Comparison of 24-hour cardiovascular and autonomic function in paraplegia, tetraplegia, and control groups: Implications for cardiovascular risk

Abstract

Background

Fluctuations in 24-hour cardiovascular hemodynamics, specifically heart rate (HR) and blood pressure (BP), are thought to reflect autonomic nervous system (ANS) activity. Persons with spinal cord injury (SCI) represent a model of ANS dysfunction, which may affect 24-hour hemodynamics and predispose these individuals to increased cardiovascular disease risk.

Objective

To determine 24-hour cardiovascular and ANS function among individuals with tetraplegia (n = 20; TETRA: C4–C8), high paraplegia (n = 10; HP: T2–T5), low paraplegia (n = 9; LP: T7–T12), and non-SCI controls (n = 10). Twenty-four-hour ANS function was assessed by time domain parameters of heart rate variability (HRV); the standard deviation of the 5-minute average R–R intervals (SDANN; milliseconds/ms), and the root-mean square of the standard deviation of the R–R intervals (rMSSD; ms). Subjects wore 24-hour ambulatory monitors to record HR, HRV, and BP. Mixed analysis of variance (ANOVA) revealed significantly lower 24-hour BP in the tetraplegic group; however, BP did not differ between the HP, LP, and control groups. Mixed ANOVA suggested significantly elevated 24-hour HR in the HP and LP groups compared to the TETRA and control groups (P < 0.05); daytime HR was higher in both paraplegic groups compared to the TETRA and control groups (P < 0.01) and nighttime HR was significantly elevated in the LP group compared to the TETRA and control groups (P < 0.01). Twenty-four-hour SDANN was significantly increased in the HP group compared to the LP and TETRA groups (P < 0.05) and rMSSD was significantly lower in the LP compared to the other three groups (P < 0.05). Elevated 24-hour HR in persons with paraplegia, in concert with altered HRV dynamics, may impart significant adverse cardiovascular consequences, which are currently unappreciated.

Keywords:

• Paraplegia
• Tetraplegia
• Autonomic nervous system
• Heart rate
• Blood pressure
• Heart rate variability
• Diurnal variation
• Spinal cord injuries
• Cardiovascular risk

Acknowledgements

We thank Dr Joseph Weir for his support with the statistical analyses. This research was supported by the Veterans Affairs Rehabilitation Research and Development Service (grant no. A6161W, B3203R and B4162C).