Predicting Successful Sleep Apnea Treatment With Acetazolamide in Heart Failure Patients

The frequency of apneas and hypopneas (apnea-hypopnea index) was assessed. The primary measure was the value for non-REM supine sleep. A higher value indicates more severe sleep apnea. A value above 15 indicates the presence of moderate-to-severe sleep apnea.

Chemoreflex "loop gain" was assessed according to Sands SA et al AJRCCM 2017 Jan 15;195(2):237-246. Loop gain is a unitless ratio measure that describes the magnitude of the increase in ventilation that occurs in response to a prior reduction in ventilation ("disturbance") and has units of L/min per L/min. A larger value indicates a more sensitive and unstable control system predisposing to oscillatory breathing. Loop gain was measured on the time scale of 1 min (i.e. response to a 1 cycle/min sinusoidal disturbance, referred to as "LG1"). The procedure involved brief administration of 7% carbon dioxide in air for 0.5 min ("pulses"); tests were repeated every 3 min for 30 min while measuring ventilation and carbon dioxide levels at the nose with patients awake and supine.

measured using 0.5 min pulses of carbon dioxide.

Urinary norepinephrine levels overnight

Left-atrial volume index, echocardiography, bi-plane method. Lower values were considered a favorable outcome. We considered values ≤28 mL/m^2 to indicate normal left atrial volume. Values indicating graded left atrial enlargement were described as follows: mild (29-33 mL/m^2), moderate (34-39 mL/m^2), severe (≥40 mL/m^2).

Brain natriuretic peptide (NT-proBNP) in morning

Pittsburgh Sleep Quality Index is a measure of self-reported sleep quality containing 19 questions that make up 7 component scores that are added to provide a total score. Total scores range from 0-21 (units on a scale) with higher scores representing reduced sleep quality. A score of 5 or more is interpreted as reduced sleep quality. The total score is reported.