Clinical Applications of Heart Rate Variability in the Triage and Assessment of Traumatically Injured Patients

Table 4

Heart rate variability analysis techniques and their uses in trauma.

Technique	Description	Metrics	Evidence of changes in trauma	Population
Time domain	Estimation of variability using statistics and measures of central tendency [3]	HRVi	↓ predicts mortality, ICH, adrenal insufficiency [11, 15, 19–22, 36]	ICU
		Uncoupling	↑ reflects acidosis, coagulopathy, MOSF, AI, severe TBI, ↑ ICP, predicts mortality [6, 9, 12, 22]	ICU
		SDNN	↓ predicts TBI, mortality, acidosis, LSI [16, 23]	Prehospital; ER; ICU
		RMSSD	↓ reflects TBI, hemorrhage, mortality [23, 28, 47]	ER; ICU
Frequency domain	Calculation of power (amplitude) of contributing frequencies to an underlying signal [18]	TP	↓ reflects ↑ICP, TBI, prolonged neurologic recovery, need for LSI, mortality, brain death [10, 28, 43]	ICU; Outpatient
		LF	↓ reflects ↑ICP, TBI, hemorrhage, need for LSI, mortality, brain; ↑ reflects ↑CI, HR, MAP death [4, 10, 27, 28, 37, 43, 48, 49].	ER; ICU
		HF	↓ reflects trauma, ↑ICP, need for LSI, hemorrhage, brain death, and mortality [10, 37, 43, 47, 50, 51]	Prehospital
		LF/HF	↑ reflects ↑ICP, ↓CPP; ↓ reflects brain death, mortality, hemorrhage, ↓GCS, poor neurologic outcome [5, 7, 10, 27, 48, 51]	Prehospital; ICU
Entropy	Measurement of overall disorder, randomness, or irregularity of a physiologic signal [18]	MSE	↓ predicts mortality [13, 35, 36, 45]	ICU
		ApEn	↓ reflects trauma, burn, hemorrhage, brain death, and ↑ICP, MOSF, predicts mortality; ↑ reflects resuscitation [8, 14, 25, 29, 34, 37, 52]	Prehospital
		SampEn	↓ reflects trauma, mortality, burn, and hemorrhage; ↑ reflects resuscitation; predicts LSI [8, 25, 43]	Prehospital
		FDCL	↓ reflects hemorrhage; ↑ reflects resuscitation; ↓ predicts LSI [17]	Prehospital
		FDDA	↓ reflects need for LSI, hemorrhage, mortality [8, 25, 43]	Prehospital
		DFA	↓ reflects mortality; predicts LSI [8, 25, 43]	Prehospital
		SOD	↑ reflects need for LSI, mortality [8, 25, 43]	Prehospital
		StatAv	↓ reflects mortality [25]	Prehospital

HRVi: integer heart rate variability; ICH: intracranial hypertension; MOSF: multiple-organ system failure; AI: adrenal insufficiency; TBI: traumatic brain injury; SDNN: standard deviation of normal-normal RR Intervals (NN); RMSSD: root mean squared successive difference; LSI: life-saving intervention; ICP: intracranial pressure; TP: total power; LF: low-frequency oscillations power spectral density; HR: heart rate; CI: cardiac index; MAP: mean arterial pressure; HF: high-frequency oscillations power spectral density; LF/HF: low-to-high-power spectral density ratio; MSE: multiscale entropy; ApEn: approximate entropy; SampEn: sample entropy; SymDyn: symbol dynamics entropy; DisnEn: symbol distribution entropy; FDCL: fractional dimension by curve length; FDDA: fractional dimension by dispersion analysis; DFA: detrended fluctuations analysis; SOD: similarity of distributions; StatAv: signal stationarity; PS2i: point correlation dimension.