Altered heart rate variability and pulse-wave velocity after spinal cord injury

Table 1 Demographic and clinical characteristics of patients with or without spinal cord injury

	SCI (n = 60)	Non-SCI (n = 60)	P value
Age, yr	49.92 ± 11.61	45.93 ± 13.99	0.09
Sex
Male	45 (75.0%)	15 (25.0%)	< 0.001a
Female	15 (25.0%)	45 (75.0%)
Education level
Elementary school	2 (3.3%)	1 (1.7%)	< 0.001a
Junior high school	6 (10.0%)	0 (0.0%)
Senior high/vocational school	32 (53.3%)	6 (10.0%)
Five-year junior college	6 (10.0%)	6 (10.0%)
University	14 (23.3%)	21 (35.0%)
Graduate school	0 (0.0%)	26 (43.3%)
Occupation
Freelancer	37 (61.7%)	0 (0.0%)	< 0.001a
Teacher	1 (1.7%)	17 (28.3%)
Public servant	1 (1.7%)	15 (25.0%)
Service industry	4 (6.7%)	10 (16.7%)
Others	17 (28.3%)	18 (30.0%)
Marital status
Unmarried	27 (45.0%)	20 (33.3%)	0.01a
Married/cohabiting	24 (40.0%)	37 (61.7%)
Divorced	8 (13.3%)	1 (1.7%)
Widowed	1 (1.7%)	2 (3.3%)
Religion
None	13 (21.7%)	22 (36.7%)	0.14
Taoism/Buddhism	24 (40.0%)	24 (40.0%)
Christianity/Catholicism	14 (23.3%)	6 (10.0%)
Folk belief	9 (15.0%)	8 (13.3%)
Comorbidity
No	31 (51.7%)	43 (71.7%)	0.04a
Yes	29 (48.3%)	17 (28.3%)
Heart attack	3 (5.0%)	1 (1.7%)	0.62
Diabetes	11 (8.3%)	2 (3.3%)	0.02a
Kidney disease	2 (3.3%)	2 (3.3%)	1.00
Pneumonia	4 (6.7%)	0 (0.0%)	0.12
Hypertension	12 (20.0%)	8 (13.3%)	0.46
Asthma	1 (1.7%)	3 (5.0%)	0.62
Hyperlipidemia	0 (0.0%)	3 (5.0%)	0.24
Malignant tumor	0 (0.0%)	1 (1.7%)	1.00
Medication
No	24 (40.0%)	49 (81.7%)	< 0.001a
Yes	36 (60.0%)	11 (18.3%)
Hypoglycemic agent	11 (18.3%)	2 (3.3%)	0.02a
Antihypertensive agent	12 (20.0%)	6 (10.0%)	0.20
Anticoagulant	2 (3.3%)	0 (0.0%)	0.50
Others	21 (35.0%)	5 (8.3%)	0.001a

SCI: Spinal cord injury.

^aStatistically significant (P < 0.05).

Table 2 Clinical characteristics of the spinal cord injury group

Variables	SCI patients (n = 60)	Subgroup
		Paraplegia (n = 30)	Tetraplegia (n = 30)
Age, yr	49.92 ± 11.61	51.53 ± 12.39	48.30 ± 10.73
Duration of injury, years	16.73 ± 11.05	17.67 ± 12.96	15.80 ± 8.88
Cause of injury
Car accident	31 (51.67%)	12 (40.00%)	19 (63.33%)
Fall from high place	11 (18.33%)	5 (16.67%)	6 (20.00%)
Sports injury	0 (0.00%)	0 (0.00%)	0 (0.00%)
Hit by a heavy object	1 (1.67%)	1 (3.33%)	0 (0.00%)
Lesions	6 (10.00%)	4 (13.33%)	2 (6.67%)
Other	11 (18.33%)	8 (26.67%)	3 (10.00%)
Injured region
Cervical	35 (47.30%)	8 (19.51%)	27 (81.82%)
Thoracic	23 (31.08%)	19 (46.34%)	4 (12.12%)
Lumbar	15 (20.27%)	13 (13.71%)	2 (6.06%)
Sacral	1 (1.35%)	1 (2.44%)	0 (0.00%)
Level of injury
Complete tetraplegia	8 (13.33%)	-	8 (26.67%)
Incomplete tetraplegia	22 (36.67%)	-	22 (73.33%)
Complete paraplegia	26 (43.33%)	26 (86.67%)	-
Incomplete paraplegia	4 (6.67%)	4 (13.33%)	-

SCI: Spinal cord injury.

Table 3 Comparison of heart rate variability parameters between patients with and without spinal cord injury

	SCI (n = 60)	Non-SCI (n = 60)	P value
Continuous variables
HRT	79.93 ± 13.19	77.03 ± 9.90	0.18b
SDNN	27.11 ± 18.45	34.30 ± 11.18	< 0.001a,c
RMSSD	21.54 ± 17.65	25.19 ± 9.51	< 0.001a,c
PSI	125.42 ± 126.02	58.68 ± 63.64	< 0.001a,c
TP	813.78 ± 2211.10	989.19 ± 671.65	< 0.001a,c
LF/HF ratio	1.80 ± 2.52	1.98 ± 2.68	0.20c
VLF	519.54 ± 1903.98	443.89 ± 372.20	0.001a,c
LF	179.09 ± 319.20	299.85 ± 292.49	< 0.001a,c
HF	115.16 ± 133.82	245.45 ± 276.53	< 0.001a,c
LF norm	51.33 ± 20.21	55.78 ± 18.33	0.21a
HF norm	48.67 ± 20.21	44.22 ± 18.33	0.21a
Categorical variables
HRT
Low (≤ 60)	1 (1.7%)	2 (3.3%)	0.51d
Normal (60–90)	45 (75.0%)	49 (81.7%)
High (> 90)	14 (23.3%)	9 (15.0%)
SDNN
Low (≤ 30)	45 (75.0%)	20 (33.3%)	< 0.001a,d
Normal (> 30)	15 (25.0%)	40 (66.7%)
RMSSD
Low (≤ 20)	41 (68.3%)	21 (35.0%)	< 0.001a,d
Normal (> 20)	19 (31.7%)	39 (65.0%)
PSI
Normal (≤ 50)	18 (30.0%)	39 (65.0%)	< 0.001a,d
High (> 50)	42 (70.0%)	21 (35.0%)
TP
Low (≤ 1000)	52 (86.7%)	32 (53.3%)	< 0.001a,d
Normal (> 1000)	8 (13.3%)	28 (46.7%)
LF/HF ratio
Low (≤ 0.5)	15 (25.0%)	9 (15.0%)	0.42d
Normal (0.5-2.0)	30 (50.0%)	33 (55.0%)
High (> 2.0)	15 (25.0%)	18 (30.0%)

HRT: Heart rate over a given period of time; SDNN: Standard deviation of all normal-to-normal intervals; RMSSD: Square root of the mean of the sum of the squares of differences between adjacent normal-to-normal intervals; PSI: Physical stress index; TP: Total power; LF/HF: The ratio or low frequency to high frequency; VLF: Very low frequency; LF: Low frequency; HF: High frequency.

^aStatistically significant (P < 0.05).

^bT-test.

^cMann–Whitney U test.

^dFisher’s exact test.

Table 4 Comparison of pulse-wave velocity parameters between patients with and without spinal cord injury

	SCI (n = 60)	Non-SCI (n = 60)	P value
Continuous variables
DPI	-63.57 ± 44.51	-75.12 ± 46.32	0.17
EC	-88.59 ± 16.95	-88.67 ± 18.05	0.98
AE	-21.17 ± 15.27	-7.18 ± 17.29	< 0.001a
RBV	-27.65 ± 17.88	-30.08 ± 17.67	0.38
Categorical variables
Vascular age
Level 1	6 (10.0%)	18 (30.0%)	0.01a
Level 2	33 (55.0%)	20 (33.3%)
Level 3	4 (6.7%)	11 (18.3%)
Level 4	15 (25.0%)	10 (16.7%)
Level 5	1 (1.7%)	1 (1.7%)
Level 6	1 (1.7%)	0 (0.0%)
DPI
Poor	8 (13.3%)	2 (3.3%)	0.12
Normal	26 (43.3%)	25 (41.7%)
Good	26 (43.3%)	33 (55.0%)
EC
Poor	12 (20.0%)	6 (10.0%)	0.24
Normal	28 (46.7%)	28 (46.7%)
Good	20 (33.3%)	26 (43.3%)
AE
Poor	24 (40.0%)	12 (20.0%)	0.001a
Normal	33 (55.0%)	31 (51.7%)
Good	3 (5.0%)	17 (28.3%)
RBV
Poor	8 (13.3%)	6 (10.0%)	0.56
Normal	21 (35.0%)	27 (45.0%)
Good	31 (51.7%)	27 (45.0%)

DPI: Differential pulse wave index; EC: Eccentric constriction power; AE: Arterial elasticity; RBV: Remaining blood volume;

^aStatistically significant (P < 0.05).