Power spectral analysis of arterial and central venous pressure signals during graded hemorrhage in anesthetized rats

Based on simultaneous power spectral analysis of systemic arterial pressure (SAP) and central venous pressure (CVP) signals in rats anesthetized with pentobarbital sodium, we assessed the hypotheses that subtle changes in the SAP spectrum exist during hemorrhagic shock, and that the CVP spectrum is a feasible index for central blood volume during acute graded blood loss. D uring Stage I hemorrhagic shock seen after reduction in 10% of total blood volume (TBV), there was a significant increase in the power of both the ver y low frequency (VLF, 0-.25 Hz) and low frequency (LF, .25-.8 Hz) component s, along with a moderate decrease in the very high frequency (VHF, 5-9 Hz) component, of SAP signals. Substantial reduction in VLF, LF, and VHF compon ents in the SAP spectrum occurred after a blood loss of 25% of TBV (Stage I I), which persisted during Stage III hemorrhagic shock when the withdrawn b lood reached 50% of TBV and the mean SAP maintained at 40 mmHg, The depress ed SAP-VLF and SAP-LF components sustained the period of spontaneous recove ry and subsequent retransfusion of shed blood, although the power of SAP-VH F component gradually elevated during these two periods. The power of the h igh-frequency (HF, .8-2.4 Hz) component of SAP signals increased discernibl y only during Stage ill, became significant on spontaneous recovery, and de clined during retransfusion, Although CVP and CVP-VHF component progressive ly declined, the power of the CVP-HF component manifested a gradual increas e that was significantly and reversely correlated with the reduction in TBV . We conclude that differential changes in individual components of the SAP spectrum occur during hemorrhagic shock, and that the CVP-HF component may be a reliable indicator for central blood volume during acute graded blood loss.