BY P. ALEXANDER DERCHAK AND DARRELL MENDENHALL
At the 2005 Fire Department Instructors Conference (FDIC) in Indianapolis, Indiana, Vivometrics Government Services, Inc. introduced and demonstrated The LifeShirt® System, a new technology that has the potential to help reduce firefighter fatalities and improve overall firefighter health and safety. This miniaturized, ambulatory version of an exercise physiology laboratory uses a respiratory measurement technology currently used in more than 1,000 hospitals worldwide. The LifeShirt® System, which was initially described in the May 2005 issue of Fire Engineering (Technology Today: “Enhancing Firefighter Safety Through Physiologic Surveillance,” 126-129) brings this monitoring technology directly into the field, right to the people who put their lives on the line.
LIFESHIRT® SYSTEM
This is how a firefighter would use the LifeShirt® System. Before entering a high-risk fire or training situation, and even before suiting up with protective or other turnout gear, a firefighter first puts on a simple vest that fits beneath other clothing, like an undershirt, close to the skin. Connected to the vest are three heart rate electrodes that are pressed onto the skin of the chest area. The front of the vest is zipped up so that it fits snugly. A push button activates the small recording and transmission device that is also attached to the vest, and the firefighter is ready to go. Other clothing and necessary gear are then layered on top as needed.
The LifeShirt® uses different sensors built into the LifeShirt® itself to gather continuous, key physiological data including respiration, heart rate, activity, and posture. In addition, blood oxygen saturation and skin or core body temperature can also be monitored. These data are recorded to a flash-card for subsequent analysis and can be transmitted over a wireless system to a remote monitoring station or command center. The wireless monitoring station displays a second-by-second picture of each firefighter’s physiologic response to the work of fighting fires, live and in real time, and also displays data trends that make it possible to evaluate changes in the physiologic response to stress.
 Photos courtesy Vivometrics Government Services, Inc. |
Respiratory sensors in the LifeShirt® System are woven into elastic bands that stretch across the firefighter’s chest and abdomen. They stretch as the firefighter breathes in and recoil as the firefighter breathes out, to give continuous respiratory measures that are essential to monitoring overall health and physiologic status. This technology is called “respiratory inductive plethysmography” (RIP).
Accelerometers embedded in the shirt detect the level of activity and determine whether the firefighter’s body is upright, at a prone or titled angle, or lying flat. Heart rate electrodes provide basic ECG measures that, with the respiratory and activity measures, provide a complete data set on the cardiopulmonary response to firefighting.
DATA COLLECTION
During the 2005 FDIC Hands-On Training (H.O.T.) days, firefighters were offered the opportunity to wear the LifeShirt® while participating in two different training evolutions. The LifeShirt® was deployed with firefighters participating in the Fireground Survival Challenge evolutions, which offered a unique opportunity to collect data because of the physically vigorous nature of the evolutions, involving entanglement, room orientation, wall breaching, no-air/low-air Mayday, basement rescue, floor collapse, and second-floor victim rescue scenarios. Five firefighters volunteered to wear the device, which collected physiologic data continuously from when the garment was initially put on through the end of the training session.
The following day, six other firefighters volunteered to wear the LifeShirt® while participating in the Flashover Simulator experience. The LifeShirt® continuously monitored and recorded each firefighter’s heart rate, tidal volume, respiratory rate, minute ventilation, body position, and level of activity while participating in these training simulations.
Students from the University of Indianapolis Human Performance Laboratory facilitated data collection, overseen by Professor Jim Brown, and also prepared summary reports of the LifeShirt® data for the firefighters who participated.
Demonstrating the LifeShirt® System at FDIC enabled us to gain valuable first-hand feedback on what it’s like to use the system from the firefighter’s perspective. Before suiting up with their turnout gear, firefighters put on the LifeShirt® vest, and the system was readied to record data. The firefighters were ready to participate in their chosen training evolution. The whole process took about five minutes.
Firefighters using the LifeShirts® wore them for the duration of the evolutions in which they participated without complaint or incident. As they wore the shirts, data were recorded to a flash-card for subsequent analysis, providing high-resolution physiologic data never before seen during H.O.T. training.
Firefighter Safety and Survival
The Fireground Safety and Survival evolutions consisted of a number of different training exercises in the absence of live fire. Figure 1 shows a typical profile of firefighter response to the training activities. The blue lines on the figure indicate minute median values for heart rate (MHR), breathing frequency (MBr/M), and motion (MAccM). The ACC trace is the raw output from the accelerometer that shows posture and movement. The vertical color bands indicate the various events in the training day.
It can be seen that heart-rate (MHR-the first trace above) was greater than 165 beats/minute several times during the training day and the heart rate often remained above 100 beats/minute between training activities, indicating that these training exercises were extremely demanding and that this individual was likely experiencing some degree of heat stress and perhaps mild dehydration. Additionally, the onset of stressful activity is indicated by the rapid onset of increased breathing frequency. A great deal of information can be derived from the accelerometer trace shown both in a raw form (ACC) and as minute median values (MAccM). Changes in the baseline level indicate changes in posture, and the vertical deflections indicate movement/impact.
Figure 2 details physiological data from an individual who made two runs through the room orientation drill, in which a hood is pulled over the firefighter’s mask and the individual has to navigate through the room and back out. During the first pass, the firefighter spent a substantial amount of time upright as indicated by the level of the accelerometer. During the second pass, the participant went through on all fours, with his head down for more of the time.
This subject experienced a very high heart right, in excess of 175 beats/minute, a very high breathing frequency (more than 40 breaths/minute) during the course of this training. It can also be seen that the second time through the training exercise, the firefighter spent much more time on all fours, with chest parallel to the ground rather than mainly upright based on the ACC trace.
Flashover Simulation
Data from the flashover simulation were interesting and surprising in that they revealed that going through a flashover was not terribly difficult physiologically. However, the LifeShirt® data revealed tell-tale signs of anxiety at the moment of ignition in all firefighters. The scale of this response was, as would be expected, much larger in first-time flashover participants than in those firefighters who had been through this sort of exercise before. The indicator of anxiety is a measure called heart rate variability, which quantifies the regularity or irregularity of a subject’s heart rate.
When an individual is relaxed, the heart rate is quite variable, speeding up when he breathes in, slowing down when he breathes out. However, when an individual is under stress, this variability is substantially reduced. In all subjects, it could be observed that there was a clear drop in heart rate variability immediately following the ignition point. This sort of data could be used to provide feedback to firefighters who may need to stay calm in these environments.
Future Directions With the LifeShirt® System
Data collected during actual firefighting and training can provide a great deal of insight into the “real” stress of firefighting and will help to develop training programs that will better prepare firefighters to be effective and safe in their profession. For instance, the heart rate increase and breathing frequency associated with training activities and firefighting can be determined, and the stress can be indexed by both the peak values reached, the time spent at certain levels of exertion, and the rate of recovery from those activities. Training activities that will stress the firefighter’s physiology can then be designed in a manner that will approximate the stress of specific training and, ultimately, real firefighting. Athletic training has long used the concept of training specificity to improve athletes’ performance capability. Specificity in training refers to the fact that an athlete’s physiology adapts specifically to the stresses placed on it. So, if an athlete wants to run a marathon, he should practice running long distances, not sprinting. For firefighters, training to fight fires should consist of activities and exercises that elicit responses that are physiologically similar to fighting fires.
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To develop truly specific firefighter training, Public Safety Medical Services (www.publicsafetymed.com), a private occupational medicine clinic that provides services exclusively to public safety professionals, is spearheading a research initiative referred to as the “Firefighter Physiologic Surveillance Research Initiative,” involving Indianapolis-area fire departments, researchers from the University of Indianapolis, Indiana University/Purdue University at Indianapolis, and VivoMetrics Government Services.
The purpose of this study is to obtain a better understanding of firefighter physiology, such as was demonstrated at FDIC, that will result in improved intervention and training programs and reduce the incidence of cardiac-related deaths in the fire service.
During this study, a number of healthy firefighter volunteers from the Indianapolis area will wear the LifeShirt® every duty day for a month. All subjects will complete a written health history/medical questionnaire prior to participation and will have been medically cleared for active duty within 12 months of the study date. A physician-supervised maximal exercise test while wearing the LifeShirt® will assess maximal physiologic parameters for each participating firefighter. Gas analysis will also allow for determination of maximal oxygen uptake. Body composition will be assessed using a BodPod body composition analyzer. Physiologic data will be collected continuously by the LifeShirt® while participants are on duty and will be correlated with the recorded runs performed during the shift. We anticipate collecting data on more than 3,000 runs during this time. Ultimately, the analysis and quantification of these data on a larger scale will lead to the development of firefighter-specific training programs.
The capability to collect high-resolution laboratory-quality data from firefighters during their normal routines and under the real stress of the job heralds the arrival of a new era of firefighter training and management. This data collection and the improved training that will follow should help firefighters provide better protection to the communities they serve while helping more of them to return home safely to their families at the end of the day as well as at the end of a full career. ■
