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Biomedical subjects

F C Clark

Publications and source records attributed to F C Clark.

At least 19 recordsLinked to original sources
PubMed1990

Mean arterial blood pressure changes in premature infants and those at risk for intraventricular hemorrhage.

Bedside microcomputer-derived, minute-to-minute mean arterial pressure (MAP) values during the first 48 hours of life were studied in 100 preterm babies with birth weight less than or equal to 1500 gm. In those babies (n = 72) with no periventricular-intraventricular hemorrhage (PV-IVH) or with grade 1 PV-IVH, the MAP values increased during the study period, with minute-to-minute variation and interval undulation. The MAP values in those with birth weight greater than 1000 gm were higher than in those of lower birth weight. Infants in whom grades 2 to 4 PV-IVH developed (n = 28) had consistently lower MAP values during the study period. Minute-to-minute variability, expressed as the average of the coefficients of variation at 15-minute intervals, did not differ between birth weight groups, nor did they differ between the PV-IVH group and their matched control subjects. However, those with PV-IVH spent a greater percentage of time, with a coefficient of variation greater than or equal to 13% or less than 3%, than their matched control subjects spent (p less than 0.005). This study provides reference data for MAP changes in premature babies. The observed MAP changes in those with PV-IVH lend support to a significant role for MAP alterations in the pathogenesis of PV-IVH.

Blood Pressure↗
PubMed1988

Effects of heavy-resistance triceps surae muscle training on strength and muscularity of men and women.

The purpose of this study was to determine selected functional and structural effects of heavy-resistance training on the triceps surae muscles of men and women. We pretested 28 men and 28 women for triceps surae muscle isotonic strength and muscularity after five practice sessions that familiarized them with the study equipment. Triceps surae muscle isotonic strength was determined using a 1-repetition maximum seated heel raise. Muscularity involved the measurement of relaxed lower leg circumference and net circumference and ultrasonically determined triceps surae muscle thickness. Twenty-eight subjects (14 men, 14 women) were selected randomly after pretesting to participate in 24 sessions of standardized weight training primarily involving the triceps surae muscles, and the remaining subjects (14 men, 14 women) served as nontraining controls. After eight weeks of training, triceps surae muscle isotonic strength had increased significantly (p less than .001) for both men and women in the Treatment Group when compared with the Control Group. No other dependent variables changed significantly. We concluded that eight weeks of heavy-resistance training involving the triceps surae muscles elicits similar significant increases in isotonic muscle strength in both men and women without concurrent increases in muscularity.

Adult↗
PubMed1987

Three protocols for measuring subcutaneous fat thickness on the upper extremities.

Three protocols for measuring subcutaneous fat thickness were compared and their level of association determined in young adults. Subjects included 21 men and 21 women, 18-24 years of age. Skinfold calipers, A- and B-mode ultrasound were used to measure the thickness of the subcutaneous fat layer overlying the anterior and posterior aspects of the upper arm. Each protocol was independently administered within a 30-min block of time in a randomly rotated sequence. Significant differences (p less than 0.05) between protocols were observed depending upon site of measurement and gender of the subject. At both the anterior and posterior sites for men, B-mode and halved skinfold were similar but significantly less than A-mode measurements. At the anterior site for women, A-mode and skinfold were similar but significantly greater than B-mode measurements. At the posterior site for women, all three measurements were similar. Correlations between the protocols were positive with men's levels ranging from 0.59 to 0.74, while women's levels were from 0.39 to 0.89. It was concluded that although skinfold calipers, A-mode ultrasound, and B-mode ultrasound may be used to obtain moderately associated measurements of upper-arm subcutaneous fat thickness in young adults, the three protocols yield inconsistently similar data.

Adolescent↗
PubMed1985

Ultrasonic protocols for separately measuring subcutaneous fat and skeletal muscle thickness in the calf area.

Information regarding the use of brightness-mode (B-mode) ultrasound for separately measuring the thickness of subcutaneous fat and skeletal muscle in the calf area was evaluated. Subjects were volunteers, 32 men and 32 women college students. Fat was measured with skinfold calipers and B-mode ultrasound. We used calf circumference and B-mode ultrasound simultaneously to assess muscle size. Ultrasonic measurements of both fat and muscle were repeated within 30 minutes to evaluate reliability. Men were 24 percent heavier than women but had a thinner fat layer as measured by skinfolds (49%) and ultrasound (29%). Men also had a relatively larger calf muscle as assessed by circumference (7%) and ultrasound (29%). Intraclass correlation coefficients were no less than .99 for repeated ultrasonic measurements of both fat and muscle for men and women; therefore, these procedures are reliable for at least a short period of time. Associations between skinfolds and fat sonograms were high in men (r = .87) and moderate in women (r = .50). Associations between circumferences and muscle sonograms were moderately high in both men (r = .80) and women (r = .76). All four associations were statistically significant (p less than .05).

Adipose Tissue↗
PubMed1975

Effects of d-amphetamine, chlorpromazine, and chlordiazepoxide on intercurrent behavior during spaced-responding schedules.

Effects of d-amphetamine, chlorpromazine, and chlordiazepoxide on lever pressing under direct control of spaced-responding schedules were compared with effects on intercurrent drinking and wheel running in the rat. Drug effects on lever pressing were systematically related to dose and were consistent for all animals; drug effects on intercurrent behavior were generally different for each animal. In the case of lever presses, increasing doses of d-amphetamine first increased and then decreased response rate, increasing doses of chlorpromazine produced graded decreases in response rate, and doses of chlordiazepoxide up to 40 mg/kg produced no effect on response rate. These data are discussed in context with the concept of schedule control, and it is suggested that the behavioral pharmacology of intercurrent behavior be explored as a useful procedure in the experimental analysis of intercurrent behavior.

Acoustic Stimulation↗
PubMed1975

Selection of artificial gravity by animals during suborbital rocket flights.

White rats selected preferred artificial gravity levels by locomotion in centrifuges consisting of two runways mounted in the nose of sounding rockets. Roll rate of the Aerobee 150A rocket was designed to produce an angular velocity of 45 r.p.m. during 5 min of free-fall, providing a gravity range range from 0.3 to 1.5 G depending on a subject's runway position. One animal was released at the high and one at the low gravity position in each flight. Animal positions were continuously recorded. Flight subjects were selected from about 100 trained animals adapted to the simulated launch environment for several months. In two flights excessive rollrates produced gravity ranges above the designed limits. In two other flights the desired range was produced. Locomotion patterns during these flights were similar. All four animals explored the entire available G-range. One rat settled at 0.4 G after 2 min; the others crossed the 1-G location in progressively narrower excursions and were near earth gravity at the end of the test period. Data were more varible than in laboratory tests above 1 G and the observation periods were necessarily few and short. Tentatively, however, the data suggest that normal earth-reared rats select earth gravity when available magnitudes include values above and below 1 B. Modification of gravity preference by prolonged exposure to higher or lower levels remains a possibility.

Animals↗
PubMed1973

Behavioral regulation of gravity: schedule effects under escape-avoidance procedures.

Squirrel monkeys were restrained in a centrifuge capsule and trained to escape and avoid increases in artificial gravity. During escape-avoidance, lever responses reduced centrifugally simulated gravity or postponed scheduled increases. The effect of variation in the interval of postponement (equal to the duration of decrease produced by escape responses) was studied under a multiple schedule of four components. Three components were gravity escape-avoidance with postponement times of 20, 40, and 60 sec. The fourth component was extinction. Each component was associated with a different auditory stimulus. Rate of responding decreased with increasing postponement time and higher mean g-levels occurred at shorter intervals of postponement. Effects of the schedule parameter on response rate and mean g-level were similar to effects of the schedule on free-operant avoidance and on titration behavior maintained by shock.

Acceleration↗
PubMed1969

Effects of d-amphetamine on observing behavior in the squirrel monkey.

Four squirrel monkeys were trained to press a lever, which produced stimuli indicating availability or non-availability of reinforcement for pushing a key. Food reinforcements were available for the key response at random intervals with an average rate of 1 per min. When food was available, a single lever response produced a red light behind the key. Reinforcement availabilities and red keylights remained until terminated by a reinforced key response. When reinforcement was not available, each lever response produced a 0.5-sec green light on the key. Except after lever responses, the key remained dark. Under this procedure, lever responses functioned as observing behavior in that they produced discriminative stimuli correlated with the availability or non-availability of reinforcement for key responses. The procedure generated a high rate of responding on the lever, short latencies of the key response after onset of red lights and few responses to the key in the absence of red lights. Intra-muscular d-amphetamine, in doses from 0.125 to 1.0 mg/kg, abolished both observing behavior and key responding for periods that increased as a function of dose. However, both observing and key rates were increased at the smallest dose in two subjects whose performances included responding to the key in the absence of red lights. Results are discussed in relation to previous findings regarding effects of amphetamines on operant behavior and on observing and monitoring performance.

Animals↗
PubMed1966

Free operant avoidance as a function of the response-shock = shock-shock interval.

Two temporal parameters of free operant or Sidman avoidance behavior are the interval by which responses postpone shocks (Response-Shock interval) and the interval between shocks when no responses occur (Shock-Shock interval). Avoidance behavior was examined in three white rats under conditions where the Response-Shock and Shock-Shock intervals were always equal. With intervals from 10 to 60 sec response rates and shock rates were similar, decreasing, negatively accelerated functions of increasing Response-Shock=Shock-Shock interval. Over this range, response and shock rates were linearly related to the reciprocal of the Response-Shock=Shock-Shock interval. It was shown, however, that this relation cannot hold at extremely long intervals. Both the ratio of responses emitted to shocks received and the percentage of shocks possible which were avoided increased at long Response-Shock=Shock-Shock intervals. These findings may be related to the fact that long intervals provide optimal conditions for conditioning avoidance behavior in the rat.

Animals↗