Whole-body vibration preconditioning reduces the formation and delays the manifestation of high-altitude-induced venous gas emboli

Eccentric exercise 24 h prior to hypobaric decompression increases decompression strain

PURPOSE

Animal studies have shown that recent musculoskeletal injuries increase the risk of decompression sickness (DCS). However, to date no similar experimental study has been performed in humans. The aim was to investigate if exercise-induced muscle damage (EIMD)-as provoked by eccentric work and characterized by reduced strength and delayed-onset muscle soreness (DOMS)-leads to increased formation of venous gas emboli (VGE) during subsequent hypobaric exposure.

METHODS

Each subject (n = 13) was on two occasions exposed to a simulated altitude of 24,000 ft for 90 min, whilst breathing oxygen. Twenty-four hours prior to one of the altitude exposures, each subject performed 15 min of eccentric arm-crank exercise. Markers of EIMD were reduction in isometric m. biceps brachii strength and DOMS as assessed on the Borg CR10 pain scale. The presence of VGE was measured in the right cardiac ventricle using ultrasound, with measurements performed at rest and after three leg kicks and three arm flexions. The degree of VGE was evaluated using the six-graded Eftedal-Brubakk scale and the Kisman integrated severity score (KISS).

RESULTS

Eccentric exercise induced DOMS (median 6.5), reduced the biceps brachii strength (from 230 ± 62 N to 151 ± 8.8 N) and increased the mean KISS at 24,000 ft, both at rest (from 1.2 ± 2.3 to 6.9 ± 9.2, p = 0.01) and after arm flexions (from 3.8 ± 6.2 to 15.5 ± 17.3, p = 0.029).

CONCLUSION

EIMD, induced by eccentric work, provokes release of VGE in response to acute decompression.

Decompression strain in parachute jumpmasters during simulated high-altitude missions: a special reference to preoxygenation strategies

PURPOSE

Military parachute operations are often executed at high altitude, from an unpressurized aircraft compartment. Parachute jumpmasters (JM) are thus regularly exposed to 29,500 ft for 60 min. The aim was to investigate the decompression strain during a simulated JM mission at high altitude and to compare two strategies of preoxygenation, conducted either at sea-level or below 10,000 ft, during ascent to mission altitude.

METHODS

Ten JM completed, on separate occasions, a 45-min preoxygenation either at sea-level (normobaric: N) or 8200ft (hypobaric: H), followed by exposure to 28,000 ft for 60 min, whilst laying supine and breathing 100% oxygen. At min 45 of the exposure to 28,000 ft, the JM performed 10 weighted squats. Decompression strain was determined from ultrasound assessment of venous gas emboli (VGE) during supine rest (5-min intervals), after three unloaded knee-bends (15-min intervals) and immediately following the weighted squats. The VGE were scored using a six-graded scale (0-5).

RESULTS

In condition H, two JM experienced decompression sickness (DCS), whereas no DCS incidents were reported in condition N. The prevalence of VGE was higher in the H than the N condition, at rest [median(range), 3(0-4) vs 0(0-3); p = 0.017], after unloaded knee-bends [3(0-4) vs 0(0-3); p = 0.014] and after the 10 weighted squats [3(0-4) vs 0(0-3); p = 0.014]. VGE were detected earlier in the H (28 ± 20 min, p = 0.018) than the N condition (50 ± 19 min).

CONCLUSIONS

A preoxygenation/altitude procedure commonly used by JM, with a 60-min exposure to 28,000 ft after pre-oxygenation for 45 min at 8200 ft is associated with high risk of DCS. The decompression strain can be reduced by preoxygenating at sea level.

Inter- and Intra-Rater Level of Agreement in Ultrasonic Video Grading of Venous Gas Emboli

INTRODUCTION: This study aimed to evaluate whether a short familiarization session is sufficient for individuals with no prior experience of sonography to both reliably and consistently evaluate the prevalence of venous gas emboli (VGE) from precordial ultrasonic videos.METHODS: A total of 10 adults with no prior experience of sonography were introduced to the Eftedal-Brubakk 6-grade scale and were shown 6 video sequences, each of a maximum of 10 heartbeats, representing each grading level. Thereafter, they independently evaluated the prevalence of VGE in 70 ultrasonic videos before and after a 14-d interval (test-retest; intra-rater), with these being compared to an experienced sonographer's grading (inter-rater).RESULTS: A significant inter-rater level of agreement was found between the naïve and experienced sonographers' bubble grading both during the first (W = 0.945) and second (W = 0.952) round of bubble evaluation. The naïve observers' evaluations were on average 79% (range: 61-95%) and 75% (range: 48-95%) in complete agreement with the experienced sonographer's gradings, while the level of agreement was 99% and 98% within 1 grade unit. There was a significant intra-rater level of agreement (κ = 0.845) during the test-retest series, with a mean percentage level of agreement of 87% (range: 72-93%).CONCLUSION: This study demonstrates that a short familiarization session enables individuals with no prior sonography experience to consistently evaluate VGE prevalence from precordial ultrasonic videos.Elia A, Ånell R, Eiken O, Grönkvist M, Gennser M. Inter- and intra-rater level of agreement in ultrasonic video grading of venous gas emboli. Aerosp Med Hum Perform. 2022; 93(1):54-57.

High-altitude decompression strain can be reduced by an early excursion to moderate altitude while breathing oxygen

Recent observations suggest that development of venous gas emboli (VGE) during high-altitude flying whilst breathing hyperoxic gas will be reduced by intermittent excursions to moderate altitude. The present study aimed to investigate if an early, single excursion from high to moderate altitude can be used as an in-flight means to reduce high-altitude decompression strain. Ten healthy men were investigated whilst breathing oxygen in a hypobaric chamber under two conditions, once during a 90-min continuous exposure to a simulated cabin altitude of 24,000 ft (High; H) and once during 10 min at 24,000 ft, followed by 30 min at 15,000 ft and by 80 min at 24,000 ft (high–low–high; H–L–H). VGE scores were assessed by cardiac ultrasound, using a 6-graded scale. In H, VGE increased throughout the course of the sojourn at 24,000 ft to attain peak value [median (range)] of 3 (2–4) at min 90, just prior to descent. In H–L–H, median VGE scores were 0 throughout the trial, except for at min 10, just prior to the excursion to 15,000 ft, whence the VGE score was 1.5 (0–3). Thus, an early, single excursion from high to moderate cabin altitude holds promise as an in-flight means to reduce the risk of altitude decompression sickness during long-duration high-altitude flying in aircraft with limited cabin pressurization. Presumably, such excursion acts by facilitating the gas exchange in decompression bubbles from a predomination of nitrogen to that of oxygen.