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 (VT), total breath duration (TTOT), minute ventilation (V˙E), oxygen saturation (SpO2) similar to the control, but the PVS-OB displayed significantly lower end-tidal CO2 tension (PETCO2) than the control. The VT, TTOT, V˙E and PETCO2 of the PVS-OB showed cyclic changes. The coefficients of variation of VT, TTOT 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.