Blood pressure measurement

Evolution of methods: from palpation to auscultation

Historically, the first non-invasive method for assessing blood pressure was proposed by Riva-Rocci in 1896. The physician inflated air into the cuff and palpated the pulse. This method allowed the determination of only systolic blood pressure (SBP) — by the moment pulse reappeared in the radial artery as the bladder was deflated.

In 1905, the Russian physician N.S. Korotkoff refined the approach by adding auscultation with a stethoscope to the cuff. Experimenting on dogs, he proved that if a large artery is compressed and then decompression is smoothly decreased, blood flow is accompanied by characteristic sounds. Today, this auscultatory approach is the global standard, and the sound phenomena are officially designated as Korotkoff sounds.

A direct method also exists (inserting a needle with a manometer directly into the vessel) — it is ideal in accuracy, but rarely used due to its invasiveness.

Korotkoff sounds and calculated parameters

The essence of the technique is registering the sounds produced by the relaxed vascular wall as the pulse wave passes during decompression. Five phases of sound phenomena are distinguished:

• Phase I: appearance of the first consistent taps. This is the key marker of SBP.
• Phase II: emergence of swishing murmurs.
• Phase III: maximum increase in loudness (the sound resembles a crunch).
• Phase IV: abrupt muffling, transitioning into a soft blowing sound.
• Phase V: complete disappearance of sounds. This is the primary marker of diastolic blood pressure (DBP).

The normal range is considered to be 100–140 mm Hg for systolic and 60–80 mm Hg for diastolic pressure. The difference between them forms the pulse pressure.

To assess hemodynamics, the mean arterial pressure is also used. It is calculated by the formula: Mean BP = DBP + (Pulse Pressure / 2).

Standard measurement technique (DAG-1)

To obtain reliable figures, it is essential to strictly follow a standardized algorithmic procedure.

1. Preparation. Caffeine and smoking should be avoided for an hour before the procedure. The measurement is taken 1–2 hours after a meal. Before the measurement, the patient must rest for at least 5 minutes. Talking during the process is strictly prohibited.
2. Cuff selection. The width of the pneumatic bladder must be at least 40% of the arm circumference. Using a cuff that is too narrow or short will falsely elevate the results.
3. Placement. The center of the bladder is positioned strictly over the palpated brachial artery, with the lower edge 2.5 cm above the antecubital fossa. One finger should easily pass between the fabric and the skin.
4. Preliminary palpation. Air is pumped until the pulse in the radial artery (a. radialis) disappears, an additional 30 mm Hg is added, and only from this point is auscultation initiated. This prevents painful over-inflation and errors.
5. Decompression. Air is released slowly — at a rate of 2 mm Hg per second. A faster release significantly reduces accuracy. The obtained values should be rounded to the nearest 2 mm Hg (according to the graduation interval of a modern aneroid manometer).

Difficulties and common errors in auscultation

In clinical practice, physicians frequently encounter non-standard situations that can distort the hemodynamic picture.

• Auscultatory gap. This is a temporary «silence» between phase I and phase II of Korotkoff sounds, which can last up to 40 mm Hg. If the pulse is not palpated before auscultation, the resumption of sounds can be mistakenly taken for the true SBP (underestimation) or lead to an overestimation of DBP.
• Pseudohypertension in the elderly. With age, the brachial artery undergoes sclerosis and becomes rigid. Excessive compression is required to occlude it, leading to a false diagnosis of hypertension. The problem can be suspected if, at a high cuff pressure (when sounds have already disappeared), the pulse at the wrist is still palpable.
• «Endless tone» phenomenon. Sounds do not disappear down to the zero mark. This is characteristic of states with high cardiac output: thyrotoxicosis, fever, pregnancy, aortic valve regurgitation. In such cases, the onset of phase IV (the moment of abrupt muffling) is taken as the DBP.
• Patients with a large arm circumference. Due to developed musculature or obesity, applying a standard cuff correctly is impossible. Measurements are performed using an enlarged cuff: BP is determined palpatorily on the forearm and auscultatorily in the antecubital fossa. If the difference exceeds 15 mm Hg, the palpatory result is considered correct.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of isolated systolic hypertension development
• Diagnostic significance of measuring blood pressure in the lower extremities in aortic coarctation
• Physiological factors influencing blood pressure variability (stress, circadian rhythms)
• Paradoxical pulse and drop in blood pressure during inspiration in pericardial pathologies
• Hemodynamic changes in various types of shock

Other topics in the "Cardiovascular system" section

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