Laminar Flow	Turbulent Flow


Gas travels in parallel concentric sheets Maximum velocity is located centrally The velocity of air at the peripheral air-wall interface is zero Follows predictable laws	The flow of gas is intermixed with areas of low and high pressure within the same tube Can lead to increased impedance to flow

The occurrence of laminar flow depends on the nature of the conducting "tube", density of the gas and it's dynamic "viscosity", and the flow rate. For flow through a cylinder, this relationship is described by calculating the Reynold's Number (Re).

Reynold's Number Equation

Under conditions where Re is low (<2100), flow is Laminar. Turbulence occurs under conditions where Re is high (>4000).

Clinical Correlate:

1- In patient's undergoing respiratory support, the characteristic linear dimension is dictated by the ventilator circuit and patient airway, along with whatever interface is employed.

2- During respiratory support, the variable that is most easily controlled is the flow rate towards a patient. Adjustments can be made to optimize flow patterns on a ventilator. Severely turbulent flow can impair the effectiveness of bulk flow in clearing dead space.

3- Heliox: Helium when compared to Nitrogen, has a lower molecular weight and significantly lower density which affords a Helium:Oxygen gas mixture very low Re numbers, and almost ensures laminar flow through even significantly obstructed (turbulent-prone) airways.