Salivary biomarkers of physical fatigue as markers of sleep deprivation.

STUDY OBJECTIVE: Determine whether a salivary biomarker of physical fatigue, referred to as the fatigue biomarker index (FBI), can discriminate a control group from a sleep deprived group when saliva is collected under controlled conditions. The study expands on previous work examining changes in the composition of saliva during periods of prolonged exercise. METHODS: Thirty (30) young adults (14 Control [CON]; 16 Sleep Deprived [SDEP]) were monitored for mood state (Profile of Mood States [POMS]), cognitive performance (Stroop Color-Conflict Tests), and salivary biomarkers of physical fatigue over a 48-h period with sampling at 3-h intervals. Trials lasted from 06:00 on day 1 (time = -3 h) to 09:00 on day 3 (time = 48 h). Levels of salivary biomarkers were calculated from liquid chromatography-mass spectrometry (LC-MS) data. Statistical comparisons were made using Wilcoxon rank sum tests with a Bonferroni correction to limit type 1 error. Receiver-operator characteristic (ROC) analysis was used to evaluate the ability of the various parameters to distinguish the SDEP population from the CON population. RESULTS: Longitudinal analysis demonstrated significant between-group differences in all three parameters. ROC analysis demonstrated that cognitive performance tests and salivary biomarkers of physical fatigue distinguish the SDEP population from the CON population. CONCLUSIONS: A previously identified salivary biomarker of physical fatigue may provide an alternative method for discriminating sleep deprived from rested individuals. The salivary biomarker of physical fatigue holds promise as an objective measure of sleep deprivation, perhaps eventually removing the reliance on self-reported sleep diaries and/or repeated polysomnographs for longitudinal tracking of sleep quality and/or diagnosis of sleep disorders.

Fatigue biomarker index: an objective salivary measure of fatigue level.

Fatigue changed the composition of the small-molecular weight (sMW) proteome of saliva during a 10h session of moderate (70% of maximum ventilatory threshold) physical exertion. Saliva samples were collected from nine recreationally trained cyclists participating in a cross-over study designed to simulate prolonged manual labor, a military operation or wildfire-suppression work. During each hour of the study, participants performed an exercise program that included upper and lower body exercises separated by short periods of recovery. Over the course of the study, fatigue level increased as suggested by a significant increase in the participants' relative perceived exertion. The composition of the sMW proteome was investigated using reversed-phase liquid chromatography with mass-spectrometric detection. Isotopes of acetic anhydride were used for mass-specific labeling of samples and subsequent identification of ions with significant changes in intensity. Cluster analysis was used to identify a pair of peptides with concentrations that changed in opposite directions with fatigue level, i.e. concentration of one peptide increased while concentration of the other decreased. The sequences of the two peptides were determined by high-resolution mass spectrometry. The ratio of the ion intensities of these two peptides, referred to as the fatigue biomarker index, was calculated for subjects throughout the study. The FBI values from the start of the study likely arose from a different distribution than the FBI values measured at the end of the study (Mann-Whitney test, P<.05). While this study is restricted to a small population of recreationally trained cyclists performing exercise under controlled conditions, it holds promise for the development of an objective salivary measurement of fatigue that is applicable to a much broader population performing in uncontrolled environments.

Linear mixed-effects modeling of the relationship between heart rate variability and fatigue arising from sleep deprivation.

INTRODUCTION: Fatigue degrades cognitive performance, yet there is no universally accepted objective measure of fatigue. We tested whether fatigue arising from sleep deprivation can be quantified objectively using heart rate variability (HRV). METHODS: There were 35 male subjects (mean +/- SD; age = 21.4 +/- 2.6 yr) who were assigned to one of two experimental groups: (1) control (N = 16), or (2) 48-h sleep-deprived (N=19). Using 3-h sampling intervals, we simultaneously tracked fatigue level, cognitive performance, and HRV. Linear mixed-effects (LME) models were used to evaluate linear relationships between fatigue level and cognitive performance, as well as between fatigue level and HRV. RESULTS: Significant negative slopes were observed in LME models of cognitive performance and fatigue level. Of the several HRV parameters examined during standing and supine rest, the ratio of low-frequency to high-frequency R-R interval in the supine position had the clearest significant relationship when modeled against fatigue level. DISCUSSION: In summary, our results suggest that HRV tracks fatigue arising from sleep deprivation. This noninvasive, objective tool can quantify fatigue in real time.

Laboratory evaluation of 10 heat and moisture exchangers using simulated aeromedical evacuation conditions.

Heat and moisture exchangers (HMEs) are used for airway humidification in mechanically ventilated patients and have been evaluated only under hospital conditions. U.S. Air Force aeromedical evacuation transports are performed under rugged conditions further complicated by the cold and dry environment in military aircrafts, and HMEs are used to provide airway humidification for patients. This study evaluated 10 commercial HMEs using a test system that simulated aeromedical evacuation conditions. Although the American National Standards Institute recommends inspired air to be at an absolute humidity value of > or = 30 mg/L for mechanically ventilated patients, the highest absolute humidity by any HME was approximately 20 mg/L. Although none of the HMEs were able to maintain a temperature high enough to achieve the humidity standard of the American National Standards Institute, the clinical significance of this standard may be less important than the relative humidity maintained in the respired air, especially on evacuation flights of short duration.

Development and characterization of a rat model of nonpenetrating liver trauma.

The aim of this study was to develop and characterize a rodent model of liver trauma suitable for preclinical evaluation of new treatments and diagnostic technologies. Liver trauma was created by dropping a steel cylinder through a plastic tube onto the abdomen of supine, anesthetized rats. Internal hemorrhage in the absence of liver trauma was simulated by instilling fresh blood into the peritoneum. Platelet counts were elevated significantly after liver trauma but not simulated hemorrhage. Liver trauma and simulated internal hemorrhage both increased blood levels of the factor growth-regulated oncogene-Kupffer cell. Transcription of plasminogen activator inhibitor 1, heat shock protein 70, and suppressor of cytokine syntheses 3 was increased 77-, 22-, and 27-fold, respectively, 2 h after liver trauma but was unaltered by simulated internal hemorrhage. Levels returned to pretrauma levels by 24 h after trauma. Transcript levels for hypoxia-inducible transcription factor 1alpha were increased 2.8-fold at 24 h but not 2 h after trauma and were not affected by simulated hemorrhage. Production of heat shock protein 70 and inducible nitric oxide synthase in liver was limited to a penumbra surrounding areas of necrosis associated with trauma. The rat model described produces lesions similar to those that occur in humans after blunt trauma.

A comparison of cognitive performance decreases during acute, progressive fatigue arising from different concurrent stressors.

Fatigue is known to impair cognitive performance, but it remains unclear whether concurrent common stressors affect cognitive performance similarly. We used the Stroop Color-Word Conflict Test to assess cognitive performance over 24 hours for four groups: control, sleep-deprived (SD), SD + energy deficit, and SD + energy deficit + fluid restricted. Fatigue levels were quantified using the Profile of Mood States (POMS) survey. Linear mixed-effects (LME) models allowed for testing of group-specific differences in cognitive performance while accounting for subject-level variation. Starting fatigue levels were similar among all groups, while 24-hour fatigue levels differed significantly. For each cognitive performance test, results were modeled separately. The simplest LME model contained a significant fixed-effects term for slope and intercept. Moreover, the simplest LME model used a single slope coefficient to fit data from all four groups, suggesting that loss in cognitive performance over a 24-hour duty cycle with respect to fatigue level is similar regardless of the cause.

Hydration status of Air Force military basic trainees after implementation of the back-mounted hydration system.

The Air Force makes an extraordinary effort to prevent heat-related illnesses associated with basic military training (BMT) in south Texas. However, inadequate hydration can still contribute to lost training time and qualified trainees leaving military service without completing BMT. The purpose of the present study was to determine whether equipping BMTs with back-mounted hydration systems (BM) is better than the standard-issue (SI) canteens with respect to hydration status. Male BMTs were randomly assigned to either BM (n = 40) or SI (n = 38) groups. Baseline values were assessed at week 0 before any physical readiness training (PRT). Subsequent data collection took place in the a.m. before PRT and in the p.m. before dinner the first 3 weeks, and during the 5 weeks of training. BMT total body water (TBW) and body composition were assessed by bioelectrical impedance. Saliva osmolality and total protein concentration were also determined. Hydration status increased daily in BM and SI and was well maintained over the duration of BMT. A significant hydration effect (p < 0.05) was observed for average daily increases in TBW and body weight with BM gaining more compared to SI. Average a.m. TBW was 0.3-0.8 L greater in SI versus BM (p < 0.05). Our findings demonstrate that adequate hydration status is maintained during Air Force BMT in a hot environment using either hydration mode and therefore do not support widespread issuance of the BM system on the premise of improved hydration during USAF BMT military training.

Evaluation of intraosseous delivery of factor VIIa during hemorraghic shock in the pig.

The purpose of this investigation is to determine if intraosseous infusion (IO) is a suitable method for the delivery of recombinant human factor VIIa (rFVIIa) during hemorrhagic shock. The measures that were used to evaluate IO delivery suitability included: (1) determination of clinically significant local or systemic toxicity and (2) demonstration that systemic blood levels of rFVIIa increased rapidly following administration. Our results indicate that there was no evidence of significant local or systemic toxicity following infusion and that the systemic blood concentration of rFVIIa peaks immediately after the end of infusion. This result suggests that the systemic blood level profiles of rFVIIa delivered by IO infusion are similar to those that could be produced by intravenous (IV) administration. Furthermore, in all 25 test animals, access to the systemic circulation during shock was achieved as evidenced by rapid increase in a marker dye (flourescein) or rFVIIa in the blood. We conclude that administration of rFVIIa via IO infusion is a reasonable safe method and is likely to produce blood levels required for improved hemostasis during shock.

Heart rate variability to assess combat readiness.

Chronic fatigue/physical exhaustion (FPE) impacts combat readiness but is difficult to identify. We tested the hypothesis that resting heart rate variability (HRV), including both time- and frequency-domain assessments, would correlate with hydration status and aerobic capacity in military recruit-age men and women with varying fitness levels. Cardiac interbeat intervals were recorded using a heart R-R monitor during 20 minutes of quiet, supine rest with paced breathing (0.25 Hz). HRV metrics included average R-R interval (RRIavg), R-R interval standard deviation (RRISD), the percentage of adjacent R-R intervals varying by > or = 50 ms (pNN50), and integrated areas of R-R interval spectral power at the high (0.15-0.4 Hz) (RRIHF) and low (0.04-0.15 Hz) (RRILF) frequencies. Treadmill maximal oxygen uptake (VO2 max), segmental bioimpedance estimates of total body water (TBW), and urine specific gravity (USG) were also assessed. All dependent variables of interest were within expected ranges, although absolute ranges of individual values were considerable. RRI correlated with VO2 max (r = 0.49; p < 0.001), with TBW (r = 0.38; p < 0.001), and inversely with USG (r = -0.23; p = 0.02). RRISD correlated with VO2 max (r = 0.21; p = 0.03), but not with TBW or USG. pNN50 correlated inversely with USG (r = -0.21; p = 0.03) but not with VO2 max or TBW. R-R interval spectral power at the high and low frequencies did not correlate with VO2 max, TBW, or USG. We have demonstrated that fitness level and hydration status may affect cardiac function via changes in autonomic tone, highlighting the potential of field-based assessment of heart rate variability metrics to identify FPE and other aspects of combat readiness.

Comparison of blood pressure and thermal responses in rats exposed to millimeter wave energy or environmental heat.

Electromagnetic fields at millimeter wave lengths are being developed for commercial and military use at power levels that can cause temperature increases in the skin. Previous work suggests that sustained exposure to millimeter waves causes greater heating of skin, leading to faster induction of circulatory failure than exposure to environmental heat (EH). We tested this hypothesis in three separate experiments by comparing temperature changes in skin, subcutis, and colon, and the time to reach circulatory collapse (mean arterial blood pressure, 20 mmHg) in male Sprague-Dawley rats exposed to the following conditions that produced similar rates of body core heating within each experiment: (1) EH at 42 degrees C, 35 GHz at 75 mW/cm, or 94 GHz at 75 mW/cm under ketamine and xylazine anesthesia; (2) EH at 43 degrees C, 35 GHz at 90 mW/cm, or 94 GHz at 90 mW/cm under ketamine and xylazine anesthesia; and (3) EH at 42 degrees C, 35 GHz at 90 mW/cm, or 94 GHz at 75 mW/cm under isoflurane anesthesia. In all three experiments, the rate and amount of temperature increase at the subcutis and skin surface differed significantly in the rank order of 94 GHz more than 35 GHz more than EH. The time to reach circulatory collapse was significantly less only for rats exposed to 94 GHz at 90 mW/cm, the group with the greatest rate of skin and subcutis heating of all groups in this study, compared with both the 35 GHz at 90 mW/cm and the EH at 43 degrees C groups. These data indicate that body core heating is the major determinant of induction of hemodynamic collapse, and the influence of heating of the skin and subcutis becomes significant only when a certain threshold rate of heating of these tissues is exceeded.

Hyperbaric oxygen treatment prevents up-regulation of angiogenesis following partial-thickness skin grafts in the pig.

We hypothesized that hyperbaric oxygen treatment (HBO) would reduce neovascularization following partial-thickness skin grafting in the Yucatan pig. Results show that capillary density 4 days post-graft is increased twofold in grafts not treated with HBO, compared to normal, ungrafted skin or skin grafts from pigs treated with HBO, p < 0.05. Similarly, the expression of vascular endothelial growth factor, a growth factor associated with neovascularization, was also reduced by HBO. Cell density in the graft boundary increased gradually after grafting, reaching a maximum 2.7-fold increase, relative to normal skin, at day 4, p < 0.05. Cell nuclei positive for proliferating cell nuclear antigen, a marker of proliferation, increased threefold by day 2, p < 0.05, and then declined to normal levels by day 7. HBO had no effect on cell density or proliferation in the boundary region or on shear strength of the graft. In the epidermis, proliferation declined 80% 2 days after grafting and then returned to levels observed in normal skin by day 4, p < 0.05; however, in pigs treated with HBO, we observed no decline in proliferation. These findings confirm the hypothesis that HBO reduces neovascularization in the partial-thickness skin graft while preserving regenerative capacity in the graft boundary and normal proliferative capacity of the epidermis.