Fig. 1. The reverse change is shown in Fig. 3. fluid, and then when activity was re-established the fluid replaced by a

Transcription

1 CARDIAC TETANUS. By W. BURRID GE, M.B. (From the Physiological Laboratory, Oxford.) WALTHER(13) gives complete references to the experiments on cardiac tetanus and in his discussion concludes that superposition of contractions and a condition approximating to the tetanus of skeletal muscle is possible in the heart. His experiments were performed. on hearts poisoned by muscarine and his illustrations show an incomplete fusion of contractions as the condition resembling tetanus. R 6hde (10) also obtained some fusion of contractions in hearts poisoned by chloral hydrate and considered the phenomena as consequent on the drug dissociating the cardiac nervous and muscular elements. His views were confirmed by Ca r lso n(6) and contested by Schultz (n1). The experiments below have been performed on hearts subjected only to alterations in the proportions of their normal environment. They indicate that the greater richness of cardiac muscle in phosphates as compared with skeletal muscle, is an important factor in determining its mode of behaviour. Method. The hearts were excited through platinum electrodes applied to the base of the ventricles as described in a former paper. The Bayliss frictionless writing point (1) was employed. The hearts were first treated with 5 p.c. potassium chloride, this solution washed out with Ringer's fluid, and then when activity was re-established the fluid replaced by a solution of the composition 06 p.c. NaCl, 003 KCI, 0-01 p.c. NaHCO3 and 0-15 p.c. CaCl2. This usually caused a temporary increase of tonus and a slight decrease in the height of the spontaneous contractions. See Fig. 1. The reverse change is shown in Fig. 3. If the heights of the spontaneous contractions were not decreased the treatment with the potassium chloride was repeated. On the other hand in stale hearts the treatment with potassium chloride might not be necessary. Special attention is drawn to the mode of beat of the heart perfused with the solution given, inasmuch as it is similar to the mode of beat described by Ring er(9) as associated with potassium, whereas these hearts were actually perfused with a solution containing large amounts of calcium. This solution of high calcium content perfused through the fresh

2 CARDIAC TETANUS 249 heart produced the effects described by Ringer as produced by calcium (prolongation of systole, slowing of diastole, etc.). Under the conditions given here, as the illustrations show, it does not. The effects are not consequent on any persisting influence of potassium because a further treatment with potassium, but using the dibasic phosphate instead of the chloride, restored and reinforced the capacity of this calcium solution to produce the effects described by Ringer as produced by calcium. Hence the actions of calcium as described bv him are not pure, but the result of calcium interacting with the phosphates abundantly present in the fresh heart. Hence also the effects described in this paper are to be ascribed to chlorides being in excess in the cardiac tissues as well as to calcium being in excess in the perfusing solution. Fig % NaCi, 0-03 % KCI, 0.01 % NaHCO8. Time every 10" 0 15 CaC2 =perfusion of solution containing O- 15 % CaC2,, Von Kries' Experiment (12) was modified to suit a rhythmical preparation. Of the pairs of stimuli used by him, the natural stimulus evoking contraction was taken as the first member and a single induction shock used as the second. By careful watching and practice, the artificial stimulus was applied at gradually decreasing intervals measured from the commencement of the natural contraction. The artificially excited contraction was greater in height according as the interval between it and the natural contraction was less until finally the spontaneous and artificially excited contractions fused into one large contraction. Examples are shown. in Fig. 2. Faradisation produced a summation of contractions in this preparation as regularly as it does in skeletal muscle. Summation of contractions

3 250 W. BURRIDGE taking place under the influence of calcium has also been recorded by Ringer, Walther, Schultz and others. Examination of the records given by Ringer and Walther shows however that the summation obtained by them was primarily consequent on slowing of the relaxation process. Before summation of contraction in the heart can be directly comparable with the phenomenon given the same name in skeletal muscle, the relaxation process should be of normal duration. Schultz's statement that the compound contractions obtained under the influence of calcium are smaller in amplitude than the single contractions of the Fig. 2. Examples of Von Kries' effect. Sp. =spontaneous contraction. S = contraction excited by a single stimulus. unpoisoned heart is incorrect. His error probably arose from the use of damaged tissues (strips of muscle) imperfectly treated by baths. My own experiments performed on hearts of known contractile capacity show that the summated contractions can utilise the whole of the contractile material. The phenomena described by Ma ys (7) and Min es (8) are probably consequent on loss of phosphates brought about by perfusion (4) or by the acid (5). The preparation described also admits of a complete unwavering tetanus (cf. Fig. 3).

4 CARDIAC TETANUS 251 The preparation also showed fatigue. An example is shown in Fig. 4. The fatigue was shown by several phenomena: (1) the refractory period was lengthened as shown by (a) replacement of unwavering by wavering tetanus, (b) diminution in the height of the tetanic contraction; (2) slowed rate of beat on cessation of stimulus; (3) diminished height of beat. Recovery slowly took place on continued perfusion. Fig. 3. In the lower tracing note the after shortening and slowing of relaxation after faradisation. Time every 10 seconds. +,=faradisation begun. + faradisation ceased. S=contractions evoked by single induced shocks. K.S. =Ringer's fluid of normal calcium content *02 p.c. CaC2-,. Fig. 4. Previous to A the heart had received four periods of faradisation lasting 2j minutes, as a result of which the height of the faradic contraction had decreased from 25 mm. to that shown here ( x j). A complete unwavering tetanus was thereby also changed to the wavering shown in the tracing. At NS the calcium content was decreased to 0-02 % CaC12. This accelerates the rate of recovery (cf. Fig. 3). B shows recovery. The rate of beat was subsequentlv increased by treatment with the dibasic phosphate of potassium. Time in minutes. N.S. =normal Ringer's fluid. PH. LIV. 17

5 252 W. BURRIDGE The phenomena in these cardiac cases confirmed my previous results in skeletal muscle that fatigue is primarily consequent on loss of ability to be excited and not on loss of capacity to contract. The potassium chloride method (3) showed that the fatigued hearts maintained an intact stock of contractile material capable of contracting, but of which only a portion could be thrown into action by an induced shock or the normal propagated disturbance. Adrenin had a very marked action in facilitating recovery so that it would appear from this that an alteration in aggregation state(14) may be an important factor in fatigue. SUMMARY. 1. A cardiac preparation is described which can be (a) fatigued, (b) thrown into tetanus, and (c) show Von Kries' phenomenon. 2. The mode of obtaining the preparation indicates that differing capacities to adsorb different elements of a common environment may be an important factor in determining differences of muscular behaviour. REFERENCES (1) Bayliss. This JournaL 45, Proc. Physiol. Soc., p. xxxi (2) Burridge. This Journal, 41, p (3) Burridge. Ibid. 51, p (4) Burridge. Ibid. 48, Proc. Physiol. Soc., p. i (5) Burridge. Quart. Journ. of Physiol. 7, p (6) Carlson. Amer. Journ. of Physiol. 17, p (7) Mays. Du Bois Raymond's Archiv, p (8) Mines. This Journal, 48, p (9) Ringer. Ibid. 3, p (10) Rohde. Archiv f. exp. Path. u. Pharm. 54, p (11) Schultz. Amer. Journ. of Physiol. 22, p (12) Von Kries. Archiv f. Anat. u. Physiol. p (13) Walther. Pfluiger's Archiv, 78, p (14) Burridge. Quart. Joun of Med. 10, p