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Biomedical subjects

R H Edwards

Publications and source records attributed to R H Edwards.

At least 343 records · Page 19Linked to original sources
PubMed1980

Sternomastoid muscle function and fatigue in man.

1. A technique has been devised to measure the effect of stimulation frequency on the contraction force in an accessory muscle of respiration, the sternomastoid, in man. The frequency/force curve was found to be very similar to that of the quadriceps and adductor pollicis muscles. 2. Fatigue of the sternomastoid due to inspiratory loading or sustained maximum voluntary ventilation resulted in reduced force generation at low stimulation frequencies compared with maximum force. This type of fatigue frequently persisted for several hours. 3. If low frequency fatigue were to develop in patients with pulmonary disease it could have important consequences for the development of respiratory failure.

Electric Stimulation↗
PubMed1980

A computer simulation of physiological factors contributing to hyperventilation and breathlessness in cardiac patients.

A computer model of human respiration is of value for teaching the basic principles of respiratory physiology to students. An extension of this educational use is in the theoretical exploration of the relative importance of individual factors which may be contributing to disordered function in common clinical problems. For example, when a cardiac patient becomes breathless with increase in ventilation during exercise there are alterations in many physiological variables. The influence of their individual contributions on the total ventilation and thence possibly on breathlessness is often difficult to estimate. We present a theoretical analysis using MACPUF, a digital computer simulation of circulation and gas exchange which can be used to extimate the quantitative contribution of relevant physiological variables by altering them singly and in combination. Alterations in dead space, physiological shunt and pulmonary compliance individually produce only small increases in ventilation. Increased neurogenic drive (e.g. from lung reflexes triggered by pulmonary congestion) is a potentially important but very variable factor. A more important influence on ventilation appears when cardiac output is reduced and anaerobic metabolism simulated, causing changes in blood gas tensions and acidaemia which then change ventilation. Any increase in ventilation becomes more significant as a cause of breathlessness when ventilatory capacity is reduced, which in cardiac patients it not infrequently is.

Cardiac Output↗
PubMed1979

Perception of effort in isometric and dynamic muscular contraction.

The perception of muscular effort was studied using estimation and production methods in the adductor pollicis and quadriceps. A psychometric scale (percentage magnitude) was used. Static contractions were studied in the adductor pollicis, and both dynamic (isokinetic) and static contractions were studied in quadriceps. Linear and logarithmic equations were fitted for the perceived effort as a percentage of the maximum in relation to the produced percentage maximal force or torque. The logarithmic exponent was around or above 1.0. No significant difference was found between mean exponent and intercept values for the adductor pollicis and the quadriceps, or when estimated or produced values for the two muscles were compared. There was no difference in the same subjects between the equations for static and dynamic contractions with low angular velocity of the quadriceps.

Adult↗
PubMed1979

Relaxation rate of constituent muscle-fibre types in human quadriceps.

1. Muscle fibres may be subdivided into type I (with slow-twitch contractile properties) and type II (fast-twitch) depending on their myosin adenosine triphosphatase activity. In voluntary isometric contractions type I fibres are utilized at low forces (less than 20% of maximum) whereas type II fibres are recruited in addition at high forces. This physiological recruitment order has enabled us to measure the relaxtion rate of type I and II fibres in vivo in normal human subjects. 2. Relaxation rate was measured in 16 subjects from low (10% of maximum) and maximum isometric quadriceps contractions and the muscle-fibre type composition determined from needle-biopsy specimens in 10 subjects. The relaxation rate of type II fibres was calculated to be twice as fast as that of type I. 3. It was not possible to estimate, from studies in 33 quadriceps muscles (25 normal subjects), the contribution of type II fibres to overall fibre area from the relaxation rate as determined from electrically stimulated isometric contractions.

Adenosine Triphosphatases↗
PubMed1979

Muscle relaxation rate, fibre-type composition and energy turnover in hyper- and hypo-thyroid patients.

1. Quadriceps strength, relaxation rate, fibre-type composition and energy-turnover rate during a submaximal contraction have been measured in hypo- and hyper-thyroid patients and compared with findings in normal subjects. 2. Six out of eight hypothyroid patients had normal strength whereas four out of five hyperthyroid patients were weak. 3. Relaxation rate was decreased in all the hypothyroid patients but increased in only three out of five hyperthyroid patients. 4. In hypothyroidism there was a marked reduction in the percentage contributed by type II fibres to muscle cross-section, partly due to type II atrophy but also due to a decrease in the relative frequency of type II fibres. In hyperthyroidism both fibre types tended to atrophy. 5. The rate of ATP turnover during submaximal contraction held to fatigue was reduced in hypothyroidism. This was probably due to decreased ATP utilization rather than an impaired supply of energy-supplying substrates. In hyperthyroidism the rate of ATP turnover was increased. 6. Altered relaxation rate and ATP-turnover rate may be explained on the basis of changes in myosin ATPase activity with thyroid status. Changes in muscle-fibre-type composition, as determined histochemically, could not per se account for the functional abnormalities.

Adenosine Triphosphate↗
PubMed1978

Central and peripheral fatigue in sustained maximum voluntary contractions of human quadriceps muscle.

1. The fatigue of force that occurs during the first 60 s of a maximum voluntary contraction of the human quadriceps has been examined by comparing the voluntary force with that obtained by brief tetanic stimulation at 50 Hz in nine healthy subjects. In three subjects the voluntary force declined in parallel with the tetanic force whereas in the remainder it fell more rapidly, suggesting that central fatigue was present. 2. For those subjects who showed little or no central fatigue, surface electromyograph (EMG) activity remained approximately constant while the force declined by about 60%. In the others, EMG activity and force declined in parallel but when an extra effort was made the subjects could briefly increase their force and this was accompanied by a proportionately greater increase in EMG activity (generally up to the original value). 3. It is concluded that in sustained maximum voluntary contractions of the quadriceps (a) central fatigue may account for an appreciable proportion of the force loss, (b) surface EMG recordings provide no evidence that neuromuscular junction failure is the limiting factor determining the loss of force in this muscle.

Adult↗
PubMed1978

Tests of skeletal muscle function in children.

The contractile properties of a large proximal muscle (quadriceps femoris) and a small distal muscle (adductor pollicis) have been measured in normal children and children with neuromuscular disorders. The method of stimulating the quadriceps femoris to contract, previously evaluated in adults, was found to be acceptable to children. In normal children a number of indices of muscle function were found to be similar to those in adults. A small study of the function of the adductor pollicis using supramaximal stimulation of the ulnar nerve was carried out in boys with Duchenne dystrophy. Decreased contractile force and prolonged relaxation times from a tetanic stimulation were noted in both the proximal and distal muscles of the boys with Duchenne dystrophy.

Adolescent↗
PubMed1978

Clinical assessment of skeletal muscle function.

A systematic clinical analysis of skeletal muscle function is presented. Tests range from assessment of muscle weakness with a new hand-held dynamometer (the "Hammersmith Myometer") to studies of the contractile properties of the quadriceps and adductor pollicis muscles described in terms of the force generated at different frequencies of stimulation of the motor nerve, the force-sustaining capability and the time course of relaxation following a brief tetanus. A new measure of the energy-exchanging capacity of muscle is given by the Myothermogram (MTG - so named by analogy with the Electromyogram - EMG). The technique measures metabolic heat production in muscles when maximally activated by voluntary effort or electrical stimulation and the heat changes during sustained contractions. The MTG offers a practical means for assessing in normal and diseased human muscle the metabolic capacity, economy of force maintenance and fatigue mechanisms. Needle biopsy provides safe, rapid and repeatable access to muscle for diagnosis, studies of chemical energy exchange and the correlation of function and metabolism with constituent muscle fibre types. This approach provides a possible basis for recognising the functional disorder and for evaluating the effects of physiotherapy and drug treatments in patients with neuromuscular disorders.

Electric Stimulation↗