FLOW THROUGH TUBES Phil Copeman

Where is the largest pressure drop in the systemic circulation? Between the arteries- arterioles

For a given pressure gradient, what is flow determined by? Resistance of the vessel (dependent on its radius) The arterioles are high resistance – narrow with stretch-resistant muscular walls

What is the clinical relevance? Arteriolar constriction/dilatation (e.g. at the renal bed) controls the blood supply to an organ or capillary bed

Blood pressure = ? Blood pressure = cardiac output x systemic vascular resistance Pressure gradient = flow x resistance BP = CO x SVR Giraffe

What term denotes normal blood flow in a tube? Laminar Laminar flow means velocity is at its lowest at the edges Why is this good?

Laminar flow means the width of the tube greatly affects its resistance (flow proportional to r4) What is the clinical significance? If there is an occlusion of the vessel (i.e. atherosclerosis) - halving the vessel radius; means either flow will fall by 16x (>>ischaemia) or pressure has to rise by 16x (>>hypertension)

What THREE factors increase the likelihood of turbulent flow? [3] High velocity Low blood viscosity Large vessel diameter

What is the clinical significance of turbulent flow? [2] We can hear it! Bruits in arteries, wheeze in airways Turbulent flow causes damage to endothelium

In distensible vessels, what is the effect of an increase in pressure on the flow? With a distensible tube, an increase in pressure stretches the walls lowering resistance The graph just shows that with distensible vessels (the yellow line), a change in pressure can be absorbed by stretching walls and increasing flow, thus keeping the pressure relatively uniform.

What is the clinical relevance? Distensibility gives them capacitance Vessels widen with increasing pressure, so more blood will flow in than out Thus the venous system can store blood (~67%) However, at low intravascular pressures the vessels may close

Alex Hammant (just plain stolen from last year’s Peer Support) Shock Alex Hammant (just plain stolen from last year’s Peer Support)

Important formulas Stroke Volume = End dyastolic volume – End systolic volume Cardiac output = Stroke volume x Heart rate Blood pressure = Cardiac output x Systemic Vascular Resitance

Define Shock Acute circulatory failure resulting in inadequate or disordered tissue perfusion and insufficient oxygen supply to cells

Name the 5 types of shock He - Hypovolaemic Called - Cardiogenic Me - Mechanical (obstructive) A - Anaphylactic Sadist - Septic Melville’s slant #CHANS Cardiogenic Hypovolaemic Anaphylaxis Neurogenic Septic In the three ‘distributive’ types of shock – the common feature is vasodilation

Hypovolemic Shock What is hypovolemic shock? Shock caused by an insufficient volume of blood What are the causes of hypovolemic shock? Major trauma (blood loss), Diarrhoea/Vomiting, massive blood loss during surgery, burns

Hypovolemic Shock What are the signs of hypovolemic shock? Tachycardia, hypotension, thready pulse, oliguria, cold clammy peripheries, Altered GCS

Cardiogenic Shock What is cardiogenic shock? Failure of the heart to pump effectively What causes cardiogenic shock? Myocardial infarction, valvular disease, myocarditis, endocarditis

Cardiogenic Shock What are the signs of cardiogenic shock? Pulmonary oedema, increased central venous pressure, murmurs, S3/S4, hypodynamic circulation, oliguria

Septic Shock What is septic shock? Shock caused by impaired utilisation of oxygen by cells due to sepsis What are the causes of septic shock? Appendicitis, pneumonia, bacteraemia, diverticulitis, pyelonephritis, meningitis, pancreatitis, and necrotizing fasciitis.

Septic Shock What are the signs of septic shock? SIRS signs: tachycardia, tachypneoa, warm

Anaphylactic Shock What are the causes of Anaphylactic Shock? Anapylaxis What are the signs of anaphylactic shock? Angiooedema, Stridor/Bronchospasm Anaphylaxis is a serious allergic reaction that is rapid in onset and may cause death.[1][2] It typically causes a number of symptoms including an itchy rash, throat swelling, and low blood pressure. Common causes include insect bites and stings, foods, and medications. Angioedema (BE: angiooedema) or Quincke's edema is the rapid swelling (edema) of the dermis, subcutaneous tissue,[1] mucosa and submucosal tissues.  Stridor (Latin for "creaking or grating noise") is a high-pitched breath soundresulting from turbulent air flow in the larynx or lower in the bronchial tree.

Mechanical/Obstructive What is mechanical shock? Obstruction of blood flow outside the heart What are the causes of obstructive shock? Tension pneumothorax, Pulmonary embolism, Pericardial tamponade

Mechanical/Obstructive What are the signs of mechanical shock? Tachynpnoea, increased CVP, reduced air entry, muffled heart sounds