Evolution and Preservation of Venous Gas Emboli at Alternating High and Moderate Altitude Exposures

2020 ◽  
Vol 91 (1) ◽  
pp. 11-17
Author(s):  
Rickard Ånell ◽  
Mikael Grönkvist ◽  
Mikael Gennser ◽  
Ola Eiken
Keyword(s):  
Ground Level ◽  
Moderate Altitude ◽  
Cardiac Ultrasound ◽  
Simulated Altitude ◽  
Fighter Aircraft ◽  
Long Duration ◽  
Grade Scale ◽  
Nitrogen Exchange ◽  
Decompression Stress ◽  
Low Nitrogen

INTRODUCTION: The evolution and preservation of venous gas emboli (VGE), as markers of decompression stress, were investigated during alternating high- and moderate altitude exposures, thus, simulating a fighter aircraft high-altitude flight, interrupted by refueling excursions to lower altitudes.METHODS: Eight men served as subjects during three normoxic simulated altitude exposures: High = 90 min at 24,000 ft; High-Low = three × 30 min at 24,000 ft, interspersed by two 30-min intervals at 15,000 ft; Low = 90 min at 15,000 ft. VGE scores were assessed by cardiac ultrasound, using a 5-grade scale. Respiratory nitrogen exchange was measured continuously using a modified closed-circuit electronic rebreather.RESULTS: Both High and High-Low induced persistent VGE, with no inter-condition difference either at rest [median (range): High: 1 (0-3), High-Low: 2 (0-3)] or during unloaded knee-bends [High: 3 (1-4), High-Low: 3 (0-4)], whereas VGE was considerably less in Low, both at rest [0 (0-1)] and during knee-bends [0 (0-2)]. In High-Low, VGE decreased temporarily during the 15,000-ft excursions, but resumed pre-excursion values upon return to 24,000 ft. During the final descent to ground level, VGE were more persistent following High-Low than High. In both High and Low, nitrogen was continuously washed out at altitude, whereas in High-Low, the washout at 24,000 ft was interrupted by nitrogen uptake at 15,000 ft.DISCUSSION: In normoxic conditions, long-duration flying at a cabin altitude of 24,000 ft is associated with substantial VGE occurrence, which is not abolished by intermittent excursions to a cabin altitude of 15,000 ft.Ånell R, Grönkvist M, Gennser M, Eiken O. Evolution and preservation of venous gas emboli at alternating high and moderate altitude exposures. Aerosp Med Hum Perform. 2020; 91(1):11–17.

Hyperoxic Effects on Decompression Strain During Alternating High and Moderate Altitude Exposures

2021 ◽  
Vol 92 (4) ◽  
pp. 223-230
Author(s):  
Rickard nell ◽  
Mikael Grnkvist ◽  
Mikael Gennser ◽  
Ola Eiken
Keyword(s):  
Gas Exchange ◽  
Decompression Sickness ◽  
The Other ◽  
Moderate Altitude ◽  
Cardiac Ultrasound ◽  
Fighter Aircraft ◽  
Lower Altitude ◽  
Healthy Men ◽  
Altitude Exposure ◽  
Long Duration

INTRODUCTION: In fighter aircraft, long-duration high-altitude sorties are typically interrupted by refueling excursions to lower altitude. In normoxia, excursions to moderate cabin altitude may increase the occurrence of venous gas emboli (VGE) at high cabin altitude. The aim was to investigate the effect of hyperoxia on VGE and decompression sickness (DCS) during alternating high and moderate altitude exposure.METHODS: In an altitude chamber, 13 healthy men were exposed to three different conditions: A) 90 min at 24,000 ft (7315 m) breathing normoxic gas (54% O2; H-NOR); B) 90 min at 24,000 ft breathing hyperoxic gas (90% O2; H-HYP); and C) three 30-min exposures to 24,000 ft interspersed by two 30-min exposures to 18,000 ft (5486 m) breathing 90% O2 (ALT-HYP). VGE occurrence was evaluated from cardiac ultrasound imaging. DCS symptoms were rated using a scale.RESULTS: DCS occurred in all conditions and altogether in 6 of the 39 exposures. The prevalence of VGE was similar in H-NOR and H-HYP throughout the exposures. During the initial 30 min at 24,000 ft, the prevalence of VGE was similar in ALT-HYP as in the other two conditions, whereas, after the first excursion to 18,000 ft, the VGE score was lower in ALT-HYP than in H-NOR and H-HYP.DISCUSSION: Hyperoxic excursions from 24,000 to 18,000 ft reduces VGE occurrence, presumably by facilitating diffusive gas exchange across the bubble surfaces, increasing the share of bubble content contributed by oxygen. Still, the excursions did not abolish the DCS risk.nell R, Grnkvist M, Gennser M, Eiken O. Hyperoxic effects on decompression strain during alternating high and moderate altitude exposures. Aerosp Med Hum Perform. 2021; 92(4):223230.

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

2021 ◽  
Vol 121 (11) ◽  
pp. 3225-3232
Author(s):  
Rickard Ånell ◽  
Mikael Grönkvist ◽  
Mikael Gennser ◽  
Ola Eiken
Keyword(s):  
Gas Exchange ◽  
High Altitude ◽  
Decompression Sickness ◽  
Continuous Exposure ◽  
Moderate Altitude ◽  
Cardiac Ultrasound ◽  
Healthy Men ◽  
Hypobaric Chamber ◽  
Long Duration ◽  
Peak Value

AbstractRecent 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.

Effects of Fatigue on Cognitive Performance in Long-Duration Simulated Flight Missions

2020 ◽  
Vol 10 (2) ◽  
pp. 82-93
Author(s):  
Eduardo Rosa ◽  
Ola Eiken ◽  
Mikael Grönkvist ◽  
Roger Kölegård ◽  
Nicklas Dahlström ◽  
...  
Keyword(s):  
Executive Functions ◽  
Task Performance ◽  
Cognitive Performance ◽  
Cognitive Tasks ◽  
Fatigue Index ◽  
Fighter Aircraft ◽  
Long Duration ◽  
Metacognitive Accuracy

Abstract. Fighter pilots may be exposed to extended flight missions. Consequently, there is increasing concern about fatigue. We investigated the effects of fatigue and cognitive performance in a simulated 11-hr mission in the 39 Gripen fighter aircraft. Five cognitive tasks were used to assess cognitive performance. Fatigue was measured with the Samn–Perelli Fatigue Index. Results showed that performance in the non-executive task degraded after approximately 7 hr. Fatigue ratings showed a matching trend to the performance in this task. Performance in tasks taxing executive functions did not decline. We interpreted that fatigue can be overridden by increased attentional effort for executive tasks but not for non-executive components of cognition. Participants underestimated their performance and metacognitive accuracy was not influenced by fatigue.

scholarly journals Simultaneous generalized and low-layer SCIDAR turbulence profiles at san pedro mártir observatory

2019 ◽  
Vol 490 (1) ◽  
pp. 1397-1405 ◽  
Author(s):  
R Avila ◽  
O Valdés-Hernández ◽  
L J Sánchez ◽  
I Cruz-González ◽  
J L Avilés ◽  
...  
Keyword(s):  
High Altitude ◽  
Wind Direction ◽  
Close Agreement ◽  
Baja California ◽  
Ground Level ◽  
Combined Effect ◽  
Moderate Altitude ◽  
San Pedro ◽  
Simultaneous Measurements

ABSTRACT We present optical turbulence profiles obtained with a Generalized SCIDAR (G-SCIDAR) and a low-layer SCIDAR (LOLAS) at the Observatorio Astronómico Nacional in San Pedro Mártir (OAN-SPM), Baja California, Mexico, during three observing campaigns in 2013, 2014, and 2015. The G-SCIDAR delivers profiles with moderate altitude-resolution (a few hundred metres) along the entire turbulent section of the atmosphere, while the LOLAS gives high altitude resolution (on the order of tens of metres) but only within the first few hundred metres. Simultaneous measurements were obtained on 2014 and allowed us to characterize in detail the combined effect of the local orography and wind direction on the turbulence distribution close to the ground. At the beginning of several nights, the LOLAS profiles show that turbulence peaks between 25 and 50 m above the ground, not at ground level as was expected. The G-SCIDAR profiles exhibit a peak within the first kilometre. In 55 per cent and 36 per cent of the nights stable layers are detected between 10 and 15 km and at 3 km, respectively. This distribution is consistent with the results obtained with a G-SCIDAR in 1997 and 2000 observing campaigns. Statistics computed with the 7891 profiles that have been measured at the OAN-SPM with a G-SCIDAR in 1997, 2000, 2014, and 2015 campaigns are presented. The seeing values calculated with each of those profiles have a median of 0.79, first and third quartiles of 0.51 and 1.08 arcsec, which are in close agreement with other long term seeing monitoring performed at the OAN-SPM.

Transient arterial lactic acid changes in unanesthetized dogs at 21,000 feet

1964 ◽  
Vol 206 (6) ◽  
pp. 1437-1440 ◽  
Author(s):  
S. M. Cain ◽  
J. E. Dunn
Keyword(s):  
Lactic Acid ◽  
Carotid Artery ◽  
Control Period ◽  
Ground Level ◽  
Simulated Altitude ◽  
Blood Samples ◽  
Control Value ◽  
Arterial Blood ◽  
Normal Ranges ◽  
Peak Value

Blood lactic acid levels have been reported by some to be elevated during exposure to altitude and by others to be unaffected. Both the hyperventilation caused by hypoxia and tissue hypoxia itself should cause a rise in blood lactic acid, the latter factor being reflected primarily as excess lactate. After a 3-hr control period at ground level, unanesthetized dogs were exposed for 8 hr to 21,000 ft simulated altitude (Pb = 335 mm Hg). Arterial blood samples were drawn frequently from a Teflon T-cannula surgically placed in a carotid artery 1 or 2 days prior to the experiment. Lactic and pyruvic acid concentrations, Pco2, Po2, and pH were measured. At altitude, the average arterial Po2 was 32 mm Hg, Pco2 was 24 mm Hg, and pH was 7.50. All control values fell in normal ranges. Although the magnitude of changes differed among animals, arterial lactic acid reached a peak value within the first 2 hr at altitude and gradually declined thereafter and, in most animals, closely approached the control value during the 8th hr at altitude. Excess lactate changed in a similar manner. The decline in lactic acid, with no concomitant relief of arterial hypoxia and hypocapnia, remains unexplained.

Respiratory alkalosis and hypokalemia in dogs exposed to simulated high altitude

1962 ◽  
Vol 202 (6) ◽  
pp. 1041-1044 ◽  
Author(s):  
D. C. Smith ◽  
J. Q. Barry ◽  
A. J. Gold
Keyword(s):  
High Altitude ◽  
Potassium Concentration ◽  
Plasma Potassium ◽  
Respiratory Alkalosis ◽  
Simulated Altitude ◽  
Simulated High Altitude ◽  
Anesthetized Dogs ◽  
Per Se ◽  
Decompression Stress

Exposure of restrained, unanesthetized dogs to a simulated altitude of 30,000 ft consistently resulted in respiratory alkalosis and marked hypokalemia. When alkalosis was prevented by increasing the pCO2 of inspired air during decompression, a smaller but statistically significant decrease in plasma potassium concentration still occurred. In comparison with previous studies, the hypokalemia observed in these restrained, unanesthetized dogs was greater than that found in either unrestrained or anesthetized dogs subjected to the same decompression stress. Consequently, the suggestion is made that in the unanesthetized, restrained dog, the hypokalemic response not attributable to respiratory alkalosis is of adrenal mediation and results from the "stress" of restraint plus hyperventilation, rather than to hypoxemia or the decompression stress, per se.

Adrenocortical responses to maximal exercise in moderate-altitude natives at 447 Torr

1984 ◽  
Vol 56 (2) ◽  
pp. 482-488 ◽  
Author(s):  
C. M. Maresh ◽  
B. J. Noble ◽  
K. L. Robertson ◽  
R. L. Seip
Keyword(s):  
High Altitude ◽  
Fluid Intake ◽  
Maximal Exercise ◽  
Bicycle Ergometer ◽  
Moderate Altitude ◽  
Simulated Altitude ◽  
Maximum Exercise ◽  
Hypobaric Chamber ◽  
Low Altitude ◽  
Adrenocortical Responses

Serum hydrocortisone and aldosterone (Aldo) responses to maximal exercise were examined in six low-altitude natives (LAN) (373 m or less, aged 19–25 yr) and eight moderate-altitude natives (MAN) (1,830–2,200 m, aged 19–23 yr) at their residence (home) altitudes (740 and 587 Torr, respectively) and later in a hypobaric chamber at a simulated altitude of 4,270 m (447 Torr). After 2 days at their respective residence altitude and in the chamber, each subject exercised to voluntary exhaustion on the bicycle ergometer. Fluid intake was similar in both groups at all testing locations. Preexercise 24-h urinary Aldo was lower in both groups at 447 Torr but only significantly reduced in the LAN group. In general, the changes in maximum exercise cardiorespiratory variables were twice as large in LAN as in MAN subjects going from residence altitude to 447 Torr. Both serum hydrocortisone and Aldo concentrations were increased (P less than 0.01) after exercise in both groups at residence altitude and 447 Torr. Aldo was lower (P less than 0.05) postexercise at 447 Torr than at residence altitude in both groups, but this decrease was more pronounced (P less than 0.01) in the LAN group. Thus it appears that high-altitude Aldo concentrations are more like resident altitude values in MAN than in LAN subjects.

Variability in venous gas emboli following the same dive at 3,658 meters

2021 ◽  
pp. 119-126
Author(s):  
Hayden W Hess ◽  
◽  
Courtney E Wheelock ◽  
Erika St. James ◽  
Jocelyn L Stooks ◽  
...  
Keyword(s):  
Decompression Sickness ◽  
Ambient Pressure ◽  
Correction Method ◽  
Simulated Altitude ◽  
Hyperbaric Chamber ◽  
Minute Exposure ◽  
The Cross ◽  
Grade 3 ◽  
Decompression Stress ◽  
The U.S

Exposure to a reduction in ambient pressure such as in high-altitude climbing, flying in aircrafts, and decompression from underwater diving results in circulating vascular gas bubbles (i.e., venous gas emboli [VGE]). Incidence and severity of VGE, in part, can objectively quantify decompression stress and risk of decompression sickness (DCS) which is typically mitigated by adherence to decompression schedules. However, dives conducted at altitude challenge recommendations for decompression schedules which are limited to exposures of 10,000 feet in the U.S. Navy Diving Manual (Rev. 7). Therefore, in an ancillary analysis within a larger study, we assessed the evolution of VGE for two hours post-dive using echocardiography following simulated altitude dives at 12,000 feet. Ten divers completed two dives to 66 fsw (equivalent to 110 fsw at sea level by the Cross correction method) for 30 minutes in a hyperbaric chamber. All dives were completed following a 60-minute exposure at 12,000 feet. Following the dive, the chamber was decompressed back to altitude for two hours. Echocardiograph measurements were performed every 20 minutes post-dive. Bubbles were counted and graded using the Germonpré and Eftedal and Brubakk method, respectively. No diver presented with symptoms of DCS following the dive or two hours post-dive at altitude. Despite inter- and intra-diver variability of VGE grade following the dives, the majority (11/20 dives) presented a peak VGE Grade 0, three VGE Grade 1, one VGE Grade 2, four VGE Grade 3, and one VGE Grade 4. Using the Cross correction method for a 66-fsw dive at 12,000 feet of altitude resulted in a relatively low decompression stress and no cases of DCS.

Early effect of moderate altitude stress on plasma potassium in the dog

1960 ◽  
Vol 15 (1) ◽  
pp. 37-39
Author(s):  
Armand J. Gold ◽  
Jeanne Q. Barry ◽  
Frederick P. Ferguson
Keyword(s):  
Initial Level ◽  
Plasma Potassium ◽  
Respiratory Alkalosis ◽  
Moderate Altitude ◽  
Human Beings ◽  
Simulated Altitude ◽  
Maximal Level ◽  
Early Effect ◽  
Blood Ph ◽  
Partial Compensation

Exposure of dogs to a simulated altitude of 30,000 feet for 30 minutes resulted in marked respiratory alkalosis and hypokalemia. The data failed to demonstrate, however, the appearance of the early transient hyperkalemic response which has been observed in human beings in the early moments of hyperventilation. Blood pH rose from an initial level of 7.46 to 7.71 after 3 minutes of exposure to altitude. At 30 minutes it had declined slightly from this maximal level to 7.63, suggesting the development of partial compensation to respiratory alkalosis. The results also indicated a temporal potassium-glucose relationship, potassium decreasing and glucose increasing simultaneously during exposure to altitude. Submitted on July 13, 1959

scholarly journals Fatigue, Emotion, and Cognitive Performance in Simulated Long-Duration, Single-Piloted Flight Missions

2021 ◽  
Vol 92 (9) ◽  
pp. 710-719
Author(s):  
Eduardo Rosa ◽  
Mikael Gronkvist ◽  
Roger Kolegard ◽  
Nicklas Dahlstrom ◽  
Igor Knez ◽  
...  
Keyword(s):  
Cognitive Performance ◽  
Air Force ◽  
Cognitive Tasks ◽  
Emotional States ◽  
Fatigue Index ◽  
Fighter Aircraft ◽  
Mission Duration ◽  
Fatigue Development ◽  
Long Duration ◽  
Negative Emotional State

BACKGROUND: Fatigue of air force pilots has become an increasing concern due to changes in mission characteristics. In the current study we investigated fatigue, emotions, and cognitive performance in a simulated 11-h mission in the 39 Gripen fighter aircraft. METHODS: A total of 12 subjects were evaluated in a high-fidelity dynamic flight simulator for 12 consecutive hours. Perceived fatigue was measured by the Samn-Perelli Fatigue Index (SPFI). Emotions were assessed with the Circumplex Affect Space. Cognitive performance was assessed by five cognitive tasks. RESULTS: Significant increase in self-reported fatigue, general decrease in two positive emotional states, as well increase of one negative emotional state occurred after approximately 7 h into the mission. Self-reported fatigue negatively correlated with enthusiasm and cheerfulness (r 0.75; 0.49, respectively) and positively correlated with boredom and gloominess (r 0.61; r 0.30, respectively). Response time in the low-order task negatively correlated with enthusiasm, cheerfulness and calmness (r 0.44; r 0.41; r 0.37, respectively) and positively correlated with boredom and anxiousness (r 0.37; r 0.28, respectively). Mission duration had an adverse impact on emotions in these environmental conditions, particularly after 7 h. DISCUSSION: These results contribute to the understanding of fatigue development in general and of emotion-cognition relationships. These findings emphasize that both emotional states and the type of cognitive tasks to be performed should be considered for planning long-duration missions in single-piloted fighter aircrafts as to increase the probability of missions success. Rosa E, Gronkvist M, Kolegard R, Dahlstrom N, Knez I, Ljung R, Willander J. Fatigue, emotion, and cognitive performance in simulated long-duration, single-piloted flight missions. Aerosp Med Hum Perform. 2021; 92(9):710719.

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