Blood Pressure Measurement Techniques

Questions and Answers

What does diastolic pressure measure?

Pressure after contraction and before the next contraction (correct)

Pressure during heart contraction

Average blood pressure over time

Pressure within the arteries during rest

What happens to the baroreceptors when there is a decrease in arterial pressure?

They decrease the stretch on the walls of the carotid sinus. (correct)

They maintain a constant level of firing regardless of pressure.

They increase the firing rate of the carotid sinus nerve.

They stimulate the sympathetic nervous system to lower heart rate.

What primary function do baroreceptors serve in relation to blood pressure?

They enhance sympathetic nervous system activity.

They regulate blood pressure over long durations.

They provide feedback to the autonomic nervous system. (correct)

They detect increases in heart rate.

Which device is used for manual measurement of blood pressure?

Aneroid or mercury sphygmomanometer Signup and view all the answers

What is the primary mechanism for short-term regulation of blood pressure?

Baroreceptor-mediated neurally regulated mechanism Signup and view all the answers

What neural response is triggered when baroreceptors detect decreased arterial pressure?

Increased heart rate and cardiac contractility. Signup and view all the answers

Why can baroreceptors not regulate blood pressure over the long term?

Their mechanism resets once normal blood pressure is restored. Signup and view all the answers

Where are baroreceptors located that are responsible for detecting changes in blood pressure?

In the Arch of the aorta and Carotid sinus Signup and view all the answers

What percentage of patients might experience inaccuracy with a digital blood pressure monitor?

5-15% Signup and view all the answers

What is the typical set point for mean arterial pressure in the vasomotor centre?

100 mmHg Signup and view all the answers

Study Notes

Blood Pressure Measurement

Diastolic pressure is the second number in blood pressure readings, indicating pressure after heart contraction and before the next contraction (80 mmHg example).
Measurement methods include:
- Manual: Using an aneroid or mercury sphygmomanometer.
- Digital: Automated monitors using oscillometric sphygmomanometers, which may be inaccurate in 5-15% of patients.
- Invasive: Direct measurement of arterial pressure through cannulation of arteries (typically radial), using non-compressible tubing with heparinized saline.

Regulation of Arterial Pressure

Regulation mechanisms include:
- Short-Term (Neurally Mediated Baroreceptor Mechanism): Rapid adjustments by the autonomic nervous system (ANS).
- Long-Term (Hormonal Regulation): Involves the renin-angiotensin-aldosterone system (RAAS).

Short-Term Blood Pressure Regulation

Baroreceptors in the aortic arch and carotid sinus detect changes in blood pressure via stretch receptors.
Increased arterial pressure triggers negative feedback to the ANS, decreasing heart rate and contractility, leading to lowered blood pressure.
Decreased arterial pressure causes sympathetic stimulation, increasing heart rate and contractility to raise blood pressure.
The baroreceptor reflex offers minute-to-minute regulation of blood pressure.

Baroreceptor Reflex Mechanism

Decrease in Arterial Pressure:
- Decreased stretch on carotid sinus walls reduces signals sent to the CNS via Hering's nerve (a branch of cranial nerve IX).
- If mean arterial pressure drops below 100 mmHg:
  - Decreased parasympathetic outflow and increased sympathetic outflow raise blood pressure by:
    - Increasing heart rate (decreased vagal tone).
    - Enhancing contractility and stroke volume.
    - Promoting vasoconstriction of arterioles and veins.
    - Increasing total peripheral resistance (TPR) and venous return, increasing cardiac output through the Frank–Starling mechanism.
Example: Valsalva maneuver tests baroreceptor function; a significant heart rate increase indicates intact reflex mechanism.

Long-Term Blood Pressure Regulation

Key physiological mechanisms include:
- Renin-Angiotensin-Aldosterone System (RAAS): Controls blood pressure by regulating fluid balance.
- Vasopressin (ADH): Promotes water retention.
- Atrial Natriuretic Peptide (ANP): Promotes sodium excretion.

Renin-Angiotensin-Aldosterone System (RAAS)

Renin is released from juxtaglomerular cells in response to:
- Sympathetic stimulation.
- Reduced sodium delivery to the distal convoluted tubule.
- Decreased renal blood flow.
Renin converts angiotensinogen (from the liver) to angiotensin I, which converts to angiotensin II (vasoconstrictor) via ACE.
Angiotensin II promotes sodium reabsorption and aldosterone secretion, leading to water retention and increased blood volume and pressure.
ACE inhibitors and angiotensin receptor blockers are used to lower blood pressure.

Clinical Relevance - Hypertension

Hypertension is a sustained increase in blood pressure and can be primary (unknown cause) or secondary to conditions like chronic renal disease.
It causes vascular damage, leading to atherosclerosis, thromboembolism (risk of MI or stroke), and aneurysms, while also increasing the heart's afterload.

Description

This quiz covers the fundamentals of blood pressure measurement, focusing on the diastolic pressure and the differences between aneroid and mercury sphygmomanometers. Additionally, it explores digital measurement techniques using automated monitors. Test your knowledge of these vital healthcare tools.