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Phase 1 Cardio > Circulation > Flashcards

Circulation Flashcards

(49 cards)

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1
Q

Why do we need to control circulation

A

In order to
–Maintain blood flow
–Maintain arterial pressure
–Distribute blood flow
–Auto-regulate/homeostasis
–Function normally
–Prevent catastrophe!
–(maladapt in disease)

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2
Q

What are the components of circulation?

A

Anatomy
•Blood
•Pressure
•Volume
•Flow

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3
Q

What is the blood flow (CO) through 11 organs?

A

Liver 27%

•Kidneys 22%

•Muscle 15%

•Brain 14%

•Skin 6%

•Bone 5%

Heart 4%

•Other 3.5%

•Bronchi 2%

•Thyroid 1%

•Adrenal 0.5%

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4
Q

What are arteries like?

A

Low resistance conduits
•Elastic
•Cushion systole
•Maintain blood flow to organs during diastole

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5
Q

What are arterioles?

A

•Principal site of resistance to vascular flow
•Therefore, TPR = Total Arteriolar Resistance
•Determined by local, neural and hormonal factors
•Major role in determining arterial pressure
•Major role in distributing flow to tissue/organs

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6
Q

What is TPR? (Arteriolar resistance)

A

• Vascular smooth muscle (VSM) determines radius
• VSM Contracts = ↓Radius = ↑Resistance ↓Flow
• VSM Relaxes = ↑Radius = ↓Resistance ↑Flow
• Or Vasoconstriction and Vasodilatation
• VSM never completely relaxed = myogenic tone

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7
Q

What are capillaries?

A

40,000km and large area = slow flow
•Allows time for nutrient/waste exchange
•Plasma or interstitial fluid flow determines the distribution of ECF between these compartments
•Flow also determined by
–Arteriolar resistance
–No. of open pre-capillary sphincters

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8
Q

What are veins like?

A

Compliant
•Low resistance conduits
•Capacitance vessels
•Up to 70% of blood volume but only 10mmHg
•Valves aid venous return (VR) against gravity
•Skeletal muscle/Respiratory pump aids return
•SNS mediated vasoconstriction maintains VR/VP

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9
Q

What are lymphatics?

A

•Fluid/protein excess filtered from capillaries
•Return of this interstitial fluid to CV system
–Thoracic duct; left subclavian vein
•Uni-directional flow aided by
–Smooth muscle in lymphatic vessels
–Skeletal muscle pump
–Respiratory pump

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10
Q

What is CO, BP, PP, MAP equations?

A

Cardiac Output (CO) = Heart Rate (HR) x Stroke Volume (SV)
Blood pressure = CO x Total Peripheral Resistance (TPR)
(like Ohm’s law: V=IR)
Pulse pressure (PP) = Systolic – Diastolic Pressure
Mean Arterial Pressure (MAP)= Diastolic Pressure + 1/3 PP

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11
Q

What governs flow?

A
  1. Ohm’s law
    F = ∆P/R Or

Flow = Pressure Gradient
Resistance

  1. Poiseuille’s equation

Flow = radius to the power of 4

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12
Q

How does the heart respond to volume?

A

Frank-starling mechanism?

SV increases as End-Diastolic Volume increases
•Due to Length-Tension (L-T) relationship of muscle
•↑EDV = ↑Stretch = ↑Force of contraction
•Cardiac muscle at rest is NOT at its optimum length
•↑VR = ↑EDV = ↑SV = ↑CO (even if HR constant)

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13
Q

What is blood volume?

A

•Venous return important beat to beat (FS mechanism)
•Blood volume is an important long term moderator
•BV = Na+, H20
•Renin-Angiotensin-Aldosterone system
•ADH
•Adrenals and kidneys
•But that’s another lecture!

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14
Q

What is the goal of controlling circulation?

A

Maintain blood flow!
CO = SV x HR

This needs pressure to push blood through peripheral resistance
MAP = CO x TPR

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15
Q

What is BP like?

A

BP = Pressure of blood within and against the arteries
•Systolic = Highest, when ventricles contract (100-150mmHg)
•Diastolic = Lowest, when ventricles relax (not zero, due to aortic valve and aortic elasticity .. 60-90mmHg)
•Mean arterial pressure = D + 1/3(S-D)
•Measured using a sphygmomanometer
•Using brachial artery
–Convenient to compress
–Level of heart

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16
Q

What is BP like?

A

BP = Pressure of blood within and against the arteries
•Systolic = Highest, when ventricles contract (100-150mmHg)
•Diastolic = Lowest, when ventricles relax (not zero, due to aortic valve and aortic elasticity .. 60-90mmHg)
•Mean arterial pressure = D + 1/3(S-D)
•Measured using a sphygmomanometer
•Using brachial artery
–Convenient to compress
–Level of heart

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17
Q

What is used to measure BP?

A

Ingredients:
Arm, Sphygmomanometer, Stethoscope, 2 Ears

Directions:
Inflate cuff to above systolic BP, until pulse
impalpable or Korotkoff sounds absent.

Serving suggestion:
Slowly deflate cuff, listening all the time.

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18
Q

What are BP sounds? (Korotkoff)

A

0) > Systolic Pressure = no flow, no sounds

1) Systolic pressure = high velocity = tap

2-4) Between S and D = thud

5) Diastolic pressure = sounds disappear

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19
Q

What are the components of BP control?

A

Autoregulation
Local mediators
Humoral factors
Baroreceptors
Central (neural) control

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20
Q

What is myogenic auto regulation like?

Study These Flashcards
A

•Intrinsic ability of an organ
•Constant flow despite perfusion pressure changes
•Renal/Cerebral/Coronary = Excellent
•Skeletal Muscle/Splanchnic = Moderate
•Cutaneous = Poor

21
Q

What is the balance of extrinsic and intrinsic control?

Study These Flashcards
A

Brain & heart: intrinsic control dominates to maintain BF to vital organs

•Skin: BF is important in general vasoconstrictor response and also in responses to temperature (extrinsic) via hypothalamus

•Skeletal muscle: dual effects:- at rest, vasoconstrictor (extrinsic) tone is dominant; upon exercise, intrinsic mechanisms predominate

22
Q

What are the local humoral factors?

Study These Flashcards
A

Vasoconstrictors

•Endothelin-1

•Internal Blood Pressure
(myogenic contraction)

Vasodilators

•Hypoxia
•Adenosine
•Bradykinin
•NO
•K+, CO2, H+
•Tissue breakdown products

23
Q

What are the control functions of endothelium

Study These Flashcards
A

•Essential for control of the circulation
•EDRF = Nitric Oxide (NO) = potent vasodilator
•L-Arg is converted into NO by NO synthetase
•Prostacyclin = potent vasodilator
•Endothelin = potent vasoconstrictor

24
Q

What is Endothelium like in local control

Study These Flashcards
A

(Furchgott’s Experiment)

Vasodilatation
(Endothelium
Derived
Relaxation
Factor) (NO)

Ach

Endothelium intact/rubbed of
Vasodilation/vasoconstriction

25
How is NO produced?
In endothelial cell: Endotoxin cytokines Ach bradykinin substance-P insulin -> R Shearing forces Citrulline?
26
How is NO produced?
In endothelial cell: Endotoxin cytokines Ach bradykinin substance-P insulin -> R Shearing forces Citrulline?
27
How is endothelin produced?
+ Angiotensin 2 Vasopressin Thrombin Oxygen free radicals Shearing forces - NO, postacyclin, ANP ECE, G-protein - smooth muscle contraction Ca2+
28
How is PG12 prostacyclin produced?
Membrane phospholipids Aspirin NSAIDS 5-HPETE Cycle-endoperoxides
29
What are circulating (hormonal) factors?
Vasocontrictors •Epinephrine (skin) •Angiotensin II •Vasopressin Vasodilators •Epinephrine (muscle) •Atrial Natriuretic Peptide
30
What are baroreceptors like?
Pressure sensing •Primary (Arterial) =carotid sinus & aortic arch •Secondary = veins, myocardium, pulmonary vessels •Afferent Glossopharyngeal (IX); •Efferents sympathetic and Vagus (X) •Firing rate proportional to MAP and PP, integrated in the medulla •↑BP ⇒ ↑Firing ⇒ ↑PNS/↓SNS ⇒ ↓CO/TPR = ↓BP •and vice versa
31
What are arterial baroreceptors like?
•Key role in short-term regulation of BP; minute to minute control, response to exercise, haemorrhage •If arterial pressure deviates from ‘norm’ for more than a few days they ‘adapt’/’reset’ to new baseline pressure eg. in hypertension •The major factor in long-term BP control is blood volume
32
What are cardiopulmonary baroceptors like?
Atria, ventricles, PA •Stimulation = ↓vasoconstrictor centre in medulla, = ↓ BP •Also ↓release angiotensin, aldosterone & vasopressin (ADH), leading to fluid loss •Play an important role in blood volume regulation
33
What is the central neural control loop?
Baroreceptors -> brainstem -> heart rest, stroke, vessel diameter -> BP (+/-) - back to baroreceptors +/- sympathetic or vasoconstrictors
34
What is the neural pathway like?
35
What is the neural pathway like?
36
What are the main neural influences on medulla
•Baroreceptors •Chemoreceptors •Hypothalamus •Cerebral cortex •Skin •Changes in blood [O2] and [CO2]
37
How do the arterial baroreceptors affect central control?
Arterial pressure -> Arterial Baroreceptors -> decreased Sympathetic Outflow to Heart, Arterioles & Veins / Parasympathetic Outflow To Heart
38
What occurs in the Autonomic NS?
39
What do other neural centres do?
CV reflexes require hypothalamus and pons •Stimulation of anterior hypothalamus ↓ BP and HR; reverse with posterolateral hypothalamus •Hypothalamus also important in regulation of skin blood flow in response to temperature •Cerebral cortex can affect blood flow & pressure. Stimulation usually ↑ vasoconstriction, but emotion can ↑ vasodilatation and depressor responses eg. blushing, fainting. Effects mediated via medulla but some directly
40
What are the central chemoreceptors?
Chemosensitive regions in medulla •↑PaCO2 = vasoconstriction, ↑peripheral resistance, ↑BP •↓PaCO2 = ↓medullary tonic activity, ↓BP •Similar changes with ↑ and ↓ pH •PaO2 less effect on medulla; Moderate ↓ = vasoconstriction; Severe ↓ = general depression •Effects of PaO2 mainly via peripheral chemoreceptors
41
What is the standard BP control?
Short term: –Baroreceptors –↑BP ⇒ ↑Firing ⇒ ↑PNS/↓SNS ⇒ ↓CO/TPR = ↓BP •Long term –Volume of blood –Na+, H20, Renin-Angiotensin-Aldosterone and ADH
42
What are the key central effectors
Peripheral • Blood vessels (vasodilatation and vasoconstriction: affects TPR) • Heart (rate and contractility: CO = HR x SV) • Kidney (fluid balance: longer term control)
43
What is the feedback loop in circulation?
Blood pressure -> baroreceptor discharge -> sympathetic and parasympathetic outflow -> vasomotor tone and CO ->
44
What is the CR of circulation ?
Physiological •Cold •Standing up •Running •Lifting •Injury •Blood loss Pathological •Fainting •Orthostatic hypotension •POTS •Heart failure •Hypovolaemic shock •Cardiogenic shock •Heart block •Cushing’s syndrome •Respiratory failure •General anaesthetic
45
What is fainting like?
‘Neuro-cardiogenic syncope’ •Aetiology = emotion, heat, standing, dehydration •Symptoms = nausea, air hunger, sweating •Physiology = Fall in HR and Venous Pooling (X nerve) •Signs = Collapse due to ↓ CO •HR falls, CO falls, BP falls, perfusion to brain reduced •‘Neuro-cardiogenic syncope’ = Faint! •Treatment = lay supine and elevate limbs to ↑VR •Frank-Starling leads to improved SV and CO •Long term: fluids, salt .. Midodrine (α agonist)
46
How does blood loss affect circulation?
Blood loss •Perfusion to brain must be maintained •Local vasoconstriction •Maintain CO/BP by ↑HR •Sympathetic outflow •Widespread cutaneous vasoconstriction •Eventually .. SHOCK (BP↓, Pulse↑, organ hypoperfusion) and death •Treat: rapid volume replacement
47
What is orthodontic hypertension?
Aetiology = standing quickly, too long, dehydration, hot room •Symptoms = lightheaded, sweating, syncope •Physiology = Fall in BP and Venous Pooling (X nerve) •Failure to reflexly maintain BP and HR •Perfusion to brain reduced •Treatment = lay supine and elevate limbs to ↑VR •Frank-Starling leads to improved SV and CO •Investigate: Lying/ standing BP; tilt test
48
What is POTS?
POTS ‘Postural orthostatic tachycardia syndrome’ •Standing •Palpitation, dizzy, near syncope, sweating, debilitating •Physiology = Excess tachycardia response •Investigate = Tilt test •HR↑ >40bpm; BP usually OK •Not well understood
49
What are the key controls of circulation?
•Autoregulation •Peripheral humoral •Circulating humoral •Baroreceptors •Central neural

Phase 1 Cardio (9 decks)

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