Aino Tietäväinen

Organ doses and effective doses in pediatric radiography: Patient-dose survey in finland

Background: Use of the effective dose in diagnostic radiology permits the radiation exposure of diverse diagnostic procedures to be quantified. Fundamental knowledge of patient doses enhances the implementation of the “as low as reasonably achievable” (ALARA) principle. Purpose: To provide comparative information on pediatric examination protocols and patient doses in skull, sinus, chest, abdominal, and pelvic radiography examinations. Material and Methods: 24 Finnish hospitals were asked to register pediatric examination data, including patient information and examination parameters and specifications. The total number of examinations in the study was 1916 (1426 chest, 228 sinus, 96 abdominal, 94 skull, and 72 pelvic examinations). Entrance surface dose (ESD) and dose-area products (DAP) were calculated retrospectively or DAP meters were used. Organ doses and effective doses were determined using a Monte Carlo program (PCXMC). Results: There was considerable variation in examination protocols between different hospitals, indicating large variations in patient doses. Mean effective doses of different age groups ranged from 5 µSv to 14 µSv in skull and sinus examinations, from 25 µSv to 483 µSv in abdominal examinations, and from 6 µSv to 48 µSv in chest examinations. Conclusion: In chest and sinus examinations, the amount of data was extensive, allowing national pediatric diagnostic reference levels to be defined. Parameter selection in pediatric examination protocols should be harmonized in order to reduce patient doses and improve optimization.

Posturographic sleepiness monitoring

Although reduced sleep often underlies traffic and occupational accidents, convenient sleepiness testing is lacking. We show that posturographic balance testing addresses this issue, because balance testing predicts hours of wakefulness, which could facilitate sleepiness testing. Here, we equate balance scores from separate trials, blinded to the experimenter, with those recorded as a function of known and increasing time awake (i.e. during sustained wakefulness); we show, that the time awake in separate trials is posturographically measurable: positive predictive value 69%, sensitivity 56%, and specificity 96%. These results encourage further work developing posturographic sleepiness monitoring.

Bayesian inference of physiologically meaningful parameters from body sway measurements

The control of the human body sway by the central nervous system, muscles, and conscious brain is of interest since body sway carries information about the physiological status of a person. Several models have been proposed to describe body sway in an upright standing position, however, due to the statistical intractability of the more realistic models, no formal parameter inference has previously been conducted and the expressive power of such models for real human subjects remains unknown. Using the latest advances in Bayesian statistical inference for intractable models, we fitted a nonlinear control model to posturographic measurements, and we showed that it can accurately predict the sway characteristics of both simulated and real subjects. Our method provides a full statistical characterization of the uncertainty related to all model parameters as quantified by posterior probability density functions, which is useful for comparisons across subjects and test settings. The ability to infer intractable control models from sensor data opens new possibilities for monitoring and predicting body status in health applications.

Saccadic eye movements estimate prolonged time awake

Prolonged time awake increases the need to sleep. Sleep pressure increases sleepiness, impairs human alertness and performance and increases the probability of human errors and accidents. Human performance and alertness during waking hours are influenced by homeostatic sleep drive and the circadian rhythm. Cognitive functions, especially attentional ones, are vulnerable to circadian rhythm and increasing sleep drive. A reliable, objective and practical metrics for estimating sleepiness could therefore be valuable. Our aim is to study whether saccades measured with electro‐oculography (EOG) outside the laboratory could be used to estimate the overall time awake without sleep of a person. The number of executed saccades was measured in 11 participants during an 8‐min saccade task. The saccades were recorded outside the laboratory (Naval Academy, Bergen) using EOG every sixth hour until 54 hr of time awake. Measurements were carried out on two occasions separated by 10 weeks. Five participants participated in both measurement weeks. The number of saccades decreased during sustained wakefulness. The data correlated with the three‐process model of alertness; performance differed between participants but was stable within individual participants. A mathematically monotonous relation between performance in the saccade task and time awake was seen after removing the circadian rhythm component from measured eye movement data. The results imply that saccades measured with EOG can be used as a time‐awake metric outside the laboratory.

A simple posturographic method detects the difference in recovery of patients receiving endoscopic sedation with propofol vs. midazolam

Background: Measurement of the residual effects of sedatives on fitness for ambulation is typically performed with subjective measures, if at all. Previous efforts to objectively measure these effects employed dynamic posturography with expensive equipment that is not easily brought to the bedside and carries a risk of patient injury. A simple test employing consumer off-the-shelf technology that exposes the patient to no more risk than standing still might permit a more reliable assessment of fitness for discharge. We have previously shown that a simple tester, using a Nintendo Wii® Balance board and software that determined fuzzy sample entropy of postural sway can separate outpatients’ postural steadiness before (PRE) and after (POST) endoscopy with midazolam/fentanyl conscious sedation. Propofol/fentanyl monitored anesthesia care also alters balance, but recovery is known to be more rapid. We hypothesized that the ability to detect decrements in postural steadiness with fuzzy sample entropy following monitored anesthesia care would be less than that seen in conscious sedation. Methods: Fuzzy sample entropy of sway was measured in 92 patients undergoing monitored anesthesia care and 103 patients undergoing conscious sedation for minor endoscopic procedures under conditions of eyes open and closed in the PRE and POST states. The ability to discriminate the PRE and POST states was assessed by the area under the receiver operating characteristic curve (AUC). Results: In patients undergoing conscious sedation, fuzzy sample entropy was lower both with eyes open and closed (0.83 and 0.80). Following monitored anesthesia care, the PRE and POST states were less separable, with AUC of 0.56 and 0.60 (eyes open and closed). Conclusions: A simple tester that determines fuzzy sample entropy of postural sway yields a result that is expected when applied to groups receiving different sedation modalities. The utility of this tester in assessing outcomes will require further evaluation. Correspondence to: Mandel JE, Department of Anesthesiology & Critical Care, Perelman School of Medicine, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA, E-mail: MandelJ@uphs.upenn.edu/Jeff. Mandel@uphs.upenn.edu Received: March 14, 2017; Accepted: April 14, 2017; Published: April 17, 2017 Introduction Patients undergoing elective endoscopy frequently require sedation. While sedation improves patient acceptance of the procedure, and may improve procedural outcome, sedation is associated with a period of impaired postural steadiness. Accurate assessment of the degree of decreased postural steadiness can be challenging, and measures such as time to recovery room discharge or ambulation without assistance may be subject to bias and inter-observer variability. An objective method of assessment could address these limitations. Posturography measures the trajectory of the ground projection of the center-of-pressure of a subject standing on an instrumented surface. Posturography may be static or dynamic, that is, employ exogenous stimuli to introduce a disturbance into posture, such as a moving platform or a shifting artificial horizon. Previous studies of sedation effects on postural stability focused on computerized dynamic posturography as it has greater sensitivity than static posturography. Fujisawa demonstrated that computerized dynamic posturography was affected by midazolam [1], that these effects persisted longer in the elderly than in young people [2], and that the effects were less persistent with propofol sedation [3]. These authors further demonstrated that the results of the timed up and go test, in which a patient stood up, walked five meters, turned, and returned to their chair, correlated with the computerized dynamic posturography score [3,4]. Although computerized dynamic posturography and the timed up and go test may be sensitive measures of recovery, these tests may not be appropriate for all patients. Patients standing on a moving platform or walking and turning may suffer injuries as severe as those we seek to avoid. Thus, static posturography may be preferable to dynamic posturography when assessing patients recovering from anesthesia or sedation. Posturography typically employs simple measures of postural sway such as velocity and sway radius. Since robust control of posture requires random perturbation of the center of pressure to permit dynamic tuning of the system [5], measures that assess entropy may more efficiently identify a decrement in capacity to maintain upright stance than the simpler measures [6,7]. We previously demonstrated the superiority of fuzzy sample entropy over other linear and nonlinear Mandel JE (2017) A simple posturographic method detects the difference in recovery of patients receiving endoscopic sedation with propofol vs. midazolam Volume 1(2): 2-4 Med Res Innov, 2017 doi: 10.15761/MRI.1000107 measures of postural sway in differentiation of the pre-sedative state from the post-recovery state in patients undergoing midazolamfentanyl based conscious sedation [8]. We have also demonstrated that time to ambulation without assistance was shorter with propofolbased sedation than with midazolam-based sedation [9] indeed, in the propofol group time to ambulation was less than the minimum time that patients are required to stay in the recovery room prior to discharge, while in the midazolam group, it was almost identical to this time. It is therefore likely that patients receiving monitored anesthesia care are more completely recovered at discharge than patients receiving conscious sedation. We hypothesized that this difference in recovery to street readiness between midazolam and propofol-based sedation would be demonstrable with fuzzy sample entropy of postural sway.

Baseline adjustment increases accurate interpretation of posturographic sway scores.

Postural steadiness may be quantified using posturographic sway measures. These measures are commonly used to differentiate between a persons baseline balance and balance related to some physiological condition. However, the difference in sway scores between the two conditions may be difficult to detect due to large inter-subject variation. We compared detection accuracy provided by three models that linearly regress a sway measure (mean distance, velocity, or frequency) on the effect of eye closure on balance (eyes open (EO) vs. eyes closed (EC)). In Model 1 the dependent variable is a single sway score (EO or EC), whereas in Models 2 and 3 it is a change score (EO-EO or EC-EO). The independent variable is always the group (group=0: EO or group=1: EC). Model 3 also accounts for the regression to the mean effect (RTM), by considering the baseline value (EO) as a covariate. When differentiating between EO and EC conditions, 94% accuracy can be achieved when using mean velocity as sway measure and either Model 2 or 3. Thus by adjusting for baseline score one increases the accurate interpretation of posturographic sway scores.