Microgravity-induced physiologic changes could impair a crewmember's performance upon return to a gravity environment. The Functional Task Test aims to correlate these physiologic alterations with changes in performance during mission-critical tasks. In this study, we evaluated spaceflight-induced cardiovascular changes during 11 functional tasks in 7 Shuttle astronauts before spaceflight, on landing day, and 1, 6, and 30 days after landing. Mean heart rate was examined during each task and autonomic activity was approximated by heart rate variability during the Recovery from Fall/Stand Test, a 2-min prone rest followed by a 3-min stand. Heart rate was increased on landing day during all of the tasks, and remained elevated 6 days after landing during 6 of the 11 tasks. Parasympathetic modulation was diminished and sympathovagal balance was increased on landing day. Additionally, during the stand test 6 days after landing, parasympathetic modulation remained suppressed and heart rate remained elevated compared to preflight levels. Heart rate and autonomic activity were not different from preflight levels 30 days after landing. We detected changes in heart rate and autonomic activity during a 3-min stand and a variety of functional tasks, where cardiovascular deconditioning was still evident 6 days after returning from short-duration spaceflight. The delayed recovery times for heart rate and parasympathetic modulation indicate the necessity of assessing functional performance after long-duration spaceflight to ensure crew health and safety.
Research Containing: Human Research
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.
Selection of Medications for the International Space Station: The Space Medicine Patient Condition Database
Medical care available to astronauts on the International Space Station has been affected by limitations on funding, space and weight availability, and crew training. A Space Medicine Patient Condition Database (PCDB) was designed to enhance inventory control, resource selection, protocol standardization, evidence-based medicine, on-orbit diagnostic skills, and materiel management. The first step in the PCDB creation was the identification of the medical conditions anticipated among the astronaut population in the flight environment. Military databases, previous spaceflight experience, and analog populations were used to create this listing. The PCDB then linked these individual conditions with the current resources available on orbit to treat them. Other features include a resource gauge, item location information, diagnosis coding, and built-in reference capabilities. Currently in the second phase of development, specific, evidence-based treatment protocols are being developed and evaluated in comparison with the terrestrial medicine standard of care. By documenting on-orbit medical systems and their associated terrestrial standards, the PCDB enables the prioritization and allocation of limited resources. In the final phase of the project, the PCDB will make use of decision support software to enhance diagnostic determination and provide an operational tool for the crew and mission teams.
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 Effects of Long-term Microgravity on Autonomic Regulation of Blood Circulation in Crewmembers of the International Space Station
The article presents the results of space experiment “Pneumocard”. The investigation involved all 25 Russian members of the ISS crew. The total of 226 sessions were made including 130 aboard the ISS, 50 prior to launch and 46 on return from mission. The objective was to study effects of the spaceflight factors on autonomic regulation of blood circulation, respiration and cardiac contractility during long-duration mission. The purpose was to secure new research data that would clarify our present view of adaptation mechanisms. Registered were the following signals: electrocardiogram, impedance cardiogram, seismic cardiogram, pneumotachogram, finger photoplethysmogram. A set of hardand software was used. Autonomic regulation of blood circulation by HRV analysis was investigated. It was shown that at the onset of a space mission parasympathetic involvement in regulation increases typically with subsequent mobilization of additional functional reserve. It guided the development of a functional states mathematical model incorporating the established types of autonomic regulation. Our data evidence that the combination of HRV analysis, pre-nosology diagnosis and probabilistic estimate of the pathology risk can reinforce the medical care program in space missions.
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.
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.
Prevalence of sleep deficiency and use of hypnotic drugs in astronauts before, during, and after spaceflight: an observational study
BackgroundSleep deprivation and fatigue are common subjective complaints among astronauts. Previous studies of sleep and hypnotic drug use in space have been limited to post-flight subjective survey data or in-flight objective data collection from a small number of crew members. We aimed to characterise representative sleep patterns of astronauts on both short-duration and long-duration spaceflight missions.