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Biomedical subjects

C A Phillips

Publications and source records attributed to C A Phillips.

At least 91 records · Page 5Linked to original sources
PubMed1984

Feedback control system for walking in man.

A computer control stimulation system is described which has been successfully tested by allowing a paraplegic subject to stand and walk through closed loop control. This system is a Z80 microprocessor system with eight channels of analog to digital and 16 channels of digital to analog control. Programming is written in CPM and works quite successfully for maintaining lower body postural control in paraplegics. Further expansion of this system would enable a feedback control system for multidirectional walking in man.

Adult↗
PubMed1984

Myocardial material mechanics: characteristic variation of the circumferential and longitudinal systolic moduli in left ventricular dysfunction.

Active systolic moduli for the circumferential (E theta) and longitudinal (E phi) axes of the left ventricle were determined along with circumferential and longitudinal contractile filament stress (sigma theta and sigma phi) and circumferential and longitudinal fiber strain (epsilon theta and epsilon phi). These material property parameters were determined at four points during cardiac systole. Thirty-nine patients comprising five clinical groups were evaluated using pressure and volume data acquired from single-plane cineangiography. The results indicate that the active moduli exponentially decrease during cardiac systole. Characteristic variations from normal differentiated the various pathological groups. With compensated volume overload, E theta was significantly reduced during the latter half of systole (p less than 0.25). With decompensated volume overload, both E theta and E phi were not significantly different from the normal group throughout cardiac systole. With compensated pressure overload, both E theta and E phi were significantly lower than the normal group at end-systole (p less than 0.005; p less than 0.005). With congestive cardiomyopathy, both E theta and E phi were significantly greater during the latter half of systole compared to the normal group (p less than 0.05 and p less than or equal to 0.025).

Adult↗
PubMed1984

The use of functional electrical stimulation for rehabilitation of spinal cord injured patients.

Computer-directed functional electrical stimulation that employs closed-loop (feedback) technology has been used for rehabilitation of spinal cord injured (SCI) patients. This paper summarizes the most recent developments in our laboratory. First, the design of an adaptive control system is described, and its resultant controllability is reviewed. Second, our current results with the isokinetic leg trainer are summarized with respect to muscular strength and mass and cardiovascular changes in paraplegics and quadriplegics. Third, our current results with the exercise bicycle ergometer are summarized regarding muscular endurance and cardiovascular changes in control, paraplegic, and quadriplegic subjects. Fourth, impact vibration is reviewed as a potential technique to reverse disuse osteoporosis, and clinical case studies are cited. Fifth and finally, thermoregulatory studies are presented for the first time on control, paraplegic, and quadriplegic subjects. Conclusions are drawn regarding mechanisms and recommendations made for exercise of SCI subjects in hot and humid environments.

Biofeedback, Psychology↗
PubMed1984

Cardiovascular responses to isometric neck muscle contractions: results after dynamic exercise with various headgear loading configurations.

Experiments were conducted to quantify the cardiovascular response (blood pressure and heart rate) elicited by sustained isometric contractions of the neck muscles. The response was secondary to dynamic exercise with various headgear loading combinations. The neck muscles were loaded by the head itself (CON), the standard U.S. Army SPH-4 helmet (HEL), and a combination of the SPH-4 helmet with Night Vision Goggles (H/NVG). During two exercise periods of 5 min and 35 min, each of the five subjects would rotate the head from side-to-side in the CON, HEL, or H/NVG configuration. Immediately thereafter, the subject would position his head in an isometric head dynamometer and exert a sustained right lateral (LAT) neck contraction or forward (FOR) neck contraction at 70% of a maximal voluntary contraction (MVC). During this isometric neck muscle contraction, the subject's endurance time to fatigue was recorded, the blood pressure was manually recorded, and the heart rate was continuously recorded. Characteristic increases in the systolic and diastolic blood pressure and heart rate occurred with sustained isometric neck muscle contractions. There was an average 40% increase in the systolic blood pressure, an average 50% increase in the diastolic blood pressure, and an average 45% increase in the heart rate from resting to the end of a fatiguing 70% MVC (p less than 0.05). These responses appear to be relatively independent of the duration of the exercise period, the loading during the exercise period, and the specific muscle mass involved. The mechanisms for the pressor response and the heart rate response are reviewed.

Adult↗
PubMed1983

Outdoor bicycle for exercise in paraplegics and quadriplegics.

The design of a three-wheel bicycle is described which can be used for exercise and locomotion in paraplegic and quadriplegic subjects. This device is constructed from a standard three-wheel bicycle which has been modified with a sensor to show the position of the pedals. The output of the sensor (a 360 degrees potentiometer) is read by the A/D converter of a small digital computer carried on the bicycle. The microprocessor system controls stimulation to four key muscle groups to allow locomotion. The speed of the bicycle is controlled with a throttle control as on a motorcycle. The device offers a potentially attractive system for increasing muscle strength and endurance, reducing muscle atrophy, increasing bone density and cardiovascular training in wheelchair bound patients.

Bicycling↗
PubMed1983

Neck muscle loading and fatigue: systematic variation of headgear weight and center-of-gravity.

An extensive series of experiments has been conducted to quantify the fatigue of neck muscles as measured by isometric endurance time. The neck muscles were dynamically and statically loaded by systematic variation of 15 headgear configurations consisting of 5 different centers-of-gravity (forward-low, center-low, center-high, right-lateral-low and afterward-low) and 3 different weights (3.2 lb, 5.0 lb, 9.0 lb, 1.45, 2.27, 4.09 kg). Each of six subjects would rotate his head laterally (from side-to-side) for 30 min in each of the 15 headgear loading combinations. Immediately thereafter, the subject would position his head in an isometric head dynamometer and exert a sustained right lateral neck contraction at 70% of his maximum strength (MVC), during which endurance time (to fatigue) was recorded. The results indicate that there were no significant differences (p greater than 0.05) in endurance time between the 3.2 lb/forward-low, 3.2 lb/lateral-right-low, and 9.0 lb/afterward-low compared to controls (endurance time for at 70% MVC isometric neck contraction in which there was no prior head loading). All other head loading configurations (weight and center-of-gravity combinations) did result in a significant reduction (p less than or equal to 0.05) in endurance times (compared to controls). These results are significant since they provide useful insights into the optimal trade-off between various centers-of-gravity and helmet weight combinations which result in the optimization of neck muscle endurance.

Adult↗
PubMed1983

Quantitative electromyography: response of the neck muscles to conventional helmet loading.

Experiments were conducted to quantify the fatigue of neck muscles which occurs during loading of these muscles by: the head itself (CON), the conventional SPH-4 helmet (HEL), and a combination of the SPH-4 helmet with Night Vision Goggles (H/NVG). Two exercise periods of 5 min and 35 min duration, respectively, were performed by the 5 subjects, during which a subject would rotate the head laterally (from side-to-side) in the CON, HEL, or H/NVG configuration. Immediately thereafter, the subject would position his head in an isometric head dynamometer and exert a sustained right lateral (LAT) neck contraction, or forward (FOR) neck contraction at 70% of his maximum strength, during which his endurance time to fatigue was recorded, and the EMG over the right sternocleidomastoid (SCM) muscle, and over the posterior trapezius/splenius muscles was continuously recorded. The root-mean-squared (RMS) amplitude of the electromyogram (EMG) continuously increased during the fatiguing contraction, being 78% greater (on the average) by the time of fatigue, and the center frequency of the EMG power spectrum continuously decreased, being 27% less (on the average) at the fatigue end-point. Some variability with head loading configuration and contraction mode was observed. These results are significant since they demonstrate that the EMG of neck muscles can be used as a noninvasive, objective and quantitative index of the neck muscle fatigue.

Adult↗
PubMed1982

Left ventricular work and power: circumferential, radial and longitudinal components. Mathematical derivation and characteristic variation with left ventricular dysfunction.

Cardiac work and power, defined as the wall stress-velocity product per unit volume, have been derived with respect to a circumferential, radial and longitudinal component for the human left ventricle during a complete cardiac cycle. Thirty-nine patients, comprising five clinical groups, were evaluated using pressure and volume data acquired from single-plane cineangiography. The results indicate that work and power are divided into approximately 60% circumferential, 23% radial and 17% longitudinal components for normals. Characteristic variations from normal are presented for selected pathological case studies. With a compensated volume overload patient, diastolic work and power are uniformly reduced in all three directions and systolic radial power approximately equals longitudinal power. With a decompensated volume overload patient, systolic radial power is greater than longitudinal power. With a compensated pressure overload patient, systolic radial work and power are greatly elevated as compared to the normals and represent about 30% of the total work and power, while longitudinal work and power represent only about 8% of the total. With a congestive cardiomyopathy patient, systolic work and power are greatly reduced in all three directions as compared to normals.

Adult↗
PubMed1982

The strength-endurance relationship in skeletal muscle: its application to helmet design.

The isometric strength and endurance of the neck muscles in man was measured in four male subjects during dorsal, ventral, and lateral flexion of the head in a helmet dynamometer. The purpose of these experiments was to quantify the maximum strength of the neck muscles in these directions and to examine the relationship between isometric strength and endurance for various submaximal isometric tensions. Isometric contractions were sustained to fatigue by these subjects at tensions of 25, 40, 55, 70, and 90% of the maximum isometric strength in each of the directions of movement. Generally, the endurance of the muscles involved in ventral flexion was less than that found in dorsal and lateral flexion of the head. However, the strength of the muscles involved was progressively greater for lateral, dorsal, and ventral flexion, respectively. The implication of these findings in helmet design and helmet loading are discussed.

Adult↗
PubMed1981

Energy cost of submaximal isometric concentrations in cat fast and slow twitch muscles.

The purpose of the present investigation was to compare the net energy cost incurred by cat soleus (slow twitch muscle) and medial gastrocnemius predominantly fast twitch muscle) muscles for isometric contractions. For this, a computer-controlled sequential stimulation system was employed that enabled fused isometric contractions at frequencies of motor unit discharge within the normal physiological range. This allowed submaximal isometric contractions to be maintained at tensions of 10%, 25%, 50% and 75% of the initial strength of each muscle (tetanic tension of the unfatigued muscle determined at the beginning of each experiment). Total net energy cost was greater for the gastrocnemius than for the soleus muscle at each tension studied. For both muscles, the metabolism shifted toward anaerobic pathways at higher contraction tensions. But in comparison to the soleus muscle, the gastrocnemius muscle consistently had a greater percentage of its total net energy cost provided by anaerobic glycolysis rather than aerobic metabolism; for the gastrocnemius and soleus muscles the percent of the total metabolism from anaerobic pathways was 74% and 18% during the 10% contraction, 96% ad 84% during the 75% contraction for the medial gastrocnemius and soleus muscles respectively.

Animals↗
PubMed1981

Prostaglandins, thromboxanes and the pregnant rat uterus at term.

1 Prostaglandin and thromboxane release from the term pregnant (Day 22) rat uterus in vitro has been measured by radioimmunoassay and gas chromatography combined with mass spectrometry. 2 Prostacyclin (prostaglandin I2, PGI2) and thromboxane A2 (TXA2) (measured as their metabolites, 6-oxo-PGF1 alpha and TXB2, respectively) were released in large amounts, while PGE2 and PGF2 alpha were released in smaller amounts. PGD2 was released in the largest quantities. 3 Treatment of the term pregnant rat uterus in vitro with the PGI2 synthesis inhibitors, 15-hydroperoxy arachidonic acid (15-OOH AA) and tranylcypromine caused spasm of the tissue. 4 15-OOH AA caused dose-dependent increases in prostaglandin release, while tranylcypromine caused a fall in the release of PGE2 but did not affect the release of other prostaglandins. A possible reason for the effect of 15-OOH AA on prostaglandin release is discussed. 5 Indomethacin prevented spontaneous activity of the term pregnant rat uterus in vitro. Contractions were restored by prostaglandins and their order or potency was PGE2 greater than PGF2 alpha greater than PGI2 greater than PGD2 much greater than 6-oxo-PGF1 alpha = TXB2.

Animals↗