Regional cerebral oxygen saturation in the healthy population of western Sichuan: a multicenter cross-sectional study
- Open Access
- 25.11.2024
- Original Research
Erschienen in:
Abstract
1 Background
Regional cerebral oxygen saturation (rSO2) is a measure of the amount of oxygen in the brain [1]. It is typically monitored in critical care settings such as during surgery or the intensive care unit (ICU) to ensure adequate oxygen supply to the brain [2]. A fluctuation in rSO2 levels serves as an indicator of potential brain injury [3]. It is also used to determine impaired cerebral oxygenation such as in the case of shock, stroke, cardiac arrest, mechanical ventilation, traumatic brain injury, or extracorporeal membrane oxygenation [1, 2, 4].
The rSO2 is typically monitored through near-infrared spectroscopy (NIRS), a non-invasive brain imaging technology that accurately and continuously measures changes in human tissue microcirculation and hemodynamics [5]. The sensor is placed on the forehead to estimate cerebral blood flow (CBF) and tissue oxygen intake (TOI). This technique measures the absorbed red and infrared wavelengths by the brain tissue shed by the shining light on the scalp [4]. Because it is fast, continuous, real-time, and convenient, NIRS is widely used in clinical settings to monitor rSO2 [6‐8]. At present, NIRS enables the continuous non-invasive monitoring of vital signs such as TOI, pulse oximetry saturation (SpO2), pulse rate, and body temperature in adults, children, and neonates during surgical anesthesia and critical care periods, it is also useful and safe for pregnant women, infants, and young children [9‐11]. Several studies have identified the clinical significance of rSO2 monitoring in predicting postoperative cognitive impairment and outcome. For example, the duration of rSO2 values below 60%, 55%, and 50%, and the decrease in the rSO2 base value area can significantly predict postoperative cognitive impairment [12, 13].
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Variations in the rSO2 values may be associated with factors such as individual differences, specificity of equipment algorithms, extracranial tissue, head circumference, body mass index (BMI), and skin pigmentation [4, 14, 15]. However, available studies primarily focused on the association between rSO2 and diseases, with limited data on rSO2 in a healthy population with different characteristics.
Western Sichuan is located in the western part of Sichuan Province, China, adjacent to the western Sichuan Basin and the eastern edge of the Qinghai-Tibet Plateau. Western Sichuan is featured by its complex and changeable terrain and is famous for its tourism and ethnic resources. The life and production processes of the ethnic minorities integrate the local and regional style, lifestyle, religious ceremonies, and ethnic culture characteristics, bearing the historical and cultural heritage of the western Sichuan ethnic minorities, making the ethnic culture of the western Sichuan distinctive.
Therefore, according to its distinctive features, the population in western Sichuan was selected as the research object, and this study aimed to explore the rSO2 values in a healthy population of western Sichuan and their variation across individual characteristics.
2 Methods
2.1 Study design and participants
This cross-sectional study enrolled healthy volunteers from the Health Management Center and Inpatient Department of Ya’an People’s Hospital, Ya’an Vocational and Technical College, Ya’an Geriatric University, and Liziping Yi Township in Shimian County, Ya’an City, Sichuan Province between January 2020 and December 2022. The inclusion criteria were (1) age ≥ 4 years, to study the baseline values of rSO2 in different age groups, (2) normal results of routine physical examination within the past year, and (3) voluntary participation in the study. To investigate whether comorbidities, such as hypertension, diabetes, and dyslipidemia, affect the rSO2 values, individuals with these chronic conditions were included in the study. These participants were selected based on having a documented diagnosis of these chronic conditions or currently taking relevant medications. The exclusion criteria were (1) severe cognitive impairment, (2) history of stroke, coronary artery disease, renal disease, epilepsy, or other ischemic and hypoxic diseases, or (3) malignancy. This study was approved by the Ethics Committee of Ya’an People’s Hospital, Ya’an, China. The participants provided written informed consent.
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2.2 Data collection
A uniform questionnaire was administered to obtain basic information about the participants. The questionnaire covered details such as age, sex, education, ethnicity, marital status, place of residence, and medical history (including previously diagnosed conditions such as hypertension, diabetes, respiratory tumors, and anemia). In addition, the height, weight, and vital signs of the subjects were measured by an independent physician. An independent investigator monitored the rSO2 levels using a cerebral oxygen saturation monitor.
2.3 Non-invasive cerebral oxygen saturation monitoring
The rSO2 values were obtained using a portable 5G non-invasive cerebral oxygen saturation monitor (Chengdu Yunwei Kang Medical Technology Co., Ltd., Chengdu, China). For analysis, the volunteer sat resting for 2 min before the two probes of the monitor were placed on their left and right foreheads and tightly secured with a bandage to ensure an adequate fit. The subject remained calm during the 6-minute data collection, and the median measurement was selected as the oxygen saturation value.
2.4 Statistical analysis
The statistical analysis was conducted using SPSS 24.0 (IBM, Armonk, NY, USA). Continuous data with a normal distribution were described as means ± standard deviations and analyzed using Student’s t-test. Skewed distributed data were presented as medians with interquartile range (IQR) and analyzed using Wilcoxon’s rank-sum test. Categorical data were described as n (%) and analyzed using the chi-square or Fisher’s exact tests. Correlation analysis was conducted using Spearman’s rank correlation. Statistical significance was set at P < 0.05 for both two-sided tests.
3 Results
A total of 661 volunteers were recruited, including 276 male, 385 female, 252 Han, 114 Tibetan, 295 Yi, 285 children (5–13 years old), 175 young (14–35 years old), 103 middle-aged adults (35–60 years old), and 97 older adults (older than 60 years old). In addition, 47 had hypertension, 19 had dyslipidemia, and 22 had diabetes (Table 1).
Table 1
Baseline demographics and clinical characteristics of participants (n = 661)
Variable | Value | |
|---|---|---|
Sex | ||
Male | 276 (41.75%) | |
Female | 385 (58.25%) | |
Ethnicity | ||
Han | 252 (38.12%) | |
Tibetan | 114 (17.25%) | |
Yi | 295 (44.63%) | |
Age (years) | 28.3 ± 23.1 | |
5–13 | 9.89 ± 1.89 | |
14–35 | 20.19 ± 3.77 | |
36–59 | 51.99 ± 6.20 | |
≥ 60 | 69.74 ± 6.28 | |
BMI, kg/m2 | ||
18.5–23.9 | 632 (95.60%) | |
< 18.5 | 22 (3.30%) | |
24.0-27.9 | 5 (0.80%) | |
≥ 28.0 | 2 (0.30%) | |
Height | 162.4 ± 7.71 | |
Weight | 60.22 ± 12.11 | |
Head circumference | 54.52 ± 2.95 | |
SBP, mmHg | 124.59 ± 17.89 | |
DBP, mmHg | 74.34 ± 12.01 | |
Past illness | ||
Hypertension | 47 (7.11%) | |
Diabetes | 22 (3.33%) | |
Dyslipidemia | 19 (2.87%) | |
Smoking history | 26 (3.93%) | |
Drinking history | 22 (3.33%) | |
The average baseline values of rSO2 on the left and right sides of the brain were 63.65 ± 3.25 and 63.28 ± 3.08, respectively. The rSO2 values of the left brain were significantly higher in females (63.46 ± 3.01 vs. 63.17 ± 2.90, P = 0.015), males (63.91 ± 3.54 vs. 63.42 ± 3.32, P = 0.002), Han ethnicity (65.10 ± 3.67 vs. 64.38 ± 3.43, P < 0.001), and volunteers aged 14–59 years (14–35: 65.92 ± 3.37 vs. 65.26 ± 2.93, P < 0.001; 36–59: 62.99 ± 3.62 vs. 62.19 ± 3.47, P = 0.001) compared with the right brain (Table 2).
Table 2
The rSO2 values of left and right brains in participants
Volunteers | rSO2 | P-value | ||
|---|---|---|---|---|
Left | Right | |||
Total | 63.65 ± 3.25 | 63.28 ± 3.08 | < 0.001** | |
Sex | ||||
Female | 63.46 ± 3.01 | 63.17 ± 2.90 | 0.015* | |
Male | 63.91 ± 3.54 | 63.42 ± 3.32 | 0.002** | |
Ethnicity | ||||
Han | 65.10 ± 3.67 | 64.38 ± 3.43 | < 0.001** | |
Yi | 63.00 ± 2.49 | 62.87 ± 2.42 | 0.258 | |
Tibetan | 63.96 ± 3.72 | 64.34 ± 3.14 | 0.609 | |
Age | ||||
5–13 | 62.85 ± 2.41 | 62.78 ± 2.39 | 0.544 | |
14–35 | 65.92 ± 3.37 | 65.26 ± 2.93 | < 0.001** | |
36–59 | 62.99 ± 3.62 | 62.19 ± 3.47 | 0.001** | |
≥ 60 | 62.87 ± 3.11 | 62.70 ± 3.32 | 0.613 | |
BMI | ||||
18.5–23.9 | 63.39 ± 5.14 | 63.29 ± 3.12 | 0.567 | |
< 18.5 | 63.07 ± 2.27 | 62.45 ± 1.92 | 0.101 | |
24.0-27.9 | 63.92 ± 2.89 | 65.02 ± 3.46 | 0.178 | |
≥ 28.0 | 61.45 ± 3.61 | 62.45 ± 0.50 | 0.728 | |
Past illness | ||||
Yes | 62.57 ± 3.37 | 62.26 ± 3.38 | 0.358 | |
No | 63.48 ± 5.22 | 63.39 ± 3.03 | 0.662 | |
Smoking history | ||||
Yes | 63.04 ± 3.39 | 63.01 ± 3.17 | 0.959 | |
No | 63.39 ± 5.11 | 63.28 ± 3.09 | 0.534 | |
Drinking history | ||||
Yes | 63.76 ± 2.75 | 62.86 ± 3.64 | 0.200 | |
No | 63.37 ± 5.12 | 63.28 ± 3.07 | 0.649 | |
Furthermore, the rSO2 values in the Han ethnicity were significantly higher than in the Yi ethnicity (64.65 ± 3.29 vs. 62.68 ± 3.66, P < 0.001). Volunteers with past illness showed significantly lower rSO2 values than those without past illness (62.41 ± 3.06 vs. 62.68 ± 3.66, P = 0.021). There were significant differences in rSO2 values between different ages and BMI (both P < 0.001) (Table 3).
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Table 3
Differences in rSO2 values among different participants (n = 661)
Variable | Participants, n (%) | rSO2 | P-value | |
|---|---|---|---|---|
Sex | 0.437 | |||
Male | 276 (41.75%) | 63.46 ± 4.08 | ||
Female | 385 (58.25%) | 63.23 ± 3.10 | ||
Ethnicity | < 0.001 | |||
Han | 252 (38.12%) | 64.65 ± 3.29# | ||
Tibetan | 114 (17.25%) | 62.08 ± 2.80$ | ||
Yi | 295 (44.63%) | 62.68 ± 3.66* | ||
Age | < 0.001 | |||
5–13 | 285 (43.20%) | 62.53 ± 3.65^ | ||
14–35 | 175 (26.50%) | 65.45 ± 2.93& | ||
36–59 | 103 (15.60%) | 62.55 ± 3.34 | ||
≥ 60 | 97 (14.70%) | 62.66 ± 2.85*** | ||
BMI | < 0.001 | |||
18.5–23.9 | 261 (39.5%) | 64.13 ± 3.34** | ||
< 18.5 | 284 (43.0%) | 62.63 ± 3.78 | ||
24.0-27.9 | 37 (5.6%) | 63.21 ± 3.19 | ||
≥ 28.0 | 78 (11.8%) | 63.22 ± 2.91 | ||
Past illness | 0.021 | |||
Yes | 72 (10.90%) | 62.41 ± 3.06 | ||
No | 589 (89.10) | 63.44 ± 3.58 | ||
Smoking history | 0.659 | |||
Yes | 26 (3.93%) | 63.02 ± 2.91 | ||
No | 635 (96.07%) | 63.34 ± 3.57 | ||
Drinking history | 0.982 | |||
Yes | 22 (3.33%) | 63.31 ± 2.81 | ||
No | 639 (96.67%) | 63.32 ± 3.57 | ||
Specifically, Pearson correlation analysis revealed a significant negative correlation between rSO2 and age, ethnicity, past illness, and BMI and a significant positive correlation with head circumference and height (all P < 0.05) (Table 4).
Table 4
Pearson correlation
Variables | rSO2 |
|---|---|
Age | -0.128 |
Sex | -0.032 |
Ethnicity | -0.247 |
Height (cm) | 0.306 |
Weight (kg) | -0.014 |
BMI | -0.166 |
Head circumference (cm) | 0.267 |
SBP | 0.071 |
DBP | 0.101 |
Past illness | -0.090 |
Drinking history | -0.001 |
Smoking history | -0.017 |
4 Discussion
The present study found that rSO2 values in the left brain were significantly higher than those in the right brain among the healthy population of western Sichuan. This difference persisted across various demographic and clinical characteristics, including sex, ethnicity, age, BMI, and past illness history. The findings provide valuable reference ranges for rSO2 in individuals with diverse characteristics, which could be considered normal for the healthy population in this region. Moreover, the significant associations of rSO2 with factors such as age, BMI, and ethnicity emphasize the need for personalized approaches when interpreting cerebral oxygenation levels, as these interindividual variations could impact the clinical assessment of brain health and the management of conditions affecting cerebral oxygenation. The study underscores the importance of accounting for demographic and health-related factors when establishing reference values for rSO2, potentially aiding in the early detection and monitoring of neurological or cerebrovascular conditions.
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Research has shown that using oxygen monitoring to identify and correct hypoxic brain events improves patient outcomes [16]. Non-invasive technologies like NIRS are increasingly used to monitor brain oxygen saturation [17], and rSO2 enables clinicians to detect the early stages of oxygen delivery and consumption imbalance. Clinicians should take more active treatment measures to prevent the prolonged reduction of rSO2 and to prevent nervous system disease and other major complications [1]. Cerebral blood flow monitoring employs the modified Lambert-Beer and absorbance sum laws. To measure this, a dual light source dual sensor model distinguishes between oxygenated hemoglobin (HbO2) and reduced hemoglobin (Hb) based on their absorption characteristics of different wavelengths.
In the present study of 661 healthy subjects, it was found that the rSO2 of the left hemisphere was significantly higher than that of the right hemisphere, with a value of 63.65 ± 3.25 in the left hemisphere and 63.28 ± 3.08 in the right hemisphere. This difference is statistically significant. Differences in function and structure between the left and right hemispheres result in different oxygen requirements and use [18, 19]. These differences lead to a higher rSO2 value in the left hemisphere compared with the right hemisphere. This study also found that there were no significant differences in rSO2 between children of different sexes, which may be because the brain is not yet lateralized in children (9–10 years old), resulting in an equal consumption of oxygen between both sides. It is consistent with the findings of this study that women have higher rSO2 values than men, as observed in the study by Robu et al., where the median baseline rSO2 values for men and women were 65% and 58%, respectively (P < 0.05), indicating that sex is an important factor influencing rSO2 values in healthy adults [20], supporting the present study. Kishi et al. did not observe a sex difference, possibly due to differences in the technique used, or the population studied [21]. Whether these differences are due to hormonal or other factors remains to be evaluated in future studies.
This study revealed that young people displayed the highest rSO2 levels, whereas children, middle-aged people, and elderly individuals had similar levels. It likely reflects the decline in cerebral blood flow in middle-aged and elderly people compared with younger individuals [21]. It is also related to lower intracranial blood flow and lower blood vessel density in children than in young adults, resulting in relatively low rSO2 levels. This study found a significant negative correlation between age and rSO2, possibly due to underlying diseases and poor hypoxia tolerance in older adults. These results are consistent with the findings of Kishi et al. [22]. A study showed the baseline rSO2 values in healthy young volunteers aged from 20 to 36 years and adults older than 65 years, supporting the present study [23].
This study also analyzed the differences in rSO2 values among various factors, such as comorbidities, ethnicity, BMI, height, head circumference, and other related factors. Previous studies demonstrated that patients with hypertension and diabetes have lower baseline rSO2 levels and are more prone to cerebral hypoxia [16]. In this study, people with basic diseases like hypertension and diabetes had lower rSO2 levels compared with healthy individuals, which could explain why they could be more susceptible to cerebral ischemia events. Cerebral vascular structure and function change with comorbidities, making such patients more prone to cerebral ischemia and saturation decline. It was reported that rSO2 is reduced in patients with hypertension [24]. In addition, diabetes can cause intracranial arteriole stenosis, contraction, and diastolic function and reduce cerebrovascular autonomic regulation function [25]. Impaired cerebrovascular structure and disrupted stability of cerebral blood flow can result in insufficient microcirculatory perfusion, possibly manifesting as decreased rSO2 [26], supporting the present study.
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This present study enrolled primarily from the Han and Yi ethnicities, and the rSO2 levels differed significantly between them, with relatively higher levels in the Han ethnicity than in the Yi ethnicity. It could be related to skin color, as darker skin color in Yi ethnicity can affect NIRS monitoring [27], resulting in lower rSO2 levels. Melanin (the main skin pigment) is known to attenuate near-infrared (NIR) light transmission and may affect estimates of cerebral oxygen saturation, as reported in African Americans and patients with jaundice. Skin pigmentation is an independent predictor of rSO2 levels because it attenuates the NIR light transmission and changes the cerebral oxygen saturation estimates, which should be interpreted in combination with all available clinical information because NIR transmission can be affected by multiple factors; skin pigmentation is one of them. In addition to race or high serum bilirubin concentrations, other reasons for skin color change must be considered [27].
Western Sichuan, with its unique geographical and cultural characteristics, presents an ideal setting for studying rSO2. The region’s diverse terrain-encompassing plateaus, hills, and basins-can influence the physiological traits of the local population, potentially leading to significant variations in rSO2 levels, especially in high-altitude areas compared to lower altitudes. Additionally, the ethnic diversity in western Sichuan allows for an exploration of rSO2 variability across different populations, filling a notable gap in the literature regarding multi-ethnic communities. The distinctive cultural practices and lifestyles of various ethnic groups, including differences in diet and daily life, may also impact rSO2 values, making this research relevant beyond the local context. Logistical considerations further justify the choice of this region. The research team’s proximity facilitates efficient coordination of the multicenter study, enhancing the representativeness of the sample and improving the external validity of the findings.
However, there are some limitations to this study. First, the NIRS measurement is confined to the prefrontal cortex, and the rSO2 values measured by NIRS devices can vary due to different algorithms and small sample sizes across different manufacturers. Secondly, a cross-sectional study design makes it difficult to establish cause-to-effect relationships. Third, the study had a relatively small sample size and a limited geographical area, which may not represent the broader population. Fourth, using a portable, non-invasive rSO2 monitor may have limitations in accuracy and precision compared to more invasive measures. Finally, the study did not consider the potential confounding factors like medication use, lifestyle, and environmental exposure. Therefore, future research should increase the sample size, examine related factors, and compare the differences in rSO2 measurement levels between different algorithms and manufacturers.
5 Conclusion
In conclusion, our study reveals that healthy individuals in western Sichuan exhibit significantly higher rSO2 values in the left brain compared to the right. Moreover, we found that rSO2 values are closely associated with individual characteristics, including age, sex, BMI, past illnesses, and ethnicity. These findings underscore the importance of considering demographic and health-related factors when interpreting rSO2 measurements, which may enhance our understanding of brain health and inform clinical practices related to cerebral oxygenation monitoring.
Acknowledgements
None.
Declarations
Ethics approval and consent to participate
All procedures were performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. This study was approved by the Ethics Committee of Ya’an People’s Hospital (202201), Ya’an, China, and participants provided signed written informed consent forms. All methods were carried out in accordance with relevant guidelines and regulations.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
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