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New measures of heart-rate complexity: effect of chest trauma and hemorrhage.

BACKGROUND
Traditional vital signs such as heart rate, blood pressure, and oxygen saturation are not ideal for timely and accurate assessment of physiologic status after trauma (TR) and hemorrhagic shock (HS). Analysis of the complex beat-to-beat variability present in the heart-rate time series has been proposed as a "new vital sign" in this setting. We determined the effect of chest TR and HS on heart-rate complexity (HRC) in a porcine model.


METHODS
Anesthetized swine in group II (n = 20) underwent blunt right chest TR with a modified captive-bolt stunner; then, 10 minutes later, hemorrhage of 12 mL/kg over 10 minutes, followed by resuscitation with lactated Ringer's solution, and reinfusion of blood. Group I (n = 15) served as time controls. Two hundred beat sections of EKG waveforms were analyzed at 7 time points: at baseline, after TR, immediately after hemorrhage (HS), and 1 hour, 2 hours, 4 hours, and 5 hours after HS. Several computationally different measures of HRC were calculated, including sample entropy, similarity of distribution, and point correlation dimension.


RESULTS
HRC was decreased after TR, HS, and at 1 hour, manifested by decreased sample entropy and point correlation dimension and increased similarity of distribution. These HRC measures were all restored by resuscitation.


CONCLUSIONS
Several independent measures demonstrated decreased HRC after combined TR/HS and restored HRC with resuscitation. Complexity analysis may be useful for diagnosis of TR/HS and for monitoring resuscitation.