Vestibular autorotation test in primary selection of military student pilots using neural networks.

BACKGROUND: Selection of student pilots to the Royal Danish Air Force involves a physical examination including a vestibular test. Usually tests for selection proposes are not well documented. HYPOTHESIS: The result of the vestibular autorotation test (VAT) is correlated to the ability to learn to fly in a military context. METHODS: A Multi Layer Perception neural network with three layers configured as a Back Propagation Network was tested using data originating from horizontal VAT of 59 student pilot candidates, given the outcome of the pre-jet basic flight check. In the analysis the leave-one-out method was used. RESULTS: Based on horizontal data only the network correctly classified the student pilot candidates as having been passed or rejected within a verification error margin < 0.1. CONCLUSION: The result indicates that VAT performed at the initial physical examination is a powerful tool for the elimination of unfit student pilot candidates when data are analyzed in neural networks.

[Barotrauma in children and adults after flying. Prevalence and treatment with Otovent]. / Barotitis hos børn og voksne efter flyvning. Praevalens og behandling med Otovent.

To prevent barotitis during descent in aviation, the ears have to be cleared several times by performing the Valsalva's manoeuvre. The manoeuvre is difficult for children to perform, and they are therefore at high risk of developing barotitis. The treatment of barotitis is either inflation by a Politzer balloon or myringotomy. An alternative treatment is autoinflation using the Otovent. This prophylaxis/treatment can be performed by the child with assistance from its parents as soon as or preferably before the descent has started. The prevalence of barotitis amongst 45 children and 49 adults in transit was found to be highest in children, 28%, compared with adults, 10%. Only 6% of the children with negative middle ear pressure after flight managed a successful Valsalva manoeuvre, whereas 33% could normalise the middle ear pressure by inflating the Otovent. In conclusion we recommend autoinflation using the Otovent set by children and adults who have problems clearing their ears during flight.

Point prevalence of barotitis in children and adults after flight, and effect of autoinflation.

The most common cause of barotitis is pressure changes during descent in aviation. Equilibration is normally achieved by swallowing, jaw movements, yawning, or chewing, but some have to perform a Valsalva maneuver several times during descent and even by these means some fail. The aim of the study was to estimate the point prevalence of barotrauma in children and adults after flight, and to test the effect of an autoinflation device (Otovent), in improving negative middle ear pressure after flight. Questionnaires and Otovent, were distributed to all air passengers in eight incoming flights. The questionnaires inquired about nasal allergy, nasal congestion, previous and actual ear pain, use of decongestants and experience of inflating the Otovent set during descent. After flight, the passengers were offered an ear examination including otoscopy and tympanometry both before and after a Valsalva maneuver, as well as after Otovent inflation. Otoscopic signs of barotitis were found in 10% of the adults and in 22% of the children. Negative middle ear pressure of more than 10 hPa after landing was found in 20% of the adults and in 40% of the children. The Valsalva maneuver normalized the pressure in 46% of the adults and in 33% of the children. Of the adults, 73%, and of the children, 69% with an unsuccessful Valsalva maneuver could improve or normalize the middle ear pressure by inflating the Otovent set. In conclusion, we recommend autoinflation using the Otovent set to air passengers with problems clearing the ears during flight.

The natural killer cell response to exercise in spinal cord injured individuals.

In order to evaluate exercise-induced changes in natural killer (NK) and other immunocompetent cells in spinal cord injured individuals, immunological competent blood cells and stress hormones were followed in five paraplegic and six quadriplegic subjects in relation to 30 min electrically stimulated cycling exercise. The leukocyte and lymphocyte concentrations increased during exercise. In the recovery period, the concentration of neutrophils increased, whereas the lymphocytes decreased. The percentage and concentration of NK cells increased during exercise in the paraplegic group and returned to pre-exercise level 2 h after, whereas no changes were seen in these measures for the quadriplegic group. No changes in activated CD38+ NK cells appeared. Unstimulated and interferon-alpha or interleukin-2 stimulated NK cell activity increased during exercise and returned to pre-exercise level 2 h after with no distinction between paraplegics and quadriplegics. The concentrations of plasma growth hormone and catecholamines increased during exercise, with the rise in epinephrine being more pronounced in paraplegic than in quadriplegic subjects, indicating a difference between the groups in sympathetic nervous system integrity. The sympathoadrenal activity is concluded to be responsible for recruitment of NK cells to the blood during exercise.

Exercise-induced immunomodulation--possible roles of neuroendocrine and metabolic factors.

Acute muscular exercise induces an increased neutrophil count concomitant with recruitment of natural killer (NK), B and T cells to the blood as reflected by an elevation in the total lymphocyte count. Meanwhile, following intense exercise of long duration the lymphocyte count declines, non-MHC-restricted cytotoxicity is suppressed, but the neutrophil concentration increases. In relation to eccentric exercise involving muscle damage, the plasma concentrations of interleukin-1, interleukin-6 and the tumor necrosis factor are elevated. In this review we will propose a model based on the possible roles that stress hormones play a mediating the exercise- related immunological changes: adrenaline and to a lesser degree noradrenaline are responsible for the immediate effects of exercise on lymphocyte subpopulations and cytotoxic activities. The increase in catecholamines and growth hormone mediate the acute effects of exercise on neutrophils, whereas cortisol may be responsible for maintaining lymphopenia and neutrocytosis after exercise of long duration. Lastly, the role of beta-endorphin is less clear, but the cytokine response is closely related to muscle damage and stress hormones do not seem to be directly involved in the elevated cytokine level. Other possible mechanisms of exercise-induced immunomodulation may include the so-called glutamine hypothesis, which is based on the fact that skeletal muscle is an important source of glutamine production and that lymphocytes are dependent on glutamine for optimal growth. Furthermore, physiological changes during exercise, e.g. increased body temperature and decreased oxygen saturation may also in theory contribute to the exercise-induced immunological changes.

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

To evaluate a possible role for beta-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-alpha 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 beta-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 beta-endorphin was too small to influence the modulation of the cellular immune system.

Adrenergic beta 1- and beta 1 + 2-receptor blockade suppress the natural killer cell response to head-up tilt in humans.

To evaluate stress-induced changes in blood leukocytes with emphasis on the natural killer (NK) cells, eight male volunteers were followed during three trials of head-up tilt with adrenergic beta 1- (metoprolol) and beta 1 + 2- (propranolol) blockade and with saline (control) infusions. The beta 1- and beta 1 + 2-receptor blockade did not affect the appearance of presyncopal symptoms, but the head-up tilt induced a transient lymphocytosis that was abolished by beta 1 + 2-receptor blockade but not by beta 1-receptor blockade. Head-up tilt also resulted in delayed neutrophilia, which was insensitive to beta-receptor blockade. Lymphocyte subset analysis revealed that the head-up tilt resulted in a twofold increase in the percentage and absolute number of CD3-/CD16+ and CD3-/CD56+ NK cells in peripheral blood and that this increase was partially blocked by metoprolol and abolished by propranolol. The NK cell activity on a per NK cell basis did not change during head-up tilt, indicating that the cytotoxic capability of NK cells recruited to circulation is unchanged. The data suggest that the head-up tilt-induced lymphocytosis was due mainly to CD16+ and CD56+ NK cells and that their recruitment to the blood was inhibited by beta 1- and especially beta 1 + 2-receptor blockade. Thus stress-induced recruitment of lymphocytes, and of NK cells in particular, is mediated by epinephrine through activation of beta-receptors on the lymphocytes.

Barotitis in children after aviation; prevalence and treatment with Otovent.

Barotitis is an acute or chronic inflammation caused by environmental pressure changes. The most common cause is the pressure change during descent in civil aviation. To prevent barotitis the middle ear pressure has to be equalised several times during descent. This can be achieved by performing the Valsalva manoeuvre, but for children, many of whom have a dysfunction of the Eustachian tube, this is difficult to perform and they are therefore at high risk of developing barotitis during flight. The traditional treatment modalities of barotitis are inflation by a Politzer balloon, myringotomy or prophylactic grommet insertion. An alternative treatment or prophylactic measure is autoinflation using the Otovent treatment set. This prophylaxis/treatment can be performed by the child with assistance from its parents as soon as possible or rather before the descent has started. The prevalence of barotitis amongst transit passengers was found to be highest in young children, 25 per cent, compared with adults, five per cent. Only 21 per cent of the youngest children with negative middle ear pressure after flight managed a successful Valsalva's manoeuvre, whereas 82 per cent could increase the middle ear pressure inflating the Otovent set. In conclusion we recommend autoinflation using the Otovent set by children and adults with problems clearing the ears during flight.

Sympathetic influence on cardiovascular responses to sustained head-up tilt in humans.

Sympathetic beta-adrenergic influences on cardiovascular responses to 50 degrees head-up tilt were evaluated with metoprolol (beta 1-blockade; 0.29 mg kg-1) and propranolol (beta 1 and beta 2-blockade; 0.28 mg kg-1) in eight males. A normotensive-tachycardic phase was followed by a hypotensive-bradycardic episode associated with presyncopal symptoms after 23 +/- 3 min (control, mean +/- SE). Head-up tilt made thoracic electrical impedance (3.0 +/- 1.0 omega), mean arterial pressure (MAP, 86 +/- 4-93 +/- 4 mmHg), heart rate (HR, 63 +/- 3-99 +/- 10 beats min-1) and total peripheral resistance (TPR, 15 +/- 1-28 +/- 4 mmHg min L-1) increase, while central venous oxygen saturation (74 +/- 2-58 +/- 4%), cardiac output (5.7 +/- 0.1-3.1 +/- 0.3 L min-1), stroke volume (95 +/- 6-41 +/- 5 mL) and pulse pressure (55 +/- 4-49 +/- 4 mmHg) decreased (P < 0.05). Central venous pressure decreased during head-up tilt (7 +/- 2-0 +/- 1 mmHg), but it remained stable during the sustained tilt. At the appearance of presyncopal symptoms MAP (49 +/- 3 mmHg), HR (66 +/- 4 beats min-1) and TPR (15 +/- 3 mmHg min L-1) decreased (P < 0.05). Neither metoprolol or propranolol changed tilt tolerance or cardiovascular variables, except for HR that remained at 57 +/- 2 (metoprolol) and 55 +/- 3 beats min-1 (propranolol), and MAP that remained at 87 +/- 5 mmHg during the first phase with metoprolol. In conclusion, sympathetic activation was crucial for the heart rate elevation during normotensive head-up tilt, but not for tilt tolerance or for the associated hypotension and bradycardia.

Effects of isoniazid treatment on human lymphocyte proliferative response, lymphocyte subsets and natural killer cell activity.

The effect of isoniazid on proliferative response, natural killer (NK) cell activity and lymphocyte subset distribution of blood mononuclear cells (BMNC) was investigated. To evaluate the effect of treatment with isoniazid in pharmacologic concentrations, twenty healthy HIV-seronegative volunteers were randomized into two groups: one group received isoniazid tablets plus pyridoxin tablets once a day for 30 days, the other group received pyridoxin only. Blood samples were collected on day 0 and day 30. Inhibition of the PHA-induced proliferative response was demonstrated in lymphocyte cultures from isoniazid-treated volunteers (p < 0.001). However, no effect was seen on the IL-2- or antigen (PPD)-induced proliferative response or the NK cell activity of isolated BMNC. Inhibition of the PHA-induced proliferative response could not be related to changes in the distribution of CD3+, CD4+, CD8+, CD14, or CD19+ lymphocyte subsets. The effects, in vitro, were investigated by addition of isoniazid to cultures of BMNC isolated from either HIV-seroposive or HIV-seronegative donors who did not receive any treatment. We found that isoniazid did not influence the mitogen- or antigen-stimulated proliferative response or the NK cell activity.

Effect of eccentric exercise on natural killer cell activity.

The effect of eccentric one-legged exercise on natural killer (NK) cell activity was studied in eight healthy males. To distinguish between local and systemic effects, blood samples were collected from veins in the exercising leg and resting arm. However, the results did not significantly differ between the leg and arm. To eliminate diurnal variations, the results were compared with a control group that did not exercise but had blood samples collected at the same time points. In the exercising group, plasma creatine kinase increased progressively during and up to 4 days after exercise. The percentage of CD16+ NK cells increased during exercise, which was paralleled by an increase in the NK cell activity per fixed number of blood mononuclear cells. The NK cell activity on a per NK cell basis did not change. The percentage of CD3+, CD4+, CD8+, CD19+, and CD14+ cells did not change significantly during exercise. The present study thus showed that eccentric exercise with a relatively small muscle mass (1 quadriceps femoris muscle) causes systemic effects on NK cells. It is suggested that the increase in plasma epinephrine during eccentric exercise is responsible for the observed increase in the percentage of CD16+ cells.

Natural killer cell response to exercise in humans: effect of hypoxia and epidural anesthesia.

For the response of immunologically competent blood cells to exercise, the importance of afferent nerve impulses was evaluated. On separate days, seven males cycled in a recumbent position approximately 60% of maximal O2 uptake with and without sensory nerve blockade by lumbar epidural anesthesia. Blood samples were collected after 60 min of rest, 20 min of exercise, and 120 min postexercise. Subsequently, on each day, the subjects were exposed to 11.5% O2-88.5% N2 for 10 min. This was followed by 20 min of hypoxic exercise at the same work rate, and a final blood sample was obtained. The concentrations of lymphocytes expressing the cluster designation (CD) cell-surface antigens CD3, CD4, CD8, and CD14 became elevated during exercise, and these responses were enhanced by hypoxia (P < or = 0.01). The most pronounced changes were within the concentrations of CD16+ and CD56+ natural killer cells, which increased twofold during normoxic and fivefold during hypoxic exercise (P < or = 0.01). Sensory nerve blockade decreased the number of CD3+ and CD4+ cells and increased the percentage of CD16+ cells, independent of exercise and hypoxia (P < or = 0.05). Sensory nerve blockade caused minor enhancement in the increase of unstimulated natural killer cell activity during exercise (P = 0.07) and enhanced the interferon-alpha-stimulated activity at normoxia (P < or = 0.05), whereas no effect was detected at hypoxia. The results demonstrate that the responses of immunological competent cells to normoxic and hypoxic exercise are not abolished by blockade of nerve impulses from active muscle.

Naloxone-provoked vaso-vagal response to head-up tilt in men.

A double-blind paired protocol was used to evaluate, in eight male volunteers, the effects of the endogenous opiate antagonist naloxone (NAL; 0.05 mg.kg-1) on cardiovascular responses to 50 degrees head-up tilt-induced central hypovolaemia. Progressive central hypovolaemia was characterized by a phase of normotensive-tachycardia followed by an episode of hypotensive-bradycardia. The NAL shortened the former from 20 (8-40) to 5 (3-10) min (median and range; P < 0.02). Control head-up tilt increased the means of thoracic electrical impedance [from 35.8 (SEM 2.1) to 40.0 (SEM 1.8) omega; P < 0.01] of heart rate [HR; from 67 (SEM 5) to 96 (SEM 8) beats.min-1, P < 0.02], of total peripheral resistance [TPR; from 25.5 (SEM 3.2) to 50.4 (SEM 10.5)mmHg.min.1-1, P < 0.05] and of mean arterial pressure [MAP; from 96 (SEM 2) to 101 (SEM 2)mmHg, P < 0.02]. Decreases were observed in stroke volume [from 65 (SEM 12) to 38 (SEM 9) ml, P < 0.01], in cardiac output [from 3.7 (SEM 0.7) to 2.5 (SEM 0.5) 1.min-1, P < 0.01], in pulse pressure [from 55 (SEM 4) to 37 (SEM 3)mmHg, P < 0.01] and in central venous oxygen saturation [from 73 (SEM 2) to 59 (SEM 4)%, P < 0.01]. During NAL, mean HR increased from 70 (SEM 3); n.s. compared to control) to only 86 (SEM 9) beats.min-1 (P < 0.02 compared to control) and MAP remained stable.(ABSTRACT TRUNCATED AT 250 WORDS)

[Laser therapy of Achilles tendinitis]. / Laserbehandling af akillessenetendinit.

The effects of low level laser treatment in soldiers with achilles tendinitis were studied in a prospective, randomized and double blind trial. Eighty-nine soldiers were enrolled in the study. Forty-six were randomized to treatment with active laser and 43 to treatment with placebo laser. No statistically significant differences in the number of consultations, morning stiffness, tenderness, crepitation, swelling, redness, VAS-score of pain and degree of unfitness for duty were found between the two treatment groups.

The effect of acute exercise on lymphocyte subsets, natural killer cells, proliferative responses, and cytokines in HIV-seropositive persons.

Eight healthy men infected with human immunodeficiency virus, type 1 (HIV) and eight HIV seronegative age- and sex-matched controls exercised on a bicycle ergometer (75% of VO2max, 1 h). The percentages of CD4+, CD4+45RA+, and CD4+45RO+ cells did not change, whereas the absolute number of CD4+ cells increased twofold during exercise and fell below prevalues 2 h after. The neutrophil count increase was more pronounced after exercise in the controls compared with in HIV-seropositive subjects. The percent CD16+ cells, and the natural killer (NK) and lymphokine activated killer (LAK) cell activity increased during exercise, but this increase was significantly less pronounced in the HIV-seropositive group. The results suggest that in response to physical stress, HIV-seropositive subjects have an impaired ability to mobilize neutrophils, NK and LAK cells to the blood. Furthermore, because the total number of CD4+ cells, but not the percentage of CD4+ cells, changed in response to exercise, this study further strengthens the idea that the percentage of CD4+ cells is preferable to the number of CD4+ cells in monitoring patients seropositive for HIV.

The immune system during exposure to extreme physiologic conditions.

It is not clear how the immune system is modulated in response to physical stress (e.g. trauma, surgery, burn and sepsis). In order to better understand the stress-induced immune changes, effects of isolated stressors are evaluated. Human experiments include hypoxia, head-up tilt, hyperthermina and exercise, which influence all lymphocyte subtypes and especially so the natural killer (NK) cells. In essence, the immune response is enhanced even by light physical stress, but suppressed after prolonged, intense stress.

Natural killer cell activity during head-up tilt-induced central hypovolemia in humans.

Changes in immunological competent blood cells were evoked in seven humans during passive head-up tilt (50 degrees anti-Trendelenburg's position maintained until appearance of presyncopal symptoms). Blood samples were collected after 60 min of rest, when presyncopal symptoms appeared during tilt, and 105 min after tilt-down. Natural killer (NK) cell activity increased during head-up tilt due to a three to four-fold increase in CD16+ NK cells in blood. In support NK cell activity boosted with interferon-alpha and interleukin 2 (IL-2) rose in parallel with unboosted NK cell activity. This effect on NK cells disappeared during recovery but was not suppressed when compared to prevalues. Lymphocyte concentration also increased during head-up tilt. Concentrations of CD3+ and CD4+ T cells were almost stable during head-up tilt, whereas the percentage of CD3+ T cells in relation to blood mononuclear cell (BMNC) concentration decreased, due to a diminished percentage of CD4+ T cells and the marked simultaneous increase in the percentage of CD16+ NK cells. Although changes in the BMNC composition occurred, the proliferative responses of BMNC following stimulation with phytohemagglutinin, purified derivative of tuberculin, or IL-2 did not change significantly. We conclude that head-up tilt induced marked changes in subpopulations of BMNC, especially the CD16+ NK cells, as they were recruited to the blood.

Effect of 8 wk of bicycle training on the immune system of patients with rheumatoid arthritis.

The effect of 8 wk of progressive bicycle training on the immune system was evaluated in a controlled study on 18 patients with rheumatoid arthritis and moderate disease activity. Maximal O2 uptake increased significantly, whereas heart rate at stage 2 and rate of perceived exertion decreased significantly, in the training group compared with the controls. Resting levels of a number of immune parameters were measured before and after 4 and 8 wk of training. Training did not induce changes in blood mononuclear cell subpopulations, proliferative response, or natural killer cell activity. Furthermore the plasma concentrations of interleukin-1 alpha, interleukin-1 beta, and interleukin-6 did not change in response to training. It is concluded that 8 wk of bicycle training does not influence the immune system of patients with rheumatoid arthritis.

Peripheral venous oxygen saturation during head-up tilt induced hypovolaemic shock in humans.

We followed central, median cubital and dorsal metacarpal venous oxygen saturations (SvO2) during 50 degrees head-up tilt (anti-Trendelenburg's position) induced central hypovolaemia in eight males. Head-up tilt resulted in slight tachycardia of 101 (60-120) beats min-1 (median with range) and a stable mean arterial pressure (MAP) of 100 (88-114) mmHg. After 13 (6-23) min presyncopal symptoms appeared, accompanied by decreases in heart rate to 75 (51-97) beats min-1 and in MAP to 59 (49-76) mmHg (p < 0.01). Cardiac output decreased 0.9 (0.3-1.6) 1 min-1 while thoracic electrical impedance increased 3.4 (-1.2-5.9) Ohm (p < 0.01). Tilt-up decreased central venous pressure, but during sustained tilt it remained unchanged. Arterial oxygen saturation did not change. Head-up tilt decreased central SvO2 by 12 (5-24)% (p < 0.01). Median cubital SvO2 decreased 8 (-5-25)% (p < 0.02) during tilting, and it remained at this level during sustained tilt. Only five of eight samples from the dorsal metacarpal vein could be obtained. In these samples SvO2 was lowered by 15 (7-26)% (p = 0.01) at the onset of presyncopal symptoms. The results indicate that loss of central blood volume is reflected in central as well as peripheral SvO2. However, for reliable monitoring of blood volume changes, central SvO2 is the most useful variable, as this SvO2 changed consistently with the central blood volume, and blood samples could be obtained readily from the central venous catheter.

Influence of in vivo hypobaric hypoxia on function of lymphocytes, neutrocytes, natural killer cells, and cytokines.

We have investigated the effects of short-term hypoxia in vivo on the human cellular immune system. Seven young healthy volunteers were placed in a decompression chamber (380 Torr) for 20 min with or without supplemental O2. The leukocyte concentration increased during hypobaric conditions because of an increased concentration of lymphocytes. The absolute and relative concentration of CD16+ natural killer (NK) cells increased markedly during hypoxia and returned to pretest values after 2 h of recovery. The NK cell activity of blood mononuclear cells (BMNC, %lysis/fixed no. of BMNC) boosted with interferon-alpha, interleukin-2 (IL-2), and indomethacin rose in parallel with unboosted NK cell activity during hypoxia. The percentage of CD4+ and CD8+ cells declined during hypoxia, whereas the absolute concentration of both CD8+ cells and CD14+ monocytes increased. Although the BMNC composition varied, the proliferative responses of BMNC after stimulation with phytohemagglutinin, purified derivative of tuberculin, and IL-2 did not change significantly. The in vitro production of interleukin-1 beta and IL-2 in supernatants obtained after stimulation of BMNC with phytohemagglutinin or lipopolysaccharide was not affected. The chemiluminescence response of neutrocytes increased 2 h after hypoxia. It was concluded that acute hypoxia induced marked alterations in the immune system and that the NK cells are especially sensitive to the hypoxic stimulus.