Assessment of autonomic function after acute spinal cord injury using heart rate variability analyses

Abstract

Objectives: Spinal cord injury (SCI) often results in severe dysfunction of the autonomic nervous system. C1-C8 SCI affects the supraspinal control to the heart, T1-T5 SCI affects the spinal sympathetic outflow to the heart, and T6-T12 SCI leaves sympathetic control to the heart intact. Heart rate variability (HRV) analysis can serve as a surrogate measure of autonomic regulation. The aim of this study was to investigate changes in HRV patterns and alterations in patients with acute traumatic SCI. Methods: As soon as possible after SCI patients who met the inclusion criteria had 24 h Holter monitoring of their cardiac rhythm, additional Holter monitoring were performed 1, 2, 3 and 4 weeks after SCI. Results: Fifty SCI patients were included. A significant increase in standard deviation of the average normal-to-normal (SDANN) sinus intervals was seen in the first month after injury (P = 0.008). The increase was only significant in C1-T5 incomplete patients and in patients who did not experience one or more episodes of cardiac arrest. Significant lower values of Low Frequency Power, Total Power and the Low Frequency over High Frequency ratio were seen in the C1-T5 SCI patients compared with T6-T12 SCI patients. Conclusions: The rise in SDANN in the incomplete C1-T5 patients could be due to spontaneous functional recovery caused by synaptic plasticity or remodelling of damaged axons. That the autonomic nervous system function differs between C1-C8, T1-T5 and T6-T12 patients suggest that the sympathovagal balance in both the C1-C8 and T1-T5 SCI patients has yet to be reached. INTRODUCTIONSpinal cord injury (SCI) patients with tetraplegia and high level paraplegia are known to suffer from dysfunction of the autonomic nervous system (ANS) including the autonomic regulation of the heart. 1 The severity and the neurological level of the SCI have major impact on ANS function. 2 Patients with SCI above T1 often have intact efferent vagal and sympathetic neural pathways innervating the heart. However, they are deprived of the supraspinal control causing reduced sympathetic activity below the level of SCI. Furthermore, the loss of supraspinal control causes morphological changes in sympathetic preganglionic neurons and peripheral alpha-adrenoceptor hyperresponsiveness. 1 Patients with T1-T5 SCI lose cardiac sympathetic preganglionic neurons as the injury occurs corresponding to the sympathetic outflow to the heart, and likewise the postganglionic sympathetic innervation to the heart undergoes plastic changes. 3 Individuals with SCI at T6 and below have intact cardiac spinal sympathetic neurons and intact innervation of the heart.In tetraplegic individuals with complete lesions, the disconnection of the spinal sympathetic neurons from cerebral control represents a unique possibility for analysis of the sympathetic influence on the heart rate (HR) variability (HRV).

Influence of neurological lesion level on heart rate variability and fatigue in adults with spinal cord injury

“…They also found high-frequency HRV (mostly associated with parasympathetic activity) differences between the paraplegia and the AB groups. Recent research has also found significantly reduced sympathetic activity in adults with tetraplegia, 4 whereas no HRV differences were found between adults with paraplegia (T2-T12) and AB controls in sympathetic activity. 5 The purpose of this report is to extend the research conducted in the area of HRV and SCI by, for instance, investigating the influence of SCI, on cardiovascular function using standard and non-linear HRV measures, as well clarifying the relationship between fatigue and HRV as a function of the neurological lesion level in adults with SCI.…”

“…11 In the frequency domain, low frequency (LF) and high frequency (HF) mostly reflect sympathetic and vagal modulations of HRV, respectively. 4,11 In the time domain, decreased variation is often associated with a shift from sympathovagal balance to sympathetic predominance, whereas in the frequency domain this is often reflected in an increase in the LF/HF ratio. The two frequency components (LF, 0.04-0.15 Hz and HF, 0.15-0.35 Hz), expressed in absolute values (ms 2 ), largely represent the degree of sympathetic and parasympathetic control, respectively.…”

“…1,2 Among other complications, SCI results in disordered cardiovascular control believed to be due to autonomic nervous system (ANS) imbalance and dysregulation of homeostatic mechanisms. 2 Generally, dysregulation is likely to be more severe the higher and more complete the lesion, 1,3,4 although inactivity associated with being wheelchair dependent may result in disordered cardiac control in lesions as low as T10. 5 In cervical and high thoracic lesions, disruption of sympathetic nervous system (SNS) pathways to the heart is associated with bradycardia, orthostatic hypotension, reduced blood pressure, as well as autonomic dysreflexia and a reduced capacity to thermoregulate.…”

“…5 The mechanisms for ANS dysfunction are complex and require further investigation. [1][2][3][4][5] Physical inactivity, metabolic syndrome and being overweight or obese increase cardiovascular risks, 2,5 and arguably these problems are likely to be associated with chronic fatigue. Fatigue has been defined as a state of excessive chronic tiredness involving pervasive feelings of exhaustion and negative emotions such as anxiety and poor mood.…”

Reponse to ‘Estimating the autonomic function from heart rate variability in mechanically ventilated patients after spinal cord injury’

“…4 We reviewed this group of patients regarding respiratory frequency throughout their admission in intensive care unit (ICU). Owing to a new data management system, three patients did not have their respiratory rate stored.…”