Cardiac output in man in rest and work during and after acclimatization to 3,800 m.
Cardiac output in man at rest and at work during and after acclimatization to 3,800 meters
PHYSICAL EXERCISE↗
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Results for “HEART FUNCTION”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Effect of high altitude on maximal working capacity.
Effect of prolonged high altitude exposure on maximal work capacity in humans
HEART FUNCTION↗
Development and evaluation of an impedance cardiac output system.
Impedance cardiac output values simultaneously compared with dye dilution techniques under rest and exercise conditions
HEART FUNCTION↗
Cardiac excitability in high magnetic fields.
High magnetic fields effect on cardiac activity in spontaneously excited isolated turtle heart by simultaneous and separate electrical and mechanical measurement
ELECTROPHYSIOLOGY↗
Flight research program. VIII.
Vibrophonocardiographic techniques for monitoring cardiac dynamics in flight environment
FLIGHT CONDITION↗
Man's acclimatization to altitude during the first week at 3,800 m.
Cardiac output of young and old men at rest and working at altitude of 3,800 m. during first week
AGE FACTOR↗
Mechanisms of Cardiopulmonary Adaptation to Microgravity
Session TP1 contains short reports concerning: (1) Autonomic Regulation of Circulation and Mechanical Function of Heart at Different Stages of 14th Month Space Flight; (2) Cardiovascular Oxygen Transport in Exercising Humans in Microgravity; (3) Venous Hemodynamic Changes Assessed by Air Plethysmography During a 16-Day Space Flight; (4) Respiratory Mechanics After 180 Days Space Mission (EUROMIR'95); (5) Assessment of the Sympathetic and the Parasympathetic Nervous Activity During Parabolic Flight by Pupillary Light Reflex; and(6) Vascular Response to Different Gravity.
Source record↗
T wave alternans as a predictor of recurrent ventricular tachyarrhythmias in ICD recipients: prospective comparison with conventional risk markers
INTRODUCTION: The current standard for arrhythmic risk stratification is electrophysiologic (EP) testing, which, due to its invasive nature, is limited to patients already known to be at high risk. A number of noninvasive tests, such as determination of left ventricular ejection fraction (LVEF) or heart rate variability, have been evaluated as additional risk stratifiers. Microvolt T wave alternans (TWA) is a promising new risk marker. Prospective evaluation of noninvasive risk markers in low- or moderate-risk populations requires studies involving very large numbers of patients, and in such studies, documentation of the occurrence of ventricular tachyarrhythmias is difficult. In the present study, we identified a high-risk population, recipients of an implantable cardioverter defibrillator (ICD), and prospectively compared microvolt TWA with invasive EP testing and other risk markers with respect to their ability to predict recurrence of ventricular tachyarrhythmias as documented by ICD electrograms. METHODS AND RESULTS: Ninety-five patients with a history of ventricular tachyarrhythmias undergoing implantation of an ICD underwent EP testing, assessment of TWA, as well as determination of LVEF, baroreflex sensitivity, signal-averaged ECG, analysis of 24-hour Holter monitoring, and QT dispersion from the 12-lead surface ECG. The endpoint of the study was first appropriate ICD therapy for electrogram-documented ventricular fibrillation or tachycardia during follow-up. Kaplan-Meier survival analysis revealed that TWA (P < 0.006) and LVEF (P < 0.04) were the only significant univariate risk stratifiers. EP testing was not statistically significant (P < 0.2). Multivariate Cox regression analysis revealed that TWA was the only statistically significant independent risk factor. CONCLUSIONS: Measurement of microvolt TWA compared favorably with both invasive EP testing and other currently used noninvasive risk assessment methods in predicting recurrence of ventricular tachyarrhythmias in ICD recipients. This study suggests that TWA might also be a powerful tool for risk stratification in low- or moderate-risk patients, and needs to be prospectively evaluated in such populations.
Non-NASA Center↗
Cardiac myofilaments: mechanics and regulation
The mechanical properties of the cardiac myofilament are an important determinant of pump function of the heart. This report is focused on the regulation of myofilament function in cardiac muscle. Calcium ions form the trigger that induces activation of the thin filament which, in turn, allows for cross-bridge formation, ATP hydrolysis, and force development. The structure and protein-protein interactions of the cardiac sarcomere that are responsible for these processes will be reviewed. The molecular mechanism that underlies myofilament activation is incompletely understood. Recent experimental approaches have been employed to unravel the mechanism and regulation of myofilament mechanics and energetics by activator calcium and sarcomere length, as well as contractile protein phosphorylation mediated by protein kinase A. Central to these studies is the question whether such factors impact on muscle function simply by altering thin filament activation state, or whether modulation of cross-bridge cycling also plays a part in the responses of muscle to these stimuli.
Review, Tutorial↗
An evaluation of the use of new Doppler methods for detecting longitudinal function abnormalities in a pacing-induced heart failure model
BACKGROUND: Doppler tissue echocardiography and color M-mode Doppler flow propagation velocity have proven useful in evaluating cross-sections of patients with left ventricular (LV) dysfunction, but experience with serial changes is limited. Purpose and methods: We tested their use by evaluating the temporal changes of LV function in a pacing-induced congestive heart failure model. Rapid ventricular pacing was initiated and maintained in 20 dogs for 4 weeks. Echocardiography was performed at baseline and weekly during brief pacing cessation. RESULTS: With rapid pacing, LV volume significantly increased and ejection fraction (57%-28%), stroke volume (37-18 mL), and mitral annulus systolic velocity (16.1-6.6 cm/s) by Doppler tissue echocardiography significantly decreased, with ejection fraction and mitral annulus systolic velocity closely correlated (r = 0.706, P <.0001). In contrast to the mitral inflow velocities, mitral annulus early diastolic velocity decreased steadily (12.3-7.3 cm/s) resulting in a dramatic decrease in mitral annulus early/late (1.22-0.57) diastolic velocity with no tendency toward pseudonormalization. The color M-mode Doppler flow propagation velocity also showed significant steady decrease (57-24 cm/s) throughout the pacing period. Multiple regression analysis chose mitral annulus systolic velocity (r = 0.895, P <.0001) and propagation velocity (r = 0.782, P <.0001) for the most important factor predicting LV systolic and diastolic function, respectively. CONCLUSIONS: Doppler tissue echocardiography and color M-mode Doppler flow could evaluate the serial deterioration in LV dysfunction throughout the pacing period. These were more useful in quantifying progressive LV dysfunction than conventional ehocardiographic techniques, and were probably relatively independent of preload. These techniques could be suitable for longitudinal evaluation in addition to the cross-sectional study.
Evaluation Studies↗
Effect of hypokinesia on cardiac contractile function and nervous regulation of the heart
Longterm hypokinesia caused cardiac deadaptation in rabbits, which resulted in the diminishing of the left ventricular rate of contraction and relaxation, joined later by decreased vascular resistance. As a results, the ejection rate as well as stroke volume and cardiac output were normal. The decrease of the relaxation speed was more obvious at a high heart rate and results in shortening of the diastolic pause and diminishing of cardiac output. Hearts of the hypokinetic animals were characterized by normal maximal pressure developed by a unit of muccardial mass aorta clamping, decreased adrenoreactivity, and increased cholinoreactivity. This complex of changes is contrary to changes observed in adaptation to exercise, but is similar to changes observed in compensatory hypertrophy of the heart.
Meyerson, F. Z.↗
Observed differences in learning ability of heart rate self-regulation as a function of hypnotic susceptibility
Three groups of eight male and female subjects (aged 20-27 yr) categorized by low and high hypnotic susceptibility were taught to control their heart rates by means of an appropriate autogenic therapy/biofeedback technique. The experimental groups were trained by autogenic therapy and biofeedback, while the control group received only biofeedback. Significant differences are observed in all psychological test scores between subjects of high and low hypnotic susceptibility. The results confirm that (1) there are qualitative and quantitative differences between the performance of individuals with high and low hypnotic susceptibility; (2) interindividual-variability tests yield data relevant to individual performance in visceral learning tasks; (3) the combined autogenic therapy/biofeedback/verbal feedback technique is suitable for conditioning large stable autonomic responses in humans; and (4) this kind of conditioning is effective in eliminating or alleviating physiological reactions to some environmental stressors.
Cowings, P. S.↗
Effect of fluorocarbons on acetylcholinesterase activity and some counter measures
An isolated vagal sympathetic heart system has been successfully used for the study of the effect of fluorocarbons (FCs) on cardiac performance and in situ enzyme activity. Dichlorodifluoromethane sensitizes this preparation to sympathetic stimulation and to exogenous epinephrine challenge. Partial and complete A-V block and even cardiac arrest have been induced by epinephrine challenge in the FC sensitized heart. Potassium chloride alone restores the rhythmicity but not the normal contractility of the heart in such a situation. Addition of glucose will, however, completely restore the normal function of the heart which is sensitized by dichlorodifluoromethane. The ED 50 values of acetylcholinesterase activity which are used as a measure of relative effectiveness of fluorocarbons are compared with the maximum permissible concentration. Kinetic studies indicate that all the fluorocarbons tested so far are noncompetitive.
Young, W.↗
Accessing FMS Functionality: The Impact of Design on Learning
In modern commercial and military aircraft, the Flight Management System (FMS) lies at the heart of the functionality of the airplane. The nature of the FMS has also caused great difficulties learning and accessing this functionality. This study examines actual Air Force pilots who were qualified on the newly introduced advanced FMS and shows that the design of the system itself is a primary source of difficulty learning the system. Twenty representative tasks were selected which the pilots could be expected to accomplish on an ' actual flight. These tasks were analyzed using the RAFIV stage model (Sherry, Polson, et al. 2002). This analysis demonstrates that a great burden is placed on remembering complex reformulation of the task to function mapping. 65% of the tasks required retaining one access steps in memory to accomplish the task, 20% required two memorized access steps, and 15% required zero memorized access steps. The probability that a participant would make an access error on the tasks was: two memorized access steps - 74%, one memorized access step - 13%, and zero memorized access steps - 6%. Other factors were analyzed as well, including experience with the system and frequency of use. This completed the picture of a system with many memorized steps causing difficulty with the new system, especially when trying to fine where to access the correct function.
Fennell, Karl↗
Keeping Hearts Pumping
A collaboration between NASA, Dr. Michael DeBakey, Dr. George Noon, and MicroMed Technology, Inc., resulted in a life-saving heart pump for patients awaiting heart transplants. The MicroMed DeBakey VAD functions as a "bridge to heart transplant" by pumping blood throughout the body to keep critically ill patients alive until a donor heart is available. Weighing less than 4 ounces and measuring 1 inch by 3 inches, the pump is approximately one-tenth the size of other currently marketed pulsatile VADs. This makes it less invasive and ideal for smaller adults and children. Because of the pump's small size, less than 5 percent of the patients implanted developed device-related infections. It can operate up to 8 hours on batteries, giving patients the mobility to do normal, everyday activities.The MicroMed DeBakey VAD is a registered trademark of MicroMed Technology, Inc.
Source record↗
Alterations in left ventricular diastolic function in conscious dogs with pacing-induced heart failure
We investigated in conscious dogs (a) the effects of heart failure induced by chronic rapid ventricular pacing on the sequence of development of left ventricular (LV) diastolic versus systolic dysfunction and (b) whether the changes were load dependent or secondary to alterations in structure. LV systolic and diastolic dysfunction were evident within 24 h after initiation of pacing and occurred in parallel over 3 wk. LV systolic function was reduced at 3 wk, i.e., peak LV dP/dt fell by -1,327 +/- 105 mmHg/s and ejection fraction by -22 +/- 2%. LV diastolic dysfunction also progressed over 3 wk of pacing, i.e., tau increased by +14.0 +/- 2.8 ms and the myocardial stiffness constant by +6.5 +/- 1.4, whereas LV chamber stiffness did not change. These alterations were associated with increases in LV end-systolic (+28.6 +/- 5.7 g/cm2) and LV end-diastolic stresses (+40.4 +/- 5.3 g/cm2). When stresses and heart rate were matched at the same levels in the control and failure states, the increases in tau and myocardial stiffness were no longer observed, whereas LV systolic function remained depressed. There were no increases in connective tissue content in heart failure. Thus, pacing-induced heart failure in conscious dogs is characterized by major alterations in diastolic function which are reversible with normalization of increased loading condition.
NASA Discipline Cardiopulmonary↗
Dynamic regulation of heart rate during acute hypotension: new insight into baroreflex function
To examine the dynamic properties of baroreflex function, we measured beat-to-beat changes in arterial blood pressure (ABP) and heart rate (HR) during acute hypotension induced by thigh cuff deflation in 10 healthy subjects under supine resting conditions and during progressive lower body negative pressure (LBNP). The quantitative, temporal relationship between ABP and HR was fitted by a second-order autoregressive (AR) model. The frequency response was evaluated by transfer function analysis. Results: HR changes during acute hypotension appear to be controlled by an ABP error signal between baseline and induced hypotension. The quantitative relationship between changes in ABP and HR is characterized by a second-order AR model with a pure time delay of 0.75 s containing low-pass filter properties. During LBNP, the change in HR/change in ABP during induced hypotension significantly decreased, as did the numerator coefficients of the AR model and transfer function gain. Conclusions: 1) Beat-to-beat HR responses to dynamic changes in ABP may be controlled by an error signal rather than directional changes in pressure, suggesting a "set point" mechanism in short-term ABP control. 2) The quantitative relationship between dynamic changes in ABP and HR can be described by a second-order AR model with a pure time delay. 3) The ability of the baroreflex to evoke a HR response to transient changes in pressure was reduced during LBNP, which was due primarily to a reduction of the static gain of the baroreflex.
Clinical Trial↗
Noninvasive estimation of transmitral pressure drop across the normal mitral valve in humans: importance of convective and inertial forces during left ventricular filling
OBJECTIVES: We hypothesized that color M-mode (CMM) images could be used to solve the Euler equation, yielding regional pressure gradients along the scanline, which could then be integrated to yield the unsteady Bernoulli equation and estimate noninvasively both the convective and inertial components of the transmitral pressure difference. BACKGROUND: Pulsed and continuous wave Doppler velocity measurements are routinely used clinically to assess severity of stenotic and regurgitant valves. However, only the convective component of the pressure gradient is measured, thereby neglecting the contribution of inertial forces, which may be significant, particularly for nonstenotic valves. Color M-mode provides a spatiotemporal representation of flow across the mitral valve. METHODS: In eight patients undergoing coronary artery bypass grafting, high-fidelity left atrial and ventricular pressure measurements were obtained synchronously with transmitral CMM digital recordings. The instantaneous diastolic transmitral pressure difference was computed from the M-mode spatiotemporal velocity distribution using the unsteady flow form of the Bernoulli equation and was compared to the catheter measurements. RESULTS: From 56 beats in 16 hemodynamic stages, inclusion of the inertial term ([deltapI]max = 1.78+/-1.30 mm Hg) in the noninvasive pressure difference calculation significantly increased the temporal correlation with catheter-based measurement (r = 0.35+/-0.24 vs. 0.81+/-0.15, p< 0.0001). It also allowed an accurate approximation of the peak pressure difference ([deltapc+I]max = 0.95 [delta(p)cathh]max + 0.24, r = 0.96, p<0.001, error = 0.08+/-0.54 mm Hg). CONCLUSIONS: Inertial forces are significant components of the maximal pressure drop across the normal mitral valve. These can be accurately estimated noninvasively using CMM recordings of transmitral flow, which should improve the understanding of diastolic filling and function of the heart.
Non-NASA Center↗