The 6-minute walk test is a common clinical instrument for assessing patient's’ functional capacity. The 6MWT should be performed preferably indoors, on a flat, straight, hard surfaced corridor usually at least 30 meter long. 

The patient is told to be calm, to have taken his/her medications and to wear comfortable clothing and shoes. The supervisor records baseline oxygen saturation, heart rate and brachial arterial blood pressure and the Borg scale rating for dyspnoea and fatigue. Once the patient has understood the instructions, he/she is ready to begin the test. During the test the participants have to walk at a rate suitable to their condition and they are allowed to stop or slow down if they feel like doing so and resume walking as soon as possible.

At the end of the test the supervisor again records the Borg scale for dyspnoea and fatigue and also measures arterial blood pressure, heart rate and oxygen saturation. The number of laps and the additional distance covered are recorded and the 6MWD is calculated. The 6MWT is self-paced, and patients are unlikely to push themselves beyond their endurance or through musculoskeletal pain. The test is easy to administer, well tolerated.

The 6MWT may be used as a tool for the measurement of functional status of a patient especially in the case of advanced diseases with multiple comorbidities who cannot perform more complex exercise tests, such as patients with Heart Failure, Chronic Obstructive Pulmonary Disease or Cystic Fibrosis. The walked distance reflects exercise capacity determined by maximal cardiopulmonary exercise testing in patients with cardiopulmonary conditions and has a strong association with mortality in primary pulmonary hypertension, heart failure, and chronic obstructive pulmonary disease (COPD).

The test is also used for assessing the effect of therapies such as pulmonary rehabilitation, oxygen therapy, longterm use of inhaled corticosteroids, and lung volume reduction surgery. The 6MWD in healthy adults has been reported to range from 400 to 700 metres. There are several nonstandardized reference equations for 6MWD from healthy adult populations; their value has not been established due to high variation mainly attributed to the fact that different methodologies were used in various studies. Age, height, weight, sex, corridor distance, impaired cognition and need for continuous oxygen supplementation may independently affect the 6MWD in patients and therefore these factors should be taken into consideration when interpreting the results of 6MWT.

The 6MWT guidelines were reported by the American Thoracic Society (ATS) 7 years ago, at a time when reference equations from healthy population-based samples were not available. The guidelines encouraged investigators to publish reference equations using these new guidelines. However, the series published until now have included a small number of individuals from a single region.

Currently, there are no universally accepted reference equations for clinical use and there are no available data from multicentre studies evaluating the possible regional differences of this test. Therefore, the present study was conducted to develop a reference equation in the Indian scenario.

AIM

To study the 6 Minute Walk Test in Healthy Individual in age group of 18 – 30 years.

OBJECTIVES

1. To measure the normal six-minute walk distance in healthy subjects and to develop prediction equation.

To examine the cardiopulmonary responses (pulse rate, blood pressure and respiratory rate, SpO2) before, immediately after completion and 10^th minutes of the test. 

This cross-sectional, observational study was conducted under the Department of Respiratory Medicine, MGM Medical College and Hospital, Navi Mumbai. A written signed informed consent was taken from all the patients prior to their enrolment in the study.

Inclusion Criteria:

1. Volunteers aged 18 years to 30 years.
2. Healthy volunteers.
3. Those giving consent to participate in the study.

Exclusion Criteria:

1. Subjects below 18 years of Age.
2. Hypertension Blood Pressure >140/90mm/hg
3. Recent illness including Upper respiratory tract infection.
4. Presence of any factors that may limit ability to participate in 6mwt e.g. impaired cognition function, neuromuscular disease, claudication, severe Musculo-skeletal problems affecting lower extremity or spine. Subjects who have any significant past medical history, asthma, smoking.
5. Subjects who refuse to enrol in this study.

ETHICAL CONSIDERATION

Prior approval of the Institutional Ethics Committee was taken before conducting the study.

DATA COLLECTION

All the healthy volunteers presenting during the study period were included in the study, provided they met the inclusion and exclusion criteria as above. A written informed consent was taken from all the subjects who were to be included in the study. They were assured about the maintenance of confidentiality and the nature of voluntary participation. Once consent was given, they were included in the study. A total of 300 subjects were included in the study.

All the healthy volunteers presenting during the study period were included in the study, provided they met the inclusion and exclusion criteria as above. A written informed consent was taken from all the subjects who were to be included in the study. They were assured about the maintenance of confidentiality and the nature of voluntary participation. Once consent was given, they were included in the study. 

Demographic details were recorded. Detailed history of present illness (if any) Along with personal and past history were recorded. General and systemic examinations were done. Height was recorded using stadiometer.

Weight was recorded using standard weighing machine.

Baseline vitals were recorded before the start of the test. These included PR, BP, SpO2 and RR. Then the test was carried out as per standard guidelines. 6MWT was administered and adhered to the guidelines of American Thoracic Society (ATS) standards. 

The subjects were given orientation to the test on the day. Each subject was instructed to walk as far as possible during a 6 min period over a 30 m course in an indoor hospital corridor. Participants were asked to eat a light morning meal and to wear comfortable clothes and shoes. Subjects were asked to indicate their level of dyspnoea perception using a modified 12-point Borg Scale, wherein each score (i.e., ranging from 0 to 10). Subjects were asked to walk as far down the length of the corridor as they could, at their own pace, for 6-min.

Subjects were allowed to stop if they developed symptoms of dyspnoea, chest pain, leg cramps or dizziness. The vitals were again measured immediately after the 6MWT and after 10 minutes. All the data was recorded in excel and analysed.

STATISTICAL ANALYSIS

The data was analysed using statistical software (IBM SPSS, IBM Corporation, Armonk, NY, USA).

Descriptive statistics: The Numerical/Continuous data were expressed as Mean ± Standard Deviation and the Categorical data were expressed as Percentages. Analytical statistics: The Numerical/Continuous data were analysed by the ‘Unpaired t test’ and ‘Paired t test’ wherever applicable and the Categorical data were analysed by the Chi square test (Fischer’s exact test was used when more than 20% of the cells had value less than 5). Multiple regression analysis was done to formulate the prediction equation for the distance walked in 6MWT. P value of less than 0.05 was considered as “statistically significant”.

In the present study, there were 150 males and 150 females. They were comparable in terms of age. The height and weight of males was more than females.

It can be concluded from the present study that there is an increase in the hemodynamic parameters immediately after the test. However, the levels return to normal/baseline when measured 4 minutes after the test.

The prediction equation developed from distance walked is:

6MWD (females) = 83.76 – (1.42*Age in years) – (3.98*Weight in kgs) + (426.60*Height in metres)

6MWD (males) = 553.46 – (2.62*Age in years) + (1.82*Weight in kgs) - (38.98*Height in metres)

Distance walked in 6MWT: In the present study, it was observed that the average distance walked in the 6MWT was significantly more in males (554.32 ± 28.69 metres) as compared to females (491.31 ± 50.39 metres); P value: less than 0.001.Thus, it can be effectively concluded from the present study that the distance walked in the 6MWT is significantly more in males as compared to females. This may be explained by the increased height, muscle mass, strength and stride length in males as compared to females.

Pulse Rate: In the present study, it was observed that there was an increase in PR in females immediately after the 6MWT as compared to baseline; P value: less than 0.001. The PR returned to baseline value 10 minutes after the 6MWT. Similar trends were observed in males. When compared between the males and females, it was observed that the PR was comparable in the two genders at all points of time; P value: more than 0.05.

Systolic Blood Pressure: In the present study, it was observed that there was an increase in SBP in females immediately after the 6MWT as compared to baseline; P value: less than 0.001. The SBP decreased 10 minutes after the 6MWT but was Similar trends were observed in males. However, the SBP after 10 minutes was significantly lower than the baseline; P value: less than 0.001.

Diastolic Blood Pressure: In the present study, it was observed that there was a females immediately after the 6MWT as compared to baseline; P value less than 0.001. The DBP was comparable to baseline value 10 minutes after the test. P value: 0.936. Similar trends were observed in males. When compared between the males and females, it was observed that the DBP was comparable in the two genders at all points of time.

SpO2: In the present study, it was observed that in females the SpO2 immediately after the 6MWT was comparable to baseline; P value: 0.961. There was a decrease in the SpO2 10 minutes after the 6MWT; P value: 0.032. The SpO2 in males was comparable to the baseline values; p value: more than 0.05. When compared between the males and females, it was observed that the SpO2 was comparable in the two genders at all points of time; P value: more than 0.05.

Respiratory Rate: In the present study, it was observed that there was an increase in RR in females immediately after the 6MWT as compared to baseline; P value: less than 0.001. There was a fall in RR 10 minutes after the 6MWT; P value: 0.044. Similar trends were observed in males. However, the rates after 10 minutes were comparable to baseline; P value: 0.164.

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