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.