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.

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.