This article was downloaded by: [University of Calgary] On: 05 February 2015, At: 03:30 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Ergonomics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/terg20
Oxygen consumption during fire suppression: error of heart rate estimation a
a
b
b
c
c
M. SOTHMANN , K. SAUPE , P. RAVEN , J. PAWELCZYK , P. DAVIS , C. DOTSON , F. d
LANDY & M. SILIUNAS
a
a
Department of Human Kinetics , School of Allied Health Professions, University of Wisconsin-Milwaukee , Milwaukee, WI, 53201, USA b
Department of Physiology , Texas College of Osteopathic Medicine , Forth Worth, TX, 76107, USA c
ARA/Human Factors, Inc , Burtonsville, MD, 20866, USA
d
Department of Psychology , Pennsylvania State University , State College, PA, 16803, USA Published online: 30 May 2007.
To cite this article: M. SOTHMANN , K. SAUPE , P. RAVEN , J. PAWELCZYK , P. DAVIS , C. DOTSON , F. LANDY & M. SILIUNAS (1991) Oxygen consumption during fire suppression: error of heart rate estimation, Ergonomics, 34:12, 1469-1474, DOI: 10.1080/00140139108964890 To link to this article: http://dx.doi.org/10.1080/00140139108964890
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
ERGONOMICS,1991, VOL. 34, NO. 12,1469- 1474
Oxygen consumption during fire suppression: error of heart rate estimation
Downloaded by [University of Calgary] at 03:30 05 February 2015
M.SOTHMANN,~ K. SAUPE,'P. RAVEN,^ J. PAWELCZYK,~ P.DAVIS,~ C.DOTSON,) F. LANDY,~ and M. SILIUNAS,' 'Department of Human Kinetics, School of Allied Health Professions, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA 2Department of Physiology, Texas College of Osteopathic Medicine, Forth Worth, TX 76 107, USA 3ARA/Human Factors, Inc. Burtonsville, MD 20866, USA 'Department of Psychology, Pennsylvania State University, State College PA 16803, USA
Keywords: Oxygen~consumption;Exercise; Firefighting; Physical fitness. Ten male firefighters were tested on a treadmill to determine their heart rate (HR) x oxygen consumption ( V 04relationship. These men then peFformed a simulated fire suppression protocol during which HR and VO, were measured. simultaneously by a protable physiological monitoring system. Average VO, in the simulated setting was 3 I.0+7.0 ml-kg-'.min-' at a HR of 176 + 9 bpm. This V02 was significantly (p50.05) less than the V 0 2 that would have been predicted by treadmill testing (38.9 f 5.0ml.kg-1.min-1) at a corresponding HR. Fifty-nine per cent of this variability could be accounted for by regression analysis. Firefighters worked on average at 73k 10% V 0 2 max with a range of 54% to 88%. There was a significant (-0.82; ps0-05) inverse relationship between performance time of the fire suppression protocol and the relative intensity of YO2 max at which the firefighters worked. These findings indicate that the prediction of energy expenditure from HR is not straightforward in fire suppression settings. Furthermore, the relative intensity of work firefighters self-select is variable and should be considered as an additional physiological determinant of work behaviour. 1. Introduction An accurate assessment of oxygen consumption (30,)provides important information for determining the energy expenditure reqirements of physically demanding tasks. Accordingly, monitoring heart rate (HR) to predict VO* has been used extensively in sport and occupational settings (Astrand and Rodahl 1977). This and HR approach is based upon the linear relationship between the increases in ~0~ during submaximal dynamic physical work performed on the treadmill or ergometer (Clausen 1978). Typically, the HR x 30, relationship is established for each individual during treadmill testing. Heart rate measurements taken in the field are then compared to the data derived from laboratory testing to estimate the corresponding v 0,. Laboratory studies have identified numerous factors that can potentially alter the relationship between HR and VO, in occupational settings. These include but are not limited to the presence of heat (Duncan el al. 1979), isometric vs isotonic muscle contraction, and upper vs lower body work (McKirnan and Froelicher 1988). Firefighting is one occupation where these factors are present. Furthermore, considerations for personal safety preclude interference with the operation of the OO~bOt39/91 $3.00 C3 1991 Taylor & Francis Ltd.
1470
M. Sothmann et al.
Downloaded by [University of Calgary] at 03:30 05 February 2015
self-contained breathing apparatus (SCBA) or restriction of movement in emergency settings. Thus, portable oxygen consumption measuring devices cannot be used in live emergencies. These limitations have 'restricted data collection on the physiological responses, particularly energy expenditure, of firefighters in actual emergency settings. This is important because recent federal legislative and judicial initiatives pertaining to public safety occupations and the ongoing desire to ensure that workers have the capability to effectively perform have accented the need for a more complete understanding of the physiological demands imposed by firefighting. In the present study, we examine the potential of using HR to predict VO, in a fire suppression setting. Furthermore, we document the association between ~0~ consumption and performance of a standardized fire suppression protocol. 2. Methods 2.1. Subjects Ten experienced men firefighters for a large municipal US fire department volunteered to participate in the research. Informed consent was obtained consistent with policies established by the University of Wisconsin-Milwaukee Institutional Review Board. They reported taking no medication and were not under medical care. All individuals were in apparent good cardiovascular health as indicated by an exercise stress test with electrocardiogram monitored by a cardiologist. Pulmonary function tests revealed no marked impairment. Table 1 indicates values of relevant physiological and anthropometric characteristics. Values obtained for ~0~max and the Davis et al. ( I 982) physical fitness test for firefighters indicate an 'average' level of physical fitness. Table I . Physiological and anthropometric characteristics of participants. Age, yrs Height, cm Weight, kg Lean body weight, kg Per cent fat, % Maximal VO,, I.min-' Maximal VO,, 5 ml.kg-I.rnin-' Physical fitness core* Values are mean + standard deviation. *Physical fitness score based upon the Davis el a/. (1982) criteria.
2.2. Apparatus The H R x VO, relationship for each individual was established during a graded exercise stress test to volitional fatigue. The modified Balke treadmill protocol was employed. Oxygen consumption was determined by open-circuit spirometry using procedures described previously (Sothmann et al. 1987). Analysis of fractional concentrations of OZ and CO, in expired air was performed using Applied Electrochemistry O2 and COz analysers (Ametek, Pittsburg, PA). Heart rate and blood pressure as a safety measure were monitored by electrocardiogram and bracial artery ascultation, respectively. Simultaneous monitoring of HR and VO, at submaximal exercise on the treadmill was then used to determine the H R x VO, relationship for each individual.
Downloaded by [University of Calgary] at 03:30 05 February 2015
Oxygen consumption during fire suppression
1471
The men then completed a simulated fire suppression protocol during which they wore a self-contained physiological recording system (Oxylog: Ambulatory Monitoring, Ardsley, NY) integrated with the SCBA for determination of VO, consumption and heart rate. The Oxylog measured the PO, difference between inspired and expired air. Three adjustments were made to a MSA Ultravue facepiece to allow it to be used in concert with the Oxylog. First, a turbine used to measure inspired air flow was built into the inspired side of the MSA Ultravue facemask; second, a gas sampling port was placed in the low pressure inspired breathing hose to ailow for continual sampling of the inspired air from the SCBA tank; and third, the pressure-demand valve on the MSA facemask was modified such that a hose could be attached to direct expired air to the Oxylog. The signals from the Oxylog and the electrocardiographic signal from electrodes positioned in the CM5 configuration were stored on magnetic tape by a Medilog MR-10 recorder. The Oxylog and the MR-I0 recorder were worn in the outside pockets of the subject's turn-out coat. The weight of the Oxylog and Medilog recorder and their associated cables totaled 3.6 kg. Values for V O , were read off directly from the Oxylog meter at designated timepoints during performance of the simulated fire suppression protocol. Heart rates corresponding to those segments were determined from the Medilog recordings. The Oxylog was calibrated and tested each day prior to use. The daily testing of the Oxylog consisted of calibrating it according to the manufacturer's instructions, drawing a gas of known 0, concentration through the inspired and expired O2 sensors, and outfitting a research assistant with the OxylogISCBA during 5 min of treadmill walking at a steady metabolic state known to elicit a VO, of 1.421.min-'. 2.3. Procedures Data pertaining to the validity of the simulation protocol and selected aspects of the V O ~measurements as they related to performance of the protocol have been published previously on this group of firefighters (Sothmann et al. 1990). Subjects completed the following sequence of tasks while wearing their turn-out gear and SCBA outfitted with the Oxylog. They were instructed to complete the tasks, 'as if involved in an actual firefighting situation'; ( I ) climb 4 flights of stairs, a total of 84 stairs (6 stairs are approx. 1 m), while carrying a standard fire-axe; (2) enter a 54°C room filled with non-toxic smoke and search for a dummy; (3) remove a 68 kg dummy from the room and drag it 15 m down a hallway; (4) re-enter the smoke room and perform 20 pulls of a simulated pike pole; (5) walk down three flights of stairs, pick up a 19 litre (23 kg) hand pump and carry it back up three flights of stairs; (6) re-enter the smoke room and chop through a 10cm wide x 10cm thick block of wood (treated pine) positioned horizontally 0-9m above the floor; (7) perform 20 more pulls on the pike pole apparatus.
These tasks were performed in series and the total time for completion was obtained by a hand-held stopwatch. Values for VO, and HR were recorded at three intervals (i.e., after tasks 3, 5, and 7) during performance of the fire suppression protocol. Those measures were averaged to obtain one value for the entire protocol.
3. Results Table 2 indicates the physiological responses of the 10 firefighters during treadmill
M. Solhmann et al.
1472
Table 2. Oxygen consumption of firefighters (n- 10) at comparable heart rates elicited by treadmill and fire simulation protocols.
Downloaded by [University of Calgary] at 03:30 05 February 2015
Subject
Treadmill Heart ratett
Qo,~
Fire simulation Heart rate yo2
?Oxygen consumption in rnbkg-l-min-l. ttHeart rate in beats per min. tttx*SD; mean f standard deviation. *Designates significant difference ( ~ 1 0 . 0 5between ) V O measured ~ in the fire suppression setting and during treadmill testing.
and fire suppression testing at comparable HR. The average HR of the 10 firefighters during the simulated protocol was 176 k 10 bpm. This value was used to identify a comparable HR from treadmill testing (1 78 k 9 bpm). Despite the HR comparability, the VO, measured in the fire suppression setting (31 -03+ 7-0ml-kg-'amin-') was lower than the VO, from treadmill testing (38.9+5.0mI.kg-'.min-l). This difference was significant at psO-05 as indicated by ANOVA. There was consistency in this error in that the true V O was ~ less than the treadmill predicted VO, for every individual. Given this pattern, multiple regression analysis was used to derive a correction factor for the error associated with the prediction of fire suppression VO, using treadmill data. he following equation accounted for 59% of the variance: fire suppression VO, = 1.09 (treadmill ~ 0 , ) -1 1-37
Figure 1 depicts the significant inverse relationship (-0.82; psO-05) between performance time and relative intensity of 90, max at which the firefighters worked. The average performance time was 8: 15 + 2:23 (min:s). Firefighters worked on average at 73 & 1 0 1 of v 0, max with a range from 54%to 8B0h. 4. Discussion The present study was conducted to examine the association between the VO, predicted by HR and the actual V O ~during performance of fire suppression activities. A simulation was designed which required work in temperatures exceeding 54°C for extended periods while the individuals were wearing the SCBA. Thus, factors such as heat stress, isometric muscle contraction, and reliance on upper body work which are known to affect the HR x VO, relationship were incorporated into the simulation setting. Our field test confirms previous laboratory studies in that the true VO, revealed by Oxylog testing was approximately 20% less than that which
Downloaded by [University of Calgary] at 03:30 05 February 2015
Oxygen consumption during fire suppression
1473
Performance time (minutes) Figure 1. .Association between relative intensity of VO, rnax and performance time of the whole fire simulation protocol by 10 firefighters. would have been predicted by using the H R x VO, relationship from treadmill testing (predicted, 38.9 k 5.0 vs actual 3 1.0 & 7.0ml.kg-I-min-I; p10.05). There was consistency in this variability in that the actual 30, was less than the predicted 30, in all subjects (table 2). Regression analysis accounted for 59% of that variability. These findings demonstrate that HR estimation of V O , should be interpreted cautiously in evaluating the energy expenditure of firefighting. Previous studies of work behaviour in emergency settings have established an inverse relationship between VO* max and performance time of critical physical tasks (Adams et al. 1986, Kamon et al. 1983, Davis et al. 1982). The direct recordings generated in this study by the Oxylog offer new insight into that relationship by showing that the average relative intensity self-selected by firefighters was 73 k 10% of ~0~max. More importantly, as shown in figure 1, there was an inverse relationship between the relative intensity of VO, max selected by firefighters and performance time. These findings show that the relative intensity a firefighter selects affects performance time. Along this line, research on exercise training suggests that chronically physically active individuals work at higher relative intensities then sedentary counterparts (Davis 1985). This would suggest that exercise training programmes which have been shown to improve the absolute work performed by firefighers in a specific time (Adams et al. 1986) may do so not just by increasing ~ 0 , max but also by increasing the relative intensity at which firefighters elect to work. This represents an additional justification for the development and implementation of well-designed fitness programmes for firefighters.
1474
Oxygen consumption during fire suppression
Acknowledgements Appreciation is extended t o D e b o r a h Jasenof, Joe Blaney, S u s a n F u h r m a n , a n d Tom Woulfe f o r their assistance i n d a t a collection. T h i s research w a s f u n d e d b y t h e C i t y of Chicago u n d e r Contract #65832.
Downloaded by [University of Calgary] at 03:30 05 February 2015
References ADAMS.T., YANOWITZ, F., CHANDLER, S., SPECHT,P., LOCKWOOD, R. and YEH,M. 1986, A study to evaluate and promote total fitness among fire fighters, Journal ojSports Medicine, 26, 337-345. A ~ N DP., and RODAHL,K. 1977, Textbook of Work Physiology (McGraw-Hill, New York). CUUSEN,J. 1977, Circulatory adjustments to dynamic exercise and effect of physical training in normal subjects and In patients with coronary artery disease, Progress in Cardiovascular Diseases, 28, 459-494. DAVIS,J. 1985, Anaerobic threshold: review of the concept and directions for future research, Medinne and Sc~encei n Sports and Exercue, 17, 6-18. DAVIS,P., DOTSON, D. and SANTAMARIA,D. 1982, Relationship between simulated fire fighting tasks and physical performance measures, Medicine and Science in Sports and Exercise, 14, 67-71. DUNCAN,H., GARDNER, G. and BARNARD, R. 1979, Physiological responses of men working in fire fighting equipment in the heat, Ergonomics, 22, 521-527. KAMON,E., DOYLE,D. and K o v ~ cJ., 1983, The oxygen cost of an escape from an underground coal mine, American Industrjal Hygrne Association Journal, 44, 552-555. MCKIRNAN,D. and FROEUCHER, V. 1988, General principles of exercise testing, in J. Skinner (ed.) Exercise Testing and Exercise Prescription fir Special Cases (Lea Febiger, Philadelphia), 3- 19. SOTHMANN, M., GUSTAFSON, T. and CHANDLER, M. 1987, Plasma free and sulfoconjugated catecholamine responses to varying exercise intensity, Journal o f ~ ~ ~ l i e d ~ h ~63, siolo~, 654-658. SOTHMANN, M, SAUPE,K., JASENOF, D., BUNEY,J., DONAHUE FUHRMAN, S., W o u m , T., RAVEN, P., PAWELCZYK, J., DOTSON,C., LANDY, F., SMITH, J. and DAVIS,P. 1990, Advancing age and the cardiorespiratory stress of fire suppression: determining a minimum standard for aerobic fitness, Human Performance, 3, 21 7-236. Submitted 16 December 1990. Accepted 2 1 August 199 1.
Ergonomics Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/terg20
Oxygen consumption during fire suppression: error of heart rate estimation a
a
b
b
c
c
M. SOTHMANN , K. SAUPE , P. RAVEN , J. PAWELCZYK , P. DAVIS , C. DOTSON , F. d
LANDY & M. SILIUNAS
a
a
Department of Human Kinetics , School of Allied Health Professions, University of Wisconsin-Milwaukee , Milwaukee, WI, 53201, USA b
Department of Physiology , Texas College of Osteopathic Medicine , Forth Worth, TX, 76107, USA c
ARA/Human Factors, Inc , Burtonsville, MD, 20866, USA
d
Department of Psychology , Pennsylvania State University , State College, PA, 16803, USA Published online: 30 May 2007.
To cite this article: M. SOTHMANN , K. SAUPE , P. RAVEN , J. PAWELCZYK , P. DAVIS , C. DOTSON , F. LANDY & M. SILIUNAS (1991) Oxygen consumption during fire suppression: error of heart rate estimation, Ergonomics, 34:12, 1469-1474, DOI: 10.1080/00140139108964890 To link to this article: http://dx.doi.org/10.1080/00140139108964890
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
ERGONOMICS,1991, VOL. 34, NO. 12,1469- 1474
Oxygen consumption during fire suppression: error of heart rate estimation
Downloaded by [University of Calgary] at 03:30 05 February 2015
M.SOTHMANN,~ K. SAUPE,'P. RAVEN,^ J. PAWELCZYK,~ P.DAVIS,~ C.DOTSON,) F. LANDY,~ and M. SILIUNAS,' 'Department of Human Kinetics, School of Allied Health Professions, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA 2Department of Physiology, Texas College of Osteopathic Medicine, Forth Worth, TX 76 107, USA 3ARA/Human Factors, Inc. Burtonsville, MD 20866, USA 'Department of Psychology, Pennsylvania State University, State College PA 16803, USA
Keywords: Oxygen~consumption;Exercise; Firefighting; Physical fitness. Ten male firefighters were tested on a treadmill to determine their heart rate (HR) x oxygen consumption ( V 04relationship. These men then peFformed a simulated fire suppression protocol during which HR and VO, were measured. simultaneously by a protable physiological monitoring system. Average VO, in the simulated setting was 3 I.0+7.0 ml-kg-'.min-' at a HR of 176 + 9 bpm. This V02 was significantly (p50.05) less than the V 0 2 that would have been predicted by treadmill testing (38.9 f 5.0ml.kg-1.min-1) at a corresponding HR. Fifty-nine per cent of this variability could be accounted for by regression analysis. Firefighters worked on average at 73k 10% V 0 2 max with a range of 54% to 88%. There was a significant (-0.82; ps0-05) inverse relationship between performance time of the fire suppression protocol and the relative intensity of YO2 max at which the firefighters worked. These findings indicate that the prediction of energy expenditure from HR is not straightforward in fire suppression settings. Furthermore, the relative intensity of work firefighters self-select is variable and should be considered as an additional physiological determinant of work behaviour. 1. Introduction An accurate assessment of oxygen consumption (30,)provides important information for determining the energy expenditure reqirements of physically demanding tasks. Accordingly, monitoring heart rate (HR) to predict VO* has been used extensively in sport and occupational settings (Astrand and Rodahl 1977). This and HR approach is based upon the linear relationship between the increases in ~0~ during submaximal dynamic physical work performed on the treadmill or ergometer (Clausen 1978). Typically, the HR x 30, relationship is established for each individual during treadmill testing. Heart rate measurements taken in the field are then compared to the data derived from laboratory testing to estimate the corresponding v 0,. Laboratory studies have identified numerous factors that can potentially alter the relationship between HR and VO, in occupational settings. These include but are not limited to the presence of heat (Duncan el al. 1979), isometric vs isotonic muscle contraction, and upper vs lower body work (McKirnan and Froelicher 1988). Firefighting is one occupation where these factors are present. Furthermore, considerations for personal safety preclude interference with the operation of the OO~bOt39/91 $3.00 C3 1991 Taylor & Francis Ltd.
1470
M. Sothmann et al.
Downloaded by [University of Calgary] at 03:30 05 February 2015
self-contained breathing apparatus (SCBA) or restriction of movement in emergency settings. Thus, portable oxygen consumption measuring devices cannot be used in live emergencies. These limitations have 'restricted data collection on the physiological responses, particularly energy expenditure, of firefighters in actual emergency settings. This is important because recent federal legislative and judicial initiatives pertaining to public safety occupations and the ongoing desire to ensure that workers have the capability to effectively perform have accented the need for a more complete understanding of the physiological demands imposed by firefighting. In the present study, we examine the potential of using HR to predict VO, in a fire suppression setting. Furthermore, we document the association between ~0~ consumption and performance of a standardized fire suppression protocol. 2. Methods 2.1. Subjects Ten experienced men firefighters for a large municipal US fire department volunteered to participate in the research. Informed consent was obtained consistent with policies established by the University of Wisconsin-Milwaukee Institutional Review Board. They reported taking no medication and were not under medical care. All individuals were in apparent good cardiovascular health as indicated by an exercise stress test with electrocardiogram monitored by a cardiologist. Pulmonary function tests revealed no marked impairment. Table 1 indicates values of relevant physiological and anthropometric characteristics. Values obtained for ~0~max and the Davis et al. ( I 982) physical fitness test for firefighters indicate an 'average' level of physical fitness. Table I . Physiological and anthropometric characteristics of participants. Age, yrs Height, cm Weight, kg Lean body weight, kg Per cent fat, % Maximal VO,, I.min-' Maximal VO,, 5 ml.kg-I.rnin-' Physical fitness core* Values are mean + standard deviation. *Physical fitness score based upon the Davis el a/. (1982) criteria.
2.2. Apparatus The H R x VO, relationship for each individual was established during a graded exercise stress test to volitional fatigue. The modified Balke treadmill protocol was employed. Oxygen consumption was determined by open-circuit spirometry using procedures described previously (Sothmann et al. 1987). Analysis of fractional concentrations of OZ and CO, in expired air was performed using Applied Electrochemistry O2 and COz analysers (Ametek, Pittsburg, PA). Heart rate and blood pressure as a safety measure were monitored by electrocardiogram and bracial artery ascultation, respectively. Simultaneous monitoring of HR and VO, at submaximal exercise on the treadmill was then used to determine the H R x VO, relationship for each individual.
Downloaded by [University of Calgary] at 03:30 05 February 2015
Oxygen consumption during fire suppression
1471
The men then completed a simulated fire suppression protocol during which they wore a self-contained physiological recording system (Oxylog: Ambulatory Monitoring, Ardsley, NY) integrated with the SCBA for determination of VO, consumption and heart rate. The Oxylog measured the PO, difference between inspired and expired air. Three adjustments were made to a MSA Ultravue facepiece to allow it to be used in concert with the Oxylog. First, a turbine used to measure inspired air flow was built into the inspired side of the MSA Ultravue facemask; second, a gas sampling port was placed in the low pressure inspired breathing hose to ailow for continual sampling of the inspired air from the SCBA tank; and third, the pressure-demand valve on the MSA facemask was modified such that a hose could be attached to direct expired air to the Oxylog. The signals from the Oxylog and the electrocardiographic signal from electrodes positioned in the CM5 configuration were stored on magnetic tape by a Medilog MR-10 recorder. The Oxylog and the MR-I0 recorder were worn in the outside pockets of the subject's turn-out coat. The weight of the Oxylog and Medilog recorder and their associated cables totaled 3.6 kg. Values for V O , were read off directly from the Oxylog meter at designated timepoints during performance of the simulated fire suppression protocol. Heart rates corresponding to those segments were determined from the Medilog recordings. The Oxylog was calibrated and tested each day prior to use. The daily testing of the Oxylog consisted of calibrating it according to the manufacturer's instructions, drawing a gas of known 0, concentration through the inspired and expired O2 sensors, and outfitting a research assistant with the OxylogISCBA during 5 min of treadmill walking at a steady metabolic state known to elicit a VO, of 1.421.min-'. 2.3. Procedures Data pertaining to the validity of the simulation protocol and selected aspects of the V O ~measurements as they related to performance of the protocol have been published previously on this group of firefighters (Sothmann et al. 1990). Subjects completed the following sequence of tasks while wearing their turn-out gear and SCBA outfitted with the Oxylog. They were instructed to complete the tasks, 'as if involved in an actual firefighting situation'; ( I ) climb 4 flights of stairs, a total of 84 stairs (6 stairs are approx. 1 m), while carrying a standard fire-axe; (2) enter a 54°C room filled with non-toxic smoke and search for a dummy; (3) remove a 68 kg dummy from the room and drag it 15 m down a hallway; (4) re-enter the smoke room and perform 20 pulls of a simulated pike pole; (5) walk down three flights of stairs, pick up a 19 litre (23 kg) hand pump and carry it back up three flights of stairs; (6) re-enter the smoke room and chop through a 10cm wide x 10cm thick block of wood (treated pine) positioned horizontally 0-9m above the floor; (7) perform 20 more pulls on the pike pole apparatus.
These tasks were performed in series and the total time for completion was obtained by a hand-held stopwatch. Values for VO, and HR were recorded at three intervals (i.e., after tasks 3, 5, and 7) during performance of the fire suppression protocol. Those measures were averaged to obtain one value for the entire protocol.
3. Results Table 2 indicates the physiological responses of the 10 firefighters during treadmill
M. Solhmann et al.
1472
Table 2. Oxygen consumption of firefighters (n- 10) at comparable heart rates elicited by treadmill and fire simulation protocols.
Downloaded by [University of Calgary] at 03:30 05 February 2015
Subject
Treadmill Heart ratett
Qo,~
Fire simulation Heart rate yo2
?Oxygen consumption in rnbkg-l-min-l. ttHeart rate in beats per min. tttx*SD; mean f standard deviation. *Designates significant difference ( ~ 1 0 . 0 5between ) V O measured ~ in the fire suppression setting and during treadmill testing.
and fire suppression testing at comparable HR. The average HR of the 10 firefighters during the simulated protocol was 176 k 10 bpm. This value was used to identify a comparable HR from treadmill testing (1 78 k 9 bpm). Despite the HR comparability, the VO, measured in the fire suppression setting (31 -03+ 7-0ml-kg-'amin-') was lower than the VO, from treadmill testing (38.9+5.0mI.kg-'.min-l). This difference was significant at psO-05 as indicated by ANOVA. There was consistency in this error in that the true V O was ~ less than the treadmill predicted VO, for every individual. Given this pattern, multiple regression analysis was used to derive a correction factor for the error associated with the prediction of fire suppression VO, using treadmill data. he following equation accounted for 59% of the variance: fire suppression VO, = 1.09 (treadmill ~ 0 , ) -1 1-37
Figure 1 depicts the significant inverse relationship (-0.82; psO-05) between performance time and relative intensity of 90, max at which the firefighters worked. The average performance time was 8: 15 + 2:23 (min:s). Firefighters worked on average at 73 & 1 0 1 of v 0, max with a range from 54%to 8B0h. 4. Discussion The present study was conducted to examine the association between the VO, predicted by HR and the actual V O ~during performance of fire suppression activities. A simulation was designed which required work in temperatures exceeding 54°C for extended periods while the individuals were wearing the SCBA. Thus, factors such as heat stress, isometric muscle contraction, and reliance on upper body work which are known to affect the HR x VO, relationship were incorporated into the simulation setting. Our field test confirms previous laboratory studies in that the true VO, revealed by Oxylog testing was approximately 20% less than that which
Downloaded by [University of Calgary] at 03:30 05 February 2015
Oxygen consumption during fire suppression
1473
Performance time (minutes) Figure 1. .Association between relative intensity of VO, rnax and performance time of the whole fire simulation protocol by 10 firefighters. would have been predicted by using the H R x VO, relationship from treadmill testing (predicted, 38.9 k 5.0 vs actual 3 1.0 & 7.0ml.kg-I-min-I; p10.05). There was consistency in this variability in that the actual 30, was less than the predicted 30, in all subjects (table 2). Regression analysis accounted for 59% of that variability. These findings demonstrate that HR estimation of V O , should be interpreted cautiously in evaluating the energy expenditure of firefighting. Previous studies of work behaviour in emergency settings have established an inverse relationship between VO* max and performance time of critical physical tasks (Adams et al. 1986, Kamon et al. 1983, Davis et al. 1982). The direct recordings generated in this study by the Oxylog offer new insight into that relationship by showing that the average relative intensity self-selected by firefighters was 73 k 10% of ~0~max. More importantly, as shown in figure 1, there was an inverse relationship between the relative intensity of VO, max selected by firefighters and performance time. These findings show that the relative intensity a firefighter selects affects performance time. Along this line, research on exercise training suggests that chronically physically active individuals work at higher relative intensities then sedentary counterparts (Davis 1985). This would suggest that exercise training programmes which have been shown to improve the absolute work performed by firefighers in a specific time (Adams et al. 1986) may do so not just by increasing ~ 0 , max but also by increasing the relative intensity at which firefighters elect to work. This represents an additional justification for the development and implementation of well-designed fitness programmes for firefighters.
1474
Oxygen consumption during fire suppression
Acknowledgements Appreciation is extended t o D e b o r a h Jasenof, Joe Blaney, S u s a n F u h r m a n , a n d Tom Woulfe f o r their assistance i n d a t a collection. T h i s research w a s f u n d e d b y t h e C i t y of Chicago u n d e r Contract #65832.
Downloaded by [University of Calgary] at 03:30 05 February 2015
References ADAMS.T., YANOWITZ, F., CHANDLER, S., SPECHT,P., LOCKWOOD, R. and YEH,M. 1986, A study to evaluate and promote total fitness among fire fighters, Journal ojSports Medicine, 26, 337-345. A ~ N DP., and RODAHL,K. 1977, Textbook of Work Physiology (McGraw-Hill, New York). CUUSEN,J. 1977, Circulatory adjustments to dynamic exercise and effect of physical training in normal subjects and In patients with coronary artery disease, Progress in Cardiovascular Diseases, 28, 459-494. DAVIS,J. 1985, Anaerobic threshold: review of the concept and directions for future research, Medinne and Sc~encei n Sports and Exercue, 17, 6-18. DAVIS,P., DOTSON, D. and SANTAMARIA,D. 1982, Relationship between simulated fire fighting tasks and physical performance measures, Medicine and Science in Sports and Exercise, 14, 67-71. DUNCAN,H., GARDNER, G. and BARNARD, R. 1979, Physiological responses of men working in fire fighting equipment in the heat, Ergonomics, 22, 521-527. KAMON,E., DOYLE,D. and K o v ~ cJ., 1983, The oxygen cost of an escape from an underground coal mine, American Industrjal Hygrne Association Journal, 44, 552-555. MCKIRNAN,D. and FROEUCHER, V. 1988, General principles of exercise testing, in J. Skinner (ed.) Exercise Testing and Exercise Prescription fir Special Cases (Lea Febiger, Philadelphia), 3- 19. SOTHMANN, M., GUSTAFSON, T. and CHANDLER, M. 1987, Plasma free and sulfoconjugated catecholamine responses to varying exercise intensity, Journal o f ~ ~ ~ l i e d ~ h ~63, siolo~, 654-658. SOTHMANN, M, SAUPE,K., JASENOF, D., BUNEY,J., DONAHUE FUHRMAN, S., W o u m , T., RAVEN, P., PAWELCZYK, J., DOTSON,C., LANDY, F., SMITH, J. and DAVIS,P. 1990, Advancing age and the cardiorespiratory stress of fire suppression: determining a minimum standard for aerobic fitness, Human Performance, 3, 21 7-236. Submitted 16 December 1990. Accepted 2 1 August 199 1.
