Journal of Applied Physiology Journal of Neurophysiology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

J Appl Physiol 83: 1775, 1997;
8750-7587/97 $5.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Seale, J. L.
Right arrow Articles by Rumpler, W. V.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Seale, J. L.
Right arrow Articles by Rumpler, W. V.

Vol. 83, Issue 5, 1775-1775, 1997


SPECIAL COMMUNICATION
Synchronous direct gradient layer and indirect room calorimetry

James L. Seale and William V. Rumpler

Diet and Human Performance Laboratory, Beltsville Human Nutrition Research Center, Agricultural Research Service, US Department of Agriculture, Beltsville, Maryland 20705

ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
ACKNOWLEDGEMENTS
FOOTNOTES
REFERENCES

ABSTRACT

Rumpler, James L., and William V. Seale. Synchronous direct gradient layer and indirect room calorimetry. J. Appl. Physiol. 83(5): 1775-1781, 1997.---A dual direct/indirect room-sized calorimeter is used at the Beltsville Human Nutrition Research Center to measure heat emission and energy expenditure in humans. Because the response times of a gradient layer direct calorimeter and an indirect calorimeter are not equivalent, the respective rate of heat emission and energy expenditure cannot be directly compared. A system of equations has been developed and tested that can correct the respective outputs of the direct gradient layer calorimeter and indirect calorimeter for delays due to the response times of the measurement systems. Performance tests using alcohol combustion to simulate a human subject indicate accurate measurements of heat production from indirect (99.9 ± 0.4%), indirect corrected for response time (99.9 ± 0.5%), direct (99.9 ± 0.8%), and direct corrected for response time (99.9 ± 0.8%) calorimetry systems. Results from 24-h measurements in 10 subjects indicate that corrected heat emission is equivalent to (99.8 ± 2.0%) corrected energy expenditure. However, heat emission measured during sleep was significantly greater (14%) than energy expenditure, suggesting a change in the energy stored as heat in the body. This difference was reversed during the day. These results illustrate how the simultaneous measurement of heat emission and energy expenditure provides insights into heat regulation.

heat emission; heat production; energy expenditure

INTRODUCTION

WHOLE BODY ROOM calorimeters are used to measure human energy expenditure and assess the sources of individual variation of energy expenditure over 24-h periods. Calorimeters use direct or indirect techniques to measure 24-h energy expenditure (5, 6, 9-12, 15, 17-20). Direct calorimetry is the measurement of the heat emission, i.e., energy released as heat, of an enclosed subject (2, 5-11, 14-20). Indirect calorimetry is the measurement of the respiratory gas exchange, i.e., oxygen consumption and carbon dioxide production, which is used to calculate energy expenditure (1, 3, 5, 6, 9-11, 15, 18-20). Direct and indirect calorimetry have been combined in room-sized chambers (15), booth- or closet-sized chambers (9, 11), and suit calorimeters (6, 17-19). The room-sized dual direct/indirect calorimeter of the Diet and Human Performance Laboratory at the Beltsville Human Nutrition Research Center (BHNRC) employs a gradient layer direct calorimetry system and an indirect calorimetry system to simultaneously measure heat emission and energy expenditure in humans over a 24-h period (15).

Simultaneous direct/indirect calorimetry measurements can be used to investigate thermal equilibrium and heat exposure, heat regulation during exercise and sleep, the thermic effect of food, and substrate (fat, protein, and carbohydrate) oxidation rates (6, 10, 11, 20). The study of the relationship between heat loss and energy expenditure has been called heat regulation (18). Because the relationship between heat emission and energy expenditure is variable, it is essential that direct and indirect calorimetry reflect the rates of heat emission and energy expenditure as a function of time. A suit calorimeter has been used to study aspects of heat regulation, including sleep, exercise, and sedentary 24-h periods (6, 19). Because a suit calorimeter has little or no excess volume, it is very responsive to changes in heat emission and energy expenditure (6, 19). Unfortunately, gradient layer and indirect room calorimetry systems measure different physical variables that have different response times. To take full advantage of a dual direct/indirect room calorimeter, simultaneous heat emission rates and energy expenditure rates must be determined. This work describes the methods used to correct the time response of the measurements of heat emission and energy expenditure so that they reflect actual whole body metabolic rate and heat loss.

MATERIALS AND METHODS

Chamber description. The dual direct/indirect BHNRC calorimeter chamber has a total physical volume of 20,390 liters and, as previously described, is designed to comfortably house subjects for >= 24 h while measuring the subject's heat emission and energy expenditure (15). The chamber is furnished with a raised carpeted floor, a foldout futon couch/bed, a small desk and chair, a wash basin and portable toilet, and an exercise bike. A remote-control television, videocassette recorder, and AM/FM stereo receiver are positioned outside one of the two windows (0.91 × 0.61 m) for the subject's entertainment. The audio signal from these devices is supplied by small self-amplified stereo speakers mounted within the chamber. The second window (0.61 × 0.91 m) is located within the chamber door, as are two small air locks used to pass meals and waste and other essential materials into and out of the chamber.

Indirect calorimeter. Indirect calorimetry has its basis in the principle that energy expenditure can be determined from respiratory gas exchange (1). Over time, an individual's respiration causes oxygen to be depleted and carbon dioxide to accumulate in the air within the chamber. The concentrations of nitrogen (FN2), oxygen (FO2), and carbon dioxide (FCO2) in the air entering and exiting the calorimeter are measured using a multiple-gas analyzer (model MGA-1200, Perkin-Elmer Industrial Instruments, Pomona, CA) every 2 min. This device is a multiple collector mass spectrometer designed to measure the partial pressure of helium [2% full scale (FS)], methane (1% FS), nitrogen (100% FS), oxygen (22% FS), carbon dioxide (2% FS), and argon (2% FS) in air within 0.1% FS. The multiple-gas analyzer can accurately measure differences in FN2 (±0.003% FS; as determined from changes in inlet air composition over 24 h and differences in inlet and outlet air composition during equilibrium), FO2 (±0.02% FS), and FCO2 (±0.03% FS) in chamber air so that oxygen depletion and carbon dioxide accumulation can be determined (15). The chamber ventilation rate (Vs), i.e., inlet dry airflow rate at standard temperature and pressure, is measured every 5 s using a laminar flow element (CME Vol-O-Flow 11-25-300A, Aerospace Control Products, Davenport, IA), and a 2-min average (typically 1.5 l/s) is determined (15). The volumetric flow rate is a function of the pressure drop across the laminar flow element (Pd; electronic manometer, Datametrics, Wilmington, MA), the inlet air temperature (Ti; model RTD PR-14-2-100, Omega Engineering, Stamford, CT), the absolute air pressure (Pi; model PX623-020A10CV, Omega Engineering), and the inlet water vapor fraction (FH2Oi; model 1200 APS dew point hygrometer, General Eastern Instrumentation, Watertown, MA) (15). Respiratory gas exchange (Vx), i.e., oxygen consumption (VO2) and carbon dioxide production (VCO2), is determined every 2 min from the product of the difference in respiratory gas concentration in outlet (Fxo) and inlet (Fxi) air and the chamber ventilation rate (Eq. 1) (15). The FN2 of the inlet (FN2 i) and outlet air (FN2 o) are used to correct for the difference in the inlet and outlet airflow rates caused by the change in air composition
<A><AC>V</AC><AC>˙</AC></A><SUB><IT>x</IT></SUB> = <A><AC>V</AC><AC>˙</AC></A><SUB>s</SUB>[F<IT>x</IT><SUB>o</SUB>(F<SC>n</SC><SUB>2i</SUB>/F<SC>n</SC><SUB>2o</SUB>) − F<IT>x</IT><SUB>i</SUB>] (l/s) (1)
Because the room calorimeter has a large dry-air volume, i.e., chamber volume (Vc) is ~18,500 liters when corrected to standard temperature and pressure (STP) using Pi, calorimeter air temperature (To), and water vapor fraction of outlet air (FH2Oo) in relation to the ventilation rate (1.5 l/s), the response time (50% of FS change) caused by changes in metabolic rate within the chamber is ~150 min. The production of gas within the calorimeter (Vax) is adjusted to correct for the delay in response time due to Vc (3). The change in metabolic rate over a specific period of time is equal to Vc × change in respiratory gas concentration inside the chamber over that period + total gas production within the chamber during that period. The numerical derivative of outlet gas fraction (dFxo/dt) is determined every 2 min to estimate the change in chamber air composition and to calculate the change in gas production inside the chamber during that interval. The corrected gas production (Vax) is determined by adding the change in gas production within the chamber to the gas production (Vx) using Eq. 2
<A><AC>V</AC><AC>˙</AC></A>a<SUB><IT>x</IT></SUB> = V<SUB>c</SUB>[dF<IT>x</IT><SUB>o</SUB>/d<IT>t</IT> − (F<IT>x</IT><SUB>o</SUB>/F<SC>n</SC><SUB>2o</SUB>)dF<SC>n</SC><SUB>2o</SUB>/d<IT>t</IT>] + <A><AC>V</AC><AC>˙</AC></A><SUB><IT>x</IT></SUB> (l/s) (2)
The rate of energy expenditure (qind) is calculated from VO2 and VCO2 by using the Weir equation (Eq. 3) (21). This relationship can also provide information about the nutritional substrate utilized for metabolic energy (4)
q<SUB>ind</SUB> = 275.0 <A><AC>V</AC><AC>˙</AC></A><SC>o</SC><SUB>2</SUB> + 77.2 <A><AC>V</AC><AC>˙</AC></A><SC>co</SC><SUB>2</SUB> (W) (3)
Total indirect energy expenditure is determined from the sum of the time-averaged rate of respiratory gas production calculated for a period of interest. Indirect calorimetry results can be corrected to account for the response time of the calorimeter volume by using corrected respiratory gas production values (Vax) or by multiplying Vc by the difference between the final and initial air composition within the chamber (residual gas volume) for the period of interest (3). The residual gas volume is added to the time-averaged sum of the gas production rate (Vx) to determine the total gas production (Vx, in liters). This correction ensures that Vx is equal to the total determined for the adjusted gas production (Vax), because they are mathematically equivalent. The daily indirect energy expenditure for human subjects within the calorimeter for a 23.5-h day is also corrected for urinary nitrogen production (UN, in g) (21)
Q<SUB>ind</SUB> = 16,500 V<SC>o</SC><SUB>2</SUB> + 4,630 V<SC>co</SC><SUB>2</SUB> − 9,080 U<SUB>N</SUB> (J) (4)
where VO2 and VCO2 are total VO2 and VCO2, respectively.

Direct calorimetry. Direct calorimetry has its basis in the principle that, in the absence of any external mechanical work, all metabolic energy is emitted from the body as heat. Direct calorimeters work by thermally isolating the environment inside the chamber and accounting for all energy entering and exiting the calorimeter. The difference between the energy exiting the chamber and energy entering the chamber is the energy produced by the individual enclosed within the chamber. The BHNRC direct calorimeter uses a gradient layer to measure the heat flux out of the chamber (2, 14). This heat flux (qg) is driven by the temperature difference between objects inside the calorimeter and outside the gradient layer on the chamber walls, ceiling, and subfloor (15). Similarly, the heat fluxes through the door (qd) and window (qw) of the calorimeter chamber are driven by the difference in the chamber temperature and the external environment. Because the quadruple-pane glass and insulated door resist heat loss, this heat flux (qd and qw) is minimal (15).

Heat is transferred into the chamber as electrical power for lights, fans, stereo speakers, and activity monitors (ql) and must be accounted for. The current and voltage from a 12-V direct-current power supply are measured outside the calorimeter to determine the electrical power (ql = vl × il, where v is voltage and i is current) entering the chamber (15). The electrical power used in the chamber is kept to a minimum to reduce the overall contribution to the total energy flux and minimize the variability caused by the electrical energy flux. Because there is no net mechanical work done in the chamber, the electrical energy entering the calorimeter is dissipated and measured as heat.

Heat is also transferred to and from the calorimeter as a result of differences in the temperature and humidity of the air entering (Ti and FH2Oi) and exiting (To and FH2Oo) the chamber. The heat exchanged as a result of changes in chamber humidity or evaporative heat loss is defined as the latent heat flux (qlat). The latent heat flux is calculated by multiplying the difference in the amount of water vapor in the inlet and outlet air by the heat of vaporization of water at the absolute outlet air temperature (Ta o = To + 273.15 K; Eq. 6). The water vapor fraction of the air is calculated from the dew point temperature and the air pressure (Eq. 5). The dew point of inlet (dpi) and outlet (dpo) air is measured with a chilled mirror dew point meter (model 1200 APS dew point hygrometer, General Eastern Instrumentation). Ti and To are measured with resistive temperature devices (model PR-14-2-100, Omega Engineering). The temperature of the air within the calorimeter and the outlet air temperature are equivalent (15). Air pressure (Pa) is measured with an absolute air pressure transducer (model PX623-050A10V, Omega Engineering). Heat transfer from the chamber due to changes in the thermal energy contained in the ventilating air is called sensible heat flux (qsen) (16), which is determined from the absolute temperature (Ta y) of air entering (Ta i = Ti + 273.15 K) and exiting (Ta o = To + 273.15 K) the chamber, the capacity to store heat (cpxy) of inlet and outlet dry air (cpa i and cpa o, in J/mol) and water vapor (cpw i and cpw o, in J/mol), &vdot;s, and FH2O i (Eqs. 7 and 8) (13, 15)
F<SC>h</SC><SUB>2</SUB><SC>o</SC> = (610.78 <IT>e</IT><SUP>17.2694[dp/(dp + 238.3)]</SUP>)/P<SUB>a</SUB> (5)
q<SUB>lat</SUB> = 3.365 <A><AC>V</AC><AC>˙</AC></A><SUB>s</SUB>[F<SC>h</SC><SUB>2</SUB><SC>o</SC><SUB>o</SUB>(FN<SUB>2i</SUB>/F<SC>n</SC><SUB>2o</SUB>) − F<SC>h</SC><SUB>2</SUB><SC>o</SC><SUB>i</SUB>]
(595.4 − 0.53T<SUB>ao</SUB>) (W) (6)
c<SUB>p<SUB><IT>xy</IT></SUB></SUB>= <IT>A</IT><SUB>1<SUB><IT>x</IT></SUB></SUB>T<SUB>a <IT>y</IT></SUB> + <IT>A</IT><SUB>2<SUB><IT>x</IT></SUB></SUB>T<SUP>2</SUP><SUB>a <IT>y</IT></SUB>/2 + <IT>A</IT><SUB>3<SUB><IT>x</IT></SUB></SUB>T<SUP>3</SUP><SUB>a <IT>y</IT></SUB>/3 + <IT>A</IT><SUB>4<SUB><IT>x</IT></SUB></SUB>T<SUP>4</SUP><SUB>a <IT>y</IT></SUB>/4 (J/mol) (7)
where A1a and A1w are polynomial coefficients equal to 28.106 and 32.238, A2a and A2w are polynomial coefficients equal to 1.967 × 10-3 and 1.924 × 10-4, A3a and A3w are polynomial coefficients equal to 4.802 × 10-6 and 1.055 × 10-6, and A4a and A4w are polynomial coefficients equal to -1.966 × 10-9 and -3.595 × 10-9 (13)
q<SUB>sen</SUB> = (<A><AC>V</AC><AC>˙</AC></A><SUB>s</SUB>/22.414){[c<SUB>p<SUB>a o</SUB></SUB>(F<SC>n</SC><SUB>2 i</SUB>/F<SC>n</SC><SUB>2 o</SUB>) − c<SUB>p<SUB>a i</SUB></SUB>]
 + F<SC>h</SC><SUB>2</SUB><SC>o</SC><SUB>i</SUB>[c<SUB>p<SUB>w o</SUB></SUB> (F<SC>n</SC><SUB>2 i</SUB>/F<SC>n</SC><SUB>2 o</SUB>) − c<SUB>p<SUB>w i</SUB></SUB>]}  (W) (8)

The direct calorimeter results represent an energy balance of the chamber. The total energy flux out of the chamber (qdir) is the sum of the component rates of energy transfer through the gradient layer system, the air circulation, and electrical energy (Eq. 9) (15).
q<SUB>dir</SUB> = q<SUB>d</SUB> + q<SUB>g</SUB> + q<SUB>w</SUB> + q<SUB>sen</SUB> + q<SUB>lat</SUB> − q<SUB>l</SUB> (W) (9)
Heat is stored in the chamber, and this can delay the response time of the calculation for qdir (Eq. 9) and can be a source of error when direct calorimeter results are determined. The direct calorimeter measurement can be corrected (qadir) to account for the heat stored in the air and furnishings within the chamber. Similar to the calculations used to correct indirect calorimeter results (Eq. 2), the water stored in the chamber as vapor can be determined by multiplying the change in the outlet water fraction (dFH2O/dt; the numerical derivative of FH2O) by Vc. The heat stored within the chamber as vaporized water (qalat) is then determined by multiplying the change in the amount of water vapor stored in the chamber by the latent heat of vaporization (Eq. 10). Heat stored in the chamber due to changes in the calorimeter air temperature is determined by calculating the change in the heat content of the chamber dry air and water vapor over time (capx) from the change in outlet air temperature (dTa o/dt) and outlet air temperature (Eq. 11) and multiplying by Vc with a correction for the change in chamber dry air volume with time [(dFN2 o/dt)/FN2 o; Eq. 12]. Heat is also stored in the actual material of the calorimeter chamber, and the output from the gradient layer door and window must be corrected to account for the stored heat (qacal). The amount of heat stored in the material of the chamber is directly related to the change in calorimeter air temperature as a function of time (dTa o/dt; Eq. 13). Similarly, heat is stored in the furniture inside the calorimeter chamber (qafur) and is also related to the change in air temperature (dTa o/dt). The corrected direct calorimeter output is determined from the sum of the heat flux and heat storage variables (Eq. 14)
qa<SUB>lat</SUB> = 3.365V<SUB>c</SUB>[dF<SC>h</SC><SUB>2</SUB><SC>o</SC>/d<IT>t</IT> − (F<SC>h</SC><SUB>2</SUB><SC>o</SC><SUB>o</SUB>/F<SC>n</SC><SUB>2 o</SUB>)dF<SC>n</SC><SUB>2 o</SUB>/d<IT>t</IT>]
⋅ (595.4 − 0.53T<SUB>a o</SUB>) + q<SUB>lat</SUB> (W) (10)
ca<SUB>p<SUB><IT>x</IT></SUB></SUB> = (dT<SUB>a o</SUB>/d<IT>t</IT>)[<IT>A</IT><SUB>1<SUB><IT>x</IT></SUB></SUB> + <IT>A</IT><SUB>2<SUB><IT>x</IT></SUB></SUB>T<SUB>a o</SUB> + <IT>A</IT><SUB>3<SUB><IT>x</IT></SUB></SUB>T<SUP>2</SUP><SUB>a o</SUB> + <IT>A</IT><SUB>4<SUB><IT>x</IT></SUB></SUB>T<SUP>3</SUP><SUB>a o</SUB>] (J/mol) (11)
qa<SUB>sen</SUB> = (V<SUB>c</SUB>/22.414){ca<SUB>p<SUB>a</SUB></SUB> + F<SC>h</SC><SUB>2</SUB><SC>o</SC><SUB>o</SUB>ca<SUB>p<SUB>w</SUB></SUB>
 − [(c<SUB>p<SUB>a o</SUB></SUB> + F<SC>h</SC><SUB>2</SUB><SC>o</SC><SUB>o</SUB>c<SUB>p<SUB>w o</SUB></SUB>)/F<SC>n</SC><SUB>2 o</SUB>]dF<SC>n</SC><SUB>2 o</SUB>/d<IT>t</IT>} + q<SUB>sen</SUB> (W) (12)
qa<SUB>cal</SUB> = 3,900(dT<SUB>a o</SUB>/d<IT>t</IT>) + q<SUB>d</SUB> + q<SUB>g</SUB> + q<SUB>w</SUB> (W) (13)
qa<SUB>dir</SUB> = qa<SUB>cal</SUB> + qa<SUB>sen</SUB> + qa<SUB>lat</SUB> + qa<SUB>fur</SUB> − q<SUB>l</SUB> (W) (14)
Total direct heat emission (Qadir) is determined from the sum of the time-averaged rate of heat emission (qadir) for the period of interest. Direct calorimetry results are corrected to account for the response time of the direct calorimeter by using the adjusted values of the heat flux (Qadir) or by correcting the adjusted total heat flux (Qdir) for the initial and final conditions for the period of interest using Eqs. 10-12. This correction ensures that the total for the heat emission (Qdir) is equal to the total determined for the adjusted heat emission (Qadir), because they are mathematically equivalent.

Performance test. The overall performance of the direct and indirect calorimetry system is evaluated using electrical heating and alcohol combustion procedures. The performance tests are used to determine the stability, response time, accuracy, and repeatability of the calorimeter measurement and data-acquisition systems.

Electrical heating within the chamber is used to assess the performance of the direct calorimeter systems. A resistive heating element is placed within the chamber and connected to a direct-current power supply (15). The chamber is closed and allowed to reach equilibrium before the heating element is energized. The current and voltage powering the heating element are continuously measured using the data-acquisition system. The element is energized at a constant level for several hours before the power is shut off, and the chamber is allowed to return to equilibrium. The total amount of energy and the power used to energize the heating element are compared with the total heat recovered and the heat flux measured during the experiment to assess the direct calorimetry systems.

Alcohol combustion is used to test the step response of the direct and indirect calorimetry systems to a known amount of heat and respiratory gas production (15). Alcohol lamps are filled with absolute ethanol, capped, and weighed before being placed in the calorimeter. The calorimeter data-acquisition systems are started ~1 h before the lamps are placed in the chamber to establish baseline equilibrium. After the baseline equilibrium period, the lamps are placed in the chamber, the caps are removed, and the lamps are ignited and allowed to burn for 3-18 h before they are extinguished and capped to prevent any alcohol from evaporating. After the chamber is allowed to return to equilibrium, the capped lamps are removed and weighed again. To ignite and extinguish the alcohol lamps, one of the air locks in the door of the calorimeter is opened for ~10 s. The error incurred by opening the air lock for 10 s was found to make no discernible difference in the direct heat recovered and in the respiratory gas recovery. The accuracy of the calorimeter is determined by comparing the amount of heat recovered by the direct system and the respiratory gas exchange of the indirect system with the theoretical amounts that result from the alcohol combusted (1.366 MJ/mol). The response time is measured by determining the time required for the uncorrected and corrected direct and indirect calorimetry systems to reach 50% of FS response after the lamps are ignited and extinguished. The absolute alcohol is purchased in small sealed bottles to prevent the absorption of water vapor from the air. The number of lamps used and the time of combustion are changed to vary the magnitude of and total heat load.

Human subjects. Results from 10 human experiments are presented to demonstrate the response of the direct and indirect calorimetry systems to the fluctuation in metabolic rate observed in humans. Human subjects were placed in the calorimeter for 2.5 days to determine daily energy expenditure. Results are presented for data recorded from 12 AM to 12 AM the following day for 2 consecutive days. Subjects were fed a mixed diet at a level to balance energy expenditure while in the chamber. While in the calorimeter, the subjects received three meals, had a full night's sleep, and were allowed to watch television, listen to the radio, or read but were not allowed to exercise. All urine was collected for the 24-h period and analyzed for nitrogen content. The 24-h and overnight urine excretions were used to calculate indirect calorimetry results.

Statistical analysis. An analysis of variance was used to determine significant differences between theoretical uncorrected and corrected indirect calorimeter results for VO2, VCO2, water production, and respiratory quotient for 25 alcohol combustion experiments (PROC GLM, SAS Institute, Cary, NC). An analysis of variance was used to determine significant differences between theoretical uncorrected and corrected indirect and direct calorimeter results for response time and heat recovery for 25 alcohol combustion experiments (PROC GLM). An analysis of variance was used to determine significant differences between heat emission and energy expenditure measurements over 24 h, during sleep and daylight periods (PROC GLM). Subject number was used as a covariant to eliminate between-subject variation in the statistical comparison.

RESULTS

Respiratory gas exchange, respiratory quotient, response time, and heat recovered using indirect calorimetry and the response time and heat recovered using direct calorimetry from 25 alcohol combustion experiments are summarized in Table 1. Also presented in Table 1 is the ratio of heat recovered to the amount produced by the alcohol burned for uncorrected indirect (99.9 ± 0.4%), corrected indirect (99.8 ± 0.5%), uncorrected direct (99.9 ± 0.8%), and corrected direct (99.9 ± 0.9%) calorimetry systems. The total heat recovered by the uncorrected and corrected direct and indirect calorimetry systems was not significantly different from the heat produced by the alcohol combustion. VO2 and VCO2 for uncorrected and corrected indirect calorimetry were not significantly different from the amount consumed and produced by the alcohol combustion. Water vapor production measured by uncorrected and corrected indirect calorimetry was significantly less than the water produced by the alcohol combustion. Because water can change phases between vapor and liquid at room temperature, some water is stored in the calorimeter furnishings. This has no effect on indirect calorimetry, and because the heat associated with the evaporation and condensation of water is measured by the direct system, it does not affect the direct calorimetry results. The response time of the uncorrected indirect calorimeter (151 min) was significantly greater (P < 0.0001) than the response time of the uncorrected direct calorimeter (10.49 min), and both were significantly greater (P < 0.0001) than the response times of the corrected indirect (3.54 min) and direct (3.50 min) calorimetry systems. The response times for the corrected indirect and direct calorimetry systems were not significantly different.

Table  1.   Results from alcohol combustion experiments for uncorrected and corrected indirect calorimetry and direct calorimetry
Uncorrected for Response Time
Corrected for Response Time
Mean ± SD Range %Recovery Mean ± SD Range %Recovery
Indirect
VCO2, liters 192.7 ± 65.3  90.1 to 357.1 99.8 ± 0.6  192.7 ± 65.3  90.1 to 356.6 99.8 ± 0.6 
VO2, liters  -288.6 ± 96.4   -137.1 to -531.4 99.8 ± 0.7   -288.6 ± 96.2   -137.4 to -523.9 99.9 ± 0.8 
VH2O, liters 266.6 ± 113.9  130.2 to 526.6 89.5 ± 13.7  267.3 ± 115.1  129.7 to 525.2 89.7 ± 13.9 
RQ (VCO2/VO2) 0.667 ± 0.007  0.649 to 0.678 0.667 ± 0.007  0.649 to 0.680
RT, min 151 ± 6* 140 to 166 3.54 ± 0.44dagger 2.42 to 4.18
Qind, MJ 5.86 ± 1.97  2.77 to 10.85 99.9 ± 0.4  5.86 ± 1.96  2.77 to 10.77 99.9 ± 0.5 
Direct
RT, min 10.49 ± 2.36Dagger 7.12 to 15.72 3.50 ± 0.38dagger 2.82 to 4.74
Qdir, MJ 5.86 ± 1.95  2.75 to 10.97 99.9 ± 0.8  5.87 ± 1.95  2.75 to 10.96 99.9 ± 0.8
Values are from 25 experiments. %Recovery, 100 × recovered amount/amount calculated for alcohol burned; VCO2, total volume CO2 production; VO2, total volume O2 consumption; VH2O, total volume H2O production; RQ, respiratory quotient; RT, response time for 50% of full scale; Qind, heat emission. Values with different symbols (*, dagger , Dagger ) are significantly different (P < 0.0001).

The results of a typical alcohol combustion experiment are presented in Figs. 1 and 2. Figure 1 shows the uncorrected heat production measured by the direct and indirect calorimetry systems as a function of elapsed time. Figure 2 shows the corrected heat production measured by the corrected direct and indirect calorimetry systems as a function of elapsed time. The exponential response to the step increase and decrease in heat production shown in Fig. 1 is characteristic of the uncorrected direct and indirect room calorimeter. The quickened response resulting from the application of the system of equations to correct the direct and indirect room calorimeter illustrates the sharp increase and decrease in heat recovery caused by igniting and extinguishing the alcohol lamps in Fig. 2. The average root-mean-square difference between corrected direct and corrected indirect calorimetry output for the heat recovery rate determined during alcohol combustion was 1.32%.

Fig. 1. Heat production as a function of time for direct (qdir) and indirect (qind) calorimetry systems for a typical alcohol combustion experiment.
[View Larger Version of this Image (12K GIF file)]

Fig. 2. Corrected heat production as a function of time for direct (qadir) and indirect (qaind) calorimetry systems for a typical alcohol combustion experiment.
[View Larger Version of this Image (12K GIF file)]

The difference between corrected indirect and corrected direct calorimeter results for heat recovery (Qaind - Qadir) was plotted against the average [(Qaind - Qadir)/2] from all 25 alcohol combustion experiments in Fig. 3. The difference was 0.004 ± 0.052 (SD) MJ. When calculated as a percentage of the heat recovered from the combustion of alcohol, the difference was 0.03 ± 0.95% (SD). This is an indication that corrected indirect calorimetry was not significantly different from corrected direct calorimetry in measuring the heat recovered from 25 alcohol combustion experiments.

Fig. 3. Difference between corrected indirect and corrected direct (Qaind - Qadir) calorimetry as a function of mean heat recovered [(QAind + QAdir)/2] during 25 alcohol combustion experiments.
[View Larger Version of this Image (13K GIF file)]

Results of respiratory quotient and energy expenditure from indirect and indirect corrected and energy expenditure from direct and direct corrected measurements in 10 human subjects for two consecutive 24-h sleep and daytime periods are summarized in Table 2. Also shown in Table 2 are the ratios of the uncorrected to corrected measurements and the direct to indirect measurements. The energy expenditure of an adult human measured over a 24-h period by uncorrected direct and indirect calorimetry is presented in Fig. 4. The energy expenditure of the same subject measured for the same 24-h period by corrected direct and indirect calorimetry is presented in Fig. 5. Figures 4 and 5 illustrate the difference in the corrected and uncorrected measurements of the rate of energy expenditure as a function of time by direct and indirect calorimetry. The results indicate that direct and indirect calorimetry give identical values for heat production in humans when integrated over a 24-h period when initial and final chamber conditions or when the response of the calorimetry systems is corrected. The results also indicate that whereas 24-h results are identical (0.22 ± 2.04%), heat emission during sleep, as determined by integrating corrected direct calorimetry values over the sleep period, is significantly greater (0.22 ± 0.09 MJ) than energy expenditure measured by corrected indirect calorimetry for the same period, and heat emission during the daytime (6 AM-6 PM), as determined by integrating corrected direct-calorimetry values over the daytime period, is significantly less (-0.26 ± 0.18 MJ) than energy expenditure measured by corrected indirect calorimetry for the same period. These results indicate that heat is lost (destored) from the body during sleep and stored during the day.

Table  2.   Results from 2-day experiments with human subjects for uncorrected and corrected indirect RQ and EE and direct EE for 24 h during sleep and daytime
Uncorrected for Response Time Corrected for Response Time 100 × (Corrected/ Uncorrected)
24-h EE
Indirect RQ 0.847 ± 0.010  0.846 ± 0.010  100.0 ± 0.1 
EE, MJ/day
  Indirect 8.82 ± 1.26  8.82 ± 1.26  100.0 ± 0.0 
  Direct 8.83 ± 1.27  8.81 ± 1.29  99.7 ± 0.5 
  Direct - indirect 0.00 ± 0.18   -0.02 ± 0.18 
Sleep EE
Indirect RQ 0.823 ± 0.017  0.829 ± 0.014  100.8 ± 0.5 
EE, MJ
  Indirect 1.55 ± 0.22* 1.54 ± 0.22dagger 99.2 ± 0.4 
  Direct 1.79 ± 0.20* 1.76 ± 0.20dagger 98.0 ± 0.5 
  Direct - indirect 0.24 ± 0.09  0.22 ± 0.09 
Daytime EE
Indirect RQ 0.853 ± 0.012  0.850 ± 0.012  99.7 ± 0.2 
EE, MJ
  Indirect 4.85 ± 0.73sDagger 4.86 ± 0.73§ 100.2 ± 0.2 
  Direct 4.52 ± 0.68Dagger 4.60 ± 0.68§ 101.9 ± 1.2 
  Direct - indirect  -0.33 ± 0.17   -0.26 ± 0.18 
Values are means ± SD for 10 subjects. RQ, respiratory quotient; EE, energy expenditure; daytime, 6 AM-6 PM. Values with symbols (*, dagger , Dagger , § ) are significantly different (P < 0.0001).

Fig. 4. Direct and indirect calorimetry results as a function of time of day for a typical 24-h human calorimetry experiment.
[View Larger Version of this Image (14K GIF file)]

Fig. 5. Corrected direct and indirect calorimetry results as a function of time of day for a typical 24-h human calorimetry experiment.
[View Larger Version of this Image (19K GIF file)]

DISCUSSION

Simultaneous measurement of direct heat production with a gradient layer calorimeter and energy expenditure with an indirect calorimeter has been accomplished with the BHNRC dual chamber for several years. The incompatibility of the response time of the direct and indirect systems has limited the usefulness of the dual calorimeter. With the development of a set of corrective equations to compensate for the response times of the different calorimetry measurement systems, it is possible to measure simultaneous heat emission and energy expenditure in a room-sized chamber.

Results from the alcohol combustion experiments indicate that the direct and indirect calorimetry systems give repeatable and accurate step responses to known amounts of energy produced and respiratory gas exchange within the chamber. These results demonstrate that uncorrected direct and indirect calorimetry results can be adjusted for starting and ending conditions over periods of interest to yield the same results. These results also demonstrate that the corrective equations can be applied to direct and indirect calorimeter outputs to compensate for the time response of the respective measurement systems. Results confirm that it is possible to accurately and simultaneously measure human heat emission and energy expenditure in a room-sized chamber.

The 24-h human experiment demonstrates the response of the corrected direct and indirect calorimetry measurement systems to human subjects. The results indicate that heat emissions and energy expenditures associated with sleep, rest, spontaneous activity, and possibly exercise can be partitioned from the 24-h total. Whereas the primary objective of the calorimeter is the accurate measurement of 24-h energy expenditure and heat emission, much additional information will be gained from observing how energy expenditure and heat emission are distributed within a 24-h period. Results from the 10 human subjects indicated that heat emission was 14% greater than energy expenditure during sleep. Heat emission during the day after the subject awakened was lower than energy expenditure. Total 24-h heat emission and energy expenditure were not different. These results suggest that heat stored within the body is liberated during sleep and stored again in the body during the day and are similar to results for 24-h sedentary heat emission and energy expenditure measured with a suit calorimeter (18).

The BHNRC dual direct/indirect calorimeter represents an accurate tool for research in human energy metabolism and heat regulation. The implications of a device that can measure simultaneous heat emission and energy expenditure include investigation of heat regulation and storage during sleep, exercise, and cold and heat exposure. Another possible application is determining the relationship of heat emission and storage to substrate oxidation rates (carbohydrate, fat, and protein) in response to a meal or physical activity as a function of time during a 24-h period.

ACKNOWLEDGEMENTS

Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.

FOOTNOTES

Address for reprint requests: J. L. Seale, DHPL, BHNRC, ARS, USDA, Rm. 317, Bldg. 308, BARC-East, 10300 Baltimore Ave., Beltsville, MD 20705.

Received 5 August 1996; accepted in final form 21 July 1997.

REFERENCES

1. Atwater, W. O., and F. G. Benedict. A Respiratory Calorimeter With Applicances for the Direct Determination of Oxygen. Washington, DC: Carnegie Institute, 1905. (Publ. 42)
2. Benzinger, T. H., and C. Kitzinger. Direct calorimetry by means of the gradient layer principle. Rev. Sci. Instrum. 20: 849-860, 1949. [Medline]
3. Brown, D., T. J. Cole, M. J. Dauncey, R. W. Marrs, and P. R. Murgatroyd. Analysis of gaseous exchange in open-circuit indirect calorimetry. Med. Biol. Eng. Comput. 22: 333-338, 1984[Medline].
4. Consolazio, F. J., R. E. Johnson, and L. J. Pecora. Physiological Measurements of Metabolic Functions in Man. New York: McGraw-Hill, 1963, p. 1-55.
5. Dauncey, M. J., P. R. Murgatroyd, and T. J. Cole. A human calorimeter for the direct and indirect measurement of 24 h energy expenditure. Br. J. Nutr. 39: 557-566, 1978[Medline].
5a. General Eastern Instrumentation. General Instruction Manual. Watertown, MA: General Eastern Instrumentation, 1985.
6. Hambraeus, L., A. Sjodin, P. Webb, A. Forslund, K. Hambraeus, and T. Hambraeus. A suit calorimeter for energy balance studies on humans during heavy exercise. Eur. J. Appl. Physiol. 68: 68-73, 1994.
7. Jacobsen, S., O. Johansen, and L. Garby. 5.8 m3 human heat-sink calorimeter with online data acquisition, processing and control. Med. Biol. Eng. Comput. 20: 29-36, 1982[Medline].
8. Jacobsen, S., O. Johansen, and L. Garby. A 24-m3 direct heat-sink calorimeter with online data acquisition, processing, and control. Am. J. Physiol. 249 ((Endocrinol. Metab. 12): E416-E432, 1985[Abstract/Free Full Text].
9. Jequier, E. Direct and indirect calorimetry in man. In: Substrate and Energy Metabolism in Man, edited by J. S. Garrow, and D. Halliday. London: Libbey, 1985, p. 82-92.
10. Jequier, E., K. Acheson, and Y. Schutz. Assessment of energy expenditure and fuel utilization in man. Annu. Rev. Nutr. 7: 187-208, 1987[Medline].
11. Murgatroyd, P. R., P. S. Shetty, and A. M. Prentice. Techniques for the measurement of human energy expenditure: a practical guide. Int. J. Obes. 17: 549-568, 1993.
12. Nagle, F. J., P. Webb, and D. M. Wanta. Energy exchange in downhill and uphill walking: a calorimetric study. Med. Sci. Sports Exerc. 22: 540-544, 1990[Medline].
13. Obert, E. F. Concepts of Thermodynamics. New York: McGraw-Hill, 1960.
14. Poppendiek, H. F., G. L. Hody, and J. J. Kacirk. The use of direct calorimetry in physiological, pharmaceutical, and medical research. Proc. San Diego Biomed. Symp. 15: 125-130, 1976.
15. Seale, J. L., W. V. Rumpler, and P. W. Moe. Description of a direct-indirect room-sized calorimeter. Am. J. Physiol. 260 ((Endocrinol. Metab. 23): E306-E320, 1991[Abstract/Free Full Text].
16. Spinnler, G., E. Jequier, R. Favre, M. Dolivo, and A. Vannotti. Human calorimeter with a new type of gradient layer. J. Appl. Physiol. 35: 158-165, 1973[Free Full Text].
17. Webb, P. Human Calorimeters. New York: Praeger, 1985. (Endocrinol. Metab. Ser.)
18. Webb, P. The physiology of heat regulation. Am. J. Physiol. 268 ((Regulatory Integrative Comp. Physiol. 37): R838-R850, 1995[Abstract/Free Full Text].
19. Webb, P., J. F. Annis, and S. J. Troutman. Human calorimetry with a water-cooled garment. J. Appl. Physiol. 32: 412-418, 1972[Free Full Text].
20. Webb, P., J. F. Annis, and S. J. Troutman. Energy balance in man measured by direct and indirect calorimetry. Am. J. Clin. Nutr. 33: 1287-1298, 1980[Abstract/Free Full Text].
21. Weir, J. B. D. V. New methods for calculating metabolic rate with special reference to protein metabolism. J. Physiol. (Lond.) 109: 1-9, 1949.



This article has been cited by other articles:


Home page
 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
K. J. Kaiyala and D. S. Ramsay
Assessment of heat production, heat loss, and core temperature during nitrous oxide exposure: a new paradigm for studying drug effects and opponent responses
Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2005; 288(3): R692 - R701.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Seale, J. L.
Right arrow Articles by Rumpler, W. V.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Seale, J. L.
Right arrow Articles by Rumpler, W. V.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online