Aviat Space Environ Med Research Articles

Vestibular perceptual thresholds for rotation about the yaw, roll, and pitch axes.

This effort seeks to further assess human perception of self-motion by quantifying and comparing earth-vertical rotational vestibular perceptual thresholds about the yaw, roll, and pitch axes. Early seminal works (Benson Aviat Space Environ Med 60:205-213, 1989) quantified thresholds for yaw, roll, and pitch rotations, using single-cycle sinusoids in angular acceleration with a frequency of 0.3Hz (3.33s motion duration) and found yaw thresholds to be significantly lower than roll and pitch thresholds (1.58-1.20deg/s vs. 2.07deg/s and 2.04deg/s, respectively). Our current effort uses modern methods and definitions to reassess if rotational thresholds differ between these three axes of rotation in ten human subjects at 0.3Hz and additionally across a range of frequencies: 0.1Hz, 0.3Hz, and 0.5Hz. In contrast to the established findings of Benson et al., no statistically significant differences were found between the three rotational axes at 0.3Hz. Further, no statistically significant differences were found at any of these frequencies. Instead, a consistent pattern was found for yaw, pitch, and roll of increasing thresholds with decreasing rotational frequency, consistent with the brain employing high-pass filter mechanisms for decision-making. We also fill a gap in the literature by extending the quantification of pitch rotation thresholds to 0.1Hz. Finally, we assessed inter-individual trends between these three frequencies and across all three axes of rotation. In thoroughly considering methodological and other differences between the current and previous studies, we conclude yaw rotation thresholds do not differ from those in roll or pitch.

Spaceflight not an eye-popping experience for astronauts.

Spaceflight not an eye-popping experience for astronauts.

Commentaries on Viewpoint: Standardization of bed rest studies in the spaceflight contextCommentaries on Viewpoint: Standardization of bed rest studies in the spaceflight contextCommentaries on Viewpoint: Standardization of bed rest studies in the spaceflight contextCommentaries on Viewpoint: Standardization of bed rest studies in the spaceflight contextCommentaries on Viewpoint: Standardization of bed rest studies in the spaceflight context

to the editor: The work presented by Sundblad et al. ([5][1]) is important and is likely to improve present international efforts to develop countermeasures against, for example, cardiovascular deconditioning during spaceflight. However, one aspect that is not addressed to a sufficient extent is the

Doppler Bubble Grades After Diving and Relevance of Body Fat

SCHELLART NAM, VAN REES VELLINGA TP, VAN DIJK FJ, STERK W. Doppler bubble grades after diving and relevance of body fat. Aviat Space Environ Med 2012; 83:951-7. Background: From the literature on venous gas embolism (VGE) and decompression sickness (DCS), it remains unclear whether body fat is a predisposing factor for VGE and DCS. Therefore, this study analyses body fat (range 16-44%) in relation to precordial VGE measured by Doppler bubble grades. Also examined is the effect of age (range 34-68 yr), body mass index (BMI; range 17-34 kg . m(-2)), and a model estimate of (V) over dotO(2max) (maximal oxygen uptake; range 24-54 ml . kg(-1) . min(-1)), Methods:, (maximal oxygen uptake; range 24-54 ml . kg(-1) . min(-1)), Methods: Bubble grades were determined in 43 recreational divers after an open sea air dive of 40 min to 20 m. Doppler bubble grade scores were transformed to the logarithm of the number of bubbles/cm(2), logB, and the logarithm of the Kissman Integrated Severity Score (KISS) to allow numerical analysis. Statistical analyses were performed with Pearson's regular and partial correlations, and uni- and multivariate linear regressions. Results: For divers in their midlife (and older), the analyses indicate that neither body fat nor BMI stimulate bubble formation, since correlations were nonsignificant. In contrast, age and especially (V) over dotO(2max) appeared to determine VGE. For these types of dives it was found that logB = -1.1 + 0.02age - 0.04(V) over dotO(2max). Conclusion: Based on these data we conclude that body fat and BMI seem less relevant for diving. We recommend that medical examinations pay more attention to (V) over dotO(2max) and age, acid that international dive institutions come to a consensus regarding (V) over dotO(2max) criteria

High-altitude ophthalmic changes: An often overlooked entity

Letter to the EditorHigh-altitude ophthalmic changes: An often overlooked entityS. KapoorS. KapoorSchaumburg, IllinoisPublished Online:15 Sep 2013https://doi.org/10.1152/japplphysiol.00508.2013MoreSectionsPDF (28 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat to the editor: I read with great interest the recent article by Martinot et al. (4). One aspect of high-altitude exposure that is often overlooked is high-altitude-related ophthalmic changes.For instance, high-altitude exposure may result in “central retinal vein occlusion.” Symptoms consistent with occlusion may appear as early as 2 days after entering higher altitudes (2). On the other hand, retinal vein occlusion has been reported as much as a year after entering higher altitudes (5). Descent to lower altitudes is accompanied by complete resolution of the symptoms in most patients. Retinal hemorrhages may also develop (1). Similarly, vitreous hemorrhages may develop. Chronic exposure to high-altitude hypoxia may result in marked intraretinal angiogenesis. Sudden ascent to higher altitudes may also result in severe hypoxia that may significantly decrease “visual sensitivity,” particularly peripheral sensitivity. For instance, Horng et al. (3) in a recent study reported a significant decline in the “mean visual sensitivity” by 7.2 dB. A slightly decreased negative impact is also seen on central visual sensitivity.Ascent into higher altitudes may also result in the development of glaucoma secondary to altitude-associated accentuation of intraocular pressure. Ascent into higher altitudes is also associated with a resulting increase in the incidence of dry eyes. Incidence rates as high as 50% have been reported (1). A significant association is seen between a Schirmer test score of <5 mm and dry eye symptoms (3). Ascent into higher altitudes also results in accentuation of central corneal thickness. This is secondary to swelling of the corneal stroma secondary to hypoxia-induced endothelial changes (5). This results in a higher incidence of refractive errors in those exposed to high altitudes.It is obvious from the above examples that ascent into high altitude may cause acute as well as chronic ophthalmic changes. Physicians should be aware of these changes, especially in those who regularly have to ascend to high altitudes.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the author(s).AUTHOR CONTRIBUTIONSAuthor contributions: S.K. drafted manuscript; S.K. edited and revised manuscript; S.K. approved final version of manuscript.REFERENCES1. Guo B, Lu P, Chen X, Zhang W, Chen R. Prevalence of dry eye disease in Mongolians at high altitude in China: the Henan eye study. Ophthalmic Epidemiol 17: 234–241, 2010.Crossref | ISI | Google Scholar2. Ho TY, Kao WF, Lee SM, Lin PK, Chen JJ, Liu JH. High-altitude retinopathy after climbing Mount Aconcagua in a group of experienced climbers. Retina 31: 1650–1655, 2011.Crossref | ISI | Google Scholar3. Horng CT, Liu CC, Wu DM, Chen JT, Chang CJ, Tsai ML. Visual fields during acute exposure to a simulated altitude of 7620 m. Aviat Space Environ Med 79: 666–669, 2008.Crossref | Google Scholar4. Martinot JB, Mule M, de Bisschop C, Overbeek MJ, Le-Dong NN, Naieje R, Guenard H. Lung membrane conductance and capillary volume derived from the NO and CO transfer in high altitude newcomers. J Appl Physiol 115: 157–166, 2013.Link | ISI | Google Scholar5. Morris DS, Somner JE, Scott KM, McCormick IJ, Aspinall P, Dhillon B. Corneal thickness at high altitude. Cornea 26: 308–311, 2007.Crossref | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: S. Kapoor, 75 Kristin Circle, Schaumburg, IL 60195 (e-mail: [email protected]com). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformationCited ByHigh altitude hypoxia: An enigmaCurrent Medicine Research and Practice, Vol. 7, No. 6 More from this issue > Volume 115Issue 6September 2013Pages 949-949 Copyright & PermissionsCopyright © 2013 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00508.2013PubMed24039258History Published online 15 September 2013 Published in print 15 September 2013 Metrics

AB0842-HPR The effect of core stability and flight time on low back pain in military helicopter pilots

BackgroundIt is known that helicopter pilots experience low back pain frequently 1. underlying factors could be vibration created compressive forces 2 faulty movement mechanics, lack of abdominal strength, loss of...

Body fat does not affect venous bubble formation after air dives of moderate severity: theory and experiment

For over a century, studies on body fat (BF) in decompression sickness and venous gas embolism of divers have been inconsistent. A major problem is that age, BF, and maximal oxygen consumption (Vo2max) show high multicollinearity. Using the Bühlmann model with eight parallel compartments, preceded by a blood compartment in series, nitrogen tensions and loads were calculated with a 40 min/3.1 bar (absolute) profile. Compared with Haldanian models, the new model showed a substantial delay in N2 uptake and (especially) release. One hour after surfacing, an increase of 14-28% in BF resulted in a whole body increase of the N2 load of 51%, but in only 15% in the blood compartment. This would result in an increase in the bubble grade of only 0.01 Kisman-Masurel (KM) units at the scale near KM = I-. This outcome was tested indirectly by a dry dive simulation (air breathing) with 53 male divers with a small range in age and Vo2max to suppress multicollinearity. BF was determined with the four-skinfold method. Precordial Doppler bubble grades determined at 40, 80, 120, and 160 min after surfacing were used to calculate the Kisman Integrated Severity Score and were also transformed to the logarithm of the number of bubbles/cm(2) (logB). The highest of the four scores yielded logB = -1.78, equivalent to KM = I-. All statistical outcomes of partial correlations with BF were nonsignificant. These results support the model outcomes. Although this and our previous study suggest that BF does not influence venous gas embolism (Schellart NAM, van Rees Vellinga TP, van Dijk FH, Sterk W. Aviat Space Environ Med 83: 951-957, 2012), more studies with different profiles under various conditions are needed to establish whether BF remains (together with age and Vo2max) a basic physical characteristic or will become less important for the medical examination and for risk assessment.

Viewpoint: Are there valid concerns for completing a marathon at 39 weeks of pregnancy?

recently, widespread media attention has been given to Amber Danielle Miller, a 27-yr-old woman (163 cm tall), who, at 39 wk of pregnancy, gave birth following her completion of the Chicago Marathon on October 9, 2011 ([17][1], [19][2], [21][3]). She completed the Marathon in 6 h, 25 min, and 50 s

Point: Counterpoint: Hypobaric hypoxia induces/does not induce different responses from normobaric hypoxia

Point: Counterpoint: Hypobaric hypoxia induces/does not induce different responses from normobaric hypoxia

Comparison of Injury Incidence in Two Different Military Parachuting Systems During United States Army Airborne Training

The United States (US) Army is currently implementing a new parachute system (T-11) that will replace the older system (T-10) in use since the 1950s. The T-11 has a larger canopy resulting in a slower decent rate and reduced kinetic energy on ground impact. Due to the recent release of the T11, no previous study has systematically compared injury rates between the two parachute systems. PURPOSE: This analysis compared injury incidence between the T-10 and T-11 military parachute systems. METHODS: Participants were students in Airborne training at the US Army Airborne School, Ft. Benning, GA, between 15 March and 15 September 2010. Over a one week period, students performed their first jump with the T-11 and several subsequent jumps with the T-10. Injury data was collect from Jump Closure Reports obtained from the Airborne School. Combat loaded jumps and night jumps were excluded since these were only conducted with the T-10 and previous studies have indicated that these types of jumps elevated injury risk (Knapik, Aviat Space Environ Med 79:408, 2008). Predictive Analytic Software version 18.0 was used to perform a chi-square analysis comparing injury incidence between the two parachute systems and to calculate a risk ratio (RR) and 95% confidence interval (95%CI). RESULTS: There were 21,404 parachute descents with the T-10 and 9,351 descents with the T-11. Injury incidence was 2.57/1,000 descents with the T-10 and 1.39/1,000 descents with the T-11 (RR [T10/T11] =1.85, 95%CI=1.03-3.52, p=0.04). CONCLUSIONS: One limitation to this analysis was that students had more jump exposures to the T-10 system than to the T-11 system. In addition, the T-11 was used on the first jump among students who had never before performed a parachute jump. Nonetheless, the data strongly suggests that injury incidence is lower with the T11 parachute, compared to the T-10 parachute, when Airborne operations are conducted during the day and without combat loads.

Exit Strategies and Safety Concerns for Machinery Occupants Following Ice Failure and Submersion

Of all drownings, 5 to 11% occur in submerged vehicles. Winter road workers are at high risk for vehicle submersion because they drive heavy vehicles over ice. A crane was used for repeated occupied and unoccupied submersions of a 5-ton truck/snow plow (N = 25) and a 1-ton truck/snow plow (N = 23); some data were compared to those from our previous study on passenger vehicles (Aviat Space Environ Med 2010; 81:779-84). The 1-ton truck sank faster than an intact car, while the 5-ton truck sank within 4 s. Four subjects could escape through the windows, doors, or roof hatch when the 1-ton truck was on the surface or submerged. Hatch exit took 2-3 times longer than windows/doors. Because the 5-ton truck sank so quickly, there was no opportunity to escape while on the surface. With windows open, exit through the window, door, or roof hatch could only occur after the cab was full of water. With windows closed, rapid pressure buildup imploded the windshield. Bulk and buoyancy of thermoprotective flotation clothing did not impede exit in any scenario. One to three 200-L sealed containers mounted to the front of the 1-ton truck increased the Floating Phase by approximately 20-40 s each. Results suggest that a heavy vehicle will sink before surface exit is possible. Occupants would, therefore, be forced to breath-hold and make an underwater exit through a window, door, or roof hatch. Front-mounted external flotation devices on a light truck increased floating time and the possibility of exit while still on the surface.

The Leisure Pilot License in Europe: Need for Evidence-Based Requirements

The proposed introduction of a leisure pilot license in Europe has resulted in controversy. The arguments against are based on opinion and past practice with appeals to emotion. In this commentary, which was invited in response to the commentary by Simons et al. (Aviat Space Environ Med 2009; 80:663-4), it is suggested that the proposals need to be judged objectively on evidence from European nations and elsewhere, and that policies be consistent between different fields of recreational aviation. Where evidence does not exist, a scientific investigation of flight safety outcomes is warranted, if only because of the large collective expenditure on medically examining pilots.

Effect of temporal relationship between respiration and body motion on motion sickness

Background This study investigated the effect controlling the phase of respiration on the development of nausea provoked by periodic motion at 0.2 Hz which is maximal for provocation of motion sickness. Methods Subjects were exposed to 60° peak–peak, pitch backwards from upright motion while viewing a video of the environment with 180° phase delay. Motion duration was a maximum of 30 min and frequency was set to match individuals' spontaneous respiration. Conditions were: A, spontaneous breathing; B, inspiration cued to begin when head-down; C, inspiration cued to begin when upright; D, inspiration cued with a ±18° desynchronizing phase drift with respect to the tilt cycle. Nausea was rated and ventilation was recorded. Results Magnitudes of nausea ratings were ordered D < C < B < A ( p = 0.008) and speed at which nausea developed were ordered A < B < C < D ( p = 0.001). Discussion The lower sickness ratings and prolonged times to develop nausea in B, C, D confirm that controlled breathing gives some protection against motion sickness. The differences between B, C and D in the development of nausea support the hypothesis of Von Gierke and Parker [von Gierke HE, Parker DE. Differences in otolith and abdominal viscera graviceptor dynamics: implications for motion sickness and perceived body position. Aviat Space Environ Med. 65:747–51, 1994.] that motion sickness can be provoked by a conflicting mismatch between visceral and otolithic signals of orientation to the vertical. The mismatch is greatest in the more provocative condition B because the viscera are mechanically unloaded due to exhalation when the body attains uprightness whereas mismatch is lessened by the mechanical reinforcement afforded by inspiration in (C) and by inconstant relationships between visceral and otolithic signals in (D), both of which afford better protection against sickness.

Commentary: Understanding the pathophysiology of poverty

discrimination and reported delay of pharmacy prescriptions and medical tests. J Gen Intern Med 2005;20:578–83. 95 Britt W. Manifestations of human cytomegalovirus infection: proposed mechanisms of acute and chronic disease. Curr Top Microbiol Immunol 2008;325:417–70. 96 Rosamond W, Flegal K, Furie K et al. Heart disease and stroke statistics—2008 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation 2008;117:e25–146. 97 Rosenthal SL, Stanberry LR, Biro FM et al. Seroprevalence of herpes simplex virus types 1 and 2 and cytomegalovirus in adolescents. Clin Infect Dis 1997;24:135–39. 98 Finch CE (ed.). Cells and Surveys: Should Biological Measures be Included in Social Science Research? Washington, DC: National Academy Press, 2001. 99 Mehta SK, Stowe RP, Feiveson AH, Tyring SK, Pierson DL. Reactivation and shedding of cytomegalovirus in astronauts during spaceflight. J Infect Dis 2000;182:1761–64. 100 Glaser R, Friedman SB, Smyth J et al. The differential impact of training stress and final examination stress on herpesvirus latency at the United States Military Academy at West Point. Brain Behavior Immunity 1999;13:240–51. 101 Glaser R, Kiecolt-Glaser JK. Chronic stress modulates the virus-specific immune response to latent herpes simplex virus type 1. Ann Behav Med 1997;19:78–82. 102 Herbert TB, Cohen S. Stress and immunity in humans: a meta-analytic review. Psychosom Med 1993;55:364–79. 103 Glaser R, Pearson GR, Jones JF et al. Stress-related activation of Epstein-Barr virus. Brain Behavior Immunity 1991;5:219–32. 104 Stowe RP, Mehta SK, Ferrando AA, Feeback DL, Pierson DL. Immune responses and latent herpesvirus reactivation in spaceflight. Aviat Space Environ Med 2001;72:884–91. 105 Compton T, Kurt-Jones EA, Boehme KW et al. Human cytomegalovirus activates inflammatory cytokine responses via CD14 and Toll-like receptor 2. J Virol 2003;77:4588–96. 106 Grahame-Clarke C. Human cytomegalovirus, endothelial function and atherosclerosis. Herpes 2005;12:42–45. 107 Zhou YF, Leon MB, Waclawiw MA et al. Association between prior cytomegalovirus infection and the risk of restenosis after coronary atherectomy. N Engl J Med 1996;335:624–30.

Body fluid volumes measurements by impedance: A review of bioimpedance spectroscopy (BIS) and bioimpedance analysis (BIA) methods

This paper reviews various bioimpedance methods permitting to measure non-invasively, extracellular, intracellular and total body water (TBW) and compares BIA methods based on empirical equations of the wrist-ankle resistance or impedance at 50 kHz, height and weight with BIS methods which rely on an electrical model of tissues and resistances measured at zero and infinite frequencies. In order to compare these methods, impedance measurements were made with a multifrequency Xitron 4200 impedancemeter on 57 healthy subjects which had undergone simultaneously a Dual X-ray absorptiometry examination (DXA), in order to estimate their TBW from their fat-free-mass. Extracellular (ECW) and TBW volumes were calculated for these subjects using the original BIS method and modifications of Matthie [Matthie JR. Second generation mixture theory equation for estimating intracellular water using bioimpedance spectroscopy. J Appl Physiol 2005;99:780–1], Jaffrin et al. [Jaffrin MY, Fenech M, Moreno MV, Kieffer R. Total body water measurement by a modification of the bioimpédance spectroscopy method. Med Bio Eng Comput 2006;44:873–82], Moissl et al. [Moissl UM, Wabel P, Chamney PW, Bosaeus I, Levin NW, et al. Body fluid volume determination via body composition spectroscopy in health and disease. Physiol Meas 2006;27:921–33] and their TBW resistivities were compared and discussed. ECW volumes were calculated by BIA methods of Sergi et al. [Sergi G, Bussolotto M, Perini P, Calliari I, et al. Accuracy of bioelectrical bioimpedance analysis for the assessment of extracellular space in healthy subjects and in fluid retention states. Ann Nutr Metab 1994;38(3):158–65] and Hannan et al. [Hannan WJ, Cowen SJ, Fearon KC, Plester CE, Falconer JS, Richardson RA. Evaluation of multi-frequency bio-impedance analysis for the assessment of extracellular and total body water in surgical patients. Clin Sci 1994;86:479–85] and TBW volumes by BIA methods of Kushner and Schoeller [Kushner RF, Schoeller DA. Estimation of total body water by bioelectrical impedance analysis. Am J Clin Nutr 1986;44(3):417–24], Lukaski et al. [Lukaski HC, Bolonchuk WW. Estimation of body fluid volumes using tetrapolar bioelectrical impedance measurements. Aviat Space Environ Med 1988;59:1163–9], Hannan et al. [Hannan WJ, Cowen SJ, Fearon KC, Plester CE, Falconer JS, Richardson RA. Evaluation of multi-frequency bio-impedance analysis for the assessment of extracellular and total body water in surgical patients. Clinical Science 1994;86:479–85], Deurenberg et al. [Deurenberg P, van der Koy K, Leenen R, Westrate JA, Seidell JC. Sex and age specific prediction formulas for estimating body composition from bioelectric impedance: a cross validation study. Int J Obesity 1991;15:17–25] These volumes were compared against those given by BIS method and, in the case of TBW, with those by DXA. For ECW, a good agreement was found between various BIS methods and that of Sergi while Hannan's values were higher. Both Matthie's and Moissl's methods gave mean TBW resistivities and volumes lower than those of Jaffrin's and DXA methods. Kushner et al. method gave values of TBW not significantly different from those of Jaffrin et al. and DXA, as Hannan's method in men, but Lukaski and Deurenberg methods led to an underestimation.

Interindividual variability in heart rate variability (HRV) and complexity (HRC) measurements

Indices of HRV and HRC have been suggested as potential tools for assisting triage decisions in trauma patients (Aviat Space Environ Med 77:1107, 2007; J Trauma 63:512, 2007). Determination of intersubject variability in these measurements in normal individuals has not been performed. We hypothesized that common indices of HRV and HRC are not highly variable in healthy human subjects, thereby allowing the establishment of “normal” values. ECG was collected for 5 min in 31 supine, resting subjects. Time domain variables included RRISD, RMSSD, pNN50, and SD1 and SD2 from Poincaré plot analysis. Frequency domain variables (LF, 0.04–0.15 Hz; HF, 0.15–0.4Hz) were calculated using Fourier transform. HRC analyses included entropy (SampEn), fractal nature (FD‐L and FD‐DA), stationarity (StatAv), symbol dynamics (SymDyn) and detrended fluctuation analysis (DFA). Data are below:Against expectations, many parameters demonstrated high interindividual variability. Since application of clinical vital signs depends on comparison to a “normal” value, a single measurement of HRV or HRC may not be beneficial for determining patient status. However, tracking changes in continuously‐measured HRV or HRC parameters over time might be more useful.

Observed bubble dynamics in oxygen or heliox breathing and altitude decompression sickness

altitude decompression sickness (DCS) is a common risk in aviation and has been extensively studied over the past two decades ([2][1], [3][2], [9][3]). Attempts have been made to find a correlation between ultrasonic bubble detection and symptoms of altitude DCS ([1][4], [8][5]). Models

Virtual conductance, real hypotension: what happens when we stand up too fast?

cardiovascular physiologists have long been curious about the mechanisms of fainting, and the goal of understanding why people faint under a variety of conditions has taken researchers to the ends of the Earth, and beyond. Some of these investigations have focused on adaptation to extreme

Commentary on Viewpoint “Heliox, nitrox, and trimix diving; hyperbaric oxygen treatment; and a flaw in Henry's law”

LETTERS TO THE EDITORCommentary on Viewpoint “Heliox, nitrox, and trimix diving; hyperbaric oxygen treatment; and a flaw in Henry's law”C. Balestra, and P. GermonpréC. Balestra, and P. GermonpréPublished Online:01 Apr 2007https://doi.org/10.1152/japplphysiol.00048.2007MoreSectionsPDF (28 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat to the editor: Although a nonlinear behavior on gas dissolution has been shown, both the nature of dissolved gases and the presence or not of bubbles (or micronuclei) have to be considered.A classical example has been shown with “hydreliox” (6), probably due in part to the polar nature of dissolved hydrogen in the final mix.Thus it seems probable that apart from the physical or electrolytic changes in solute behavior affecting the linearity of Henry's law, other mechanisms, such as gas-solute interfaces found in the presence of macroscopic bubbles or micronuclei or even the surface tension of such interfaces, play an important role (3).With helium, even local temperature gradients are likely to influence the driving forces of Henry's law.Recent experiments conducted in divers (2) show that changes in fluid compartments induce concomitant changes in surface tension of body fluids that will widely affect the radius of pre-existing or de novo gas (micro)bubbles (5) and thus the contact surface and finally dissolution speed of gases (4).In conclusion, it is undeniable that the simple linear concept of Henry's law is probably untrue, even in relatively “simple” circumstances and certainly in situations where “exotic gas” mixes are breathed. We cannot agree more with Arieli (1). We would like to stress, however, that, as the exact nature of these changes is extremely difficult to model, one has to consider that these changes can occur in both ways; therefore, the observation that nitrox dives seem to be safer than air dives is possibly also due to other factors, rather than this hypothesis alone.REFERENCES1 Arieli R. Heliox, nitrox, and trimix diving; hyperbaric oxygen treatment; and a flaw in Henry's law. J Appl Physiol. In press.Google Scholar2 Blatteau J, Boussuges A, Gempp E, Pontier JM, Castagna O, Galland FM, Robinet C, Bourdon L. Hemodynamic changes induced by sub-maximal exercise prior to a dive and its consequences on bubble formation. Br J Sports Med In press. [2006 Nov. 30. Epub ahead of print].Google Scholar3 Blatteau JE, Souraud JB, Gempp E, Boussuges A. Gas nuclei, their origin, and their role in bubble formation. Aviat Space Environ Med 77: 1068–1076, 2006.Google Scholar4 Boussuges A, Blanc F, Carturan D. Hemodynamic changes induced by recreational scuba diving. Chest 129: 1337–1343, 2006.Crossref | PubMed | ISI | Google Scholar5 Hjelde A, Koteng S, Eftendal O, Brubakk AO. Surface tension and bubble formation after decompression in the pig. Appl Cardiopulm Pathophys 1: 47–52, 2000.Google Scholar6 Sebert P, Barthelemy L, Caroff J, Cann-Moisan C. Effects of breathing an O2-H2 (20%–80%) mixture on the energy metabolism of the eel at 1 ATA. Aviat Space Environ Med 59: 754–757, 1988.Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: C. Balestra, 91, Ave. C. Schaller, Brussels, Belgium B-1160 (e-mail: [email protected]) Download PDF Previous Back to Top Next FiguresReferencesRelatedInformationCited ByEnvironmental Physiology and Diving Medicine2 February 2018 | Frontiers in Psychology, Vol. 9 More from this issue > Volume 102Issue 4April 2007Pages 1720-1720 Copyright & PermissionsCopyright © 2007 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00048.2007PubMed17409297History Published online 1 April 2007 Published in print 1 April 2007 Metrics

Reply to Valic, Palada, and Dujic

LETTERS TO THE EDITORReply to Valic, Palada, and DujicMøollerløokken Andreas, and Brubakk AlfMøollerløokken Andreas, and Brubakk AlfPublished Online:01 Apr 2007https://doi.org/10.1152/japplphysiol.00016.2007MoreSectionsPDF (29 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations reply: We thank both Dr. Moon (5) for his editorial and Dr. Valic et al. (8) for their response to the very same editorial regarding our manuscript in the December issue of the Journal of Applied Physiology (4).As has been stated previously, exercise and nitrates do affect the vascular gas bubbles, but how they do this is not clear. Several studies have been performed with smaller rodents and humans, but there are conflicting results (1–3, 6, 7). The value in doing translational research, going from models with smaller animals through larger ones before doing human testing, is important to be recognized by all those interested in finding the basal mechanisms behind decompression-related disorders. The work that has been done and still is being conducted by Dr. Dujic and his colleagues in Croatia is of great importance. As stated both in the editorial by Dr. Moon (5) in the December issue, and in the letter from Dr. Valic et al. (8), there are several possibilities/options in how to more deeply investigate the mechanisms behind all the recent findings. It should be possible to test whether hemodynamic effects may play a role. The suggestion by Dr. Valic et al. to look into one of the cofactors in the synthesis of nitric oxide, tetrahydrobiopterine, is also exiting.As Dr. Moon (5) stated in the editorial and again outlined by Dr. Valic et al. (8) in the letter, and as we tried to say in our article (4), it is premature to recommend nitrates being used in diving. But the potential of pharmacological means to increase safety in emergency situations such as submarine escapes must be explored. Several questions remain unanswered and need further research, and to target the investigations more to the biochemical mechanisms seems reasonable based on the latest findings.REFERENCES1 Blatteau JE, Gempp E, Galland FM, Pontier JM, Sainty JM, Robinet C. Aerobic exercise 2 hours before a dive to 30 msw decreases bubble formation after decompression. Aviat Space Environ Med 76: 666–669, 2005.Google Scholar2 Dujic Z, Duplancic D, Marinovic-Terzic I, Bakuvik D, Ivancev V, Valic Z, Eterovic D, Petri NM, Wisløff U, Brubakk AO. Aerobic exercise before diving reduces venous gas bubble formation in humans. J Physiol 555: 637–642, 2004.Crossref | ISI | Google Scholar3 Dujic Z, Palada I, Valic Z, Dupancic D, Obad A, Wisløff U, Brubakk AO. Exogenous nitric oxide and bubble formation in divers. Med Sci Sports Exerc 38: 1432–1435, 2006.Crossref | ISI | Google Scholar4 Møllerløkken A, Berge VJ, Jørgensen A, Wisløff U, Brubakk AO. Effect of a short-acting NO donor on bubble formation from a saturation dive in pigs. J Appl Physiol 101: 1541–1545, 2006.Link | ISI | Google Scholar5 Moon RE. Nitroglycerine: relief from the heartache of decompression sickness? J Appl Physiol 101: 1537–1538, 2006.Link | ISI | Google Scholar6 Wisløff U, Richardson RS, Brubakk AO. Exercise and nitric oxide prevent bubble formation: a novel approach to the prevention of decompression sickness? J Physiol 555: 825–829, 2004.Crossref | ISI | Google Scholar7 Wisløff U, Rickadson RS, Brubakk AO. NOS inhibition increases bubble formation and reduces survival in sedentary but not exercised rats. J Physiol 546: 577–582, 2003.Crossref | PubMed | ISI | Google Scholar8 Valic Z, Palada I, and Dujic Z. Short-acting NO donor and decompression sickness in humans. J Appl Physiol 102: 1725, 2007.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: A. Møllerløkken, Dept. of Circulation and Medical Imaging, Faculty of Medicine, Norwegian Univ. of Science and Technology, Olav Kyrres gt. 3, N-7489 Trondheim, Norway (e-mail: [email protected]) Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 102Issue 4April 2007Pages 1726-1726 Copyright & PermissionsCopyright © 2007 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00016.2007History Published online 1 April 2007 Published in print 1 April 2007 Metrics