Sustained weightlessness affects all body functions, among these also cardiac autonomic control mechanisms. How this may influence neural response to central stimulation by a mental arithmetic task remains an open question. The hypothesis was tested that microgravity alters cardiovascular neural response to standardized cognitive load stimuli. Beat-to-beat heart rate, brachial blood pressure, and respiratory frequency were collected in five astronauts, taking part in three different short-duration (10 to 11 days) space missions to the International Space Station. Data recording was performed in supine position 1 mo before launch; at days 5 or 8 in space; and on days 1, 4, and 25 after landing. Heart rate variability (HRV) parameters were obtained in the frequency domain. Measurements were performed in the control condition for 10 min and during a 5-min mental arithmetic stress task, consisting of deducting 17 from a four-digit number, read by a colleague, and orally announcing the result. Our results show that over all sessions (pre-, in-, and postflight), mental stress induced an average increase in mean heart rate (Δ7 ± 1 beats/min; P = 0.03) and mean arterial pressure (Δ7 ± 1 mmHg; P = 0.006). A sympathetic excitation during mental stress was shown from HRV parameters: increase of low frequency expressed in normalized units (Δ8.3 ± 1.4; P = 0.004) and low frequency/high frequency (Δ1.6 ± 0.3; P = 0.001) and decrease of high frequency expressed in normalized units (Δ8.9 ± 1.4; P = 0.004). The total power was not influenced by mental stress. No effect of spaceflight was found on baseline heart rate, mean arterial pressure, and HRV parameters. No differences in response to mental stress were found between pre-, in-, and postflight. Our findings confirm that a mental arithmetic task in astronauts elicits sympathovagal shifts toward enhanced sympathetic modulation and reduced vagal modulation. However, these responses are not changed in space during microgravity or after spaceflight.
Research Containing: Space Flight
A habitable atmosphere is a fundamental requirement for human spaceflight. To meet this requirement, the cabin atmosphere must be constantly scrubbed to maintain human life and system functionality. The primary system for atmospheric scrubbing of the US on-orbit segment (USOS) of the International Space Station (ISS) is the Trace Contaminant Control System (TCCS). As part of the Environmental Control and Life Support Systems' (ECLSS) atmosphere revitalization rack in the US Lab, the TCCS operates continuously, scrubbing trace contaminants generated primarily by two sources: the metabolic off-gassing of crew members and the off-gassing of equipment in the ISS. It has been online for approximately 95% of the time since activated in February 2001. The TCCS is comprised of a charcoal bed, a catalytic oxidizer, and a lithium hydroxide post-sorbent bed, all of which are designed to be replaced on-orbit when necessary. In 2006, all three beds were replaced following an observed increase in the system resistance that occurred over a period several months. The beds were returned to ground and subjected to a test, teardown and evaluation (TT&E) to investigate the root cause(s) of the decrease in flow rate through the system. In addition, various chemical and physical analyses of the bed materials were performed to determine contaminant loading and any changes in performance. This paper will mainly focus on the results of these analyses and how this correlates with what has been observed from archival sampling and on-orbit events. This has provided insight into the future performance of the TCCS and rate of change for orbital replacement units in the TCCS.
The five-year experience of experimentation in the autonomic regulation of blood circulation on board the International Space Station is presented. The heart rate variability (HRV) analysis was the basic methodical approach in these investigations. The probabilistic approach to the estimation of the risk of pathology under long-term spaceflight conditions based on HRV analysis is described. The individual type of autonomic regulation was taken into account in the analysis of the results of the investigations. The type of regulation inherent in every cosmonaut under the conditions of weightlessness has been shown to be retained during subsequent flights. New scientific data on the relationship between the character of the adaptive response of the body to spaceflight factors and the individual type of autonomic response have been obtained. Staying in weightlessness has been shown to be connected with the readjustment of regulatory systems and with transition to the zone of prenosological states. Adaptation responses in weightlessness are characterized by the increased tension of the regulatory systems and the preservation of sufficient functional reserves. The mobilization of additional resources is required after returning to earth, due to which the functional reserve of the mechanisms of regulation decreases. Cosmonauts with the vagotonic and normosympathotonic types of autonomic regulation appear to be the most resistant. The knowledge of the type of autonomic regulation allows us to judge the potential response of the cosmonaut to spaceflight factors. The likelihood estimates were calculated, and the risk categories were determined by the results of HRV analysis in the last months of the flight. Three pathology risk groups were identified. In conclusion, the theoretical and applied significance of the experiments was considered.
The development of space cardiology is considered, from the first flights of animals and humans to the studies conducted on board International Space Station (ISS). The material is recounted in four sections in accordance with the theoretical statements presented in the book “Space Cardiology” (1967). The first section is analysis of rearrangement of blood circulation under the conditions of microgravity. Long-term microgravity has been demonstrated to require mobilization of additional functional reserves of the body. During the first six months of the flight, the cardiovascular homeostasis is supported by the regulatory mechanisms of the blood circulation system, whereas in the case of a more prolonged impact of microgravity, intersystem control is actively involved (suprasegmental divisions of autonomic regulation). In the second section dealing with the roles of the right and left divisions of the heart in adaptation to microgravity of the cardiovascular system, the important role of the right heart at the initial stage of a space flight (SF) is emphasized. The third section addresses the problem of reducing the orthostatic stability; this study has been initiated as early as the first manned space flights. The results obtained on board ISS testify to the importance of evaluating the functional reserves of the blood circulation system. The fourth section presents data on the new methods of myocardial examination that are to be soon introduced into SF medical provision. In conclusion, some new projects in space cardiology are discussed.
Autonomic cardiovascular and respiratory control during prolonged spaceflights aboard the International Space Station
Impaired autonomic control represents a cardiovascular risk factor during long-term spaceflight. Little has been reported on blood pressure (BP), heart rate (HR), and heart rate variability (HRV) during and after prolonged spaceflight. We tested the hypothesis that cardiovascular control remains stable during prolonged spaceflight. Electrocardiography, photoplethysmography, and respiratory frequency (RF) were assessed in eight male cosmonauts (age 41–50 yr, body-mass index of 22–28 kg/m2) during long-term missions (flight lengths of 162–196 days). Recordings were made 60 and 30 days before the flight, every 4 wk during flight, and on days 3 and 6 postflight during spontaneous and controlled respiration. Orthostatic testing was performed pre- and postflight. RF and BP decreased during spaceflight (P < 0.05). Mean HR and HRV in the low- and high-frequency bands did not change during spaceflight. However, the individual responses were different and correlated with preflight values. Pulse-wave transit time decreased during spaceflight (P < 0.05). HRV reached during controlled respiration (6 breaths/min) decreased in six and increased in one cosmonaut during flight. The most pronounced changes in HR, BP, and HRV occurred after landing. The decreases in BP and RF combined with stable HR and HRV during flight suggest functional adaptation rather than pathological changes. Pulse-wave transit time shortening in our study is surprising and may reflect cardiac output redistribution in space. The decrease in HRV during controlled respiration (6 breaths/min) indicates reduced parasympathetic reserve, which may contribute to postflight disturbances.
Prospects of medical monitoring of long-duration space flights by means of non-contact recording of physiological functions during sleep time
The methods used to investigate the body functional state in sleep under the conditions of a long-duration space flight are of great scientific and practical interest. The Sonocard experiment is based on the method of seismocardiography. The goal of this experiment is to validate and improve the procedure of non-contact recording the in-sleep physiological data for monitoring the crew state. The very first results have demonstrated that, as on Earth, sleep is crucial for recovery of the functional reserves expended during the daytime under the conditions of microgravity. Using the new technology, the recovery processes, as well as individual adaptation to a long-term space flight, can be studied. This method makes it possible to evaluate the sleep quality, mechanisms of recreation, and body functionality. These data may enrich substantially the information used by medical operators of space missions in the control centers.
Assessment of individual adaptation to microgravity during long term space flight based on stepwise discriminant analysis of heart rate variability parameters
Optimization of the cardiovascular system under conditions of long term space flight is provided by individual changes of autonomic cardiovascular control. Heart rate variability (HRV) analysis is an easy to use method under these extreme conditions. We tested the hypothesis that individual HRV analysis provides important information for crew health monitoring. HRV data from 14 Russian cosmonauts measured during long term space flights are presented (two times before and after flight, monthly in flight). HRV characteristics in the time and in the frequency domain were calculated. Predefined discriminant function equations obtained in reference groups (L1=−0.112⁎HR−1.006⁎SI−0.047⁎pNN50−0.086⁎HF; L2=0.140⁎HR−0.165⁎SI−1.293⁎pNN50+0.623⁎HF) were used to define four functional states. (1) Physiological normal, (2) prenosological, (3) premorbid and (4) pathological. Geometric mean values for the ISS cosmonauts based on L1 and L2 remained within normal ranges. A shift from the physiological normal state to the prenosological functional state during space flight was detected. The functional state assessed by HRV improved during space flight if compared to pre-flight and early post-flight functional states. Analysis of individual cosmonauts showed distinct patterns depending on the pre-flight functional state. Using the developed classification a transition process from the state of physiological normal into a prenosological state or premorbid state during different stages of space flight can be detected for individual Russian cosmonauts. Our approach to an estimation of HR regulatory pattern can be useful for prognostic purposes.
The devices “Puls” and “Pneumocard” were developed to further investigate autonomic cardiovascular and respiratory function on board the ISS. Investigations on board the “Mir” station showed transient changes in neurohumoral regulation indicating individual adaptation of regulatory systems. Therefore, an experiment “Pulse” has been performed starting with the fifth expedition on the ISS. The aim of the experiment is to investigate adaptation of the autonomic nervous system by measuring cardiorespiratory parameters during standardized tests at zero-gravity. Our results suggest that the adaptation to zero-gravity in terms of the autonomic cardiorespiratory control was adequate in all cosmonauts ( n = 5 ) . However, the characteristics of the responses during flight depend on the individual regulatory type. The individual evaluation of the regulatory systems especially during the initial stages of flight, during episodes of space sickness and after landing may shed light on critical changes of functional reserves and allow to reduce inflight and postflight disturbances.
Prolonged exposure to microgravity during spaceflight is thought to adversely affect the human spine because of reports that disc herniation risk is increased post-spaceflight. The increased herniation risk is highest during the first post-spaceflight year, and gradually subsides thereafter. Consequently, we hypothesized that the biomechanical properties of the intervertebral disc (IVD) deteriorate during spaceflight but then recover after acclimation to normal gravity. To test this hypothesis, we compared the compressive creep properties of caudal IVDs of murine subjects that had returned from a 13-day Shuttle mission (STS-133) to those of ground-based control mice. Spaceflight (n=6) and control (n=10) groups consisted of 13-week-old, BALB/c mice (11 weeks at launch). Mice were sacrificed +1 day, +5 days, or +7 days after the landing of STS-133. Disc height was measured in situ, and compressive creep rate was fit to a fluid transport model to determine disc biomechanical properties. Compared to controls, spaceflight mice had 12.6% lower disc height and 23.1% lower straindependence on swelling pressure. Biomechanical properties did not recover significantly over the 7-day post-flight period. Biomechanical properties of the murine caudal IVD were diminished by spaceflight, consistent with observations that prolonged exposure to microgravity increases disc herniation risk. These properties did not recover after short-term reacclimation to 1g loading.
BACKGROUND: The mollusk statocyst is a mechanosensing organ detecting the animal's orientation with respect to gravity. This system has clear similarities to its vertebrate counterparts: a weight-lending mass, an epithelial layer containing small supporting cells and the large sensory hair cells, and an output eliciting compensatory body reflexes to perturbations. METHODOLOGY/PRINCIPAL FINDINGS: In terrestrial gastropod snail we studied the impact of 16- (Foton M-2) and 12-day (Foton M-3) exposure to microgravity in unmanned orbital missions on: (i) the whole animal behavior (Helix lucorum L.), (ii) the statoreceptor responses to tilt in an isolated neural preparation (Helix lucorum L.), and (iii) the differential expression of the Helix pedal peptide (HPep) and the tetrapeptide FMRFamide genes in neural structures (Helix aspersa L.). Experiments were performed 13–42 hours after return to Earth. Latency of body re-orientation to sudden 90° head-down pitch was significantly reduced in postflight snails indicating an enhanced negative gravitaxis response. Statoreceptor responses to tilt in postflight snails were independent of motion direction, in contrast to a directional preference observed in control animals. Positive relation between tilt velocity and firing rate was observed in both control and postflight snails, but the response magnitude was significantly larger in postflight snails indicating an enhanced sensitivity to acceleration. A significant increase in mRNA expression of the gene encoding HPep, a peptide linked to ciliary beating, in statoreceptors was observed in postflight snails; no differential expression of the gene encoding FMRFamide, a possible neurotransmission modulator, was observed. CONCLUSIONS/SIGNIFICANCE: Upregulation of statocyst function in snails following microgravity exposure parallels that observed in vertebrates suggesting fundamental principles underlie gravi-sensing and the organism's ability to adapt to gravity changes. This simple animal model offers the possibility to describe general subcellular mechanisms of nervous system's response to conditions on Earth and in space.