Subudhi AW, Lorenz MC, Fulco CS, Roach RC. Cerebrovascular responses to incremental exercise during hypobaric hypoxia: effect of oxygenation on maximal performance. Am J Physiol Heart Circ Physiol 294: H164-H171, 2008. First published November 21, 2007 doi:10.1152/ajpheart.01104.2007.-We sought to describe cerebrovascular responses to incremental exercise and test the hypothesis that changes in cerebral oxygenation influence maximal performance. Eleven men cycled in three conditions: 1) sea level (SL); 2) acute hypoxia [AH; hypobaric chamber, inspired PO2 (PIO 2 ) 86 Torr]; and 3) chronic hypoxia [CH; 4,300 m, PIO 2 86 Torr]. At maximal work rate (Ẇ max), fraction of inspired oxygen (FIO 2 ) was surreptitiously increased to 0.60, while subjects were encouraged to continue pedaling. Changes in cerebral (frontal lobe) (COX) and muscle (vastus lateralis) oxygenation (MOX) (near infrared spectroscopy), middle cerebral artery blood flow velocity (MCA Vmean; transcranial Doppler), and end-tidal PCO2 (PETCO 2 ) were analyzed across %Ẇ max (significance at P Ͻ 0.05). At SL, PETCO 2 , MCA Vmean, and COX fell as work rate rose from 75 to 100% Ẇ max. During AH, PETCO 2 and MCA Vmean declined from 50 to 100% Ẇ max, while COX fell from rest. With CH, PETCO 2 and COX dropped throughout exercise, while MCA Vmean fell only from 75 to 100% Ẇ max. MOX fell from rest to 75% Ẇ max at SL and AH and throughout exercise in CH. The magnitude of fall in COX, but not MOX, was different between conditions (CH Ͼ AH Ͼ SL). FIO 2 0.60 at Ẇ max did not prolong exercise at SL, yet allowed subjects to continue for 96 Ϯ 61 s in AH and 162 Ϯ 90 s in CH. During FIO 2 0.60, COX rose and MOX remained constant as work rate increased. Thus cerebral hypoxia appeared to impose a limit to maximal exercise during hypobaric hypoxia (PIO 2 86 Torr), since its reversal was associated with improved performance. altitude; near infrared spectroscopy; cerebral blood flow; fatigue; muscle oxygenation CEREBRAL HYPOXIA HAS BEEN proposed to be a critical factor limiting exercise performance (37), particularly in hypoxia (7), yet little evidence exists to directly support this theory. Kayser et al. (31) were the first to show that rapidly increasing the fraction of inspired oxygen (FI O 2 ) at the point of maximal exertion prolonged exercise in hypoxia-acclimatized subjects. They concluded that the effect of increased FI O 2 was too quick to have reversed metabolic factors associated with peripheral (intramuscular) fatigue and suggested that cerebral reoxygenation was a more likely explanation for the improvement in exercise performance. Calbet et al. (11) arrived at similar conclusions after using a comparable model to study factors limiting O 2 uptake (V O 2 ). They suggested that exercise under hypoxic conditions may have presented a significant threat to cerebral oxygenation; thus cardiac and/or motor output was curtailed to maintain favorable tissue oxygenation status.While these studies insinuate the importance of preserving cerebral oxygenation during exer...

POSTURAL KEACTIONS IN J'lENTAL UISEASErise to necrosis of the skin under the same conditions. -4,fter intramuscular injection in rats all three drugs gave an early inflammatory response &a.racterized by the appearance of a polyrnorphonuclear exudate. In the case of Thiomerin this exudate was entirely resorbed without evidem of residual damage. After injection of Mercuzanthin, or Mercuhydrin, however, the irreversible nature of the re-sponse was indicated by marked fibroblastic proliferation.These results would seem to furnish an adequate experimental basis for the clinical use of Thiomerin by subcutaneous injection.The au.thors wish to thank the Misses Florence Ka.tine and Josephine Brosseau for able technical assis tame.

Standard Form 298 (Rev. 8/98) REPORT DOCUMENTATION PAGEPrescribed by ANSI Std. Z39.18 Form Approved OMB No. 0704-0188The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, Approved for public release; distribution unlimited. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S)While performing demanding physical activity for long durations, fluid and electrolyte imbalance is common in athletes, military personnel, and recreational hikers. The military and civilian communities have introduced extensive heat mitigation measures to manage heat strain and reduce the risk of serious exertional heat illnesses (EHI). These heat mitigation measures include fluid and electrolyte replacement guidelines, vigilance, and identifying high-risk individuals. Despite these measures, exercise in hot weather continues to result in preventable injuries and deaths in young, healthy individuals. With existing emphasis on appropriate fluid intake during exercise for the avoidance of dehydration, heat illness, and associated performance decrements, there has been a subsequent increase in reported exertional hyponatremia (HYPO) cases related to excessive water intake, elevated sweating rates, excessive sodium losses in sweat, and inadequate sodium intake in soldiers (1), athletes (2,3,4), and recreational hikers (5,6). The primary purpose of this article is to systemically examine the epidemiological literature of fluid and electrolyte imbalances that occur during physical activity. The secondary purpose of this article is to examine signs and symptoms of HYPO and EHI cases from the literature (1,2,5,7Y26) and the U.S. Army Research Institute of Environmental Medicine (USARIEM) Total Army Injury and Health Outcomes Database (TAIHOD). While it is acknowledged that the populations at risk for HYPO and EHI may differ, reasonable comparisons are made by examining incidence rates to better understand relative magnitude of each condition. It has been reported that these two conditions have several overlapping clinical features, which has led to misdiagnosis in some rare cases. This article is not intended to persuade the reader of the relative importance of either condition.altitude; near infrared spectroscopy; cerebral blood flow; fatigue; muscle oxygenation intact animal to the cellular, subcellular, and molecular levels. It is published 12 times a year (monthly) by the American lymphatics, including experimental and theoretical studies of cardiovascular function at all levels of organization ranging from the publishes original investigations on the physiology of the heart, blood vessels, and AJP -...