Near infrared spectroscopy for measuring changes in bone hemoglobin content after exercise in individuals with spinal cord injury

Abstract

Bone blood perfusion has an essential role in maintaining a healthy bone. However, current methods for measuring bone blood perfusion are expensive and highly invasive. This study presents a custom built near-infrared spectroscopy (NIRS) instrument to measure changes in bone blood perfusion. We demonstrated the efficacy of this device by monitoring oxygenated and deoxygenated hemoglobin changes in the human tibia during and after exercise in able-bodied and in individuals with spinal cord injury (SCI), a population with known impaired peripheral blood perfusion. Nine able-bodied individuals and six volunteers with SCI performed a 10 min rowing exercise (functional electrical stimulation rowing for those with SCI). With exercise, during rowing, able-bodied showed an increase in deoxygenated hemoglobin in the tibia. Post rowing, able-bodied showed an increase in total blood content, characterized by an increase in total hemoglobin content due primarily to an increase in deoxygenated hemoglobin. During rowing and post-rowing, those with SCI showed no change in total blood content in the tibia. The current study demonstrates that NIRS can non-invasively detect changes in hemoglobin concentration in the tibia. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:183-191, 2018.

Keywords: bone blood perfusion; exercise; hemoglobin content; near infrared spectroscopy; spinal cord injury.

© 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Figures

Figure 1

NIRS device for measuring blood perfusion in tibia.

Figure 2

The computed differential pathlength factors (DPF) using open source Monte Carlo photon modeling software for the considered wavelength range of 700 – 900 nm. (Notations: 1, A represents the light absorbed by the 1st layer that reaches detector A; 2, A represents the light absorbed by the 2nd layer that reaches detector A; 1, B represents the light absorbed by the 1st layer that reaches detector B; 2, B represents the light absorbed by the 2nd layer that reaches detector B.)

Figure 3

Changes in total hemoglobin concentration (μM*cm) in the muscle during sustained quadriceps contraction in an able-bodied individual. The two responses represent sustained quadriceps contraction at 30% and 100% of maximum voluntary contraction.

Figure 4

Intensity of light absorbed by the two detectors for a representative able-bodied individual during a rowing exercise (NIRS probe placed on the skin over the tibia; source-detector A distance = 1 cm; source-detector B distance = 2 cm; Light intensity spectrum at wavelength λ = 810 nm).

Figure 5

Intensity of light absorbed by the two detectors for an able-bodied individual during a rowing exercise, when an inert material (i.e. rubber eraser) is placed between the leg and NIRS probe.

Figure 6

Changes in O2Hb, HHb, and tHb in the tibia in able-bodied individuals during rowing and post rowing (* p<0.1, ** p<0.05 different from zero). For each concentration, boxplots show the median and the maximum and minimum non-outliers (whiskers).

Figure 7

Changes in O2Hb, HHb, and tHb in the tibia in those with SCI during FES-rowing and post FES-rowing (* p<0.1, ** p<0.05). For each concentration, boxplots show the median, the maximum and minimum non-outliers (whiskers), and outliers (+ points).