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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

NASA's Functional Task Test: High Intensity Exercise Improves the Heart Rate Response to a Stand Test Following 70 Days of Bedrest

Cardiovascular adaptations due to spaceflight are modeled with 6deg head-down tilt bed rest (BR) and result in decreased orthostatic tolerance. We investigated if high-intensity resistive and aerobic exercise with and without testosterone supplementation would improve the heart rate (HR) response to a 3.5-min stand test and how quickly these changes recovered following BR. During 70 days of BR male subjects performed no exercise (Control, n=10), high intensity supine resistive and aerobic exercise (Exercise, n=9), or supine exercise plus supplemental testosterone (Exercise+T, n=8; 100 mg i.m., weekly in 2-week on/off cycles). We measured HR for 2 min while subjects were prone and for 3 min after standing twice before and 0, 1, 6, and 11 days after BR. Mixed-effects linear regression models were used to evaluate group, time, and interaction effects. Compared to pre-bed rest, prone HR was elevated on BR+0 and BR+1 in Control, but not Exercise or Exercise+T groups, and standing HR was greater in all 3 groups. The increase in prone and standing HR in Control subjects was greater than either Exercise or Exercise+T groups and all groups recovered by BR+6. The change in HR from prone to standing more than doubled on BR+0 in all groups, but was significantly less in the Exericse+T group compared to the Control, but not Exercise group. Exercise reduces, but does not prevent the increase in HR observed in response to standing. The significantly lower HR response in the Exercise+T group requires further investigation to determine physiologic significance.

Laurie, Steven S.↗
NASA NTRS2003

New insights into differential baroreflex control of heart rate in humans

Recent data indicate that bilateral carotid sinus denervation in patients results in a chronic impairment in the rapid reflex control of blood pressure during orthostasis. These findings are inconsistent with previous human experimental investigations indicating a minimal role for the carotid baroreceptor-cardiac reflex in blood pressure control. Therefore, we reexamined arterial baroreflex [carotid (CBR) and aortic baroreflex (ABR)] control of heart rate (HR) using newly developed methodologies. In 10 healthy men, 27 +/- 1 yr old, an abrupt decrease in mean arterial pressure (MAP) was induced nonpharmacologically by releasing a unilateral arterial thigh cuff (300 Torr) after 9 min of resting leg ischemia under two conditions: 1) ABR and CBR deactivation (control) and 2) ABR deactivation. Under control conditions, cuff release decreased MAP by 13 +/- 1 mmHg, whereas HR increased 11 +/- 2 beats/min. During ABR deactivation, neck suction was gradually applied to maintain carotid sinus transmural pressure during the initial 20 s after cuff release (suction). This attenuated the increase in HR (6 +/- 1 beats/min) and caused a greater decrease in MAP (18 +/- 2 mmHg, P < 0.05). Furthermore, estimated cardiac baroreflex responsiveness (DeltaHR/DeltaMAP) was significantly reduced during suction compared with control conditions. These findings suggest that the carotid baroreceptors contribute more importantly to the reflex control of HR than previously reported in healthy individuals.

Non-NASA Center↗
NASA NTRS1994

Comparing the effects of two in-flight aerobic exercise protocols on standing heart rates and VO(2peak) before and after space flight

The effects of regular aerobic exercise on orthostatic tolerance have been the subject of a long-standing controversy that will influence the use of exercise during space flight. To examine these effects, astronauts performed continuous (CE) aerobic exercise (n = 8), interval (IE) aerobic exercise (n = 4), or no (NE) exercise (n = 5) during flights of 7 to 11 days. Heart rate (HR) responses to an orthostatic challenge (stand test) were measured 10 days before flight and on landing day. VO(2peak) (graded treadmill exercise) was measured 7 to 21 days before and 2 days after flight. No significant differences across the groups were observed in standing HRs before or after flight. However, the within-group mean HRs significantly increased in the NE (71-89 beats/min) and CE (60-85 beats/min) groups after space flight. The HRs for the IE group did not significantly increase (75-86 beats/min) after space flight. VO(2peak) decreased (P < .05) in the NE (-9.5%) group, but did not change in the CE (-2.4%) and IE (1%) groups. The relationship (r = 0.237) between the delta HR and delta VO(2peak) was not significant. These preliminary results indicate that: (1) continuous exercise does not affect the orthostatic HR response after space flight; (2) interval exercise may minimize an increase in the postflight orthostatic HR; and (3) both exercise protocols can maintain VO(2peak).

NASA Discipline Musculoskeletal↗
DOE OSTI2014

Wearable and sensitive heart-rate detectors based on PbS quantum dot and multiwalled carbon nanotube blend film

Wearable and sensitive photodetectors (PDs) have been demonstrated based on a blend film of PbS quantum dots (QDs) and QDs modified multiwalled carbon nanotubes (MWCNTs). Owing to the synergetic effect from high light sensitivity of PbS QDs and excellent conductive and mechanical properties of MWCNTs, the blend PDs show high sensitivity and flexibility performance: device responsivity and detectivity reach 583 mA/W and 3.25 × 10{sup 12 }Jones, respectively, and could stand large number (at least 10 000 cycles) and wide angle (up to 80°) bending. Furthermore, the wearable and sensitive PDs have been applied to measure the heart rate in both red and near infrared (NIR) ranges. The presented PDs are expected to work as sensor candidates in integrated electronic skin.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1974

Rhythmic variation in heart rate and respiration rate during space flight - Apollo 15

As part of the operational biomedical monitoring for Apollo manned missions, ECG and respiration rate are telemetered at selected intervals to mission control. The data were collected as part of this monitoring program. These data were evaluated for circadian and ultradian rhythmicity because of their uniqueness. The ability to detect and quantitate biorhythms in living systems during space flight is an important aspect of evaluating hypotheses concerning the underlying mechanisms of these phenomena. Circadian variation in heart rate during space flight is demonstrated here. In analyzing generated time series data it has been found that period discrimination is much better than the theoretical limit.

Rummel, J. A.↗
NASA NTRS2016

Heart Rate Responses to Unaided Orion Side Hatch Egress in the Neutral Buoyancy Laboratory

NASA is developing the Orion capsule as a vehicle for transporting crewmembers to and from the International Space Station (ISS) and for future human space exploration missions. Orion and other commercial vehicles are designed to splash down in the ocean where nominally support personnel will assist crewmembers in egressing the vehicle. However, off-nominal scenarios will require crewmembers to egress the vehicle unaided, deploy survival equipment, and ingress a life raft. PURPOSE: To determine the heart rate (HR) responses to unaided Orion side hatch egress and raft ingress as a part of the NASA Crew Survival Engineering Team's evaluation of the PORT Orion mockup in the Neutral Buoyancy Laboratory (NBL). METHODS: Nineteen test subjects, including four astronauts (N=19, 14 males/5 females, 38.6+/-8.4 y, 174.4+/-9.6 cm, 75.7+/-13.1 kg), completed a graded maximal test on a cycle ergometer to determine VO2peak and HRpeak and were divided into five crews of four members each; one subject served on two crews. Each crew was required to deploy a life raft, egress the Orion vehicle from the side hatch, and ingress the life raft with two 8 kg emergency packs per crew. Each crew performed this activity one to three times; a total of ten full egresses were completed. Subjects wore a suit that was similar in form, mass, and function to the Modified Advanced Crew Escape Suit (MACES) including helmet, gloves, boots, supplemental O2 bottles, and a CO2-inflated life preserver (approx.18 kg); subjects began each trial seated supine in the PORT Orion mockup with seat belts and mockup O2 and communication connections and ended each trial with all four crewmembers inside the life raft. RESULTS: VO2peak was 40.8+/-6.8 mL/kg/min (3.1+/-0.7 L/min); HRpeak was 181+/-10 bpm. Total egress time across trials was 5.0+/-1.6 min (range: 2.8-8.0 min); all subjects were able to successfully complete all trials. Average maximum HR at activity start, at the hatch opening, in the water, and in the raft, was 108, 137, 147, and 153 bpm, respectively; these values corresponded to 59+/-10%, 73+/-8%, 82+/-3%, and 84+/-6% of HRpeak, respectively. The highest HRs were seen after raft ingress and ranged from 72-99% HRpeak. Across all trials, cumulative averages of 5.4, 3.0, 1.1, and 0.2 min were spent at HRs >60%, >70%, >80%, and >90% HRpeak, respectively. CONCLUSION: Unaided Orion side hatch egress in the NBL is a relatively short-duration activity that elicits a high HR response for several min. Although all crewmembers successfully completed this activity, additional factors such as high seas, poor visibility, an incapacitated crewmember, neurovestibular perturbation, and neuromuscular deconditioning characteristic of a true operational environment may increase the physiologic demand (or decrease crewmembers' physiologic capacity) of unaided Orion side hatch egress. Additionally, landing conditions may require the crewmembers to egress from the top hatch, which is expected to be even more physiologically demanding; this condition will be evaluated in subsequent collaborative testing with the NASA Crew Survival Engineering Team.

English, Kirk L.↗
NASA NTRS1990

Heart rate and pulmonary function while wearing the launch-entry crew escape suit (LES) during + Gx acceleration and simulated Shuttle launch

Space shuttle crewmembers have been equipped with a launch-entry crew escape system (LES) since the Challenger accident in 1986. Some crewmembers, wearing the new pressure suit, have reported breathing difficulties and increased effort to achieve the desired range of motion. This study was conducted to quantify the reported increased physical workloads and breathing difficulty associated with wearing the LES. Both veteran astronauts and centrifuge panel members were exposed to various + Gx profiles (including simulated shuttle launch) + Gx on the USAF School of Aerospace Medicine (USAFSAM) human-use centrifuge. Maximum heart rate data showed no increased workload associated with arm and head movement in the LES when compared to the flight suit/helmet ensemble (LEH). However, the LES did impose a significant increase in breathing difficulty beginning at +2.5 Gx which was demonstrated by a decrease in forced vital capacity and subjected questionnaries.

Krutz, Robert W., Jr.↗
DOE OSTI2022

Development and validation of a mathematical model of heart rate response to fluid perturbation

Physiological closed-loop controlled (PCLC) medical devices monitor and automatically adjust the patient’s condition by using physiological variables as feedback, ideally with minimal human intervention to achieve the target levels set by a clinician. PCLC devices present a challenge when it comes to evaluating their performance, where conducting large clinical trials can be expensive. Virtual physiological patients simulated by validated mathematical models can be utilized to obtain preclinical evidence of safety and assess the performance of the PCLC medical device during normal and worst-case conditions that are unlikely to happen in a limited clinical trial. A physiological variable that plays a major role during fluid resuscitation is heart rate (HR). For in silico assessment of PCLC medical devices regarding fluid perturbation, there is currently no mathematical model of HR validated in terms of its predictive capability performance. This paper develops and validates a mathematical model of HR response using data collected from sheep subjects undergoing hemorrhage and fluid infusion. The model proved to be accurate in estimating the HR response to fluid perturbation, where averaged between 21 calibration datasets, the fitting performance showed a normalized root mean square error (NRMSE) of 7.41 ± 2.8%. The model was also evaluated in terms of model predictive capability performance via a leave-one-out procedure (21 subjects) and an independent validation dataset (6 subjects). Two different virtual cohort generation tools were used in each validation analysis. The generated envelope of virtual subjects robustly met the defined acceptance criteria, in which 95% of the testing datasets presented simulated HR patterns that were within a deviation of 50% from the observed data. In addition, out of 16000 and 18522 simulated subjects for the leave one-out and independent datasets, the model was able to generate at least one virtual subject that was close to the real subject within an error margin of 9.56 ± 3.15% and 11.1 ± 1.22% NRMSE, respectively. In conclusion, the model can generate valid virtual HR physiological responses to fluid perturbation and be incorporated into future non-clinical simulated testing setups for assessing PCLC devices intended for fluid resuscitation.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2000

Differential baroreflex control of heart rate in sedentary and aerobically fit individuals

PURPOSE: We compared arterial, aortic, and carotid-cardiac baroreflex sensitivity in eight average fit (maximal oxygen uptake, VO2max = 42.2+/-1.9 mL x kg(-1) x min(-1)) and eight high fit (VO2max = 61.9+/-2.2 mL x kg(-1) x min(-1)) healthy young adults. METHODS: Arterial and aortic (ABR) baroreflex functions were assessed utilizing hypo- and hyper-tensive challenges induced by graded bolus injections of sodium nitroprusside (SN) and phenylephrine (PE), respectively. Carotid baroreflex (CBR) sensitivity was determined using ramped 5-s pulses of both pressure and suction delivered to the carotid sinus via a neck chamber collar, independent of drug administration. RESULTS: During vasoactive drug injection, mean arterial pressure (MAP) was similarly altered in average fit (AF) and high fit (HF) groups. However, the heart rate (HR) response range of the arterial baroreflex was significantly attenuated (P < 0.05) in HF (31+/-4 beats x min(-1)) compared with AF individuals (46+/-4 beats x min(-1)). When sustained neck suction and pressure were applied to counteract altered carotid sinus pressure during SN and PE administration, isolating the ABR response, the response range remained diminished (P < 0.05) in the HF population (24+/-3 beats x min(-1)) compared with the AF group (41+/-4 beats x min(-1)). During CBR perturbation, the HF (14+/-1 beats-min(-1)) and AF (16+/-1 beats-min(-1)) response ranges were similar. The arterial baroreflex response range was significantly less than the simple sum of the CBR and ABR (HF, 38+/-3 beats x min(-1) and AF, 57+/-4 beats x min(-1)) in both fitness groups. CONCLUSIONS: These data confirm that reductions in arterial-cardiac reflex sensitivity are mediated by diminished ABR function. More importantly, these data suggest that the integrative relationship between the ABR and CBR contributing to arterial baroreflex control of HR is inhibitory in nature and not altered by exercise training.

NASA Discipline Cardiopulmonary↗
NASA NTRS1997

Cycle-Powered Short Radius (1.9 m) Centrifuge: Effect of Exercise Versus Passive Acceleration on Heart Rate in Humans

In addition to extensive use of lower extremity physical exercise training as a countermeasure for the work capacity component of spaceflight deconditioning, some form of additional head-to-foot (+Gz) gravitational (orthostatic) stress may be required to further attenuate or prevent the signs and symptoms (nausea, vertigo, instability, fatigue) of the general reentry syndrome (GRS) that can reduce astronaut performance during landing. Orthostatic (head-to-foot) stress can be induced by standing, by lower body negative pressure, and by +Gz acceleration. One important question is whether acceleration training alone or with concurrent leg exercise would provide sufficient additive stimulation to attenuate the GRS. Use of a new human-powered centrifuge may be the answer. Thus, the purpose for this study was to compare heart rate (HR), i.e., a stress response during human-powered acceleration, in four men (35-62 yr) and two women (30-31 yr) during exercise acceleration versus passive acceleration (by an off-board operator) at 100% (maximal acceleration = A(max)), and at 25%, 50%, and 75% of A(max). Mean (+/-SE) A(max) was 43.7 +/- 1.3 rpm (+3.9 +/- 0.2Gz). Mean HR at exercise A(max) was 189 +/- 13 b/min (50-70 sec run time), and 142 +/- 22 b/min at passive A(max) (40-70 sec run time). Regression of mean HR on the various +Gz levels indicated explained variance (correlations squared) of r(exp 2) = 0.88 (exercise) and r(exp 2) = 0.96 (passive): exercise HR of 107 +/- 4 (25%) to 189 +/- 13 (100%) b/min were 43-50 b/min higher (p less than 0.05) than comparable passive HR of 64 +/- 2 to 142 +/- 22 b/min. Thus, exercise adds significant physiological stress during +Gz acceleration. Inflight use of this combined exercise and acceleration countermeasure may maintain work capacity as well as normalize acceleration and orthostatic tolerances which could attenuate or perhaps eliminate the GRS.

Greenleaf, J. E.↗
NASA NTRS1979

A long-range and long-life telemetry data-acquisition system for heart rate and multiple body temperatures from free-ranging animals

The system includes an implantable transmitter, external receiver-retransmitter collar, and a microprocessor-controlled demodulator. The size of the implant is suitable for animals with body weights of a few kilograms or more; further size reduction of the implant is possible. The ECG is sensed by electrodes designed for internal telemetry and to reduce movement artifacts. The R-wave characteristics are then specifically selected to trigger a short radio frequency pulse. Temperatures are sensed at desired locations by thermistors and then, based on a heartbeat counter, transmitted intermittently via pulse interval modulation. This modulation scheme includes first and last calibration intervals for a reference by ratios with the temperature intervals to achieve good accuracy even over long periods. Pulse duration and pulse sequencing are used to discriminate between heart rate and temperature pulses as well as RF interference.

Lund, G. F.↗
NASA NTRS2010

Heart Rate Response During Mission-Critical Tasks After Space Flight

Adaptation to microgravity could impair crewmembers? ability to perform required tasks upon entry into a gravity environment, such as return to Earth, or during extraterrestrial exploration. Historically, data have been collected in a controlled testing environment, but it is unclear whether these physiologic measures result in changes in functional performance. NASA?s Functional Task Test (FTT) aims to investigate whether adaptation to microgravity increases physiologic stress and impairs performance during mission-critical tasks. PURPOSE: To determine whether the well-accepted postflight tachycardia observed during standard laboratory tests also would be observed during simulations of mission-critical tasks during and after recovery from short-duration spaceflight. METHODS: Five astronauts participated in the FTT 30 days before launch, on landing day, and 1, 6, and 30 days after landing. Mean heart rate (HR) was measured during 5 simulations of mission-critical tasks: rising from (1) a chair or (2) recumbent seated position followed by walking through an obstacle course (egress from a space vehicle), (3) translating graduated masses from one location to another (geological sample collection), (4) walking on a treadmill at 6.4 km/h (ambulation on planetary surface), and (5) climbing 40 steps on a passive treadmill ladder (ingress to lander). For tasks 1, 2, 3, and 5, astronauts were encouraged to complete the task as quickly as possible. Time to complete tasks and mean HR during each task were analyzed using repeated measures ANOVA and ANCOVA respectively, in which task duration was a covariate. RESULTS: Landing day HR was higher (P < 0.05) than preflight during the upright seat egress (7%+/-3), treadmill walk (13%+/-3) and ladder climb (10%+/-4), and HR remained elevated during the treadmill walk 1 day after landing. During tasks in which HR was not elevated on landing day, task duration was significantly greater on landing day (recumbent seat egress: 25%+/-14 and mass translation: 26%+/-12; P < 0.05). CONCLUSION: Elevated HR and increased task duration during postflight simulations of mission-critical tasks is suggestive of spaceflight-induced deconditioning. Following short-duration microgravity missions (< 16 d), work performance may be transiently impaired, but recovery is rapid.

Arzeno, Natalia M.↗
NASA NTRS2003

Three Experiments Examining the Use of Electroencephalogram,Event-Related Potentials, and Heart-Rate Variability for Real-Time Human-Centered Adaptive Automation Design

Adaptive automation represents an advanced form of human-centered automation design. The approach to automation provides for real-time and model-based assessments of human-automation interaction, determines whether the human has entered into a hazardous state of awareness and then modulates the task environment to keep the operator in-the-loop , while maintaining an optimal state of task engagement and mental alertness. Because adaptive automation has not matured, numerous challenges remain, including what the criteria are, for determining when adaptive aiding and adaptive function allocation should take place. Human factors experts in the area have suggested a number of measures including the use of psychophysiology. This NASA Technical Paper reports on three experiments that examined the psychophysiological measures of event-related potentials, electroencephalogram, and heart-rate variability for real-time adaptive automation. The results of the experiments confirm the efficacy of these measures for use in both a developmental and operational role for adaptive automation design. The implications of these results and future directions for psychophysiology and human-centered automation design are discussed.

Prinzel, Lawrence J., III↗
NASA NTRS1986

Effect of posture on arterial baroreflex control of heart rate in humans

The effects of blood-volume redistribution induced by postural changes on baroreflex activity are investigated. The central blood volume and baroreceptor functions of ten males between 23-51 years old were examined while they were in the head-up tilt (HUT), head-down tilt (HDT), and supine positions. It is observed that during HDT at 15 deg the pulse interval over the first five cardiac cycles following neck suction onset is 51 + or - 18 ms longer, at 30 deg it is 61 + or - 20 ms longer, and at 45 deg it is 74 + or - 35 ms longer than at supine; during HUT at 15 deg the pulse interval is 25 + or - 9 ms shorter than when supine, but for the 30 and 45 deg there is no significant difference in pulse interval detected. The data reveal that posture does modify arterial baroreflex control of heart rate.

Harrison, M. H.↗
NASA NTRS2000

Effect of head-down-tilt bed rest and hypovolemia on dynamic regulation of heart rate and blood pressure

Adaptation to head-down-tilt bed rest leads to an apparent abnormality of baroreflex regulation of cardiac period. We hypothesized that this "deconditioning response" could primarily be a result of hypovolemia, rather than a unique adaptation of the autonomic nervous system to bed rest. To test this hypothesis, nine healthy subjects underwent 2 wk of -6 degrees head-down bed rest. One year later, five of these same subjects underwent acute hypovolemia with furosemide to produce the same reductions in plasma volume observed after bed rest. We took advantage of power spectral and transfer function analysis to examine the dynamic relationship between blood pressure (BP) and R-R interval. We found that 1) there were no significant differences between these two interventions with respect to changes in numerous cardiovascular indices, including cardiac filling pressures, arterial pressure, cardiac output, or stroke volume; 2) normalized high-frequency (0.15-0.25 Hz) power of R-R interval variability decreased significantly after both conditions, consistent with similar degrees of vagal withdrawal; 3) transfer function gain (BP to R-R interval), used as an index of arterial-cardiac baroreflex sensitivity, decreased significantly to a similar extent after both conditions in the high-frequency range; the gain also decreased similarly when expressed as BP to heart rate x stroke volume, which provides an index of the ability of the baroreflex to alter BP by modifying systemic flow; and 4) however, the low-frequency (0.05-0.15 Hz) power of systolic BP variability decreased after bed rest (-22%) compared with an increase (+155%) after acute hypovolemia, suggesting a differential response for the regulation of vascular resistance (interaction, P < 0.05). The similarity of changes in the reflex control of the circulation under both conditions is consistent with the hypothesis that reductions in plasma volume may be largely responsible for the observed changes in cardiac baroreflex control after bed rest. However, changes in vasomotor function associated with these two conditions may be different and may suggest a cardiovascular remodeling after bed rest.

Non-NASA Center↗
NASA NTRS1994

The effects of autogenic-feedback training on motion sickness severity and heart rate variability in astronauts

Space motion sickness (SMS) affects 50 percent of all people during early days of spaceflight. This study describes the results of two Shuttle flight experiments in which autogenic-feedback training (AFT), a physiological conditioning method, was tested as a treatment for this disorder. Of the six who were designated as flight subjects (two women and four men), three were given treatment and three served as controls (i.e., no AFT). Treatment subjects were given 6 hours of preflight AFT. Preflight results showed that AFT produced a significant increase in tolerance to rotating chair motion sickness tests. Further, this increased tolerance was associated with changes in specific physiological responses and reports of reduced malaise. Flight results showed that two of the three control subjects experienced repeated vomiting on the first mission day, while one subject experienced only moderate malaise. Of the three treatment subjects, one experienced mild discomfort, one moderate discomfort, and one severe motion sickness. Only the three control subjects took medication for symptom suppression. Measures of cardiac function reflective of vagal control were shown to be affected especially strongly on the first day of space flight. AFT given for control of heart rate, respiration, and other autonomic activity influenced both the vagal control measures and SMS. These data suggest that AFT may be an effective treatment for space motion sickness; however, this cannot be demonstrated conclusively with the small number of subjects described.

Toscano, William B.↗
NASA NTRS1995

Fractal mechanisms and heart rate dynamics. Long-range correlations and their breakdown with disease

Under healthy conditions, the normal cardiac (sinus) interbeat interval fluctuates in a complex manner. Quantitative analysis using techniques adapted from statistical physics reveals the presence of long-range power-law correlations extending over thousands of heartbeats. This scale-invariant (fractal) behavior suggests that the regulatory system generating these fluctuations is operating far from equilibrium. In contrast, it is found that for subjects at high risk of sudden death (e.g., congestive heart failure patients), these long-range correlations break down. Application of fractal scaling analysis and related techniques provides new approaches to assessing cardiac risk and forecasting sudden cardiac death, as well as motivating development of novel physiologic models of systems that appear to be heterodynamic rather than homeostatic.

NASA Discipline Cardiopulmonary↗