Zengyong Li

Wavelet analysis of cerebral oxygenation signal measured by near infrared spectroscopy in subjects with cerebral infarction

The objective of this study is to assess the cerebral oxygenation oscillations in subjects with cerebral infarction (CI) based on the wavelet transform of near infrared spectroscopy (NIRS) signals. A total of twenty subjects were recruited from a local hospital to participate in this study. The subjects lay in the supine position and cerebral oxygenation signal was monitored for 20 min from the frontal lobe using NIRS. With spectral analysis based on wavelet transform, five frequency intervals were identified (I, 0.005-0.02 Hz, II, 0.02-0.06 Hz, III, 0.06-0.15 Hz, IV, 0.15-0.40 Hz and V, 0.40-2.0 Hz). The amplitude of the [HbO(2)] in frequency interval I (0.005-0.02 Hz), II (0.02-0.06 Hz), III (0.06-0.15 Hz) and V(0.15-2 Hz) for the subjects with CI were found to be significantly lower by 36%, 45%, 50% and 69% compared to that for the normal subjects (p<0.05). The amplitude of the [Hb] in frequency interval I (0.005-0.02 Hz), II (0.02-0.06 Hz) and V(0.15-2 Hz) for the subjects with CI were found to be significantly lower by 40%, 36% and 69% compared to that for the normal subjects (p<0.05). The reduction of spontaneous oscillations in subjects with CI may suggest an increased stiffness in arterial vessels. This indicates the possibility of applying spontaneous oscillations to assessing atherosclerosis in high risk subjects for CI based on the wavelet transform of NIRS signals.

Age-related changes in spontaneous oscillations assessed by wavelet transform of cerebral oxygenation and arterial blood pressure signals

The study aims to assess the spontaneous oscillations in elderly subjects based on the wavelet transform of cerebral oxygenation (CO) and arterial blood pressure (ABP) signals. Continuous recordings of near-infrared spectroscopy (NIRS) and ABP signals were obtained from simultaneous measurements in 20 young subjects (age: 27.3 ± 7.1 years) and 15 elderly subjects (age: 70.8 ± 5.1 years) at rest. Using spectral analysis based on wavelet transform, five frequency intervals were identified (I, 0.005 to 0.02 Hz; II, 0.02 to 0.06 Hz; III, 0.06 to 0.15 Hz; IV, 0.15 to 0.40 Hz; and V, 0.40 to 2.0 Hz). The average amplitudes of the Δ[HbO2] and tissue oxygenation index in intervals I to V and the relative amplitudes in intervals IV and V were significantly lower in elderly subjects than in young subjects (P < 0.05). In addition, the relative amplitudes of the ABP in interval I were significantly lower in elderly subjects than in young subjects (P = 0.016). The present findings suggest the presence of a cerebrovascular degenerative process caused by aging. Spontaneous oscillations in the CO could be used as an indicator of cerebrovascular changes and could be used to identify the risk for cerebrovascular degenerative processes.

Effects of prolonged surface pressure on the skin blood flowmotions in anaesthetized rats--an assessment by spectral analysis of laser Doppler flowmetry signals.

The objective of this study is to assess the effect of prolonged surface compression on the skin blood flowmotion in rats using spectral analysis based on wavelets transform of the periodic oscillations of the cutaneous laser Doppler flowmetry (LDF) signal. An external pressure of 13.3 kPa (100 mmHg) was applied to the trochanter area and the distal lateral tibia of Sprague-Dawley rats via two specifically designed pneumatic indentors. The loading duration was 6 hours/day for 4 consecutive days. Five frequency intervals were identified (0.01-0.04 Hz, 0.04-0.15 Hz, 0.15-0.4 Hz, 0.4-2 Hz and 2-5 Hz) corresponding to endothelial related metabolic, neurogenic, myogenic, respiratory and cardiac origins. The absolute amplitude of oscillations of each particular frequency interval and the normalized amplitude were calculated for quantitative assessments. The results showed that (1) tissue compression following the above schedule induced significant decrease in the normalized amplitude in the frequency interval of 0.01-0.04 Hz both in the trochanter area (p < 0.001) and tibialis area (p = 0.023), (2) prolonged compression induced significant increase in the absolute amplitude (p = 0.004 for the trochanter area and p = 0.017 for the tibialis area) but significant decrease in the normalized amplitude (p = 0.023 for the trochanter area and p = 0.026 for the tibialis area) in the frequency interval of 0.15-0.4 Hz, and (3) at the tibialis area, the flowmotion amplitude (frequency interval 0.15-0.4 Hz) measured prior to the daily tissue compression schedule was found to be significantly higher on day 4 than the measurements obtained on day 1. However, this finding was not observed at the trochanter area. Our results suggested that prolonged compression might induce endothelial damage and affect the endothelial related metabolic activities.

Spectral analysis of near-infrared spectroscopy signals measured from prefrontal lobe in subjects at risk for stroke.

PURPOSE The objective of this study was to assess the spontaneous cerebral oscillations based on the wavelet transform of near-infrared spectroscopy (NIRS) signals in subjects at risk for atherosclerotic stroke. METHODS A total of 32 subjects were recruited from the university to participate in this study: 20 were normal subjects (age = 59.6 ± 10.2 year) and the other 12 were subjects at risk for ischemic stroke (age = 60.2 ± 10.1 year).The cerebral oxygenation signal was monitored for 10 min from the left prefrontal lobe using NIRS. RESULTS With spectral analysis based on wavelet transform, five frequency intervals were identified (I, 0.005-0.02 Hz; II, 0.02-0.06 Hz; III, 0.06-0.15 Hz; IV, 0.15-0.40 Hz; and V, 0.40-2.0 Hz). The amplitude of the [Hb] in the frequency intervals from I to V and of the [HbO(2)] in frequency intervals I and V in subjects at risk for stroke were found to be significantly lower compared to the amplitudes in normal subjects. CONCLUSIONS The reduction of spontaneous oscillations in these subjects suggests an increased stiffness in the cerebral artery. This indicates the possibility of applying spontaneous oscillations, based on the wavelet transform of NIRS signals, to assess the risk in subjects with atherosclerosis.

Effects of Ankle Arthrodesis on Biomechanical Performance of the Entire Foot.

Background/Methodology Ankle arthrodesis is one popular surgical treatment for ankle arthritis, chronic instability, and degenerative deformity. However, complications such as foot pain, joint arthritis, and bone fracture may cause patients to suffer other problems. Understanding the internal biomechanics of the foot is critical for assessing the effectiveness of ankle arthrodesis and provides a baseline for the surgical plan. This study aimed to understand the biomechanical effects of ankle arthrodesis on the entire foot and ankle using finite element analyses. A three-dimensional finite element model of the foot and ankle, involving 28 bones, 103 ligaments, the plantar fascia, major muscle groups, and encapsulated soft tissue, was developed and validated. The biomechanical performances of a normal foot and a foot with ankle arthrodesis were compared at three gait instants, first-peak, mid-stance, and second-peak. Principal Findings/Conclusions Changes in plantar pressure distribution, joint contact pressure and forces, von Mises stress on bone and foot deformation were predicted. Compared with those in the normal foot, the peak plantar pressure was increased and the center of pressure moved anteriorly in the foot with ankle arthrodesis. The talonavicular joint and joints of the first to third rays in the hind- and mid-foot bore the majority of the loading and sustained substantially increased loading after ankle arthrodesis. An average contact pressure of 2.14 MPa was predicted at the talonavicular joint after surgery and the maximum variation was shown to be 80% in joints of the first ray. The contact force and pressure of the subtalar joint decreased after surgery, indicating that arthritis at this joint was not necessarily a consequence of ankle arthrodesis but rather a progression of pre-existing degenerative changes. Von Mises stress in the second and third metatarsal bones at the second-peak instant increased to 52 MPa and 34 MPa, respectively, after surgery. These variations can provide indications for outcome assessment of ankle arthrodesis surgery.

Posture-related changes in brain functional connectivity as assessed by wavelet phase coherence of NIRS signals in elderly subjects.

Postural instability and falls are commonly seen because of aging and motor disabilities. This study aims to assess the posture-related changes in brain functional connectivity by wavelet phase coherence (WPCO) of oxyhemoglobin concentration change (Δ[HbO2]) signals measured through near-infrared spectroscopy (NIRS) in elderly subjects. The NIRS signals were continuously recorded from the prefrontal cortex and sensorimotor cortical areas in 39 healthy elderly subjects and 22 young healthy subjects during 20min resting and 10min standing states. Eight connection types were obtained from the recorded brain areas. The WPCO were calculated in five frequency intervals in each channel pair as follows: I, 0.6-2Hz; II, 0.145-0.6Hz; III, 0.052-0.145Hz; IV, 0.021-0.052Hz; and V, 0.0095-0.021Hz. Results show that posture change and age significantly interacts with the right prefrontal cortex (PFC) and left sensorimotor cortex (SMC) connectivity in interval V (F=5.010, p=0.028). The left and right PFC connectivity in interval I, the left and right SMC connectivity in interval IV, and the connectivity in interval V, including right PFC and right SMC connectivity, left PFC and left SMC connectivity, and right PFC and left SMC connectivity, showed a significant difference between the Group Elderly and Group Young in response to posture change (p<0.05). This study provides new insight into the mechanism of posture control, and results may be useful in assessing the risk of postural instability in aged persons.

Wavelet coherence analysis of spontaneous oscillations in cerebral tissue oxyhemoglobin concentrations and arterial blood pressure in elderly subjects

This study aims to assess the relationship between spontaneous oscillations in changes in cerebral tissue oxyhemoglobin concentrations (Delta [HbO2]) and arterial blood pressure (ABP) signals in healthy elderly subjects during the resting state using wavelet coherence analysis. Continuous recordings of near-infrared spectroscopy (NIRS) and ABP signals were obtained from simultaneous measurements in 33 healthy elderly subjects (age: 70.7±7.9 years) and 27 young subjects (age: 25.2±3.7 years) during the resting state. The coherence between Delta [HbO2] and ABP oscillations in six frequency intervals (I, 0.4-2 Hz; II, 0.15-0.4 Hz; III, 0.05-0.15 Hz; IV, 0.02-0.05 Hz, V, 0.005-0.0095 Hz and VI, 0.005-0.0095 Hz) was analyzed using wavelet coherence analysis. In elderly subjects, the Delta [HbO2] and ABP oscillations were significantly wavelet coherent in interval I, and wavelet phase coherent in intervals I, II and IV. The wavelet coherence in interval I was significantly higher (p=0.040), in elderly subjects than in young subjects whereas that in interval V significantly lower (p=0.015). In addition, the wavelet phase coherence in interval IV was significantly higher in elderly subjects than in young subjects (p=0.028). The difference in the wavelet coherence of the elderly subjects and the young subjects indicates an altered cerebral autoregulation caused by aging. This study provides new insight into the dynamics of Delta [HbO2] and ABP oscillations and may be useful in identifying the risk for dynamic cerebral autoregulation processes.

Wavelet analysis of sacral tissue oxygenation oscillations by near-infrared spectroscopy in persons with spinal cord injury

The objective of this study is to assess the blood oxygenation oscillations in the tissue over the sacrum, a high risk area for pressure ulcer, using spectral analysis of near-infrared spectroscopy (NIRS) signals based on wavelet transform. A total of twenty subjects were recruited for this study, of which ten were persons with spinal cord injury (SCI) (3 women, 7 men, age=34.5±5.2years) and the other ten were healthy subjects (3 women, 7 men, age=36.5±6.2years). Waterlow Scale was used for the pressure ulcer risk assessment. External pressure of 26.6kPa (200mm Hg) was applied to the sacrum via a specifically designed indentor. The loading duration was 3min. The subjects were examined lying face-down. Tissue oxygenation signal was monitored for 20min prior to and after the loading period from the tissue over the sacrum area using NIRS. With spectral analysis based on wavelet transform, five frequency intervals were identified (I, 0.005-0.02Hz, II, 0.02-0.06Hz, III, 0.06-0.15Hz, IV, 0.15-0.40Hz and V, 0.40-2.0Hz) corresponding to endothelial related metabolic, neurogenic, myogenic, respiratory and cardiac activities, respectively. The results showed that the amplitude of the [HbO(2)] and [Hb] component in intervals I, II and III for persons with SCI was significantly lower during the resting conditions than that for normal subjects (p<0.05). During the post-loading period, the response of [HbO(2)] and [Hb] oscillatory activities in intervals II and III were significantly lower in the tissue over the sacrum for persons with SCI than that for normal subjects (p<0.05). Also significant negative correlation was found between oscillatory activities and Waterlow scale in persons with SCI. The results indicated that the low oscillatory activities might be related to early tissue injury in persons with SCI.

Biomechanical study of tarsometatarsal joint fusion using finite element analysis

Complications of surgeries in foot and ankle bring patients with severe sufferings. Sufficient understanding of the internal biomechanical information such as stress distribution, contact pressure, and deformation is critical to estimate the effectiveness of surgical treatments and avoid complications. Foot and ankle is an intricate and synergetic system, and localized intervention may alter the functions to the adjacent components. The aim of this study was to estimate biomechanical effects of the TMT joint fusion using comprehensive finite element (FE) analysis. A foot and ankle model consists of 28 bones, 72 ligaments, and plantar fascia with soft tissues embracing all the segments. Kinematic information and ground reaction force during gait were obtained from motion analysis. Three gait instants namely the first peak, second peak and mid-stance were simulated in a normal foot and a foot with TMT joint fusion. It was found that contact pressure on plantar foot increased by 0.42%, 19% and 37%, respectively after TMT fusion compared with normal foot walking. Navico-cuneiform and fifth meta-cuboid joints sustained 27% and 40% increase in contact pressure at second peak, implying potential risk of joint problems such as arthritis. Von Mises stress in the second metatarsal bone increased by 22% at midstance, making it susceptible to stress fracture. This study provides biomechanical information for understanding the possible consequences of TMT joint fusion.

Wavelet coherence analysis of prefrontal tissue oxyhaemoglobin signals as measured using near-infrared spectroscopy in elderly subjects with cerebral infarction

This study aims to assess the prefrontal functional connectivity using wavelet coherence analysis of cerebral tissue oxyhaemoglobin concentration (Delta [HbO2]) signals in elderly subjects with cerebral infarction (CI) during the resting state. Continuous recordings of near-infrared spectroscopy (NIRS) signals were obtained from the left and right prefrontal lobes in 10 subjects with CI (age: 74.4±9.0years) and 18 healthy elderly subjects (age: 69.9±7.3years) during the resting state. The coherence between left and right prefrontal Delta [HbO2] oscillations in four frequency intervals (I, 0.6-2Hz; II, 0.145-0.6Hz; III, 0.052-0.145Hz and IV, 0.021-0.052Hz) was analyzed using wavelet coherence analysis. In healthy elderly subjects, the Delta [HbO2] oscillations were significantly wavelet coherent in intervals I and III (p<0.05), wavelet phase coherent in intervals from I to IV. In elderly subjects with CI, the left and right Delta [HbO2] oscillations were significantly wavelet coherent and phase coherent in interval I (p<0.05). In elderly subjects with CI, the power and phase coherences were significantly lower in interval III (p<0.01) than in healthy subjects. The difference in wavelet coherence between the healthy elderly and elderly with CI indicates an altered brain functional connectivity in CI patients. This may be useful for assessing the effectiveness of functional recovery following a CI.