The effect of long term ventilatory support on hemodynamics in children with spinal muscle atrophy (SMA) type II.

Background: Bi-level Positive Airway Pressure (Bi-PAP) treatment improves breathing efficiency and ventilation in children with SMA type II, but the effects of positive airway pressure swings on heart rate (HR) and blood pressure are not known. Here we studied children with SMA to determine whether Bi-PAP administered during sleep is associated with changes in hemodynamics.

Methods: Ten children aged 8-12 years on long term Bi-PAP therapy were evaluated during a routine overnight sleep study. We recorded HR, ECG, thoraco-abdominal movements and blood gases. Blood pressure was estimated indirectly from pulse transit time (PTT) and the efficiency ("work") of breathing from the phase angle between chest and abdominal movements. We compared periods of unsupported (spontaneous) and supported (i.e., on Bi-PAP) breathing during a split-night study. We also compared periods when Bi-PAP was judged optimal with periods that were sub-optimal due to mask leakage.

Results: HR and PTT during unsupported breathing and on optimal Bi-PAP were comparable (p=0.85 and 0.79, respectively), as were blood gases (SaO2, TcO2, TcCO2p=0.79, 0.88, 0.79, respectively). Breathing efficiency improved as expected when Bi-PAP was optimal (decrease in phase angle from 42 degrees to 22 degrees ). Sub-optimal Bi-PAP due to air leaking from the mask was associated with marked increases in breath-to-breath variability of HR, PTT and phase angle.

Conclusions: Bi-PAP therapy does not appear to adversely influence hemodynamics in children with SMA if pressures are optimized and the mask is correctly applied and sealed.