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Biomedical subjects

D R Jones

Publications and source records attributed to D R Jones.

At least 415 records · Page 23Linked to original sources
PubMed1971

The effect of variations in heart rate and regional distribution of blood flow on the normal pressor response to diving in ducks.

1. During a 2 min period of submersion of normal ducks, sciatic artery blood flow fell to 10 +/- 1.5% control and carotid artery blood flow was reduced to 71 +/- 7% control. Mean arterial blood pressure (M.A.P.), however, was maintained at 83 +/- 3.5% of control. The whole animal showed a constrictor response during submersion, with the sciatic vascular bed showing average constriction. Both resistance to flow and yield pressure increased in the sciatic bed but changed little in the carotid bed. After 1 min submersion P(a,O2) was 52 +/- 1 mm Hg.2. Upon emersion, as soon as ventilation commenced, the whole animal showed a dilator response. The carotid bed exhibited marked vasodilatation whereas the sciatic bed returned to its control level.3. After alpha-receptor blockade, ducks were submerged for 1 min. During this time M.A.P. fell to 64 +/- 5.6% of control and heart rate was reduced to 49 +/- 8.3% of control. Blood flow through the sciatic and carotid arteries also fell to values of 41 +/- 6.9% of control and 91 +/- 13% of control respectively. There was little change in either resistance to flow or yield pressure in the sciatic bed compared to normal ducks, and the carotid bed showed reductions in resistance to flow and yield pressure during submersion. P(a,O2) after 1 min under water was 41 +/- 1.1 mm Hg.4. beta-receptor blockade had no effect on any of the measured variables during submersion. Upon surfacing, however, although the whole animal response was one of dilatation, the carotid bed was less dilated than in normal ducks at this time and the sciatic bed was more constricted.5. Injection of atropine not only abolished the bradycardia during submersion but also caused a rise in M.A.P. and sciatic blood flow during the period under water. After 1 min submersion P(a,O2) was 30 +/- 1.2 mm Hg.6. It is concluded that stimulation of adrenergic alpha-receptors is responsible for the increase in resistance to flow through the sciatic artery and the maintenance of blood pressure during submersion in the normal animals. This selective constrictor activity and the resulting ischaemia is important in the maintenance of P(a,O2) during submersion. Adrenergic beta-receptors (cardiac and/or peripheral) are involved, to a small extent, in the blood pressure and blood flow changes that occur when ventilation commences upon emersion.

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↗
PubMed1968

Onset of and recovery from diving bradycardia in ducks.

1. No evidence was found of a ;postural reflex' in ducks. Neither the position of the head nor the water temperature affected the cardiac response to diving.2. In ducks with access to air through a tracheal cannula, submersion did not invariably cause apnoea until the water level reached the glottis. Heart rate was closely related to respiratory frequency, and bradycardia did not occur during submersion unless there was a reduction in respiratory frequency or a cessation of ventilation altogether.3. When apnoea and bradycardia did occur during submersion, the first inspiration upon surfacing was 2-3 times larger than normal and was accompanied by an instantaneous rise in heart rate.4. Atropinization or cold block of the vagus abolished diving bradycardia. Only one vagal trunk was involved in cardiac chronotropic control at any one time. This vagal trunk also appeared to be more important in control of respiratory frequency.5. beta-adrenergic receptor blockade did not affect either diving bradycardia or post-dive tachycardia.6. The results show that the cardiac chronotropic response both during and after submergence is controlled solely by changes in parasympathetic vagal activity.

Anesthesia, Conduction↗