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Biomedical subjects

M J Purves

Publications and source records attributed to M J Purves.

At least 55 records · Page 3Linked to original sources
PubMed1970

The relation between carotid body chemoreceptor discharge, carotid sinus pressure and carotid body venous flow.

1. Activity in forty-two single chemoreceptor afferent fibres from the carotid body in thirty-nine cats was measured when the carotid body was naturally and artificially perfused. In nine of these cats, carotid body venous flow was also measured.2. When pressure within the carotid sinus segment was suddenly raised or lowered, chemoreceptor activity changed in the opposite direction within the first 5-10 sec by an amount which was significantly greater than the variation of activity in the control period. Thereafter activity stabilized at a level which was not different from control.3. Whether the carotid body was naturally or artificially perfused, carotid body chemoreceptor activity, following this initial transient change, was unaffected in eight out of twelve fibres by alterations in carotid sinus pressure within the range 60-160 mm Hg and carotid body venous flow 10-60 mul./min, blood gas tensions and pH being maintained constant. In the four remaining fibres, chemoreceptor activity increased slightly but significantly as pressure was lowered in this range. Chemoreceptor activity increased in all fibres tested when pressure was lowered below 50-60 mm Hg.4. Chemoreceptor response curves to changes in P(a,O2) (30-450 mm Hg), P(a,CO2) (27-62 mm Hg) or [H(+)](a) (3-7 x 10(-5) m-equiv/l.) were not significantly different whether the carotid body was perfused (a) naturally at the prevalent systemic pressure, (b) artificially at the same pressure, or (c) artificially at one higher pressure, 130 or 140 mm Hg.5. These results indicate that the carotid body chemoreceptors are relatively unaffected by sustained changes in arterial pressure or in total carotid body flow within the physiological range.

Animals↗
PubMed1970

The frequency of nerve impulses in single carotid body chemoreceptor afferent fibres recorded in vivo with intact circulation.

1. The responses of single afferent fibres of carotid body chemoreceptors to independent changes in arterial O(2) and CO(2) tensions and pH were studied in the cat in vivo.2. The response curve obtained relating chemoreceptor activity to changes in arterial P(O2) was similar to an hyperbola; the frequency of nerve impulses at first decreased rapidly as the P(a,O2) was raised and then more slowly. The arterial P(O2) at which the slow decrease was reached varied among the different fibres; the mean level was 190 mm Hg (S.D. +/- 40 mm Hg).3. Single chemoreceptor afferent fibres continued to discharge even when the arterial P(O2) was more than 600 mm Hg.4. The discharges of single chemoreceptor afferent fibres increased both with increasing P(a,CO2) at constant pH and P(a,O2), and with increasing arterial H(+) at constant P(a,CO2) and P(a,O2).5. It is concluded that single carotid body chemoreceptor afferent fibres of the cat can be activated in vivo by an increase in either arterial H(+) or arterial P(CO2) as well as by a decrease in arterial P(O2).

Action Potentials↗
PubMed1970

The effect of hypoxia, hypercapnia and hypotension upon carotid body blood flow and oxygen consumption in the cat.

1. Carotid body blood flow (c.b.f.), the arterio-venous oxygen (A-V O(2)) difference and oxygen consumption were measured in forty-seven cats, anaesthetized with pentobarbitone, paralysed with gallamine and ventilated artificially. Carotid sinus and cervical sympathetic nerves were intact throughout.2. A system for perfusing the carotid body artificially with blood is described and evidence is given which shows that similar results were obtained whether the carotid body was naturally or artificially perfused.3. With arterial pressure, blood gas tensions and pH within physiological limits, c.b.f. varied between 33 and 68 mul./min, average 41.5; A-V O(2) difference between 0.21 and 0.46 ml./100 ml., average 0.34, and calculated oxygen consumption between 0.115 and 0.195 mul. O(2)/min, average 0.147.4. With constant mean arterial pressure, hypoxia (30-40 mm Hg P(a, O2)) or hypercapnia (> 50 mm Hg P(a, CO2)) resulted in a small increase of c.b.f., up to 14 mul./min above control; an average fall of A-V O(2) difference by 49% of control and an average fall of oxygen consumption by 36% of control.5. Carotid body blood flow fell linearly with mean arterial pressure over the range 100-170 mm Hg, the slope of the curve varying between 0.78 and 1.22 mul. min(-1). mm Hg(-1). M.A.P. A-V O(2) difference was unaffected so that oxygen consumption fell in proportion to c.b.f.6. It is concluded that the unique response of the carotid body to these stimuli is a fall in oxygen consumption and that this bears a closer relation to the known pattern of chemoreceptor discharge than do changes in total blood flow.

Animals↗
PubMed1970

The role of the cervical sympathetic nerve in the regulation of oxygen consumption of the carotid body of the cat.

1. Carotid body blood flow (c.b.f.) and carotid arterial-carotid body venous oxygen (A-V O(2)) difference were measured and carotid body oxygen consumption calculated in twenty-six cats anaesthetized with pentobarbitone sodium, paralysed with gallamine triethiodide and ventilated mechanically.2. With the sinus nerves intact and with blood gas tensions and carotid sinus pressure within physiological limits, section of either the pre- or post-ganglionic cervical sympathetic nerve on the same side caused an average rise in c.b.f. of 9.2 mul./min, in A-V O(2) difference of 0.09 ml./100 ml. and in carotid body oxygen consumption of 0.075 mul./min.3. When the pre- or post-ganglionic cervical sympathetic nerves were stimulated, c.b.f. and A-V O(2) difference fell. The fall in c.b.f. was enhanced at high P(a, CO2); the fall in A-V O(2) difference and in calculated oxygen consumption was enhanced at low mean arterial pressure (M.A.P.) or P(a, O2).4. Following sympathectomy, a reduction of M.A.P. at constant P(a, O2) and P(a, CO2) caused a fall in c.b.f. and a commensurate rise in A-V O(2) difference so that carotid body oxygen consumption remained approximately constant.5. When P(a, O2) was altered over the range 35 to > 400 mm Hg, or P(a, CO2) over the range 27-70 mm Hg at constant M.A.P., c.b.f. changed by amounts which were similar to those observed when the sympathetic nerves were intact and A-V O(2) difference changed in the opposite direction so that carotid body oxygen consumption similarly remained constant.6. Comparison of these results with those observed when the sympathetic nerves were intact indicates that the sympathetic nerves exert a vasoconstrictor effect upon carotid body blood vessels over a wide range of blood gas tensions and arterial pressure and that they also tend to diminish the rate of carotid body oxygen consumption. The mechanisms which may be involved in this regulation are discussed.

Animals↗
PubMed1970

The carotid body in the duck and the consequences of its denervation upon the cardiac responses to immersion.

1. The anatomy of the carotid body and its afferent nerve supply was studied in the duck and a method of denervating the carotid body which ensures a satisfactory post-operative course is described.2. The effect of denervating the carotid body upon the cardiac response to immersion of the head in water was studied in ten ducks which at the time of the test were unanaesthetized.3. When the nerves were intact, immersion of the head caused a fall in heart rate after a latent period of between 1 and 9 sec to an average of 24% of the resting rate after 30 sec. Simultaneous measurement of arterial oxygen tension (P(a, O2)) in the brachiocephalic artery showed a rapid initial fall during the initial 10 sec from control levels, 93-103 mm Hg, to between 42 and 47 mm Hg, followed by a gradual fall of 3-5 mm Hg for each subsequent 30 sec period of submergence.4. Following carotid body denervation, the latent period before heart rate started to fall was no different from control but the average fall in heart rate was now to 90% of the resting rate and brachiocephalic P(a. O2) continued to fall steadily during submergence reaching levels of between 10 and 21 mm Hg by the end of the second minute.5. Stimulation of the central end of branches of the IXth (glossopharyngeal) nerve supplying the glottis caused apnoea and bradycardia.6. It is concluded that apnoea and bradycardia during submergence in the duck is initiated reflexly from receptors in the nares, pharynx and glottis but that the profound degree of bradycardia and mechanisms which maintain a relatively high P(a, O2) are regulated by peripheral chemoreceptor activity.

Animals↗
PubMed1970

The effect of carotid body denervation upon the respiratory response to hypoxia and hypercapnia in the duck.

1. Respiratory responses to altered P(a, O2) at constant P(a, CO2) and altered P(a, CO2) at constant P(a, O2) were measured in fourteen unanaesthetized ducks 5-9 weeks old.2. All the ducks responded to the inhalation of a few breaths of 100% O(2) with a fall in V(E) of between 11 and 17% of control, and to the reduction in P(a, O2) from control levels (93-101 mm Hg) to 38-47 mm Hg with an average increase in V(E) of 190% of control which was potentiated by raising the level of CO(2).3. Ventilation approximately doubled when P(a, CO2) was raised to 55 mm Hg, the greatest sensitivity to changes in P(a, CO2) being over the range 40-45 mm Hg.4. Carotid body denervation was carried out in nine ducks and the respiratory responses were modified. The fall in V(E) with inhalation of 100% O(2) was abolished in all ducks and the rise in V(E) with hypoxia was abolished in six. The increase in V(E) as P(a, CO2) was altered in steps was unaffected but the rate at which V(E) increased in response to 4% CO(2) was markedly reduced.5. It is concluded that the chemoreceptor regulation of respiration in ducks is similar to that observed in non-diving animals.

Animals↗
PubMed1969

Types of nervous activity which may be recorded from the carotid sinus nerve in the sheep foetus.

1. In the sinus nerve of mature foetal sheep (120-147 days gestational age) three types of nerve activity have been demonstrated: (a) baroreceptor afferent, in which the nerve activity was synchronous with the pulse pressure wave and which followed pressure changes in the carotid sinus including those caused by compressing the umbilical cord. The discharge of nine out of twelve baroreceptor afferents increased with sympathetic stimulation, (b) a subtype of (a) in which there was irregular activity from pressure receptors which most probably represented baroreceptors discharging at or about threshold, and (c) in the older foetuses (130-147 days), there was activity which was unaffected by changes in carotid sinus pressure, P(a, O2) or NaCN but which increased in discharge rate with compression of the umbilical cord or with stimulation of the cervical sympathetic; this activity then increased with injection of NaCN and was thus identified as chemoreceptor in origin. In addition, a pathway originating in the cervical sympathetic and which passed through the superior cervical ganglion was demonstrated by evoking a compound action potential on stimulation of the preganglionic cervical sympathetic nerve.2. Recordings from pre- or post-ganglionic cervical sympathetic nerves showed that spontaneous activity was present and increased when the umbilical cord was compressed.3. These results suggest that the carotid body chemoreceptors in the foetus are relatively insensitive to chemical changes and that, in their activation at birth, the sympathetic could be involved. Possible neural pathways and the mechanism of activation are discussed.

Action Potentials↗
PubMed1967

Observations on the rhythmic variation in the cat carotid body chemoreceptor activity which has the same period as respiration.

1. The activity in carotid body chemoreceptor afferent fibres in the cat has been recorded and found to have a rhythm with the same period as respiration.2. This rhythm is not an artifact; it is not due to arterial pressure changes with respiration nor to cyclical changes in pulmonary venous admixture. It is caused by changes in blood gas tensions during each respiratory cycle.3. The amplitude of the rhythm is modified by transient and long-term changes in inspired oxygen or CO(2) so that a rise or fall in O(2) or CO(2) tensions of arterial blood (P(a,O2), P(a,CO2)) from the physiological range reduces it. The ratio of the rhythm amplitude to the mean rate of chemoreceptor discharge increases with P(a,O2) over the range 40-240 mm Hg.4. The rhythm is modified by changes in respiratory frequency and volume.5. The fluctuations of arterial oxygen tension which have the same period as respiration are shown to be conducted up the vertebral artery at least as far as the vertebro-occipital anastomosis.6. It is proposed that the chemoreceptor rhythm reflects the moment to moment changes in blood gas tensions.

Action Potentials↗