Table 2.

Heart rate variability components demonstrating sympathetic and parasympathetic changes pre– to post–cervical or thoracic spinal segment adjustments

Components†	Cervical Segments		Age (y)	Time⁎ (h)	Thoracic Segments		Age (y)	Time⁎ (h)
n = 7	Pre	Post			Pre	Post
	Subjects				Subjects
T Power♂	524.4	434.7	44	48	874♂	2216	55	48
LF (s)‡	150.8	188.9			433	1301
HF (p)	34.1	49.1			137	265
LF/HF	4.40	3.90a			3.20	4.90e
T Power♀	2630	1540	46	168	3701♂	1559	47	48
LF	1034	433			1659	406
HF	746	681			1547	363
LF/HF	1.40	0.60b			1.07	1.11f
T Power♂	865	645	50	144	5868♀	4002	54	144
LF	369	274			1829	2062
HF	141	192			3181	1308
LF/HF	2.60	1.40c			0.60	1.60g
T Power♀	746	825			53	48
LF	214	241
HF	263	494
LF/HF	0.80	0.50d

Data were derived from 4 participants given cervical adjustments when indicated and 3 given thoracic adjustments. Cervical adjustments were all C1, whereas thoracic adjustments were T1 for the first subject listed and T4 for the following two. Superscript letters a to d indicate that the decrease in LF/HF ratios represents a shift to increased parasympathetic activity (HF). Superscript letters e to g indicate that the increase in LF/HF ratios represents a shift to increased sympathetic activity (LF). s, Sympathetic activity; p, parasympathetic activity; T Power, total power.

^⁎Time, in hours, between pre- and postadjustment HRV readings.

^†Components of HRV. See “Methods” for descriptions.

^‡LF represents sympathetic activity; HF represents parasympathetic activity.