Niro 200

To measure cognitive function, we used a computer-based Stroop test program (designed by one of the researchers, H. Chang) in which a neutral task (NT) and an incongruent task (IT) were performed for 60 seconds each. We measured and compared reaction times (milliseconds) and the number of problems solved per 60 seconds.
Measurements of TOI in the PFC were performed using near infrared spectroscopy (NIRS; NIRO-200, Hamamatsu, Japan). Sensors were connected to the left and right PFC, and changes occurring throughout the Stroop test were recorded. TOI was defined as the ratio of oxygenated hemoglobin to total tissue hemoglobin, and was expressed as follows: TOI = (HbO2/HbO2 + Hb)×100. The TOI was calculated from the slope of light attenuation along the distance from the emitting probe, and measured with the spatially resolved spectroscopy method. To reduce artifacts, participants were asked to minimize head and body movement.

Continuous recordings of cerebral oximetry (NIRO 200, Hamamatsu Photonics, Hamamatsu, Japan) (HbO₂, Hb, total oxygenation index), blood pressure from an indwelling arterial line (Philips IntelliVue MP70, MA, USA), arterial oximetry (Masimo Corporation, CA, USA) from four newborns were collected in a time-locked manner at a rate of 1 kHz using a custom software developed in LabView (National Instruments, TX, USA). The newborns were receiving therapeutic hypothermia for encephalopathy according to the National Institute of Child Health and Human Development Protocol (Shankaran et al., 2005 (link)). Cerebral oximetry was obtained bilaterally, one from the left and another from the right fronto-temporal regions. We calculated HbD as HbO₂–Hb for each hemisphere. We calculated MAP for each cycle of the continuous blood pressure signal using a combination of the lowpass filtering and a peak detection approach. We resampled the MAP into uniformly sampled data using cubic spline at a sample rate of 10 Hz. We also down sampled the HbD signal to 10 Hz. All processing was done off-line using MATLAB (Mathworks, Inc). The study was approved by the Children’s National Medical Center Institutional Review Board and informed consent was obtained from the parents of the patients.

During the first visit to the laboratory, the participants familiarized themselves with the test procedures and completed an incremental one‐legged ramp test on a modified electromagnetic ergometer (Ergometric 900S, Ergoline, Germany) until exhaustion, as described previously (Kuznetsov et al. 2015). The initial load, load increment and knee extension rate were 0 W, 2.5 W/min, and 60 cycles/min, respectively. Three days later, each participant performed an incremental one‐legged ramp test until exhaustion to evaluate the anaerobic threshold (AT) of the m. vastus lateralis according to electromyography activity and changes in deoxyhemoglobin content, as described previously (Kuznetsov et al. 2015). EMG activity in the middle part of the m. vastus lateralis was measured continuously using a CP511 amplifier (Grass Telefactor, USA) and Ag/AgCl electrodes. Changes at the concentration of deoxyhemoglobin were measured continuously using a tissue infrared spectrometer NIRO‐200 (Hamamatsu Photonics K.K., Japan). The infrared source and receiver were placed 40 mm apart and close to the EMG electrodes; they were fixed onto the skin with tape and an elastic bandage. The incremental one‐legged ramp test until exhaustion was repeated 48 h after the last training session of the 8 week aerobic cycle training program.

Tissue oxygen saturation was measured using near-infrared spectroscopy (NIRO−200, Hamamatsu Photonics Deutschland GmbH, Herrsching am Ammersee, Germany) with four laser diodes which emit light at different wavelengths (776, 826, 845, and 905 nm). Both the emitter and detector were sheathed in a rubber holder with 4 cm spacing and attached to the distal third of the forearm at a reproducible point ∼5 cm proximal to the laser Doppler probe using a double-sided adhesive sticker. Oxygenated (HbO₂) and deoxygenated (HHb) haemoglobin were continuously determined during the FMD protocol at a frequency of 1 Hz. Tissue oxygen saturation (StO₂) was estimated as (HbO₂)/[(HbO₂ + HHb)] and expressed as a percentage. In line with McLay et al. (2016a) (link), the following parameters were derived from the NIRS measurement: StO₂ baseline (%) was calculated as the average StO₂ during the 1 min period before cuff occlusion. The nadir reached during the last 30 s of ischaemia was defined as StO₂ minimum (%). The desaturation rate of tissue oxygen saturation was quantified as the downslope of StO₂ during ischaemia (StO₂ slope 1, %·s⁻¹). The StO₂ reperfusion rate was calculated using the upslope of the StO₂ signal in the first 10 s following cuff release (StO₂ slope 2, %·s⁻¹). StO₂ peak (%) was defined as the highest StO₂ value achieved after cuff release.