Hemodynamics of the sternocleidomastoid measured with frequency domain near-infrared spectroscopy towards non-invasive monitoring during mechanical ventilation

Continuous measurements of respiratory muscle blood flow and oxygen consumption using noninvasive frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy

Prior studies of muscle blood flow and muscle-specific oxygen consumption have required invasive injection of dye and magnetic resonance imaging, respectively. Such measures have limited utility for continuous monitoring of the respiratory muscles. Frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy (FD-NIRS & DCS) can provide continuous surrogate measures of blood flow index (BFi) and metabolic rate of oxygen consumption (MRO2). This study aimed to validate sternocleidomastoid FD-NIRS & DCS outcomes against electromyography (EMG) and mouth pressure (Pm) during incremental inspiratory threshold loading (ITL). Six female and six male healthy adults (means ± SD; 30 ± 7 yr, maximum inspiratory pressure 118 ± 61 cmH2O) performed incremental ITL starting at low loads (8 ± 2 cmH2O) followed by 50-g increments every 2 min until task failure. FD-NIRS & DCS continuously measured sternocleidomastoid oxygenated and deoxygenated hemoglobin + myoglobin (oxy/deoxy[Hb + Mb]), tissue saturation of oxygen (StO2), BFi, and MRO2. Ventilatory parameters including inspiratory Pm were also evaluated. Pm increased during incremental ITL (P < 0.05), reaching -47[-74 to -34] cmH2O (median [IQR: 25%-75%]) at task failure. Ventilatory parameters were constant throughout ITL (all P > 0.05). Sternocleidomastoid BFi and MRO2 increased from the start of the ITL (both P < 0.05). Deoxy[Hb + Mb] increased close to task failure, concomitantly with a constant increase in MRO2, and decreased StO2. Sternocleidomastoid deoxy[Hb + Mb], BFi, StO2, and MRO2 obtained during ITL via FD-NIRS & DCS correlated with sternocleidomastoid EMG (all P < 0.05). In healthy adults, FD-NIRS & DCS can provide continuous surrogate measures of respiratory BFi and MRO2. Increasing sternocleidomastoid oxygen consumption near task failure was associated with increased oxygen extraction and reduced tissue saturation.NEW & NOTEWORTHY This study introduces a novel approach, frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy (FD-NIRS & DCS), for noninvasive continuous monitoring of respiratory muscle blood flow and metabolic rate of oxygen consumption. Unlike prior methods involving invasive dye injection and magnetic resonance imaging, FD-NIRS & DCS offers the advantage of continuous measurement without the need for invasive procedures. It holds promise for advancing muscle physiology understanding and opens avenues for real-time monitoring of respiratory muscles.

Tutorial on methods for estimation of optical absorption and scattering properties of tissue

Significance

The estimation of tissue optical properties using diffuse optics has found a range of applications in disease detection, therapy monitoring, and general health care. Biomarkers derived from the estimated optical absorption and scattering coefficients can reflect the underlying progression of many biological processes in tissues.

Aim

Complex light-tissue interactions make it challenging to disentangle the absorption and scattering coefficients, so dedicated measurement systems are required. We aim to help readers understand the measurement principles and practical considerations needed when choosing between different estimation methods based on diffuse optics.

Approach

The estimation methods can be categorized as: steady state, time domain, time frequency domain (FD), spatial domain, and spatial FD. The experimental measurements are coupled with models of light-tissue interactions, which enable inverse solutions for the absorption and scattering coefficients from the measured tissue reflectance and/or transmittance.

Results

The estimation of tissue optical properties has been applied to characterize a variety of ex vivo and in vivo tissues, as well as tissue-mimicking phantoms. Choosing a specific estimation method for a certain application has to trade-off its advantages and limitations.

Conclusion

Optical absorption and scattering property estimation is an increasingly important and accessible approach for medical diagnosis and health monitoring.

Intermittent neck flexion induces greater sternocleidomastoid deoxygenation than inspiratory threshold loading

PURPOSE

To compare deoxygenation of the sternocleidomastoid, scalenes, and diaphragm/intercostals (Dia/IC) during submaximal intermittent neck flexion (INF) versus submaximal inspiratory threshold loading (ITL) in healthy adults.

METHODS

Fourteen participants performed a randomized, cross-over, repeated measures design. After evaluation of maximal inspiratory pressures (MIP) and maximum voluntary contraction (MVC) for isometric neck flexion, participants were randomly assigned to submaximal ITL or INF until task failure. At least 2 days later, they performed the submaximal exercises in the opposite order. ITL or INF targeted 50 ± 5% of the MIP or MVC, respectively, until task failure. Near-infrared spectroscopy (NIRS) was applied to evaluate changes of deoxy-hemoglobin (ΔHHb), oxy-hemoglobin (ΔO2Hb), total hemoglobin (ΔtHb), and tissue saturation of oxygen (StO2) of the sternocleidomastoid, scalenes, and Dia/IC. Breathlessness and perceived exertion were evaluated using Borg scales.

RESULTS

Initially during INF, sternocleidomastoid HHb slope was greatest compared to the scalenes and Dia/IC. At isotime (6.5-7 min), ΔtHb (a marker of blood volume) and ΔO2Hb of the sternocleidomastoid were higher during INF than ITL. Sternocleidomastoid HHb, O2Hb, and tHb during INF also increased at quartile and task failure timepoints. In contrast, scalene ΔO2Hb was higher during ITL than INF at isotime. Further, Dia/IC O2Hb and tHb increased during ITL at the third quartile and at task failure. Borg scores were lower at task failure during INF compared to ITL.

CONCLUSION

Intermittent INF induces significant metabolic activity of the sternocleidomastoid and a lower perception of effort, which may provide an alternative inspiratory muscle training approach for mechanically ventilated patients.

Combined frequency domain near-infrared spectroscopy and diffuse correlation spectroscopy system for comprehensive metabolic monitoring of inspiratory muscles during loading

Significance

Mechanical ventilation (MV) is a cornerstone technology in the intensive care unit as it assists with the delivery of oxygen in critically ill patients. The process of weaning patients from MV can be long and arduous and can lead to serious complications for many patients. Despite the known importance of inspiratory muscle function in the success of weaning, current clinical standards do not include direct monitoring of these muscles.

Aim

The goal of this project was to develop and validate a combined frequency domain near-infrared spectroscopy (FD-NIRS) and diffuse correlation spectroscopy (DCS) system for the noninvasive characterization of inspiratory muscle response to a load.

Approach

The system was fabricated by combining a custom digital FD-NIRS and DCS system. It was validated via liquid phantom titrations and a healthy volunteer study. The sternocleidomastoid (SCM), an accessory muscle of inspiration, was monitored during a short loading period in fourteen young, healthy volunteers. Volunteers performed two different respiratory exercises, a moderate load and a high load, which consisted of a one-minute baseline, a one-minute load, and a six-minute recovery period.

Results

The system has low crosstalk between absorption, reduced scattering, and flow when tested in a set of liquid titrations. Faster dynamics were observed for changes in blood flow index (BF i ), and metabolic rate of oxygen (MRO 2 ) compared with hemoglobin + myoglobin (Hb+Mb) based parameters after the onset of loads in males. Additionally, larger percent changes in BF i , and MRO 2 were observed compared with Hb+Mb parameters in both males and females. There were also sex differences in baseline values of oxygenated Hb+Mb, total Hb+Mb, and tissue saturation.

Conclusions

The dynamic characteristics of Hb+Mb concentration and blood flow were distinct during loading of the SCM, suggesting that the combination of FD-NIRS and DCS may provide a more complete picture of inspiratory muscle dynamics.

In vivocharacterization of the optical and hemodynamic properties of the human sternocleidomastoid muscle through ultrasound-guided hybrid near-infrared spectroscopies

Objective.In this paper, we present a detailedin vivocharacterization of the optical and hemodynamic properties of the human sternocleidomastoid muscle (SCM), obtained through ultrasound-guided near-infrared time-domain and diffuse correlation spectroscopies.Approach.A total of sixty-five subjects (forty-nine females, sixteen males) among healthy volunteers and thyroid nodule patients have been recruited for the study. Their SCM hemodynamic (oxy-, deoxy- and total hemoglobin concentrations, blood flow, blood oxygen saturation and metabolic rate of oxygen extraction) and optical properties (wavelength dependent absorption and reduced scattering coefficients) have been measured by the use of a novel hybrid device combining in a single unit time-domain near-infrared spectroscopy, diffuse correlation spectroscopy and simultaneous ultrasound imaging.Main results.We provide detailed tables of the results related to SCM baseline (i.e. muscle at rest) properties, and reveal significant differences on the measured parameters due to variables such as side of the neck, sex, age, body mass index, depth and thickness of the muscle, allowing future clinical studies to take into account such dependencies.Significance.The non-invasive monitoring of the hemodynamics and metabolism of the sternocleidomastoid muscle during respiration became a topic of increased interest partially due to the increased use of mechanical ventilation during the COVID-19 pandemic. Near-infrared diffuse optical spectroscopies were proposed as potential practical monitors of increased recruitment of SCM during respiratory distress. They can provide clinically relevant information on the degree of the patient's respiratory effort that is needed to maintain an optimal minute ventilation, with potential clinical application ranging from evaluating chronic pulmonary diseases to more acute settings, such as acute respiratory failure, or to determine the readiness to wean from invasive mechanical ventilation.

A combined frequency domain near infrared spectroscopy and diffuse correlation spectroscopy system for comprehensive metabolic monitoring of inspiratory muscles during loading

Significance

Mechanical ventilation (MV) is a cornerstone technology in the intensive care unit as it assists with the delivery of oxygen in critical ill patients. The process of weaning patients from MV can be long, and arduous and can lead to serious complications for many patients. Despite the known importance of inspiratory muscle function in the success of weaning, current clinical standards do not include direct monitoring of these muscles.

Aim

The goal of this project was to develop and validate a combined frequency domain near infrared spectroscopy (FD-NIRS) and diffuse correlation spectroscopy (DCS) system for the noninvasive characterization of inspiratory muscle response to a load.

Approach

The system was fabricated by combining a custom digital FD-NIRS and DCS system. It was validated via liquid phantom titrations and a healthy volunteer study. The sternocleidomastoid (SCM), an accessory muscle of inspiration, was monitored during a short loading period in fourteen young healthy volunteer. Volunteers performed two different respiratory exercises, a moderate and high load, which consisted of a one-minute baseline, a one-minute load, and a six-minute recovery period.

Results

The system has low crosstalk between absorption, reduced scattering, and flow when tested in a set of liquid titrations. Faster dynamics were observed for changes in blood flow index (BFi), and metabolic rate of oxygen (MRO2) compared to hemoglobin + myoglobin (Hb+Mb) based parameters after the onset of loads in males. Additionally, larger percent changes in BFi, and MRO2 were observed compared to Hb+Mb parameters in both males and females. There were also sex differences in baseline values of oxygenated Hb+Mb, total Hb+Mb, and tissue saturation.

Conclusion

The dynamic characteristics of Hb+Mb concentration and blood flow were distinct during loading of the SCM, suggesting that the combination of FD-NIRS and DCS may provide a more complete picture of inspiratory muscle dynamics.

Assessment of power spectral density of microvascular hemodynamics in skeletal muscles at very low and low-frequency via near-infrared diffuse optical spectroscopies

In this work, we used a hybrid time domain near-infrared spectroscopy (TD-NIRS) and diffuse correlation spectroscopy (DCS) device to retrieve hemoglobin and blood flow oscillations of skeletal muscle microvasculature. We focused on very low (VLF) and low-frequency (LF) oscillations (i.e., frequency lower than 0.145 Hz), that are related to myogenic, neurogenic and endothelial activities. We measured power spectral density (PSD) of blood flow and hemoglobin concentration in four muscles (thenar eminence, plantar fascia, sternocleidomastoid and forearm) of 14 healthy volunteers to highlight possible differences in microvascular hemodynamic oscillations. We observed larger PSDs for blood flow compared to hemoglobin concentration, in particular in case of distal muscles (i.e., thenar eminence and plantar fascia). Finally, we compared the PSDs measured on the thenar eminence of healthy subjects with the ones measured on a septic patient in the intensive care unit: lower power in the endothelial-dependent frequency band, and larger power in the myogenic ones were observed in the septic patient, in accordance with previous works based on laser doppler flowmetry.

Review of recent advances in frequency-domain near-infrared spectroscopy technologies [Invited]

Over the past several decades, near-infrared spectroscopy (NIRS) has become a popular research and clinical tool for non-invasively measuring the oxygenation of biological tissues, with particular emphasis on applications to the human brain. In most cases, NIRS studies are performed using continuous-wave NIRS (CW-NIRS), which can only provide information on relative changes in chromophore concentrations, such as oxygenated and deoxygenated hemoglobin, as well as estimates of tissue oxygen saturation. Another type of NIRS known as frequency-domain NIRS (FD-NIRS) has significant advantages: it can directly measure optical pathlength and thus quantify the scattering and absorption coefficients of sampled tissues and provide direct measurements of absolute chromophore concentrations. This review describes the current status of FD-NIRS technologies, their performance, their advantages, and their limitations as compared to other NIRS methods. Significant landmarks of technological progress include the development of both benchtop and portable/wearable FD-NIRS technologies, sensitive front-end photonic components, and high-frequency phase measurements. Clinical applications of FD-NIRS technologies are discussed to provide context on current applications and needed areas of improvement. The review concludes by providing a roadmap toward the next generation of fully wearable, low-cost FD-NIRS systems.