Comparison of cardiorespiratory parameters between 6-minute walk test and 1-minute sit to stand test in young adults with post-COVID-19: follow-up 3 months

Introduction

Background

The major medical problem of coronavirus disease 2019 (COVID-19) infection is respiratory dysfunction due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) activated respiratory tract that leads to respiratory inflammation (1,2). Furthermore, this impairment was also present after COVID-19 infection or in post-COVID-19 patients (3). Post-COVID-19 are the individuals who have a history of confirmed SARS-CoV-2 infection, usually 3 months from the onset of COVID-19 (4). Most symptoms were found in these populations including dyspnea, fatigue, cough, and muscle weakness (3,5). These symptoms cause decreased quality of life and physical activity levels in post-COVID-19 patients (3,6). A previous study reported that higher physical fitness and cardiorespiratory function were associated with lower severity of post-COVID-19 symptoms (7). In addition, the conditions of physical restrictions on maximal and submaximal exercise capacity and increased ventilator inefficiency were found in individuals with mild forms of acute illness and post-COVID-19 conditions (8,9). Therefore, the fatigue and dyspnea symptoms of post-COVID-19 individuals occurred due to a reduction in oxygen diffusion in the peripheral circulation (9,10). The symptoms of fatigue and dyspnea were mostly presented in young adults after 6 months of COVID-19 infection (11). A previous report found that lung dysfunction was associated with the duration of hospitalization and oxygen requirement in patients who had recovered from COVID-19 infection at 3 months (12). Moreover, post-COVID-19 patients still exhibited decreased maximal exercise capacity and impaired submaximal exercise performance 3 to 6 months after recovering from COVID-19 (8).

The investigation of cardiorespiratory fitness in young adults post-COVID-19 is interesting because this information may help in understanding cardiorespiratory function in these populations. Moreover, it helps to know that these impairments possibly interfere with study, learning, and the activities of daily life in young adults post-COVID-19. Cardiorespiratory fitness could be assessed using submaximal exercise tests such as the Chester step test (CST), 1-minute sit-to-stand test (1-min-STST), and 6-minute walk test (6MWT) (13-15). The 6MWT is widely used to evaluate the submaximal level of cardiorespiratory fitness in individuals who have various conditions such as chronic obstructive pulmonary disease (COPD) and metabolic dysfunction (16,17). However, this test has shown a low execution rate in some COVID-19 patients at hospital discharge (18). Therefore, it is important to look at alternatives to a 6MWT to investigate COVID-19 patients during the follow-up. The 1-min-STST was developed to investigate submaximal cardiopulmonary fitness. This test used shorter corridors than the 6MWT (19). In addition, the number of steps of 1-min-STST was positively correlated with the distance of the 6MWT (20). However, the selected test was necessary in order to provide specific information on cardiorespiratory fitness in each individual.

Rationale and knowledge gap

Although both the 6MWT and 1-min-STST were used to investigate cardiorespiratory fitness in post-COVID-19 patients (14,21), there are no reports of using the 6MWT and 1-min-STST to assess the effects of a mild-COVID-19 infection and comparing between the two tests on cardiorespiratory parameters.

Objective

Therefore, this study aims to investigate and compare cardiorespiratory parameters between 6MWT and 1-min-STST in healthy young adults and post-COVID-19 and at a 3-month follow-up. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-44/rc).

Methods

Study design

A cross-sectional study design was used to investigate and compare cardiorespiratory parameters including heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse oxygen saturation (SpO₂), rate of perceived exertion (RPE), and leg fatigue between 6MWT and 1-min-STST in healthy young adults and post-COVID-19 and at a 3-month follow-up.

Participants

Forty-six young adults were recruited and divided into two groups including healthy young adults group (n=23) and young adults with post-COVID-19 group (n=23). The sample size was calculated using a power of 0.95, power analysis with an alpha of 0.05, and an effect size f of 0.58 (22). The participants who were recruited were 18–24 years old with or without post-COVID-19 and had polymerase chain reaction (PCR) or antigen test kit (ATK) confirmed infection with SARS-CoV-2 at less than 3 to 4 months before the evaluation procedure. The exclusion criteria are as follows participants who had cardiorespiratory diseases, neurological diseases, and musculoskeletal diseases that interfered with the performance during tests. This study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). All participants provided written informed consent after being informed of the purposes and methods of the study. This study was approved by the Clinical Research Ethics Committee of the University of Phayao, Phayao, Thailand (HREC-UP-HSST 1.3/063/66).

Procedure

Participants were assessed by age, weight, height, and body mass index (BMI) for the baseline demographic data. Each participant was investigated for cardiorespiratory parameters including HR, SBP, DBP, SpO₂, RPE, and leg fatigue through a 6MWT and a 1-min STST. Test sequences were randomly assigned using the website randomizer.org. The HR and SpO₂ were measured with a finger pulse oximeter (SB200, Rossmax International Ltd., Taiwan). SBP and DBP were measured using an automatic blood pressure monitor (HEM-8712, Omron Healthcare Co., Ltd., Kyoto, Japan). Dyspnoea was assessed using the Borg rating of perceived exertion scale (6–20 scales). Leg fatigue was measured using the Borg CR10 scale.

In the 6MWT procedure, each participant was assessed and the cardiorespiratory parameters of HR, SBP, DBP, SpO₂, RPE, and leg fatigue were recorded before performing the test. Participants were instructed to walk as far as possible for 6 minutes without running for the test in the corridor space of 30 meters. The distance completed in each 6MWT was recorded (23). Subsequently, the cardiorespiratory parameters were assessed and recorded after performing the test.

In the 1-min-STST procedure, each participant was assessed and the cardiorespiratory parameters of HR, SBP, DBP, SpO₂, RPE, and leg fatigue were recorded before performing the test. Participants were instructed to sit on a chair without armrests and with a seat height of 46 centimeters and to repeatedly stand up until the hips and knees were fully extended, and then to sit down again while the arms were folded across the chest as quickly as possible for 1 minute. The number of completed actions during the test was recorded (14). After performing the test, the cardiorespiratory parameters were again assessed and recorded. There was a 30-minute interval between each test.

Both tests were performed at a 3-month follow-up. The flow chart of this study protocol is shown in Figure 1.

Figure 1 The flow chart of this study protocol. COVID-19, coronavirus disease 2019.

Statistical analysis

The normality of the data distribution was assessed using the Shapiro-Wilk test. Continuous variables are expressed as means and standard deviations (SDs). A paired t-test was used to compare cardiorespiratory parameters within the group. An independent sample t-test was used to compare cardiorespiratory parameters between groups and tests. IBM SPSS Statistics software, version 26.0, was used in this study, with a P value of less than 0.05 set to denote significance.

Results

The variables of age, weight, height, and BMI were not significantly different between healthy young adults and post-COVID-19. The results are presented in Table 1.

At the 3-month follow-up, post-COVID-19 had significantly decreased post-HR, post-SBP, post-SpO₂, post-RPE, and post-leg fatigue, and increased the distance of 6MWT when compared to the baseline (P<0.05). In addition, post-COVID-19 patients had significantly increased post-HR and post-RPE when compared to healthy young adults at the baseline. However, cardiorespiratory parameters were not statistically significantly different between healthy young adults and post-COVID-19 at the 3-month follow-up (Table 2).

For the cardiorespiratory parameters using the 1-min-STST, the results showed that at the 3-month follow-up, post-COVID-19 had significantly decreased post-HR, post-SBP, post-SpO₂, post-RPE, post-leg fatigue and increased the number of steps of 1-min-STST when compared to baseline (P<0.05). While, post-COVID-19 had significantly increased post-HR, post-RPE, and post-leg fatigue and reduced the number of steps of 1-min-STST when compared to healthy young adults at the baseline. However, cardiorespiratory parameters and the number of steps of 1-min-STST were not statistically significantly different between healthy young adults and post-COVID-19 at the 3-month follow-up (Table 3).

Comparison of cardiorespiratory parameters between the 6MWT and the 1-min-STST, the results showed that all cardiorespiratory parameters after performing the 6MWT were not statically significantly different when compared with the 1-min-STST in healthy young adults at the baseline and the 3-month follow-up (P>0.05). Moreover, cardiorespiratory parameters after performing the 6MWT also showed not statistically significant different when compared with the 1-min-STST in post-COVID at the baseline and the 3-month follow-up (P>0.05). Whereas the 1-min-STST significantly increased leg fatigue when compared to the 6MWT at baseline (P<0.05) (Table 4).

Discussion

Key findings

Our study indicated that post-COVID-19 had recovered in some of the variables of the cardiorespiratory parameters at baseline when compared with healthy young adults. In addition, the cardiorespiratory parameters in post-COVID-19 recovered to the value of healthy young adults at the 3-month follow-up. Moreover, the cardiorespiratory parameters were not statistically significantly different between the 6MWT and the 1-min-STST in both groups at the baseline and the 3-month follow-up. There is only leg fatigue showed a significantly increased in the 1-min-STST when compared to the 6MWT at the baseline. These responses may be due to post-COVID-19 in this study having had mild-COVID-19 history without pneumonia during their COVID-19 infection. Therefore, our results suggested that young adults who recovered from mild-COVID-19 infection after about 6 months had recovered cardiorespiratory parameters using the 6MWT and 1-min-STST. Moreover, the 1-min-STST is an alternative test for used to evaluate cardiorespiratory fitness levels in post-COVID-19 who recovered from mild-COVID-19 infection when the 6MWT cannot be performed.

Strengths and limitations

The strength of our study includes an adequately powered sample size. In addition, we used field tests to assess the cardiorespiratory parameters in post-COVID-19 at the 3-month follow-up. However, the study may be limited by the omission of some variables that impact aerobic performance, such as oxygen uptake capacity (VO₂). Therefore, future studies should evaluate this variable. Moreover, it may be limited by additional variables that impact aerobic performance such as an anthropometric profile and activity level. Therefore, future studies should place the anthropometric profile and activity level of participants in the inclusion criteria.

Explanations of findings

This study showed that young adults who recovered from mild-COVID-19 infection after about 3 months had increased post-HR and post-RPE after performing the 6MWT when compared to healthy young adults. However, these parameters could have recovered to equal the values of healthy young adults at the 3-month follow-up. Our results were consistent with a previous study which found that adults who had recovered from mild- to moderate-COVID-19 infection after 4 weeks had significantly increased HR and dyspnea after performing a 6MWT when compared with healthy subjects (22). These impairments cause the SARS-CoV-2-activation of the immune system during the COVID-19 infection, resulting in an imbalance of the autonomic nervous system. These responses were also presented post-COVID-19 after performing a 6MWT (24). The dyspnea presented after performing a 6MWT in post-COVID-19 was due to the disrupted lungs from SARS-CoV-2 during COVID-19 infection, which leads to lung injury and dysfunction (25,26). Furthermore, several studies found that post-COVID-19 patients recovering from COVID-19 pneumonia had increased RPE and leg fatigue and decreased distance of 6MWT and O₂ sat after performing a 6MWT (27,28). Moreover, a previous study showed that the decreased O₂ sat while performing the 6MWT was found in severe post-COVID-19 patients. These responses may be due to ventilator-activated lung injury in patients with severe respiratory failure during COVID-19 infection for several months after recovery. Therefore, post-COVID-19 dyspnea may have had different physiological correlates in mild- and severe-COVID-19 patients. Furthermore, patients with mild disease and normal gas transfer had dyspnea. This finding indicated that dyspnea is a complex symptom that may involve several other mechanisms than those of the respiratory system (29). Moreover, a previous study reported that post-COVID-19 patients who had not required hospitalization or home oxygen therapy and recovering from one month of COVID-19 infection had significantly increased blood pressure after performing cardiopulmonary exercise testing (CPET) when compared with the control group (30). Additionally, post-COVID-19 patients had increased SBP and DBP at the 1-month follow-up when compared with admission (31). The increased blood pressure may be due to SARS-CoV-2-activated renin-angiotensin-aldosterone system (RAAS) or the sympathetic nervous system (32). In contrast, blood pressure, SpO₂, leg fatigue, and distance of 6MWT were not different between groups because the post-COVID-19 in this study had recovered from only mild-COVID-19 at about 3 months before the investigation procedure.

Young adults who recovered from mild-COVID-19 infection for about 3 months had increased post-HR, post-RPE, post-leg fatigue, and decreased the number steps of 1-min-STST after performing the 1-min-STST when compared with healthy young adults. At the 3-month follow-up it was found that these parameters had recovered to the values of healthy young adults. These findings suggested that young adults who recovered from mild-COVID-19 infection for about 3 months had decreased some cardiorespiratory parameters. These findings are consistent with a previous study, which found that post-COVID-19 patients had reduced physical capacity after 1 month of COVID-19 infection (33). However, participants in our study could recover their cardiorespiratory fitness levels at about 6 months after COVID-19 infection. Moreover, several earlier studies reported that a reduction in physical capacity using the 1-min-STST was found in post-COVID-19 patients who had a history of admission to the hospital for more than 10 days or older adult patients (14,33). In addition, a previous study showed that post-COVID-19 patients had significantly decreased numbers of step for the 1-min-STST and increased dyspnea and leg fatigue after performing the 1-min-STST when compared to individuals without COVID-19 infection (28). These responses were due to post-COVID-19 patients in that study having recovered from COVID-19 pneumonia and had comorbidities such as obesity, arterial hypertension, cardiac diseases, and diabetes and having had a length of stay in hospital of about 22 days (28). This study, however, involved no patients with post-COVID-19 pneumonia with a prolonged hospital stay.

The cardiorespiratory parameters were not statistically significantly different between the 6MWT and the 1-min-STST in healthy young adults and post-COVID-19 patients. In contrast, post-COVID-19 patients had significantly increased post-leg fatigue from the 6MWT when compared to the 1-min-STST at the baseline. This response may be due to the 1-min-STST stressing lower extremities when performing the test, in contrast walking along a flat corridor as in the 6MWT (34). However, the 6MWT and the 1-min-STST provided similar cardiorespiratory results in the populations of this study. It is crucial to consider that a more significant effort in the lower extremities is required to execute the 1-min-STST (35,36). This result was confirmed by the reported perception of leg fatigue when compared with the 6MWT. According, the 1-min-STST should not be considered in individuals who had extreme lower extremity fatigue before the evaluations. Therefore, our study indicated that the 1-min-STST could be used as an alternative in post-COVID-19 patients if the 6MWT could not be performed.

Conclusions

Post-COVID-19 recovered from mild-COVID-19 after about 6 months could recover their cardiorespiratory parameters to the values of healthy young adults.

Acknowledgments

We would like to thank all young adult volunteers for participating in this study.

Funding: This research was funded by the Thailand Science Research and Innovation Funds and the University of Phayao (No. FF66-UoE009 to P.A.).

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-44/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-44/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-44/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-44/coif). P.A. reports that this research was funded by the Thailand Science Research and Innovation Funds and the University of Phayao (No. FF66-UoE009). The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). This study was approved by the Clinical Research Ethics Committee of the University of Phayao, Phayao, Thailand (HREC-UP-HSST 1.3/063/66). All participants provided written informed consent after being apprised of the study’s protocol.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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