Intracardiac Pressure

INTRACARDIAC PRESSURE is measured in animals: with an intact chest using a cardiac catheter (Chauveau and Marey) introduced through a cervical blood vessel into one or another cavity of the heart (except the left atrium, which is inaccessible to this method), and with an opened chest by introducing the catheter directly into the atrium or ventricle. The other end of the catheter is connected to a manometer. The values of the maximum intracardiac pressure in different cavities of the heart with an intact chest were obtained as follows: in the dog, in the left ventricle 174–234 mm of mercury, in the right 28–72 mm (Jager); in the cat, in the left ventricle 250 mm, in the right 40–50 mm (Piper); in the rabbit, in the left ventricle 174 mm, in the right 30 mm (Tigerstedt). In the atria, the pressure is significantly lower: in the cat, from 5 to 10 mm of mercury, according to Piper. The figures obtained by Chauveau and Marey for the horse (in the left ventricle 95–140 mm) are considered too low by Tigerstedt. The magnitude of the maximum intracardiac pressure increases with an increase in vascular resistance (adrenaline). The minimum intracardiac pressure is lower than atmospheric. Thus, Goltz and Gaule at the beginning of diastole found a pressure of up to -30 mm in the left ventricle of a dog, and Tigerstedt found up to -6 mm of mercury in the left ventricle of a rabbit. Negative pressure promotes the filling of the heart with blood during diastole. To record fluctuations in intracardiac pressure, an elastic manometer connected to the heart cavity is equipped with writing devices or a mirror that records its fluctuations on photographic paper (Straub, Wiggers). In Garten's apparatus, the fluctuations of the manometer change the strength of the current passing through a ZnSO₄ solution and are recorded by a string galvanometer. The pressure curve in the ventricles has the following features: a small rise corresponding to atrial systole; then a steep and high rise at the beginning of ventricular systole. Before the start of this rise, there is sometimes a more sloping rise, the so-called intersystole, which depends, according to Tigerstedt, on the elastic collapse of the stretched walls of the ventricle after the end of atrial systole. During ventricular systole, the pressure remains at approximately the same height (plateau), increasing only slightly if vascular resistance is significant, or decreasing slightly if resistance is small. At the end of systole, the pressure curve goes steeply downward, and on the descending limb, there is often a notch due to the invagination of the semilunar valves. The atrial pressure curve does not have a plateau during systole (low ventricular resistance); during diastole, the pressure gradually increases due to the filling of the atria with blood.