The purpose is to verify the enhancement of inhibitory control in hypoxic sedentary participants by a 30-day HBO intervention and the positive modulation of GFR.
4.1 Participant
Efficacy analysis was performed using G-power 3.1 software, and the data of 45 people in each group met the experimental requirements (power= 0.95, effect size = 0.5, α = 0.05). Therefore, the study selected 60 young Tibetan male participants aged 22-27, with 28 participants in the HBO intervention group (M=24.08 years, SD=1.47) and 32 participants in the control group (M=24.81 years, SD=1.48).
Other variables of interest as control conditions were measured in this study, including subjects' demographic variables (age), body mass index (BMI), sleep quality (PSQI) and physical and mental health index (SCL-90). A one-way ANOVA revealed that there were no significant differences (p > 0.05) in all the tested indicators, indicating that there were no differences between subjects in the experimental groups in the relevant demographic and physical and mental health status indicators.
4.2 Experimental materials
The Flanker task, SaO2 testing, as well as the materials related to GFR and other variables used as control conditions, are the same as those in Study 1.
4.3 Experimental instruments
The HBO intervention was conducted using the negative ion software hyperbaric oxygen chamber (model NBYY-HYDT-003, Ningbo Oxygen Health Technology Co., Ltd.). The chamber has an elliptical shape with a height of 2.13 meters, width of 2.55 meters, and a floor area of 7.88 square meters. The intervention pressure was set at 0.11 MPa, with an oxygen concentration of 25% and oxygen flow rate of 10 L/min. Once the pressure inside the chamber reached its maximum, the partial pressure of oxygen was 27.86 kPa.
4.4 Experimental procedure
Prior to and following HBO intervention, we conducted separate assessments of the performance of the Flanker task and the biochemical markers associated with kidney function. All participants underwent their initial venous blood draw and inhibitory control ability test one day before the formal experiment commenced. The experimental group underwent 5 weekly interventions, each lasting 90 minutes, which involved a 15-minute pressure increase, followed by a continuous oxygen supply at a constant pressure for 60 minutes, and a subsequent 15-minute decompression before exiting the chamber. A total of 10 oxygen interventions were completed within a one-month period. The control group, at the same designated time, entered a simulated HBO chamber without undergoing any pressurized oxygen supply. Twenty-four hours after the completion of the last intervention in the experimental group, a second assessment was conducted on all participants to evaluate their blood parameters and inhibitory control ability. Please refer to Figure 6 for details.
4.5 Statistical analysis
In this study, we conducted a comprehensive statistical analysis on the collected data using SPSS 23.0 software, with the aim of delving deeper into the relationships between blood oxygen saturation, glomerular filtration rate, and inhibitory control ability. The following are the specific analysis steps and methods we employed:
Firstly, we utilized the Pearson correlation analysis method to assess the linear relationship between blood oxygen saturation, glomerular filtration rate, and inhibitory control ability. By calculating correlation coefficients and their corresponding P-values, we were able to determine whether there were statistically significant associations among these variables. This analysis helped us gain an initial understanding of the strength and direction of the relationships between the variables.
Next, in order to further explore the impact of blood oxygen saturation on executive function and whether glomerular filtration rate played a moderating role, we employed the PROCESS model 1 developed by Hayes. This model allowed us to simultaneously assess relationships between variables while considering both mediation and moderation effects. Specifically, we used blood oxygen saturation as the independent variable, inhibitory control ability as the dependent variable, and glomerular filtration rate as the moderating variable.
We set the significance level at a P-value of 0.05 as the criterion for statistical significance. When the P-value was less than or equal to 0.05, we considered the results to be statistically significant. This approach helped us determine whether the analysis results of correlations and moderation effects held practical significance and statistical support.
4.6 Forward-side difference test
Because the demographic variables, sleep quality and physical and mental health index affect the level of inhibitory function, the following indicators were measured in this study: age, BMI, PSQI and SCL-90. Through one-way variance analysis, there was no significant difference in all the tested indicators (p> 0.05), indicating that the participants did not differ in any of the relevant demographic and physical and mental health indicators. There was no significant difference in mean SaO2 7 days before study entry (t= 0.38 p=0.71) between experimental group (M= 91.54 SD =4.32) and control group (M=91.84 SD=1.221); no significant difference in GFR (t=1.682 p=0.09) between experimental group (M=103.59 SD=12.87) and control group (M=107.73 SD =10.67); no significant difference in the correct rate on Flanker task (t=1.01 p=0.32) between experimental group (M=1 SD =0.01) and control group (M= 0.99 SD=0.01).The intervention group (M=0.98 SD=0.02), and the control group (M=0.97 SD=0.02) did not differ significantly in accuracy on the Flanker inconsistency task (t=1.38 p=0.171).The above results showed that the grouping before the HBO intervention was reasonable and the participants’ conditions were balanced.
4.7 Results
4.7.1 HBO intervention prevented the decline in inhibitory control ability caused by low temperature:
To examine the positive effects of HBO intervention on inhibitory control ability among high-altitude residents, a 2(Temperature: high, low) × 2(Group: control,treating) repeated-measures analysis of variance was conducted.
For the congruent condition, the results revealed a marginally significant main effect of temperature on the correct response rate [F(1,56) = 3.386, p = 0.071, ηp2 = 0.057], indicating a trend towards differences. There was a significant main effect of group [F(1,56)=4.319, p=0.042, ηp2= 0.072], suggesting significant differences between the groups. The interaction effect between temperature and group was marginally significant [F(1,56)=3.723, p=0.059, ηp2=0.062].Further analysis using simple effects revealed a significant difference in the correct response rate in the control group before and after the experiment [F(1,56)=7.925, p=0.007, ηp2=0.124]. The correct response rate at the beginning of the experiment was significantly higher than at the end of the experiment for the control group. Additionally, after 10 sessions of HBO intervention, a significant difference was observed between the control group and the treating group [F(1,56)=4.025, p=0.05, ηp2 = 0.067], with the high-pressure oxygen group showing a significantly higher correct response rate compared to the control group.
For the incongruent condition, the results showed a significant main effect of temperature on the correct response rate [F(1,56) = 4.075, p = 0.048, ηp2 = 0.068], indicating significant differences related to temperature. There was also a significant main effect of group [F(1,56) = 10.643, p = 0.002, ηp2 = 0.160], suggesting significant differences between the groups. The interaction effect between temperature and group was found to be significant [F(1,56) = 6.531, p = 0.013, ηp2 = 0.104].Further analysis using simple effects revealed a significant difference in the correct response rate in the control group before and after the oxygen intervention [F(1,56) = 11.669, p = 0.001, ηp2 = 0.172]. The control group exhibited a significantly higher correct response rate at the beginning of the experiment compared to the end of the experiment (see Figure 6). Additionally, after 10 sessions of oxygen intervention, a significant difference was observed between the control group and the high-pressure oxygen group [F(1,56) = 8.549, p = 0.005, ηp2 = 0.132], with the high-pressure oxygen group showing a significantly higher correct response rate compared to the control group. The above findings partially support Hypothesis 4, as HBO intervention prevented the decrease in inhibitory control ability caused by low temperature. Refer to Table 5 and Figure 7 for details.
Table 5 Flanker task accuracy (M ± SD)
|
Group
|
Control group (n=32)
|
Treating group (n=28)
|
congruent condition
|
Accuracy rate before intervention
|
0.99±0.01
|
1±0.01
|
Accuracy rate after intervention
|
0.91±0.22
|
1±0.01
|
incongruent condition
|
Accuracy rate before intervention
|
0.97±0.02
|
0.98±0.02
|
Accuracy rate after intervention
|
0.88±0.19
|
0.99±0.01
|
4.7.2 Moderation Analysis of GFR:
To examine the moderating effect of GFR on the relationship between high-pressure oxygen intervention and inhibitory control ability, a moderation analysis was conducted with group as the independent variable, GFR as the moderating variable, and inhibitory control ability as the dependent variable. Following the recommendations of Preacher and Hayes (2008), the SPSS Process plug-in (version 2.16) provided by Hayes (2013) was utilized (selecting Model 1). The analysis employed bias-corrected bootstrap with a sample size of 5,000 and conducted moderation analysis within a bias-corrected 95% confidence interval. The results revealed a significant moderation effect of GFR on the relationship between oxygen intervention intensity and executive function (β = -0.393, p = 0.001, ΔR2 = 0.151). The specific results are shown in Table 6.
To further examine the moderation effect, the interaction effect was plotted for different levels of GFR. Simple slope tests indicated that for participants with high GFR, HBO intervention had a positive effect (simple slope = 0.222, t = 2.620, p = 0.009); for individuals with low GFR, high-pressure oxygen intervention led to a significant improvement in executive function (simple slope = 1.372, t=15.810, p=0.001), reaching even higher levels than those with high GFR. (See Figure8). These results support the hypothesis that GFR has a positive moderating effect on the enhancement of inhibitory control ability through HBO intervention among high-altitude residents.
Table 6 Analysis of the moderating effect of GFR on the Relationship between HBO Intervention and Inhibitory Function
variable
|
Dependent variable: executive function
inhibitory control ability
|
β
|
S E
|
t
|
95%CI
|
SaO2
|
0.475
|
0.04
|
12.209***
|
[0.48,0.64]
|
G. F. R
|
0.359
|
0.04
|
8.781***
|
[-0.24,-0.07]
|
SaO2 *GFR
|
0.595
|
0.02
|
-10.451*
|
[0.01,0.08]
|
R2
|
|
|
0.446
|
|
F
|
|
|
64.527***
|
|