Engineering topics

Deavers, D. R.

Publications and source records attributed to Deavers, D. R..

6 records

NASA NTRS1990

Fluid/electrolyte balance and cardiovascular responses - Head-down tilted rats

Results are presented on cardiovascular and fluid/electrolyte balance responses of rats to a 7-day-long whole-body suspension (WBS) with about 20-deg head-down tilt (HDT), followed by 7 days of recovery. Compared with horizontally positioned (N-HDT) rats serving as controls, the Na intake of HDT rats was significantly reduced during the first 3 days of HDT, and urinary and fecal Na loss exceeded the Na intake during days 5 and 6. Changes during the days of recovery showed adjustments and reestablishment of Na balance. Urinary K losses increased progressively during the 7 days of HDT, but, with the exception of days 1-3 of HDT, when the K intake was significantly reduced, the K balance was retained. Changes in cardiac responses (including elevations in mean, diastolic, and systolic arterial pressures) paralleled changes in fluid and electrolyte balance during the HDT period.

Musacchia, X. J.↗

NASA NTRS1983

Rat hindlimb muscle responses to suspension hypokinesia/hypodynamia

Hypokinetic/hyupodynamic (H/H) whole body suspension of rats eliminates hindlimb load bearing functions while permitting continued use of the forelimbs. Responses of hindlimb muscles were assessed in terms of absolute and relative weights during 1 and 2 weeks of H/H suspension. Muscle mass loss was in the order soleus greater than gastrocnemius equal to plantaris greater than extensor digitorum longus (EDL). The soleus, a postural antigravity muscle composed mainly of slow twitch fibers, was most sensitive, losing 35 and 45 percent of its weight during the first and second weeks, respectively. The gastrocnemius and plantaris showed losses during the first week but no significant loss during the second wee. The EDL showed little or no weight loss. During post suspension recovery all muscles showed a weight gain. H/H suspended rats failed to grow; following removal from suspension they gained weight linearly, comparable to controls. Products of muscle metabolism including urea, ammonia, and 3-methylhistidine increased in the urine during H/H suspension and were significantly reduced approaching control levels during recovery. This suspension model offers considerable promise for comparison with H/H responses during weightlessness.

Musacchia, X. J.↗

NASA NTRS1982

A new rat model for studies of hypokinesia and antiorthostasis

A new rat model (suspension and immobilization) is described for induction of hypokinesia and orthostatic manipulations. Hypokinetic responses were comparable to those in prolonged bed rest and weightlessness in humans, body or limb casted and small cage restrained animals. Responses to antiorthostasis (15 to 20 deg head down tilt) in rats were similar to those in neutral bouyancy tests in humans and animals and to those in prolonged bed rest in humans. During seven days of hypokinesia there was an atrophy of the gastrocnemius and increased excretion of urinary nitrogeneous end products. The antiorthostatic (AOH) 15 to 20 deg head down tilt resulted in diuresis, natriuresis and kaliuresis. No comparable responses were observed in orthostatic hypokinetic (OH) rats. Readaptation from AOH and OH occurred during one week recovery in metabolic cage conditions.

Musacchia, X. J.↗

NASA NTRS1982

Suspension restraint - Induced hypokinesia and antiorthostasis as a simulation of weightlessness

Muscle, renal, fluid and electrolyte responses were measured in suspended rats; the hind limbs are non-load bearing and the front limbs can be used for feeding and grooming. Hind limb hypokinesia reverses after removal from the suspension harness. This suspension system is adjustable for a head-down tilt to produce antiorthostatic responses which are also reversible. Responses to hypokinesia or antiorthostatic hypokinesia for up to 14 days were measured, e.g., muscle atrophy: soleus greater than gastrocnemius equals plantaris greater than extensor digitorum longus, kaliuresis, and increased excretion of urea, NH3, and 3 methylhistidine. Muscle protein loss, a response to a reduction in RNA, is also reversible. A head-down tilt for 7-14 days results in diuresis and natriuresis. These changes are reversed within 24 hours after removal from the restraint harness. Physiological effects of suspension restraint can be used to simulate and predict responses to microgravity exposure.

Musacchia, X. J.↗

NASA NTRS1980

Model for antiorthostatic hypokinesia - Head-down tilt effects on water and salt excretion

Water and electrolyte excretion was investigated in antiorthostatic hypokinetic and orthostatic hypokinetic and control rats in metabolic cages. Significant (t test, P less than 0.05) diuresis, natriuresis, and kaliuresis occurred in the antiorthostatic hypokinetic subjects but did not occur in either the orthostatic hypokinetic or controls. Recovery from antiorthostatic hypokinesia was characterized by retention of water, sodium, and potassium. Patterns of changes in body weight and food and water consumption were virtually identical in antiorthostatic and orthostatic hypokinetic rats and thus could not account for the differences in renal handling of water and electrolytes. Also, differences in ingestion of food and water in controls could not account for differences in excretion of water and electrolytes between these and antiorthostatic hypokinetic rats. It was concluded that the antiorthostatic position was responsible for the diuresis and natriuresis and that the antiorthostatic hypokinetic rat appears to be a good model for the study of water and elecrolyte excretion during conditions such as bed rest, water immersion, and exposure to weightlessness.

Deavers, D. R.↗

NASA NTRS1980

A model for hypokinesia: Effects on muscle atrophy in the rat

Hypokinesia in the hindlimbs of rats was induced by suspension; a newly developed harness system was used. The animal was able to use its forelimbs to maneuver, within a 140 deg arc, to obtain food and water and to permit limited grooming of the forequarters. The hindlimbs were nonload bearing for 7 days; following a 7-day period of hypodynamia, selected animals were placed in metabolic cages for 7 days to study recovery from hypokinesia. During the 7-day period of hypokinesia there was evidence of muscle atrophy. Gastrocnemius weight decreased, renal papillary urea content increased, and daily urinary losses of NH3 and 3-methylhistidine increased. During the 7-day recovery period muscle mass and excretion rate of urea, NH3 and 3-methylhistidine returned to control levels. Calcium balance was positive throughout the 7-day period of hypokinesia. Hypertrophy of the adrenals suggested the occurrence of some level of stress despite the apparent behavioral adjustment to the suspension harness. It was concluded that significant muscle atrophy and parallel changes in nitrogen metabolism occur in suspended rats and these changes are readily reversible.

Musacchia, X. J.↗