Lab 5 & 6 -Bruce Protocol/Measurement of Maximal Oxygen Consumption- TA Joshua PDF

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Estimating VO2max: Bruce Protocol Test Introduction Maximal exercise tests are preferred because they provide a very accurate measurement of VO2max and offer increased sensitivity in diagnosing the risk of cardiovascular diseases in asymptomatic individuals (Mangum, 2013). Disadvantages of maximal exercise tests include the requirement of physician supervision, the requirement of subjects to exercise to volitional fatigue, and the high risk associated with the test (Mangum, 2013). The Bruce Protocol test, the maximal test used for this study, has 5 main goals: To assess aerobic capacity, to measure cardiorespiratory performance, to observe mechanisms of cardiac impairment, especially due to decreased blood flow to heart tissues, to establish standards for normal responses, and to differentiate between changes due to aging and those due to disease states (Mangum, 2013). The following criteria was developed to verify achieving maximal effort: failure of heart rate to increase with further increase in exercise intensity, plateau in oxygen uptake, an RER value greater than 1.15, blood lactate concentration greater than 8 mmol/L, and an RPE value greater than 17 (Mangum, 2013). The purpose of this experiment was to use a maximal exercise test to estimate VO2max and compare the VO2max calculated using an equation and a computer gas analysis. It was hypothesized that as the exercise workload increased the subject’s VO2 would increase, but as recovery began the subject’s VO2 would decrease.

Methods 1. Treadmill equipment calibration Treadmill elevation was checked through the range of 5, 10, and 15 degrees using pre-cut standard angles of wood and a carpenter’s level. If needed, elevation was adjusted by turning the adjustment screw located under the elevation gauge on the treadmill control panel using a small screwdriver. To check treadmill speed, a small piece of tape was placed on the rear end of the treadmill belt the circumference of the belt was measured using a steel carpenter’s measuring tape. The treadmill was turned on, a random speed was selected, and the number of belt revolutions in 1 minute was timed. The actual treadmill speed was compared using the following formula: MPH: = rev/min * inches/rev * 1 mil/63360 inches * 60 minutes/hour Then, the actual speed was compared to the speed displayed on the treadmill speed gauge and adjusted if necessary. This procedure was performed over several other speeds to insure linearity in speed change. 2. Subject screening Health and/or medical data are required before a subject undergoes a GXT. Blood assays, current medications, pulmonary function, nutritional/dietary history, resting ECG and blood pressure, body composition, and personal and family history of cardiovascular diseases were all collected. The primary physician will refer much of the screening data. 3. Informed consent The entire procedure was explained to the subject. The “Informed consent for graded exercise testing” document was signed by both the subject and administrator and

witnessed by a neutral person. The subject was made aware that any questions may be asked at any time. 4. Pre-GXT Instructions The entire procedure was explained to the subject, including safety precautions, and the subject was told that he/she is always in control of his/her GXT and can instruct the administrators to terminate the GXT at any time. The Borg Rate of Perceived Exertion, Dyspnea Scale, Claudication Scale, and Angina Scale were all explained to the subject. The criteria for GXT termination were explained and the subject was told to allow the testing staff at least 30 seconds before GXT termination, if possible, in order to record the GXT termination data. The Immediate Post Exercise procedures were also explained to the subject. 5. Bruce Treadmill Exercise Testing Proper mounting procedures were demonstrated before the subject began exercising on the treadmill. A general explanation for the GXT protocol, i.e., stage length, change in speed and elevation, and anticipated gait per stage was given to the subject. Data collection for 3 minute stages: Prior to the start of the GXT, the blood pressure cuff was secured on the left arm and the blood pressure was recorded while the arm was supported at heart level. The subject began a warm-up phase, walking at 1.7mph at a 10% grade for 1 minute. After the 1 minute warm-up, testing began. Heart rates were recorded after each minute, blood pressure was recorded at the end of the second minute, and the Borg RPE was recorded during the final 15 seconds of the stage. GXT Termination: The cool down phase began immediately after the subject notifies the testing staff to end GXT. Once the subject notifies termination of the GXT, the total

exercise time was recorded, not including the warm-up phase. Then the recovery phase began. The grade was lowered to 0% and speed to 1.7mph and the heart rate was recorded after 1 minute, 2 minutes, 3 minutes, and 5 minutes. Blood pressure and Borg RPE was taken after 2 minutes and 5 minutes. The following equations were used with the Bruce Treadmill Protocol to estimate functional aerobic capacity: Males: Estimated VO 2max = (0.056*Bruce GXT time in seconds) + 3.88 Females: Estimated VO2max = (0.056*Bruce GXT time in seconds) + 1.00 Results Table 1: Demographics for both subjects Subjec t 1: Male 2: Male

Ag e 22 20

Resting BP 118/76 mmHg 118/80 mmHg

Resting HR 66 bpm

Age-predicted HRmax 191.82 bpm

85% Age-predicted HRmax 163.05 bpm

72 bpm

193.20 bpm

164.22 bpm

Figure 1: HR/Stages for the subject that tested once (Subject 2)

Chart Title 200 180

Heart Rate (bpm)

160 140 120 100 80 60 40 20 0 Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

Recovery 1 Recovery 2 Recovery 3 Recovery 4

Stages

Figure 2: BP/Stages for the subject that tested once (Subject 2)

Blood Pressure 160

Blood Pressure (mmHg)

140 120 100 Column2 Diastolic

80 60 40 20 0 Stage 1

Stage 2

Stage 3

Stage 4

Recovery 2

Stages

Figure 3: HR/Stages for the subject that tested twice (Subject 1)

Heart Rate 160 140

Heart Rate (bpm)

120 100 80 60 Trial 1 Trial 2

40 20 0 Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

Recovery 1 Recovery 2 Recovery 3 Recovery 4

Stages

Figure 4: Trial 1 BP/Stages for the subject that tested twice (Subject 1)

Blood Pressure 160

Blood Pressure (mmHg)

140 120 100 Column2 Diastolic

80 60 40 20 0 Stage 1

Stage 2

Stage 3

Stage 4

Stage 5

Recovery 2 Recovery 4

Stages

Figure 5: Trial 2 BP/Stages for the subject that tested twice (Subject 1)

Blood Pressure 160

Blood Pressure (mmHg)

140 120 100 Column2 Diastolic

80 60 40 20 0 Stage 1

Stage 2

Stage 3 Stages

Figure 6: RER at 30 second intervals (Gas analysis)

Recovery 2

Recovery 4

0: 00 1: 00 2: 00 3: 00 4: 00 5: 00 6: 00 7: 00 8: 00 9: 00 10 :0 11 0 :0 12 0 :0 13 0 :0 0 14 :0 15 0 :0 16 0 :0 0 17 :0 18 0 :0 19 0 :0 20 0 :0 21 0 :0 22 0 :0 23 0 :0 0

VO2 (ml/kg/min) 0: 00 1: 00 2: 00 3: 00 4: 00 5: 00 6: 00 7: 00 8: 00 9: 0 10 0 :0 11 0 :0 12 0 :0 13 0 :0 14 0 :0 15 0 :0 16 0 :0 0 17 :0 18 0 :0 19 0 :0 20 0 :0 21 0 :0 22 0 :0 23 0 :0 0

RER

Chart Title

1.4

1.2

1

0.8

0.6

0.4

0.2

0

Time

Figure 7: VO2 at 30 second intervals (Gas analysis)

VO2

60

50

40

30

20

10

0

Time

Table 2: VO2max values

Subject 1: Male, Age 22Tested twice

VO2max Trial 1: (0.056*982 seconds) + 3.88 = 58.87 ml/kg/min Trial 2, Gas analysis: 50.01ml/kg/min

2: Male, Age 20 – Tested once

Trial 1: (0.056*950 seconds) + 3.88 = 57.08 ml/kg/min

Discussion The experiments all went as planned and equipment errors were encountered. Subject 1, who performed the Bruce Protocol both times, had heart rate values that were similar during both trials, but the blood pressure values varied quite significantly from time to time. The similarity in heart rate could be because the subject was exercising at his maximal effort both times, which yields an increasing heart rate during the exercise stages and a decreasing heart rate during the recovery periods, and also because of the ease of measurement for the test administrator. The difference in the blood pressure could be because it is difficult to accurately get a blood pressure reading due to the noise made by the treadmill, preventing the test administrator from hearing the Korotkoff sounds well, and the constant movement of the subject’s arm. During some stages the blood pressure reading could not even be taken because the test administrator could not hear the Korotkoff sounds at all, thus skewing the results significantly. For Subject 1, the VO 2max value calculated using the equation was 58.87 ml/kg/min and the value collected from the gas analysis was 50.01 ml/kg/min. The difference was not extremely significant, however I feel the gas analysis was more accurate. The equation uses two constants and the exercise duration in order to calculate the VO2max; it does not use any of the person’s demographics to tailor the results to the subject, it is more of a general estimation. However, the gas analysis directly measured the subject’s oxygen expenditure every 30 seconds,

which is more subjective to the person; therefore I believe the gas analysis results would be more accurate rather than a general equation. Based upon the RER I believe Subject 1 did reach his true VO 2max because the criteria for achieving maximal effort states that there should be an RER greater than 1.15 (Mangum, 2013) and Figure 6 shows two measurements recorded above 1.15. Based upon the heart rate, I believe both subjects did reach their true VO 2max because the criteria for achieving maximal effort states that heart rate should increase with exercise intensity (Mangum, 2013) and Figure 3 shows heart rate increasing during every exercise stage and heart rate decreasing during every recovery stage. According to Figure 7, our hypothesis that VO 2 would increase during exercise and decrease during recovery was supported. The figure shows a steady increase in VO2 during the exercise time of 16 minutes and 30 seconds, and immediately after, when recovery began, the figure shows a steady decrease in VO2. Subject 1 recorded a VO2max value of 58.87 ml/kg/min for Trial 1. According to the VO2max normative values, he would fall above the 99th percentile and has excellent aerobic capacity. Subject 1 recorded a VO2max value of 50.01 ml/kg/min for Trial 2. According to the VO2max normative values, he would fall between the 85th and 90th percentile and has excellent aerobic capacity. Subject 2 recorded a VO2max value of 57.08 ml/kg/min for Trial 1. According to the VO2max normative values, he would fall between the 95th and 99th percentile and has excellent aerobic capacity. The only error encountered during testing was the inability to record blood pressure for both subjects during some of the later exercise stages which led us to omit those blood pressure readings as shown in Figures 2 and 5. These skewed results hinder us from verifying whether

the blood pressure actually increased during exercise and decreased during recovery like it should have, but it did not have any impact on our calculations of the subject’s VO2max. Literature Cited Mangum, J. 2013. Resting and Exercise Measurement of Heart Rate and Blood Pressure. [Powerpoint slides]....