Hypopnea was defined as a reduction in the respiratory amplitude of > 50% compared to the preceding signals. All apneas and hypopneas were required to have a duration of at least 10 s. The apnea-hypopnea index (AHI) was obtained by dividing the total number of these events through the total sleep time (TST). An AHI of > 10/h of sleep was considered to be diagnostic of SDB. PB was required to show a crescendo-decrescendo pattern of hyperventilatory phases between central apneas and hypopneas (at least three consecutive cycles). Furthermore, the obstructive AHI had to be < 10/h. While breathing room air, the sleep recordings revealed the presence of severe PB with marked nocturnal oxygen desaturations (Table 2; Fig 1, top). During a second night, oxygen was administered via nasal prongs at a flow rate of 3 L/min. This led to an improvement in nocturnal Sao2; however, the PB pattern persisted (AHI, 58/h; mean Sao2, 91.5%; Sao2 < 90% during 7% of TST; lowest Sao2, 72%).
In June 1999, the patient was readmitted because of clinical deterioration. Lung function and blood gases had not significantly changed (Dlco, 60% of predicted; Pao2, 44 mm Hg; Paco2, 27 mm Hg) but right-heart catheterization demonstrated a further progress of the pulmonary hypertension (mean PAP, 64 mm Hg; pulmonary vascular resistance, 2,023 dyne-s-cm; pulmonary capillary wedge pressure, 6 mm Hg; CI, 1.32 L/min/m2; right ventricular ejection fraction, 5%). Polysomnography performed under oxygen administration continued to show PB (AHI, 64/h; mean Sao2, 90.2%; Sao2 < 90% during 3% of TST; lowest Sao2, 66%). The patient was switched to IV iloprost and set on a transplant waiting list. At this time, left-heart catheterization was performed and ruled out significant coronary artery disease, intracardiac shunting, or left ventricular dysfunction.
Figure 1. Polysomnographic recordings before (top) and after (bottom) double-lung transplantation (time interval, 5 min). C3A2/C4A1 = EEG electrodes at positions of the international 10-20 system; EOG1/EOG2 = left/right electrooculogram; EMG1/EMG2 = submental/pretibial muscle electromyogram; NAF = oronasal airflow (prongs); THO/ABD = thoracic/abdominal breathing movements (inductive plethysmography).
Table 2—Sleep Study Results Before and After Double-Lung Transplantation
|AHI, no./h of TST||78||3|
|AHI obstructive, no./h of TST||8||1|
|AHI central, no./h of TST||70||2|
|PB, % of TST||87||2|
|Nocturnal Sao2 mean, %||90.5||93.5|
|Lowest nocturnal Sao2, %||73||84|
|Nocturnal Sao2 < 90%, % of TST||34||3|
|NREM 1 + 2, % of TST||59||58|
|NREM 3 + 4, % of TST||21||20|
|REM, % of TST||20||22|
|Sleep efficiency, % of TIB||78||84|
|Arousal index, no./h of TST||65||12|