Saxon William White

The relative roles of the aortic and carotid sinus nerves in the rabbit in the control of respiration and circulation during arterial hypoxia and hypercapnia

1. The respiratory and circulatory effects of graded arterial hypoxia, alone or with superadded hypercapnia, were studied in four groups of unanaesthetized rabbits including normal animals and those with selective section of the aortic nerves, selective section of the carotid sinus nerves and section of both sets of nerves.

The peripheral vascular response to severe exercise in untethered dogs before and after complete heart block

The peripheral vascular response to severe exercise was studied in 11 healthy conscious dogs instrumented with Doppler ultrasonic flow probes on the mesenteric, renal, and iliac arteries, and miniature pressure gauges in the aorta. The response to severe exercise was restudied in six of these dogs after recovery from a second operation producing complete heart block by the injection of formalin into the atrioventricular (AV) node. Three of these dogs also exercised while their ventricles were paced at rates of 100/min and 200/min. The untethered normal dogs ran at speeds of 15-25 miles/hr behind a mobile recording unit for a distance averaging 1.5 miles, while continuous measurements of arterial blood pressure and blood flow were telemetered and recorded on magnetic tape. Severe exercise in normal dogs increased heart rate from 84 to 259/min, arterial pressure from 89 to 140 mm Hg, flow resistance in the mesenteric and renal beds by 59 and 52% respectively, and iliac blood flow 479% above control, while mesenteric and renal blood flows remained constant and iliac resistance decreased by 73%. In dogs with complete AV block, severe exercise at speeds of 10-18 miles/hr increased heart rate from 47 to 78/min, mean arterial pressure from 81 to 89 mm Hg, iliac flow 224%, resistance in the renal bed by 273%, and mesenteric bed by 222% while it decreased blood flow in mesenteric and renal beds by 61 and 65% respectively, and iliac resistance by 62%. A similar response occurred during exercise with pacing at 100/min, but when paced at 200/min a more normal exercise response reappeared. Thus, in normal dogs the peripheral vascular response to severe exercise involved increases in heart rate, arterial pressure and visceral resistance but visceral blood flow did not decrease. In dogs with heart block, where the ability to increase heart rate is severely compromised, compensatory reduction of mesenteric and renal blood flows occurred.

Central Nervous Integration of the Circulatory and Respiratory Responses to Arterial Hypoxemia in the Rabbit

Neural integration during arterial hypoxia was studied in sham-operated, rhinencephalic, thalamic, high mesencephalic, and pontine rabbits, 3 hours after operation under halothane anesthesia. All preparations except the pontine recovered normal movement and posture 40 to 60 minutes after the operation, and effects on the resting circulation specifically ascribable to transection were small. Activation of diencephalic, and to a lesser extent of rhinencephalic, centers was necessary to produce the large increase in autonomic peripheral resistance effect and the autonomic slowing of heart rate characteristic of normal rabbits. In animals with only pontine and high mesencephalic centers, the autonomic peripheral resistance effect was smaller and there was an autonomic rise in heart rate. The neocortex and rhinencephalon exerted inhibitory influences related to the effects of hyperventilation. Suprabulbar respiratory mechanisms were also activated during hypoxia, with diencephalic mechanisms limiting the reflex response mediated by the pontine centers and the cortex exerting disinhibitory effects on the diencephalic centers. The cardiorespiratory response at different degrees of hypoxia probably depends on differences in relative magnitude of inputs from the arterial chemoreceptors, baroreceptors, and lung inflation receptors, producing different degrees of excitation and inhibition of the various suprabulbar and bulbar centers.

Circulatory effects of chloralose‐urethane and sodium pentobarbitone anaesthesia in the rabbit

1. The effects of chloralose‐urethane and sodium pentobarbitone anaesthesia on heart rate, blood pressure and cardiac output were studied in normal rabbits, in animals given atropine and in animals without functioning autonomic effectors. The findings under anaesthesia were compared during spontaneous and artificial intermittent positive pressure respiration.

Local and reflex factors affecting the distribution of the peripheral blood flow during arterial hypoxia in the rabbit

1. The effects of severe arterial hypoxia on the blood flow in the portal vein, and in kidney, muscle and skin beds have been determined in normal unanaesthetized rabbits, in animals without functioning autonomic effectors, and in rabbits with section of the carotid sinus and aortic nerves.

Circulatory control in hypoxia by the sympathetic nerves and adrenal medulla

1. The effects of severe arterial and primary tissue (carbon monoxide) hypoxia on cardiac output, arterial and right atrial pressures, heart rate and ventilation, have been studied in unanaesthetized normal rabbits, and in animals subjected to adrenalectomy, ‘sympathectomy’ (guanethidine), adrenalectomy + ‘sympathectomy’, and section of the carotid sinus and aortic nerves.

The effects of chloralose-urethane and sodium pentobarbitone anaesthesia on the local and autonomic components of the circulatory response to arterial hypoxia.

1. The circulatory and respiratory responses to severe arterial hypoxia were studied in normal rabbits, ‘de‐efferented’ rabbits without functioning autonomic effectors, and atropinized animals before anaesthesia and during chloralose‐urethane and sodium pentobarbitone anaesthesia. Net systemic autonomic activity and autonomic activity to the heart was assessed from a comparison of the responses of the various preparations.

The effects of haemorrhage in the unanaesthetized rabbit

1. The circulatory response following acute loss of 26% of the blood volume was examined in unanaesthetized rabbits. The groups of animals studied were normal rabbits; adrenalectomized rabbits; animals subjected to prolonged treatment with guanethidine in which peripheral adrenergic nerve transmission is blocked, but which can reflexly liberate adrenal medullary hormones; animals subjected to combined adrenalectomy and guanethidine treatment with no functional adrenergic effectors; in each case with or without administration of atropine. The responses of animals with section of the carotid sinus and aortic nerves were also examined.

Evaluation of blood resistivityin vivo for impedance cardiography in man, dog and rabbit

The accuracy of impedance cardiography for measurement of stroke volume (SV2) has been controversial. This could be, in part, due to the use in the Kubicek formula of the bench-determined blood resistivity (ϱ)-haematocrit (Hct) relationship, which does not take into account factors such as complex blood-velocity movements. In the present studyin vivo, ϱ was calculated in dog, rabbit and man from the rearranged Kubicek formula, ϱ=(SV. Zo2)/(L2. dZ/dt max T); the stroke volumes used in the calculation being derived at different Hcts in the different species from the independent techniques of electromagnetic flowmeter, direct Fick, and direct Fick and thermodilution, respectively. Thein vivo ϱ-Hct relationship is linear, inverse and nearly constant over the range of Hcts tested (dog 26–62%, man 31–48%, rabbit 37%). No significant difference exists between meanin vivo ϱ values determined for the three species at corresponding haematocrits despite different thoracic anatomy and circulatory dynamics. Thus, the best estimate of mean ϱin vivo within the normal Hct range is 135Ω cm, the use of which will result in a SV2 accuracy of better than ±10%.

A comparison between thermodilution, electromagnetic and Doppler methods for cardiac output measurement in the rabbit

SUMMARY 1. Electromagnetic and Doppler flowmeter methods were compared with the thermodilution technique for the measurement of cardiac output in unanaesthetized rabbits. Cardiac output was varied by haemorrhage and transfusion.