Biomedical subjects

Matthew R Marler

Publications and source records attributed to Matthew R Marler.

7 recordsLinked to original sources

PubMed2006

The sigmoidally transformed cosine curve: a mathematical model for circadian rhythms with symmetric non-sinusoidal shapes.

We introduce a family of non-linear transformations of the traditional cosine curve used in the modelling of biological rhythms. The non-linear transformation is the sigmoidal family, represented here by three family members: the Hill function, the anti-logistic function, and the arctangent function. These transforms add two additional parameters that must be estimated, in addition to the acrophase, MESOR, and amplitude (and period in some applications), but the estimated curves have shapes requiring many more than two additional harmonics to achieve the same fit when modelled by harmonic regression. Particular values of the additional parameters can yield rectangular waves, narrow pulses, wide pulses, and for rectangular waves (representing alternating 'on' and 'off' states) the times of onset and offset (hence duration, as when modelling the duration of the large night-time melatonin secretory epoch). We illustrate the sigmoidally transformed cosine curves, and compare them to harmonic regression modelling, in a sample of eight activity recordings made on patients in a nursing home.

Aged↗

PubMed2006

Social-cognitive correlates of CPAP adherence in experienced users.

BACKGROUND AND PURPOSES: Obstructive sleep apnea (OSA) is a condition with serious medical and psychosocial consequences. However, poor adherence with nasal continuous positive airway pressure (CPAP) treatment limits the effectiveness of treatment. Behavior change factors offer one avenue of research to better understand the correlates of CPAP adherence. PATIENTS AND METHODS: Fifty-eight participants who had been diagnosed with OSA and prescribed CPAP treatment agreed to complete questionnaires that assessed sleep apnea symptoms, behavior change factors, and CPAP side effects, and to have their CPAP data downloaded. Behavior change factors from both social cognitive theory (SCT) and the transtheoretical model (TM) were assessed. The primary aim of the study was to examine the relationship between these social-cognitive factors and objectively measured CPAP adherence. RESULTS: Participants had been using CPAP for a mean of 2.1 years. SCT variables (adjusted R(2)=0.115, P=.008) and TM variables (adjusted R(2)=0.157, P<.0001) each accounted for a statistically significant amount of variance in CPAP adherence. CONCLUSIONS: The results suggest that social-cognitive factors may be associated with CPAP adherence in experienced CPAP users. The principal advantage to these theory-driven and empirically validated factors is that they are modifiable and can provide the basis for effective interventions to increase CPAP adherence.

Body Mass Index↗

PubMed2005

Fatigue, sleep, and circadian rhythms prior to chemotherapy for breast cancer.

GOALS: Previous investigations have shown that women undergoing chemotherapy for breast cancer experience both disturbed sleep and fatigue. However, most of the previous research examined women either during or after chemotherapy. This study examined sleep, fatigue, and circadian rhythms in women with breast cancer before the start of chemotherapy. PATIENTS AND METHODS: Eighty five women with Stages I-IIIA breast cancer who were scheduled to begin adjuvant or neoadjuvant anthracycline-based chemotherapy participated. Each had sleep/wake activity recorded with actigraphy for 72 consecutive hours and filled out questionnaires on sleep, fatigue, depression, and functional outcome. MAIN RESULTS: On average, the women slept for about 6 h a night and napped for over an hour during the day. Sleep was reported to be disturbed and fatigue levels were high. Circadian rhythms were robust, but women who were more phase-delayed reported more daily dysfunction (p<0.01). CONCLUSIONS: The data from the current study suggest that the women with breast cancer likely experience both disturbed sleep and fatigue before the beginning of chemotherapy. Although their circadian rhythms are robust, breast cancer patients with more delayed rhythms experience more daily dysfunction secondary to fatigue. These data suggest that strategies to improve disturbed sleep and to phase-advance circadian rhythms prior to initiation of chemotherapy may be beneficial in improving daily function in breast cancer patients.

Adult↗

PubMed2005

The relationship between fatigue and light exposure during chemotherapy.

BACKGROUND: Fatigue is one of the most common and distressing complaints among cancer patients, not only during radiation and chemotherapy, but also for months to years after the completion of treatment. Fatigue interferes with patients' daily lives, reduces their quality of life, and is often a significant reason why patients discontinue treatment. We hypothesized that some of the fatigue may be related to disrupted circadian rhythms and low light exposure. The main objective of this study therefore was to investigate the association between fatigue and light exposure among patients with breast cancer. METHODS: As part of a larger, ongoing prospective study on fatigue, sleep, and circadian rhythms in patients with breast cancer, an analysis of 63 women newly diagnosed with stage I-IIIA breast cancer and scheduled to receive four cycles of adjuvant or neoadjuvant anthracycline-based chemotherapy was conducted. Data were collected before and during weeks 1, 2, and 3 of cycle 1 and cycle 4. Fatigue was assessed using the Short Form of Multidimensional Fatigue Symptom Inventory. Light exposure was recorded with a wrist actigraph. RESULTS: There were significant correlations between fatigue levels and light exposure (r=-0.28 to -0.45) within both cycle 1 and cycle 4, such that higher levels of fatigue were associated with less light exposure. There were also significant correlations between changes in light exposure and changes in fatigue within the first 2 weeks of each cycle (r=-0.28 to -0.52). CONCLUSIONS: Increased fatigue was significantly correlated with decreased light exposure among patients with breast cancer. Although the cause and effect of exacerbated fatigue and decreased light exposure cannot be confirmed by the current study, and lower light exposure may just in part be due to the fatigued patients spending less time outdoors in bright light, two hypotheses are proposed about the mechanisms by which light may alleviate the fatigue of patients with breast cancer. These results suggest the need for prospective intervention studies of light therapy for breast-cancer-related fatigue.

Adult↗

PubMed2003

PRC bisection tests.

This communication presents a new method for evaluating phase response curves (PRCs). A PRC describes the phase shifts produced in an oscillator by stimuli applied at different initial phase-states of that oscillator. In the PRC bisection tests, we repeatedly cut in half the circular distribution of the initial phase-states of the oscillator when stimuli are given. Empirically, we locate that optimal diameter which best bisects the circular distribution of phase responses into arcs of relative phase advance and phase delay. We compute a D score reflecting the success of the best bisection. The null hypothesis of a random distribution of phase responses by initial phase is tested with a Monte Carlo procedure, which computes Dr scores from random combinations of phase shifts with initial phases, thus determining the probability, given the null hypothesis, that the observed D score was from a random distribution. The bisection procedure can be extended to examine whether stronger phase shifts are produced in one phase response curve than in contrasting curves. Also, the bisection procedure yields an estimate of the inflection point of the phase response curve. A method is given to estimate the power of the PRC bisection test.

Animals↗

PubMed2002

Mortality associated with sleep duration and insomnia.

BACKGROUND: Patients often complain about insufficient sleep or chronic insomnia in the belief that they need 8 hours of sleep. Treatment strategies may be guided by what sleep durations predict optimal survival and whether insomnia might signal mortality risks. METHODS: In 1982, the Cancer Prevention Study II of the American Cancer Society asked participants about their sleep duration and frequency of insomnia. Cox proportional hazards survival models were computed to determine whether sleep duration or frequency of insomnia was associated with excess mortality up to 1988, controlling simultaneously for demographics, habits, health factors, and use of various medications. RESULTS: Participants were more than 1.1 million men and women from 30 to 102 years of age. The best survival was found among those who slept 7 hours per night. Participants who reported sleeping 8 hours or more experienced significantly increased mortality hazard, as did those who slept 6 hours or less. The increased risk exceeded 15% for those reporting more than 8.5 hours sleep or less than 3.5 or 4.5 hours. In contrast, reports of "insomnia" were not associated with excess mortality hazard. As previously described, prescription sleeping pill use was associated with significantly increased mortality after control for reported sleep durations and insomnia. CONCLUSIONS: Patients can be reassured that short sleep and insomnia seem associated with little risk distinct from comorbidities. Slight risks associated with 8 or more hours of sleep and sleeping pill use need further study. Causality is unproven.

Adult↗

PubMed2002

Determinants of nasal CPAP compliance.

BACKGROUND: Obstructive sleep apnea is a prevalent condition with potentially serious medical and psychosocial consequences. Nasal continuous positive airway pressure (CPAP) is the treatment-of-choice and has been shown to reduce the frequency of nocturnal respiratory events, improve sleep architecture and decrease daytime sleepiness. Patient compliance with CPAP is disappointingly low. Previous studies examining determinants of CPAP compliance have limited the variables studied to patient (sociodemographic), disease status, and treatment variables, with few reliable determinants found. METHODS: The purpose of the current study was to investigate the relationship between objectively measured CPAP compliance and variables from social cognitive theory (SCT) and the transtheoretical model (TM). Scales that measure variables from each model were developed and reliability evaluated. The relationship between the SCT and TM variables and compliance at 1-month post-CPAP-fitting was prospectively evaluated on 51 first-time CPAP users. SCT and TM variables were measured on the day of CPAP-fitting, at 1-week post-CPAP-fitting, and at 1-month post-CPAP-fitting. RESULTS: SCT variables measured 1-week post-CPAP-fitting (R(2)=0.261, P=0.001) and TM variables measured 1-week post-CPAP-fitting (R(2)=0.17, P=0.002) accounted for a statistically significant amount of variance in objective CPAP compliance measured at 1 month. The decisional balance index (from TM) individually accounted for a significant amount of variance in objective CPAP compliance in the above analyses. CONCLUSIONS: The ability of these new behavior change scales to predict CPAP compliance provides us with a new direction of research to better understand factors associated with compliance. The principal advantage of these theory-driven and empirically validated scales are that they measure modifiable factors that can provide the basis for sound interventions to improve CPAP compliance.

Journal Article↗