Investigation Of Interaction Between Physiological Signals And fMRI Dynamic Functional Connectivity Using Independent Component Analysis.

The blood oxygen level dependent (BOLD) fMRI signal is influenced not only by neuronal activity but also by fluctuations in physiological signals, including respiration, arterial CO2 and heart rate/ heart rate variability (HR/HRV). Even spontaneous physiological signal fluctuations have been shown to influence the BOLD fMRI signal in a regionally specific manner. Consequently, estimates of functional connectivity between different brain regions, performed when the subject is at rest, may be confounded by the effects of physiological signal fluctuations. In addition, resting functional connectivity has been shown to vary with respect to time (dynamic functional connectivity - DFC), with the sources of this variation not fully elucidated. The effect of physiological factors on dynamic (time-varying) resting-state functional connectivity has not been studied extensively, to our knowledge. In our previous study, we investigated the effect of heart rate (HR) and end-tidal CO2 (PETCO2) on the time-varying network degree of three well-described RSNs (DMN, SMN and Visual Network) using mask-based and seed-based analysis, and we identified brain-heart interactions which were more pronounced in specific frequency bands. Here, we extend this work, by estimating DFC and its corresponding network degree for the RSNs, employing a data-driven approach to extract the RSNs (low-and high-dimensional Independent Component Analysis (ICA)), which we subsequently correlate with the characteristics of simultaneously collected physiological signals. The results confirm that physiological signals have a modulatory effect on resting-state, fMRI-based DFC.

Spontaneous physiological variability modulates dynamic functional connectivity in resting-state functional magnetic resonance imaging.

It is well known that the blood oxygen level-dependent (BOLD) signal measured by functional magnetic resonance imaging (fMRI) is influenced-in addition to neuronal activity-by fluctuations in physiological signals, including arterial CO2, respiration and heart rate/heart rate variability (HR/HRV). Even spontaneous fluctuations of the aforementioned physiological signals have been shown to influence the BOLD fMRI signal in a regionally specific manner. Related to this, estimates of functional connectivity between different brain regions, performed when the subject is at rest, may be confounded by the effects of physiological signal fluctuations. Moreover, resting functional connectivity has been shown to vary with respect to time (dynamic functional connectivity), with the sources of this variation not fully elucidated. In this context, we examine the relation between dynamic functional connectivity patterns and the time-varying properties of simultaneously recorded physiological signals (end-tidal CO2 and HR/HRV) using resting-state fMRI measurements from 12 healthy subjects. The results reveal a modulatory effect of the aforementioned physiological signals on the dynamic resting functional connectivity patterns for a number of resting-state networks (default mode network, somatosensory, visual). By using discrete wavelet decomposition, we also show that these modulation effects are more pronounced in specific frequency bands.

Arterial CO2 effects modulate dynamic functional connectivity in resting-state fMRI.

It is well known that the blood-oxygen level dependent (BOLD) signal measured by functional magnetic resonance imaging (fMRI) is influenced - in addition to neuronal activity - by fluctuations in physiological signals, including arterial CO2. For instance, even spontaneous CO2 fluctuations have been shown to influence the BOLD fMRI signal regionally. Related to this, studies of functional connectivity between different brain regions, performed when the subject is at rest, may be confounded by the effects of physiological noise. Moreover, resting functional connectivity has been shown to vary with respect to time (dynamic functional connectivity), with the sources of this variation not fully understood at present. In this context, in the present paper we examine the relation between dynamic functional connectivity patterns and the properties of the end-tidal CO2 signal (PETCO2) using resting-state fMRI measurements from 12 healthy subjects. The results demonstrate that there exists a modulatory effect of the correlation strength between PETCO2 and the BOLD signal on dynamic resting functional connectivity. The extent to which this effect was observed was found to be strongly dependent on the data analysis methodology.

Prophylactic feeding tubes for patients with locally advanced head-and-neck cancer undergoing combined chemotherapy and radiotherapy-systematic review and recommendations for clinical practice.

GOALS: This work aimed to determine the benefits and risks of prophylactic feeding tubes for adult patients with squamous cell carcinoma of the head and neck who receive combined chemotherapy and radiotherapy with curative intent and to make recommendations on the use of prophylactic feeding tubes and the provision of adequate nutrition to this patient population. METHODS: A national multidisciplinary panel conducted a systematic review of the evidence and formulated recommendations to guide clinical decision-making. The draft evidence summary and recommendations were distributed to clinicians across Canada for their input. MAIN RESULTS: No randomized controlled trials have directly addressed this question. Evidence from studies in the target population was limited to seven descriptive studies: two with control groups (one prospective, one retrospective) and five without control groups. Results from ten controlled studies in patients treated with radiotherapy alone were also reviewed. CONCLUSIONS: The available evidence was insufficient to draw definitive conclusions about the effectiveness of prophylactic feeding tubes in the target patient population or to support an evidence-based practice guideline. After review of the evidence, of guidelines from other groups, and of current clinical practice in Canada, the multidisciplinary panel made consensus-based recommendations regarding comprehensive interdisciplinary clinical care before, during, and after cancer treatment. The recommendations are based on the expert opinion of the panel members and on their understanding of best clinical practice.

Anomalies in dual energy X-ray absorptiometry measurements of total-body bone mineral during weight change using Lunar, Hologic and Norland instruments.

A previous study showed that measurements of total-body bone mineral changes made with a Hologic QDR 1000W were unreliable when the subjects underwent weight change. The study has been extended to dual energy X-ray absorptiometry (DXA) apparatus from other manufacturers. Re-analysis of published results during weight loss using a Lunar DPX showed that they varied with the software used. Using the Extended mode, there was a 1% loss of bone mineral areal density (BMD), but no significant change in bone mineral content (BMC) or bone area (BA) following a weight loss of 16 kg, whereas the use of the Standard mode led to a larger fall of BMC and BMD. Similar findings arose from the consideration of two studies using Norland XR 26 HS absorptiometers. On the other hand, separation of two groups with similar weight changes from the population studied with a Hologic QDR 1000W confirmed that BMC changed directly with weight, but there was an inverse relationship for BMD, owing to an inappropriate change of BA. The use of Hologic Enhanced and Standard software modes led to significant differences in initial readings and measured changes. With each instrument there was a strong correlation between changes in BA and changes in BMC. When 6 kg of lard was wrapped around the limbs of volunteers or a semi-anthropomorphic phantom to simulate weight change, there were spurious increases of measured BMC and BA by about 5% with each instrument. There were no changes of BMD with Lunar, variable results with Norland, but decreases with Hologic. The results observed in vivo could be explained by the effects of fat changes, without there being any real change of bone mineral. Changes of BMD in the skeleton of the phantom were underestimated with all three brands. The anomaly observed with the Hologic QDR 1000W is less apparent with a Lunar DPX or a Norland XR 26, but there are sufficient uncertainties for all total-body measurements during weight change to be treated with suspicion.

Changes in body composition and fat distribution after short-term weight gain in patients with anorexia nervosa.

The most commonly described psychologic abnormality associated with anorexia nervosa is a distorted perception of body weight and shape. This perception may contribute to the anorexic patient's resistance to gaining weight even when it is a medical necessity. The purpose of this study was to assess body-composition and fat-distribution changes after short-term weight gain in 26 female anorexia nervosa patients 27.6 +/- 6.6 (mean +/- SD) y of age, with a body mass index (BMI; in kg/m2) of 16.5 +/- 1.9. They participated in a refeeding protocol both as inpatients (n = 21) and as outpatients (n = 5) until they achieved maximum weight gain. Body-composition and fat-distribution changes were measured by using dual-energy X-ray absorptiometry (DXA) and skinfold thickness and circumference measurements. A mean weight gain of 6.7 +/- 5.3 kg (P < 0.001) was observed, which included significant increases in body fat (P < 0.001), lean body mass (P < 0.05), and bone mineral content (P < 0.01), with body fat being the component that increased the most. When measured by DXA, fat gain was not significantly different among the three central regions: subscapular, 1.7 +/- 1.2 kg; waist, 1.8 +/- 1.3 kg; and thigh, 1.5 +/- 1.0 kg (P = 0.10). Thus, although fat was the largest component of the weight gained, there was no preferential fat deposition in any one area and the female gynoid body shape was maintained.

The reliability of bioelectrical impedance analysis for measuring changes in the body composition of patients with anorexia nervosa.

OBJECTIVE: To determine whether bioelectrical impedance analysis (BIA) is a valid measure of change in body fat in anorexia nervosa (AN) patients during refeeding, as compared to skinfold calipers (SF). METHODS: Prospective cohort study with measures of BIA and SF performed once a month for 3 months on patients meeting the DSM-III-R criteria for AN who received treatment from the Eating Disorders Clinic of a university teaching hospital as inpatients or outpatients. RESULTS: Twenty patients completed the study. Comparison of the two methods by the Pearson correlation coefficient showed a weak negative correlation of r = -.305. Analysis by a graphical method confirmed the poor agreement that exists between the two methods. DISCUSSION: The inability of BIA to detect changes in body composition due to altered hydration, and to accurately assess the distribution of water between intracellular and extracellular compartments, limits its clinical usefulness in AN. It appears that SF measurements are preferable to BIA as a measure of body fat change in patients with AN.

Accuracy of subcutaneous fat measurement: comparison of skinfold calipers, ultrasound, and computed tomography.

OBJECTIVE: The purpose of this study was to compare skinfold caliper and ultrasound measurement of subcutaneous body fat at three abdominal sites with computed tomography, which is considered to be the gold standard. DESIGN: This was a cross-sectional study in which computed-tomography, ultrasound, and skinfold caliper measurements were made at three distinct abdominal sites. All body composition and anthropometric measurements were performed on each subject on one occasion. SUBJECTS: Twenty-two subjects were recruited (13 men and 9 women). Mean ages (+/- standard deviation) were 43 +/- 4 years for the women and 51 +/- 18 years for the men. All subjects had been previously scheduled for an abdominal or pelvic computed-tomography scan at the Department of Radiology, St Paul's Hospital, Vancouver, British Columbia, Canada, and participated in the study on a volunteer basis. MAIN OUTCOME MEASURES: A better agreement was found between the skinfold calipers and computed-tomography methods than between the ultrasound and computed-tomography method for the measurement of subcutaneous body fat. This was observed when the data were analyzed for both correlational agreement and for graphical interpretation. STATISTICAL ANALYSES PERFORMED: The relationships among skinfold, ultrasound, and computed-tomography measurements were analyzed by determining Pearson correlation coefficients. A graphical method described by Bland and Altman was also used to assess agreement among the three methods. RESULTS: Significant correlation coefficients were observed between skinfold calipers and computed tomography at all three abdominal sites (site 1, r = .60, P = .003; site 2, r = .70, P = .0001; site 3, r = .73, P = .0001). Ultrasound and computed-tomography methods only showed a significant correlation at site 3 (r = .54; P = .009). The graphical method revealed that the variation in the ultrasound measurements was much greater than that of the skinfold measurements when compared to computed-tomography values. APPLICATIONS/CONCLUSIONS: The results of this study indicated that relative agreement in the measurement of subcutaneous body fat between skinfold and computed-tomography measurements was superior to that exhibited between ultrasound and computed-tomography measurements. This finding enhances the potential use of skinfold calipers in the clinical setting, particularly in view of the fact that measurement of subcutaneous body fat at different body sites is becoming increasingly important for the characterization of risk of certain disease states.