scholarly journals Inotropic Effects of Trains of Impulses Applied during the Contraction of Cardiac Muscle

1960 ◽  
Vol 44 (2) ◽  
pp. 415-432 ◽  
Author(s):  
A. J. Brady ◽  
B. C. Abbott ◽  
W. F. H. M. Mommaerts
Keyword(s):  
Cell Membrane ◽  
Cardiac Muscle ◽  
Direct Effect ◽  
Refractory Period ◽  
Muscle Preparation ◽  
Inotropic Effects ◽  
Absolute Refractory Period ◽  
The Absolute ◽  
Stimulation Of

The application of a train of supramaximal stimuli during the absolute refractory period of a cardiac muscle preparation has two effects: a depression of the contraction during which it is applied, and a large potentiation of subsequent contractions. The former is ascribed to a direct effect upon the cell membrane, and is an indication of the continued control of the contractile event by this membrane. The latter is explained as a sudden liberation of norepinephrine by a stimulation of embedded nerve elements, which norepinephrine then distributes itself through the tissue and finally diffuses away.

scholarly journals On The Excitation of Crustacean Muscle

1936 ◽  
Vol 13 (1) ◽  
pp. 111-130
Author(s):  
C. F. A. PANTIN
Keyword(s):  
Refractory Period ◽  
Motor Nerve ◽  
Carcinus Maenas ◽  
Motor Units ◽  
Repetitive Stimulation ◽  
Muscle Fibres ◽  
Absolute Refractory Period ◽  
Excitable System ◽  
Crustacean Muscle ◽  
The Absolute

1. The response of certain limb muscles in Carcinus maenas to stimuli of different frequencies and intensities has been analysed. The precautions necessary to obtain reproducible results in crustacean muscle are recorded. The material must be fresh; the duration of stimulation short; and each individual shock must be less than the true chronaxie, to prevent multiple excitation of the nerve. 2. A single stimulus produces a microscopic response or none at all. A succession of shocks, however, causes a contraction, the rate of which increases with the frequency, till this reaches the high values of 300-400 shocks per sec. The rate of contraction varies absolutely continuously with the frequency from 300 per sec. down to the microscopic response observed at less than 10 per sec. The rate of contraction increases very rapidly indeed between frequencies of 50 and 200 per sec, so that this range includes almost all rates of contraction. 3. The limiting frequency of 300-400 per sec. is close to the refractory period. For pairs of stimuli, the absolute refractory period is about 1σ at 18° C. This is followed by a relative refractory phase and sometimes by a supernormal phase. The excitability has returned to normal after about 4σ. In repetitive stimulation the absolute refractory period lengthens. 4. With stimuli of increasing intensity, the responses of both flexor and extensor muscles show first a threshold for excitation of the motor nerve, and, at a higher intensity, a threshold for inhibition. At very high intensities (10-20 times the true threshold) large contractions may be obtained owing to repetitive excitation. 5. With suitable precautions it can be shown that between the threshold of excitation and the threshold of inhibition there is great independence between the response and the intensity of the stimulus. The system behaves as a single excitable system and possibly in some cases a single axon supplies the entire muscle. 6. The chronaxie of the nerve to single shocks and to repetitive stimulation is of the order of 0.2-0.4σ. Single shocks of high intensity give multiple excitation, and the thresholds for this simulate a chronaxie curve. False chronaxies up to 30σ can be obtained in this way. 7. There is no evidence of a double excitable system in the muscles of the walking leg of Carcinus such as has sometimes been recorded in crustacean claws. There is no doubling of intensity-duration or refractory period curves. 8. All the effects observed are explicable in terms of neuromuscular facilitation. The response is governed entirely by the frequency and number of stimuli. Each shock in a series brings more and more muscle fibres into action. With increasing frequency of stimulation, not only are there more contraction increments in a given time, but the increment following each shock is larger. 9. At low and moderate frequencies the rate of development of tension is governed by the rate at which impulses reach the muscle. At the highest frequencies a limit is set to the rate of contraction by the physical properties of the muscle. 10. There is a close analogy between the neuromuscular mechanism disclosed here and the neuromuscular mechanism of the Coelenterata. In both there is a tendency for an entire effector to behave as a single system in which the response is governed by the number and frequency of impulses received by the muscle. This system is distinguished sharply from that of vertebrate skeletal muscle in which gradation of response is brought about through the multiplicity of motor units.

Hyperprolactinaemia abolishes sensitivity of stria terminalis neurones to testosterone

1984 ◽  
Vol 102 (1) ◽  
pp. 109-113 ◽  
Author(s):  
K. M. Kendrick ◽  
A. F. Dixson
Keyword(s):  
Refractory Period ◽  
Male Rats ◽  
Stria Terminalis ◽  
Absolute Refractory Period ◽  
Treated Male ◽  
The Absolute

ABSTRACT Hyperprolactinaemia was induced in castrated, testosterone-treated male rats using ectopic pituitary grafts under the kidney capsules. After 6 weeks the absolute refractory period of stria terminalis neurones in these animals did not differ significantly from long-term castrated rats (mean = 1·72 vs 1·69 ms) in spite of the presence of normal testosterone concentrations. Gonadally intact animals, and sham-operated castrated animals treated with testosterone, showed by comparison the characteristic significantly shorter absolute refractory period normally associated with testosterone stimulation (mean = 1·15 and 1·08 respectively). These results provide the first demonstration that hyperprolactinaemia can abolish central sensitivity to testosterone. J. Endocr. (1984) 102, 109–113

scholarly journals The effect of temperature upon the absolute refractory period in nerve

1930 ◽  
Vol 69 (1) ◽  
pp. 60-66 ◽  
Author(s):  
William R. Amberson
Keyword(s):  
Refractory Period ◽  
Effect Of Temperature ◽  
Absolute Refractory Period ◽  
The Absolute

scholarly journals Real-Time Closed-Loop Suppression of Repolarization Alternans Reduces Arrhythmia Susceptibility In Vivo

2020 ◽  
Vol 13 (6) ◽  
Author(s):  
Faisal M. Merchant ◽  
Omid Sayadi ◽  
Kwanghyun Sohn ◽  
Eric H. Weiss ◽  
Dheeraj Puppala ◽  
...  
Keyword(s):  
Real Time ◽  
Body Surface ◽  
Refractory Period ◽  
Pulse Width ◽  
Closed Loop ◽  
The Body ◽  
Swine Model ◽  
Absolute Refractory Period ◽  
The Absolute

Background: Repolarization alternans (RA) has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death. Methods: We have developed a real-time, closed-loop system to record and analyze RA from multiple intracardiac leads, and deliver dynamically R-wave triggered pacing stimuli during the absolute refractory period. We have evaluated the ability of this system to control RA and reduce arrhythmia susceptibility, in vivo. Results: R-wave triggered pacing can induce RA, the magnitude of which can be modulated by varying the amplitude, pulse width, and size of the pacing vector. Using a swine model (n=9), we demonstrate that to induce a 1 µV change in the alternans voltage on the body surface, coronary sinus and left ventricle leads, requires a delivered charge of 0.04±0.02, 0.05±0.025, and 0.06±0.033 µC, respectively, while to induce a one unit change of the K score , requires a delivered charge of 0.93±0.73, 0.32±0.29, and 0.33±0.37 µC, respectively. For all body surface and intracardiac leads, both Δ(alternans voltage) and ΔK score between baseline and R-wave triggered paced beats increases consistently with an increase in the pacing pulse amplitude, pulse width, and vector spacing. Additionally, we show that the proposed method can be used to suppress spontaneously occurring alternans (n=7), in the presence of myocardial ischemia. Suppression of RA by pacing during the absolute refractory period results in a significant reduction in arrhythmia susceptibility, evidenced by a lower S rank score during programmed ventricular stimulation compared with baseline before ischemia. Conclusions: We have developed and evaluated a novel closed-loop method to dynamically modulate RA in a swine model. Our data suggest that suppression of RA directly reduces arrhythmia susceptibility and reinforces the concept that RA plays a critical role in the pathophysiology of arrhythmogenesis.

Temperature Acclimation of the Functional Parameters of the Giant Nerve Fibres in Lumbricus Terrestris L

1967 ◽  
Vol 47 (3) ◽  
pp. 481-484
Author(s):  
ANTTI TALO ◽  
KARI Y. H. LAGERSPERTZ
Keyword(s):  
Refractory Period ◽  
Lumbricus Terrestris ◽  
Temperature Acclimation ◽  
Maximum Response ◽  
Nerve Fibres ◽  
Response Frequency ◽  
Giant Fibre ◽  
Absolute Refractory Period ◽  
The Absolute ◽  
Giant Fibres

1. The temperature dependence of the absolute refractory period and of the maximum response frequency was studied in the median and lateral giant fibres of the nerve cord of earthworms acclimated to 13° or 23° C. 2. Compensatory acclimation of the absolute refractory period in the median giant fibre was statistically significant at 6° and 13° C. The temperature coefficient Q10) was significantly lower in cold-acclimated animals. 3. Compensatory acclimation of the maximum response frequency was significant at 6° C. The ratio between the minimum impulse interval and the absolute refractory period was about 2.2. It was unaltered by temperature acclimation.

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