Clinical Trial Details
— Status: Terminated
Administrative data
| NCT number |
NCT03585335 |
| Other study ID # |
IIT-17-01 |
| Secondary ID |
|
| Status |
Terminated |
| Phase |
|
| First received |
|
| Last updated |
|
| Start date |
September 27, 2018 |
| Est. completion date |
March 18, 2020 |
Study information
| Verified date |
December 2020 |
| Source |
HealthPartners Institute |
| Contact |
n/a |
| Is FDA regulated |
No |
| Health authority |
|
| Study type |
Observational
|
Clinical Trial Summary
Cardiorespiratory fitness is of vital importance to firefighters and yet is rarely, if ever,
tested in a systematic fashion over the course of an individual firefighter's career.
Investigators know that there are incremental health benefits to increased levels of fitness
and reduced morbidity and mortality associated with lower levels of fitness. The proposed
study will address this gap by enrolling up to 135 firefighters from local metropolitan fire
departments. The goal of this cross-sectional correlational study is to address which body
composition methods best correlate with cardiorespiratory fitness (CRF) in firefighters in
order to define a method to combine data into a risk score predictive of fitness.
Specifically, this study will 1) measure body composition data and evaluate the correlation
of BMI with non-BMI body composition measures, such as body fat percentage (BF%), lean body
mass percentage (LBM%), or waist circumference (WC), 2) measure cardiorespiratory fitness in
terms of VO2max and evaluate the correlation of body composition measures such as BMI, BF%,
LBM%, and/or WC with VO2max,, 3) evaluate diagnostic test metrics, such as sensitivity and
specificity, of population meeting obesity criteria by BMI and WC, as compared to BF% as the
reference standard, 4) develop a cardiorespiratory fitnessscore (CVFS) from a conjunction of
body composition measures (BMI, as BF%, LBM%, WC) and demographic variables that is
well-correlated with measured VO2max, evaluate the CVFS performance in age and
gender-stratified subpopulations relative to the accepted standard of gender-stratified
VO2max criteria, and identify age and gender-stratified CVFS threshold and diagnostic test
performance; and 5) correlate CVFS performance with cardiovascular risk measures. Results of
this analysis will provide pilot data and inform future work to assess whether providing more
accurate data on body composition can lead to more effective reductions in cardiorespiratory
risk in this population.
Description:
Firefighters are exposed to extreme metabolic and cardiopulmonary stressors in the
performance of their vocation that are recognized to exceed the actual physical or
environmental hazards. The current medical literature regarding firefighting highlights two
frequently cited statistics: (1) based on body mass index (BMI), upwards of 73-80% of
firefighters are considered overweight or obese, and (2) >45% of firefighter line-of-duty
deaths are due to cardiovascular events.
This finding regarding BMI has been widely reported in the U.S. media after being published
in a 2014 CDC medical journal. Such a finding is particularly relevant to firefighters given
that there are recommended cardiorespiratory performance standards for firefighters, commonly
12 metabolic equivalents (METs) or maximum oxygen consumption during aerobic exercise
(VO2max) of 42 mL O2/kg of body weight/min. As a consequence, failure to meet such a standard
may limit a firefighter's ability to perform (or be employed) in full-duty tasks based on
individual fire station requirements.
Fire suppression activities account for 1-5% of a firefighter's duty time yet result in 32%
of firefighter deaths. This is attributable to the extreme physical demands of firefighting
activities in which anaerobic threshold (typically 85% of maximal heart rate) may be exceeded
and sustained throughout an engagement. Few professions, other than elite athletes, require
this level of cardiorespiratory fitness (CRF). As such, CRF is of vital importance to
firefighters and yet is rarely, if ever, tested in a systematic fashion over the course of an
individual firefighter's career.
The vital importance of CRF is well-established in the medical literature, such that many
advocate for its addition as a clinical vital sign. Epidemiological studies have demonstrated
an inverse relationship between CRF and coronary heart disease (CHD) and all-cause mortality
in healthy individuals. There are incremental health benefits to increased levels of fitness
and reduced morbidity and mortality associated with lower levels of fitness. The fitness
standard of 12 METs (the equivalent of a VO2max of 42 mL/kg/min) remains the testing metric
for firefighters in the NFPA 1582 guidelines; it is applied to all candidates, male or
female, and of any age. While a VO2max of 42 may be "good" to "excellent" for a 50-59 year
old male, it is only "good" for a 40-49 year old male, and only "fair" for a 30-39 or "poor"
for a 20-29 year old male. In women, a VO2max of 42 indicates a "good" level of CRF for a
20-29 year old female and "superior" CRF for a 50-59 year old female. Knowing that CRF
declines inevitably with age argues that a firefighter whose VO2max is 42 mL/kg/min at age 20
will decline significantly by age 50 and raises the question of their ability to safely
participate in fire suppression activities at that age. CRF measures in firefighters would
benefit from age-adjustment and gender stratification. This research would begin that
process.
While elevated BMI is associated with cardiovascular disease morbidity and mortality, BMI has
been demonstrated to be a non-specific metric of body composition. Specifically, BMI "is
limited as an index of obesity (body fatness) because it does not account for the composition
of body weight," and the concurrence of BMI and body fat percentage (BF%) is affected by age,
gender, ethnicity, and body shape. The misclassification of firefighters as overweight and
obese based on BMI has been discussed in a several studies. These studies utilized
bioimpedance testing or skin calipers for BF% measurement, methods known to have significant
levels of error in terms of false positives and false negatives. Interestingly, a series of
these studies cite a single article with a sample size of 39 individuals as validation of
bioimpedance in comparison to dual-energy X-ray absorption (DXA), but also report DXA as the
gold standard for BF% measurement. This inaccuracy of BF% compared to BMI was addressed
thoroughly in one study of U.S. firefighters, demonstrating the potential for false positive
and false negative identification of obesity in this population; specifically, they reported
rates of 15.4% false positive and 18.2% false negative identification of obesity when
identified by BMI as opposed to BF%.
The primary advantages of using BMI in a clinical setting include the long-established
history of BMI usage and its extremely low cost (simply measuring someone's height and
weight). However, waist circumference (WC) is easily measured, and has demonstrated
comparable prediction of cardiovascular risk as compared to and in conjunction with BMI.10
Although classification of obesity has not been conducted by WC, an elevated cardiovascular
risk has been identified for men with WC > 102 cm and women with WC > 88 cm.More
specifically, WC classifications of very low, low, high, and very high have been developed.
For purposes of this study, WC measurements within the high and very high classifications are
considered as obese, with this population (WC > 100 cm in males, WC > 90 cm in females)
representing a similar population to those identified with an increased cardiovascular risk.
The knowledge gap between BF% and cardiovascular risk as it pertains to clinical use of BMI
and other body composition metrics has been identified by the National Heart, Lung, and Blood
Institute (NHLBI), whose 2013 systematic review noted, "studies using BMI and waist
circumference compared to more valid measures of percent body fat are needed to examine the
predictive role of various adiposity measures." However, strong correlations between body
composition metrics and CRF were found in a recent study in Brazilian firefighters, and in
this case, BMI was considered to be an adequate surrogate for other body composition methods
evaluating body composition. A limitation of this study was that it used skin caliper testing
for BF% measurement and a non-respiratory-based exercise test to indirectly estimate VO2max.
Thus, there is an evident need to clarify which among several potential measures of body
composition best predicts CRF, with firefighters serving as a relevant population for study.
To the best of our knowledge, there are no studies that utilize the accepted criterion
standard of dual X-ray energy absorption (DXA) scanning coupled with measured VO2max testing
that would allow coupling these two metrics into a reference fitness-leanness measure.
DXA is a widely-available technology that is relatively inexpensive compared with other
diagnostic technologies, is safe, and can accurately measure BF%. DXA studies can be
completed in less than ten minutes and provide data that is valid and reproducible over time.
The radiation from a DXA scan is less than that received from routine environmental exposure
in a single day. Americans typically receive approximately 3.0 milliSieverts (mSv) of
radiation exposure annually from cosmic radiation, household radon, and other environmental
sources. This does not include elective diagnostic imaging sources. The radiation exposure of
a DXA scan is ~0.005 mSv, about a tenth of that from a single chest x-ray (CXR). 19 By
comparison a CT scan of the pelvis, chest or abdomen can expose the patient to 6.0 -10.0 mSv
in one study (the equivalent of 2-3 years of environmental exposure in a single medical
study). A CT scan of the head is ~2.0 mSv.20 A lumbar spine X-ray series is ~1.5 mSv and a
single PA (posterior-anterior) chest X-ray (CXR) is ~0.06 mSv. The precept of As Low As
Reasonably Achievable (ALARA) in order to minimize radiation exposure is easily honored in
the case of DXA scanning due to the extremely low mSv exposures. The Biological Effects of
Ionizing Radiation (BEIR) VII report and executive summary provide definitive recommendations
regarding radiation exposure and cancer risk.
DXA has been identified an accurate method of measuring BF%, with the additional benefit of
also measuring lean body mass percentage (LBM%) and, of course, bone mineral density (BMD),
as well. This is supported by numerous studies including BF% measured by DXA as the reference
against their study variable of interest. Obesity has been defined for BF% by age categories,
with classifications of low, mid, high, and obesity, where the bottom of the low range is the
minimum of essential body fat. On the other hand, LBM% has not been extensively studied in
correlation with obesity in adults, though contemporary work has been conducted to estimate
LBM% in children and adolescents.
As such, this study aims to address which body composition methods best correlate with CRF in
firefighters. Investigators hypothesize that BF% will better correlate with CRF metrics than
traditional (but technologically outdated) body composition methods, such as BMI or waist
circumference (WC), and furthermore in conjunction with measurement of LBM%. Additionally,
investigators hypothesize that these data, in conjunction with demographic, employment,
physical activity, and medical history data, can comprise a simplified metric (a
cardiorespiratory fitness score) to estimate firefighter CRF. In this context, a cost
analysis of the evaluated surveillance methods will be generated.
Cardiovascular risk has been evaluated in the context of CRF previously, but not specifically
in terms of correlating VO2max and cardiovascular risk measures in firefighters. Most
recently, Yang et al. reported significantly decreased cardiovascular risk in a firefighter
population relative to increased number of push-ups performed.24 A well-accepted measure of
cardiovascular risk in adults is the Framingham Risk Score, which estimates a percentage of
cardiovascular disease risk over 10 years as a function of age, serum cholesterol measures,
blood pressure, diabetes history, and smoking status; this tool is often considered the gold
standard of evaluating 10-year cardiovascular disease risk.25 Studies have demonstrated an
inverse association between CRF - in terms of VO2max or otherwise - and the Framingham Risk
Score, in a variety of populations, including men, women, and diabetics.26-30 Notably, Gander
et al. (2017) specifically discussed the added utility of correlating Framingham Risk with
estimated cardiorespiratory fitness in an asymptomatic male population, which to some degree
may mimic much of the firefighter population, wherein most are primarily male and
asymptomatic.31 This study aims to add to the literature base demonstrating that higher
cardiorespiratory fitness is correlated with lower cardiovascular risk, but uniquely in the
context of the firefighter population. As cardiorespiratory fitness is a good measure of
performance, the concurrent demonstration of decreased cardiovascular risk in a
cost-effective way can add significant value to evaluation of firefighters, in whom these
more elevated risks have been identified.
Results of this analysis will provide pilot data and inform future work to assess whether
providing more accurate data on body composition can lead to more effective reductions in
cardiorespiratory risk in this population. This study has the additional benefit of creating
the availability of DXA three-compartment (fat mass, lean mass, bone mineral content) body
composition at our institution, where this study is not currently performed despite the
required technology already being used for bone studies.
