Understanding Blood Pressure

Blood Pressure (BP)

• It's the force exerted on blood by blood vessel walls.
• Compliance influences it, specifically the ability of blood vessel walls to stretch.
• Compliance: how much the blood vessel wall stretches in response to pressure
• Arteries and arterioles have low compliance and high resistance and generate a pressure gradient.
• Veins, venules, and capillaries have higher compliance and lower resistance.
• It fluctuates between maximum (systolic) and minimum (diastolic) pressure.
  • Systolic pressure measures 120 mm Hg.
  • Diastolic pressure measures 80 mm Hg.
• Average stays closer to diastolic values because more time is spent there.
• Mean Arterial Pressure (MAP) also stays consistent at rest.
• Pulse is the difference between systolic and diastolic pressure.

Blood Pressure Steps and Factors

• Laminar flow means blood flows smoothly.
• Turbulent flow causes vibrations and audible sounds.
• A sphygmomanometer is used to instrument BP.
• During BP measurement:
  • The cuff inflates to a pressure higher than systole, blocking the artery and resulting in no flow (silent).
  • Pressure is released, reaching systole pressure, there's turbulent flow, creating the first sound.
  • Release continues until blood flow returns to normal. Minimum pressure (diastole) is when the last sound is heard, indicating laminar flow.
• MAP equals Cardiac Output multiplied by Total Peripheral Resistance.
  • Cardiac Output is Stroke Volume multiplied by Cardiac Rate.
  • Total Peripheral Resistance depends on vessel diameter, viscosity, and vessel length.
• Factors influencing BP include Cardiac Output, Total Peripheral Resistance, and Blood Volume.

Cardiac Output and TPR

• Higher stroke volume or cardiac rate results in higher BP.
• Cardiac rate is regulated by the autonomic nervous system, specifically the sympathetic and parasympathetic divisions.
• Stroke volume is affected by factors such as the sympathetic division and venous return
  • Atrial pressure
  • Blood volume
  • Respiratory activity
  • Skeletal muscle contraction strength
• TPR depends on the vessel size and surface area and is inversely proportional to surface area.
• Arteries and arterioles need to maintain pressure with smaller surface areas.
• Arterioles' regulation comes from intrinsic and extrinsic factors.

Extrinsic vs Intrinsic Factors for Arterioles

• Extrinsic factors that adjust arteriole diameter:
  • Sympathetic nervous system maintains constant input for resistance, influencing the pressure gradient.
    • Increased sympathetic activity leads to vasoconstriction.
• Intrinsic factors that adjust their own diameter:
  • Passive stretching via autoregulation:
    • Stretch depends on blood volume.
    • More stretch causes vasoconstriction.
    • Less stretch causes vasodilation.
  • It is important to have enough pressure to get to the capillaries through vasodilation
    • Less blood volume to arterioles, causes less the stretch and vasodilation of the capillaries even with less pressure from blood flow
• Chemical changes: vasodilation
  • Histamine (allergies)
  • Nitric Oxide (NO)
• Temperature changes:
  • Heat causes vasodilation and increases blood flow.
  • Cold causes vasoconstriction and decreases blood flow.

Blood Volume and Pressures Overview

• Blood and plasma volume is the volume of blood in the system.
• Capillaries are exchange sites with fluid moving across the endothelial that is lining the interstitial space/fluid.
  • Pressure gradient decrease occurs from the arteriole to the venule
• Hydrostatic pressure is the pressure of any fluid enclosed in a space.
  • Capillary hydrostatic pressure is that exerted by blood on the capillary wall.
  • Interstitial fluid hydrostatic pressure is that exerted by interstitial fluid on capillaries.
• Osmotic colloid (oncotic) pressure is exerted by proteins that draw in the water
  • Plasma-colloid osmotic pressure occurs with plasma proteins in the blood that creates a contrast.
  • Movement of fluid is determined by net exchange.

Capillary Hydrostatic Pressure

• If capillary hydrostatic pressure is greater than colloidal osmotic pressure, fluid is pushed out (filtration)
  • Occurs when there's high capillary hydrostatic pressure and low interstitial hydrostatic and plasma-colloid pressures, typically at the arteriole end.
• If capillary hydrostatic pressure is less than colloidal osmotic pressure, fluid is brought in (reabsorption).
  • Occurs with low capillary hydrostatic and high interstitial hydrostatic and plasma colloid pressures at the venule end.
• If more fluid is filtered than reabsorbed, excess fluid is picked up by the lymphatic system, and edema may occur

Blood Volume Adjustments

• Proper blood pressure depends on blood volume.
• Short-term adjustments in response to hemorrhage:
  • Blood volume and pressure decreases, decreasing net outward force.
  • Inward pressure stays the same, leading to interstitial fluid being drawn in to maintain volume.
• Short-term adjustments to excessive fluid intake:
  • More fluid in capillaries increases the movement of fluid into the interstitial fluid.

Blood Pressure Monitoring and Regulation

• Changes in MAP trigger the Baroreceptor reflex in the heart and vessels.
• Information is relayed by different baroreceptors:
  • Carotid Sinus: vessels to the brain.
  • Aortic Arch Baroreceptors: major arterial trunks.
  • Information goes to the cardiovascular control center, which regulates sympathetic and parasympathetic activity.
• In response to an increase in MAP:
  • Increased baroreceptor firing rate.
  • Decreased sympathetic and increased parasympathetic activity.
  • Decreased heart rate and stroke volume reduces cardiac output
  • Widespread vasodilation reduces TPR
  • Causing reduced blood pressure

Hypertension vs. Hypotension

• Hypertension is high blood pressure above 140/90 mm Hg, detected by mechanoreceptors.
  • Stage 1: 130-139/or 80-89
  • Stage 2: 140+/or 90+
  • Hypertensive Crisis: 180+/and/or 120+.
• Hypotension is low blood pressure below 100/60 mm Hg, also detected by mechanoreceptors.

Categories of Hyper/Hypotension

• Primary hypertension is genetic or hereditary.
  • It is pushed by obesity, smoking, stress, and diet.
• Secondary hypertension is not genetic and is influenced by factors like:
  • Heart loss of elastin fibers.
  • Kidney disease, which increases salt concentration, water retention, EDV, and blood volume.
• Hypertension increases stress on the heart and vessels.
  • Increases TPR, leading to congestive heart failure or stroke.
• Hypotension is low blood pressure due to not enough blood or a heart that is too weak.
• Orthostatic hypotension is the inability to respond to gravity on venous return.
  • For example, baroreceptors on a bedridden person may lead to pooling in legs, less venous return, less cardiac output, and dizziness.
• Circulatory shock is when blood flow is inadequate to organs due to:
  • Hemorrhage
  • Weak heart
  • Vasodilation (histamines)
  • Impaired neuro-vasoconstriction
• Adaptability is countered by the baroreceptor reflex, increasing the absorption of interstitial fluid, reducing urine output, and increasing RBCs.

Heart Failure

• Heart failure occurs when the heart can't sustain enough blood to organs or remove waste.
• Decreased cardiac contractility impairs the length-tension relation and decreases stroke volume.
• It is caused by damage to the heart muscle
  • or chronic elevated BP that damages blood vessels over time.
• Stages of heart failure
  • Compensated heart failures: Early
    • There is an increase in the sympathetic division to increase the contraction and cardiac rate
    • Kidney retention of salt and water-increase volume/pressure-EDV-Length-Stroke Volume
  • Decompensated heart failure: Late
    • Forward failure: diminished flow to the kidneys
    • Backward failure: caused when blood is backed up in venous blood
  • Result is congestive heart failure, which is more detrimental

Respiration Overview

• Respiration is the exchange of gas between the air and the blood vessels.
• External respiration is the exchange between air and tissue.
• The respiratory system brings air in and out of the lungs with alveolar lung cells which have pulmonary capillaries for air exchange (O2/CO2).
• The circulatory system transports oxygen and carbon dioxide to and from tissues via systemic capillaries for gas exchange (O2/CO2).

Steps of Ext to In Respiration

1. Atmosphere and alveoli exchange
2. Pulmonary capillaries exchange w/ air O²/CO²
3. Oxygenated blood goes to the heart via the pulmonary vein and to the aorta.
4. Oxygenated blood goes to systemic capillaries for cell respiration.

Ventilation Overview

• Ventilation is the movement of air
  • Occurs when you inhale into lungs and exhale air out of lungs
• Pulmonary ventilation is the total volume of gas that enters the respiratory system.
  • "EDV"
• Alveolar ventilation is the volume of gas that reaches the alveoli.
  • "ESV”
• It is influenced by CO²/O² concentration

Anatomy Pathway for Respiration

1. Nasal passage
2. Pharynx
3. Trachea
4. Left/Right Bronchi
5. Bronchioles
6. Conduction Zone
7. Alveoli
   • The last area is the site of gas exchange between the air and blood

Respiratory V Conducting Zone

• The conducting zone includes the: - Trachea - Bronchus - Bronchioles
• This zone guides air to the respiratory zone and takes care of air quality by including: - Heat - Humidification - Filtration
• This zone is also used for voice production
• Respiratory zone promotes gas exchange
  • Uses respiratory bronchioles- alevoli

Alveoli and Lungs

• The alveoli are made up of hundreds of millions of small sacs
• The alveoli are built with a large surface area
• The alveolar are well-suited for gas exchange and diffusion
• The pulmonary capillaries surround the alveoli
• Type I Alveolar: one cell thick and does gas exchange
• Type II Alveolar: uses surfactant for tension and/or lubrication and/or humidification
• Macrophages: cleans and removes unwanted material
• Lungs are located left (L) and right (R)
• The diaphragm separates the lungs from the abdomen
• The ribs, sternum, vertebrata enclose the lungs
• The pleura is the membrane that lines the lungs
  • Pleural Cavity: space between lungs and pleural sac, provides lubrication via intrapleural fluid
• Pleurisy: inflammation of pleural sac -Occurs if there is not enough lubrication

Lung Volume

• Tidal Volume: volume (vol.) of air taken in is called tidal volume
• Functional Residual Volume: the volume (vol.) of air at the end of breathing out
• Total Lung Capacity: the greatest amounts of volume (vol.) which the air lungs can hold
• NOTE: Only SOME air reaches the respiratory zone
• NOTE: Alveolar Ventilation: air exhange between the alveoli and the atmosphere - pulmonary ventilation is ALWAYS bigger than alveolar ventilation because you will only be taking in air that reaches the zone
• If tidal volume changes, then alveolar ventilation changes - Deep Breath is inc - Shallow Breath is dec - Breathing more rapidly is dec

Breathing Mechanics and Pressures

• Breathing depends on both what alters the lung and movement of air which depends on: - Pressure - Resistance
• OPTIMAL BREATHING: diaphragmatic breathing
• Air must flow so there is a pressure gradient (from high to low concentrations)
• Pressure Sources:
  • Atmospheric (A.P.)
    • Pressure from out side the body
  • Intra-alveolar Pressure (IAP)
    • Pressure from out side the body
  • Intrapleural Pressure (IP)
    • Pressure within the intrapleural space, usually less than AP