Hypoxia differentially affects healthy men and women during a daytime nap with a dose-response relationship: a randomized, cross-over pilot study

CONTEXT: The use of daytime napping as a countermeasure in sleep disturbances has been recommended but its physiological evaluation at high altitude is limited. OBJECTIVE: To evaluate the neuroendocrine response to hypoxic stress during a daytime nap and its cognitive impact. DESIGN, SUBJECT, AND SETTING: Randomized, single-blind, three period cross-over pilot study conducted with 15 healthy lowlander subjects (8 women) with a mean (SD) age of 29(6) years (Clinicaltrials identifier: NCT04146857, https://clinicaltrials.gov/ct2/show/NCT04146857?cond=napping&draw=3&rank=12). INTERVENTIONS: Volunteers underwent a polysomnography, hematological and cognitive evaluation around a 90 min midday nap, being allocated to a randomized sequence of three conditions: normobaric normoxia (NN), normobaric hypoxia at FiO(2) 14.7% (NH15) and 12.5% (NH13), with a washout period of 1 week between conditions. RESULTS: Primary outcome was the interbeat period measured by the RR interval with electrocardiogram. Compared to normobaric normoxia, RR during napping was shortened by 57 and 206 ms under NH15 and NH13 conditions, respectively (p < 0.001). Sympathetic predominance was evident by heart rate variability analysis and increased epinephrine levels. Concomitantly, there were significant changes in endocrine parameters such as erythropoietin (∼6 UI/L) and cortisol (∼100 nmol/L) (NH13 vs. NN, p < 0.001). Cognitive evaluation revealed changes in the color-word Stroop test. Additionally, although sleep efficiency was preserved, polysomnography showed lesser deep sleep and REM sleep, and periodic breathing, predominantly in men. CONCLUSION: Although napping in simulated altitude does not appear to significantly affect cognitive performance, sex-dependent changes in cardiac autonomic modulation and respiratory pattern should be considered before napping is prescribed as a countermeasure

Comparison of double sensor, skin, and rectal temperature recording for determining circadian rhthm

Background: 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\ub0 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 (\ub1 SD) of Pearson\u2019s 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

Breathing exercises during late pregnancy in a microgravity-like environment

Background. Breathing exercises are commonly used as a relaxation technique during pregnancy and to help in labour, but whether the burden of the fetus may cause a cardiovascular reflex activation during deep breathing is poorly known. Water immersion (WI), which mimic a microgravity condition, may relieve breath discomfort during deep breathing in late pregnancy. Nevertheless, body position may play a role, as during WI the hydrostatic drive is directed toward the diaphragm in sitting but not in supine position. Aims. To compare the cardiovascular activation due to deep low-frequency breathing exercises in a gym (DRY) and during water immersion (WI) in different positions (supine and sitting) in late pregnant women. Methods. We collected in 11 pregnant women (age 31\ub12 [m\ub1SD] yrs; gestational age 29\ub16 wks) RR interval series by a heart rate monitor at baseline, while sitting comfortably, and during deep and slow ventilation (about 0.05 Hz), in both DRY and WI conditions, either in supine and sitting position (10 min each). The following parameters were calculated for each series: Low Frequency (LFnu, 0.06-0.15 Hz) and High Frequency (HFnu, 0.15-0.4 Hz) power (FFT method), LF/HF ratio. Results. Compared to baseline (86\ub18 bpm), heart rate significantly increased during breathing while sitting in both conditions (DRY: 95\ub13 bpm, p<0.01; WI: 93\ub111 bpm, p<0.01 vs baseline) but more slightly in WI (p<0.05 vs DRY). Conversely, heart rate did not change during breathing in supine position in DRY (81\ub19 bpm) and WI (84\ub110 bpm) state. Baseline LF/HF ratio was 2.0\ub11.2. Breathing while sitting significantly increased LF/HF ratio vs baseline in both DRY (3.9\ub10.9, p<0.01) and WI condition (3.7\ub12.5, p<0.05). During breathing supine LF/HF increased significantly in DRY only (4.4\ub13.1, p<0.04) but not in WI (2.1\ub11.5) condition. The observed modifications in LF/HF ratio were due to a significant shift in normalized LF (+34%, +28% and +26% in sitting DRY, supine DRY and sitting WI, respectively) and HF (-40%, -30% and \u201327%, respectively) power compared to baseline, but this effect was significantly reversed in WI (LF: -4%; HF: +10%, p=0.08 vs DRY) supine condition. Conclusions. Deep slow breathing seems to activate a significant autonomic response in sitting position. WI tends to mitigate such reactions, partially in sitting and completely in supine position. Therefore, in late pregnant women WI may alleviate the fetal burden on respiration, but exercise position is relevant

Comparison of double sensor, skin, and rectal temperature recordings for determining circadian rhythm

Introduction 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\ub0 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 (\ub1 SD) of Pearson\u2019s 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

Haben die intrathorakalen Rezeptoren des Niederdrucksystems einen Einfluss auf das erythropoietische System Abschlussbericht

SIGLEAvailable from TIB Hannover: F96B1176+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDeutsche Agentur fuer Raumfahrtangelegenheiten (DARA) GmbH, Bonn (Germany); Bundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Erythropoietin und Vaskulaerer Endothelialer Wachstumsfaktor (VEGF) beim Menschen unter simulierten Mikro-g Bedingungen Abschlussbericht

SIGLEAvailable from TIB Hannover: DtF QN1(90,25) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Head-Down Tilt Body Positioning Impairs Brain Function and Cognitive Performance

There is limited but increasing evidence from both human and animal studies that exposure to microgravity may affect brain function and cognitive performance. Anecdotal reports and observations provide evidence of occasional disturbance in cognitive abilities during spaceflight [1,2] and effects on cortical activity have been reported, particularly in the lower frequency range [3,4,5]. We hypothesized that changes in cortical activation during micro gravity might also be related to baroreceptor control concomitant with fluid shifts to the upper extremities. Thus, in order to assess the impact of immediate head down tilt positioning, we simulated fluid shifts observed during parabolic flight using a tilt-table experiment. 24 (12 men and 12 women) healthy, young subjects were exposed to a supine position for 10 min (baseline), then tilted 9 degree head down (HDT) for 30 seconds after which they were immediately tilted to 45 degree head-up tilt (HUT). EEG was recorded at Cz during all phases (PowerLab 8/30, ADInstruments, CO, USA) and assessed with respect to individually determined alpha- and theta frequency bands. During each phase subjects were asked to perform a visual cognitive test. As indicated in Fig. 1 Theta-Power increased during HUT and decreased during HDT with a significant higher Theta-Power during HUT compared to HDT (P < 0.05), while Alpha-Power revealed a diametrically adverse effect. In addition, mean reaction time significantly decreased during HUT compared to HDT (P < 0.05). Low Alpha-Power and increased Theta-Power during cognitive performance has been associated with increased cortical activation. Thus, the reduced reaction times observed during HUT are in line with the changes in spectral power from HDT to HUT. These findings are very well in line with previous short-term HDT studies on cortical excitation [6,7,8]. While it cannot be excluded that these findings are related to the vestibular system and /or changes in cerebral perfusion, we suggest that the effects might also be explained by baroafferent feedback control as various studies have shown that intense baroreceptor stimulation can provoke a reduction in cortical excitability [9]. In conclusion, we found that HDT can impair cognitive performance and is associated with respective changes in neurophysiological correlates