Increased lung water without hypocapnia does not cause central sleep apnoea in a lamb model.
OBJECTIVE
Central sleep apnoea (CSA) in patients with heart failure is associated with an extremely poor prognosis. It is unclear as to whether pulmonary congestion contributes to CSA.


METHODS
We developed a sheep model of congestive cardiac failure (CCF) to address the question of whether pulmonary congestion without hypocapnia could cause CSA. Fourteen lambs were given CCF by overdrive pacing for 3 weeks. CCF was defined by a pulmonary artery occlusion pressure (PAOP) > or = 15 mmHg. There were 11 controls. Extravascular lung water (EVLW) was measured by the double indicator dilution method.


RESULTS
The CCF lambs had a PAOP = 18 +/- 3 mmHg and controls had a PAOP = 10 +/- 2 mmHg (P < 0.01). EVLW was 12.6 +/- 1.8 (CCF) compared to 8.9 +/- 2 mL/kg (controls) (P < 0.01). The respiratory rate was 74 +/- 21 b.p.m. (CCF) compared to 47 +/- 6 b.p.m. (controls) (P < 0.05). Acute volume loading with saline raised PAOP without changing respiration. pH and PaCO(2) were the same in both groups (PaCO(2)-37 mmHg).


CONCLUSIONS
These results support the view that hypocapnia is essential for CSA, and demonstrated that increased EVLW causes tachypnoea but not CSA.
Department of Critical Care, Manly Hospital, Manly, and University of Sydney, Sydney, New South Wales, Australia. kburgess@doh.health.nsw.gov.au
Keith R
KR
Burgess
Norbert
N
Berend
D000818:Animals; D001784:Blood Gas Analysis; D004195:Disease Models, Animal; D015633:Extravascular Lung Water / Q000502:physiology*; D006333:Heart Failure / Q000503:physiopathology; D012756:Sheep; D020182:Sleep Apnea, Central / Q000503:physiopathology*; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology