The variations with respiration in effective right and left atrial pressures in the dog

Abstract

Opdyke & Brecher (1950) have described the effect of respiration on effective right and left atrial pressures in anaesthetized dogs. Like all previous workers, they had first to open the chest in order to cannulate the left atrium; but Opdyke & Brecher then closed the chest and reduced the pneumothorax to restore natural respiration. However, with the development of a technique for cannulating the left atrium through the trachea (ARlison & Linden, 1953) and its application to the recording of effective atrial pressures in the dog (Coleridge & Linden, 1953), it became possible to make a direct study of the respiratory changes in effective pressure in the two atria without the necessity of opening the chest. This paper reports the respiratory changes in atrial pressures recorded by this method. The results differ in several respects from the findings of Opdyke & Brecher (1950). The results will also be discussed in relation to the respiratory variations in the discharge of receptors situated in the atria or great veins near the heart. METHODSExperiments were performed on ten dogs; two were anaesthetized with ether and chloralose (0-1 g/kg intravenously) and the remainder, following premedication with morphine sulphate (3 mg/kg subcutaneously), were given intravenously 0-25 ml./kg of a 1:1 mixture of Dial Compound (allobarbitone-urethane, Ciba) and sodium pentobarbitone (Nembutal, Abbott Laboratories Ltd.) solutions, followed 1 hr later by morphine sulphate (1.5 mg/kg subcutaneously).Pressure recording. The animals were placed supine with their chests intact. Pressures were recorded simultaneously from the right and left atria, and the aorta; intrathoracic pressure was recorded from the right medial pleural space. The right atrium was cannulated through the right external jugular vein, the left atrium and the right medial pleural space were approached through the trachea, and the aorta was cannulated through the left carotid artery, which was ligated. The technique of cannulation and the optical manometers used for recording pressures have been described previously (Coleridge & Linden, 1954).Complete manometer systems had undamped natural frequencies of 180 c/s for the right atrial system, 120 c/s for the left atrial system and 200-400 c/s for the arterial pressure recording system;

Mechanism of Pulsus Paradoxus in Clinical Shock*

“…Although PA blood flow rises during normal inspiration, the concomitant increase in the capacity of the pulmonary vascular bed usually results in a slight decrease in left heart filling (13)(14)(15). This hemodynamic effect of inspiration superimposed on the transmission of negative inspiratory intrathoracic pressure to the aorta usually produces a slight inspiratory fall in arterial pressure.…”