The relationship between pressure and flow during nasal breathing is curvilinear. The reason is that the nasal airflow is composed of laminar and turblent flows. According to Rohrer, the relationship is expressed by the formula P=K
1V+K
2V
2. Employing posterior rhinomanometry, we measured the patency of both nasal cavities. In addition to the ordinary air measurement, a gas mixture of 80% helium and 20% oxygen was used because turbulent flow is mainly dependent on gas density. The gas viscosity is 1.12 times and the gas density is 0.34 times those of air. The nasal patency in inspiration and expiration were separately assessed by Rohrer's formula using computer analysis. In breathing the mixture, K
1 increased by about 25% and K
2 decreased by about 45%, which are theoretically expected, but there were considerable individual variations. If K
1 and K
2 are the indices which represent exactly laminar and turbulent components, the difference of K
1 or K
2 should be more uniform. Therefore, K
1 and K
2 indicate the characteristics of both laminar and turbulent flows only to a certain extent. It can be assumed that they are dependent on some other factors as well.
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