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.

Figure 1

Twenty-four-hour SBP among the groups; controls (asterisks), low paraplegia (open squares), high paraplegia (closed triangles), and tetraplegia (closed circles). Main effects for group (P < 0.05) and time (P < 0.0001) were significant; such that 24-hour SBP was significantly lower in the tetraplegic group compared with the control and HP groups (P < 0.05).

Figure 2

Twenty-four-hour HR among the groups; controls (asterisks), low paraplegia (open squares), high paraplegia (closed triangles), and tetraplegia (closed circles). Effects for group (P < 0.01), time (P < 0.0001), and the interaction (P < 0.0001) were significant; such that 24-hour HR was significantly elevated in the HP group compared to the control (P < 0.05) and TETRA (P < 0.01) groups, and in the LP group compared to the control (P < 0.01) and TETRA groups (P < 0.001).

Figure 3

(A) SDANN (ms) in the control (open box), LP (dotted box), HP (hatched box), and TETRA (gray box). *: P < 0.01 versus LP and TETRA; δ: P < 0.08 versus controls. (B) rMSSD (ms) in the control (open box), LP (dotted box), HP (hatched box), and TETRA (gray box). *: P < 0.01 versus TETRA; δ: P < 0.001 versus controls; λ: P = 0.05 versus HP.