Blood Pressure & Flow Flashcards
Cardiac output = Heart rate x Stroke volume
CO problems:
Bradycardia
Tachycardia
Vol of blood pumped by each ventricle in 1 min
Number of beats per min
Vol of blood pumped out by one ventricle w/ each beat (SV = EDV - ESV)
- Determined by contractility, preload, afterload
Heart rate too slow (not pumping enough blood, overfilling of ventricles)
Heart rate too fast (ventricles fill too quickly)
Regulation of heart rate:
- Chronotropic factors
- Ionotropic factors
- Nervous and endocrine system (Sympathetic and parasympathetic)
- Calcium channel blockers
Modulate heart rate
Modulate force of contraction
Sympathetic - Increase and decrease HR, Parasympathetic - Decrease HR
Treat high blood pressure and abnormal heart rates
Starling curve
Resting values
(stroke volume)
Relationship between stretch (ESD) in x-axis and force (stroke volume) in y-axis
70 mL of force at 135 mL of stretch
Cardiac preload
- Frank-starling effect
Afterload
Contractility
Venous return
(Stroke volume)
Muscle length (ventricles) prior to contraction; dependent on EDV
- When more than normal blood returns to heart, muscle stretches, leading to more forceful contraction of ventricles
Pressure heart has to overcome to eject blood into body
Intrinsic ability of cardiac muscle to develop force for a given muscle length
Amount of blood returning to heart
Flow rate: Q = V/t
Law of bulk flow: Q = deltaP/R
Volume of a fluid that moves past a given point per min
Q - Flow
deltaP - Pressure gradient
R - Resistance
3 sources of blood flow resistance
Blood viscosity
Total blood vessel length
Blood vessel diameter
Resistance:
R = 8nL/Pi•r^4
Poiseuille’s equation:
Q = (deltaP•Pi•r^4)/8nL
3 parameters determining resistance:
1) Tube length (L)
2) Tube radius (r)
3) Fluid viscosity (n)
Higher resistance = Higher length
- Constant in adulthood
Resistance proportional to 1/r^4
- If radius is doubled, resistance decreases 1/16
Resistance proportionate to fluid viscosity
- Affected by hematocrit, dehydration, anemia, policythemia
Blood flow rate (L/min) = Q/A
Q - Flow, A - Cross-sectional area
Effect of cross-sectional area and resistance on blood flow rate?
Cross-sectional area inversely proportional to velocity
Higher resistance leads to lower velocity
Myogenic autoregulation (negative feedback in arterioles)
- Vasoconstriction/Vasodilation occurs from changes in concentration of… (5)
Increased blood pressure cause smooth muscle cells to contract
- Maintains constant blood flow to tissue
O2, CO2, H+, K+, paracrine signals
Vasodilation - Nitric oxide
Vasoconstriction - Norepinephrine
Nitric oxide activates Guanylate cyclase, forming cGMP
- Promotes myosin for relaxation
- Inhibits PIP to reduce contraction
Pressure in arteries
1) Ejection phase of ventricular contraction -> Aorta walls expand
2) Elastic recoil of aorta propels blood into arteries
Where is blood pressure highest and lowest?
Pulse
Highest - Heart
Lowest - Capillaries, veins, right atrium
Pulse: Rhythmic expansion and recoil of an artery caused by ejection of blood from the ventricle
MAP (mean arterial pressure) = CO x Total peripheral resistance (TPR)
MAP at rest and when beating rapidly?
Avg pressure in arteries thruout cardiac cycle
- Fluctuates and is pulsatile
Rest: 2/3 diastolic pressure, 1/3 systolic pressure
Rapid: 1/2 diastolic pressure, 1/2 systolic pressure
Pumps that help w/ venous return:
- Skeletal muscle
- Respiratory pumps
Venomotor tone
How much % of blood is in veins in mammals?
Skeletal muscle
- Pushes against gravity w/ valves
Respiratory pumps:
- Inhalation - Pressure in thoracic cage decreases, draws blood into veins
- Exhalation - Pressure increases in thoracic cage, pushes blood to heart
Altering diameter of veins changes resistance of veins
60% of blood
Baroreceptor reflex
- What happens when you stand up too quickly?
- Found in carotid artery and aorta (signals if stretching is normal)
- Regulates MAP by causing rapid changes in BP thru sympathetic changes in cardiac and arteriolar tone (resistance)
Baroreceptor reflex slow to respond to changes in BP as gravity pulls down blood when standing up suddenly
- Causes faint feeling
Kidney’s influence in BP (2)
How? (2)
1) Causing constriction of arteries and veins
2) Increasing blood volume
How?
- Simple filtration of salts
- Hormone regulation (Atrial natriuretic peptide, renin-angiotensin-aldosterone system (RAS), antidiuretic hormone (ADH))
Hypertension
- Primary (90-95%) vs Secondary cases (5-10%)
Consequences:
- Heart has to push against higher mean arterial BP
- Hypertrophy (left ventricle increases in size/strength)
- Pulmonary edema (right ventricle normal but blood backs up in lungs)
- Increased diffusion distance and reduced O2 exchange
- Can lead to congestive heart failure (damage to heart)
Sustained BP greater than 139 mmHg systolic and 89 mmHg diastolic
Primary: No identifiable cause (mix of genetics and enviro), normal cardiac output, increased peripheral resistance
Secondary: Renal or adrenal disease
Hydrostatic pressure (P)
deltaP = P2 - P1 = pgh
delta P - Diff in pressure
p - density of fluid
g - Acceleration due to gravity
h - height of fluid in column
Where is arterial BP lowest and highest in humans when standing and lying down?
Pressure exerted on walls of container by fluid within the container
Standing - Highest in feet, lowest in head (Gravity pushing down)
Lying down - Highest at heart, lowest in feet (No gravitational component)
How do giraffes deal with the effect of gravity on blood circulation standing up and bending down?
Standing -> Thick walled and muscular arterioles, tight skin in legs
Bending down -> Jugular vein has one-way valves, highly elastic blood vessels in brain serve as pressure reservoir
Muscular heart (170 bpm)
Much higher systolic (280 mmHg) and diastolic (180 mmHg) than in humans
Starling forces
Starling principle: Net filtration pressure (NFP) = (Pcap-Pif) - (pcap-pif)
Movement if fluid across capillary wall
- Higher pressure on arterial end, lower pressure on venous end
Pcap - Capillary hydrostatic pressure (transmural pressure)
Pif - Interstitial hydrostatic pressure (in fluid outside of capillary)
pcap - Capillary colloid osmotic pressure (proteins in blood)
pif - Interstitial colloid osmotic pressure (proteins outside of blood)
Lymphatic system
2 schools of thought on evolution
Lymphatic system in:
- Amphibians, reptiles, flightless birds
- Flying birds and mammals
- Picks up excess fluid from tissues
- Has blind ended capillaries
- Important part of immune system (lymphocytes)
- Found by Hippocrates
1) Originates from venous system (Progenitor cells that turn into venous tissue became lymphatics tissue too)
2) Originates from independent lymphatic endothelial cell precursors
- Primitive lymphatic system using lymph hearts
- Open lymphatic system w/ lymph nodes
