ABSTRACT Muscle oxygenation in respiratory and limb muscles during incremental threshold loaded breathing using near infrared spectroscopy (NIRS) B. Shadgan MD, MSc Sports Med, PhD Candidate 1, J.A. Guenette BHK, MSc, PhD Candidate 2, W.D. Reid, BMR(PT), PhD 3, A.W. Sheel PhD 2 1 2 3
Department of Medicine, University of British Columbia, Vancouver, Canada School of Human Kinetics, University of British Columbia, Vancouver, Canada Department of Physical Therapy, University of British Columbia, Vancouver, Canada
Purpose: To assess the changes of muscle oxygenation in sternocleidomastoid (SCM) and the parasternal (PS) and external intercostal (EIC) muscles during incremental inspiratory threshold loading in healthy subjects using non invasive near-infrared spectroscopy (NIRS). METHODS: Ten healthy males (28+4yr) performed maximal inspiratory pressure (MIP) maneuvers and then an inspiratory muscle threshold loading test, during which NIRS and EMG monitoring was performed via surface probes or electrodes on the SCM, 2nd PS intercostal, 8th EIC, and the vastus lateralis (VL). Muscle tissue oxygenation, deoxygenation and blood flow were estimated from the oxygenated (O2Hb), deoxygenated (HHb) and total hemoglobin (tHb) signals, respectively using NIRS. Subjects started at a load of 100 gm and 50 gm were added at 2-minute intervals until task failure. Respiratory rate was 10 breaths/min with a duty cycle of 33%. Results: ∆tHb increased in PS and SCM during progressive threshold loading and task failure whereas the quiescent VL showed a decrease in ∆ tHb during loading and task failure. Conclusion: During incremental loading in healthy young men, tHb increases and O2Hb is maintained in the inspiratory muscles. Our results are consistent with the hypothesis that blood flow “steal” from quiescent limb muscles is a mechanism to maintain muscle tissue oxygenation of the inspiratory muscles during loading.
Muscle oxygenation in respiratory and limb muscles during incremental threshold loaded breathing using near infrared spectroscopy (NIRS) Babak Shadgan, Jordan A. Guenette, W. Darlene Reid, A. William Sheel Department of Medicine, Department of Physical Therapy, School of Human Kinetics THE UNIVERSITY OF BRITISH COLUMBIA, VANCOUVER, CANADA METHODS After informed consent, ten healthy people (males) aged 25 to 32 years, participated in the study. Elite athletes, smokers, and those with a history of asthma, COPD or other respiratory conditions (FEV1/FVC ratio of lesser than 70%) were excluded from the study. Maximal inspiratory pressure (MIP) using an inspiratory force meter (MicroRPM, Vacumed) was assessed. Next, subjects performed an inspiratory muscle threshold loading test, during which NIRS and EMG monitoring was performed. For NIRS monitoring, probes were placed on the left 1) sternocleidomastoid muscle, 2) second parasternal intercostal space, 3) eighth intercostal space at the axillary line, and 4) the vastus lateralis muscle 15 cm above the joint line of the knee. Muscle tissue oxygenation deoxygenation and blood flow were estimated from the oxygenated (O2Hb), deoxygenated (HHb) and total hemoglobin (tHb) signals from NIRS monitoring (Oxymon III, Artinis). Electromyographic activity of muscles was continuously monitored during the experiment by surface EMG electrodes. Subjects started at an initial threshold load of 100 gm and an additional 50 gram weight was added at 2minute intervals until the point of task failure. Breathing pattern was set at 10 breaths per minute with a duty cycle of 33%. End-tidal CO2 was maintained at resting levels by titrating 100% CO2 into the inspiratory circuit. Heart rate, blood pressure and oxygen saturation were monitored using a pulse oximeter.
Figure 4. NIRS signals in Sternocleidomastoid, Parasternal, Intercostalis and Vastus lateralis muscles of a subject in a threshold loaded breathing trial.
Monitor Data Analyzer Signal Processor Photon Counting Hardware Optical Fibers
Emitter Optode Receiver Optode Skin
INTRODUCTION People with chronic obstructive pulmonary disease (COPD) experience high inspiratory loads for prolonged periods of time due to inflamed airways, which causes airflow limitation. These patients recruit their primary as well as accessory inspiratory muscles to perform the added work of ventilation. Prolonged exertional overloads can contribute to inspiratory muscle dysfunction and ventilatory failure in people with COPD. An appreciation of the relationship of inspiratory muscle deoxygenation and decreased force output in response to inspiratory loading in healthy people will provide a foundation to investigate this relationship in people with chronic respiratory disease.
RESULTS The parasternal and sternocleidomastoid, showed trends of increasing DtHb during progressive threshold loading and task failure. Of interest, the quiescent vastus lateralis showed a decrease in DtHb during loading and task failure.
Adipose Muscle
Figure 1. Schematic set up of Near infrared spectroscopy.
Figure 2. A subject during threshold loaded breathing while is monitored by NIRS.
CONCLUSION During incremental loading in healthy young men, DtHb increases and O2Hb is maintained in the inspiratory muscles. Our results are consistent with the hypothesis that blood flow “steal” from quiescent limb muscles is a mechanism to maintain muscle tissue oxygenation of the inspiratory muscles during high respiratory motor output. NIRS seems to be a useful and non invasive method to study the respiratory muscle oxygenation.
ACKNOLEDGMENT Funding for this research was provided by the British Columbia Lung Association, Michael Smith Foundation for Health Research and VCHRI. Figure 3. NIRS optodes placement over vastus lateralis muscle.
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