Biomedical subjects

Hernando Ombao

Publications and source records attributed to Hernando Ombao.

5 recordsLinked to original sources

PubMed2003

Statistical tests for fMRI based on experimental randomization.

Statistical parametric mapping (SPM) analysis of fMRI data requires specifying correctly the temporal and spatial noise covariance structure. This is a difficult if not impossible task. When these assumptions are not satisfied, statistical inference can be invalid or inefficient. Permutation tests are free of strong assumptions on the distribution of signal noise. We propose permutation tests of fMRI data based on experimental randomization of the stimulus sequences. Smooth hemodynamic response curves are estimated using quadratic B-splines. We study fMRI data obtained from event-related potential (ERP) oddball paradigm. Tests of two-tone and three-tone stimulus sequences are conducted to illustrate the application of the proposed method. Comparisons of the SPM and proposed method show that a permutation test is more specific and less susceptible to artifacts.

Arousal↗

PubMed2002

A "gender blind" relationship of lean body mass and blood pressure in the Tecumseh study.

BACKGROUND: Body size correlates positively with blood pressure (BP) but there is controversy about the roles of obesity versus muscularity in this relationship. METHODS: We examined the BP relationship with overweight, lean body mass (LBM), and muscle performance in 231 adolescents (17.25 +/- 3.07 years, 123 males). The skinfold thickness (SKINT) was used to measure overweight, as this was a growing population. RESULTS: Maximal foot torque, a measure of muscle strength, correlated strongly (r = 0.51, P < .001) to LBM attesting to the validity of the calculated LBM. Anthropometric measurements were available also in 944 adults (29.9 +/- 5.5 years, 461 men). Correlations of LBM to systolic (adolescents r = 0.52, adults r = 0.19, both P < .001) and diastolic (adolescents r = 0.47, adults r = 0.20, both P < .001) BP were highly significant. SKINT also correlated significantly to systolic and diastolic BP in adolescents and in adults, respectively. In both genders and populations an increasing SKINT was associated with a similar increase in BP, but this effect was superimposed on an average 10 mm Hg between-gender BP difference. The LBM in both groups and genders related to the BP in an identical fashion; the men were on the high and the women on the low end of the same BP/LBM correlation line. Thus, the amount of LBM erased categoric BP differences between the genders. CONCLUSIONS: The gender-related BP differences appear to reflect the inherent gender differences in muscle bulk.

Adolescent↗

PubMed2002

Human regional cerebral glucose metabolism during non-rapid eye movement sleep in relation to waking.

Sleep is an essential human function. Although the function of sleep has generally been regarded to be restorative, recent data indicate that it also plays an important role in cognition. The neurobiology of human sleep is most effectively analysed with functional imaging, and PET studies have contributed substantially to our understanding of both rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. In this study, PET was used to determine patterns of regional glucose metabolism in NREM sleep compared with waking. We hypothesized that brain structures related to waking cognitive function would show a persistence of function into the NREM sleep state. Fourteen healthy subjects (age range 21-49 years; 10 women, 4 men) underwent concurrent EEG sleep studies and [(18)F]fluoro-2-deoxy-D-glucose PET scans during waking and NREM sleep. Whole-brain glucose metabolism declined significantly from waking to NREM sleep. Relative decreases in regional metabolism from waking to NREM sleep occurred in wide areas of frontal, parietal, temporal and occipital association cortex, primary visual cortex, and in anterior/dorsomedial thalamus. After controlling for the whole-brain declines in absolute metabolism, relative increases in regional metabolism from waking to NREM were found bilaterally in the dorsal pontine tegmentum, hypothalamus, basal forebrain, ventral striatum, anterior cingulate cortex and extensive regions of the mesial temporal lobe, including the amygdala and hippocampus, and in the right dorsal parietal association cortex and primary somatosensory and motor cortices. The reductions in relative metabolism in NREM sleep compared with waking are consistent with prior findings from blood flow studies. The relative increases in glucose utilization in the basal forebrain, hypothalamus, ventral striatum, amygdala, hippocampus and pontine reticular formation are new observations that are in accordance with the view that NREM sleep is important to brain plasticity in homeostatic regulation and mnemonic processing.

Adult↗

PubMed2002

Masking effects of posture and sleep onset on core body temperature have distinct circadian rhythms: results from a 90-min/day protocol.

Both recumbency and sleep affect core body temperature (CBT). To characterize their circadian effects and interactions, the authors examined the bedtime temperature drops (TDs) of nine men and eight women (aged 20 to 30) who repeated 90-min sleep-wake cycles over 2.5 days. While awake, subjects were exposed to 50 to 250 lux; while asleep, lights were off. Electroencephalogram-monitored time inbed lasted 30 min during each cycle. Cosinor nonlinear mixed-effects regressions modeled the circadian rhythm of TDs. The circadian maximum of TDs occurred approximately 4 h before the time of circadian CBT minimum, in a model that included the effects of baseline expected CBT, deviations from baseline CBT, time in study, and gender-dependent 24- and 12-h adjustments. Rates of temperature drops were faster during initial periods of lying awake than during periods of initially sleeping. Both rates followed separate circadian rhythms. The circadian maximum of TDs was located near customary nocturnal bedtimes, suggesting its role in fostering sleep during a normal bedtime routine. The apparent deceleration of temperature dropping at sleep onset supports the notion that the sleep onset period has complicated circadian neuroregulatory dynamics. These findings confirm the need for nonlinear models of temperature responses to postural changes and sleep that incorporate circadian variability in these masking effects.

Adult↗

PubMed2002

Prevalence of obesity and weight change during treatment in patients with bipolar I disorder.

BACKGROUND: Obesity is a major public health concern in the United States and its prevalence is increasing. Individuals with bipolar disorder tend to be overweight, and their treatment may exacerbate obesity and increase the risk of concurrent medical disease in this population. METHOD: This retrospective report from the Pittsburgh Study of Maintenance Therapies in Bipolar Disorder examines the prevalence of overweight (body mass index [BMI] = 25.0-29.9) and obesity (BMI > or = 30.0) in 50 consecutive subjects with bipolar I disorder (DSM-IV) and evaluates weight change during acute treatment and the first year of maintenance treatment. RESULTS: At entry into the study, 34 (68%) of the patients in this sample with bipolar disorder were obese or overweight. The prevalence of obesity was high (16 [32%] of the 50 patients in our sample). The number of previous depressive episodes contributed to the likelihood of being overweight or obese at study entry. During the trial, most of the weight gain occurred during acute treatment rather than during maintenance treatment. During acute treatment, the amount of increase of BMI was positively related to the score on the Hamilton Rating Scale for Depression and negatively related to the score on Bech-Rafaelsen Mania Scale. There was a negative relationship between BMI and tendency to gain weight, during both acute and maintenance treatment. CONCLUSION: The high prevalence of obesity in subjects with bipolar disorder emphasizes the need for specific treatment strategies and programs for weight control for these individuals. The minimal weight gain during the maintenance phase, the relationship of acute depressive episodes to weight gain, and the fact that stabilization on maintenance medication may facilitate the participation in specific interventions for weight loss provide additional support for the practice of maintenance treatment.

Adult↗