Makindo Medical Notes

How to Measure BP Properly

• Preparing the Patient: Patients should be seated quietly for 5 minutes in a chair, with their feet on the floor and their arm supported at heart level.
• Proper Cuff Placement: Use the correct size cuff. A cuff that is too small will overestimate BP. The blood pressure cuff’s bladder should encircle at least 80% of the arm. The bladder should be centered over the brachial artery, and the cuff applied snugly.
• Estimating Systolic Pressure: Inflate the cuff while palpating the brachial artery until the pulse disappears. This provides an estimate of systolic pressure.
• Measuring Blood Pressure: Inflate the cuff to 20–30 mm Hg above the estimated systolic pressure, then place the stethoscope over the brachial artery. Deflate the cuff at a rate of 2 mm Hg per second.
• Identifying Systolic and Diastolic Pressure:
  • Systolic pressure: The appearance of repetitive sounds (Korotkoff phase 1).
  • Diastolic pressure: Usually the disappearance of sounds (Korotkoff phase 5). In some individuals (e.g., pregnant women), sounds are present until the zero point. In this case, use the muffling of sounds, Korotkoff phase 4.
• Recording the Measurement: Record the pressure, patient position (e.g., seated), arm used, and cuff size. Obtain two readings, separated by at least 30 seconds, and average them.

Blood Pressure in Humans

• Arterial Pulse Waveform: The arterial pulse waveform is generated as the heart pumps blood into the arteries, creating a percussion wave that travels along the artery at a much higher speed than the actual blood flow. The waveform includes a distinct feature called the dicrotic notch, which signifies the closure of the aortic valve.
• Blood Pressure Measurement: Blood pressure is commonly measured with an inflatable cuff. When inflated above systolic pressure, it occludes arterial blood flow. As the cuff is gradually deflated, a stethoscope detects a series of sounds, known as Korotkov sounds, to determine systolic and diastolic pressures.
• Korotkov Sounds:
  • Phase 1 (Systolic): The first knocking sound, heard as the cuff pressure drops to match the arterial systolic pressure.
  • Phase 5 (Diastolic): The point at which the sound disappears, indicating the diastolic pressure as the cuff deflates.

Clinical Findings

• Hypertension: Defined as blood pressure above 140/90 mmHg.
• Pulse Pressure: Calculated as the difference between systolic and diastolic pressure.
• Aortic Stenosis: Characterized by a low pulse pressure due to restricted aortic valve opening.
• Aortic Regurgitation: Leads to a high pulse pressure due to backflow through the aortic valve.
• Blood Pressure Differences Between Arms:
  • A right arm pressure > left arm pressure by more than 20 mmHg may suggest stenosis of the left subclavian artery, potentially from dissection or atheroma.
  • A left arm pressure > right arm pressure by more than 20 mmHg could indicate right subclavian artery stenosis.
  • A significant difference between arm (brachial) and ankle pressures may suggest peripheral vascular disease or a coarctation of the aorta.
• Normal Variation: A slight difference of 5-10 mmHg between the right and left arms is typical in healthy individuals.

The biggest drop in BP is across the arterioles which exact the most control

Control of Blood Pressure

• Nervous System: Blood pressure is regulated by the autonomic nervous system (ANS) through baroreceptors and chemoreceptors.
  • Baroreceptors: Located in the carotid arteries and aorta, they detect changes in blood pressure and send signals to the brain to adjust heart rate and vascular resistance.
  • Sympathetic Nervous System: In response to low blood pressure, the sympathetic system increases heart rate and constricts blood vessels, raising blood pressure.
  • Parasympathetic Nervous System: In high blood pressure situations, parasympathetic signals decrease heart rate and promote vasodilation.
• Hormonal Control: Various hormones help to regulate blood pressure:
  • Renin-Angiotensin-Aldosterone System (RAAS): Activated by low blood pressure or blood volume. Renin, released by the kidneys, converts angiotensinogen to angiotensin I, which becomes angiotensin II in the lungs. Angiotensin II constricts blood vessels and stimulates aldosterone release to retain sodium and water, increasing blood volume and pressure.
  • Antidiuretic Hormone (ADH): Also known as vasopressin, ADH promotes water reabsorption in the kidneys, increasing blood volume and pressure.
  • Atrial Natriuretic Peptide (ANP): Released from the heart when blood pressure is high, ANP promotes sodium and water excretion, reducing blood volume and pressure.
• Kidneys: Play a key role in long-term regulation of blood pressure by adjusting blood volume. Through mechanisms like RAAS, kidneys can control sodium and water balance, influencing overall blood pressure.