomnography; D012119:Respiration; D015656:Respiratory Mechanics; D020182:Sleep Apnea, Central / Q000209:etiology* / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000209:etiology* / Q000503:physiopathology; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide