Upper Airway here refers to the throat and trachea (our windpipe / “breathing tube”) (see Diagram — Upper Respiratory System). Sudden onset of shortness of breath from tracheal obstruction is most commonly cause by choking on something. It can also be due to various infections (see Sore Throat), or swelling from Anaphylaxis (acute allergy).
More gradual shortness of breath due to tracheal obstruction can develop from growing tumors, either inside the trachea or larynx (voice box), or in the neck. A key sign we can hear with stethoscopes is stridor, squeaky like a wheeze but during inspiration (breathing in; true wheezes from the lungs, like in asthma, occur during expiration). It can also be diagnosed by pulmonary function tests.
If someone is choking on food, perform a Heimlich maneuver if you know how. But never do this unless the person cannot utter a single sound more than a bare squeak, or if they fall unconscious. Never perform a Heimlich on somebody actively coughing.