Body position of the human during hypokinesia and water-salt metabolism

Two groups of 5 healthy volunteers each were exposed for 7 days to: 1) group 1 to horizontal bed rest and 2) group 2 to head-down tilt at -6 degrees. The purpose of the study was to determine the effect of body position on fluid-electrolyte metabolism and renal function. During the control period (14 days), bed rest and the recovery period the consumption of fluids and mineral substances and their renal excretion were measured. The typical changes in fluid-electrolyte metabolism during head-down tilt developed faster than during horizontal bed rest. The fluid-electrolyte balance became negative in the course of the exposure and returned to normal during the recovery period. The group 2 subjects showed greater body weight losses due to both fluid and muscle mass losses.     

Dietary salt and urinary calcium excretion in a human bed rest spaceflight model

BACKGROUND: Dietary salt is known to increase the excretion of urinary calcium (Ca). To determine the potential role of dietary sodium (Na) on the calciuria associated with a spaceflight simulation model, we evaluated urinary Ca in two groups of bed rest subjects fed either high or low normal amounts of salt. METHODS: We analyzed urinary Ca excretion expressed in terms of creatinine (UCa/Cr), fractional Ca excretion (FECa), and urinary cAMP (UCAMP) as an index of parathyroid function, in the urine of 30-50-yr-old male volunteers for 6 degrees head down tilt bed rest studies. Dietary Na was in the high normal range (190 mmol x d(-1)) in 8 men for 7 d (HiNa), and in the low normal range (114 mmol x d(-1)) in 11 men for 30 d (LoNa) bed rest. Dietary Ca averaged 20 mmol x d(-1) in both studies. RESULTS: Within the first 3 bed rest days, subjects in the HiNa study showed increases in UCa/Cr (0.1130 +/- 0.05 to 0.161 +/- 0.05, p < 0.002) and in FECa (1.95 +/- 0.70 to 3.19 +/- 0.93, p < 0.001); those in LoNa showed no change in UCa/Cr (0.125 +/- 0.06 to 0.121 +/- 0.07, NS) or FECa (1.93 +/- 0.75 to 2.22 +/- 0.63). After the 5th bed rest day UCa/Cr stabilized at similar levels in both dietary groups. UCAMP decreased 20% during the first week of bed rest with HiNa, but not until the third week with LoNa diets (p < 0.05). CONCLUSION: These findings implicate high salt diets in Ca excretion in a spaceflight model and suggest that low normal salt diets may reduce early calciuria associated with spaceflight.     

Effects of 1-week head-down tilt bed rest on bone formation and the calcium endocrine system.

To understand the potential early responses of human bone and the calcium endocrine system to spaceflight, we studied 8 healthy men, aged 35-44 years before, during, and after bed rest in a -6 degrees head-down tilt model for microgravity. Based on a novel single-dose labeling schedule, average rates of bone formation in the iliac crest were reduced in 6, unchanged in 1, and increased in 1 following the bed rest period. The decrease was greatest for subjects whose daily walking miles were highest (r = -0.762, p less than 0.05, n = 7). Before a measurable increase in ionized serum calcium the sixth bed rest day, there was increased excretion of urinary calcium and sodium, evident the first 2 bed-rest days and parallel for the entire week (r = 0.92, p less than 0.001). Reduced excretion of phosphorus and 3', 5' cyclic adenosine monophosphate on the first and second bed rest days was followed by an increase in serum phosphorus by the sixth bed rest day. Depressed serum concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D were manifest by the sixth and seventh bed rest days. The similarity of the response of bone and the calcium endocrine system of healthy men after only 7 days to results of longer term bed rest studies emphasizes the responsiveness of the adult human skeleton to biomechanical stimuli induced by changes in activity and/or position.     

Use of the ferrocerone test for measuring iron reserves in different types of daily activities

A test using an iron containing agent, i.e. ferrocerone, was developed to measure iron reserves in the body. After breakfast the subject took a ferrocerone tablet (0.3 g) containing 0.04 g iron. Iron content was measured in 24 hour urine samples with the aid of bathophenanthroline++. Iron excretion was assessed in 24 ambulatory test subjects, aged 18-21 years. Two basic types differing in the excretion rate in different times of the day. After testing the renal excretion rate of the agent in healthy people was 20.8 +/- 0.7 mg. Iron reserves during head-down tilt tests of various duration were estimated in 20 test subjects, 6 of whom participated in a 50-day study (-6 degrees) and 14 in a 120-day study (-4.5 degrees). Iron utilization was highest on readaptation day 13 (in the 50-day study) and on bed rest days 65-75 (in the 120-day study). Increase in iron requirements coincided in time with the period of hemoglobin recovery.     

The influence of air-cushion shoes on post-exercise proteinuria

Fourteen trained males participated in three sets of progressive 1 min exercise till exhaustion comparing proteinuria after bicycling, treadmill running under barefoot and air-cushion shoe conditions. Venous lactate rose to about 11 moles.l-1 after the three bouts of exercise while total protein and albumin urinary excretion increased 7 (rest micrograms.min-1) and 19 (rest 11 micrograms.min-1) fold respectively. Creatinine clearance declined to 75% (88 ml.min-1) of the resting values for all three exercises. Albumin clearances increased from 0.24 microliter.min-1 at rest to 4.08 microliters.min-1 during the recovery period. None of the above values were statistically different while comparing the three protocols. On the contrary, plasma hemoglobin showed a significant rise with bare-footed-running (rest 10 mg.100 ml-1; exercise 21 mg.100 ml-1). The lack of hemoglobin in urine postulated that the renal threshold for excretion was not attained in the present conditions. The results indicate that haemolysis and repeated shocks on the foot sole do not lead to the urinary excretion of proteins induced by short-term progressive and exhaustive exercise in humans.     

Effects of resistance training during bed rest on the viscoelastic properties of tendon structures in the lower limb

The purpose of this study was to investigate the effects of resistance training on the tendon properties in knee extensors during 20 days of bed rest. Sixteen men were assigned to the resistance training group (BR-Tr) or the non-training, control group (BR-Con). Leg-press exercises were performed as five sets of 10 repetitions at 90% of maximum load daily for 20 days during bed rest. Before and after bed rest, the elongation of the tendon structures of the vastus lateralis muscle during isometric knee extension was determined using ultrasonography, while subjects performed ramp isometric contraction up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force ( F _m) and tendon elongation ( L ) was fitted to a linear regression curve, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the F _m– L loop to the area beneath the load portion of the curve. The stiffness decreased significantly after bed rest for BR-Con, but not for BR-Tr. Similarly, the hysteresis increased significantly after bed rest for BR-Con, but not for BR-Tr. These results suggested that the bed rest caused the stiffness of tendon structures to decrease and their hysteresis to increase, and that leg-press training prevents the deconditioning of the tendon structures in knee extensors.     

Intracranial pressure dynamics assessed by noninvasive ultrasound during 30 days of bed rest

INTRODUCTION: Intracranial pressure (ICP) may be an important contributor to symptoms of space adaptation syndrome during the initial days of microgravity exposure. The temporary nature of these symptoms suggests that some physiologic adaptation or compensation occurs. Fluid shifts similar to those in microgravity can be simulated on Earth using head-down tilt (HDT) bed rest. This study was performed to calibrate a new noninvasive ICP instrument and to investigate ICP adaptation during 30 d of HDT bed rest. METHODS: A noninvasive ultrasound technique that measures small skull expansions with fluctuations in ICP was used to measure cranial oscillations before and near the end of 30-d HDT bed rest in eight healthy, male volunteers. Pulse phase-locked loop (PPLL) output voltage and arterial BP were continuously monitored and correlated. RESULTS: The amplitude of intracranial distance pulsation decreased during 30-d bed rest. Prior to bed rest, the PPLL amplitude was 25 +/- 9 mV and this amplitude was reduced by 60% to 9 +/- 4 mV (a value consistent with that of upright posture) at the end of HDT bed rest (p = 0.01). DISCUSSION: PPLL measurements of skull pulsations are acutely posture dependent, being significantly higher in supine and HDT as compared with upright posture. A cephalad fluid shift is probably the responsible mechanism. Our results indicate that there are adaptations to intracranial pooling of blood and tissue fluid during bed rest that reduce skull pulsation amplitudes to values similar to those obtained in normal upright posture. Detailed studies of the time course of cranial vessel and bone adaptations may provide insights into the potential adaptative mechanisms.     

Effects of acute exercise on attenuated vagal baroreflex function during bed rest.

We measured carotid baroreceptor-cardiac reflex responses in six healthy men, 24 h before and 24 h after a bout of leg exercise during 6 degrees head-down bed rest to determine if depressed vagal baroreflex function associated with exposure to microgravity environments could be reversed by a single exposure to acute intense exercise. Baroreflex responses were measured before bed rest and on day 7 of bed rest. An exercise bout consisting of dynamic and isometric actions of the quadriceps at graded speeds and resistances was performed on day 8 of bed rest and measurements of baroreflex response were repeated 24 h later. Vagally-mediated cardiac responses were provoked with ramped neck pressure-suction sequences comprising pressure elevations to +40 mm Hg, followed by serial, R-wave triggered 15 mm Hg reductions, to -65 mm Hg. Baroreceptor stimulus-cardiac response relationships were derived by plotting each R-R interval as a function of systolic pressure less the neck chamber pressure applied during the interval. Compared with pre-bed rest baseline measurements, 7 d of bed rest decreased the gain (maximum slope) of the baroreflex stimulus-response relationship by 16.8 +/- 3.4% (p < 0.05). On day 9 of bed rest, 24 h after exercise, the maximum slope of the baroreflex stimulus-response relationship was increased (p < 0.05) by 10.7 +/- 3.7% above pre-bed rest levels and 34.3 +/- 7.9% above bed rest day 7. Our data verify that vagally-mediated baroreflex function is depressed by exposure to simulated microgravity and demonstrate that this effect can be acutely reversed by exposure to a single bout of intense exercise.     

Central blood circulation in the healthy human being during 7 days' head-down tilt hypokinesia

The effect of 7-day head-down tilt (-15 degrees) and lower body negative pressure on circulation and oxidative metabolism was investigated on 13 healthy male test subjects. For 7-10 days they had Swan-Ganz catheters implanted in the pulmonary artery and a special cannula in the radial artery. The most marked changes were seen in the pulmonary artery pressure (PAP) and central venous pressure (CVP) that varied in a phase-like manner. By the 7th hour of bed rest the PAP increased significantly; this was followed by increases in the total lung resistance and the right ventricle function, as well as by a slight decrease of renin and aldosterone. Beginning with bed rest days 2 or 3 the PAP and CVP declined and remained lowered, as compared to the pretest level, till the end of bed rest. The responses to LBNP tests changed by bed rest day 2. Possible mechanisms of the above changes at rest and during LBNP tests are discussed.     

卧床中及卧床后头高位倾斜对心率及血压变异谱的变化

观察了男性青年２１ｄ头低位６°卧床过程中以及卧床前、后７５°头高位倾斜（ＨＵＴ）时心率变异（ＨＲＶ）与动脉收缩压变异（ＳＢＰＶ）谱变化。卧床期间，完成者ＨＲＶ和ＳＢＰＶ谱的低，高频谱峰功率（ＬＦ和ＨＦ）均显著减小，ＨＲＶ谱低，高频谱峰功率比值（ＬＦ：ＨＦＨＲＶ）在卧床第１６ｄ有增大趋势，未完成者的相应谱指标有类似变化趋向，在卧床后ＨＵＴ初始６ｍｉｎ，所有被试者心率显著快于卧床前ＨＵＴ时相应值，而Ｌ     

Effect of prolonged bed rest on the anterior hip muscles

Prolonged bed rest and inactivity is known to cause muscular atrophy with previous research indicating that muscles involved in joint stabilisation are more susceptible. The anterior hip muscles are important for hip joint function and stability but little is known about the effects of prolonged inactivity on their function. This study investigated the effect of prolonged bed rest on the size of the anterior hip muscles and their pattern of recovery. The effect of resistive vibration exercise (RVE) as a countermeasure to muscle atrophy was also investigated. 12 male participants, randomly assigned to either a control or an exercise group, underwent 8 weeks of bed rest with 6 months follow-up. Changes in muscle cross-sectional area (CSA) of the iliacus, psoas, iliopsoas, sartorius and rectus femoris muscles were measured by magnetic resonance imaging at regular intervals during bed rest and recovery phases. CSAs of iliopsoas and sartorius decreased at the hip joint (p < 0.05) during bed rest but iliacus, psoas, and rectus femoris CSAs were unchanged (p > 0.05). No significant difference was found between the two groups for all muscles (all p > 0.1), suggesting inefficacy of the countermeasure in this sample. These findings suggest that prolonged bed rest can result in the atrophy of specific muscles across the hip joint which may affect its stability and function.     

Evaluation of a Reverse Gradient Garment for prevention of bed-rest deconditioning

A Reverse Gradient Garment (RGG) was used to intermittently induce venous pooling in the extremities of a magnitude similar to that seen in going from a lying to standing position during the course of a 15-d period of horizontal bed rest. Venous pooling failed to improve bed-rest-induced losses in +2.5 Gz and +3.0 Gz centrifugation tolerance or to prevent increased heart-rate responses to lower-body negative pressure (LBNP). Four subjects served as controls, four were treated. Tests during the 7-d recovery period showed fluid/electrolyte and body composition values to have returned to pre-bed-rest levels with continued depression of acceleration tolerance times (56% decreased at +2.5 Gz and 74% decreased at +3.0 Gz compared to pre-bed-rest levels) and exaggerated blood insulin response on glucose tolerance testing (blood insulin for treated group increased 95% at 1 h before bed rest and 465% during recovery). This study demonstrates that the physiologic changes after bed rest persist for significant periods of time. Acceleration tolerance time proved to be a sensitive test for the deconditioning process.     

头低位卧床对眼内压、近视力、视野的影响及其中药防护

目的观察头低位卧床模拟失重对人体眼压、视野、近视力的影响 ,及中药对抗模拟失重的效果。方法 1 0名被试者随机分成对照组和中药组 ,用头低位 - 6° 2 1d卧床模拟失重 ,分别于卧床前、中、后测量两组被试者眼内压、近视力及视野。结果眼内压及近视力在卧床期间呈波动下降趋势 ,两者间存在一定相关性 ;中心视野变化无显著性 ;服中药可在一定程度上防止近视力下降。结论 1 )头低位卧床可引起眼压、近视力下降 ;2 )服中药可在一定程度上对抗模拟失重对近视力的不良影响     

模拟失重条件下长时间脑力负荷始末前额区脑电多尺度墒的变化分析

目的 观察头低位卧床模拟失重期间脑电信号复杂度的变化,研究脑电信号多尺度熵与脑疲劳的关系.方法 8名健康男性志愿者以-15°头低位卧床(HDBR)为模拟失重,+15°头高位卧床(HUBR)为对照,志愿者静息30 min后进行2h内容为1-back图片记忆匹配VDT作业.结果 实验初HDBR条件下志愿者前额区脑电多尺度熵...     

Supine LBNP exercise maintains exercise capacity in male twins during 30-d bed rest

INTRODUCTION: Exercise capacity is reduced after both short- and long-duration exposures to microgravity. Previously, we have documented that supine treadmill exercise within lower-body negative pressure (LBNP(ex)) maintains upright exercise responses in men after 5 and 15 d of bed rest, as a simulation of microgravity. PURPOSE: The purpose of this study was to determine whether LBNP(ex) would protect against loss of upright exercise capacity (VO2peak) and sprint performance during a longer-duration bed rest. METHODS: Eight sets of male twins participated in 30 d of bed rest. Within each twin pair, one was randomly assigned to a control group (CON) who performed no exercise, and the other was assigned to an exercise group (EX) that performed a 40-min interval (40-80% pre-bed rest VO2peak) LBNP(ex) (55 +/- 4 mm Hg) protocol, plus 5 min of resting LBNP, 6 d.wk(-1). LBNP produced footward force equivalent to 1.0-1.2 body weight. Before and after bed rest, subjects completed an upright graded exercise test to volitional fatigue and a sprint test of 30.5 m. RESULTS: After bed rest, VO2peak was decreased significantly in the CON subjects (-23 +/- 4%, P < 0.01) but was maintained in the EX subjects (-3 +/- 3%). Sprint time was increased in the CON subjects (24 +/- 8%, P < 0.05) but was maintained in the EX group (8 +/- 2%). CONCLUSIONS: This exercise countermeasure protocol may help prevent microgravity-induced deconditioning during long-duration space flight.     

A large renal pelvic diverticulum,presenting incomplete excretion during tc-99m mag-3 scintigraphy and tracer accumulation on tc-99m dmsa scintigraphy; a case report

This case report illustrates the dynamic and static renal scintigraphic images of a patient with an unusual large diverticulum of the renal pelvis. The initial diagnosis by intravenous pyelography (IVP) and ultrasonographic (US) examination was a renal pelvic diverticulum of the left kidney, and the patient was referred to the nuclear medicine department for exploration of the effect of the pelvic diverticulum on renal functions. We performed dynamic renal scintigraphy with technetium-99m (Tc-99m) labeled mercaptoacetyl triglycine (MAG-3) and static renal scintigraphy with Tc-99m labeled dimercaptosuccinic acid (DMSA). In dynamic renal scintigraphy, bilaterally normal concentration function was observed. While right kidney excretion function was normal, an incomplete excretion pattern was seen on the left side. Complete urinary flow obstruction occurred approximately at the 10th minute of the acquisition, which did not seem to respond to the i.v. furosemide application. However, when only the renal cortex was included in the region of interest, the obstructive pattern disappeared. In static renal scintigraphy, a large renal pelvic diverticulum localized antero-medially was clearly visualized in the left-anterior oblique projection, most probably due to accumulation of radiopharmaceutical inside it. This case showed that a renal pelvic diverticulum should be thought of when an incomplete excretion pattern is seen on dynamic renal scintigraphy. Using only a cortical region of interest may also help to distinguish other types of obstructive pattern from diverticulum. Additionally, Tc-99m DMSA scintigraphy may show diverticulum localization with antero-oblique projections in addition to routine projections.     

Synthesis and biological evaluation of the four isomers of technetium-99m labeled ethylenecysteamine cysteine ((99m)Tc-ECC), the mono-acid derivative of (99m)tc-L,L-ethylenedicysteine

A few years ago (99m)Tc-ethylenedicysteine ((99m)Tc-L,L-EC) had been proposed as an interesting substitute for technetium-99m labeled mercaptoacetyltriglycine (MAG3) as renal function tracer agent. It possesses in its structure two carboxylate functions and is in this respect different from other renal tracers such as (99m)Tc-N, N'-bis-(mercaptoacetyl)-2,3-diaminopropionate ((99m)Tc-CO(2)DADS), (99m)Tc-MAG3, and Hippuran, which have only one carboxylic group. To study whether both carboxylic acid groups of (99m)Tc-L,L-EC contribute to the efficient renal handling of this compound we synthesized and biologically evaluated the technetium-99m labeled isomers of L- and D-ethylenecysteamine cysteine (ECC), the mono-acid derivative of (99m)Tc-L,L-EC. Labeling of L-ECC or D-ECC with (99m)Tc using a direct or exchange labeling method yields for each of them two diastereomeric (99m)Tc complexes (A and B, in the order of elution during reversed phase high performance liquid chromatography) in relative amounts depending on the pH during labeling. In mice, all four isomers of (99m)Tc-ECC (LA, LB, DA, and DB) are cleared rapidly from the blood, mainly by the renal system. The isomers LB and DB show the most efficient renal handling, but none of the mono-acid derivatives has a urinary excretion rate as high as that of (99m)Tc-L,L-EC. The renal handling of the isomers of (99m)Tc-ECC is partly due to tubular secretion because the urinary excretion of these compounds is significantly lower in mice pretreated with probenecid. In the baboon, isomers DA and DB show a plasma clearance comparable to that of (99m)Tc-L,L-EC. The plasma clearance of isomers LA and LB is lower but still comparable to or higher than that of (99m)Tc-MAG3. In a human volunteer, isomer DB shows a plasma clearance rate only slightly lower than that of (99m)Tc-L,L-EC. Thus, it appears that the presence of one carboxylate in (99m)Tc-EC-like compounds can be sufficient for efficient renal handling. However, it is also evident that the configuration at the chiral carbon atom and the orientation of the oxotechnetium core determine in a significant way the biological characteristics.     

Serum enzyme activity of healthy subjects during modeling of the effects of weightlessness

The enzymic activity of blood of healthy male volunteers was examined during 8-day bed rest in the horizontal and head-down (-6 degrees) position, water immersion up to the neck and 6-hour head-down tilt (-15 degrees). Alkaline phosphatase, cholinesterase (CE), leucine arylamidase (LA), glutamate dehydrogenase (GDH) and gamma-glutamyl transpeptidase (GGTP) were measured. During horizontal bed rest the activities of all the enzymes, except for GDH, decreased in a moderate degree which was very distinct at an early stage of exposure. The activity of GDH and CE decreased significantly after the exposure. The enzymic activity tended to decline during head-down tilt at -6 degrees. The LA and GGTP activity decreased to a greater extent, being statistically significant during head-down tilt at -6 degrees and in the recovery period. The enzymic activity insignificantly increased during water immersion and 6-hour head-down tilt at -15 degrees, remaining in some cases elevated during 5 days after exposure. The lower activity of enzymes (which was significant for some of them) during horizontal and antiorthostatic bed rest was primarily associated with diminished motor activity, whereas increased enzymic activity was related to the gravity-induced blood shift to the intrathoracic area.     

Comparison of 99mTc-mercaptoacetyltriglycine and [131I]-o-iodohippurate elimination in perfused rat kidney

Renal elimination of two renal radiodiagnostic agents, (99m)Tc-mercaptoacetyltriglycine ((99m)Tc-MAG3) and [(131)I]-o-iodohippurate (OIH) has been studied using the method of the perfused rat kidney. The experiments showed significant differences between renal handling of (99m)Tc-MAG3 and OIH in the perfused rat kidney. While the renal clearance for (99m)Tc-MAG3 was relatively stable, the renal clearance values of OIH rapidly decreased after the OIH administration in a bolus dose. The infusion administration of OIH resulted in stable clearance values during the perfusion. The OIH/(99m)Tc-MAG3 renal clearance ratio was 2.47. Both compounds were bound to proteins in the perfusate to a considerable extent. An analysis of renal handling showed that contribution of tubular secretion to the total excretion was 95% for OIH, and 97% for (99m)Tc-MAG3.     

Effects of 20 days of bed rest on the viscoelastic properties of tendon structures in lower limb muscles

Objectives: The purpose of this study was to investigate the effects of 20 days' bed rest on the viscoelastic properties of human tendon structures in knee extensor and plantar flexor muscles in vivo.

Methods: Eight healthy men (age: 24±4 years, height: 172±9 m, body mass: 69±13 kg) carried out a 6° head-down bed rest for 20 days. Before and after bed rest, elongation (L) of the tendon and aponeurosis of vastus lateralis (VL) and medial gastrocnemius muscles (MG) during isometric knee extension and plantar flexion, respectively, were determined using real-time ultrasonic apparatus, while the subjects performed ramp isometric contraction up to the voluntary maximum, followed by ramp relaxation. The relationship between estimated muscle force (Fm) and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the Fm-L loop to the area beneath the load portion of the curve.

Results: L values above 100 N were significantly greater after bed rest for VL, while there were no significant differences in L values between before and after for MG. The stiffness decreased after bed rest for VL (70.3±27.4 v 50.1±24.8 N/mm, before and after bed rest, respectively; p = 0.003) and MG (29.4±7.5 v 25.6±7.8 N/mm, before and after bed rest, respectively; p = 0.054). In addition, hysteresis increased after bed rest for VL (16.5±7.1% v 28.2±12.9%, before and after bed rest, respectively; p = 0.017), but not for MG (17.4±4.4% v 17.7±6.1%, before and after bed rest, respectively; p = 0.925).

Conclusions: These results suggested that bed rest decreased the stiffness of human tendon structures and increased their hysteresis, and that these changes were found in knee extensors, but not the plantar flexors.