Murmurs Arising from Ductus Arteriosus in Normal Newborn Swine

Abstract

The natural history of murmurs arising from the ductus arteriosus was investigated in normal newborn swine and compared with observations in other animals and infants at term. Ausenltation of 206 swine examined between birth and two weeks of age revealed a high incidence of continuous murmurs in the first six hours of life, crescendo systolic murmurs in 5% to 10% of animals during the first 24 hours and early systolic murmurs in a large proportion of the animals throughout the first week. Absence of a murmur was rare one to two hours after birth but, by 24 hours, less than 50% of the swine had murmurs of any type and after one week only one of 34 animals studied had a murmur. The continuous murmur was often preceded or followed by a crescendo systolic or early systolic murmur and it is proposed that all three murmurs arise from the ductus arteriosus under different conditions.Internal sound recordings with a phonocatheter in the thoracic aorta demonstrated a systolic murmur loudest at the orifice of the ductus arteriosus in all swine in the first six hours of life and in a decreasing proportion of animals thereafter. Evidence is presented to suggest that this murmur is closely linked to patency of the ductus arteriosus but is different in origin from the murmur normally heard on auscultation of the chest. In four animals under six hours of age the phonocatheter passed through the ductus into the pulmonary artery and a continuous murmur was recorded. In two older swine the phono-catheter traversed the ductus but in these cases the murmur in the main pulmonary artery was confined to systole.Since the occurrence of the different murmurs could not be satisfatorily explained on the basis of the systolic pressure gradient across the ductus nor on the basis of the anatomical size of the ductus at necropsy, it is postulated that the type of murmur generated is a reflection of the degree of narrowing of the lumen of the ductus produced by active constriction of its muscular wall during life.