G Tolerance Prediction Model Using Mobile Device-Measured Cardiac Force Index for Military Aircrew: Observational Study.

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.

A Rare Case of Rib Fractures During Centrifuge Training.

There are several injuries potentially related to high-G exposure, including neck and back pain, spinal fractures, and pneumomediastinum. We present a young military pilot diagnosed with isolated fractures of the right 9th and 10th ribs via X-ray after high-G exposure (maximum G level: 9G). This patient presented with progressive and localized pain in the right anterior chest and flank region. After conservative treatment with rest and pain management, he recovered from the rib fractures and completed all profile challenges in the advanced high-G training program. A review of the annual health examination of the pilot did not show any rib lesions or other related illnesses. He was qualified for flying class II and considered fit for flight training. His medication history was unremarkable, and he did not have a family history of malignancy, osteoporosis, or osteopenia. He also denied having previously experienced trauma of the rib cage or participated in any strenuous military training program or exercise before centrifuge training. The potential explanations for the multiple rib fractures are repetitive stress from the anti-G straining maneuver and anti-G suit compression of the abdominal bladder. To our knowledge, consecutive rib fractures related to high-G exposure have never been documented. This report may increase the awareness of flight surgeons and training units regarding the risk of chest wall injuries during high-G exposure and encourage them to use multiple diagnostic tools to determine the correct diagnosis.

Effect of Standardized Yelling on Subjective Perception and Autonomic Nervous System Activity in Motion Sickness.

This study investigated the effects of yelling intervention on symptoms and autonomic responses in motion sickness. Forty-two healthy participants were recruited, and they participated in Coriolis stimulation, a technique for inducing motion sickness. The experimental procedure comprised five 1-min rotating stimuli with 1-min rest after each stimulus. Then, the symptom severity was assessed using the Motion Sickness Symptom Rating (MSSR). The d2 Test of Attention scores and cardiovascular responses were recorded before and after Coriolis stimulation. The electrocardiogram results were documented to analyze heart rate variability (HRV). During Coriolis stimulus, the participants were required to yell 5-8 times in the experimental trial, and to keep quiet for each minute of rotation in the control trial. The yelling intervention significantly reduced the MSSR score (p < 0.001). Nevertheless, it did not significantly affect the d2 Test of Attention scores. Yelling while rotating did not significantly affect the heart rate nor blood pressure. However, it decreased the normalized low frequency of HRV (p = 0.036). Moreover, it improved motion sickness, but its effect on attention was not evident. Motion sickness could significantly affect cardiovascular responses and HRV. However, yelling did not affect cardiovascular response, and it reduced sympathetic nervous system activity.

Analysis of Altitude Hypoxia Training and In-Flight Hypoxia Events among the Helicopter Aircrews.

All aircrews are required to undertake the altitude hypoxia training and be familiarized with the hypobaric effect on their physiological regulation. Due to the characteristics of the helicopter aircrafts, few researches have reported in-flight hypoxia events among the helicopter aircrews. The main goal of this study was designed to compare the hypoxia symptoms of helicopter aircrews between the altitude hypoxia training and during flight. We developed a questionnaire to collect the details of chamber flights and in-flight hypoxia events in 2019. All data were managed by the SPSS software and two-tailed 0.05 alpha level was considered as a significant level. Of the 213 study participants, there were eight (3.8%) cases that experienced hypoxia symptoms during the flight. The top five symptoms that appeared both in the last and current altitude hypoxia trainings were visual impairment (20.7%), difficulty concentrating (12.7%), tiredness (12.2%), cognitive impairment (8.0%), and air hunger (5.2%). Meanwhile, the frequency of those symptoms above was not significantly different from the last or current training compared with those in-flight hypoxia events. The survey unveiled a series of consistency correlations of hypoxia symptoms between the chamber flights and in-flight environment for the helicopter aircrew group.

A Cardiac Force Index Applied to the G Tolerance Test and Surveillance among Male Military Aircrew.

Military aircrew are occupationally exposed to a high-G environment. A tolerance test and surveillance is necessary for military aircrew before flight training. A cardiac force index (CFI) has been developed to assess long-distance running by health technology. We added the parameter CFI to the G tolerance test and elucidated the relationship between the CFI and G tolerance. A noninvasive device, BioHarness 3.0, was used to measure heart rate (HR) and activity while resting and walking on the ground. The formula for calculating cardiac function was CFI = weight × activity/HR. Cardiac force ratio (CFR) was calculated by walking CFI (WCFI)/resting CFI (RCFI). G tolerance included relaxed G tolerance (RGT) and straining G tolerance (SGT) tested in the centrifuge. Among 92 male participants, the average of RCFI, WCFI, and CFR were 0.02 ± 0.04, 0.15 ± 0.04, and 10.77 ± 4.11, respectively. Each 100-unit increase in the WCFI increased the RGT by 0.14 G and the SGT by 0.17 G. There was an increased chance of RGT values higher than 5 G and SGT values higher than 8 G according to the WCFI increase. Results suggested that WCFI is positively correlated with G tolerance and has the potential for G tolerance surveillance and programs of G tolerance improvement among male military aircrew.

Contributions of Hypoxia-Awareness Training to the Familiarization of Personal Symptoms for Occupational Safety in the Flight Environment.

Hypoxia remains a flight-safety issue in terms of aviation medicine. Hypoxia-awareness training has been used to help aircrew members recognize personal hypoxia symptoms. There is still no study, as yet, to establish the association of within-subject data between inflight hypoxia events and the altitude chamber. The main purpose of our study was to use paired subjects' data on inflight hypoxia symptoms compared with those experienced during training. A questionnaire was developed to obtain information on military aircrew members in 2018. Among 341 subjects, 46 (13.49%) suffered from inflight hypoxia. The majority of the subjects detected ongoing inflight hypoxia on the basis of their previous experience with personal hypoxia symptoms or sensations in previous chamber flights. Of the top five hypoxia symptoms, the data revealed that hot flashes, poor concentration, and impaired cognitive function appeared both during the inflight events and during the hypoxia-awareness training. The occurrence rate of hypoxia symptoms was found to not be significantly different between the in-flight events and the past chamber flights through an analysis of within-subject data. Because the individual memory had faded away over time, fresher hypoxia awareness training is still mandatory and valuable to recall personal hypoxia experience for military aircrew members.

The Effect of Religion on Psychological Resilience in Healthcare Workers During the Coronavirus Disease 2019 Pandemic.

Background: Healthcare workers in the front line of diagnosis, treatment, and care of patients with coronavirus disease 2019 (COVID-19) are at great risk of both infection and developing mental health symptoms. This study aimed to investigate the following: (1) whether healthcare workers in general hospitals experience higher mental distress than those in psychiatric hospitals; (2) the role played by religion and alexithymic trait in influencing the mental health condition and perceived level of happiness of healthcare workers amidst the stress of the COVID-19 pandemic; and (3) factors that influence the resilience of healthcare workers at 6 weeks' follow-up. Methods: Four-hundred and fifty-eight healthcare workers were recruited from general and psychiatric hospitals, and 419 were followed-up after 6 weeks. All participants filled out the 20-item Toronto Alexithymia Scale, five-item Brief-Symptom Rating Scale, and the Chinese Oxford Happiness Questionnaire. Results: Under the stress of the COVID-19 pandemic, 12.3% of frontline healthcare workers in general hospitals reported having mental distress and perceived lower social adaptation status compared with those working in psychiatric hospitals. Christians/Catholics perceived better psychological well-being, and Buddhists/Taoists were less likely to experience mental distress. The results at 6 weeks of follow-up showed that the perceived lower social adaptation status of general hospital healthcare workers was temporary and improved with time. Christian/Catholic religion and time had independent positive effects on psychological well-being; however, the interaction of Christian/Catholic religion and time had a negative effect. Conclusions: Collectivism and individualism in the cultural context are discussed with regard to alexithymic trait and Buddhist/Taoist and Christian/Catholic religious faiths. Early identification of mental distress and interventions should be implemented to ensure a healthy and robust clinical workforce for the treatment and control of the COVID-19 pandemic.

Combined effect of heart rate responses and the anti-G straining manoeuvre effectiveness on G tolerance in a human centrifuge.

Increased heart rate (HR) is a reaction to head-to-toe gravito-inertial (G) force. The anti-G straining manoeuvre (AGSM) is the crucial technique for withstanding a high-G load. Previous studies reported the main effects of HR only or AGSM only on G tolerance. We assessed the combined effect of HR and AGSM on the outcome of 9G profile exposure. A total of 530 attempts for the 9G profile were extracted to clarify the association of interest. Subjects with an AGSM effectiveness of less than 2.5G had a 2.14-fold higher likelihood of failing in the 9G profile. Trainees with HR increases of less than 20% in the first five seconds also had higher odds of 9G profile intolerance (adjusted OR 1.83, 95% CI 1.09-3.07). The adjusted OR of 9G profile disqualification was 2.93 (95% CI 1.19-7.20) for participants with smaller HR increases and lower AGSM effectiveness. The negative effect of a smaller HR increase on the outcome was likely to be affected by improved AGSM effectiveness (adjusted OR 1.26, 95% CI 0.65-2.42). We speculate that low AGSM effectiveness and a small HR increase were separately associated with failure of high-G challenge. Nonetheless, good AGSM performance seemed to reduce the negative effect of weak HR responses on the dependent variable.

Roles of Physiological Responses and Anthropometric Factors on the Gravitational Force Tolerance for Occupational Hypergravity Exposure.

Gravity in the head-to-toe direction, known as +Gz (G force), forces blood to pool in the lower body. Fighter pilots experience decreases in blood pressure when exposed to hypergravity in flight. Human centrifuge has been used to examine the G tolerance and anti-G straining maneuver (AGSM) techniques of military pilots. Some factors that may affect G tolerance have been reported but are still debated. The aim of this study was to investigate the physiological responses and anthropometric factors correlated with G tolerance. We retrospectively reviewed the training records of student pilots who underwent high G training. Variables were collected to examine their correlations with the outcome of 7.5G sustained for 15 s (7.5G profile). There were 873 trainees who underwent 7.5G profile training, 44 trainees (5.04%) could not sustain the test for 15 s. The group with a small heart rate (HR) increase (less than 10%) during the first 1-5 s of the 7.5G profile had a nearly ten-fold higher failing chance compared with the large HR increase group (adjusted odds ratio: 9.91; 95% confidence interval: 4.11-23.88). The chances of failure were inversely related to the HR increase percentage (p for trend <0.001). Factors, including body mass index, relaxed and straining G tolerance, and AGSM, were found to be negatively correlated with the outcome.

Comparison of hypobaric hypoxia symptoms between a recalled exposure and a current exposure.

BACKGROUND: Aircrew members are required to attend hypoxia awareness training regularly to strengthen their memory of their personal hypoxia symptoms by undergoing training inside a hypobaric chamber. The aim of this study was to examine the association between hypoxia symptoms experienced during two training sessions that were 4 years apart. METHODS: This was a crossover study to compare hypoxia symptoms and self-reported physiological effects of trapped gas between a previous training session and a current training session in an altitude chamber. The subjects were military crew members who undertook a 25,000-feet refresher training course in 2018. We used a structured questionnaire to obtain the target information before and during hypoxia exposure. Data were analyzed using SPSS software. RESULTS: A total of 341 trainees participated in this survey and completely filled out the questionnaire. Gastrointestinal tract discomfort caused by the expansion of trapped gas was the main physiological reaction during the previous and current training sessions. Frequently reported symptoms were poor concentration (30.5%), impaired cognitive function (20.5%), visual disturbances (16.4%), hot flashes (15.8%), and paresthesia (12.6%) during both exposures. However, the proportions of participants reporting poor concentration (P = 0.378) and visual disturbances (P = 0.594) were not significantly different between the recalled and current training sessions. The five most common symptoms among the subjects with less than 1,000 flight hours were poor concentration (29.8%), visual disturbance (27.3%), impaired cognitive function (14.9%), dizziness/lightheadedness (11.6%), and hot flashes (9.9%), which overlapped substantially with the symptoms reported by other subjects. The occurrence of those five most common symptoms in the group with more than 1,000 flight hours did not significantly differ between the recalled training session and the current training session. CONCLUSIONS: The most common hypoxia symptoms reported were similar between the recalled and current training sessions in an environment with a low oxygen concentration. This finding was also clearly affected by the duration of flight experience. Moreover, GI effects of the expansion of trapped gas were commonly observed at low atmospheric pressure.

Fighter Pilots With Nasopharyngeal Carcinoma Successfully Returning to Flight After Radiotherapy: A Case Series.

For nasopharyngeal carcinoma (NPC), radiotherapy is the primary treatment. However, complications occur after radiation to the nasopharynx, which could potentially affect the flying safety. Four fighter pilots with NPC were reported. With early to locally advanced NPC, they received radiotherapy with or without concurrent chemotherapy. The prescribed radiation dose was 70 Gy to the primary tumor over the nasopharynx. Before treatment, all patients presented with various degrees of hearing loss on pure tone audiometry (main frequencies of 20-45 dB at 3-4.5 kHz for affected ears). After the full course of radiotherapy, tumor regression was noticed during months to years of follow-ups. The follow-up audiometry evaluation showed gradually recovered hearing function (average improvement of 5 dB at pretreatment frequencies) in all pilots. They then returned back to the flight line on annual waiver points. Here, we conclude that fighter pilots with NPC could successfully return to the flight line after radiotherapy. However, detailed physical examinations and confirmation of adaptation to flying condition are warranted.

No difference in the functional improvements between unilateral and bilateral total knee replacements.

BACKGROUND: Differences between staged bilateral total knee replacement (TKR) and simultaneous bilateral TKR have been investigated, but few studies have investigated differences in the functional improvements resulting from these methods. Therefore, this study investigates the different functional improvements between staged bilateral total knee TKR and simultaneous bilateral TKR. METHODS: Among 144 potential bilateral TKR patients who were included in this study, 93 (64.6%) patients selected unilateral TKR and 51 (35.4%) selected bilateral TKR. Functional improvements were assessed using the Western Ontario and McMaster University osteoarthritis index (WOMAC) and the Medical Outcomes Trust Short Form-36 (SF-36), and patients were interviewed pre-operatively and after 6 months. A generalized equation was used to test for differences in functional improvements. RESULTS: After TKR, pain, stiffness, function and total WOMAC scores were significantly reduced in both groups, with mean changes from - 26.6 to - 41.4 and from - 27.5 to - 42.2.The mean health change of SF-36 scores, physical component and mental component scores changed to 45.2 ± 18.2, 74.0 ± 15.4 and 77.0 ± 9.6, respectively, in Group 1 and 47.1 ± 17.1, 74.0 ± 15.2 and 75.5 ± 12.1, respectively, in Group 2. Unilateral and simultaneous bilateral TKR produce similar functional improvements, although current work status may be a novel impact factor. CONCLUSION: No differences in functional improvements were identified between patients who selected unilateral versus bilateral TKR, indicating no recommendation for one procedure over the other.

Dermatofibrosarcoma protuberans, a rare but locally aggressive tumor on finger: clinical and aeromedical considerations.

Dermatofibrosarcoma protuberans (DFSP) is a rare, slow growing, locally infiltrative tumor of intermediate malignancy. It is mostly found on the trunk and head, rarely on hands. The course of evaluation and treatment of a young pilot with DFSP on left middle finger is reported. The clinical issues and aeromedical considerations of this rare tumor is discussed.

Repeated hypoxic syncope in a helicopter pilot at a simulated altitude of 18,000 feet.

BACKGROUND: Military aircrew members undergo regular aviation physiology training, including hypobaric chamber flight to demonstrate the effects of hypoxia at altitude on human physiology and to strengthen hypoxia awareness. Premature near syncope under hypoxia will jeopardize flight safety. However, the causes of such abnormality may not be apparent. CASE REPORT: We present a case of a healthy army helicopter pilot who suffered repeated premature near syncope and bradycardia during chamber flight at 18,000 ft (5486 m). He had no previous record of fainting. A passive head-up tilt table study under normoxia revealed cardiovascular responses compatible with vasovagal syncope. After considering the nature of the abnormality, mission characteristics, and the operating altitude for the helicopter, the pilot was granted a restricted waiver, with missions limited to below 10,000 ft (3048 m) in multicrew helicopters. DISCUSSION: Evaluation of hypoxic syncope focuses on cardiovascular, neurologic, and psychiatric systems. The possibility of newly acquired dysautonomia as the cause of hypoxia syncope was supported by normal hypoxia tolerance in previous chamber flights and the results of the head-up tilt table study. The possible pathophysiology of hypoxic syncope and its association with a vasovagal constitution is presented. For a previously healthy helicopter pilot, impaired hypoxia tolerance may cause in-flight incapacitation. The cause should be investigated and the possibility of recurrence in flight should be evaluated before an adequate aeromedical decision can be made.