Increased brain 1H-MRS glutamate and lactate signals following maximal aerobic capacity exercise in young healthy males: an exploratory study.

Physical exercise involves increased neuronal activity of many brain structures, but 1H-MRS investigations on the effects of human brain glutamate (Glu) concentrations on acute exercise have been sparse. Previous studies consistently found increases in brain lactate (Lac) concentrations following graded exercise up to 85% of the predicted maximal heart rate. However, the reported effects on brain concentrations of glutamine and glutamate were not consistent. This study aimed to determine the effect of acute intense graded maximal exercise on 1H-MRS signals related to concentrations of Glu, glutamate+glutamine (Glx), and Lac. Young adult males were randomly divided into two groups and subjected to 1H-MRS when resting (NE) or shortly after cessation of the intense graded exercise intended to pass the anaerobic threshold (E). 1H-MRS spectra were acquired from the large voxel encompassing the occipito-parietal cortex only once. Estimates of Glu, Glx, and Lac concentrations were calculated in institutional units by normalizing to a spectroscopic signal originating from creatine-containing compounds (Cr). Concentrations of Glu, Glx, and Lac were respectively 11%, 12.6%, and 48.5% higher in E than in NE (p < 0.001). The increased brain Lac signal in the exercising group indicated that in our experiment, vigorous exercise resulted in passing the anaerobic threshold and lactate apparently entered the brain. Concomitantly glutamate-related resonance signals from the vicinity of the occipito-parietal cortex were significantly increased; physiological mechanisms underlying these phenomena require further study. Future studies should evaluate whether the normalization rate of these concentrations is a marker of general physical fitness.

Development of a new method for assessing the heart rate increase during tests in human carrying centrifuge.

Exposition to head to foot accelerations (+Gz) on human carrying centrifuge are associated with increase in heart rate (HR). Sometimes, especially with extremely high HR values it is almost impossible to distinguish between fast sinus rhythm and supraventricular tachycardia which is essential for the safety of the subject and therefore the decision regarding break the centrifuge examination earlier. AIM: The aim of the work was to answer the question: what is the maximum physiological rise of the sinus heart rate, recorded beat to beat, during tests in the overload centrifuge, which should lead to the suspicion of paroxysmal supraventricular tachycardia? MATERIALS AND METHODS: The material tested was an electrocardiogram (ECG) digital records of 150 pilots, achieved during both GOR and ROR tests, carried out in the human centrifuge. The HR, increase of HR (ΔHR) and their changes accompanying the + Gz acceleration ware analysed. RESULTS: Mean values of the parameters determined from all centrifuge exposures were: HR - 105.8 beats per minutes (bpm,) ΔHR 2.5, + Gz 4.06. There was no relationship between ΔHR and + Gz increase The values of ΔHR, meeting the eligibility criteria for the possible PT, were in the range 2.41 to 11.19 bpm on average 2.5 bpm. CONCLUSIONS: Rapid/unexpected HR beat to beat acceleration (ΔHR) during a GOR or ROR centrifugal test, exceeding 11 beats/min, in relation to the HR rate immediately preceding it and persisting for at least 4 consecutive heart evolutions, requires the attention of the examining doctor, and ECG should be examined for paroxysmal tachycardia.

Cardiac arrhythmias during aerobatic flight and its simulation on a centrifuge.

INTRODUCTION: It is well known that accelerations during centrifuge training and during flight can provoke cardiac arrhythmias. Our study was designed to investigate both the similarities and differences between heart rhythm disturbances during flights and centrifuge tests. METHOD: There were 40 asymptomatic, healthy pilots who performed two training flights and were also tested in a human centrifuge according to a program of rapid onset rate acceleration (ROR) and of centrifuge simulation of the actual acceleration experienced in flight (Simulation). During the flight and centrifuge tests ECG was monitored with the Holter method. ECG was examined for heart rhythm changes and disturbances. RESULTS: During flights, premature ventricular contractions (PVCs) were found in 25% of the subjects, premature supraventricular contractions (PSVCs) and PVCs with bigeminy in 5%, and pairs of PVCs in 2.5% of subjects. During the centrifuge tests, PVCs were experienced by 45% of the subjects, PSVCs and pairs of PVCs by 7.5%, and PVCs with bigeminy by 2.5%. Sinus bradycardia was observed during flights and centrifuge tests in 7.5% of subjects. DISCUSSION: Comparative evaluation of electrocardiographic records in military pilots during flights and centrifuge tests demonstrated that: 1) there were no clinically significant arrhythmias recorded; and 2) the frequency and kind of heart rhythm disturbances during aerobatic flight and its simulation on a centrifuge were not identical and did not occur repetitively in the same persons during equal phases of the tests.

Activities of red blood cell anti-oxidative enzymes (SOD, GPx) and total anti-oxidative capacity of serum (TAS) in men with coronary atherosclerosis and in healthy pilots.

BACKGROUND: Reactive oxygen species (ROS) have been proposed to play important pathogenic roles, especially in harmful oxidative modifications of low-density cholesterol. Redox balance within the organism is largely determined by the activities of anti-oxidative enzymes of red blood cells and by the total anti-oxidative capacity of the serum (TAS). MATERIAL/METHODS: SOD and GPx activities and TAS in 13 men aged 42-65 years with coronary atherosclerosis (group I) were compared with those of both 15 clinically healthy pilots matched for age and lipid abnormalities (cholesterol and triglycerides) (group II) and 14 age-matched pilots without lipid abnormalities (group III). RESULTS: There were statistically significant differences in SOD and GPx activities and in TAS between the groups. CONCLUSIONS: 1. SOD and GPx activities and TAS were lower in men with advanced coronary atherosclerosis that in age-matched clinically healthy men with similar dyslipidemia and were even further decreased compared with clinically healthy men without dyslipidemia. 2. The decrease in SOD and GPx activities and TAS in men with advanced coronary atherosclerosis was more pronounced than the degree of hypercholesterolemia or hypertriglyceridemia. 3. If hyperlipidemia and the activity of antioxidative enzymes and TAS were considered without reference to other risk factors of atherosclerosis, it appeared that the decreases in SOD, GPx, and TAS may play a more important role in the development of the atherosclerotic process than isolated increases in free cholesterol or triglyceride levels.

Centrifuge braking effects on cardiac arrhythmias occurring at high +Gz acceleration.

Abrupt onset and offset of acceleration induces hemodynamic changes that activate a number of reflex cardiovascular responses. At high +Gz on a centrifuge, apparently healthy subjects occasionally develop a serious cardiac arrhythmia such as supraventricular tachycardia or asystole. We report on four such cases and examine the effect of rapid centrifuge braking (1 G x s(-1)) on the arrhythmia. It appears that the hemodynamic consequences and reflex responses produced by rapid deceleration may have a positive effect on paroxysmal supraventricular tachycardia, slowing the heart rate or terminating the arrhythmia. On the other hand, deceleration tends to intensify sinus bradycardia. If further study confirms these findings, medical monitors and centrifuge operators may want to consider using gradual braking in cases of bradycardia.