Blood Oxygenation Dynamics Research Articles

Objective Evaluation of Local Muscle Fatigue in Cerebral Palsy Using A Gait Corrector

The participants were seven individuals (age range 7–36 years) whose walking ability ranged from independent to requiring assistance with a cane, walker, etc. The protocol consisted of resting for at least five minutes before starting to walk, wearing a Gait Corrector device, and walking with light and heavy loads based on the participant's rating of perceived exertion (RPE), followed by resting for 10 minutes before the end of the protocol.Near-infrared spectroscopy (NIRS) electrodes were attached bilaterally to the tibialis anterior and lateral gastrocnemius muscles. NIRS was used to measure blood oxygenation dynamics in local muscles from rest before walking to 10 minutes after walking, and evoked electromyography was used to measure the nerve conduction velocity of the peripheral nerves before and during early and late walking.The tone state of the lateral gastrocnemius muscle was measured three times using an evoked potential-testing device: before walking, immediately after heavy-load walking, and 10 minutes after walking. A recording electrode was attached to the abductor digitorum medialis muscle and a reference electrode was attached to the base of the toe. The M and F waves were recorded using tibial nerve stimulation. The average F/M ratio was used as a parameter of the F-wave.Regarding the change in muscle tone, four of the seven patients exhibited no change or a lower mean F/M ratio after walking than before walking, whereas three patients who exhibited resistance to other dorsiflexion movements of the ankle joint had higher values. Blood oxygenation dynamics revealed a greater disparity between oxyhemoglobin and deoxyhemoglobin concentrations after walking in all participants, suggesting local muscle fatigue, the degree of which showed no improvement even after 10 minutes of rest.

Intraoperative optical mapping of epileptogenic cortices during non-ictal periods in pediatric patients.

Complete removal of epileptogenic cortex while preserving eloquent areas is crucial in patients undergoing epilepsy surgery. In this manuscript, the feasibility was explored of developing a new methodology based on dynamic intrinsic optical signal imaging (DIOSI) to intraoperatively detect and differentiate epileptogenic from eloquent cortices in pediatric patients with focal epilepsy. From 11 pediatric patients undergoing epilepsy surgery, negatively-correlated hemodynamic low-frequency oscillations (LFOs, ~ 0.02–0.1 Hz) were observed from the exposed epileptogenic and eloquent cortical areas, as defined by electrocorticography (ECoG), using a DIOSI system. These LFOs were classified into multiple groups in accordance with their unique temporal profiles. Causal relationships within these groups were investigated using the Granger causality method, and 83% of the ECoG-defined epileptogenic cortical areas were found to have a directed influence on one or more cortical areas showing LFOs within the field of view of the imaging system. To understand the physiological origins of LFOs, blood vessel density was compared between epileptogenic and normal cortical areas and a statistically-significant difference (p < 0.05) was detected. The differences in blood-volume and blood-oxygenation dynamics between eloquent and epileptogenic cortices were also uncovered using a stochastic modeling approach. This, in turn, yielded a means by which to separate epileptogenic from eloquent cortex using hemodynamic LFOs. The proposed methodology detects epileptogenic cortices by exploiting the effective connectivity that exists within cortical regions displaying LFOs and the biophysical features contributed by the altered vessel networks within the epileptogenic cortex. It could be used in conjunction with existing technologies for epileptogenic/eloquent cortex localization and thereby facilitate clinical decision-making.

SU-E-T-292: In-Vivo Blood Oxygen Measurements Via Interstitial Fiber Optic Probe and Photoacoustic Imaging

Purpose: Better understanding of hemodynamics and oxygen transport in response to radiation will enable clinicians to optimize radiotherapy treatment regimens. It is well‐known that oxygenated tissue is significantly more responsive to damage caused by irradiation. We sought to explore the real‐time hemodynamics and blood oxygenation dynamics in response to radiation using a novel interstitial fiber‐optic probe and a photoacoustic imaging system. Methods: Mice bearing xenografted tumors composed of a head and neck cancer cell line (UM‐SCC47) and a patient‐derived xenograft (UW‐SCC36) were irradiated (10 Gy). Blood oxygena saturation (S) and blood volume fraction (B) were monitored in real time using an interstitial fiber optic probe as well as a photoacoustic imaging system (using a 21 MHz transducer, and infra red wavelengths of 750 and 850nm on the Vevo LAZR (R)). Results: A significant drop in blood oxygen saturation was found within 15 minutes following irradiation using the interstitial fiber optic probe. Meanwhile, Blood volume fraction remained constant. Preliminary photoacoustic imaging provided evaluation of the spatial characteristics of blood‐oxygen dynamics and showed qualitative agreement with probe measurements. The measurements were compared to gain a better understanding of the fiber optic probe's spatial averaging, also. Conclusion: While development of the interstitial fiber optic probe continues, it appears to provide real‐time assessment of blood‐oxygen dynamics. Correlation of optimal reoxygenation with split dose radiation response is ongoing and may provide insight that could lead to improvements in the delivery of radiation therapy. This is particularly valuable for hypofractionated treatments as this information can guide the timing, size, and number of fractions for radiotherapy treatments. Minalini Lakshman is an employee of the VisualSonics company; however, the company did not provide any financial support for this work.

COHERENCE BETWEEN FLUCTUATIONS IN BLOOD FLOW AND OXYGEN SATURATION

We have determined the wavelet phase coherence between simultaneously recorded microvascular blood flow and oxygen saturation signals from 88 healthy subjects, thus enabling us to study their common fluctuations. Measurements were taken for 30 min from the arm and leg, at two depths. In the skin, blood flow and oxygen saturation were found to be coherent both at the cardiac frequency and below 0.1 Hz down to about 0.01 Hz. Coherence in the arm extends to lower frequencies than that in the leg. From the deeper recordings, no coherence was found on either limb. The existence of coherence between skin blood flow and oxygen saturation demonstrates causal connections between them within certain frequency ranges. The method has yielded the first detailed insight into the dynamics of blood oxygenation.

Dynamics of blood oxygenation gives better insight into tissue hypoxia than averaged values

normal cellular function requires a continuous supply of oxygen. In higher animals a cardiovascular system is used to provide for a convective delivery of oxygen to the smallest branches of the network of blood vessels—the microcirculation—from which oxygen then passes to the cells through

Noninvasive, in vivo imaging of blood-oxygenation dynamics within the mouse brain using photoacoustic microscopy

Photoacoustic microscopy (PAM) has been used to obtain high-resolution, noninvasive images of the in vivo mouse brain. In this work, we exploit the high-depth and temporal resolutions of PAM to noninvasively image the blood-oxygenation dynamics of multiple cortex vessels in the mouse brain simultaneously in response to controlled hypoxic and hyperoxic challenges. These results confirm the ability of PAM to track blood oxygenation in the mouse brain, a critical aspect of imaging brain activity through the hemodynamic response.

Noninvasive investigation of blood oxygenation dynamics of tumors by near-infrared spectroscopy

The measurement of dynamic changes in the blood oxygenation of tumor vasculature could be valuable for tumor prognosis and optimizing tumor treatment plans. In this study we employed near-infrared spectroscopy (NIRS) to measure changes in the total hemoglobin concentration together with the degree of hemoglobin oxygenation in the vascular bed of breast and prostate tumors implanted in rats. Measurements were made while inhaled gas was alternated between 33% oxygen and carbogen (95% O(2), 5% CO(2)). Significant dynamic changes in tumor oxygenation were observed to accompany respiratory challenge, and these changes could be modeled with two exponential components, yielding two time constants. Following the Fick principle, we derived a simplified model to relate the time constants to tumor blood-perfusion rates. This study demonstrates that the NIRS technology can provide an efficient, real-time, noninvasive means of monitoring the vascular oxygenation dynamics of tumors and facilitate investigations of tumor vascular perfusion. This may have prognostic value and promises insight into tumor vascular development.