Wingo JE, Low DA, Keller DM, Crandall CG. Cutaneous vascular responses to hypercapnia during whole-body heating. Aviat Space Environ Med 2008; 79:1081–5. Introduction: Hypercapnia may be encountered in lung disease as well as during situations involving rebreathing of previously expired air (e.g., occupational diving). Inhibitory effects of elevated arterial carbon dioxide partial pressure on the central nervous system may result in impaired thermoregulation. This study tested the hypothesis that in heat-stressed subjects, cutaneous vascular responsiveness [expressed as cutaneous vascular conductance (CVC)] would be reduced during hypercapnic exposure. Methods: Four men and three women (mean ± SD; age: 35 ± 7 yr) rested supine while wearing a tube-lined suit perfused with 34°C water (normothermia). Following normothermic data collection, 50°C water was perfused through the suit to increase internal temperature approximately 1°C (whole-body heating). In both thermal conditions, a normoxic-hypercapnic (5% CO₂, 21% O₂, balance N₂) gas mixture was inspired while forearm skin blood flux (laser-Doppler flowmetry) was measured continuously and was used for calculation of CVC (skin blood flux/mean arterial pressure). Results: End-tidal CO₂ increased similarly throughout hypercapnic exposure during both normothermic and whole-body heating conditions (7.9 ± 2.4 and 8.3 ± 1.9 mmHg, respectively). However, CVC was not different between normocapnia and hypercapnia under either thermal condition (normothermia: 0.42 ± 0.24 vs. 0.39 ± 0.21 flux units/mmHg for normocapnia and hypercapnia, respectively; heat stress: 1.89 ± 0.67 vs. 1.92 ± 0.63 flux units/mmHg for normocapnia and hypercapnia, respectively). Discussion: Based on these findings, mild hypercapnia is unlikely to impair heat dissipation by reducing cutaneous vasodilation.

Lu W-H, Hsieh K-S, Li M-H, Ho C-W, Wu Y-C, Ger L-P, Wang J-S, Chu H. Heart status following high G exposure in rats and the effect of brief preconditioning. Aviat Space Environ Med 2008; 79:1086–90. Introduction: Acceleration on the +G_z axis increases pressure in the cardiac chambers. Our research was designed to study whether: 1) such acceleration would impair cardiac function; and 2) a “preconditioning” exposure to +G_z would protect the heart from any such effects. Methods: There were 45 male Sprague-Dawley rats that were randomly divided into 3 groups of 15: 1) control without acceleration (CTRL); 2) exposure to 5 min of +15 G_z (EXP); and 3) pretreatment whereby the 5-min exposure was preceded by two exposures of 30 s at +15 G_z (PRE). Within each group of 15, subsets of 7 animals were used to study: 1) echocardiographic heart function or 2) myocardial injury [lactic dehydrogenase (LDH) and malondialdehyde (MDA)], and 1 animal was used to examine the histology of cardiac tissue. Results: Acceleration (EXP) was found to have a significant effect on cardiac function; specifically the early diastolic myocardial velocity (E_m) and systolic myocardial velocity (S_m) in both ventricles decreased in EXP compared to CTRL, while PRE significantly reduced this effect. The systolic mitral annular velocity in the left ventricular lateral wall was significantly less affected in PRE than in EXP (1.99 ± 0.65 vs. 1.2 ± 0.39 cm · s⁻¹, P = 0.017). Enzyme levels showed only minor changes. In histology, no neutrophil infiltration was found in three groups. Conclusions: These results suggest that short bouts of acceleration might offer cardiac protection. Confirmation using larger animal models may allow application of the concept to pilots preparing to undertake sustained high G maneuvers and may explain some aspects of the “G layoff” effect.

Kanikowska D, Sato M, Iwase S, Shimizu Y, Inukai Y, Nishimura N, Sugenoya J. Immune and neuroendocrine responses to head-down rest and countermeasures. Aviat Space Environ Med 2008; 79:1091–5. Introduction: Head-down bed rest (HDBR) at −6° is used as a model for studying physiological changes during microgravity in spaceflight. The aim of the present study was to investigate whether exposure to such an environment is associated with alterations in the synthesis of some acute-phase proteins and cytokines, and whether countermeasures would prevent these changes. Methods: There were 12 male volunteers who were subjected to HDBR for 20 d; 6 formed the countermeasure (CMS) group and exercised on a short-arm centrifuge for 30 min/d, while the other 6 served as controls (CTL). Variables measured before and after HDBR included plasma noradrenaline, adrenaline, dopamine, leukocyte count, interleukin 6, total serum protein, C-reactive protein, and α-1antichimotrypsin. Results: Adrenaline and noradrenaline concentrations increased significantly in both groups, while the concentration of C-reactive protein decreased. The concentration of C-reactive protein was significantly higher (CTL: 0.028 ± 0.005 mg · dl⁻¹; CMS: 0.025 ± 0.003 mg · dl⁻¹), and that of adrenaline was significantly lower in CTL compared to CMS (CTL: 46.8 ± 7.5 pg · ml⁻¹; CMS: 71 ± 22.5 pg · ml⁻¹). Discussion: The results indicate that several neuroendocrine and immunological parameters are modulated by prolonged HDBR and these changes may be counteracted at least in part by artificial gravity with exercise.

Pontier J-m, Jimenez C, Blatteau J-E. Blood platelet count and bubble formation after a dive to 30 msw for 30 min. Aviat Space Environ Med 2008; 79:1096–9. Introduction: Previous human studies reported that platelet count (PC) is decreased following decompression. Platelet aggregation and adherence to the bubble surface has been demonstrated in severe decompression sickness (DCS). The present study was designed to clarify the relationship between post-dive changes in blood PC and the level of bubble formation in divers. Methods: There were 40 healthy experienced divers who were assigned to 1 experimental group (N = 30) with an open-sea air dive to 30 msw for 30 min in field conditions and 1 control group (N = 10) without hyperbaric exposure. Bubble grades were monitored with a pulsed Doppler according to the Spencer scale and Kissman integrated severity score (KISS). Blood samples for red blood cell counts (RBC), hematocrit (Hct), and PC were taken 1 h before and after exposure in two groups. Results: None of the divers developed any signs of DCS. In two groups, the results showed significant increase in RBC count and Hct related with hemoconcentration and no change in PC. Divers with a high KISS score (39 ± 5.8; mean ± SD) presented a significantly more pronounced percent fall in PC than divers with a lower KISS score. We found a significant correlation between the percent fall in PC after a dive and the bubble KISS score. Discussion: The present study highlighted a relationship between the post-dive decrease in PC and the magnitude of bubble level after decompression. Our primary result is that the post-dive decrease in PC could be a predictor of decompression severity after diving.

Blatteau J-É, Gempp E, Balestra C, Mets T, Germonpre P. Predive sauna and venous gas bubbles upon decompression from 400 kPa. Aviat Space Environ Med 2008; 79:1100–5. Introduction: This study investigated the influence of a far infrared-ray dry sauna-induced heat exposure before a simulated dive on bubble formation, and examined the concomitant adjustments in hemodynamic parameters. Methods: There were 16 divers who were compressed in a hyperbaric chamber to 400 kPa (30 msw) for 25 min and decompressed at 100 kPa · min⁻¹ with a 4-min stop at 130 kPa. Each diver performed two dives 5 d apart, one with and one without a predive sauna session for 30 min at 65°C ending 1 h prior to the dive. Circulating venous bubbles were detected with a precordial Doppler 20, 40, and 60 min after surfacing, at rest, and after flexions. Brachial artery flow mediated dilation (FMD), blood pressure, and bodyweight measurements were taken before and after the sauna session along with blood samples for analysis of plasma volume (PV), protein concentrations, plasma osmolality, and plasma HSP70. Results: A single session of sauna ending 1 h prior to a simulated dive significantly reduced bubble formation [−27.2% (at rest) to 35.4% (after flexions)]. The sauna session led to an extracellular dehydration, resulting in hypovolemia (−2.7% PV) and −0.6% bodyweight loss. A significant rise of FMD and a reduction in systolic blood pressure and pulse pressure were observed. Plasma HSP70 significantly increased 2 h after sauna completion. Conclusion: A single predive sauna session significantly decreases circulating bubbles after a chamber dive. This may reduce the risk of decompression sickness. Sweat dehydration, HSP, and the NO pathway could be involved in this protective effect.

Vats P, Singh VK, Singh SN, Singh SB. Glutathione metabolism under high-altitude stress and effect of antioxidant supplementation. Aviat Space Environ Med 2008; 79:1106–11. Introduction: Humans have a number of mechanisms for protection against reactive oxygen species, but under stressful conditions these defenses are not completely successful. Glutathione plays an important role in protection against free radicals and reactive oxygen species induced damages. The present study was undertaken to understand the effect of high-altitude (HA) exposure on glutathione metabolism and antioxidant status along with the effects of N-acetyl cysteine (NAC) and vitamin E supplementation in humans. Methods: The study was conducted on 30 healthy male volunteers (age 22.9 ± 2.6, mean ± SD) divided into three groups. Group 1 was placebo control and 2 and 3 were supplemented with 400 mg of NAC or vitamin E, respectively, per day. The study was conducted initially at sea level (Phase I, 320 m); then the subjects were taken to high altitude (Phase II, 3600 m) by air. After a week at this altitude, subjects ascended on foot to an altitude of 4580 m (Phase III). Results: Significant decreases in reduced glutathione and increases in oxidized glutathione levels were observed on HA exposure. Increase in glutathione peroxidase and glutathione reductase levels were also observed on HA exposure. Lower levels of plasma vitamin C and total antioxidant status were observed during HA exposure. The changes observed were less in the supplemented groups as compared to placebo control. Discussion: Results indicate that HA exposure adversely affects glutathione metabolism and antioxidant defense mechanisms and these changes can be ameliorated through supplementation of NAC and vitamin E.

Gempp E, Blatteau J-E, Stephant E, Pontier J-M, Constantin P, Pény C. MRI findings and clinical outcome in 45 divers with spinal cord decompression sickness. Aviat Space Environ Med 2008; 79:1112–6. Background: Decompression sickness (DCS) affecting the spinal cord is the most dangerous form of diving-related injury with potential sequelae. This study was conducted to evaluate the relationship between spinal cord lesions on MRI and clinical findings in divers with spinal DCS. Methods: We studied 45 cases of DCS that were referred to our hyperbaric facility with clinical evidence of spinal involvement during the period 2002–2007. The study included only patients who underwent MRI within 10 d of injury. The severity of spinal DCS for each patient was rated numerically for both the acute event and 1 mo later. The presence or absence of back pain was also noted. Results: Spinal cord lesions were significantly more frequent in divers with severe DCS, and did not occur in any diver who experienced a favorable outcome (sensitivity = 67%, specificity = 100%, negative predictive value = 77%, positive predictive value = 100%). The presence of vertebral degenerative changes that impinged on the spinal cord was strongly associated with MRI abnormalities, but not with a negative outcome. Acute back pain was associated with hyperintense lesions and persistence of neurological sequelae [OR = 14 (95% CI, 3.1 to 63.5)]. Conclusion: The results show that MRI could be helpful in predicting clinical outcome in divers with spinal cord DCS. The presence of medullary compressive factors and vertebral back pain after surfacing indicate increased likelihood of severe myelopathy with incomplete recovery.