Understanding the Physiology of Airway in Snoring and Obstructive Sleep apnea(OSA)
Many factors combine to cause the pharyngeal collapse associated with snoring and sleep apnea- forces that promote airway dilation and forces that promote collapse.
Two basic principles of fluid flow, the Bernoulli principle and the Venturi effect, can be applied to give additional insight to the effects of airway narrowing.
The Venturi effect is named after Giovanni Battista Venturi (1746â€“1822), an Italian physicist. When the air passes through the tube\’s throat (narrow section) it moves faster. When the air moved faster the pressure decreased. That means the greater the speed of the air the less pressure exerted. The Venturi effect describes the acceleration of airflow that occurs as a current of air enters a narrow passageway. The water spraying out of a hose that is partially occluded by the thumb is an example of this effect.
Bernoulli’s Principle states that as the speed of a moving fluid increases, the pressure within the fluid decreases.
The Bernoulli principle describes fluid flow in a column. A partial vacuum exists at the outer edges of a column of moving fluid. As airflow speed increases, the partial vacuum pressure increases. The smaller the column, the faster the flow. This principle is illustrated by a drinking straw: if too much negative pressure is generated within the straw, it collapses; as the negative pressure decreases, the straw becomes more rigid and does not collapse.
In a non snoring adult, the negative pressure required to close the upper airway is less than (more negative than) -25 cm water. Snoring adults have a much more pliable airway, with closure during sleep occurring at pressures that range from -2 to -10 cm water.
Physiologically, the pharyngeal muscles work to keep the airway open. During sleep, the cortical input to these muscles decreases and therefore increases the chance of collapse. In a normal person, negative intrapharyngeal pressures during sleep reflexively stimulate pharyngeal dilator tone to keep the airway patent.
Knowing the physiological aspects of the above principles is good for theoretical purposes only. It is all too complicated and difficult to understand for the suffering patient.