Javaheri 1996.

Study characteristics
Methods	RCT with a cross‐over design
Participants	Number randomised/analysed: 15 Sex (% male): 100% Age: not reported (adults) Inclusion criteria Compensated heart failure (LVEF ≤ 45 %) > 10 apnoea‐hypopnoea episodes/hour No change in signs or symptoms of heart failure within previous 4 weeks Optimal therapy, with no change in medications within previous 4 weeks Exclusion criteria Unstable angina Unstable congestive heart failure Acute pulmonary oedema Congenital heart disease Intrinsic pulmonary diseases, including interstitial lung disease and obstructive lung defects (ratio of predicted forced expiratory volume to forced vital capacity: 80%) Intrinsic renal and liver disorders Untreated hypothyroidism or kyphoscoliosis Use of morphine derivatives, benzodiazepines or theophylline
Interventions	Intervention group: theophylline (methylxanthine derivative) 3.3 mg/kg orally twice daily for 5 days  Control group: placebo (inactive control) for 5 days Wash‐out period: 1 week Details of intervention: no further details Co‐interventions: optimal therapy, which included angiotensin‐converting‐enzyme inhibitors (in 13 participants), hydralazine (in 2 participants), digoxin (in 11 participants), isosorbide dinitrate (in 7 participants) and furosemide (in all 15 participants)
Outcomes	cAHI measured objectively by polysomnography at baseline, during administration of placebo, and during administration of theophylline (reported at baseline and on day 5) AHI measured objectively by polysomnography at baseline, during administration of placebo, during administration of theophylline (reported at baseline and on day 5)
Notes	Study funding source: supported by Merit Review grants from the US Department of Veterans Affairs Conflicts of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The patients received placebo or theophylline orally twice daily for five days, in a randomised, double‐blind fashion." Comment: no further details; insufficient information to judge selection bias.
Allocation concealment (selection bias)	Unclear risk	Quote: "The patients received placebo or theophylline orally twice daily for five days, in a randomised, double‐blind fashion." Comment: no further details; insufficient information to judge selection bias.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "To maintain blinding, the patients were monitored during both the theophylline and the placebo phases of the study." Comment: no further details of how blinding was achieved.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "The polysomnograms were scored blindly."
Incomplete outcome data (attrition bias) All outcomes	Low risk	No missing data.
Selective reporting (reporting bias)	Unclear risk	There is insufficient information about the study protocol to judge reporting bias.
Other bias	Low risk	The study appears to be free of other sources of bias.