Instability of spontaneous breathing patterns in patients with persistent vegetative state.

We investigated the breathing patterns of 27 patients in a persistent vegetative state (PVS) and 15 normal control volunteers. During the baseline period breathing air, 15 patients (the PVS-IB) exhibited irregular breathing (IB), whereas the other 12 (the PVS-OB) displayed oscillatory breathing (OB). Both groups maintained an average value for tidal volume (V(T)), total breath duration (T(TOT)), minute ventilation (V (E)), oxygen saturation (SpO2) similar to the control, but the PVS-OB displayed significantly lower end-tidal CO2 tension (P(ET)CO2) than the control. The V(T), T(TOT), V (E) and P(ET)CO2 of the PVS-OB showed cyclic changes. The coefficients of variation of V(T), T(TOT) and V (I) were: PVS-OB>PVS-IB>control. Inhalation of 100% O2 significantly reduced the respiratory variability and prevented OB of the PVS-OB. We concluded that PVS patients display respiratory instability and that brain damage, hypocapnia, and/or increased loop gain of arterial chemoreceptors may contribute to the pathogenesis of OB, whereas brain damage presumably may be the cause of IB.