Printed in Great Britain THE GENESIS OF CERTAIN CARDIAC ARRHYTHMIAS IN FISH
The hearts of both elasmobranch and teleost fish are known at times to beat at a particular phase of the respiratory cycle and thus to exhibit a regular rhythm locked to that of respiration (Lyon, 1926; Lutz, 1930; Satchell, i960; Shelton & Randall, 1962). In the laboratory, the hearts of Squalu...
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| Format: | Text |
| Language: | English |
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1968
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.531.1347 http://jeb.biologists.org/content/49/1/129.full.pdf |
| Summary: | The hearts of both elasmobranch and teleost fish are known at times to beat at a particular phase of the respiratory cycle and thus to exhibit a regular rhythm locked to that of respiration (Lyon, 1926; Lutz, 1930; Satchell, i960; Shelton & Randall, 1962). In the laboratory, the hearts of Squalus acanthias and Mustelus antarcticus usually exhibit a 1:2,1:3 or 1:4 rhythm, the P wave of the electrocardiogram occurring as the mouth opens in the appropriate respiratory cycle. Lyon (1926) reported a 1:1 co-ordination in Carcharias sp. In Squalus acanthias it is known that respiration stimulates receptors in the pharynx, the afferent fibres of which pass up the branchial branches of the glossopharyngeal and vagus nerves to the medulla; the efferent limb of the reflex is the cardiac vagus nerve (Satchell, i960). In addition to this locked rhythm, electrocardiograms exhibit a variety of arrhyth-mias. Both the locking with respiration and these arrhythmias are abolished by atropine which blocks the vagal control of the heart, and by partial curarization which enfeebles respiratory movements to a level at which the pharyngeal receptors no longer fire. These observations suggest that the locked rhythm and these arrhythmias are related pheno-mena. This hypothesis has been investigated by constructing a mathematical model based upon established data of branchiocardiac co-ordination in fish. In this model varying proportions of the output of a ' respiratory ' oscillator were allowed to modulate the output of a 'cardiac ' oscillator. It will be shown that certain common arrhythmias of the fish heart beat can be explained as stages of incomplete coupling between the respiratory centre in the medulla and the cardiac pacemaker in the sinus venosus. Fish hearts are known to undergo some of the well-known arrhythmias of mammals; A-V block was reported by McWiUiam (1885) and paroxysmal ventricular tachycardia has been noted in experiments involving manipulation of the heart. The arrhythmias described in this paper are of a ... |
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