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Phase 1 Cardio > Circulation > Flashcards

Circulation Flashcards

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?

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?

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?

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

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

A

(Furchgott’s Experiment)

Vasodilatation
(Endothelium
Derived
Relaxation
Factor) (NO)

Ach

Endothelium intact/rubbed of
Vasodilation/vasoconstriction

25
Q

How is NO produced?

A

In endothelial cell:

Endotoxin cytokines
Ach bradykinin substance-P insulin -> R
Shearing forces
Citrulline?

26
Q

How is NO produced?

A

In endothelial cell:

Endotoxin cytokines
Ach bradykinin substance-P insulin -> R
Shearing forces
Citrulline?

27
Q

How is endothelin produced?

A

+
Angiotensin 2
Vasopressin
Thrombin
Oxygen free radicals
Shearing forces

  • NO, postacyclin, ANP

ECE, G-protein - smooth muscle contraction Ca2+

28
Q

How is PG12 prostacyclin produced?

A

Membrane phospholipids
Aspirin NSAIDS
5-HPETE
Cycle-endoperoxides

29
Q

What are circulating (hormonal) factors?

A

Vasocontrictors
•Epinephrine (skin)
•Angiotensin II
•Vasopressin

Vasodilators
•Epinephrine (muscle)
•Atrial Natriuretic Peptide

30
Q

What are baroreceptors like?

A

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
Q

What are arterial baroreceptors like?

A

•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
Q

What are cardiopulmonary baroceptors like?

A

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
Q

What is the central neural control loop?

A

Baroreceptors -> brainstem -> heart rest, stroke, vessel diameter -> BP (+/-) - back to baroreceptors

+/- sympathetic or vasoconstrictors

34
Q

What is the neural pathway like?

A
35
Q

What is the neural pathway like?

A
36
Q

What are the main neural influences on medulla

A

•Baroreceptors
•Chemoreceptors
•Hypothalamus
•Cerebral cortex
•Skin
•Changes in blood [O2] and [CO2]

37
Q

How do the arterial baroreceptors affect central control?

A

Arterial pressure -> Arterial Baroreceptors -> decreased Sympathetic Outflow to Heart, Arterioles & Veins
/ Parasympathetic Outflow To Heart

38
Q

What occurs in the Autonomic NS?

A
39
Q

What do other neural centres do?

A

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
Q

What are the central chemoreceptors?

A

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
Q

What is the standard BP control?

A

Short term:
–Baroreceptors
–↑BP ⇒ ↑Firing ⇒ ↑PNS/↓SNS ⇒ ↓CO/TPR = ↓BP

•Long term
–Volume of blood
–Na+, H20, Renin-Angiotensin-Aldosterone and ADH

42
Q

What are the key central effectors

A

Peripheral

• Blood vessels (vasodilatation and vasoconstriction: affects TPR)

• Heart (rate and contractility: CO = HR x SV)

• Kidney (fluid balance: longer term control)

43
Q

What is the feedback loop in circulation?

A

Blood pressure -> baroreceptor discharge -> sympathetic and parasympathetic outflow -> vasomotor tone and CO ->

44
Q

What is the CR of circulation ?

A

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
Q

What is fainting like?

A

‘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
Q

How does blood loss affect circulation?

A

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
Q

What is orthodontic hypertension?

A

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
Q

What is POTS?

A

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
Q

What are the key controls of circulation?

A

•Autoregulation
•Peripheral humoral
•Circulating humoral
•Baroreceptors
•Central neural

Phase 1 Cardio (9 decks)

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