J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Bajracharya S, et al. Bajracharya S, et al. Effectiveness of Structured Teaching Program on Menstrual Hygiene among Adolescent School Girls. . Licensed under CC BY 4.0 International License which permits use, distribution and reproduction in any medium, provided the original work is properly cited. ___________________________________________________________________________________ Submitted: 13 January, 2020 Accepted: 06 May, 2020 Published: 22 May, 2020 a - Lecturer, Department of Physiology b - Lumbini Medical College Teaching Hospital, Palpa, Nepal. Corresponding Author: Shaligram Chaudhary e-mail: shaligram20@gmail.com ORCID: https://orcid.org/0000-0002-7242-1846 _______________________________________________________ —–———————————————————————————————————————————— ABSTRACT Introduction: The six-minute walk test is a simple test used to assess the exercise capacity. Variability is noted in the six-minute walk distance in different population. Obesity also affects the six-minute walk test results. The aims of the study were to examine the relationship between body mass index and post exercise oxygen saturation and to establish reference equation for the six-minute walk distance in young adults. Methods: A cross-sectional study was conducted with 106 subjects of age 18-25 years. The participant walked as fast as possible on a flat surface for six minutes. After six-minute walk test, oxygen saturation and the distance walked were recorded. Results: Body mass index was negatively correlated with oxygen saturation (r=-0.587,p<0.001). Mean six-minute walk distance for males was 584.43±23.71 m and for females 469.85±30.38 m (p<0.001). Multiple linear regression analysis revealed sex and height as independent predictors of six-minute walk distance. The contributions of sex and height were statistically significant and explained 87.3% variance in the six-minute walk distance. Conclusion: Although the correlation between body mass index and oxygen saturation was statistically significant, the oxygen saturation values were still within normal range. Sex and height were the most significant predictors of the six-minute walk distance. Keywords: Body mass index, Obesity, Oxygen saturation, Six minute walk distance, Six minute walk test Original Research Articlehttps://doi.org/10.22502/jlmc.v8i1.310 Shaligram Chaudhary,a,b Bibek Koju,a,b Lok Raj Joshia,b Six-Minute Walk Test in Healthy Nepalese Young Adults Aged 18 to 25 Years: A Cross- Sectional Study How to cite this article:How to cite this article: Chaudhary S, Koju B, Joshi LR. Six-Minute Walk Test in Healthy Nepalese Young Adults Aged 18 to 25 Years: A Cross- Sectional Study. Journal of Lumbini Medical College. 2020;8(1):6 pages DOI: Journal of Lumbini Medical College. 2020;8(1):6 pages DOI: https://doi.org/10.22502/jlmc.v8i1.310. Epub: 2020 May 22.https://doi.org/10.22502/jlmc.v8i1.310. Epub: 2020 May 22. INTRODUCTION: The six-minute walk test (6MWT) is a safe, easy to administer, and well tolerated submaximal test to evaluate exercise capacity that reflects activities of daily living better than other walk test. [1,2] The participant walks as fast as possible on a flat surface for six minutes, the distance walked is recorded as six-minute walk distance (6MWD).[2] Various factors including age, sex, height, weight, physical activity and body mass index (BMI) have been reported to affect 6MWD in healthy people. [3,4,5,6] Abnormally high BMI is now one of the major health problems worldwide.[7,8] It causes accumulation of fat in the chest and abdomen causing restriction of lung expansion.[9] It has been found to be associated with lower oxygen saturation (SpO2) after exercise and lower 6MWD.[10,11] Besides these factors, 6MWD is variable in healthy population due to population related differences.[12] American Thoracic Society (ATS) encourages the investigators to publish reference values of the 6MWD for several healthy ethnicities using 6MWT.[2] The 6MWD reference value obtained from healthy participants helps the clinicians to interpret the 6MWD in patients and their expected 6MWD in the absence of disease of that age group. Recent studies have established J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Chaudhary S, et al. Chaudhary S, et al. Six-Minute Walk Test in Healthy Nepalese Young Adults Aged 18 to 25 Years: A Cross- Sectional StudySix-Minute Walk Test in Healthy Nepalese Young Adults Aged 18 to 25 Years: A Cross- Sectional Study jlmc.edu.np regression equations to predict the 6MWD in healthy Nigerians,[3] Chinese population,[5] Western Indian Population,[4] Korean adults,[12] Brazilians,[13] and Arab populations.[14] However, regression equation has not been established in the Nepalese context. This study attempted to assess the relationship between BMI and oxygen saturation of hemoglobin after 6MWT. It also aimed to establish the regression equation for 6MWD in 18-25 years old healthy students of a medical college in Nepal. METHODS: This was a cross-sectional study conducted in the Department of Physiology, Lumbini Medical College (LMC), Pravas, Palpa. The study was carried out over a period of four months from August 2019 to November 2019. It included apparently healthy male and female students between age group of 18-25 years willing to participate voluntarily. Participants having physical disability affecting test procedure, basal heart rate < 50bpm or >100 bpm, basal systolic blood pressure >150 mmHg or diastolic blood pressure >100 mmHg, basal SpO2< 85% and respiratory symptoms for a month before the study were not included in the study. Ethical clearance was obtained from Institutional Review Committee of the institute (IRC-LMC 08-J/018) prior to data collection. The sample size was calculated using the formula N= [(Zα + Zβ) /C] 2 + 3 Where, N=total number of subjects required Zα and Zβ = the standard normal deviate for α and β C = 0.5* ln {(1 + r) / (1 - r)} r = expected correlation coefficient.[15] For this study, the expected correlation coefficient was r = 0.27 based on study by Kapur VK et al.[10] with α = 0.05 and the power of study 80%. According to the calculations, a total of 106 health science students were selected by convenient sampling method. Test procedure: One hundred six students who fulfilled inclusion criteria were recruited for the study after obtaining their verbal consent. Initial explanation about the aim and purpose of study, test procedure, method of testing, and instructions on how to perform the test was given. They were requested to complete the Physical Activity Readiness Questionnaire before test procedure.[16] The 6MWT was performed according to the standardized protocol of American Thoracic Society between 09:00 and 13:00 hours in order to reduce intra-day variability.[2] The participants were asked to come with comfortable cloth and light meals. At the starting point, basic medical history and clinical examination were taken for check on contraindications. BMI, resting heart rate, BP, Borg scores for dyspnea[17] and fatigue, and SpO2 (Dr. Morepen Pulse Oximeter P004) were recorded after rest for 10 minutes. For the 6MWT, the participants were asked to walk while attempting to cover as much distance as possible in six minutes. The test was performed on a flat surface corridor of 15- meter length marked with small cones at the starting and end points and at every three meter distance the corridor was marked, the time and laps were recorded on a worksheet. Participants were encouraged in every minute with standard statements “You are doing well”, “keep up the good work”. They were allowed to stop and rest during the test when tired, developed symptoms of dyspnea, dizziness, leg cramps or chest pain, but were instructed to resume walking as soon as they could. After completion of the test again heart rate, BP, SpO2 and Borg dyspnea score were recorded. Also, the distance covered over the six minutes was recorded as the 6MWD.[3] Data analysis: Data were reported as mean and standard deviation (SD). Independent t-test was used to compare means of continuous variables. The relationship between SpO2 after 6MWT and BMI was examined using Pearson’s correlation coefficient. Pearson’s correlation coefficients were also used to analyze relationships between 6MWD and participant’s characteristics. Stepwise regression analysis was performed on the following characteristics: age, height, weight, sex and BMI to determine their contribution to 6MWD. All data were analyzed using Statistical Package for Social Sciences (SPSSTM) software 16.0. p value less than 0.05 was considered as significant. RESULTS: Out of 106 participants, 53 were males and 53 were females. A summary of the physical characteristics of the participants is shown in Table 1. The mean height was higher in males (171.06±5.25 cm) than in females (157.26±5.89 cm). The mean values of SpO2 before and after 6MWT were 98.03 ± 0.47% and 95.82 ± 0.88% respectively [t(105) = 28.361, p<0.001].There was no statistically significant correlation between SpO2 before 6MWT and BMI (r=-0.108, p=0.27). SpO2 after 6MWT was J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Chaudhary S, et al. Chaudhary S, et al. Six-Minute Walk Test in Healthy Nepalese Young Adults Aged 18 to 25 Years: A Cross- Sectional StudySix-Minute Walk Test in Healthy Nepalese Young Adults Aged 18 to 25 Years: A Cross- Sectional Study jlmc.edu.np negatively correlated with BMI (r=-0.587, p<0.001) i.e. decrease in SpO2 is associated with increasing BMI. However, the SpO2 values were within normal range for all the participants. The mean 6MWD was 584.43±23.71 m for male participants and 469.85±30.38 m for female participants. The females walked significantly shorter distance than the males [t(104) =12.730,p<0.001]. (Table 1) Pearson’s correlation matrix showed that 6MWD was positively correlated with age (r=0.248, p=0.010), height (r=0.852, p<0.001), weight (r=0.629, p<0.001), and BMI (r=0.265,p=0.006) in the overall analysis of the participants (Table2). 1 shows the relationship between the 6MWD and height in the combined group. Weight and BMI did not have significant contribution to 6MWD. The regression equation for 6MWD (cm) when sex (male=1, female=2) and height (cm) are known is: 6MWD = 204.043 -77.652 X Sex + 2.678 X Height (Standard error of estimate = 22.903) Variables Males (Mean ± SD) Females (Mean ± SD) Statistics Age (years) 22 ± 1.37 21.32 ± 0.73 t (104) = 3.18, p = 0.002 Height (cm) 171.06 ± 5.25 157.26 ± 5.89 t (104) = 12.73, p<0.001 Weight (kg) 69.40 ± 11.64 54.36 ± 9.12 t (104) = 7.39, p<0.001 BMI (kg/m2) 23.61 ± 2.90 21.95 ± 3.54 t (104) = 2.64, p = 0.010 SpO2 before exercise (%) 97.98 ± 0.31 98.08 ± 0.58 t (104) = 1.04, p = 0.301 SpO2 after exercise (%) 95.68 ± 0.87 95.96 ± 0.85 t (104) = 1.69, p = 0.094 Pulse rate before 6MWT (bpm) 83.15 ± 9.52 83.81 ± 7.82 t (104) = - 1.04, p = 0.301 Pulse rate after 6MWT (bpm) 121.74 ± 17.14 121.87 ± 8.66 t (104) = 1.688, p = 0.094 Modified Borg score 0.72 ± 0.30 0.62 ± 0.32 t (104) = 1.55, p = 0.124 6MWD (m) 584.43 ± 23.71 469.85 ± 30.38 t (104) = 21.64, p<0.001 Table 1: Characteristics of the study participants (N=106) Table 2: Correlation of 6MWD with different parameters in combined participants. Parameters Pearson’s Correlation with 6MWD p value Age 0.248 0.010 Height 0.852 <0.001 Weight 0.629 <0.001 BMI 0.265 0.006 To analyze if the predictor variables were independently related to 6MWD, variables showing overall significant correlation were considered for stepwise regression analysis (Table 3). Stepwise regression analysis gave the model with sex and height that predicted 6MWD statistically significantly [F(2,103)= 353.774, p<0.001] with an R2(coefficient of determination) of 0.873. Figure Fig 1: Relationship of 6MWD after 6MWT and Height DISCUSSION The aims of this study were to determine the correlation of SpO2 with BMI, and also to determine 6MWD, to establish prediction equation for 6MWD in apparently healthy young adults aged 18-25 years. The present study showed a significant J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Chaudhary S, et al. Chaudhary S, et al. Six-Minute Walk Test in Healthy Nepalese Young Adults Aged 18 to 25 Years: A Cross- Sectional StudySix-Minute Walk Test in Healthy Nepalese Young Adults Aged 18 to 25 Years: A Cross- Sectional Study jlmc.edu.np decrease in SpO2 after 6MWT with increasing BMI. Lower SpO2 observed in the obese participants may be related to an imbalance in the ventilation/perfusion (V/Q) ratio during the exercise test. During exercise, cardiac output increases and increased cardiac output is not accompanied by increased ventilation, leads to decrease in (V/Q) ratio in obese participants. The result is decrease in oxygen saturation.[18] Pulmonary function decreases in obesity which may be due to the added mechanical load of adipose tissue that reduces chest wall compliance and impedes diaphragm descent.[10] In our study the magnitude of correlation with SpO2 after 6MWT and BMI was r = -0.587.The correlation was statistically significant (p<0.001) though, the SpO2 values were still within normal range. This result is consistent with the previously published studies (r = -0.27, r = -0.81, p<0.001). [10,19]Similarly Faria AG et al.[18] and Anupama N et al.[20] had found lower oxygen saturation with increased BMI. Another study done by Zou H et al.[21] found a significant difference between oxygen saturation before and after the test both in males and females. Whereas in one study by Ahmed YB et al.[22] there was no significant correlation between SpO2 and BMI. This difference may be explained by difference in the measurement of resting oxygen saturation. The author did not take the oxygen saturation after exercise. There was a significant difference in the distance walked between male and female groups in our study. The male group walked a greater distance than the female group possibly because the males were taller and had higher levels of physical activity and a greater muscle mass. These results are consistent with the previous studies.[3,4,21] The result of this study showed negative correlation between the 6MWD and sex and positive correlation with height, weight and BMI. In the previous studies the results showed negative correlation of the 6MWD with weight and BMI which may be due to the fact that severe obesity rises the workload for a given exercise intensity, reducing the 6MWD.[11] These studies also showed positive correlation between 6MWD and height.[3,4,21] The contrast correlation of 6MWD with weight and BMI may be due to the fact that in our study the participants did not have severe obesity and those with higher BMI or weight also had greater height (evaluated with scatter plot). The significant effect of height on the 6MWD was attributed to a longer stride in the taller individuals. The stride length is one of the foremost determinants of gait velocity.[23] Moreover, physical activity level was a predictor factor for 6MWD.[6] The major determinants of 6MWD in the overall analysis were sex followed by height. The forward stepwise multiple linear regression showed only sex and height were independent predictors explaining 87.3% of the variance in distance for combined group (coefficient of determination R2=0.873) as shown in Table 3. These finding are comparable with previously published results (R2=0.587, R2=0.62, R2= 20-78%).[6,13,14] There are some limitations to our study. We did not recruit individuals who were older than 25 years of age. Our reference equation may not be applicable to the population beyond this age. In this study the subjects were medical students and many of them did not have severe obesity. We used convenience sample rather than a random sample which may not be representative of a wider Nepalese population. CONCLUSION: Although there was moderate negative statistically significant correlation between BMI and SpO2 after 6MWT in young adults in the study, SpO2 values were still within normal range. Sex and height were the most significant predictors of the 6MWD and the regression equation explained 87.3% of the variance in the distance for both sexes of same age. Conflict of interest: The authors declares that no competing interests exist Source of Fund: No funds were available. Table 3: Stepwise regression analysis of predictors of 6MWD in combined participants. Model Unstandardized coefficient(B) Standard error (SE) R R2 Standard error of estimate (SEE) p value Constant 204.043 74.763 0.934 0.873 22.903 0.007 Sex -77.652 7.116 <0.001 Height 2.678 0.403 <0.001 R2 = Coefficient of determination J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Chaudhary S, et al. Chaudhary S, et al. 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