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Cardiovascular adaptations during sustained acceleration in a short-arm human centrifuge Increases in heart rate, and total peripheral resistance are the main counter-measures during consecutive +g-force exposure
No full textIntroduction: During exposure to hyper gravity (+Gz), a massive strain on the cardiovascular system takes place, via blood sequestration in the lower extremities and splanchnic vessels of the pelvis. This blood sequestration leads to a substantial decline in cardiac output (CO) and stroke volume (SV). In order to maintain adequate mean arterial pressure (MAP) , upsurges in heart rate (HR) and total peripheral resistance (TPR) occur as physiologic counter-measures. The objective of this study was to examine how these counter measures react during 2 consecutive rounds of +Gz in a short arm human centrifuge (SAHC).
Methods: 20 non-pilot G-force test subjects were exposed to 9 phases of alternating +Gz in an SAHC To measure hemodynamics during the +Gz profile, cardiac output (CO),heart rate (HR), left ventricular ejection time (LVET), mean arterial pressure (MAP), pulse interval (PI), stroke volume (SV), and total peripheral resistance (TPR) were continuously monitored.
Results: Out of 20 G-Force test subjects, 14 accomplished all 9 phases of shifting sustained acceleration. The hemodynamics of these 14 successfully maintained a stabile mean arterial pressure (MAP) (13% above baseline values) under conditions of +Gz . This was accomplished via increases in heart rate (HR) (35% above baseline) and total peripheral resistance (TPR) (50% above baseline). Decreases in left ventricular ejection time (LVET) & pulse interval (PI) (24% below baseline) were also significant factors in maintaining MAP.
Discussion: The results from this study show that the cardiovascular system can adapt to consecutive +Gz via alternating increases in HR and TPR, as well as decreases in LVET and PI. Through this orchestration of physiologic countermeasures, MAP can be sufficiently maintained, thereby retaining adequate perfusion throughout continued hyper gravitational stress
PHYSIOLOGICAL CHANGES IN PARTICIPANTS OF AN ULTRAMARATHON IN SUBARCTIC CLIMATE
No full textIntroduction
The Yukon Arctic Ultra (YAU) is an ultramarathon in the Yukon-Territory of Canada taking place during February.
We assessed changes in participants entering the 690km footrace and evaluated energy expenditure (EE),
energy intake (EI), energy deficit (ED), body weight (BW) and composition (fat mass FM, fat-free mass FFM),
sleep parameters (sleep time ST, REM-sleep RS, deep-sleep DS) and heart rate variability HRV (pNN50 and lowfrequency
to high-frequency ratio LF/HF). We hypothesized that high levels of physical exertion in the extremely
cold environment would lead to changes in these parameters.
Material & Methods
N=4 of n=6 volunteers finished and were included in the analysis. BW, FM, FFM were measured using a scale
and the bio-impedance-analysis. EI, ED were estimated using food protocols. EE, ST were measured using the
SenseWear-actimeter continuously and RS and DS using the Zeo-Sleep-device at distinctive nights. HRV
(pNN50, LF/HF) was evaluated using the Polar-monitor RS800CX and beat-to-beat analysis. Resulting data were
statistically analyzed using respective statistical software.
Results
The evaluation revealed high rates of daily EE (an average of 4.5 MET/d with peak values of 38,000 kJ/d). We
also found a considerable ED: only 44% of the EE was covered by EI (p<0.001). Considerable changes in BW,
FM, FFM occurred: participants lost an average 6.2 kg of BW (p<0.001) with a maximum loss of 7.9 kg. Regarding
body composition, there was an initial loss in FM (p<0.001) and in progression a loss in FFM (p=0.052). The
average FM loss was 3.9 kg and 2.3 kg in FFM (=27.9% from starting-FM, 3.4% from starting-FFM). We found a
sleep deficit at the start and end of the race; however, ST decreases were not significant (p=0.05). There were
changes in the sleep phases: a decrease in RS after the beginning (p=0.005) and increase in DS after the end of
the race (p=0.386). Analysis of HRV revealed a decrease in the pNN50 (p=0.429) and a significant decrease in
the LF/HF (p=0.035).
Discussion & Conclusions
Participation in the YAU leads to extensive increases in EE, ED; decreases in BW, FM, FFM; decreases in ST
and changes in sleep-phases. We found decreases in pNN50 and LF/HF-ratio indicating an increase of rhythms
predominantly influenced by the parasympathetic nervous system
EFFECTS OF AUTONOMIC TONE ON SHORT VERSUS LONG DISTANCE PERFORMANCES IN SWIMMERS
No full textWhatever the swimming specialty, swim training programs generally consist of high volume, which may shifts the heart rate (HR) autonomic control towards vagal predominance. Although it is accepted that an enhanced parasympathetic tone may improve performance on long distances, it is poorly known whether it may affect performance on short distances. PURPOSE. To evaluate resting autonomic tone and swimming performance on short and long distances in highly trained swimmers. METHODS. Two groups of national–level swimmers (all males, crawl specialists) were evaluated: short (S: 50-100 m; n=13; 24±3 yrs) and long (L: 1500 m; n=9; age 19±1 yrs) distance specialists. All swimmers belonged to the same team and were similar for training level. Beat-by-beat HR was recorded at rest in the morning, in supine position, by a HR monitor for 15 minutes. HR variability indexes were calculated from time (RMSSD, pNN50, indexes of vagal tone) and frequency (LF, Low Frequency and HF, High Frequency as absolute values and in normalized units (nu); LF/HF ratio, index of sympathovagal balance) domains. The anaerobic threshold was evaluated by an incremental swimming test with lactate measurements. RESULTS. The percentage of swimmers who showed resting bradycardia tended to be higher in L (78%) than in S (54%) group. HRV indexes did not significantly differ between groups: RMSSD 67±23 vs 66±11 ms, pNN50 40±17 vs 48±10%, LFnu 62.3±12.3 vs 54.4±14.8, HFnu 37.6±12.3 vs 45.6±14.8, LF/HF 2.1±1.9 vs 1.5±1.0 (S vs L group, respectively). In S group, 50 m best time correlated positively (p<0.05) with RMSSD (r=0.64), pNN50 (r=0.73) and absolute HF power (r=0.64), and negatively with LFnu (r=-0.56), but not with anaerobic threshold. On the contrary, in L group 1500 m did not correlate with RMSSD, pNN50 and absolute HF power (although negative trends were perceived), negatively correlated with absolute LF power (r=-0.65 p=0.05), positively correlated to LFnu (r=0.72, p=0.02), and tended to increase with anaerobic threshold. CONCLUSION. L swimmers were not more hypervagotonic than S swimmers, and such adaptation tended to be positively associated with anaerobic threshold. Conversely, high vagal tone appeared somehow detrimental on short swimming performance, as it negatively predicts performance on 50 m events, whereas anaerobic threshold did not
Comparison of double sensor, skin, and rectal temperature recording for determining circadian rhthm
No full textBackground: In chronobiology studies, the circadian rhythm of core body temperature has often been monitored via rectal temperature recordings. Compliance with rectal recordings, however, limits voluntary participation and prevents a broader spectrum of investigations. With the progress of technology, systems have been developed which allow a measurement of the core body temperature from an intact skin surface, such as the Double Sensor [1], a skin surface temperature and heat-flux combining device. Studies regarding how well such systems reflect the circadian rhythm of core body temperature, however, are lacking.
Material & Methods: As part of the 2nd Berlin BedRest Study (BBR2-2), subjects underwent micro-g simulated conditions, i.e. 6° head-down tilt bed-rest. On bed-rest day 49, 24 hours temperature profiles were obtained in seven health men by a single skin surface temperature sensor and the Double Sensor, each placed at forehead (Tfhd, DSfhd) and sternum (Tste, DSste), and by a rectal probe (Trec). The degree of parallelism between measured temperature variables was assessed by calculating the Pearson correlation coefficient r. Rhythm characteristics determined by fitting a single cosine curve included MESOR, amplitude, and acrophase, and were statistically tested for significance by Student's paired t- test.
Results: Averaged value (± SD) of Pearson’s r was .867 (.059), .797 (.097), .519 (.373), -.021 (.549) for correlation between Trec with DSfhd, Tfhd, DSste, and Tste, respectively. The correlation mean demonstrated a good parallelism between Trec and temperatures obtained from the forehead. Regarding the rhythm parameters MESOR, amplitude, and acrophase, no significant difference was found between Trec and DSfhd, but between Tfhd and DSfhd as well as between Tfhd and Trec.
Discussion & Conclusions: Not the skin surface temperature recordings, but the temperatures of the Double Sensor from the forehead seem promising for determining the circadian rhythm of core body temperature in occupational and environmental medicine on earth and space, where the use of rectal probes is not feasible or desired.
References: 1. Gunga HC, Sandsund M, Reinertsen RE, Sattler F and Koch J. A non-invasive device to continuously determine heat strain in humans. Journal of Thermal Biology 33: 297-307, 2008
Comparison of double sensor, skin, and rectal temperature recordings for determining circadian rhythm
No full textIntroduction
In chronobiology studies, the circadian rhythm of core body temperature has often been monitored via rectal
temperature recordings. Compliance with rectal recordings, however, limits voluntary participation and prevents a
broader spectrum of investigations. With the progress of technology, systems have been developed which allow a
measurement of the core body temperature from an intact skin surface, such as the Double Sensor [1], a skin
surface temperature and heat-flux combining device. Studies regarding how well such systems reflect the
circadian rhythm of core body temperature, however, are lacking.
Material & Methods
As part of the 2nd Berlin BedRest Study (BBR2-2), subjects underwent micro-g simulated conditions, i.e. 6° headdown
tilt bed-rest. On bed-rest day 49, 24 hours temperature profiles were obtained in seven healthy men by a
single skin surface temperature sensor and the Double Sensor, each placed at forehead (Tfhd, DSfhd) and sternum
(Tste, DSste), and by a rectal probe (Trec). The degree of parallelism between measured temperature variables was
assessed by calculating the Pearson correlation coefficient r. Rhythm characteristics determined by fitting a single
cosine curve included MESOR, amplitude, and acrophase, and were statistically tested for significance by
Student's paired t-test.
Results
Averaged value (± SD) of Pearson’s r was .867 (.059), .797 (.097), .519 (.373), -.021 (.549) for correlation
between Trec with DSfhd, Tfhd, DSste, and Tste, respectively. The correlation mean demonstrated a good parallelism
between Trec and temperatures obtained from the forehead. Regarding the rhythm parameters MESOR,
amplitude, and acrophase, no significant difference was found between Trec and DSfhd, but between Tfhd and DSfhd
as well as between Tfhd and Trec.
Discussion & Conclusions
Not the skin surface temperature recordings, but the temperatures of the Double Sensor from the forehead seem
promising for determining the circadian rhythm of core body temperature in occupational and environmental
medicine on earth and space, where the use of rectal probes is not feasible or desired
Phase shifts of circadian core body temperature profiles during Mars500
No full textA growing body of research indicates that a misalignment of circadian rhythms can be detrimental
to mental and physical health. Long-term space missions may also potentially alter circadian rhythms,
and pose a critical risk to crew health and safety. The long-term impact of isolation and confinement on
circadian rhythms has not been fully characterized. We here assessed the impact of the Mars500 study
on the circadian phase of core body temperature (CBT). CBT was recorded continuously for 24 h at
the forehead using a recently proposed heat-flux technique (Double Sensor) [1] before (BDC) and during
(ISO-20, ISO-60, ISO-140, ISO-200, ISO-260, ISO-320, ISO-400, ISO-460) the mission. Each recording
was then subjected to cosinor analysis to determine acrophase for each subject and session. A linear mixed
model treating “Time” as fixed e↵ect was fit to phase, including random e↵ects (intercepts and slopes) to
account for individual subject variation. To analyze whether the rate of change in CBT was characterized
by nonlinear changes over time, quadratic and cubic models were also considered. In spite of substantial
inter-individual variation, visual inspection of the data indicated a phase advance during the first half of
the mission (+1.4 h), after which phase returned to baseline again (phase delay of about -1.2 h relative
to first mission half). At ISO-460 phase sharply advanced again to similar levels observed during the first
half of the mission. This pattern was confirmed by significant linear, quadratic and cubic components of
the mixed model (P<0.05). This third degree polynomial trend is well in line with recent data, showing
substantial di↵erences for sleep-wake cycles between the first and last the part of the 520-d mission [2].
We suggest that this specific pattern is related to a highly controlled diet, which was administered during
the first half of the mission. This diet required very strict meal times, which are well known to be strong
nonphotic cues for circadian entrainment [3]. In contrast, we speculate that the sudden phase advance
after 400 mission days could be related to the exposure of blue light, which was exclusively employed
during days 439-499 only. In conclusion, the present results indicate that long-term isolation can induce
significant changes in the circadian timing system, which might be attributed to specific nonphotic and
photic cues of the Mars500 experiment.
[1] Respir Physiol Neurobiol, 169 (2009) S63-S68 [2] PNAS, 110 (2013) 2635-2640 [3] Science, 320
(2008) 1074–107
Can skin temperature recordings predict GLOC?
No full textBackground: Modern aerial combat manouevres are an enormous challenge for human physiology [1,2].To predict the probability of a g- force induced loss of consciousness (GLOC) has been subject of numerous studies. Changes in perfusion (NIRS) and/or function of the brain (EEG, evoked potentials) have been the primary focus searching a predictor while centrifugal reallocation of blood volume is the primary cause for this blackout.To determine the peripheral bloodflow skin temperature might be used [3]. We present a pilot study using fast measurements of peripheral temperatures to predict this peripheral pooling effect.
Material & Methods: 9 of the 20 subjects suffered an almost loss of consciousness (ALOC). Peripheral temperatures tended to be higher in subjects with an almost blackout.The strongest effect regarding the difference of the two groups was recorded at the upper arm (p<0.05). 20 healthy subjects were tested using a combined lower body negative pressur/tilt table.The produced push-pull effect has been used to select pilots suited to fly a forth generation jet fighter. The complete procedure was split in two phases before, one phase during and one phase after the induced push-pull effect. Recording skin III temperatures proximal and distal of the upper and lower limbs allowed to quantify the effect of a peripheral perfusion change.
Results & Discussion: The probability of ALOC in this experiment could be predicted recording peripheral temperatures. Higher peripheral temperatures before the push-pull phase might be an indicator for peripheral vasodilation or a lowered sympathetic activation [4]. However, to verify this effect, the experiment has to be repeated using more subjects and different hyper-g scenarios as the short and long arm centrifuge and real aircraft manoeuvres.
References: 1. Hanousek, J, P Dosel, J Cmiral, and J Petricek. "Physiological Response of Pilots to the Load of Lower Body Negative Pressure." J Gravit Physiol 4, no. 2 (1997): P33-4 2. Dosel, P, J Hanousek, J Cmiral, and J Petricek. "Physiological Response of Pilots to the LBNP-, Flight-, and Centrifuge Load." J Gravit Physiol 5, no. 1 (1998): P41-2 3. Rubinstein, E H, and D I Sessler. "Skin-surface Temperature Gradients Correlate with Fingertip Blood Flow in Humans." Anesthesiology 73, no. 3 (1990): 541-5 4. Charkoudian, Nisha. "Skin Blood Flow in Adult Human Thermoregulation: How It Works, When It Does Not, and Why." Mayo Clinic proceedings. Mayo Clinic 78, no. 5 (2003): doi:10.4065/78.5.60
Stretching and deep and superficial massage do not influence blood lactate levels after heavy-intensity cycle exercise
No full textThe study aimed to assess the role of deep and superficial massage and passive stretching recovery on blood lactate concentration ([La-]) kinetics after a fatiguing exercise compared to active and passive recovery. Nine participants (age 23 ± 1 years; stature 1.76 ± 0.02 m; body mass 74 ± 4 kg) performed on five occasions an 8-min fatiguing exercise at 90% of maximum oxygen uptake, followed by five different 10-min interventions in random order: passive and active recovery, deep and superficial massage and stretching. Interventions were followed by 1 hour of recovery. Throughout each session, maximum voluntary contraction (MVC) of the knee extensor muscles, [La-], cardiorespiratory and metabolic variables were determined. Electromyographic signal (EMG) from the quadriceps muscles was also recorded. At the end of the fatiguing exercise, [La-], MVC, EMG amplitude, and metabolic and cardiorespiratory parameters were similar among conditions. During intervention administration, [La-] was lower and metabolic and cardiorespiratory parameters were higher in active recovery compared to the other modalities (P < 0.05). Stretching and deep and superficial massage did not alter [La-] kinetics compared to passive recovery. These findings indicate that the pressure exerted during massage administration and stretching manoeuvres did not play a significant role on post-exercise blood La- levels
Effect of different recovery modalities on lactic acid removal after a cycle exercise of heavy intensity
No full textThe strategy to accelerate blood lactate concentration [La-] removal and to restore resting values at the end of a competition or among training sessions is actually a matter of debate. In particular, the role of alternative modalities (massage and stretching) in respect to active recovery in accelerate [La-] removal has been investigated with controversial findings. The aim of the study was to assess the effect of five different recovery modalities on [La-] removal and on maximum force output restoration after a fatiguing exercise. On 8 active male participants [age 23±1 yrs; stature 1.76±0.07 m; body mass 74±11 kg; mean±standard deviation (SD)], the maximum oxygen uptake (VO2max) on a cycle ergometer was assessed. Thereafter, on five different occasions, an 8-min heavy-intensity exercise at 90% VO2max, followed by five different recovery modalities, each lasting 10 min, in a random order (passive, active, sports massage, fascial release massage and passive stretching) was performed. Throughout each session, the maximum voluntary contraction (MVC) of the knee extensor muscles, the surface electromyogram (EMG) from the vastus lateralis muscle, [La-], VO2 and other cardiorespiratory variables were recorded. During the 10-min recovery, [La-] was sampled every minute, to calculate the time constant (τ) of [La-] kinetics. Despite all variables were significantly changed at the end of the heavy-intensity exercise compared to pre-exercise condition, no differences in metabolic, cardiorespiratory and EMG parameters were found among the 5 different sessions. Active recovery showed the lowest [La-] values and the shortest τ (P<0.05) compared to the other recovery modalities, among which no significant differences were found. Although widely used after competitions or during training sessions, massage and passive stretching did not accelerate [La-] removal, thus making questionable their administration instead of active recovery
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