Applications of diffuse optical spectroscopy in exercise physiology and metabolic disease
Abstract
While medical practitioners increasingly appreciate the importance of exercise and diet in management of metabolic disorders, there are still few clinical diagnostic tools to assess the effects of these "lifestyle" interventions. Near-infrared spectroscopy (NIRS) is uniquely suited to this purpose because it is non-invasive, non-harmful, and can be used in a variety of tissues. The purpose of these studies is to apply two techniques of NIRS: time-resolved NIRS (TR-NIRS), and frequency domain diffuse optical spectroscopic imaging (DOSI) to physiological studies in humans. The first set of studies describes the use of TR-NIRS to study incremental exercise in children and adolescents. TR-NIRS signals are use to quantify tissue-specific responses to increasing exercise intensity, as well as to determine correlation of thresholds with those occurring in ventilation data. Secondly, the effect of training is assessed by conducting cerebral TR-NIRS measurements before an 8 week training session. And finally, the paradigm of blood flow restriction exercise is investigated as a way of perturbing muscle and cerebral hemodynamics during resistance exercise.
The second portion of these studies involves the application of DOSI to the study of subcutaneous adipose tissue (AT). The role of AT in the pathophysiology of metabolic disease is increasingly appreciated, but method to measure AT function are limited. We hypothesized that DOSI would be sensitive to changes in AT optical properties with calorie restriction, and conducted a pilot study along those lines. DOSI detected changes in both optical scattering and absorption that are consistent with known phenomena that occur in AT with weight loss, ie reduction in fat cell volume, increased O2 extraction, and increased hydration. These findings might constitute an optical signature of AT that correlates with improvement in overall metabolism.
Taken together, these studies introduce novel contributions in the field of optical imaging in the context of obesity, metabolism and exercise.