Biomedical subjects

P A Blombery

Publications and source records attributed to P A Blombery.

3 recordsLinked to original sources

PubMed1979

Relative contributions of aortic and carotid sinus baroreceptors to the baroreceptor-heart rate reflex of the conscious rabbit.

Conscious rabbits with previously implanted perivascular balloons for altering blood pressure were studied before and 6 days after: (i) sham-operation (n = 6); (ii) section of carotid sinus nerves alone (n = 7); (iii) section of aortic nerves alone (n = 5); and (iv) combined sino-aortic denervation (n = 5). Sigmoid mean arterial pressure (MAP)-heart period (HP) baroreflex curves were derived and were characterized by: (i) the HP range (HPR) between upper and lower plateau levels; (ii) the median blood pressure (BP50); and (iii) the average gain (G). Resting MAP and HP and the 3 baroreflex parameters were not altered significantly 6 days after sham-operation. After section of the carotid sinus nerves alone resting MAP and BP50 rose by 18 +/- 2.6 mm Hg, resting HP fell by 31 +/- 4.2 msec, whilst HPR and G fell to about 45% and 20 % respectively of initial preoperative control. After cutting the aortic nerves alone there was a similar fall in resting HP as after carotid denervation. However, the rises in resting MAP and BP50 were only about half of those observed after carotid denervation (P < 0.05) and the changes in HPR and G to 65% and 58% of control respectively were also less marked (P ¿ 0.01). The aortic baroreceptor zone also exerted smaller effects on the sympathetic efferent component of the baroreflex HP response. Despite the different effects exerted by each zone on the reflex parameters there was little difference in threshold pressure for producing cardiac slowing. After combined sino-aortic denervation there was a similar rise in resting MAP (19 mm Hg) as after carotid sinus denervation alone, but there was more marked tachycardia, with a fall in resting HP of 82 msec (P < 0.001) and both resting and baroreflex-mediated vagal tones were completely abolished. The small residual pressure-determined HP changes of about 8 msec were entirely sympathetic and probably mediated through cardiopulmonary baroreceptors.

Animals↗

PubMed1976

Valsalva vasoconstrictor reflex in human hypertension in after beta-adrenoreceptor blockade in conscious rabbits.

1. A Valsalva-like manoeuvre was used to elicit graded rises in total peripheral resistance (TPR) in conscious rabbits. The rises were reflex and mediated through sympathetic constrictors. Propranolol infused at different rates reaching plasma concentrations up to 240 (SEM 33) ng/ml had no effect on this reflex but reduced mean arterial pressure. However, the response was attenuated by clonidine in a dose-dependent manner. 2. Valsalva manoeuvres were used to elicit graded sympathetically mediated rises in TPR index in twenty-nine subjects with mean arterial pressure ranging from 75 to 165 mmHg. Absolute sensitivity of the constrictor response increased with rising resting TPR index, resulting in some enhancement of constrictor responses in the hypertensive subjects. It seems likely that non-autonomic factors (e.g. vessel structure) rather than hyperactive neural constrictor effects are involved in the enhanced constrictor responses in essential hypertension.

Adrenergic beta-Antagonists↗

PubMed1976

Action of propranolol on arterial pressure and on cardiovascular reflexes.

In the rabbit, administration of 500 mug (+/-) propranolol into the lateral cerebral ventricle resulted in rapid leakage of drug into the blood. The drug produced a small reduction in blood pressure at 2 and 4 hours after injection but because of the rapid leakage, this could have been due to its peripheral actions. To investigate possible central mechanisms of action which were independent of peripheral effects, we tested the action of intravenously administered propranolol on the reflex rise in TPR evoked in rabbits by graded Valsalva-like manoeuvres. This was performed in unanaesthetised rabbits with Doppler flowmeters for measuring cardiac output. Graded expiratory pressures (EP) were applied to the inlet and outlet tubes of the tracheotomised animal's respiratory valve and to the cuff around their thorax and abdomen. Administration of propranolol at two levels (168 +/- 35 ng/ml, and 240 +/- 33 ng/ml) for 1 hour had no effect on slope and threshold of the EP-TPR relationship. By contrast to the minimal effects on the reflex with propranolol, the EP-related rise in TPR was attenuated by clonidine. We conclude that propranolol does not lower blood pressure in the rabbit by attenuating sympathetic constrictor activity.

Animals↗