A pilot study of high frequency accelerometry-based sedation and agitation monitoring in critically ill patients

OBJECTIVE

The degree of sedation or agitation in critically ill patients is typically assessed with the Richmond Agitation and Sedation Scale (RASS). However, this approach is intermittent and subject to unrecognised variation between assessments. High frequency accelerometry may assist in achieving a quantitative and continuous assessment of sedation while heralding imminent agitation.

DESIGN

We undertook a prospective, observational pilot study.

SETTING

An adult tertiary intensive care unit in Melbourne, Australia.

PARTICIPANTS

20 patients with an admission diagnosis of trauma.

MAIN OUTCOME MEASURES

Accelerometers were applied to patients' wrists and used to continuously record patient movement. Video data of patient behaviour were simultaneously collected, and observers blinded to accelerometry data were adjudicated the RASS score every 30 seconds. Exploratory analyses were undertaken.

RESULTS

Patients were enrolled for a median duration of 9.7 hours (interquartile range [IQR], 0-22.8) and a total of 160 hours. These patients had a median RASS score of 0 (IQR, -4 to 0). A 2-minute moving window of amplitude variance was seen to reflect contemporaneous fluctuations in motor activity and was proportional to the RASS score. Furthermore, the moving window of amplitude variance was observed to spike immediately before ≥ 2 point increases in the RASS score.

CONCLUSIONS

We describe a novel approach to the analysis of wrist accelerometry data in critically ill patients. This technique not only appears to provide novel and continuous information about the depth of sedation or degree of agitation, it is also notable in its aptitude to anticipate impending transitions to higher RASS values.

Electromyographic patterns suggest changes in motor unit physiology associated with early osteoarthritis of the knee

OBJECTIVE

To assess characteristics of active motor units (MUs) during volitional vastus medialis (VM) activation in adults with symptomatic knee osteoarthritis (OA) across the spectrum of radiographic severity and age-comparable healthy control volunteers.

METHODS

We evaluated 39 participants (age 65+/-3 years) in whom weight-bearing knee X-rays were assigned a Kellgren & Lawrence (KL) grade (18 with KL grade=0; four each with KL grades=1, 2 and 4; nine with grade 3). Electromyography (EMG) signals were simultaneously acquired using surface [surface EMG (S-EMG)] and intramuscular needle electrodes, and analyzed by decomposition-enhanced spike-triggered averaging to obtain estimates of size [surface-represented MU action potentials (S-MUAP) area], number [MU recruitment index (MURI)] and firing rates [MU firing rates (mFR)] of active MUs at 10%, 20%, 30% and 50% effort relative to maximum voluntary force [maximal voluntary isometric contraction (MVIC)] during isometric knee extension.

RESULTS

Knee extensor MVIC was lower in OA participants, especially at higher KL grades (P=0.05). Taking the observed force differences into account, OA was also associated with activation of larger MUs (S-MUAP area/MVICx%effort; P<0.0001). In contrast, the estimated number of active units (MURI/MVICx%effort) changed differently as effort increased from 10% to 50% and was higher with advanced OA (KL=3, 4) than controls (P=0.0002).

CONCLUSION

VM activation changes at the level of the MU with symptomatic knee OA, and this change is influenced by radiographic severity. Poor muscle quality may explain the pattern observed with higher KL grades, but alternative factors (e.g., nerve or joint injury, physical inactivity or muscle composition changes) should be examined in early OA.

Hormone replacement therapy and longitudinal changes in blood pressure in postmenopausal women

BACKGROUND

The incidence of hypertension in postmenopausal women exceeds that in age-matched men. Longitudinal studies relating hormone replacement therapy (HRT) to blood pressure changes are sparse.

OBJECTIVE

To investigate the association between HRT and longitudinal changes in blood pressure in postmenopausal women.

DESIGN

Longitudinal observational study.

SETTING

Community-dwelling volunteers.

PATIENTS

226 healthy, normotensive postmenopausal women from the Baltimore Longitudinal Study of Aging with a mean (+/-SD) age of 64 +/- 10 years were followed for 5.7 +/- 5.3 years. Seventy-seven women used both estrogen and progestin, and 149 used neither.

MEASUREMENTS

Lifestyle variables, blood pressure, and traditional cardiovascular risk factors were measured at baseline and approximately every 2 years thereafter.

RESULTS

Systolic blood pressure at baseline was similar in HRT users and nonusers (133.9 +/- 16.0 mm Hg vs. 132.4 +/- 14.8 mm Hg). Over time, average systolic blood pressure increased less in HRT users than nonusers, independent of other cardiovascular risk factors, physical activity, and alcohol use. For example, HRT users who were 55 years of age at their first Baltimore Longitudinal Study of Aging visit experienced a 7.6-mm Hg average increase in systolic blood pressure over 10 years; in contrast, the average increase in nonusers was 18.7 mm Hg. The lesser increase in systolic blood pressure in HRT users was more evident at older age. Diastolic blood pressure, which did not change statistically over time in either group, was not associated with HRT.

CONCLUSION

Postmenopausal women taking HRT have a smaller increase in systolic blood pressure over time than those not taking HRT. This difference is intensified at older ages.

Preliminary studies to develop a personal dosemeter for use by aircraft crew

This paper describes preliminary work to develop a cosmic-radiation dosemeter for use by military aircraft crew. The dosemeter is based on a combination of CR-39 etched-track detectors and TLD-700 thermoluminescent detectors. It is intended that the CR-39 be used to assess the neutron dose, while the TLD-700 is used to assess the photon and charged particle dose. The sensitivity of CR-39 to the neutron component of cosmic radiation was estimated by irradiating samples of the plastic at the CERN-CEC High Energy Reference Field Facility. This facility produced a radiation field with a neutron spectrum resembling that of the neutron component of cosmic radiation at typical airflight altitudes. The response of the CR-39 was linear over the range of doses studied (0.2-6.0 mSv) and there was no significant fading in the 6-month period after irradiation. The TLD-700 component of the dosemeter was calibrated using 137Cs gamma rays. The response of the TLD-700 was linear over the range of doses studied (0.01-5.0 mSv) with no significant fading in the 6-month period after irradiation. It was concluded that a combination of CR-39 and TLD-700 detectors would provide an effective cosmic-radiation dosemeter for use by military aircraft crew.

Accuracy of Doppler catheter measurements: effect of inhomogeneous beam power distribution on mean and peak velocity

OBJECTIVES

We sought to determine the effect of inhomogeneous distribution of beam power produced by Doppler catheters on measurements of mean and peak velocity of coronary blood flow.

BACKGROUND

Measurements of mean velocity of coronary blood flow by Doppler catheters have significant systematic errors that have not been completely characterized. We hypothesized that one error is the inhomogeneous distribution of the ultrasonic beam power and that this inhomogeneity makes measurements of mean, but not peak, velocity inaccurate.

METHODS

We constructed a scaled-up model of a Doppler catheter to allow for accurate measurement of the distribution of beam power by miniature hydrophones. This catheter was placed in a model of coronary blood flow in which the fluid velocity was accurately measured by an external laser Doppler velocimeter. The laser Doppler measurements of mean velocity were compared with the measurements of mean velocity made by the catheter, using fast Fourier transform analysis, both without and with correction for inhomogeneous beam power distribution. Peak velocity measurements were also compared, as predicted from theory, without the need of correction for inhomogeneous beam power distribution. To investigate the clinical relevance of our results, we conducted studies using a clinical Doppler catheter both in a scaled model of coronary flow and in a series of eight patients. In the model and in each patient, we rotated the catheter without changing the axial position to systematically alter the relation of the beam power distribution to the local fluid dynamics.

RESULTS

The measurement of beam power distribution revealed significant inhomogeneity. Comparison of the measured mean frequency shifts without correction for inhomogeneities in the distribution yielded a statistically significant difference. After correction for inhomogeneities, there was no statistically significant difference. Also, there was no significant difference for the peak frequency shifts. Rotation of the clinical catheter in the scaled model and in the patients changed the measured mean velocity (average change 18.8% and 20.6%, respectively), but not the measured peak velocity (average change 5.0% and 4.3%, respectively).

CONCLUSIONS

For signal analysis using a fast Fourier transform, the inhomogeneous distribution of power of the ultrasonic beam produced by Doppler catheters makes measurements of mean, but not peak, velocity inaccurate. Measurements of peak velocity may therefore prove superior to measurements of mean velocity in estimating the response to pharmacologic intervention and in estimating stenosis severity.

Cardiovascular assessment of the patient with renal problems

A focused cardiovascular system assessment of patients with renal problems is essential in determining an overall state of health. The patient history and physical examination are the primary components of assessment. This article reviews cardiovascular assessment specific to patients with renal problems. The assessment techniques of inspection, palpation, percussion and auscultation are presented. A variety of cardiovascular indicators are reviewed to assist in detecting abnormalities related to patients with renal problems.

The challenges of assessing skin indicators in people of color

Expert physical assessment skills are critical in the practice of home healthcare nursing. This article describes ways nurses can assess and document skin indicators in people of color that are meaningful to everyone involved in the patient's care.

Assessing ability to drive following an acute neurological event: are we on the right road?

Every day in Canada occupational therapists are asked to assess clients with neurological impairments and to provide recommendations to provincial licensing bureaus regarding the individual's fitness to drive. These decisions have great impact on the client and on society. In this paper we briefly review the findings that have been published regarding the assessment of individuals with neurological conditions who wish to resume driving. In addition, a description of the tools commonly used to assess individuals is provided, along with where available, the measurement properties of each. Finally, the Driving Evaluation Service of a physical rehabilitation centre is described.

Analysis of pulsed wave Doppler ultrasound spectra obtained from a model intracoronary catheter

Abnormal arterial blood flow patterns have been implicated in the evolution of various vascular disease processes. Intravascular ultrasound techniques using the pulsed wave Doppler catheter offer the opportunity to characterize these abnormal flow patterns. We have developed a mathematical model that predicts the first two moments of the Doppler spectrum obtained using a Doppler catheter based on the distribution of ultrasonic beam power and velocity profile of fluid flow with an arbitrary distribution of flow disturbances. A scaled-up, in vitro experimental arterial system was used to confirm the validity of the model. Comparison of the predicted first two moments of the Doppler spectrum to the experimental values in this system demonstrated that the distribution of beam power significantly affects the magnitude of the first two moments. Additionally, both velocity gradient and velocity fluctuation broadening effects play prominent roles in determining the magnitude of the second moment. These phenomena must therefore be considered when evaluating in vivo Doppler spectra used for the characterization of abnormal flow patterns.

Differentiation of abnormal blood flow patterns in coronary arteries based on Doppler catheter recordings

Abnormal arterial blood flow patterns have been implicated as etiologic factors in thrombosis and atherosclerosis. Intravascular pulsed Doppler ultrasound techniques with fast-Fourier transform analysis offer the opportunity to measure these abnormalities. The authors hypothesized that statistical analysis of radial-directed beam spectra could be used to distinguish disturbed from non-disturbed flow and that analysis of conventional axial-directed beam spectra could then be used to distinguish laminar high-shear from laminar low-shear flow. They developed a scaled-up in-vitro model of coronary flow consisting of a glycerol/H2O test fluid flowing through an acrylic cylinder at Reynolds numbers spanning the typical physiologic range within the coronary arteries. A scaled-up Doppler catheter with the capacity for 90 degrees reflection of the beam was placed centrally. Disturbed flow was created by introducing a flow screen, and altered shear rates were produced by changing the Reynolds number. For the radial-directed beam studies, the coefficients of variation of the Doppler spectra for the disturbed flow states were significantly greater than for the nondisturbed flow states (p less than 0.01). For the axial-directed beam studies, the coefficients of variation of the Doppler spectra for the laminar high-shear flow states were significantly greater than for the laminar low-shear flow states (p less than 0.01). They conclude that abnormal blood flow patterns can be differentiated by the selective use of radial-directed and axial-directed Doppler catheter recordings.

Wall shear stress distribution along the cusp of a tri-leaflet prosthetic valve

High levels of wall shear stress on the surface of valvular cusps can cause mechanical damage to the blood cells and the cusp surfaces. The shear stresses are also responsible for mechanical failure of prosthetic heart valves. Qualitative measurements of wall shear stress in the vicinity of the leaflets are thus essential for diagnosis of suspected complications and provide important information for the design and fabrication of bioprosthetic heart valves. For this purpose we measured the velocity distribution along the inside wall of the cusps of a tri-leaflet heart valve with a two colour laser Doppler anemometer system. The wall shear stresses on the cusp surface were computed and found to range from 80 to 120 N/m2 during the ejection phase. Wall shear stresses of up to 180 N/m2 were measured in loci of cusp flexure and the accelerated boundary layer. The results of this study show a correlation between the high shear stress loci and the clinically (animal) observed regions of cusp calcification.

The frequency response of electrochemical wall shear probes in pulsatile flow

The frequency response of surface-mounted electrochemical mass transfer probes used to deduce wall shear rates has been investigated experimentally for the case of fully developed laminar pulsatile flow in a straight tube. Generally good agreement is found with the asymptotic results obtained by Lighthill's methods. The significance of the results with regard to the investigation of models of pulsatile flows of physiological interest is discussed. It is concluded that the frequency-dependent phase and amplitude corrections required to obtain accurate wall shear measurements are of such magnitudes as to render impractical the use of electrochemical probes to determine wall shear rates in these flows.

Hydrophobic Grid Membrane Filter Method for Aerobic Plate Count in Foods: Collaborative Study

Twenty-one laboratories participated in a collaborative study to validate a hydrophobic grid membrane filter (HGMF) method for aerobic plate count by comparing its performance against the AOAC/APHA pour plate method. Raw milk, raw poultry, whole egg powder, flours, and spices were included in the study. Counts obtained by the HGMF and pour plate methods did not differ significantly, except in the case of whole egg powder, for which the HGMF method produced significantly higher counts. The hydrophobic grid membrane filter method for aerobic plate count in foods has been adopted official first action.