Cardiorespiratory Responses of Adults and Children during Normoxic and Hypoxic Exercise.

We aimed to elucidate potential differential effects of hypoxia on cardiorespiratory responses during submaximal cycling and simulated skiing exercise between adults and pre-pubertal children. Healthy, low-altitude residents (adults, N=13, Age=40±4yrs.; children, N=13, age=8±2yrs.) were tested in normoxia (Nor: PiO2=134±0.4 mmHg; 940 m) and normobaric hypoxia (Hyp: PiO2=105±0.6 mmHg; ~3 000 m) following an overnight hypoxic acclimation (≥12-hrs). On both days, the participants underwent a graded cycling test and a simulated skiing protocol. Minute ventilation (VE), oxygen uptake (VO2), heart rate (HR) and capillary-oxygen saturation (SpO2) were measured throughout both tests. The cycling data were interpolated for 2 relative workload levels (1 W·kg-1 & 2 W·kg-1). Higher resting HR in hypoxia, compared to normoxia was only noted in children (Nor:78±17; Hyp:89±17 beats·min-1; p<0.05), while SpO2 was significantly lower in hypoxia (Nor:97±1%; Hyp:91±2%; p<0.01) with no between-group differences. The VE, VO2 and HR responses were higher during hypoxic compared to normoxic cycling test in both groups (p<0.05). Except for greater HR during hypoxic compared to normoxic skiing in children (Nor:155±19; Hyp:167±13 (beats·min-1); p<0.05), no other significant between-group differences were noted during the cycling and skiing protocols. In summary, these data suggest similar cardiorespiratory responses to submaximal hypoxic cycling and simulated skiing in adults and children.

Knee stiffness and viscosity: New implementation and perspectives in prosthesis development.

The pendulum test is a method applied to measure passive resistance of the knee. A new and simple pendulum test with instrumentation based on infrared camera was used to evaluate knee stiffness and viscosity on a female human cadaver. The stiffness and viscosity were calculated based on the kinetic data. During the measurements, the periarticular and intraarticular soft tissue of the knee was gradually removed to determine the stiffness and viscosity as a function of the tissue removal rate. The measurements showed that the removal of tissue around the joint reduces the damping of leg oscillation, and therefore decreases the stiffness and viscosity. The contribution to knee joint damping was 10% for the skin, 20% for ligaments, and 40% for muscles and tendons. Tissue removal has a very large impact on the knee stiffness and viscosity.

Organization of functional postural responses following perturbations in multiple directions in elderly fallers standing quietly.

The objective of the study was to assess functional postural responses by analyzing the center-of-pressure trajectories resulting from perturbations delivered in multiple directions to elderly fallers. Ten elderly individuals were standing quietly on two force platforms while an apparatus delivered controlled perturbations at the level of pelvis in eight directions: 'forward (FW)' and 'backward (BW)' [anterioposterior plane (AP)], 'left (LT)' and 'right (RT)' [mediolateral plane (ML)] and four combinations of these principal directions: forward-left (FL), forward-right (FR), backward-left (BL) and backward-right (BR). Perturbations were repeated randomly four times in each direction. Peak amplitude responses (PAR AP and PAR ML) and times to reach peak amplitude responses (TPAR-AP and TPAR-ML) were extracted for each perturbation direction from acquired center-of-pressure data. One-way analysis of variance was used to test differences between directionally-similar perturbation directions. Balance abilities were assessed by means of Berg Balance Scale. Average Berg Balance Scale for the group resulted in 33.9±5.8 points, which means that the participants were at greater risk of fall. The comparison of the group averaged PARAP and TPAR-AP in all 'forward' directions (FW, FL, FR) as well in all 'backward' directions (BW, BL, BR) have not shown statistically significant differences. The comparison of the group averaged PARML and TPAR-ML in all 'left' directions (LT, FL, BL) as well in all 'right' directions (RT, FR, BR) have not shown statistically significant differences. These results suggest that a principle of decoupled control may to a large extent be preserved also in elderly with clearly diminished balancing abilities, which implies that the accuracy in the assessment of perturbation direction may be well preserved also in very old age.

Inert gas narcosis has no influence on thermo-tactile sensation.

Contribution of skin thermal sensors under inert gas narcosis to the raising hypothermia is not known. Such information is vital for understanding the impact of narcosis on behavioural thermoregulation, diver safety and judgment of thermal (dis)comfort in the hyperbaric environment. So this study aimed at establishing the effects of normoxic concentration of 30% nitrous oxide (N(2)O) on thermo-tactile threshold sensation by studying 16 subjects [eight females and eight males; eight sensitive (S) and eight non-sensitive (NS) to N(2)O]. Their mean (SD) age was 22.1 (1.8) years, weight 72.8 (15.3) kg, height 1.75 (0.10) m and body mass index 23.8 (3.8) kg m(-2). Quantitative thermo-tactile sensory testing was performed on forearm, upper arm and thigh under two experimental conditions: breathing air (air trial) and breathing normoxic mixture of 30% N(2)O (N(2)O trial) in the mixed sequence. Difference in thermo-tactile sensitivity thresholds between two groups of subjects in two experimental conditions was analysed by 3-way mixed-model analysis of covariance. There were no statistically significant differences in thermo-tactile thresholds either between the Air and N(2)O trials, or between S and NS groups, or between females and males, or with respect to body mass index. Some clinically insignificant lowering of thermo-tactile thresholds occurred only for warm thermo-tactile thresholds on upper arm and thigh. The results indicated that normoxic mixture of 30% N(2)O had no influence on thermo-tactile sensation in normothermia.

Reliability of the method of levels for determining cutaneous temperature sensitivity.

Determination of the thermal thresholds is used clinically for evaluation of peripheral nervous system function. The aim of this study was to evaluate reliability of the method of levels performed with a new, low cost device for determining cutaneous temperature sensitivity. Nineteen male subjects were included in the study. Thermal thresholds were tested on the right side at the volar surface of mid-forearm, lateral surface of mid-upper arm and front area of mid-thigh. Thermal testing was carried out by the method of levels with an initial temperature step of 2°C. Variability of thermal thresholds was expressed by means of the ratio between the second and the first testing, coefficient of variation (CV), coefficient of repeatability (CR), intraclass correlation coefficient (ICC), mean difference between sessions (S1-S2diff), standard error of measurement (SEM) and minimally detectable change (MDC). There were no statistically significant changes between sessions for warm or cold thresholds, or between warm and cold thresholds. Within-subject CVs were acceptable. The CR estimates for warm thresholds ranged from 0.74°C to 1.06°C and from 0.67°C to 1.07°C for cold thresholds. The ICC values for intra-rater reliability ranged from 0.41 to 0.72 for warm thresholds and from 0.67 to 0.84 for cold thresholds. S1-S2diff ranged from -0.15°C to 0.07°C for warm thresholds, and from -0.08°C to 0.07°C for cold thresholds. SEM ranged from 0.26°C to 0.38°C for warm thresholds, and from 0.23°C to 0.38°C for cold thresholds. Estimated MDC values were between 0.60°C and 0.88°C for warm thresholds, and 0.53°C and 0.88°C for cold thresholds. The method of levels for determining cutaneous temperature sensitivity has acceptable reliability.

Psychomotor function during mild narcosis induced by subanesthetic level of nitrous oxide: individual susceptibility beyond gender effect.

OBJECTIVE: We investigated the effect of narcosis induced by subanesthetic concentrations of nitrous oxide (N2O), a behavioral analogue for hyperbaric nitrogen, on psychomotor performance. In particular, we assessed individual susceptibility to narcosis. METHODS: The participants were 12 female and 12 male undergraduate students. Psychomotor assessment was conducted with a computerized Visual Simple Reaction Time (VSRT) test, and Trail Making Tests Part A (TMTA) and Part B (TMT-B). The tests were conducted on two separate occasions in the following order: VSRT, TMT-A, TMT-B. On the first occasion participants conducted the tests breathing room air (air trial), and during the second test they conducted the tests while breathing a normoxic mixture containing 30% N2O (N2O trial). RESULTS: Males had significantly (p = 0.036) shorter VSRT in the air trials. There was no effect of gender on psychomotor performance in the N2O trials. Overall, mean performance in the N2O trials degraded significantly (p = 0.004) only in VSRT. Performance of individual participants exhibited different and inconsistent direction of change in the N2O trials. CONCLUSION: N2O-induced alterations in psychomotor function are primarily dependent on individual susceptibility to narcosis (i.e., concentration threshold).

Predictive validity of a modified fall assessment tool in nursing homes: experience from Slovenia.

The aim of the study was to evaluate the predictive validity of the Modified Fall Assessment Tool (MFAT) in a nursing home setting. The study involved 83 residents from a nursing home in Slovenia with an average age of 81 years. To determine the predictive characteristics of the MFAT, a receiver operating characteristic curve analysis was applied. During the observation period of 12 weeks, 18 residents fell. The fallers had a significantly higher history of falls, a higher number of diagnoses, more medication, and a higher MFAT score than the non-fallers. Using the estimated criterion of 20 points, the sensitivity of the MFAT score was 61%, its specificity was 80%, its classification accuracy was 64%, its positive likelihood ratio was 3.1, its negative likelihood ratio was 0.5, its positive predictive value was 46%, and its negative predictive value was 88%. The results showed that the MFAT is suitable for the prediction of falls and, hence, also the prevention of falls in nursing homes, whereby the recommended criterion score is 20 points.

Heart rate variability--a shape analysis of Lorenz plots.

A new quantitative geometrical method to analyse heart rate variability is presented. The standard image analysis techniques were applied to the grey scale images of Lorenz plots, and the outlines of the attractor areas were determined via a contour following procedure based on a maze walking algorithm. For graphs of simple compact shape, the attractor region contours were described in terms of Fourier coefficients.