Integrative reflex control of heart rate in the rabbit during hypoxia and hyperventilation

Baroreceptor mean arterial blood pressure-heart period curves were obtained for unanesthetized sham-operated, thalamic, or pontine rabbits at an arterial Po 2 of 100 or 30 mm Hg. Each curve was S-shaped: it had a lower heart period plateau below threshold pressure, a part where heart period increased monotonically with rising mean arterial blood pressure, and an upper heart period plateau above upper saturation pressure. In spontaneously breathing rabbits, the pressure-dependent parameters of the curves were altered during hypoxia; in addition, there were baroreflex-independent shifts in heart period plateau levels. Suprapontine centers participated in both of these changes. An afferent analysis performed in rabbits treated with atropine and subjected to controlled ventilation showed that the changes in curve parameters were due to afferent interactions in cardiac sympathetic motoneurons between (1) arterial baroreceptor and chemoreceptor inputs which increased threshold, (2) arterial baroreceptor and cardiopulmonary baroreceptor inputs which lowered threshold and increased gain, and (3) cardiopulmonary baroreceptor and chemoreceptor inputs which increased gain and heart period range. Baroreflex-independent shifts in plateau levels were due to increased chemoreceptor and lung inflation receptor activity. The baroreflex-dependent and the baroreflex-independent components of the heart period response were mediated (as in spontaneously breathing rabbits) through both suprapontine centers and pontine centers.

Autonomic and non-autonomic circulatory components in essential hypertension in man

The circulatory effects of blocking cardiac and peripheral autonomic effectors were studied in 32 subjects with established essential hypertension, and in 15 normotensives. The mean resting arterial pressure, heart rate and total peripheral resistance index (TPRI) were significantly higher in the hypertensives, but cardiac index was the same in both groups. In subjects with blocked cardiac effectors (atropine + beta-blocking drugs, i.v.) the sympathetic constrictor effects on TPRI were estimated from the changes after giving i.v. guanethidine + phentolamine. The autonomic component of TPRI was higher in hypertensives than in normotensives. The residual resistance after `total' autonomic block (non-autonomic TPRI) was higher in hypertensives, accounting for 60 to 80% of the initial difference in resting TPRI between the two groups. With an increase in non-autonomic TPRI, the increased autonomic TPRI effect in hypertension is not necessarily due to increased sympathetic nerve activity. Vagal and cardiac sympathetic effects on heart rate were compared in the two groups. Each estimate was based on the average of the responses to the appropriate blocking drug (1) in subjects not previously given a blocking drug, and (2) in subjects with the other cardiac effector pathway already blocked. The higher heart rate in established hypertension was predominantly due to change in vagal rather than cardiac sympathetic effects.

Pulmonary contusion in children due to rubber bullet injuries

Three cases of pulmonary contusion occurred in children as a result of injuries from "rubber bullets." Radiological changes were evident soon after the injury, and in one case these persisted for two months. Symptoms disappeared quickly in all three cases.

Central nervous system control of baroreceptor reflexes in the rabbit

Aortic and inferior vena caval balloons were used to alter mean arterial blood pressure, pulse pressure ( PP ), and right atrial pressure ( RAP ) in unanesthetized rabbits and to reflexly evoke changes in heart period (pulse interval). Curves relating mean arterial blood pressure to heart period were compared in different groups of rabbits at similar Δ PP and Δ RAP . Median blood pressure ( BP 50 ), average gain (G), and heart period range (maximum to minimum heart period) were calculated from the S-shaped curves. The reflex was evoked from arterial baroreceptors and probably from cardiac and pulmonary baroreceptors. Curves relating mean arterial blood pressure and heart period differed with regard to BP 50 and G in sham-operated, thalamic, and pontine rabbits, indicating that suprabulbar centers normally play a role in the reflex. Curves from sham-operated and pontine rabbits treated with atropine also differed, suggesting suprabulbar control of sympathetic effectors. In intact rabbits, forebrain and diencephalic centers caused vagal and sympathetic effectors to respond over the same arterial blood pressure range, but, in pontine rabbits, the effectors responded over dissimilar ranges. In intact rabbits, changes in mean arterial blood pressure evoked reciprocal and nearly equal changes in vagal and sympathetic effectors, but, in pontine rabbits, a given pressure change altered heart period predominantly through one effector. In sham-operated rabbits, vagal effects on heart period were lower by a constant amount at every level of mean arterial blood pressure than they were in pontine rabbits, suggesting that suprabulbar centers exerted a tonic inhibitory effect on vagal motoneurons not involved in the reflex.

Bulbar and suprabulbar control of the cardiovascular autonomic effects during arterial hypoxia in the rabbit

The autonomic effects on heart rate, portal, renal, cutaneous and muscle blood flows were studied during approximately constant severe arterial hypoxia in unanesthetized sham-operated, thalamic and pontine rabbits, 3 hours after operations conducted under halothane anesthesia. Neural and adrenal effects were estimated by comparing the responses of different groups of animals: (a) with all neural effectors intact, (b) after adrenalectomy, (c) after selective and (d) after complete pharmacological block of neural effector mechanisms. In pontine animals hypoxia greatly increased cardiac sympathetic activity and seemed to evoke a greater release of adrenal catecholamine (epinephrine) than in other preparations, but caused significant neural peripheral sympathetic constrictor effects in only the portal bed. In thalamic animals, hypoxia caused reflex bradycardia, striking neural constrictor effects in the portal, renal and muscle beds, and cutaneous dilatation. There was little evidence of an increase in epinephrine secretion. It is suggested that there is an inhibitory pathway between diencephalon and bulb that limits the release of epinephrine. Sham-operated animals exposed to hypoxia secreted epinephrine which played an important role in the total reflex response; this group had similar cardioinhibitory and cutaneous effects to thalamic animals, but a more rapid onset of portal and renal constriction and a marked increase in muscle blood flow. The sympathetic responses of the different preparations resulted in different rates of metabolic H + ion production.