Dispensa di Biomachines Practice Flashcards

A set of 150 practice flashcards covering fluid mechanics, blood physiology, heart valve prosthesis, and extracorporeal circulation based on lecture notes.

How is fluid viscosity defined in terms of its physical behavior?

It is responsible for «internal friction» and measures the resistance to gradual deformation when shear stress is applied.

What is the relationship between shear stress and shear rate in Newtonian fluids?

They have a simple linear relation.

What characterizes non-Newtonian fluids in terms of relationship, yield stress, and history?

They display a non-linear relation between shear stress and shear rate, have a yield stress, or have a viscosity dependent on time or deformation history.

At what dimension scale can blood be considered a Newtonian fluid?

From $2\,mm$ to higher measures.

Under what diameter threshold does blood viscosity become very high and behave as a non-Newtonian fluid?

Under $8\,\mu m$.

How is blood flow generally described in the human body?

LAMINAR.

In what part of the anatomy can laminar blood flow become disturbed and TURBULENT under high flow conditions?

The ascending aorta.

What is the effect of turbulence on the energy required to drive blood flow?

It increases the energy required due to loss of energy in the form of friction, which generates heat.

What criteria describes whether fluid flow is steady (laminar) or has small unsteady fluctuations (turbulent)?

Reynolds number.

What is the Reynolds number threshold for blood flow to be generally laminar in a pipe?

Less than about $2'000$.

At what Reynolds number value is flow usually turbulent?

Higher than $4'000$.

What is the range of the Reynolds number where the transition between laminar and turbulent flow occur?

$2'000$ to $4'000$.

What dimensionless number expresses pulsatile flow frequency in relation to viscous effects?

The Womersley number.

What principle states that fluid flow is a specific case of energy conservation, assuming steady state and no thermal/mechanical losses?

Bernoulli’s principle.

In Bernoulli’s principle, energy $E$ is the sum of which three components?

Kinetic energy, potential energy, and flow work (pressure-volume work).

What two factors must be taken into account in the «real world» according to Bernoulli’s principle?

Frictional losses ($\mu \neq 0$) and Local Losses (curvature, valve, variation of section, etc.).

In what direction does fluid flow naturally move according to pressure?

From higher to lower pressure.

Which equation defines the hydraulic slope as part of fluid mechanics?

The Darcy-Weisbach equation.

What is the name of the chart where experimental data for Darcy friction factor and Reynolds numbers are collected?

MOODY CHART.

What are the conditions required for the Hagen-Poiseuille Law to apply?

A smooth, horizontal, cylindrical, and rigid tube with a laminar flow field.

What physical term describes the factors governing blood flow within the circulatory system?

Haemodynamic.

How is blood flow ($Q$) through an organ determined?

The perfusion pressure ($\Delta P$) driving the flow divided by the resistance ($R$) to flow.

What is the normal concentration of platelets in the blood?

$(1.5 \div 4) \times 10^3/mm^3$.

What is the normal concentration of white blood cells (WBCs) in the blood?

$(4 \div 10) \times 10^3/mm^3$.

What is the normal concentration of red blood cells (RBCs) or erythrocytes in the blood?

$5 \times 10^6/mm^3$.

What percentage of blood volume do RBCs account for when «spun down» in a centrifuge?

About $45\%$.

What is the name for the percentage of blood volume made of RBCs?

Haematocrit.

What is the normal haematocrit range for males?

$40\%$ to $50\%$.

What is the normal haematocrit range for females?

$35\%$ to $45\%$.

What is the «buffy coat» composed of?

White blood cells (leukocytes) and platelets.

What makes up the remaining $55\%$ of blood volume after RBCs, WBCs, and platelets?

Plasma.

How is serum defined?

Plasma with the clotting factors removed.

Name five functions of blood listed in the notes.

Transport of gases/nutrients/wastes/hormones, prevention of fluid loss, immune defense, regulation of pH/electrolytes, and thermoregulation.

What is the estimated percentage of RBCs among the total cells in the body?

About $25\%$.

What is the mean diameter of a red blood cell?

About $7\text{--}8\,\mu m$.

What percentage of carbon dioxide waste is picked up by erythrocytes at the tissues?

About $24\%$.

Why do RBCs lack most organelles?

To provide more interior space for hemoglobin molecules to transport gases.

At what concentration does free hemoglobin circulating in the plasma become toxic?

$> 150\,mg/dm^3$.

What is the specific name of the red blood cell membrane?

Stroma.

What is the effect of decreasing capillary diameter on whole blood viscosity?

Viscosity is affected because the size of corpuscular elements can no longer be neglected in interaction with fluid-dynamics.

What is coagulation described as regarding its reversibility?

It is an irreversible process.

What insoluble filamentous protein forms the mesh of a clot during coagulation?

Fibrin.

What plasma protein produced by the liver is the precursor to fibrin?

Fibrinogen.

Why must atrial fibrillation be avoided in terms of coagulation?

It causes blood to be too static inside the chambers, allowing platelets to start the coagulation process.

What fluid dynamic design feature is necessary in blood-conducting structures to avoid coagulation?

Avoiding vortexes, stagnation, and abrupt variations of section.

What synthesized drug is used to avoid coagulation during extracorporeal circulation?

Heparin.

What are the two common kinds of heparin mentioned?

Heparin calcium and heparin sodium.

What is the purpose of re-clotting in vascular prostheses like Dacron tubes?

To allow the blood to populate the material and form a new vascular endothelium/neointima layer.

What drug is used to reverse the action of heparin after surgery?

Protamine.

How does heparin specifically interrupt the coagulation chain?

It blocks the transformation of fibrinogen into fibrin.

Why does blood clot in an arterial vessel isolated from the body even if the vessel is natural?

The vessel dies (not nourished by vasa vasorum) and altered fluid-dynamics.

What correlation did the experiment by Vorhauer and Taray (1970s) demonstrate?

A correlation between increased vortex formation and increased clot formation.

What is the name of the tail vortex pattern used to order thrombogenicity in the Vorhauer and Taray experiment?

Von K\'{a}rm\'{a}n vortex street.

What is the definition of haemolysis?

The rupture of the membrane of the red blood cells.

What is the physiological lifespan of a red blood cell?

120 days.

What instrument is used to determine the severity of haemolysis by measuring free haemoglobin?

Spectrophotometer.

What are the three main types of agents responsible for haemolysis?

Chemical, thermal, and mechanical.

At what temperature do cells die, according to the notes on thermal haemolysis?

$42\,^{\circ}C$.

What is the main responsible factor for thermal haemolysis regarding temperature changes?

The temperature gradient ($dT/dt$).

What is the maximum allowed temperature gradient for re-warming blood?

$< 3,4\,^{\circ}C/5\,min$.

What is the maximum allowable temperature difference between the cooling/warming phase and the blood?

$10\,^{\circ}C$.

What causes mechanical haemolysis when using water solutions?

Osmotic effect (water flows into RBCs causing them to swallow and rupture).

According to the Tillman diagram, RBC stroma rupture is proportional to which two factors?

Magnitude of the stress and duration of the stress.

How is the induced haemolytic damage estimated using the Tillman diagram?

By knowing the value of the shear stress and its application time.

What is a major disadvantage of the Tillman diagram?

Variation in the threshold and high variability due to factors like whether animals were fasting.

Through which structures does venous blood return to the right atrium?

Superior vena cava (SVC) and inferior vena cava (IVC).

Which region of the heart's conduction system has the highest velocity?

Purkinje fibers.

Which region of the heart's conduction system has the lowest velocity?

Atrioventricular (AV) node.

What is the major exception to the parallel arrangement of organs in the circulatory system?

The hepatic (liver) circulation.

What is the formula for Cardiac Output (CO)?

$CO = SV \times HR$.

How is preload defined?

The initial stretching of the cardiac myocytes prior to contraction, related to sarcomere length at the end of diastole.

What does the Frank-Starling mechanism state?

Increasing venous return and ventricular preload leads to an increase in stroke volume (SV).

What diagram shows cardiac pressure and cardiac volume tracing together?

Wiggers diagram.

What model studies the heart's capacity to self-adjust cardiac output?

Guyton Model.

In the Guyton Model simulation, how was Right Atrium Mean Pressure (RAMP) adjusted?

By varying the height of a large reservoir.

What is the formula for Venous Return (VR) in the Guyton Model?

$VR = \frac{MSP - RAMP}{R_{venous}}$.

What does MSP stand for in the context of Venous Return?

Mean Systemic Pressure.

What happens to CO in a CO-RAMP relationship if RAMP increases too much (e.g., coronary stenosis)?

CO decreases because the heart follows the muscle's inability to contract correctly with higher pressure to win.

What are four common causes of heart valve disease needing substitution?

Bicuspid aortic valve, Rheumatic heart disease, Age-sclerosis, and Endocarditis.

List four design criteria for a Heart Valve Prosthesis (HVP).

Unidirectional, Passive, Light (low density), and Biocompatible.

What was the first artificial heart valve and what was it made of?

The caged-ball (Starr-Edwards), using a metal cage and a silicone elastomer ball.

Why does a caged-ball valve increase the risk of haemolysis during opening?

The ball bumpering causes a variation in cross section, increasing velocity and shear stresses.

What was the catastrophic risk of a silicone ball in the aortic position in the first prosthetic valves?

Reduction in dimension over time causing it to escape the cage, leading to immediate death.

What material was used for the disk in the tilting disc valve to provide durability?

Pyrolytic carbon.

Why can the tilting disc in an HVP NOT open to a full 90 degrees?

A cross-sectional area is needed for pressure forces to act on the disk to ensure closure.

What is the primary advantage of modern bileaflet valves over tilting disc valves?

They close faster and the back-flow during closure is smaller.

Name the three families of biological heart valves.

Autograft, Homograft, and Hetero/Xeno-graft.

What is an autograft heart valve?

A valve from the same individual (e.g., pulmonary to aortic).

What is a homograft heart valve?

A valve from a different individual (e.g., cadaveric).

What is a xeno-graft heart valve?

A valve from a different species (e.g., porcine, bovine).

In HVP diameter determination, what is the constant 'k' characteristic of?

The specific heart valve prosthesis model.

Who reported the relationship between aortic valve flow and time during the ejection phase (1977)?

Swanson and Clark.

How is the cardiac cycle duration related to cardiac frequency (f)?

$T = \frac{1}{f}$.

What is Extracorporeal Circulation (ECC) used for?

To substitute the functions of the lungs and the heart during open-heart surgery.

Why was the discovery of silicon important to ECC?

It provided a permeable material necessary for the oxygenation of blood.

How long can tissues survive without oxygen at normal body temperature before necrosis?

2-3 minutes.

What is hibernation in the context of surgery?

Lowering the body temperature to reduce metabolism, allowing longer surgery time (e.g., at $13\,^{\circ}C$).

What is the purpose of systemic circulation?

To provide oxygen and nutrients to tissues and return deoxygenated blood to the heart.

What is pulmonary circulation?

The movement of blood from the heart to the lungs for oxygenation and back.

What is coronary circulation?

The circulation of blood in the blood vessels of the heart muscle (myocardium).