Hemodynamic Observations During Birth of the Lamb

Abstract

In the process of birth, very complex circulatory changes occur during the transition from fetal to neonatal states. Because of the rapidity of these important changes and the dangers involved in their study, observations of the human infant have been limited. Studies of some of the physiologic changes that occur at birth of the newborn lamb have been performed by Barcroft,1 Barron,2 Dawes,3-11 Born,12-15 and others.16-18 The findings of these workers have provided insight into the circulatory changes at birth of the human infant. In their investigations, sequential observations of the birth of the unanesthetized lamb have been few. It is the purpose of this paper to describe the sequential hemodynamic changes during the birth of the unanesthetized lamb delivered by hysterotomy when the lamb is subjected to controlled stimuli similar to those encountered during birth. Materials and MethodsExperiments were performed on 18 lambs from 13 ewes. The ewes were given spinal anesthesia, 2 cc. of tetracaine (Pontocaine) hydrochloride in¬ jected into the lumbar region, with the ewe stand¬ ing in her usual manner. As the anesthesia becomes effective, the ewe's lower extremities be¬ come immobile. The neck and abdomen were then prepared by clipping. The ewe was then placed in the supine position in a specially built cradle which encloses the animal except for the neck and lower extremities which are brought out through U-shaped slots. Through a small cannula introduced into the external jugular vein, the blood was treated with heparin sodium. A tracheostomy was done under local anesthesia (lidocaine hydrochloride 2%) and a soft rubber tracheostomy tube was introduced to guarantee control of respiration. The extremities were tied securely with rope. Hys¬ terotomy was performed through a lower abdomi¬ nal incision avoiding the larger mammary veins.The lamb was cautiously delivered, preferablyhead first ; and the head was immediately capped with a saline-filled rubber glove. The lamb was then removed from the mother's abdomen and placed on a separate wooden platform attached to a Mayo stand. A U-shaped wedge in the platform protects the cord from undesirable pressure. The lamb was placed on its right side on this plat¬ form with its abdomen bridging the wedge. The lax umbilical cord lies in this wedge immediately above the uterus. One per cent lidocaine hydro¬ chloride was sprayed directly on the cord inter¬ mittently throughout the experiment to minimize constriction due to incidental trauma.After the lamb was secured to the platform, simultaneous incisions were made in the left jugular region and the right femoral triangle. Catheters were introduced through the left external jugular vein and through the right femoral artery. In this manner, samples were obtained from the pul¬ monary artery, right ventricle, and right atrium by way of the external jugular vein, and from the aorta, left ventricle, and left atrium by way of the femoral arteo'. For several experiments, a cannula was introduced also into the right femoral vein and...

Effect of Oxygen and Umbilical Cord Clamping on Closure of the Ductus Arteriosus in the Guinea‐Pig and the Rat. Studies on Closure of the Ductus Arteriosus. VI

“…This is in agreriiient with earlier reports of the stimulating effect on breathing of hypoxia I ci-05~. Killich and Hugget 1954) and of umbilical cord clamping (Harned et al 1961 , . The lowering of the heart rate observed in newborn rats kept in an atmosphere of reducr-bd oxygen is similar to observations on lambs in utero (Assali, Holm and Sehgal 1962 I . Lowering of the heart rate in newborn rats also follows a decrease in the en\-ircmniental teniprrature (Fairfield 1948). A decrease in the temperature from 37 C: to 30' C reduced the heart rate from 310 to 210 cycles per minute, without an) dfect on the ductal closure (Hornblad and Larsson 196713).…”

Measuring Physiological Changes during the Transition to Life after Birth

“…However, as FBM are restricted to levels of fetal activity, they are discontinuous, occurring <50% of the time. Further, although most FBM generate transpulmonary pressures of <20 cm H 2 O, fetuses commonly can make large inspiratory efforts (>30 cm H 2 O) [9,10], demonstrating that they are capable of generating transpulmonary pressures needed to aerate the lungs after birth [7]. The mechanisms controlling the switch to continuous breathing after birth are currently unknown.…”

“…Data on this matter are scarce, although animal studies have shown that cooling lambs at birth elicits normal quiet breathing, but no large initial gasps [8]. In contrast, painful stimuli elicit gasps in unanesthetized lambs with an intact umbilical cord, but not sustained respiratory movements [9]. …”