ABSTRACT. The purpose of this study is to describe the conscious animals. The unaltered integrated baroreflex response developmental course of arterial baroreflex control of heart can be fully evaluated only in a conscious state because anesthesia rate in swine. Tests of baroreflex function were performed depresses the reflex at multiple peripheral and central sites (17, with eight conscious piglets serially over their first 2 mo 18). of life. Systemic blood pressure was raised with phenylephrine (pressor test) and lowered with nitroprusside (depressor test), and stimulus-response curves relating heart MATERIALS AND METHODS rate to mean blood pressure were constructed. Baroreflex ~~i~~l preparation, ~~~~r were with eight sensitivity was determined as the slope of the linear portion farm piglets from three litters (spotted China-Poland breed). The of the curve. Baroreflex sensitivity decreased with increas-animals were weaned and brought to the research facility at 3 d ing age. ~aroreflex sensitivity was not different between of age. Chronic indwelling vascular catheters (Vascular-Accesspressor and tests except when the piglets were Ports, Access Technologies, Skokie, IL) were placed in the right >52 d old and sensitivity was greater with the depressor common carotid artery and left internal jugular vein as previtest. The heart rates at and and ously described (19). Briefly, Vascular-Access-Ports consist of a therefore the heart rate response range, shifted lower catheter and a reservoir that are totally implanted in the subcuheart rates with increasing age. This shift was more than taneous tissue. The reservoir contains a self-sealing rubber sepcan be for by the simultaneousl~ decreasing tum that is pierced by a deflected-point Huber needle to gain resting heart rate. (Pediatr Res 27: [148][149][150][151][152] 1989) access to the vascular system. The ports were placed in the animals under general halothane anesthesia using aseptic surgical technique. Two reservoirs were placed in the dorso-lateral neck, one on each side of the mid-line. The catheters were tunneled to ~~~~i~l baroreceptors maintain hemostasis in the the ipsilateral ventral neck and inserted into either the carotid system by buffering acute alterations in arterial blood pressure artery or jugular vein. For arterial access, the right common with adjustments in cardiac output and peripheral vascular re-carotid artery was cannulated with a 3.5 Fr. polyurethane cathsistance. These acute alterations in blood pressure happen with eter and the tip was passed to the For common occurrences such as changes in posture, emotions, and access, the left internal jugular vein was cannulated with a 5 Fr. exercise, and the ability of the newborn organism to tolerate silicone catheter and the tip was passed to the right atrium. The these and other stressful disturbances depends on the functional carotid catheter was secured in the vessel with non-occluding state of the arterial baroreflex. several investigators have dem-ligatures, but because of its relatively lar...