Critical physiology: flow dynamics in intensive care
Flow dynamics and its application in critical care
Fluid dynamics is a subdiscipline of fluid mechanics that study fluid flow.Dynamics is a science of fluids (liquids and gases) in motion.Rheology is the study of the flow of matter, primarily in the liquid state.
Terminologies: 4 basic terms
Types of flow: Lamellar vs Turbulence
How to decide which type of flow ?:
If NR < 2000 – laminar flowNR > 4000 – Turbulent flow
1) AIRWAY OBSTRUCTION
2) HIGH FREQUENCY VENTILATION
4) CARDIOVASCULAR BLOOD FLOW
PERFUSION PRESSURE AND TUERBULENT FLOW
NEWTONIAN AND NON-NEWTONIAN FLUID
What generates Viscosity ?
Whats is coefficient of viscosity?
The layer of fluid in contact with the stationary wall will retard the flow of the layer just near to it. This layer will retard the layer near and so on. The max flow velocity will be present in centre. With different adhesive forces for different fluid, the velocity will vary. This is coefficient of viscosity (n).
Viscosity of blood increases with
- Increased hematocrit
- Constrictions in vessels
- Decrease flow rate of blood through vessel (RBCs adhere to each other, and the vessel walls.)
Viscosity of blood decreases with
- Increased flow velocity
- Vessel diameter below 300 μm (Reduced η when RBCs get aligned in small vessels. (This is called as Fahraeus-Lindqvist effect.)
- In very small vessels (< 20 μm), η increases as RBCs fill the capillaries, “tractor tread” motion.
DYNAMICS OF BLOOD FLOW (RHEOLOGY)
INVASIVE BP WAVEFORM
FLOW IN CURVED TUBES
FLOW IN MICROCIRCULATION
The viscosity of blood has a primary influence on flow in the larger arteries, while the elasticity, which resides in the elastic deformability of red blood cells, has primary influence in the arterioles and the capillaries.