Y Gao

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 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.

Cerebral autoregulation in response to posture change in elderly subjects-assessment by wavelet phase coherence analysis of cerebral tissue oxyhemoglobin concentrations and arterial blood pressure signals

This study aims to assess the dynamic cerebral autoregulation (dCA) in response to posture change using wavelet phase coherence (WPCO) of cerebral tissue oxyhemoglobin concentrations (Delta [HbO2]) and arterial blood pressure (ABP) signals in healthy elderly subjects. Continuous recordings of near-infrared spectroscopy (NIRS) and ABP signals were obtained from simultaneous measurements in 16 healthy elderly subjects (age: 68.9±7.1 years) and 19 young subjects (age: 24.9±3.2 years). The phase coherence between Delta [HbO2] and ABP oscillations in six frequency intervals (I, 0.6-2 Hz; II, 0.15-0.6 Hz; III, 0.05-0.15 Hz; IV, 0.02-0.05 Hz, V, 0.0095-0.02 Hz and VI, 0.005-0.0095 Hz) was analyzed using WPCO. The sit-to-stand posture change induces significantly lower WPCO in interval III (F=5.50 p=0.025) in the elderly subjects than in the young subjects. However, the stand-to-sit posture change induces higher WPCO in intervals II (F=5.25 p=0.028) and V (F=6.22 p=0.018) in the elderly subjects than in the young subjects. The difference of WPCO in response to posture change between the elderly and the young subjects indicates an altered CA due to aging. This study provides new insight into the dynamics of CA and may be useful in identifying the risk for dCA processes.

Phase synchronization analysis of prefrontal tissue oxyhemoglobin oscillations in elderly subjects with cerebral infarction

PURPOSE This study aims to assess the phase relationship of prefrontal tissue oxyhemoglobin oscillations using wavelet phase coherence analysis of cerebral Delta [HbO₂] signals in cerebral infarction (CI) patients during the resting state. METHODS Continuous recordings of near-infrared spectroscopy signals were obtained from the left and right prefrontal lobes in 21 subjects with CI (Group CI, age: 76.6 ± 8.5 yr) and 21 healthy elderly subjects (Group Healthy, age: 69.0 ± 7.4 yr) during the resting state. The Group CI was further divide into two groups: CI with hypertension and CI without hypertension. The phase synchronization between left and right prefrontal Delta [HbO₂] oscillations in four frequency intervals (I, 0.6-2 Hz; II, 0.145-0.6 Hz; III, 0.052-0.145 Hz; and IV, 0.021-0.052 Hz) was analyzed using wavelet phase coherence method. RESULTS The phase coherences in intervals III and IV were significantly lower in CI with hypertension than in healthy elderly subjects (F = 12.974, p = 0.001 for III and F = 10.073, p = 0.004 for interval IV). The phase coherence of CI without hypertension in interval III was significantly lower than in healthy elderly subjects (F = 9.909, p = 0.004). Also, the phase coherence in interval IV was significantly lower in CI with hypertension than in CI without hypertension (F = 5.665, p = 0.028). Also, the phase agreement in interval IV showed evident difference between Group CI with hypertension and without hypertension. CONCLUSIONS The difference in phase characteristics of prefrontal tissue oxyhemoglobin oscillations between the CI patients and healthy elderly indicates altered phase synchronization. Moreover, the CI combined with hypertension would aggravate this process. This study provides new insight into the phase dynamics of cerebral oxygenation and may be useful in assessing the risk for stroke.

Assessing the prefrontal functional connectivity using wavelet coherence analysis of oxygenation signals

This study aims to assess the prefrontal functional connectivity using wavelet coherence analysis of cerebral tissue oxyhaemoglobin concentrations (Delta [HbO2]) signals in subjects with cerebral infarction(CI) during the resting state. Continuous recordings of near-infrared spectroscopy (NIRS) signals were gained from the right and left prefrontal lobe in 15 elderly subjects with CI (age: 75.1 ± 9.2 years) and 18 healthy elderly subjects (age: 69.9 ± 7.3 years) during the resting state. The coherence between right and left prefrontal lobe Delta [HbO2] oscillations in 4 frequency intervals (I, 0.6-2 Hz; II, 0.145-0.6 Hz; III, 0.0520.145 Hz; IV, 0.021-0.052 Hz) was analyzed by the wavelet coherence analysis. In healthy subjects, the Delta [HbO2] were significantly wavelet coherent in interval I (0.6-2 Hz) and III (0.052-0.145 Hz) (p<;0.05). In elderly subjects with CI, the left and right Delta [HbO2] were significantly wavelet coherent in interval I (0.6-2 Hz) (p<;0.05). The wavelet coherence was significantly lower in interval II (F=6.658, p=0.014), III (F=18.164, p=0.000) and IV (F=4.295, p=0.046). The difference using the wavelet coherence of the CI subjects and the healthy subjects demonstrates an vary cerebral autoregulation caused by CI. This research gives a original insight into the dynamics of Delta [HbO2] oscillations. This method may be beneficial in detecting the risk for alter cerebral autoregulation. This might indicate a damaged brain functional connectivity due to CI in the subjects.

Response of cerebral tissue oxygenation and arterial blood pressure to postural change assessed by wavelet phase coherence analysis

The article is aimed at studying the relationship between arterial blood pressure (ABP) and cerebral oxygen hemoglobin signals to the change of the posture in healthy elderly subjects using wavelet phase coherence (WPCO) analysis. ABP and HbO2 (NIRS) signals of 35 subjects (young group: 19, Age: 24.9; elderly group: 16, Age: 68.9) were acquired from experimental apparatus with continuous recordings. We assess the phase coherence between ABP and Delta [HbO2] using WPCO in six frequency bands. The WPCO of elderly group was significantly lower in band III (F=5.50 p=0.025) during standing posture than young group. However, during post standing posture the WPCO of elderly group was significantly higher in intervals II (F=5.25 p=0.028) and V (F=6.22 p=0.018) than young group. Different wavelet phase coherence of young group and elderly group suggests the change of cerebral autoregulation (CA) because of the effect of age. The article introduces a new way to assess the relationship between ABP and cerebral oxygen hemoglobin. It might be beneficial to identify the danger of CA.