Speed of Robotic Leg Movements and Orthostatic Hypotension in Subacute SCI

This study seeks to evaluate whether the speed (cadence) of lower extremity robotic movement has an impact on orthostatic hypotension and upright tolerance when training with the ErigoPro robotic tilt-stepper. It is hypothesized more frequent short-lasting leg movements (faster cadence) reduces the occurrence/severity of orthostatic hypotension better than less frequent longer-lasting leg movements (slower cadence).

Orthostatic hypotension (OH) refers to a drop in blood pressure as a result of sitting up or standing up (moving against gravity). OH has been defined as a decrease in systolic (≥20 mmHg) or diastolic (≥10 mmHg) blood pressure upon transition from lying down to an upright position regardless of the presence or absence of overt symptoms (dizziness, lightheadedness, blurred vision, loss of consciousness).

OH is quite common after a spinal cord injury (SCI), especially with more severe injuries above the T6 level. OH can significantly interfere with activities of daily living and it can also interfere with participation during inpatient rehabilitation. Nearly 75% of acute SCI subjects were found to have OH and \~60% reported symptoms of OH during physical therapy activities, which limited almost 50% of the treatment sessions. Developments in rehabilitation technology have culminated in a device, a robotic tilt-stepper (RTS), e.g., known as the Erigo (Hocoma). In an RTS, the robot moves the legs through a pre-selected range of motion at different speeds to limit blood pooling during verticalization. This can be augmented by patterned functional electrical stimulation (FES), e.g., the ErigoPro.

The proof-of-principle study by the developers of the Erigo showed that passive leg movements can stabilize hemodynamic responses in healthy subjects who exhibited near-syncope when placed at 75-deg. for 30 min. Two earlier studies that examined the effect of passive leg movements on hemodynamic responses in healthy subjects used only one movement speed. Two other studies in chronic SCI (which compared the hemodynamic effects of passive leg movements alone or in combination with FES during a tilt-table verticalization) also used only one movement speed. Chi et al. showed no difference in vital signs between application of passive leg movements, FES, or the combination thereof in comparison to baseline.

Based on the literature review, it appears that no previous study has systematically examined the effects of different speeds of robotic leg movements on hemodynamic responses, which is the simplest and most user-friendly way to use RTS in a busy clinical setting. Moreover, no study recruited the most relevant target population, that is, persons with a subacute SCI who often develop OH when moved from lying down to a sitting or standing position. Therefore, it is the intent of this study to determine whether the speed of leg movement during progressive movement towards an upright position has a meaningful impact on a subjects blood pressure and onset of OH.

To test this hypothesis, healthy subjects and subjects with SCI will be recruited to participate in a one time training session with the ErigoPro. The study will occur in the SCI floor of a large rehab center. The sit-up test will be performed to assess if transitioning from supine to sitting position provokes symptoms/signs of OH. All prescribed medication will be noted and allowed as to not interfere with regular care and to reflect a real clinical practice. Each subject will then be transferred to the Erigo and secured to the device. Once secured to the device, the trial will be initiated and the subject will remain in supine for a resting period of approximately 5 minutes (to allow the subjects cardiovascular system to reach steady state) followed by another 2 minutes with their hemodynamic values continuously monitored by a beat-to-beat monitoring device (the Finapres Nova) which will aid in establishment of baseline hemodynamic thresholds. The assigned cadence (either 0, 40, or 80 steps per minute) will be initiated and the subject will then be progressed through angles of elevation including 0, 25, 50, and 75 degrees, spending approximately 2 minutes in each position with hemodynamic responses continuously monitored. If the subject demonstrates any signs/symptoms of OH or their blood pressure falls below or exceeds the established thresholds for safety or any other significant issues arise, they will be immediately returned to the supine position (0 degrees), the assigned cadence discontinued, and that portion of the trial terminated. If the subject demonstrates a return to baseline hemodynamic values within 5 - 10 minutes and they agree to continuation of the trial, they will be progressed to the next assigned speed. Should they not return to baseline values, the medical team will be contacted and the attending physician consulted. Any signs noted by the investigator or symptoms reported by the patient will be recorded and should a portion of the trial be terminated, the cause will be investigated to determine if it was truly due to OH or another issue. If the subject achieves 75 degrees for 2 minutes with no significant issues, they will be returned to supine followed by the next assigned speed being tested in the same fashion as the previously tested assigned speed.

Eligibility Criteria:
Healthy subjects and subjects with SCI:

Inclusion Criteria:

1. Reported overt signs/symptoms of OH during and/or outside of therapy sessions or primary therapist reports a drop in blood pressure consistent with OH during therapy sessions (SCI)
2. Age 16 - 70 years (Healthy \& SCI)
3. Traumatic SCI AIS A - C or non-traumatic SCI, all levels of injury (SCI)
4. Time since SCI ≤ 12 weeks (SCI)
5. Weight ≤ 297 lb, leg length 29" - 39" (per ErigoPro manual) (Healthy \& SCI)
6. Systolic BP \>80 mmHg and \<140 mmHg in supine measured by nursing staff in the 24 hours prior to recruitment. (Healthy \& SCI)

Exclusion Criteria:

1. Weight bearing precautions per medical record or primary therapist report (SCI)
2. Skin lesions preventing fitting on the tilt-table or in robot cuffs (Healthy \& SCI)
3. History of uncontrolled diabetes (diabetic autonomic issues) (Healthy \& SCI)
4. Increase in pain/spasticity during passive leg movements during a hands-on eligibility assessment (SCI)
5. Severe fixed contractures affecting the lower limbs (hip, knee, ankle joints) (SCI)