Biophysics - Basics of Hemodynamics

Vocabulary practice flashcards covering fluid mechanics, hydrostatics, fluid dynamics, blood pressure parameters, flow conservation, viscosity, and hemodynamics laws.

Fluid

A continuous material medium composed of molecules mobile relative to one another, deformable with no fixed shape (taking the shape of its container), isotropic in all spatial directions, and capable of flowing.

Ideal Fluid (Perfect Fluid)

A theoretical liquid with zero viscosity ($\eta = 0$), experiencing no internal friction forces and no energy or heat dissipation during movement.

Real Fluid

A fluid with non-zero viscosity ($\eta \neq 0$), in which internal friction forces dissipate mechanical energy into heat during movement.

Newtonian Fluid

A real fluid whose viscosity is non-zero and remains constant at a given temperature regardless of flow velocity gradient or shear rate (e.g., water, plasma).

Non-Newtonian Fluid

A real fluid whose viscosity is non-zero and varies depending on the velocity gradient or shear rate at a given temperature (e.g., blood).

Hydrostatic Pressure

The pressure exerted by a stationary fluid on the surface of an immersed object or on the wall of a container holding it.

Pascal's Law

The principle stating that in a stationary liquid of uniform density, pressure is equal at all points at the same depth, and any pressure variation applied at one point is transmitted equally throughout the entire liquid.

Fundamental Law of Hydrostatics

The relationship governing incompressible fluids at rest, stating that the pressure difference between two points equals the weight of the liquid column separating them: $\text{d}P = P_2 - P_1 = \rho g h = \rho g (z_1 - z_2)$.

Pascal (Pa)

The SI unit of pressure, equivalent to $1\,\text{N}\cdot\text{m}^{-2}$ or $1\,\text{kg}\cdot\text{m}^{-1}\cdot\text{s}^{-2}$, representing the pressure exerted by $102\,\text{g}$ over an area of $1\,\text{m}^2$.

Centimetre of Water (cm H2O)

A unit of pressure derived from liquid column manometers used for low pressures, where $1\,\text{cm H}_2\text{O} = \rho g h \approx 98\,\text{Pa}$ (approximately $100\,\text{Pa}$).

Millimetre of Mercury (mmHg)

A unit of pressure derived from liquid column manometers used for higher pressures, where $1\,\text{mmHg} = \rho g h \approx 133.3\,\text{Pa}$.

Systolic Blood Pressure (PAS)

The maximum pressure in the arteries during left ventricular contraction and blood ejection, with a standard reference value around $130\,\text{mmHg}$ ($17\,\text{kPa}$).

Diastolic Blood Pressure (PAD)

The minimum arterial pressure at the end of blood flow toward peripheral organs during cardiac relaxation, with a standard reference value around $80\,\text{mmHg}$ ($10\,\text{kPa}$).

Mean Arterial Pressure (PAM)

The equivalent steady pressure during non-pulsatile flow, calculated as $\text{PAM} = \frac{\text{PAS} + 2 \times \text{PAD}}{3}$, with a standard value around $96\,\text{mmHg}$ ($13\,\text{kPa}$).

Central Venous Pressure (PVC)

The venous pressure measured via catheter at the level of the right atrium, with a normal value of $10\,\text{cm H}_2\text{O} = 1\,\text{kPa} = 7.5\,\text{mmHg}$.

Flow Rate (Q)

The volume of fluid passing through a given cross-section per unit time, defined as $Q = \frac{\text{d}V}{\text{d}t} = S \times v$ and measured in SI units of $\text{m}^3\cdot\text{s}^{-1}$.

Permanent Flow (Stationary Flow)

A flow regime in which all physical parameters characterizing the fluid flow (such as velocity and pressure) remain constant over time at any fixed point.

Equation of Flow Rate Conservation

The principle stating that for an incompressible fluid in permanent flow, volumetric flow rate remains constant throughout a conduit: $Q_1 = Q_2 = S_1 v_1 = S_2 v_2$.

Venturi Effect

The fluid dynamics principle stating that when a conduit narrows ($S_2 < S_1$), fluid velocity increases ($v_2 > v_1$) and lateral pressure decreases.

Vascular Cone

The structural model of vascular branching where total flow rate is conserved across all parallel sub-branches ($Q_1 = \sum Q_i$), while flow velocity remains equal in all daughter ramifications of a bifurcation regardless of individual cross-sections.

Bernoulli's Theorem

The statement of energy charge conservation for an ideal fluid in steady flow, expressed in pressure terms as $P + \rho g z + \frac{1}{2}\rho v^2 = \text{constant}$.

Stenosis

A narrowing of a blood vessel cross-section ($S_2 < S_1$) that causes blood flow velocity to increase ($v_2 > v_1$) and lateral pressure to drop.

Aneurysm

An abnormal dilation or enlargement of a blood vessel ($S_2 > S_1$) that causes flow velocity to decrease ($v_2 < v_1$) and lateral pressure to increase against the vessel wall.

Viscosity (η)

The fluid property representing resistance to flow caused by internal friction forces opposing relative sliding between adjacent fluid layers, measured in $\text{Pa}\cdot\text{s}$ or Poiseuille.

Shear Rate (γ)

The velocity gradient perpendicular to the direction of flow, calculated as $\gamma = \frac{\Delta v}{\Delta x}$.

Rheofluidification

The property of non-Newtonian blood where viscosity decreases at high shear rates due to red blood cell deformation in rapid flow.

Laminar Flow

A smooth fluid flow regime occurring at lower average velocities where fluid layers slide parallel to one another without crossing, resulting in a parabolic velocity profile.

Turbulent Flow

A chaotic fluid flow regime occurring at high average velocities where fluid streamlines cross, forming swirling vortices that consume energy and create audible sounds or murmurs.

Reynolds Number (Re)

A dimensionless index predicting flow regime, calculated as $\text{Re} = \frac{\rho v_m d}{\eta}$, where $\text{Re} < 2400$ indicates laminar flow and $\text{Re} > 2400$ indicates turbulent flow.

Hagen-Poiseuille Law

The formula governing laminar flow of a real Newtonian fluid in a horizontal cylinder, expressing pressure drop as $\Delta P = R \times Q$, where $R = \frac{8 \eta L}{\pi r^4}$.

Vascular Resistance (R)

The force opposing blood flow through a vessel, given by $R = \frac{8 \eta L}{\pi r^4}$, which is directly proportional to fluid viscosity $\eta$ and vessel length $L$, and inversely proportional to vessel radius to the fourth power ($r^4$).

Bypass Grafting

A surgical intervention inserting a graft in parallel with an obstructed vessel to reduce overall vascular resistance ($\frac{1}{R_{\text{total}}} = \frac{1}{R_{\text{stenosis}}} + \frac{1}{R_{\text{graft}}}$) and increase total blood flow.