Sonoma State University
Department of Biology Hanes
HUMAN BASAL METABOLIC RATES AND ENERGY METABOLISM
Purpose
To become familiar with the terms and calculations involved in
determining metabolic rates.
To estimate basal and exercising metabolic rates and calculate muscle
efficiency.
Definitions
Metabolism is all of the chemical reactions that occur in an organism. In the absence of external work or storage of chemical energy, all energy released during metabolism is converted to heat. Therefore, heat production is an index of energy metabolism.
This means that the basal metabolic rate (BMR) of a homeothermic animal is its rate of heat production in a post-absorptive state during complete rest and at a temperature within its zone of thermal neutrality. In other words, it is the resting energy metabolism uncomplicated by the heat increment of feeding, heat, or cold stress. The term basal metabolic rate is sometimes erroneously used in connection with the energy metabolism of poikilothermic animals, but is inappropriate because they do not possess capacities for physiologically regulated body temperature.
Since the basal metabolic rate represents the "irreducible" energy cost of maintenance for a bird or mammal under the conditions specified above, it is a particularly useful physiological measurement because it represents the starting point for the measurement of heat increments of such things as fever, feeding, lactation, gestation, work, and regulation of body temperature at environmental temperatures beyond the limits of the zone of thermal neutrality. It is also the function which has been used in analyzing the relationship between energy metabolism and body weight in birds and mammals. Its clinical uses include tests for hyper- and hypothyroidism and other influences of hormones on the metabolic rate. In animals it can be used as a starting point for the measurements of the metabolic costs of osmoregulation, thermoregulation, etc...
Accurate measurement of the basal metabolic rate requires that the subject has had 8 hours of sleep just before the test, no food, alcoholic beverages, coffee, tea, or tobacco for the previous 12 hours. We will be a bit inaccurate in our own measurements and not adhere to such rigor.
Oxygen consumption will be used as the measure of energy metabolism. It will be determined with an oxygen analyzer to measure the oxygen fraction of air and a spirometer to measure volumes. The subject should lie quietly on the mat provided for 5 min. or so before measurements for basal metabolic rate are begun.
When measurements of basal metabolic rates are complete, the next phase of the experiment can be carried out. This deals with measurement of energy metabolism during exercise including an estimation of muscular efficiency.
Procedures
Equipment needed:
Sling Psychrometer
Handbook of Chemistry & Physics
70% Alcohol: 350 ml
500 ml beaker
O2 Analyzer
CO2 analyzer
First, measure the relative humidity of the room with the sling psychrometer and record. To do this, fill the cap of the psychrometer with deionized water to wet the wick. Put the cap on and swing the psychrometer around in the air until the wet thermometer cools no further. Read the wet and dry thermometers. Push the psychrometer back into its sheath and line up the wet and dry temperatures. The "Y" mark will point to the relative humidity in percent saturation. Measure and record the air temperature and barometric pressure of the air in the room. (The barometer and thermometer are located in front of the main classroom). Calculate the vapor pressure of the room air by multiplying the relative humidity by the value of the water vapor pressure in water saturated air at that temperature as found in the Handbook of Chemistry and Physics. (See Formula #1)
Record room temperature, relative humidity, saturation vapor pressure (from Handbook of Chemistry and Physics) and the calculated room vapor pressure. Calculate the fraction of oxygen in room air (Formula #2) (always remember that percents are converted to fractions in all formulae) and set the oxygen analyzer as follows:
1. Turn on the flow control and put inlet tube in room air to draw
room air into the analyzer.
2. With the selection knob on "UNKNOWN", unlock and set the dial
marked "CELL ZERO" to the % oxygen value calculated and relock the
dial.
3. Turn the selection knob to "REFERENCE ADJUST", then adjust the
dial to the same % oxygen value that you calculated and relock the
dial. Turn the selection knob back to "UNKNOWN" and you have set the
machine for the day.
4. Place the inlet tube back into the mixing chamber.
Never allow moisture from the tubing to enter the analyzer.
Basal Metabolism
While the subject is resting quietly, rinse the mouthpiece with
70% alcohol and dry. Insert the mouthpiece and observe how the
spirometer works. The dial is marked in liters and a full revolution
is 10 liters. The subject should be allowed to come to equilibrium (5
minutes of rest?) The spirometer can be reset to zero, so with a
watch, note the time, reset the spirometer and begin the experiment.
Allow the subject to breathe normally for five minutes while
recording the number of breaths per minute as well as the total
volume of air moved. Also record the oxygen fraction of exhaled
air at the end of the 5 minute period. Calculate and/or record:
(See Formulae #3-7).
You may also want to record the carbon dioxide levels in the air and
exhaled air. There is no place on the data sheet, but write it in and
I will tell you what can be done with this data. Record or calculate
the following data:
breaths/min
minute volume
tidal volume
O2
fraction exhaled air
Oxygen consumed/min
Heat produced/min
Standard Metabolic Rate
Basal metabolic rates vary with the size of the individual. Individuals are more comparable to each other if size is adjusted for as the surface area of the individual. Calculate the surface area of the person tested (formula #8) and then calculate the person's standard metabolic rate (formula #9). Compare this value to the following chart of mean standard metabolic rates to see if he or she falls close to the mean standard metabolic rate of their age class. Note that the mean standard metabolic rate declines with age. Us old folk just aren't quite so alive anymore.
Mean Standard Metabolic Rates per square meter of Surface Area in Kcal/sq. M hr
|
AGE(YR) |
MALES |
FEMALES |
|
14-16 |
46.0 |
43.0 |
|
16-18 |
43.0 |
40.0 |
|
18-20 |
41.0 |
38.0 |
|
20-30 |
40.0 |
37.0 |
|
30-40 |
39.5 |
36.5 |
|
40-50 |
38.5 |
36.0 |
|
50-60 |
37.5 |
35.0 |
|
60-70 |
36.5 |
34.0 |
|
70-80 |
35.5 |
33.0 |
Exercise Metabolic Rate
The ergometer is constructed so that one turn of the pedals moves the rim of the wheel 6 meters. Set the metronome at 100/min and have the subject keep time so that 50 complete turns of the pedal are completed in one minute (300 M/min). The weight and scale are graduated in Kilo-ponds (Kp). One Kp is the force acting on the mass of one Kg at normal acceleration of gravity. (1 Kp Meter/min = 723 foot-pounds/min = 16.35 watts = 234 cal/min.) The scale is most accurately read from the side and the mark on the weight. Start work with a slack drag. The seat height is adjustable. Once the wheel is moving, apply a drag of 2 Kp (600 KpM/min) or 3 Kp (900 KpM/min), record. Check the drag occasionally and adjust as necessary to maintain a constant work load. Keep the work load at 50 complete revolutions/min with all of the gas monitoring equipment in place for 5 minutes. During the last minute accurately record minute volume, tidal volume, breaths/min, Oxygen fraction exhaled, etc... Calculate O2 consumed/min, O2 consumed/min STPD, Heat Production.
Muscle Efficiency
Calculate the efficiency of the muscular work as the rate of calories required to do the work (calculated from the ergometer settings) divided by the rate of calories used to do the work (calculated from O2 consumption data during exercise minus the basal rate) times 100. (See Formulae #11-13)
Terms to Know:
BMR
Mean Standard Metabolic Rate
Vapor Pressure
Minute Volume
Tidal Volume
Oxygen Debt
Relative Humidity
Efficiency
Calorie
Kilopond meter
References:
Guyton. Textbook of Medical Physiology. Chap 70. 1971. Astrand, Per-Olof. Work tests with the bicycle ergometer.
Formulae
1. Room vapor pressure = Relative Humidity X Sat. Vapor pressure
2. Dry air is .2095 oxygen. Determine the fraction of oxygen in room air as follows:
4. O2 consumed/min = minute volume(O2 fraction inhaled - O2 fraction exhaled)
6. g O2 cons./min STPD = L O2 Cons/min STPD X 1.43
7. Heat produced per minute in cal/min = L O2 cons/min STPD X 4825 cal/ L O2
8. Surface area can be calculated with a formula using weight in Kg and height in centimeters. Surface area ( M2 = 0.007184 X Kg0.425 X cm0.725)
10. 1 KpM = 234 cal
11. Calories required/min = KpM</min X 234 cal/Kpm
12. Calories used for muscle work = (Exercise Heat production/min - BMR/min) = ((cal/min at work) - (cal/min BMR)) = cal/min
1 inch = 2.54 cm
1 pound = 0.454 Kg
METABOLIC RATES DATA SHEET
1994
Name ____________________________ Group #____________ Date __________
Air Temp._____C Barom. Pressure _______Torr Relative Humidity _____%
Vapor Pressure(Saturation)________Torr *Rm Vapor Press. ____Torr
*O2 fraction in Rm Air_______ (Set Analyzer at this value) (BE AWARE THE
ANALYZER READS % - YOU WANT THE FRACTION)
Subject: Sex___ Age___ Height_____cm Weight______Kg
BASAL METABOLIC DATA
Breaths/min________ Minute Volume _____L/min (Amt of Air inhaled/min)
*Tidal Volume_______L/breath O2 fraction exhaled___________(from
ending
analyzer
reading)
*O2 consumed/min_______L/min *O2 consumed/min STPD______L/min _______*g
O2/min
*Heat Production________ cal/min [This is the basal metabolic rate]
*Surface area _______ sq. M *Standard Metabolic Rate_______Kcal/sq. M. hr
EXERCISE DATA:
O2 fraction in Rm Air________ O2 fraction in exhaled
Air_______
KpM/min _______ Breaths/min________ Minute Vol________L/min
*Tidal Vol______L/breath
*O2 consumed/min________L/min *O2 consumed/min STPD______________L/min
*Heat Production_______________cal/min [This is the exercise metabolic rate]
*Muscle Efficiency = Calories required divided by calories used times 100. The result will be in percent.
* Data that needs to be calculated.