Vagal reflexes appearing in asphyxia in rabbits at different ages

Bauer, Dirk

doi:10.1113/jphysiol.1939.sp003719

Cited by 45 publications

(21 citation statements)

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“…The mean arterial pressure in the kitten and puppy more than doubled during the first 6 weeks of life and approached the adult level; this confirms the rise found in the puppy by Clark and Holling [1931] and a marked but smaller rise, probably related to the lower level in the adult, was also found during a similar period in the rabbit [Bauer, 1939;Dawes, Handler and Mott, 1957]. The heart rate did not change during this period, but since the pulse 208 pressure doubled, an increase in stroke volume and therefore of cardiac output must be a contributing factor to the rise in pressure.…”

Section: Discussionsupporting

confidence: 71%

Development of Cardiovascular Responses in the Kitten

1962

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In anaesthetized kittens the mean arterial pressure and the pulse pressure double during the first 6 weeks of life; the heart rates recorded were the same as in the adult cat and did not change during this period. The vasomotor sympathetic system was active within 4 days of birth: there was both tonic activity, as demonstrated by a rise in arterial pressure after carotid occlusion, and a rise in pressure during asphyxia; the carotid sinus-cardiac centre mechanism responded to a rise in arterial pressure at birth. All these responses increased with age but had not reached adult activity by the 6th week of life. The carotid sinus-cardiac centre mechanism did not respond to a fall in blood pressure until 4 weeks of age. The infant heart was apparently more sensitive to the direct action of acetylcholine and the peripheral blood vessels relatively less sensitive than in the adult.THE responses both to asphyxia and to the intravenous administration of drugs have been used to examine the activity of the cardiovascular reflexes shortly after birth. The neonatal period has been studied in the kitten and puppy [Clark, 1934], the pig [Adams, Hirvonen, Lind and Peltonen, 1958] and the human infant [James and Rowe, 1957;Adams, Lind and Rauramo, 1958]: observations have also been made in the growing rabbit [Bauer, 1938;Dawes, Handler and Mott, 1957]. The present paper gives an account of a similar investigation into some of the cardiovascular responses of kittens during the first 6 weeks of life when the central arterial pressure is found to increase from 50/40 mm. Hg, at birth, to 120/90 mm. Hg at 6 weeks of age; the cardiovascular responses to positive intrathoracic pressure have been studied; graded doses of the autonomic transmitter drugs have also been used in an attempt to alter the balance between the direct action on the myocardium and peripheral vessels and the regulatory mechanisms involved. The responses are compared with similar observations made on fully grown animals under comparable experimental conditions and discussed in relation to the change in blood pressure during growth. METHODSNineteen kittens, 96-305 g. in weight, aged from 1 to 46 days and eight adult cats, 2-7-4-5 kg. in weight, were used in the experiments. A few observations were also made on five puppies aged 5-110 days, weighing 475 g.-3-3 kg.Aneesthesia was induced with sodium pentobarbitone, 20-30 mg./kg. injected into the saphenous vein exposed after the subcutaneous injection of procaine. The arterial pressure was measured in a carotid or a femoral artery cannulated with a saline-filled polythene tube connected to a capacitance-or inductance-type manometer; recordings were taken with a Sanborn or a New Electronic Products recorder

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Section: Discussionsupporting

confidence: 71%

Development of Cardiovascular Responses in the Kitten

1962

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“…For instance, in the dog and cat, Clark (1934) and, in the rabbit, Bauer (1938Bauer ( , 1939 concluded that functional activity of the cardiovascular reflexes was not established until after birth. It is notable that in these species the blood pressure at birth is low, only 20-35 mm Hg, in contrast FOETAL ANOXAEMIA to the new-born lamb.…”

Section: Discussionmentioning

confidence: 99%

Oxygen lack and autonomic nervous control of the foetal circulation in the lamb

Born¹,

Dawes²,

Mott³

1956

The Journal of Physiology

110

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Tying the umbilical cord in the mature foetal lamb causes an abrupt increase of blood pressure and a large decrease in heart rate (Barcroft, 1946). As Barcroft was well aware, this procedure not only removes the normal channel of gaseous exchange from the foetus, and thus (in the absence of pulmonary ventilation) induces acute asphyxia, but also causes a profound circulatory disturbance, because more than half the output of the foetal heart normally passes through the placenta. Tying the cord, therefore, cannot give a reliable indication of the response of the foetus in utero to oxygen lack alone. In this paper the effect of oxygen lack has been investigated in lambs delivered by Caesarean section by supplying the ewe with a gas mixture of low oxygen content. The immediate effect was to cause a rise of foetal blood pressure and heart rate, provided that the foetal arterial 02 saturation did not fall too rapidly or too low. Very immature lambs did not react in this way. METHODS Experiments were performed on lambs of from 59 to 143 days gestation age, from ewes of Clun-Hampshire, Suffolk or Kerry Hill breeds. The methods employed were usually the same as in the preceding paper (Dawes, .The more mature lambs were removed from the amniotic sac and the blood pressure was recorded from a femoral artery. In some younger lambs, weighing 45-100 g, the uterus was opened and the amniotic sac was exposed intact. A fine needle, attached to a condenser manometer, was introduced into one umbilical artery through the foetal membranes. There was no appreciable leak of fluid from the amniotic sac, and the umbilical artery did not go into spasm. Blood could be seen flowing past the needle tip within the artery, and the preparation remained in good condition for an hour or more.The trachea of the ewe was cannulated, and gas mixtures of varying oxygen content were delivered through calibrated rotameters.In some unanaesthetized ewes blood samples (0-8 ml.) were withdrawn under local procaine anaesthesia by direct puncture of a carotid artery. The ewes were then anaesthetized with pentobarbitone and samples were taken from a catheter passed a few cm up a median malleolar artery, and from a catheter in the left carotid artery of the foetus. In the smaller foetuses the total quantity of blood withdrawn was kept as small as possible, though in two foetuses of less than 300 g weight it exceeded 1% of the body weight. The samples were mixed with a trace of heparin

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“…1). After several weeks of life the heart rate begins to decrease according to Bauer (1939). Throughout the whole of this period of time blood pressure is gradually rising.…”

Section: Discussionmentioning

confidence: 99%

“…It will be recalled that Schmidt (1932), Gernandt (1946 and Neil, Redwood & Schweitzer (1949) Bauer (1939) and Barcroft (1946) came to the conclusion that the baroreceptor reflexes were not normally in action in the new-born rabbit. With the apparatus then available Bauer found it difficult to record the arterial pressure in new-born rabbits, and relied mainly upon the heart rate as an index of changes in the cardiovascular system.…”

Section: Discussionmentioning

confidence: 99%

Baroreceptor reflexes in new‐born rabbits

Downing¹

1960

The Journal of Physiology

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This paper describes an investigation of the baroreceptor reflexes from the carotid sinus and aortic arch in the new-born rabbit. Bauer (1939) concluded from measurement of the heart rate in rabbits that the depressor reflex was not activated during asphyxia until the 30th day from birth, and the carotid sinus reflex until the 40th day. He also stated that 'faradic stimulation of the depressor nerves and carotid sinus regions in rabbits produces a reflex inhibition of the heart as early as the 11th and 14th days, respectively '. Both Bauer (1939) and Barcroft (1946) inferred from these and other observations in Bauer's paper that the threshold pressures for the baroreceptor reflexes were high, 65 mm Hg for the depressor and 80 mm Hg for the carotid sinus reflex; the normal blood pressure of a new-born rabbit did not reach these levels until several weeks from birth.The implication is that in the new-born rabbit the cardiovascular system is not under the control of the baroreceptors unless the blood pressure rises above the threshold levels quoted above. The object of the experiments now to be described was to determine by more direct methods whether the baroreceptor reflexes are functioning in the rabbit during the first few days of life at the low arterial pressure which is then normally present. METHODSObservations were made on seventeen adult, nine young (3-weeks-old or more, 0-2-1.0 kg body weight) and seventy-five new-born (0-15 days) rabbits, anaesthetized witb pentobarbitone and/or urethane. Of the new-born rabbits fifty-five were given pentobarbitone (10-15 mg/kg intraperitoneally, supplemented with additional pentobarbitone as necessary), and the remainder received urethane (1.2 g/kg intraperitoneally). Older rabbits were given pentobarbitone (20-25 mg/kg intravenously) followed by urethane (1.2 g/kg subcutaneously). The trachea was cannulated. In most experiments rectal temperature was recorded by a thermocouple, and was maintained at 38 + 10C by application of external heat as necessary. This was found to be particularly desirable in very young rabbits.Pres*ure changes applied to the carotid 8inus. In new-born rabbits the left carotid sinus was isolated from the rest of the circulation. The cardiac end of the right or left common carotid artery was cannulated to record systemic blood pressure. The cephalic end of the left common carotid artery was connected by a polyethylene tube to a pressure bottle filled with saline and to a manometer. The left external carotid was tied, together with all branches of the common carotid above the polyethylene tube and the internal carotid distal to the sinus. Static and pulsatile pressures were applied to the carotid sinus. Pulsations were

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Vagal reflexes appearing in asphyxia in rabbits at different ages

Cited by 45 publications

References 1 publication

Development of Cardiovascular Responses in the Kitten

Development of Cardiovascular Responses in the Kitten

Oxygen lack and autonomic nervous control of the foetal circulation in the lamb

Baroreceptor reflexes in new‐born rabbits

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