Pulse

The pulse is the rhythmic expansion and contraction of an artery. It occurs in response to the cardiac cycle, which is the sequence of a heartbeat. This movement is a vital sign that provides information about a person's cardiovascular health. By feeling the pulse, a trained observer can estimate systolic blood pressure. Systole is the phase where the heart contracts and pushes blood out. The pressure between these beats is called diastolic pressure. Diastolic pressure is non-palpable, meaning it cannot be felt by touch.

To understand the mechanism, we must look at how pressure waves move through the body. During systole, the heart generates pressure waves that travel through the arterial system. These waves move the walls of the arteries. For a pulse to be palpable, the arterial boundaries must be pliable and compliant. This means the vessels must be able to stretch and move easily. When these conditions are met, a detectable pressure wave is created. In intensive care settings, doctors often use an invasive technique to see these waves. Since the 1970s, they have used arterial catheters connected to a transducer and an oscilloscope.

There are many different sites where a pulse can be detected. These are divided into central pulses and peripheral pulses. Central pulses include the carotid artery in the neck and the femoral artery in the groin. Peripheral pulses are found further from the heart. Common sites include the radial artery at the wrist and the ulnar artery. In infants and very young children, the brachial artery in the upper arm is often used. Other locations include the popliteal artery behind the knee and the dorsalis pedis artery on the foot.

Medical professionals categorize the pulse by its rate, rhythm, volume, and force. The rate is measured in beats per minute, or BPM. While the pulse and heartbeat are related, they are not identical. There is a delay called the pulse transit time between the heartbeat and the pulse. A pulse deficit occurs when there is a difference between the heart rate and the pulse rate. This is often seen in conditions like atrial fibrillation. Rhythm refers to how regular the beats are. An irregular rhythm might be caused by ectopic beats or atrial flutter.

Volume and force provide deeper details about the state of the circulatory system. Volume, also called amplitude, is the degree of arterial expansion. A hypokinetic pulse is weak and may signify low cardiac output. Conversely, a hyperkinetic pulse is bounding and signifies high pulse pressure. This can happen during a fever or due to increased cardiac output. Force is a rough indication of systolic blood pressure. Tension is determined by the mean arterial blood pressure. A high tension pulse feels rigid even between the actual beats.

History shows that humans have studied these rhythms for centuries. Claudius Galen was perhaps the first physiologist to describe the pulse. Since his time, technology has advanced significantly. We can now use pulse oximetry to observe blood indirectly. This technology uses light absorbances to look at hemoglobin. It compares oxygenated hemoglobin to deoxygenated hemoglobin using mathematical ratios. This allows for a non-invasive way to monitor blood oxygen levels.

Specific pulse patterns can also signal serious medical conditions. For example, pulsus alternans is a pattern of strong and weak pulses. This is an ominous sign of progressive systolic heart failure. Another pattern is the dicrotic pulse, which has two beats per cardiac cycle. This can be caused by reflected waves from the lower extremities. There is also pulsus paradoxus, where some beats cannot be detected during inspiration. This can indicate a condition called cardiac tamponade. Understanding these complex patterns helps doctors diagnose specific issues within the heart and vessels.