I read that the ancient Roman Dr. Galen had made that connection way back
then!

The first step in linking allergic rhinitis and asthma was taken centuries
ago. Galen, a Greek physician and one of the fathers of Western medicine,
postulated during the 2nd century A.D. that the nose serves a critical
function in warming and filtering inspired air on its way to the lungs. He
also believed that abnormal secretions originating from the interior of the
skull--such as those seen during head colds--could drip into the chest and
elicit lower respiratory symptoms such as cough.
In the 1500s however, human anatomists began to question the
interconnectedness of the upper and lower airways. In fact, any discussion
of a connection between the nose and lungs disappeared entirely from medical
literature until early in the 20th century, when ear, nose and throat
surgeons noticed that some cases of bronchitis and asthma showed striking
improvements when chronic nasal and sinus conditions were successfully
treated.

Still, it wasn't until the mid-to late-20th century--when the prevalence of
both allergic rhinitis and asthma began to rise--that physicians first took
notice of how often the two disorders occurred together in the same patient.
In fact, the most recent epidemiologic study of allergic diseases from the
Johns Hopkins School of Medicine revealed that over 95 percent of patients
who have allergic asthma also suffer from nasal allergies, in stark contrast
to the general population, of which only 20 percent are allergy sufferers.
Conversely, between 19 and 38 percent of allergic rhinitis patients are
asthmatic as well, while only 3 to 5 percent of the general population
suffer from asthma.

ASTHMA AND ALLERGY LINK

Results from research completed over the past two years suggest that
patients who have both allergic rhinitis and asthma also suffer more
debilitating chest symptoms than patients with asthma alone. A recent
analysis of over 1200 asthmatics, half of whom had rhinitis and half of whom
did not, showed that patients who had both rhinitis and asthma were much
more likely to have nighttime awakening due to asthma (19.6 percent versus
11.8 percent), meet the criteria for "moderate to severe asthma" as defined
by the National Asthma Education and Prevention Program (60.2 percent versus
51.2 percent), or miss work because of asthma attacks (24.1 percent versus
12.1 percent). In addition, these patients were more likely to require more
potent medications, such as oral steroids, to treat their disease.

You can read entire article at:

http://www.findarticles.com/p/articles/mi_m1511/is_3_20/ai_54359927

This explains why the Xylitol nasal wash is so helpful.