Intensive longitudinal assessment of human olfaction

Summary Olfactory (i.e., smell) disorders are incredibly impactful. Gas leaks and spoiled food are undetectable dangers. Eating habits and the pleasure from food are compromised as meals become unpalatable. Affected individuals can feel disconnected from other people and the world, contributing to an increased incidence of depression. Changes in olfactory function may also be early indicators of other serious health problems such as rhinosinusitis, skull base tumors, cerebrospinal fluid leaks, viral infection, or neurodegenerative diseases. Routine testing of olfactory function can facilitate the early detection of smell disorders and comorbidities. Research studies and clinical assessments of the human sense of smell typically operate under the assumption that – barring insult from injury or disease – olfactory function is largely invariant on the time scale of hours, days, and even months. However, this common assumption is demonstratively false. For example, smell function varies on short timeframes like circadian cycles, and long timeframes like normal aging. Thus, clinicians and researchers need a better understanding of normal variation in olfactory ability if they are to accurately differentiate pathological dysfunction from normal fluctuations in function. Our proposed study will document typical olfactory fluctuations in healthy people, in people experiencing natural physiological changes or in those with smell disorders. In Aim 1, we will determine how olfactory detection thresholds (OdorDTs) fluctuate on a daily, monthly and yearly basis in a large age-, sex- and race-diverse cohort of healthy adults. In Aim 2, we will measure daily and weekly Odor DT changes accompanying either the menstrual cycle or pregnancy. Aim 3 will focus on determining daily, monthly and yearly fluctuations in OdorDT in people with quantitative smell disorders (i.e., anosmia or hyposmia) associated with previous upper respiratory viral infections or with Parkinson's disease. Collectively, these studies will provide the first intensive longitudinal assessment of olfactory function in healthy people and those with olfactory disorders. Further, they will result in an invaluable open resource for clinicians and researchers who are assessing olfactory function in different contexts.