Blood Pressure and Vascular Health

Blood Pressure

• Blood Pressure (BP) is the pressure exerted by blood on the vessel walls of the circulatory system
• BP is a vital sign and is modified by physiological conditions
• BP varies over time and locations in the circulatory system
• BP is highest at the point of maximal cardiac output and lowest between contractions
• Systolic BP is the maximum arterial pressure during contraction of the heart
• Diastolic BP is the lowest pressure within the arterial blood stream
• Mean arterial pressure (MAP) is the average blood pressure in an individual during a single cardiac cycle
• Cardiac output: the volume of blood being pumped by the heart per unit time (5~ 6 L/min)

Arteriosclerosis

• Hardening, stiffening, and loss of elasticity of the walls of arteries
• Restricts blood flow to the body
• Can lead to severe health risks

Atherosclerosis

• A form of arteriosclerosis
• Artery narrowing due to plaque build-up (sticky deposits)
• Plaque is a small, distinct, raised patch resulting from local damage or deposition of material

Blood Pressure Measurement History

• Invasive BP measurement:
  • Stephen Hales (1733), intra-arterial BP of a horse body with a glass tube
• Non-invasive BP measurement:
  • N.C. Korotkoff (1905), Auscultation of brachial artery, still used today

Blood Pressure Value

• Two main factors influencing BP:
  • Cardiac output: More blood volume results in higher BP
  • Resistance of blood flow: Higher resistance causes higher BP
    • Vessel diameter, blood viscosity, and smoothness of blood vessel wall affect resistance

BP Measurement: Invasive vs. Non-invasive

• Invasive BP:
  • Invasive, used for continuous monitoring.
  • Requires expertise and specialized equipment.
  • Examples: intra-arterial pressure catheter and arterial line
• Non-invasive BP:
  • Less invasive, widely used.
  • Requires human attention, time-consuming.
  • Variation can result from medical staff attention
  • Examples: Auscultatory method, Oscillometric method

Oscillometric Method (Non-invasive)

• Based on blood flow oscillations during pulsation
• Uses a sphygmomanometer cuff and pressure sensor to observe cuff pressure oscillations
• Pressure sensor within the cuff detects pulsation of the artery wall as a pressure vibration
• Amplitude of the vibration provides the BP value
• Pros: Simple, reliable, can be used with hypotension and infants
• Cons: Motion artifact
• Most automated NIBP (non-invasive BP) devices use this method

Blood Carrying Oxygen

• Blood carries oxygen to organs
• Hemoglobin is the main way oxygen is carried in the blood
• Oxygen Saturation: Total amount of saturated hemoglobin (oxyhemoglobin) compared to unsatured hemoglobin (deoxyhemoglobin)
  • Indication of ventilation and gas exchange effectiveness in the lungs
  • Normal oxygen saturation values are 97% to 99% in a healthy individual

Pulse Oximeter

• Measures oxygen saturation (SpO2) in the body
• A device that shines light through tissue, measuring the amount of oxygen in the blood
• Used to assess oxygen levels in the blood
• Examples of usage: Operating room, Emergency room, ICU, and Home
• Normal SpO2 values are 97% to 99%

Pulse Oximetry Principle

• Uses two LED lights (650 nm and 805 nm) and a photodetector
• Red light is absorbed more by deoxygenated hemoglobin, and infrared light is absorbed more by oxygenated hemoglobin.
• The difference in absorption is used to calculate oxygen saturation.

Issues that Interfere with Pulse Oximetry

• Nail polishes
• CO binding to hemoglobin
• Toxins or disease conditions that alter normal hemoglobin levels and produce methemoglobin
• Low perfusion (blood flow)
• High levels of ambient light

Blood Chemistry Analyzers

• Used to assess various conditions and monitor organ function
• Analyze blood for electrolytes, minerals, and other chemicals including glucose, etc.
• Benchtop or cart-based devices
• Analyze samples of serum, plasma, urine, cerebrospinal fluid (CSF) and body fluids
• Can be used for point-of-care testing (POCT)

POCT Blood Analysis

• Point-of-care testing with smaller samples of blood providing faster results
• Performed at or near the patient's location, outside of clinical laboratories
• Smaller samples, quicker results, and used at the point of care

Glucometer Kits (Conventional & Modern)

• Conventional glucometers are handheld devices that require a finger prick.
• Modern glucometers are faster, more accurate, and painless.
• Some newer glucometers use non-invasive methods, which may eventually replace finger pricks

Glucometers

• Determine the approximate concentration of glucose in the blood
• Noninvasive are emerging
• Continuous Glucose Monitors (CGMs):
  • Disposable sensor placed under the skin, a transmitter, and a reader
  • Real-time measurements, reduce the need for frequent finger prick testing.
  • Less accurate than blood glucose readings as they measure in interstitial fluid, which lags behind blood levels

Components of Glucometer kit

• Lancet: Puncture the skin
• Test strips: Hold a droplet of blood and are inserted into the reader
• Calibration strip for each batch of test strips: For internal calibration
• Strip reader: Measures and displays blood glucose level

Blood Glucose levels

• Measured in mg/dL or mmol/L
• Normal blood glucose levels fluctuate
• Fasting blood glucose levels are usually measured.
  • Normal: < 110 mg/dL
  • Diabetic: > 126 mg/dL
• Hypoglycemia (low blood sugar):
  • Symptoms: Unsteadiness, perspiration, dizziness, rapid heart rate, confusion.
  • May lead to insulin shock (< 50 mg/dL)
• Hyperglycemia (high blood sugar):
  • Symptoms: Excess thirst, headache, blurred vision, fatigue.
  • Chronic hyperglycemia can lead to: impaired nerve function, vision problems, decreased healing ability.

Carotid Ultrasound for Blood Flow

• A non-invasive way to measure blood flow in the carotid arteries
• Uses sound waves to create images of the arteries
• Can measure blood flow velocity and direction
• Helps to diagnose carotid artery disease and assess the risk of stroke

Doppler Effect for Flow Measurements

• The change in frequency or wavelength of a wave when the observer is moving relative to the wave source.
• Used in ultrasound imaging to measure blood flow
• higher frequency shift = faster blood flow