Application of the hand. Palpation. In conditions of health and in quietude the hand applied on the side of the chest, close behind the left elbow only just perceives the beat of the heart with each contraction. If the animal is excited whether from fear, joy or physical suffering the heart’s impulse becomes more powerful and by this alone the state of its function may be very satisfactorily ascertained. The impulse is strong in all active fevers and extensive inflammations of important organs, but it is especially marked in diseases of the heart and lungs. Irregularity in the force of successive beats is seen in various heart diseases and debilitated conditions are recognized in the same way.
Any want of harmony between the heart’s action and the pulse may be observed by laying the right hand over the region of the heart and applying the fingers of the left on the radial artery. In debility and especially if from a deficiency of blood the violent or tumultuous action of the heart contrasts strangely with the weak jerking and compressible pulse. The same symptoms are noticed when the valves of the heart close their orifices imperfectly. In convalescence from lung diseases and in certain diseases of the heart a beat may be felt by the right hand for which no corresponding pulsation is felt in the radial artery by the left.
When the heart is hypertrophied the impulse is stronger and is associated with a full, strong, and rolling pulse. When it is atrophied the impulse on the chest and pulse beat are equally weak. When water exists in the pericardium the heart strikes the ribs with less force.
Sounds of the Heart. Synchronous with each beat of the heart two distinct sounds are heard, separated by a short interval, inappreciable to most ears, and followed by a period of silence. These sounds are distinct alike in character and duration. The first sound is dull and prolonged; the second is short and quick. Some idea of these sounds may be formed by the pronunciation of the two syllables, lub—tip, but an acquaintance with the sounds themselves is essential to a correct conception of them. The period of time occupied by the first sound is double that taken up by the second and in man and the smaller quadrupeds the subsequent period of silence is of equal duration with the second sound. Dividing the time belonging to one revolution of the heart into four equal periods the first two are taken up by the first sound, the third by the second sound and the fourth by the interval of silence. In the horse the silence is more prolonged, and occupies the entire latter half of the period of a revolution. The relations stand thus:—the first sound extends over two-sixths of the time, the second sound over one-sixth, and the silence over three-sixths.
The first sound, synchronous with the beat of the heart against the ribs corresponds also in point of time with the contraction of the ventricles, the closure and tension of the auriculo-ventricular valves and the rush of the blood into the great arteries. The second sound corresponds to the reflux of blood in the arteries and the closure of the valves between them and the heart. The period of silence represents the period of rest during which the heart is being filled from the veins.
In the horse, at rest, the first is the only sound that can be distinctly heard in many cases, but during the excitement of exercise, or in febrile conditions the second is sufficiently apparent and any deviation from the natural character is easily noted.
These sounds are most distinct over the lower end of the fifth and sixth ribs on the left side, but they may be heard distinctly behind the middle of the shoulder on either side when the corresponding limb is advanced. In birds they may be heard beneath the wings but above all and most clearly over the breastbone.
In disease these sounds may be heard in unusual situations, they may be altered in force duration or rythm, or they may be associated with other sounds or superseded by them.
The sounds may be heard in new situations, in displacements of the heart from tumors or effusions in the chest, structural changes in the lungs, pleuræ, or pericardium, aneurism of the aorta, etc., etc.
The heart sounds are clearly heard over any part of the chest when the lung tissue intervening between that part of the surface and the heart is solid (hepatized). They are heard distinctly behind the median part of the right shoulder, when liquid effusion into the left pleural sac has displaced the heart to the right; and when the right cavities of the heart are extensively dilated as exists so commonly in the advanced stages of “heaves.”