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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Jet pump assisted artery

A procedure for priming an arterial heat pump is reported; the procedure also has a means for maintaining the pump in a primed state. This concept utilizes a capillary driven jet pump to create the necessary suction to fill the artery. Basically, the jet pump consists of a venturi or nozzle-diffuser type constriction in the vapor passage. The throat of this venturi is connected to the artery. Thus vapor, gas, liquid, or a combination of the above is pumped continuously out of the artery. As a result, the artery is always filled with liquid and an adequate supply of working fluid is provided to the evaporator of the heat pipe.

Source record↗
NASA NTRS1978

Jet pump assisted arterial heat pipe

This paper discusses the concept of an arterial heat pipe with a capillary driven jet pump. The jet pump generates a suction which pumps vapor and noncondensible gas from the artery. The suction also forces liquid into the artery and maintains it in a primed condition. A theoretical model was developed which predicts the existence of two stable ranges. Up to a certain tilt the artery will prime by itself once a heat load is applied to the heat pipe. At higher tilts, the jet pump can maintain the artery in a primed condition but self-priming is not possible. A prototype heat pipe was tested which self-primed up to a tilt of 1.9 cm, with a heat load of 500 watts. The heat pipe continued to prime reliably when operated as a VCHP, i.e., after a large amount of noncondensible gas was introduced.

Bienert, W. B.↗
NASA NTRS1988

Effect of the Trendelenburg position on the distribution of arterial air emboli in dogs

The effect of Trendelenburg position (TP) on the distribution of arterial air emboli in dogs was examined in a two-part investigation. In the first part, the effects of the bubble size and the vessel angle on the bubble velocity and the direction of flow were investigated in vitro, using a simulated carotid artery preparation. It was found that larger bubbles increased in velocity in the same direction as the blood flow at 0-, 10-, and 30-deg vessel angles, and decreased when the vessel was positioned at 90 deg. Smaller bubbles did not change velocity from 0 to 30 deg, but acted to increase the velocity, in the same direction as the flood flow, at 90 deg. The second series of experiments examined the effect of 0 to 30 deg TP on carotid-artery distribution of gas bubbles injected into the left ventricle or ascending aorta of anesthetized dogs. It was found that, regardless of the degree of the TP, the bubbles passed into the carotid artery simultaneously with the passage into the abdominal aorta. It is concluded that the TP does not prevent arterial bubbles from reaching the brain.

Butler, Bruce D.↗
NASA NTRS2001

Absence of arterial baroreflex modulation of skin sympathetic activity and sweat rate during whole-body heating in humans

1. Prior findings suggest that baroreflexes are capable of modulating skin blood flow, but the effects of baroreceptor loading/unloading on sweating are less clear. Therefore, this project tested the hypothesis that pharmacologically induced alterations in arterial blood pressure in heated humans would lead to baroreflex-mediated changes in both skin sympathetic nerve activity (SSNA) and sweat rate. 2. In seven subjects mean arterial blood pressure was lowered (approximately 8 mmHg) and then raised (approximately 13 mmHg) by bolus injections of sodium nitroprusside and phenylephrine, respectively. Moreover, in a separate protocol, arterial blood pressure was reduced via steady-state administration of sodium nitroprusside. In both normothermia and heat-stress conditions the following responses were monitored: sublingual and mean skin temperatures, heart rate, beat-by-beat blood pressure, skin blood flow (laser-Doppler flowmetry), local sweat rate and SSNA (microneurography from peroneal nerve). 3. Whole-body heating increased skin and sublingual temperatures, heart rate, cutaneous blood flow, sweat rate and SSNA, but did not change arterial blood pressure. Heart rate was significantly elevated (from 74 +/- 3 to 92 +/- 4 beats x min(-1); P < 0.001) during bolus sodium nitroprusside-induced reductions in blood pressure, and significantly reduced (from 92 +/- 4 to 68 +/- 4 beats x min(-1); P < 0.001) during bolus phenylephrine-induced elevations in blood pressure, thereby demonstrating normal baroreflex function in these subjects. 4. Neither SSNA nor sweat rate was altered by rapid (bolus infusion) or sustained (steady-state infusion) changes in blood pressure regardless of the thermal condition. 5. These data suggest that SSNA and sweat rate are not modulated by arterial baroreflexes in normothermic or moderately heated individuals.

Clinical Trial↗
NASA NTRS1989

External artery heat pipe

An improved heat pipe with an external artery. The longitudinal slot in the heat pipe wall which interconnects the heat pipe vapor space with the external artery is completely filled with sintered wick material and the wall of the external artery is also covered with sintered wick material. This added wick structure assures that the external artery will continue to feed liquid to the heat pipe evaporator even if a vapor bubble forms within and would otherwise block the liquid transport function of the external artery.

Gernert, Nelson J.↗
NASA NTRS2008

Arterial Structure and Function in Women and Men Following Long Duration Bed Rest

Orthostatic intolerance is a well-recognized consequence of space flight and bed rest (BR), with a greater incidence reported in women. We hypothesized that leg, but not arm, arterial structure and function would be altered following prolonged BR, as a model of space flight, and that women would be more susceptible to BR-induced deconditioning than men. METHODS: Ten volunteers (5 males, 5 females) completed 90 d of 6 head-down BR. Subjects participated in tests of brachial (BA) and anterior tibial (AT) artery endothelium-dependent (flow mediated dilation [FMD] following 5-7 min of arterial occlusion) and endothelium-independent (0.4 mg sublingual nitroglycerin [SN]) vasodilation before BR (PRE) and on days 7 (BR7), 21 (BR21), and 90 (BR90) of BR. Vessel diameter and intimal medial thickness (IMT) were measured by ultrasound. IMT, baseline diameter, and percent change in diameter from baseline during FMD and SN tests were compared across BR and between genders using repeated measures two-way ANOVA with Bonferroni post-hoc tests in which PRE and women were control conditions. RESULTS: Baseline vessel diameter was lower in women than in men in both the BA (p=0.005) and AT (p=0.01) across all days. Baseline AT diameter decreased during BR (p=0.01) and tended to be more profound in women (interaction, p=0.06). AT diameter was reduced in women at BR21 and BR90 (p<0.01) but not in men. In contrast, there was no BR effect on baseline BA diameter. IMT also decreased in the AT (p<0.001) but not in the BA during BR; AT IMT was reduced by BR21 (p<0.05). As a group, there was no effect of BR on AT FMD, BA FMD, and AT SN-dilation, although BA SN-dilation was significantly reduced on BR21 (p=0.01). Across all BR days, women exhibited higher AT FMD (p=0.03), BA FMD (p=0.02), and BA SN-dilation (p=0.01) and tended to demonstrate greater AT SN-dilation (p=0.11). CONCLUSIONS: These preliminary results suggest that arterial remodeling occurs during BR in the leg (decreased diameter and IMT), but not in the arm, and that women appear to be more responsive to BR than men. These changes in the leg, coupled with larger responses to direct and indirect stimulation of the arterial smooth muscle, may be related to the greater incidence of orthostatic intolerance in women after BR and space flight.

Lee, Stuart M. C.↗
NASA NTRS2014

Analysis of Arterial Mechanics During Head-Down-Tilt Bed Rest

Carotid, brachial, and tibial arteries reacted differently to HDTBR. Previous studies have not analyzed the mechanical properties of the human brachial or anterior tibial arteries. After slight variations during bed-rest, arterial mechanical properties and IMT returned to pre-bed rest values, with the exception of tibial stiffness and PSE, which continued to be reduced post-bed rest while the DC remained elevated. The tibial artery remodeling was probably due to decreased pressure and volume. Resulting implications for longer duration spaceflight are unclear. Arterial health may be affected by microgravity, as shown by increased thoracic aorta stiffness in other ground based simulations (Aubert).

Elliott, Morgan B.↗
NASA NTRS1992

Vasopressin responses to unloading arterial baroreceptors during cardiac nerve blockade in conscious dogs

We examined the relative contributions of afferent input from the heart and from arterial baroreceptors in the stimulation of arginine vasopressin (AVP) secretion in response to hypotension caused by thoracic inferior vena caval constriction (TIVCC). Afferent input from cardiac receptors was reversibly blocked by infusing 2% procaine into the pericardial space to anesthetize the cardiac nerves. Acute cardiac nerve blockade (CNB) alone caused a rise in mean arterial pressure (MAP) of 24 +/- 3 mmHg but no change in plasma AVP. If the rise in MAP was prevented by TIVCC, plasma AVP increased by 39 +/- 15 pg/ml, and if MAP was allowed to increase and then was forced back to control by TIVCC, plasma AVP increased by 34 +/- 15 pg/ml. Thus the rise in MAP during CNB stimulated arterial baroreceptors, which in turn compensated for the loss of inhibitory input from cardiac receptors on AVP secretion. These results indicate that the maximum secretory response resulting from complete unloading of cardiac receptors at a normal MAP results in a mean increase in plasma AVP of 39 pg/ml in this group of dogs. When MAP was reduced 25% below control levels (from 95 +/- 5 to 69 +/- 3 mmHg) by TIVCC during pericardial saline infusion, plasma AVP increased by 79 +/- 42 pg/ml. However, the same degree of hypotension during CNB (MAP was reduced from 120 +/- 5 to 71 +/- 3 mmHg) led to a greater (P less than 0.05) increase in plasma AVP of 130 +/- 33 pg/ml. Because completely unloading cardiac receptors can account for an increase of only 39 pg/ml on average in this group of dogs, the remainder of the increase in plasma AVP must be due to other sources of stimulation. We suggest that the principal stimulus to AVP secretion after acute CNB in these studies arises from unloading the arterial baroreceptors.

NASA Center ARC↗
NASA NTRS1974

Arterial pulse wave pressure transducer

An arterial pulse wave pressure transducer is introduced. The transducer is comprised of a fluid filled cavity having a flexible membrane disposed over the cavity and adapted to be placed on the skin over an artery. An arterial pulse wave creates pressure pulses in the fluid which are transduced, by a pressure sensitive transistor in direct contact with the fluid, into an electric signal. The electrical signal is representative of the pulse waves and can be recorded so as to monitor changes in the elasticity of the arterial walls.

Kim, C.↗
NASA NTRS1984

Pulmonary artery location during microgravity activity: Potential impact for chest-mounted Doppler during space travel

Doppler, or ultrasonic, monitoring for pain manifestations of decompression sickness (the bends) is accomplished by placing a sensor on the chest over the pulmonary artery and listening for bubbles. Difficulties have arisen because the technician notes that the pulmonary artery seems to move with subject movement in a one-g field and because the sensor output is influenced by only slight degrees of sensor movement. This study used two subjects and mapped the position of the pulmonary artery in one-g, microgravity, and two-g environments using ultrasound. The results showed that the pulmonary artery is fixed in location in microgravity and not affected by subject position change. The optimal position corresponded to where the Doppler signal is best heard with the subject in a supine position in a one-g environment. The impact of this result is that a proposed multiple sensor array on the chest proposed for microgravity use may not be necessary to monitor an astronaut during extravehicular activities. Instead, a single sensor of approximately 1 inch diameter and mounted in the position described above may suffice.

Hadley, A. T., III↗
NASA NTRS1993

Arterial gas emboli in altitude-induced decompression sickness

Exposure to high altitudes can result in the evolved-gas condition referred to as decompression sickness (DCS). Ultrasonic monitoring techniques have clearly demonstrated the presence of venous gas emboli (VGE) during decompression. Although important to DCS research and our understanding of the physiological mechanisms of this condition, Venus gas emboli have not been considered clinically hazardous, unless in extreme numbers. Arterial gas emboli (AGE), on the other hand, are generally viewed with great concern. Arterial gas emboli can enter the cerebral arterial circulation and arrest blood flow resulting in potentially serious injury. Left ventricular gas emboli were observed with echo imaging in five volunteer subjects during exposure to simulated altitude. These serendipitous findings occurred during altitude exposure under 3 separate research protocols involving 79 subject exposures. The voluntary, fully informed consent of the subjects used in this research was obtained as required by AFR 169-3. A Hewlett-Packard SONOS 1000 Echo Imaging System was used to monitor for precordial gas emboli. The improved resolution of the SONOS 1000 appears to account for these new findings. Four subjects had high incidence DCS and VGE during previous research flights. One subject only had one flight. The altitudes and AGE onset times for the five cases were: (1) 25,500 ft/2:23, (2) 29,000 ft/0:27, (3) 19,500 ft/3:49, (4) 29,500 ft/3:15, and (5) 29,500 ft/1:31. In all five cases, at the time of AGE onset, the VGE scores were high from all monitored locations. Four of the cases were symptomatic at the time of AGE onset (pain and skin mottling). No cerebral manifestations were observed. All subjects were immediately recompressed to ground level and successfully treated with 2 hours of post-breathing or with hyperbaric oxygen therapy. In conclusion, previously undetected AGE were demonstrated--with and without DCS symptoms--during exposure to altitude. It appears that this gas transferred from the venous side to the arterial side via either intracardiac defects or the pulmonary circulation. The clinical and operational implications of this finding are yet to be determined.

Pilmanis, Andrew A.↗
NASA NTRS2010

Characterizing Methods of Measuring Flow-Mediated Dilation in the Brachial Artery

Regulation of vascular tone is one of the many important functions of the vascular endothelium. Endothelial dysfunction is a critical early event in the pathogenesis of atherosclerosis and occurs in the absence of angiographic disease. Flow-Mediated Dilation (FMD) is a noninvasive technique commonly used to evaluate endothelium-dependent vasodilation in humans and gauge the health of the cardiovascular system. Reductions in brachial artery FMD have been strongly correlated with disease progression and are predictive of future cardiac events. The flow stimulus for brachial artery FMD occurs as a result of the increased shear stress following deflation of an occlusion cuff around the upper arm. Using 2-dimensional ultrasound, changes in arterial diameter up to 5-minutes following cuff deflation are calculated from baseline image measurements. Along with pulsed Doppler measures of flow velocity through the artery, flow-mediated, endothelium-dependent vasodilation can be assessed. There is debate among investigators, however, about the proper positioning of the occlusion cuff during FMD testing. It is thought that placement of the cuff around the upper arm may not accurately reflect the impact of nitric oxide, a critically important molecule released as a result of the increased shear stress created by the FMD technique. Data suggest that the production of other endogenous metabolites may also contribute to FMD-related changes when positioning the cuff around the upper arm. To overcome the potential influence of such molecules, researchers now suggest that the occlusion cuff be placed below the elbow allowing a more precise estimate of nitric oxide mediated dilation. The purpose of this study is to compare the differences in FMD between the two methodologies of occlusion cuff placement. In addition, this study will determine the method that is easier for ultrasound technicians to perform and will produce a low coefficient of variance between technicians. Ultimately, the results of this study will help in tracking any adverse cardiovascular effects of spaceflight.

Callender, Ariane R.↗
NASA NTRS2014

Analysis of Arterial Mechanics During Head-down Tilt Bed Rest

Arterial health may be affected by microgravity or ground based analogs of spaceflight, as shown by an increase in thoracic aorta stiffness1. Head-down tilt bed rest (HDTBR) is often used as a ground-based simulation of spaceflight because it induces physiological changes similar to those that occur in space2, 3. This abstract details an analysis of arterial stiffness (a subclinical measure of atherosclerosis), the distensibility coefficient (DC), and the pressure-strain elastic modulus (PSE) of the arterial walls during HDTBR. This project may help determine how spaceflight differentially affects arterial function in the upper vs. lower body.

Elliot, Morgan↗
NASA NTRS1971

Arterial and grooved cryogenic heat pipes.

Tests were conducted on two cryogenic heat pipes using nitrogen as the working fluid. Both pipes are 1.27 cm in diameter. The first pipe is 141 cm long and uses longitudinal grooves in the aluminum wall as the wick structure. The second pipe is 91 cm long and has an arterial wick adjacent to the wall. In addition, circumferential screw threads are machined along the entire length of the inside pipe wall. Both heat pipes primed with no difficulty in the horizontal position. Start-up after burn-out was obtained repeatedly. However, more testing is required to determine whether the artery pipe is as reliable as the grooved pipe with respect to priming. Once primed, the artery heat pipe is much less sensitive to elevation than the grooved design and, consequently, offers a significant advantage with respect to ground testing. Heat-transfer characteristics of the two pipes were comparable, with both pipes achieving the initial goal of 1000 watt-cm of heat-transport capability.

Brennan, P.↗
NASA NTRS1972

A nonlinear analysis of pulsatile flow in arteries.

An approximate numerical method for calculating flow profiles in arteries is developed. The theory takes into account the nonlinear terms of the Navier-Stokes equations as well as the nonlinear behaviour and large deformations of the arterial wall. Through the locally measured values of the pressure, pressure gradient, and pressure-radius function, the velocity distribution and wall shear at a given location along the artery can be determined. The computed results agree well with the corresponding experimental data.

Ling, S. C.↗
NASA NTRS1974

Investigation of arterial gas occlusions

The effect of noncondensable gases on high-performance arterial heat pipes was investigated both analytically and experimentally. Models have been generated which characterize the dissolution of gases in condensate, and the diffusional loss of dissolved gases from condensate in arterial flow. These processes, and others, were used to postulate stability criteria for arterial heat pipes under isothermal and non-isothermal condensate flow conditions. A rigorous second-order gas-loaded heat pipe model, incorporating axial conduction and one-dimensional vapor transport, was produced and used for thermal and gas studies. A Freon-22 (CHCIF2) heat pipe was used with helium and xenon to validate modeling. With helium, experimental data compared well with theory. Unusual gas-control effects with xenon were attributed to high solubility.

Saaski, E. W.↗
NASA NTRS1975

Arterial gas occlusions in operating heat pipes

The effect of noncondensable gases on high performance arterial heat pipes has been investigated both analytically and experimentally. Models have been generated which characterize the dissolution of gases in condensate and the diffusional loss of dissolved gases from condensate in arterial flow. These processes, and others, have been used to postulate stability criteria for arterial heat pipes. Experimental observations of gas occlusions were made using a stainless steel heat pipe equipped with viewing ports, and the working fluids methanol and ammonia with the gas additives helium, argon, and xenon. Observations were related to gas transport models.

Saaski, E. W.↗
NASA NTRS1976

Role of arterial baroreceptors in mediating cardiovascular response to exercise

Experiments were conducted to define the role of the major arterial baroreceptors during moderately severe exercise by comparing the responses of untethered conscious dogs instrumented for the measurement of aortic pressure and cardiac output with those of dogs with total arterial baroreceptor denervation. The reflex heart rate responses to intravenous bolus doses of methoxamine were also examined in intact animals, both at rest and during exercise. Methoxamine is found to cause striking bradycardia at rest, but little bradycardia during exercise. Experimental findings suggest that the arterial baroreceptor reflex is normally inhibited during severe exercise and therefore plays little role in modulating the cardiovascular response to exercise.

Mcritchie, R. J.↗