Study Description

Without blood flow, bone cannot maintain its integrity. Bone blood flow responds to various local and systemic factors, however, bone perfusion in humans remains relatively unstudied. This study will investigate key mechanisms that regulate bone perfusion in able-bodied and contrast responses to those with spinal cord injury (SCI). SCI is a model of chronic reduced loading with loss of sympathetic regulation.

In tibial cortical bone, the study team will: 1) determine the impact of compressive loading with and without muscle contractions; 2) determine the impact of vascular sympathetic activity and systemic perfusion pressure; 3) compare the response between able- bodied and those with SCI. 

Acute metabolic needs of bone due to loading increase flow substantially. In addition, the bone vasculature is innervated by a rich network of sympathetic nerves that serve a functional purpose in the control of blood flow. A critical limitation to the study of bone blood flow in humans has been the lack of non-invasive assessments. We developed a near infrared spectroscopy (NIRS) device to non-invasively assess blood content in bone and assessed tibial perfusion in response to exercise. Here, the study team will test the hypothesis that bone blood flow increases proportional to loading conditions in both able-bodied individuals and those with SCI. The study team will also test the hypothesis that there are decreases in blood bone flow that are proportional to increases in leg vascular sympathetic outflow in the able-bodied, but that changes in bone blood flow are proportional to changes in blood pressure in those with SCI. The proposed research will be some of the first to determine the control of bone flow in humans.

ELIGIBILITY CRITERIA:

Ages Eligible for Study:           18 Years to 40 Years   (Adult)

Sexes Eligible for Study:          All

Accepts Healthy Volunteers:  Yes

Inclusion Criteria:

• healthy males and females
• individuals with spinal cord injuries, between 3 and 24 months post injury, with complete injuries according to the American Spinal Injury Association Impairment Scale A and B, with injuries at T6 and below

Exclusion Criteria:

• clinical signs or symptoms of heart disease
• hypertension
• coronary disease
• diabetes
• other neurological disease
• cancer
• recent weight change >15 pounds
• abnormal resting ECG
• pregnant and/or breastfeeding women
• underweight and obese individuals (body mass index between 18.5 and 29.9)
• use of amphetamines (Ritalin, Adderall, Concerta) in the past 48 hours
• tibial fracture or tibial stress fracture in the past year
• those with SCI will have no extreme spasticity to avoid spontaneous contractions
• use of baclofen for those with SCI

Study Design:

Intervention Model: Single Group Assignment

Masking: None (Open Label)

Primary Purpose: Basic Science

Study Location(s):

Spaulding Hospital, Boston, Massachusetts, United States, 02129

Study Website:

https://www.clinicaltrials.gov/ct2/show/NCT04083794?term=NCT04083794&draw=2&rank=1