SPONTANEOUS CHANGES OF UNILATERAL NASAL AIR-FLOW IN MAN - A REEXAMINATION OF THE NASAL CYCLE

It is now over 100 years since Kayser (Arckiv fur Laryngol Rhinol 1895 ; 3: 101-120) first reported in the scientific literature that the hum an nasal passages exhibit spontaneous changes in unilateral nasal airw ay resistance, yet our understanding of this unusual phenomenon is sti ll very confused. Spontaneous. reciprocal changes in unilateral nasal resistance are often referred to as a ''nasal cycle'' and although thi s term is now commonly used to describe spontaneous changes in nasal r esistance in man and animals, there is little evidence for any true pe riodicity. A major problem in increasing our knowledge and understandi ng of the so-called ''nasal cycle'' is that most studies have relied o n simple descriptions of the changes in nasal resistance and have not developed any numerical parameters to quantify the changes in resistan ce over time. This lack of definition of what actually constitutes a n asal cycle has meant that the literature of the present day generally accepts the views put forward by Heetderks (Am J Med Sci 1927: 174: 23 1-244) and Stoksted (Acta Otolaryngol (Stockh) 1953; Suppl 109:159-175 ) that around 80% of the healthy population exhibit a regular cycle. I n order to define the characteristics of the spontaneous changes in na sal airway resistance we have used numerical measures of reciprocity a nd also developed a measurement of the division of airflow between the nasal passages over time. With these two parameters it is possible to describe the nature of the spontaneous changes in airflow in numerica l terms and to define what exactly constitutes a nasal cycle. Fifty-tw o volunteers underwent hourly measurement of unilateral nasal airflow for 8 h. For each volunteer, two values were derived from the graph of unilateral nasal airflows against time: the correlation coefficient b etween unilateral airflows (r) and the airflow distribution ratio betw een the two nasal airways (ADR). The spread of different types of airf low pattern (nasal cycle) throughout the population was illustrated by plotting r against ADR for each subject. A nasal cycle was defined as having an I value between -0.6 and -1.0, and an ADR value between 0.7 and 1.0. Only 21% (11 of the 52 volunteers) exhibited airflow pattern s that could be defined as a nasal cycle in these terms. This finding contradicts the generally accepted, but undefined, view that around 80 % of the population exhibit a regular nasal cycle. The numerical defin ition of a nasal cycle in terms of both reciprocity and airflow distri bution. as described in this payer may help to clarify our understandi ng of this interesting phenomenon and allow rhinologists to describe t he spontaneous changes in nasal airflow in more exact terms than have been used previously in the literature.