Resistance and hemodynamic reactions in healthy pilots under the conditions of passive orthostatic loading

The results of the analysis of materials on the expert assessment of 66 healthy pilots subjected to a passive orthostatic stress test (POT) by the generally accepted technique of a 20-min head-down tilt bed rest at an angle of 80° to the horizontal are presented. The obtained hemodynamic responses to the test were typified using the generally accepted concepts of functional classes (FC). A good POT tolerance was recorded in 86.4% of the observations, with 36.4% assigned to the first functional class (FC-I) and 50%, to the second functional class (FC-II). A satisfactory orthostatic test tolerance (FC-III) was recorded in 10.6% of the observations, whereas a reduced and poor tolerance (FC-IV and FC-V) was found in 3% of the observations. According to ECGs and computer-assisted tachooscillography, subjects of the FC-I group reached the optimum indicators in their adaptive hemodynamic responses, compared to the pilots of the FC-II group and, particularly, the FC-III group. The latter two groups were found to exhibit some previously unknown objective symptoms, such as marked blood pressure (BP) lability and reversible hypo- and hypertensive responses, which allowed us to differentiate the FC-I pilots from the latter two groups. Based on the obtained results, additional clinical functional tolerance assessment criteria have been developed for a passive orthostatic test as part of the medical expert assessment of flight personnel with different levels of functional stability.     

Dynamic time course of hemodynamic responses after passive head-up tilt and tilt back to supine position.

Mechanisms involved in the control of arterial pressure during postural changes were studied by analysis of the dynamic time course of cardiovascular changes during head-up tilt (HUT) and tilt back to supine position (TB). Beat-to-beat values of cardiovascular variables were recorded continuously before, during, and after passive HUT to 30 degrees in seven healthy humans. Left cardiac stroke volume (SV, Doppler ultrasound), mean arterial blood pressure (MAP), heart rate (HR), cardiac output (CO), and total peripheral conductance (TPC) were recorded. During HUT, MAP at the level of the carotid baroreceptors decreased by approximately 5 mmHg. There was a striking asymmetry between the time courses of cardiovascular changes on HUT and on TB. Adjustments generally took up to 30 s after HUT, whereas most changes were completed during the first 10 s after TB. Cardiovascular reflex adjustments of HR and TPC were more symmetrical. After HUT, SV was maintained during the first 4-6 s and then decreased steadily during the next 30 s to a stable level approximately 25% below its pretilt value. However, after TB, SV increased rapidly to its pretilt value in <10 s. This asymmetry in SV dynamics may be explained in part by a more rapid change in left cardiac filling after TB than after HUT. On TB, there must be a rapid inflow of stagnant blood from the legs, whereas venous valves will impede backward filling of veins in the lower body on HUT. In conclusion, we have revealed a characteristic asymmetry in cardiovascular responses to inverse variations in gravity forces in humans. This asymmetry can be explained in part by nonlinear, hydrodynamic factors, such as the one-way effect of venous valves in the lower part of the body.     

Influence of incubation conditions on the specific methanogenic activity test

The main objective of this work was to evaluate the influence of incubating conditions on the specific methanogenic activity (SMA) test in order to harmonize the test protocol. For this serum bottles were incubated with anaerobic sludge (from UASB reactor treating domestic sewage) in factorial planned experiments which assessed the influence of the temperature, substrate concentration, food/microorganism (F/M) ratio, presence of yeast extract in the medium, as well as type of carbon and nutrient solution. The results showed that the tested methane measuring methods (volumetric with biogas characterization, volumetric with gas wash in alkaline solution, and manometric by using the OxiTop^® system) presented a similar performance. The maintenance of a small gaseous phase volume (e.g. 10% of the total volume) resulted in higher SMA values; and the ideal substrate concentration for the SMA test ranged from 0.5 to 3.0 gCOD/l since higher acetate concentration caused sludge inhibition. The suggested temperature for the test is 35°C and the best F/M ratio varied from 0.125 to 0.750 gCOD/gVS, and this seemed to be the most influent parameter for the SMA test. Finally tests performed with nutrient solution complemented by yeast extract resulted in the highest SMA values.     

Influence of Naloxone on the cellular immune response to head-up tilt in humans

To evaluate a possible role for β-endorphin in the stress-induced modulation of natural killer (NK) cells, immunologically competent blood cells were followed in eight male volunteers administered either Naloxone or saline (control) during head-up tilt maintained until the appearance of presyncopal symptoms (PS). The PS appeared more rapidly with Naloxone compared to control [5.7 (SEM 1.1) vs 22.3 (SEM 5.1) min; P = 0.01]. The NK cell activity increased threefold during PS partly due to an increase in CD16⁺ and CD56⁺ NK cells in blood. In support, NK cell activity boosted with interferon-α and interleukin 2 rose in parallel with unboosted NK cell activity and NK cell concentration and activities returned to the baseline level after 105 min. The total lymphocyte count and the concentrations of CD3⁺, CD4⁺, CD8⁺, CD16⁺, and CD56⁺ cells increased during PS. Head-up tilt also induced an increase in plasma adrenaline concentration during control PS and a rise in plasma cortisol and adrenocorticotropic hormone concentrations up to 30 min thereafter, whereas no significant changes were found in plasma concentrations of noradrenaline, growth hormone, or β-endorphin. The results would indicate an influence of endorphin on the increase in plasma adrenaline concentration during head-up tilt and at the same time contra-indicate a significant role for adrenaline in the provocation of PS. The influence of head-up tilt on plasma β-endorphin was too small to influence the modulation of the cellular immune system. Accepted: 22 May 1997     

Physiological reactions of primates to 9-D immersion and head-down tilt

Purpose of the investigation was to compare physiological reactions of primates (Macaca mulatta) to microgravity simulated by immersion and head-down tilt (HDT). In immersion experiments, primates in waterproof suits were put into motion-restraining chairs and immersed into water (t=35.4 degrees C) breast-deep for 9 days. In 9-d HDT experiments, prone primates were motor restrained in dedicated tilt beds at -5 degrees. It was found that the CNS functioning was significantly affected, the plasma volume reduced and the marrow erythropoietic function declined. Atrophy developed in leg muscles on a backdrop of iliopectineal spongy osteopenia. Loss in hydration, inhibition of erythropoietic hemopoiesis and iliopectineal spongy osteopenia were more pronounced following immersion than HDT.     

Influence of gender on the response to hemodynamic overload after myocardial infarction

After myocardial infarction (MI), the left ventricle (LV) undergoes ventricular remodeling characterized by progressive global dilation, infarct expansion, and compensatory hypertrophy of the noninfarcted myocardium. Little attention has been given to the response of remodeling myocardium to additional hemodynamic overload. Studies have indicated that gender may influence remodeling and the response to both MI and hemodynamic overload. We therefore determined 1) structural and function consequences of superimposing hemodynamic overload (systemic hypertension) on remodeling myocardium after a MI and 2) the potential influence of gender on this remodeling response. Male and female Dahl salt-sensitive and salt-resistant rats underwent coronary ligation, resulting in similar degrees of MI. One week post-MI, all rats were placed on a high-salt diet. Four groups were then studied 4 wk after initiation of high-salt feeding: MI female, MI female + hypertension, MI male, and MI male + hypertension. Hypertension-induced pressure overload resulted in additional comparable degrees of myocardial hypertrophy in both females and males. In females, hypertension post-MI resulted in concentric hypertrophy with no additional cavity dilation and no measurable scar thinning. In contrast, in males, hypertension post-MI resulted in eccentric hypertrophy, further LV cavity dilation, and scar thinning. Physiologically, concentric hypertrophy in post-MI hypertensive females resulted in elevated contractile function, whereas eccentrically hypertrophied males had no such increase. Female gender influences favorably the remodeling and physiological response to hemodynamic overload after large MI.     

The effect of fermented-milk bifidumbacterin on the intestinal microflora of test pilots]

Bacteriological study of intestinal microflora in test pilots, regularly exposed to excessive physical, as well as nervous and emotional strain, has revealed changes in the composition of their intestinal microflora. Correction of microflora by means of bifidumbacterin, a curative lactic fermentation alimentary product, was carried out. Rapid and effective restoration of intestinal microflora and improvement of the general state of patients were noted, which made it possible to recommend this product as a prophylactic remedy for subjects at risk of development of dysbiotic disturbances.     

Effect of organic solvents in the course of professional exposure on the E rosette test and skin reactions against distreptase and tuberculin

The study comprised 106 workers having professional contact with organic solvents containing benzene, toluene, and xylene during 1 to 122 months. The reduction of the total lymphocyte and the T lymphocyte count (T cells forming both "early" and "late" rosettes with sheep erythrocytes) corresponding to the prolongation of the exposure time to the solvents (the negative correlation) was observed. These alterations are not associated with disturbances of delayed skin hypersensitivity against tuberculin and distreptase. The E rosette test may serve as a practical test for monitoring the biological effects of exposure to organic solvents.     

Physostigmine effects on activity and reactions to novelty

Effects of 4 doses of physostigmine on reactions to novelty, rearing and ambulation in rats were observed in an exploration box which allowed free choice of novel and familiar halves. All 3 responses tended towards decreases with higher doses but, whereas this trend was significant for rearing and ambulation, it was only suggestive for reactions to novelty. The results were discussed in the light of views on cholinergically controlled habituation processes.     

A variant of the integrate-and-fire model to simulate the adaptive neural firing pattern

The integrate-and-fire (IF) based modeling technique has been long employed to study the neural firing activities. This paper introduces a variant of the IF model in order to simulate the adaptive neural firing pattern. An inductor branch is integrated into the IF model to track the variance of the external stimulus, and subsequently control the decrease of the instantaneous firing rate in response to the sustained stimulation. Simulation results demonstrated that the proposed model was able to reproduce the adaptive neural firing pattern. Besides, the inductor branch might adjust the decay rate of the adaptive firing curve and the prominent firing rate upon the onset of the adaptation. The proposed model is characterized by its structure simplicity and simulation efficiency, which would be helpful for the analysis and prediction of the adaptive firing responses of the sensory neurons.     

Evaluation of the effect of fentanyl on nociceptive hemodynamic reactions using multifactorial analysis

It has been demonstrated in chronic experiments on cats that the reactions on the part of arterial pressure and heart rate evoked by dental pulp stimulation are highly resistant to the depressant action of phentanyl (1-30 micrograms/kg). Using multifactorial analysis of the data obtained one could reveal individual features of the effect of the analgetic on the nociceptive hemodynamic reactions determined by the initial status of the animals. The effect of phentanyl on cardiovascular shifts was found to develop regardless of the analgetic (emotiotropic) action.     

On the adaptive pattern of "Ramapithecus".

A reconstruction of the adaptive pattern of the Miocene hominoid "Ramapithecus," supported by comparative data and morphological comparisons, is presented. It is based upon the completely known dentition, inferior portion of the face, and on the paleoecology and geographic distribution of "Ramapithecus" bearing deposits. The known adaptive and morphological patterns of the "Ramapithecus" species are almost indistinguishable from those of the contemporary species of Sivapithecus, which has taxonomic priority. The "Ramapithecus" species are therefore referred to Sivapithecus, a dryopithecine genus which apparently radiated throughout Eurasia and Africa during the Middle Miocene.     

Patient acceptance of adequately filled breast implants using the tilt test

Adequate fill of any breast implant, regardless of shell characteristics, shape, or filler material, is important to prevent implant shell wrinkling, folding, or collapse that could potentially decrease the life of the implant. Implant shell life is a major factor that affects reoperation rates. The greater the necessity of reoperations, regardless of implant type, the greater the rate of local complications, necessitating additional surgery with additional risks and costs to patients. Palpable shell folding, visible wrinkling or rippling, palpable shifts of filler material, sloshing, and compromised aesthetic results can result from an under-filled implant. Any of these complications can necessitate reoperations with increased risks and costs to patients. This is a study of 609 consecutive patients from January of 1993 to December of 1998 who were given detailed preoperative informed consent and a choice of implant shape and type and who chose the increased firmness associated with an implant that is adequately filled to pass the tilt test. This study addresses two questions: (1) Will patients accept the increased firmness of an implant that is filled to pass the tilt test? and (2) Is adequate fill by the tilt test useful clinically to help reduce the incidence of postoperative rippling, wrinkling, and spontaneous deflation in saline implants? Patients were followed by postoperative examinations and questionnaires. No patient requested implant replacement to a softer implant postoperatively, and no reoperations were performed for visible rippling or wrinkling. The spontaneous deflation rate over this 6-year period was 9 of 1218 implants, or 0.739 percent. If patients will accept more firmness with an adequately filled implant, regardless of the filler material, surgeons might worry less about recommending an adequately filled implant to patients, and manufacturers might feel more comfortable producing adequately filled implants and redefining fill volumes for underfilled implants. More adequately filled implants could potentially reduce risks of reoperations by reducing premature shell failure and shell wrinkling complications.     

Influence of the porous texture of silica gels on the enzymatic activity of lipases in esterification reactions

Pseudomonas Cepacia lipases were encapsulated in hybrid silica-polyvinyl alcohol gels, which were dried either supercritically in order to form aerogels or by evaporation so as to obtain xerogels. In each case, the catalytic activity of the encapsulated enzymes was studied and compared to free enzyme biocatalysis. This study demonstrates that the activity of the enzyme is increased when the procedure used allows it to resist capillary stresses occurring during the drying of the gel. That is, esterification rates are higher when the gels are synthesized with a base catalyst, such as NaF, in the presence of polyvinyl alcohol and then dried supercritically.     

Effects of lower body positive pressure on muscle sympathetic nerve activity response to head-up tilt

The present study was performed to test the hypothesis that application of lower body positive pressure (LBPP) during orthostasis would reduce the baroreflex-mediated enhancement in sympathetic activity in humans. Eight healthy young men were exposed to a 70 degrees head-up tilt (HUT) on application of 30 mmHg LBPP. Muscle sympathetic nerve activity (MSNA) was microneurographically recorded from the tibial nerve, along with hemodynamic variables. We found that in the supine position with LBPP, MSNA remained unchanged (13.4 +/- 3.3 vs. 11.8 +/- 2.3 bursts/min, without vs. with LBPP; P > 0.05), mean arterial pressure was elevated, but arterial pulse pressure and heart rate did not alter. At 70 degrees HUT with LBPP, the enhanced MSNA response was reduced (33.8 +/- 5.0 vs. 22.5 +/- 2.2 bursts/min, without vs. with LBPP; P < 0.05), mean arterial pressure was higher, the decreased pulse pressure was restored, and the increased heart rate was attenuated. We conclude that the baroreflex-mediated enhancement in sympathetic activity during HUT was reduced by LBPP. Application of LBPP in HUT induced an obvious cephalad fluid shift as well as a restoration of arterial pulse pressure, which reduced the inhibition of the baroreceptors. However, the activation of the intramuscular mechanoreflexes produced by 30 mmHg LBPP might counteract the effects of baroreflexes.     

Effect of adaptive biocontrol sessions on persons with strong professional skills

We studied the effect of adaptive biocontrol on the quality of the professional activity of an operator possessing stable skills in modeling manual control of station-keeping and berthing to the International Space Station (ISS) of the Soyuz transport ship. The operational quality was evaluated in terms of time, energy, and precision parameters. A computer model of the dynamic ISS image and machinery identical to the real machinery were used in the study.