Time-Dependent Sensitization of Heart Rate and Blood Pressure over Multiple Laboratory Sessions in Elderly Individuals with Chemical Odor Intolerance

Abstract

In this study, we tested the hypothesis that low-level chemical odor intolerance (i.e., “cacosmia”) is a manifestation of heightened sensitizability to environmental stimuli. We examined supine heart rate and blood pressure of elderly individuals, who were classified as either having a higher degree of chemical odor intolerance (n = 12) or a lower degree of chemical odor intolerance (n = 13), upon awakening in a sleep research laboratory on 6 different days during an 8-wk protocol. During the 2 initial wk, they consumed a customary baseline diet (including ad lib milk and other dairy products), followed by 3 wk each of nondairy-containing and dairy-containing diets in randomly assigned, counterbalanced order. Measurements were made on 3 pairs of successive days, distributed over a 6-wk period, and on which different diets were consumed. The high-intolerance group had significantly higher mean supine systolic and diastolic blood pressures than did the low-intolerance group. Although subjects consumed milk products during both the initial baseline and subsequent dairy diet periods, the high-intolerance group had significantly higher heart rates and diastolic blood pressures later in the study than at baseline, especially when they were on the dairy diet. In contrast, the cardiovascular measures of the low-intolerance group lowered on average with time. The high-intolerance subjects had an increased mean diastolic blood pressure on the second days versus the first days in the laboratory (averaged across all diets). Collectively, the data suggest that elderly individuals with a high degree of chemical odor intolerance evidence (a) increased sympathetic tone in the cardiovascular system at rest over multiple measurements; and (b) greater sensitizability and/or lesser habituation of heart rate and diastolic blood pressure over time as a function, in part, of repeated environmental stressor exposures (i.e., a novel laboratory contextual setting and/or specific dietary constituents). Consistent with a sensitization model, the findings emphasize the need for two or more identical sessions at least 24 h apart in physiological studies of individuals with a high degree of intolerance for chemical odors versus normal individuals. The results of the blood pressure observations suggest that the possibility of abnormally labile autonomic function and cognitive sequelae in individuals with a high degree of intolerance for chemical odor increases with age.