Effect of Heat Exposure on Cognition in Persons With Tetraplegia
Condition: Tetraplegia; Hypothermia; Mild Cognitive Impairment
MeSH terms: Quadriplegia; Hypothermia; Cognitive Dysfunction
Study type: Interventional

Summary: 
      The ability to maintain normal body temperature (Tcore) is impaired in persons with
      tetraplegia: subnormal Tcore and vulnerability to hypothermia (<95 F) have been documented in
      this population after exposure to even mild environmental temperatures. However, no work to
      date has addressed the effect of subnormal Tcore on cognitive performance in persons with
      tetraplegia despite studies with able-bodied (AB) individuals that have documented
      progressive decline in various aspects of cognitive performance associated with the magnitude
      of the depression in Tcore. The investigators' study will confirm and extend their initial
      observations in persons with higher cord lesions who have subnormal Tcore to show that
      cognitive performance will be improved by raising Tcore to euthermic levels. This improvement
      should be associated with greater function and independence, reintegration into society, and
      an improved quality of life.

      Specific Aims: During exposure to 95 F for up to 120 minutes in the seated position, the
      investigators' aims are:

      Primary Specific Aim: To determine if a modest rise in Tcore to euthermic levels has a
      positive effect on cognitive performance (attention, working memory, processing speed, and
      executive function) in persons with higher-level spinal cord injury (SCI).

      Primary Hypothesis: Based on the investigators' pilot data: (1) 80% of persons with SCI will
      demonstrate an increase of 1 F in Tcore, while none of the AB controls will demonstrate such
      an increase; (2) 80% of persons with SCI will have an improvement of at least one T-score in
      Stroop Interference scores (a validated measure of executive function), while none of the AB
      controls will demonstrate a change in cognitive performance.

      Secondary Specific Aim: To determine changes in: (1) The average of distal skin temperatures;
      (2) Sweat rate; and (3) Subjective rating of thermal sensitivity.

      Secondary Hypothesis: Persons with SCI will have less of a percent change in average distal
      skin temperatures and sweat rate, and will report blunted ratings of thermal sensitivity
      compared to that of AB controls.
    

Detailed description: 
      This study will investigate the physiological and cognitive responses to warm exposure in
      persons with SCI who have subnormal Tcore and in AB persons who are euthermic. The positive
      effect that an increase in Tcore will be expected to have on cognitive performance,
      specifically working memory and executive function, will be demonstrated. These two areas of
      cognitive performance are vital for the ability to optimally care for one's self, at which
      persons with higher cord lesions must excel in order to ensure health, and for the ability to
      attain the maximal degree of independence possible.

      Preparation for Study Visits: Subjects will be instructed to avoid caffeine and alcohol,
      maintain normal salt and water intake, and avoid strenuous exercise for 24 hours prior to the
      study. Subjects will be asked to eat a light, standard meal (plain bagel or 2 pieces of
      toast) 2 hours prior to their visit. Subjects will be asked to empty their bladders prior to
      their visit and again upon arrival, if needed. Subjects will wear minimal clothing during the
      study to maximize skin exposure to the warm temperature.

      Instrumentation: Subjects with SCI will be asked to remain in their wheelchairs and AB
      controls will be placed in a manual wheelchair where they will remain seated and relatively
      still for the duration of the study visit. A thin, flexible rectal sensor will be placed 4
      inches beyond the anal sphincter for Tcore collection, and skin sensors will be secured at 15
      sites above and below the level of lesion for collection of skin temperature (Tsk). Sweat
      collection capsules will be placed on the left bicep, the left forearm, the left thigh and
      the left calf for measurement of sweat rate by QSweat methodology (QS). Laser Doppler
      flowmetry will be used to measure changes in microvascular perfusion (MVP) by placing a
      Doppler probe on the back of both hands and both feet to confirm peripheral blood vessel
      dilation. An automated blood pressure cuff will be placed above the left elbow to measure
      brachial BP.

      Baseline Collection (BL): At the end of a 30-minute acclimation period at 81 F, a baseline
      collection of the following parameters will be performed for 15 minutes: Tcore and Tsk will
      be continuously monitored; BP, heart rate (HR), and thermal sensitivity (TS) will be measured
      in 10-minute intervals; and MVP and QS will be measured in 15-minute intervals. After 15
      minutes, a battery of cognitive tests will be administered to establish baseline cognitive
      performance.

      Thermal Challenge (Heat): Following completion of the BL period, subjects will be wheeled
      into a pre-heated (95 F) thermal chamber for up to 120 minutes or until Tcore increases 1 F.
      Tcore and Tsk will be continuously monitored to ensure subjects' safety throughout the
      protocol, while HR, BP, and TS will be assessed at 10-minute intervals. MVP and QS will be
      measured every 30 minutes. The battery of cognitive tests utilized during BL collection will
      be administered when Tcore increases 1 F from BL values (for subjects with tetraplegia) or
      after 100 minutes (for controls) to determine any change in cognition after exposure to 95 F.
      An increase in Tcore 1 F, significant changes in BP, or subject discomfort will result in
      termination of the protocol.
    

Intervention name(s): Warm Temperature
Intervention type(s): Procedure
Intervention description(s): Subjects will be exposed to a routinely encountered warm temperature (95 F) for up to to 2 hours, depending on their vital signs (BP, HR, Tcore) and tolerance (comfort).
Other intervention name(s): 95 F
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Quadriplegia; Paraplegia; Spinal Cord Injury; Body Temperature Regulation; Mild Cognitive Impairment