Author(s): HODGKISS, D., BALTHAZAAR, S.J.T., WELCH, J.F., WADLEY, A.J., COX, P.A., LUCAS, R.A.I., VELDHUIJZEN VAN ZANTEN, J., CHIOU, S.Y., LUCAS, S.J.E., NIGHTINGALE, T.E., Institution: UNIVERSITY OF BIRMINGHAM, Country: UNITED KINGDOM, Abstract-ID: 1551

INTRODUCTION:
Individuals with a cervical or upper-thoracic spinal cord injury (SCI ≥T6) typically exhibit impaired exercise responses due to disrupted supraspinal sympathetic control of the cardiovascular (CV) system. This results in low blood pressure (BP), and reduced peak heart rate (HR) and stroke volume (SV) during exercise. The purpose of this study was to investigate the effects of transcutaneous spinal cord stimulation (TSCS) on arm-crank time to exhaustion (TTE) in individuals with SCI.
METHODS:
Ten individuals (9 male, 1 female) with a chronic, motor-complete SCI between the C4-T6 spinal segments underwent an individualised TSCS mapping session. A neuromodulation device (SCONE, SpineX Inc., USA) delivered specific stimulation parameters to optimise cardiovascular responses (CV-TSCS) without exceeding the 150 mmHg systolic BP (SBP) cut-off for pharmacologically-mediated autonomic dysreflexia intervention. Stimulation parameters included waveform (biphasic or monophasic), intensity (40-200mA) and cathode electrode locations (T10-L2 spinal segments). Fixed parameters included a 10kHz carrier frequency with low-frequency bursts (30Hz), each with a 1ms pulse width. Left-ventricular cardiac contractility (dP/dtmax) was predicted via the Modelflow algorithm. A sham condition (SHAM-TSCS) served as a comparison. A graded arm-crank exercise test identified peak oxygen uptake (V̇O2peak). Following a familiarisation trial, participants exercised to exhaustion in a randomised order with CV-TSCS and SHAM-TSCS, consisting of light (7 min), moderate (7 min) then vigorous (>7 min) intensity bouts prescribed as %V̇O2peak. TTE was defined as the duration performed at or above vigorous-intensity. Paired t-tests were conducted with Cohen’s d effect sizes (small >0.2; medium >0.5; large >0.8).
RESULTS:
At rest during the mapping session, CV-TSCS increased SBP (97 ± 12 vs 122 ± 12 mmHg; p<0.01, d=2.61) and peak dP/dtmax (551 ± 134 vs 729 ± 249 mmHg/s; p<0.01, d=1.28), relative to baseline. Prior to exercise, the change in SBP was greater with CV-TSCS versus SHAM-TSCS (Δ-1 ± 8 vs 22 ± 9 mmHg; p<0.01, d=1.86). TTE improved by 35 ± 9% (788 ± 322 vs 1037 ± 371 secs; p<0.01, d=1.91), with large effects on peak oxygen pulse (8.5 ± 2.3 vs 9.1 ± 2.2 mL/beat; p=0.02, d=0.85), a surrogate for SV, and peak HR (117 ± 24 vs 124 ± 23 bpm; p=0.02, d=0.90) with CV-TSCS relative to SHAM-TSCS. Subjective ratings of perceived exertion tended to be lower, whilst exercise enjoyment was significantly greater, with CV-TSCS.
CONCLUSION:
These findings have important ramifications for supporting elite athletes (e.g., Paralympians), trained or sedentary individuals with SCI. This evidence will be strengthened with recruitment of an adequately powered cohort as part of an ongoing clinical trial (ISRCTN17856698) that is also exploring the wider effects of CV-TSCS on short- and long-term autonomic cardiovascular dysfunction in individuals with SCI.