A New Integrated Variable Based on Thermometry, Actimetry and Body Position (TAP) to Evaluate Circadian System Status in Humans

The disruption of the circadian system in humans has been associated with the development of chronic illnesses and the worsening of pre-existing pathologies. Therefore, the assessment of human circadian system function under free living conditions using non-invasive techniques needs further research. Traditionally, overt rhythms such as activity and body temperature have been analyzed separately; however, a comprehensive index could reduce individual recording artifacts. Thus, a new variable (TAP), based on the integrated analysis of three simultaneous recordings: skin wrist temperature (T), motor activity (A) and body position (P) has been developed. Furthermore, we also tested the reliability of a single numerical index, the Circadian Function Index (CFI), to determine the circadian robustness. An actimeter and a temperature sensor were placed on the arm and wrist of the non-dominant hand, respectively, of 49 healthy young volunteers for a period of one week. T, A and P values were normalized for each subject. A non-parametric analysis was applied to both TAP and the separate variables to calculate their interdaily stability, intradaily variability and relative amplitude, and these values were then used for the CFI calculation. Modeling analyses were performed in order to determine TAP and CFI reliability. Each variable (T, A, P or TAP) was independently correlated with rest-activity logs kept by the volunteers. The highest correlation (r = −0.993, p<0.0001), along with highest specificity (0.870), sensitivity (0.740) and accuracy (0.904), were obtained when rest-activity records were compared to TAP. Furthermore, the CFI proved to be very sensitive to changes in circadian robustness. Our results demonstrate that the integrated TAP variable and the CFI calculation are powerful methods to assess circadian system status, improving sensitivity, specificity and accuracy in differentiating activity from rest over the analysis of wrist temperature, body position or activity alone

Baby-Lag: Methods for assessing parental tiredness and fatigue

Altered sleep patterns, inadequate sleep, and fatigue are extremely common among new parents and form a major part of postpartum life. The first months of a new infant’s life are a time of extensive adjustment for families, and the experience of new parenthood is often colored by sleep deprivation and chronic tiredness—what has popularly been termed ‘Baby-Lag’. Studies of stress, depression, anxiety, and measures of parenting function and behaviors would all benefit from the inclusion of information about parental tiredness and fatigue. However, the measurement of states of tiredness and fatigue is complex and inconsistent. In this chapter, we review existing ‘etic’, or externally generated, methods that measure fatigue and tiredness, and assess their relevance and feasibility for use with new parents. Objective measures including polysomnography, actigraphy, and psychomotor vigilance tests have been widely used in the clinical arena. Subjective measures in which respondents rate their sleep within a given period, report on some aspects of sleep, or give details of their sleep ecology have been used in clinical populations and extended into community studies. We are not aware of sleep evaluations that successfully measure the invisible experience of parental sleep loss in the postpartum period from an internal or ‘emic’ perspective. The final section of the chapter presents narrative data from focus groups of mothers caring for infants under a year old. We propose the need for a novel instrument to capture key elements of the Baby-Lag phenomenon and offer suggestions for the development of such a tool