摘要:

Summary.Determinations are described of the excitability of the respiratory centre during a waking state during spontaneous sleep and evipan sleep and during evipan anaesthesia by studying the reactions to the breathing of CO2mixtures (Lindhard1933).2 experiments with spontaneous sleep show in both cases reduced excitability in the respiratory centre during sleep. 3 experiments with sleep after giving of evipan in hypnotic doses show a larger reduction in the excitability which is solely due to deeper sleep, as it can be proved, that the evipan in hypnotic doses does not affect the centre depressively. From this the conclusion is drawn, that the reduction in excitability during sleep increases in proportion to the depth of the sleep.Finally 8 experiments with evipan anaesthesia show that the excitability of the respiratory centre, even during light anaesthesia, is affected far more in a depressive direction than during sleep. The results of the experiments further show thak this depression is increasing with the depth of the anaesthesia — i.e. with the concentration of evipan in the blood. At a certain concentration ‐ as a rule this occurs by a sudden overdosing ‐ the centre as the first of the vital ones will be put out of function, and the respiration paralysed.During sleep ventilation was decreased 20–38 %, during anaesthesia falls of 48–80 % appeared. While during deep the percentage fall occasionally was about the same with atmospheric and CO2breathing, a proportionally larger fall was caused by CO2during anaesthesia.The tension of carbon dioxide in alveolar air rose during sleep 3–6 mm, during anaesthesia up to 8–9 mm. The fall in ventilation during sleep was first and foremost due to a reduction in frequency, during anaesthesia on the other hand both to reduction in frequency and in depth o

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1944.tb03047.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.1A new method is devised for continuous measurement of stiffness at rest and during contraction.2Tension increase in tetanic contraction is limited by a plastic lengthening of equilibrium length in the contracted fibre (yielding), the occurrence of which is most marked in the first 0.5 see of tetanic contraction. Yielding is characterised by a change in the gradient of static length‐tension diagrams and dynamically by a sudden decrease in stiffness occurring at a critical tension value. This tension may be due either to contraction or to tension induced externally in the contracted fibre.3Comparative determinations of stiffness with low and high frequencies of periodic length alterations show that stiffness proper is masked by yielding when low frequencies are applied while a frequency of 100 cycles per sec is well suited to measurements of actual stiffness.4In physiological muscular activity yielding ensures constant contraction tension over a large range of stretch.5Apart from yielding the increasing stiffness with increasing frequency is due to viscosity, not uniformly distributed over the fibre.6In the resting fibre no measurable dependence of stiffness on temperature can be observed at different frequencies (3–25°C). During contraction stiffness decreases essentially with increasing temperature.7Evidence is given that this frequency dependence of stiffness is due to “linkage modifications” in contractile elements and that intrinsic friction is quantitatively of minor importance.8The difference in temperature dependence of stiffness at rest and during contraction is probably due to the chain reaction occurring during contraction, the propagation of which is highly dependent on temperature.9At all degrees of stretch, tension in the resting muscle fibre increases with increasing temperature. The temperature dependence is highest at medium elongations and is always less than proportional with absolute tem

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1944.tb03048.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY

摘要:

Summary.The mechanical factors determining tension in contraction of the single cross striated muscle fibre are investigated by a continuous registration of stiffness and tension at rest and during contraction. The method applied is in principle the same as that described in the preceding paper and stiffness is determined with a measuring frequency of 100 cycles per sec.Dynamic stiffness varies proportionally with tension at rest and during contraction, the proportionality factor at the contraction maximum being from 30–90 per cent above that of the resting fibre. It depends on the initial length and decreases when the contracted fibre is subjected to higher tensions (yielding).From tension, dynamic stiffness and their mutual interdependence the dynamic shortening ability can be computed, andthe influence of stiffness and equilibrium length on tension is investigated under different conditions.At all elongationsthe maximum in stiffness precedes that of tension. Changes in dynamic equilibrium length contribute relatively less to the initial stage of contraction than to the other phases and its influence on the resulting tension decreases with increasing stretch. At the beginning of contraction dynamic shortening may even attainnegative values, this decrease being the more pronounced the higher the strength of stimulation and the degree of stretch.Whenincreasing the strength of direct stimuli, tension, stiffness and dynamic shortening increase, the latter varying more with grading than does static equilibrium length.The contribution of stiffness to the resulting contraction tension increases considerably with fallingtemperaturewhile that given by dynamic shortening correspondingly decreases.The continuously falling tension duringfatigueis accompanied by a gradual decrease in stiffness, while equilibrium length has a lowered but rather constant value in different stages of fatigue. Increase in extra‐tension after partialrestitutionis due to a higher dynamic shortening, stiffness still being essentially lower than in the fatigued and the non‐fatigued fibre. The falling contraction tension during fatigue is not caused by a decrease in number of active elements but is propably due to gradual changes in equilibrium length occurring in the single minute structural eleients proper.Proportionality between stiffness and tension is lacking in theinitial phase of contraction(10–20 ms), and within a period where extra‐tension is slight, often so slight that it is difficult to decide whether tension is present or not, considerable changes occur in fiber stiffness which are inherent in the contraction process itself.On the basis of the molecular model previously described astructural interpretationof mechanical factors determining tension is attempted.Apart from extrinsic tension, stiffness is caused by properties of the molecular links and their modifications, by properties of the chains and by the mutual interaction of different chains. The initial difference in the developing rate of stiffness and tension is due to intrinsic tension caused by the interaction of contracting and shunting resting elements, before mechanical consolidation between the elements is established. This increase in stiffness can be so considerable that it inhibits shortening and causes anegativecontribution of equilibrium length to the resultin

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1944.tb03049.x

出版商:Blackwell Publishing Ltd    

年代:1944

数据来源: WILEY