Zephyr Technology

Jul 26, 2023

JMIR mHealth and uHealth This paper is in the following e-collection/theme issue: May 19, 2023 . G Tolerance Prediction Model Using Mobile Device–Measured Cardiac Force Index for Military Aircrew: Observational Study G Tolerance Prediction Model Using Mobile Device–Measured Cardiac Force Index for Military Aircrew: Observational Study Authors of this article: 2Thoracic Department, China Medical University Beigang Hospital, Yunlin County, Taiwan 3Aviation Physiology Research Laboratory, Kaohsiung Armed Forces General Hospital Gangshan Branch, Kaohsiung City, Taiwan 4Superintendent Office, Taipei Veterans General Hospital Fonglin Branch, Hualien County, Taiwan 5School of Public Health, National Defense Medical Center, Taipei City, Taiwan 6Graduate Institute of Aerospace and Undersea Medicine, National Defense Medical Center, Taipei City, Taiwan 7Orthopedics Division, Taichung Armed Forces General Hospital, Taichung City, Taiwan 8Department of Health Business Administration, Meiho University, Pingtung County, Taiwan 9Department of Life Sciences, National Chung Hsing University, Taichung City, Taiwan 10Graduate Institute of Life Sciences, National Defense Medical Center, Taipei City, Taiwan 11Big Data Research Center, College of Medicine, Fu-Jen Catholic University, New Taipei City, Taiwan 12Department of Public Health, Kaohsiung Medical University, Kaohsiung City, Taiwan 13Department of Public Health, China Medical University, Taichung City, Taiwan Corresponding Author: National Defense Medical Center Neihu Dist Abstract Background: During flight, G force compels blood to stay in leg muscles and reduces blood flow to the heart. Cardiovascular responses activated by the autonomic nerve system and strengthened by anti-G straining maneuvers can alleviate the challenges faced during G loading. To our knowledge, no definite cardiac information measured using a mobile health device exists for analyzing G tolerance. However, our previous study developed the cardiac force index (CFI) for analyzing the G tolerance of military aircrew. Objective: This study used the CFI to verify participants’ cardiac performance when walking and obtained a formula for predicting an individual’s G tolerance during centrifuge training. Methods: Participants from an air force aircrew undertook high-G training from January 2020 to December 2022. Their heart rate (HR) in beats per minute and activity level per second were recorded using the wearable BioHarness 3.0 device. The CFI was computed using the following formula: weight × activity / HR during resting or walking. Relaxed G tolerance (RGT) and straining G tolerance (SGT) were assessed at a slowly increasing rate of G loading (0.1 G/s) during training. Other demographic factors were included in the multivariate regression to generate a model for predicting G tolerance from the CFI. Results: A total of 213 eligible trainees from a military aircrew were recruited. The average age was 25.61 (SD 3.66) years, and 13.1% (28/213) of the participants were women. The mean resting CFI and walking CFI (WCFI) were 0.016 (SD 0.001) and 0.141 (SD 0.037) kg × G/beats per minute, respectively. The models for predicting RGT and SGT were as follows: RGT = 0.066 × age + 0.043 × (WCFI × 100) – 0.037 × height + 0.015 × systolic blood pressure – 0.010 × HR + 7.724 and SGT = 0.103 × (WCFI × 100) − 0.069 × height + 0.018 × systolic blood pressure + 15.899. Thus, the WCFI is a positive factor for predicting the RGT and SGT before centrifuge training. Conclusions: The WCFI is a vital component of the formula for estimating G tolerance prior to training. The WCFI can be used to monitor physiological conditions against G stress. JMIR Mhealth Uhealth 2023;11:e48812 Principal Findings Several studies have measured HR responses to determine G tolerance [ 19 - 21 ]. We used the mHealth BioHarness device to collect HR data during physical activity performed before centrifuge training. Regarding the CFI values, the results revealed that the WCFI was positively related to G tolerance when the G level was increased at a gradual rate, which was consistent with other studies [ 12 ]. Additionally, this study successfully developed a new model for predicting G tolerance on the basis of changes in cardiac function. Age, height, resting blood pressure, and resting HR variables also influenced G tolerance. Age and Height We observed that for every 1 extra year of age of the individuals undergoing centrifuge training, their RGT increased by 0.066 G. Older participants had higher G tolerance than younger participants, which was similar to the results of another study [ 22 ]. According to Webb et al [ 11 ], the RGT and SGT of fighter pilots in the US Air Force were both positively associated with age. In the Korean Air Force, older trainees were more likely to be able to tolerate 6 G exposure profile [ 8 ]. Several researchers have also observed that younger aircrew members, those with less flying experience, and those with fewer hours more frequently experience GLOC during flight [ 23 - 25 ]. Park et al [ 26 ] suggested that for well-experienced young aviators, age may not affect the frequency of GLOC episodes in centrifuge trials. In one study in the US Navy, Johanson et al [ 27 ] revealed that the mean age of those experiencing GLOC was not different from those not experiencing GLOC, which may be linked to past experience, aircraft type, flight maneuver, and situational awareness. Older jet and fighter pilots often have more years of flying experience. Such pilots are also more frequently exposed to high-G forces during flight. Some evidence indicates that the cardiac performance of fighter pilots is higher after they have been repeatedly exposed to G force [ 28 , 29 ]. This adaptation to G force increases baroreflex activity and G tolerance by altering the G-time tolerance curve [ 30 ]. Therefore, our study participants may have had experience in adapting to G force in flight. Because of greater hydrostatic pressure in taller people, height has been identified as a factor negatively affecting both G tolerance and sustained duration of G force exposure [ 10 , 11 , 31 ]. In a neutral standing posture, brain-level blood pressure is theoretically approximately 22 mm Hg lower than heart-level blood pressure in a 1 G environment. Thus, a longer distance between the brain and heart might mean lower blood pressure in taller aircrew. In agreement with previous findings, the height of our participants was negatively correlated with their G tolerance in our predictive model. SBP and HR The heart ejects blood into cerebral tissue, and BP gradually decreases as blood travels further from the heart. Theoretically, elevated BP is conducive to modulating the effect of G stress. The cardiovascular system can sustain effective cerebral perfusion at up to approximately 4.5 to 5.5 G when the rate of increase is slow. However, the average resting SBP of our participants on the ground was approximately 140 mm Hg, which was slightly higher than usual. This may have been caused by the participants wearing the fitted AGS on their lower body and feeling stressed about their training. In our study, we also discovered that resting SBP was positively associated with RGT and SGT, similar to the US Air Force study that concluded that BP influences G tolerance [ 11 ]. In contrast to blood pressure, increased resting HR was disadvantageous for tolerating hypergravity. Our previous report similarly concluded that air force academy student pilots with elevated HR are less likely to tolerate a peak of 7.5 G when sustained for 15 seconds [ 9 ]. When arterial pressure and stroke volume drop due to exposure to high-G force, the sympathetic nerves trigger an increase in HR and strengthen cardiovascular function. Exertion levels during exercise can be determined using the maximum HR. The HR response is closely related to sport performance. By subtracting the participant’s age from 220, the target HR zones for different activities could be estimated. High-G training is a type of vigorous physical activity, and HR can rise to 160 bpm during G loading [ 7 , 9 ]. Nonetheless, if resting HR was elevated during the pretraining stage, the HR reserve (HRR) would be limited to a narrow range. HRR is one parameter of cardiovascular fitness. Consistent with some reports, we found that trainees with a lower HR or higher HRR were better able to resist the effects of G force [ 32 , 33 ]. This study verified the need to use mobile technology applications for obtaining cardiac data and understanding changes in the G tolerance levels of aviators. RGT and SGT At slow acceleration, RGT is mainly determined by BP and baroreflexes. RGT typically ranges from 4.5 to 6 G and varies depending on the individual and the time [ 34 ]. When the G force surpasses the RGT, trainees initiate the AGSM to assist their cardiovascular system against the G stress. Inside the centrifuge, visual loss was subjectively assessed using a light bar. To avoid variation between participants, we used a large sample size. Our previous study indicated that the mean RGT and SGT were 5.1 and 7.8 G, respectively [ 12 ]. We identified nearly the same RGT and SGT values (RGT: 4.9 G and SGT: 7.9 G) in our sample of 213 participants. We used the wearable mHealth BioHarness 3.0 device to record cardiovascular function and found that G tolerance was associated with the cardiac data. The CFI is composed of 3 factors, namely body weight, activity, and HR. Our findings indicated that cardiovascular responses on the ground can be used to predict the resistance of z-axis forces during exercise involving mild exertion. Research on the prevention of GLOC may focus on the development of a precaution system based on the CFI. Further monitoring of the CFI during G loading is recommended to track any instantaneous changes in the CFI prior to GLOC. Until now, there is still no convenient and proper method to monitor the cardiac performance and G tolerance on the ground. Our study showed that the ability for G tolerance could be predicted by the WCFI. Because G tolerance changes every day, therefore, mobile technology combined with a wearable device is highly applicable to calculate the real-time WCFI and predict G tolerance. Military aircrew can directly understand their G tolerance anytime and anywhere by monitoring their cardiac health and performance via a mobile device during their daily activity. Before the flight, they can know their “low-G day” and maintain the good G awareness. Warning mechanisms based on the cardiac health recorded by a mobile device could be considered to develop and prevent in-flight GLOC and catastrophic mishap. Limitations This study has some limitations. We included data obtained from women in our analysis, and our results suggest that gender did not have a significant effect on the outcome. However, this result may have been due to the small proportion of women. Second, for the calculation of the WCFI, the participants were asked to walk at their normal speed, but “normal” was subjective and their speed varied. Their HR values during walking were lower than 120 bpm, and the walking activity data covered a narrow range and exhibited a central tendency. Therefore, walking speed variation was unlikely to have significantly affected the outcomes. Although we have collected more data to develop and verify the predictive model, more participants are required to conduct an analysis and perform an external validation. Finally, depending on the airframes they were training on, aircrew had to have reached different levels and profiles relating to high-G training before they could participate in flight training. In this study, all participants met the standards of all the test profiles during training. Therefore, the authors could not clarify the relationship between the pass rate of high-G training and the CFI on the ground. Conclusions Using mobile devices, we monitored the cardiac function of aircrew while they walked in a relaxed manner. We verified that the WCFI is positively associated with the level of G tolerance. Moreover, this study developed a model for estimating the G tolerance of military aircrew before they begin high-G training. The development and application of a WCFI-monitoring system for daily life could be considered to evaluate their G tolerance prior to flights. Acknowledgments The authors thank the Medical Affairs Bureau, Ministry of National Defense (MND-MAB-C05-111018) and Kaohsiung Armed Forces General Hospital Gangshan Branch, Taiwan (MND-MAB-110-150 and MND-MAB-D-111158), for their support. Conflicts of Interest References Rickards CA, Newman DG. G-induced visual and cognitive disturbances in a survey of 65 operational fighter pilots. Aviat Space Environ Med 2005 May;76(5):496-500 [ Medline ] Yilmaz U, Cetinguc M, Akin A. Visual symptoms and G-LOC in the operational environment and during centrifuge training of Turkish jet pilots. Aviat Space Environ Med 1999 Jul;70(7):709-712 [ Medline ] Cao XS, Wang YC, Xu L, Yang CB, Wang B, Geng J, et al. Visual symptoms and G-induced loss of consciousness in 594 Chinese Air Force aircrew--a questionnaire survey. Mil Med 2012 Feb;177(2):163-168 [ CrossRef ] [ Medline ] Burton R, Whinnery J. Biodynamics: sustained acceleration. In: DeHart R, Davis J, editors. Fundamentals of Aerospace Medicine. 3rd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2002:122-153 Newman DG. The cardiovascular system at +1 Gz. In: Newman DG, editor. High G Flight: Physiological Effects and Countermeasures. 1st ed. England, UK: Ashgate Publishing Limited; 2016:39-55 Kobayashi A, Kikukawa A, Kimura M, Inui T, Miyamoto Y. Cerebral near-infrared spectroscopy to evaluate anti-G straining maneuvers in centrifuge training. Aviat Space Environ Med 2012 Aug 01;83(8):790-794 [ CrossRef ] [ Medline ] Tu MY, Chu H, Lin YJ, Chiang KT, Chen CM, Chen HH, et al. Combined effect of heart rate responses and the anti-G straining manoeuvre effectiveness on G tolerance in a human centrifuge. Sci Rep 2020 Dec 10;10(1):21611 [ https://doi.org/10.1038/s41598-020-78687-3 ] [ CrossRef ] [ Medline ] Yun C, Oh S, Shin YH. AGSM proficiency and depression are associated with success of high-G training in trainee pilots. Aerosp Med Hum Perform 2019 Jul 01;90(7):613-617 [ CrossRef ] [ Medline ] Tu M, Chu H, Chen H, Chiang K, Hu J, Li F, et al. Roles of physiological responses and anthropometric factors on the gravitational force tolerance for occupational hypergravity exposure. Int J Environ Res Public Health 2020 Nov 02;17(21):8061 [ https://www.mdpi.com/resolver?pii=ijerph17218061 ] [ CrossRef ] [ Medline ] Park M, Yoo S, Seol H, Kim C, Hong Y. Unpredictability of fighter pilots' G duration tolerance by anthropometric and physiological characteristics. Aerosp Med Hum Perform 2015 Apr;86(4):397-401 [ CrossRef ] [ Medline ] Webb JT, Oakley CJ, Meeker LJ. Unpredictability of fighter pilot G tolerance using anthropometric and physiologic variables. Aviat Space Environ Med 1991 Feb;62(2):128-135 [ Medline ] Chiang KT, Tu MY, Lin YJ, Hsin YH, Chiu YL, Li FL, et al. A cardiac force index applied to the G tolerance test and surveillance among male military aircrew. Int J Environ Res Public Health 2021 Aug 21;18(16):8832 [ https://www.mdpi.com/resolver?pii=ijerph18168832 ] [ CrossRef ] [ Medline ] Chu C. Method for detecting cardiac status, method for monitoring cardiac status during exercise, and apparatus for monitoring cardiac status. United States Patent Office US9566010B2. Google Patents. 2016. URL: https://patents.google.com/patent/US20160058314 [accessed 2021-03-23] Chu C. Method for detecting cardiac status, method for monitoring cardiac status during exercise, and apparatus for monitoring cardiac status. Taiwan Patent No. 408 I546051. Google Patents. 2016. URL: https://patents.google.com/patent/TWI546051B/en [accessed 2021-03-24] Hsiao PJ, Chiu CC, Lin KH, Hu FK, Tsai PJ, Wu CT, et al. Usability of wearable devices with a novel cardiac force index for estimating the dynamic cardiac function: observational study. JMIR mHealth uHealth 2020 Jul 21;8(7):e15331 [ https://mhealth.jmir.org/2020/7/e15331/ ] [ CrossRef ] [ Medline ] Wu YS, Wang WY, Chan TC, Chiu YL, Lin HC, Chang YT, et al. Effect of the Nintendo Ring Fit Adventure exergame on running completion time and psychological factors among university students engaging in distance learning during the COVID-19 pandemic: randomized controlled trial. JMIR Serious Games 2022 Mar 22;10(1):e35040 [ https://games.jmir.org/2022/1/e35040/ ] [ CrossRef ] [ Medline ] BioHarness 3.0 user manual. Zephyr Technology Corporation. 2012 Sep 12. URL: https://www.zephyranywhere.com/media/download/bioharness3-user-manual.pdf [accessed 2023-05-01] Johnstone JA, Ford PA, Hughes G, Watson T, Garrett AT. Bioharness(™) multivariable monitoring device: part. I: validity. J Sports Sci Med 2012 Sep 1;11(3):400-408 [ https://europepmc.org/abstract/MED/24149346 ] [ Medline ] Pipraiya M, Tripathi KK, Dogra MM. Effects of +Gz acceleration on indices of heart rate variability. Ind J Aerospace Med 2005 Jun 30;49:37-47 [ https://indjaerospacemed.com/effects-of-gz-acceleration-on-indices-of-heart-rate-variability/ ] Newman DG, White SW, Callister R. Evidence of baroreflex adaptation to repetitive +Gz in fighter pilots. Aviat Space Environ Med 1998 May;69(5):446-451 [ Medline ] Lai C, Tu M, Chu H, Liu C. Cardiac performance of cadets during the centrifuge training with rapid onset rate. Aerosp Med Hum Perform 2019;90:225 Whinnery JE. +Gz tolerance correlation with clinical parameters. Aviat Space Environ Med 1979 Jul;50(7):736-741 [ Medline ] Slungaard E, McLeod J, Green NDC, Kiran A, Newham DJ, Harridge SDR. Incidence of G-induced loss of consciousness and almost loss of consciousness in the Royal Air Force. Aerosp Med Hum Perform 2017 Jun 01;88(6):550-555 [ CrossRef ] [ Medline ] Sevilla NL, Gardner JW. G-induced loss of consciousness: case-control study of 78 G-Locs in the F-15, F-16, and A-10. Aviat Space Environ Med 2005 Apr;76(4):370-374 [ Medline ] Green NDC, Ford SA. G-induced loss of consciousness: retrospective survey results from 2259 military aircrew. Aviat Space Environ Med 2006 Jun;77(6):619-623 [ Medline ] Park J, Yun C, Kang S. Physical condition does not affect gravity-induced loss of consciousness during human centrifuge training in well-experienced young aviators. PLoS One 2016 Jan 26;11(1):e0147921 [ https://dx.plos.org/10.1371/journal.pone.0147921 ] [ CrossRef ] [ Medline ] Johanson DC, Pheeny HT. A new look at the loss of consciousness experience within the U.S. Naval forces. Aviat Space Environ Med 1988 Jan;59(1):6-8 [ Medline ] Newman DG, White SW, Callister R. Evidence of baroreflex adaptation to repetitive +Gz in fighter pilots. Aviat Space Environ Med 1998 May;69(5):446-451 [ Medline ] Scott JPR, Jungius J, Connolly D, Stevenson AT. Subjective and objective measures of relaxed +Gz tolerance following repeated +Gz exposure. Aviat Space Environ Med 2013 Jul;84(7):684-691 [ CrossRef ] [ Medline ] Newman DG. Cardiovascular adaptation to acceleration. In: High G Flight: Physiological Effects and Countermeasures. 1st ed. England, UK: Ashgate Publishing Limited; 2016:131-149 Whinnery JE. +Gz-induced loss of consciousness in undergraduate pilot training. Aviat Space Environ Med 1986 Oct;57(10 Pt 1):997-999 [ Medline ] Sundblad P, Kölegård R, Eiken O. G tolerance and the vasoconstrictor reserve. Eur J Appl Physiol 2014 Dec;114(12):2521-2528 [ CrossRef ] [ Medline ] Eiken O, Mekjavic I, Sundblad P, Kölegård R. G tolerance vis-à-vis pressure-distension and pressure-flow relationships of leg arteries. Eur J Appl Physiol 2012 Oct 16;112(10):3619-3627 [ CrossRef ] [ Medline ] G awareness for aircrew. United States Air Force. 2014 Oct 17. URL: https://static.e-publishing.af.mil/production/1/af_a3_5/publication/afpam11-419/afpam11-419.pdf [accessed 2023-04-28] ‎