Dynamics and Propagation in the Vascular Bed
As the pulse wave propagates from the heart to the periphery, the following phenomena are observed:
- Pressure attenuation — pressure oscillations gradually decrease.
- Peripheral pulse amplification — the amplitude of each pulse phase in peripheral arteries increases.
- Pulse disappearance — the mechanical oscillation completely fades out in arterioles. The pulse is absent in capillaries, venules, as well as small and medium veins.
Components of the Sphygmogram
To study the pulse wave, sphygmography is used—a method for the graphical recording of the arterial pulse. The sphygmogram features the following primary elements or waves:
- Anacrotische wave (anacrote).
- Catacrotische wave (catacrote).
- Incisure (dicrotic notch).
- Dicrotic wave.
Role in the Baroreceptor Reflex
The pulse wave participates in the pressor-depressor reflex. The chain of events is as follows:
- A positive inotropic effect leads to an increase in cardiac output.
- The pulse wave stimulates the baroreceptors of the aortic arch and carotid sinuses.
- Afferent signaling to the nucleus tractus solitarii (NTS) increases.
- Secondarily, the tone of the vagus nerve nucleus increases.
Clinical Significance: Pulse Deficit
During rhythm disturbances, particularly in atrial fibrillation, a pulse deficit (pulsus deficiens) may occur. This is the difference between the heart rate (HR) determined by auscultation and the pulse rate determined by palpation at a peripheral artery, such as the radial artery.
- Mechanism: Diastolic pauses of varying duration lead to inconsistent left ventricular filling and fluctuations in stroke volume. During some contractions, the systolic output is so small that the pulse wave does not reach the periphery and cannot be palpated.
- Clinical Presentation: The patient may experience palpitations and skipped beats. On palpation, the pulse is irregular (arrhythmic), and the pulse waves vary in volume, making rate calculation difficult.
- Calculation Example: If the auscultatory heart rate is 90 bpm and only 72 beats are palpated at the radial artery, the pulse deficit is 18.
Artificial Pulse Wave in Resuscitation
During clinical death, an artificial pulse wave is generated via closed-chest cardiac massage.
- Mechanism: The heart is compressed between the sternum and the spine, forcing blood into the major vessels. To achieve this, the chest is energetically compressed by 1/3 of its anteroposterior diameter, or 3–5 cm. After compression, the hands are relaxed without losing contact with the chest to allow the heart chambers to refill with blood.
- Efficacy Monitoring: During chest compressions, an artificial pulse wave should be palpable in major vessels such as the carotid or femoral artery. Every 2–3 minutes, compressions are interrupted for a few seconds to check for the return of a spontaneous pulse.
- Pharmacological Support: Epinephrine (adrenaline) is administered to enhance the efficacy of chest compressions and stimulate spontaneous contractions. It increases vascular tone, improves blood flow, and enhances myocardial tone.