Mechanisms of Orthostatic Intolerance in Spinal Cord Injured Individuals and Following Bed Rest
Condition: Spinal Cord Injury
MeSH terms: Spinal Cord Injuries; Orthostatic Intolerance
Study type: Observational

Summary: 
      The primary purpose of this study is to investigate the relationship between the extent of
      neurologic (nerve) impairment in patients with spinal cord injuries and how well the nerves
      passing down the spine to the heart and blood vessels are working. These nerves are called
      the descending spinal sympathetic pathway (DSSP) and are important in controlling many
      functions, including blood pressure. We also wish to examine how injury severity and DSSP
      function influence blood levels of nor-epinephrine and epinephrine. Nor-epinephrine and
      epinephrine are hormones released into the blood that are also important in controlling blood
      pressure. Thus, we will also look at how the effect of the extent of DSSP dysfunction
      influences heart rate and blood pressure and blood levels of certain enzymes.
    

Detailed description: 
      Subjects Healthy able-bodied control volunteers, individuals with acute and chronic spinal
      cord injury, and individuals who have undergone a period of bed rest.

      ASIA and SSR Assessment. The severity of injury to the motor and sensory spinal pathways will
      be documented in accordance to the American Spinal Injury Association (ASIA). The sympathetic
      skin response (SSR) will be examined in order to determine the completeness of injury to the
      DSSP. SSRs will be recorded in subjects in supine position, with the room temperature between
      21-25oC. Subjects will rest supine for at least 30 min before the beginning of the
      examination. The procedure will take approximately 20-30 min. Self-adhesive electrodes will
      be applied to the hands and feet of the patient. SSRs will be recorded bilaterally and
      simultaneously from both hands and feet over 5 s and sampled at a band pass of 3Hz to 3 kHz.
      The median nerve will be stimulated (0.2ms duration, 10-20mA intensity) and 5-10 SSRs samples
      will be recorded. The latency and amplitude of SSRs will be measured and compared in each
      case.

      "Sit up test". We will use a sit-up test to evaluate blood pressure control and orthostatic
      tolerance. Before the test the subject will lie down on a tilt table, in a temperature
      controlled environment for a period of 10 min. Then the subject will be passively seated to
      90° and will keep this position without moving for 20 minutes. The test will be aborted if
      subjects become lightheaded or symptomatic. All individuals with SCI will be assessed for the
      continuity of the DSSP. Continuous non-invasive BP (Finometer, FMS, Arnhem, The Netherlands)
      and ECG (lead II, 3 electrodes on the thorax), monitoring will be performed pre-test, during
      and post-test. In all subjects the following measurements are planned: recordings of BP and
      ECG during 10 min in supine and 20 min in sitting position. Two blood samples will be
      collected prior to the sit-up test after 30 min of rest in supine position and 3-5 min after
      sit-up test. Serum level catecholamines will be examined. Butterfly catheters will be
      inserted at least 30 min prior to the sit-up test. This will allow the collection of blood
      without additional stress to the participant and activation of catecholamines release by
      venopuncture. Two blood samples will be drawn to determine the serum levels of NE and E from
      the antecubital vein of each individual before and immediately after the orthostatic
      challenge.

      Circadian rhythm and 24hr Holter monitoring of ECG. We will obtain continuous HR recordings
      and following analysis will determine the beat-to-beat HRV during the 24 hr period. The
      subject will wear a portable unit connected with electrodes on the chest-wall. During the day
      the subject can do normal daily activities. We will analyze at least 3 measurement points (10
      min interval) during the day and night periods in each individual. HRV analysis will occur
      off-line: briefly, we will use an autoregressive model for the frequency domain variables of
      HRV: low-frequency power (LF, 0.04-0.15 Hz), and high-frequency power (HF, 0.15-0.4 Hz). LF
      power is believed to represent sympathetic tone while HF power represents parasympathetic
      tone.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        SCI individuals (19 to 55 years of age) with a functionally complete or a functionally
        incomplete spinal cord injury will constitute the study population.
      
Keywords: Orthostatic stress