Percutaneous perfusion monitoring for the detection of hemodialysis induced cardiovascular injury.

INTRODUCTION: The safe delivery of hemodialysis (HD) faces dual challenges; the accurate detection of systemic circulatory stress producing cardiovascular (CV) injury, and the ability to enable effective preemptive intervention for such injury. We performed a pilot study to examine the capability of a new noninvasive, real-time monitoring system to detect the deleterious effects of HD on CV stability. METHODS: Eight patients were evaluated with echocardiography prior to the initiation of HD and again at peak HD stress. Continuous CV physiologic monitoring was performed throughout using oximeter-based pulse waveform analysis (CVInsight® Monitoring System, Intelomed, Inc., Warrendale, PA, USA). Longitudinal strain (LS) values for 12 left ventricular segments were generated using speckle-tracking software (EchoPac, GE), to assess the presence of HD-induced regional wall motion abnormalities (RWMA), indicative of myocardial stunning. FINDINGS: A reduction in pulse strength (PS) of ≥40% detected by CVI was associated with the development of RWMA (P = 0.005). This reduction occurred in 6/8 patients, all of whom exhibited myocardial stunning. Two patients had no significant reduction in PS nor evidence of myocardial stunning. In subjects with cardiac stunning, the decrease in PS was evident early during HD, 11.49 ± 10 minutes into HD treatment, prior to the detection of RWMA, which were assessed at peak HD stress, mean 210 ± 16.43 minutes into HD treatment. DISCUSSION: Percutaneous perfusion monitoring, using pulse wave analysis, appears to be useful in identifying circulatory stress during HD and predicting the development of HD-induced myocardial stunning with a lead time long enough to consider timely intervention.

Digital pulse contour analysis: investigating age-dependent indices of arterial compliance.

The resting peripheral volume pulse wave of 44 subjects within three age categories (30-39, 40-49, 50) has been characterized using a novel algorithm for the automated determination of a mean pulse function. The contour of this resting mean pulse has been analyzed with regard to its systolic and diastolic characteristics. Previously described indices of arterial stiffness and viscoelasticity have been investigated for age-dependent variations associated with arterial mechanical properties. Measures of the minimum rise time (MRT) and the stiffness index (SI) demonstrated strong correlations with age and each other, although their derivations are unrelated. While significant correlations existed (|r| = 0.50-0.78, p < or = 0.002), pairwise comparisons between the right and left hands did not demonstrate significant differences for the minimum rise time parameter; however, the stiffness index was significantly lower in the left hand versus the right (p = 0.009). With regard to age, the youngest age group had significantly lower MRT and SI values than the two older groups. For these data, this was only demonstrated in parameters calculated for the right hand because of higher variability within age groups for the left hand. A normalized average mean pulse for each age group was determined which visually illustrated the contour changes associated with the MRT and SI parameters that occur in both the systolic and diastolic portions of the pulse. The finding that differences between the age groups were significantly more evident for the right hand suggests that the physical site for such testing may be an important consideration. This study provides further evidence regarding the merit of using contour analysis when assessing the peripheral volume pulse and the importance of establishing ageing indices for such analysis.

Comparison of mechanical properties of rat tibialis anterior tendon evaluated using two different approaches.

Tendon injuries may result in variations of its mechanical properties. The published data of the tendon stiffness of small animals, such as mouse and rat, are exclusively obtained by measuring grip-to-grip (g-t-g) displacement. Local strain concentration and relative sliding of the specimens in the clamps might significantly affect the measured tendon deformation. In the present study, the mechanical properties of the rat tibialis anterior tendon measured using the proposed tendon mark method were compared to those evaluated using the g-t-g displacement method. Five male Sprague Dawley rats ( approximately 418 g) were used in this study. For the proposed method, reference marks were made on the tendons using permanent ink. A microscope video system was customized to observe and record the tendon deformation. Pattern recognition software was developed to obtain the displacement time-histories of the reference marks. The distance between the grips was approximately 7 mm; and the distance between the reference marks used for the data processing was approximately 5 mm. The cross-section areas of the specimens were measured using a custom-made slot gauge and by applying a constant compressive stress (0.15 MPa). The tendons were clamped between two custom-made metal grips and stretched on a testing machine at a constant speed (1 mm/s) up to failure. Throughout the tests, the tendon specimens were submerged in a PBS bath at 22 degrees C. The deformation of the specimens was evaluated using the g-t-g displacement method and the proposed method. The stress/strain curves obtained by using the g-t-g displacement can be characterized by an initial toe zone, a quasi-linear zone, and a final failure stage. The stress/strain curves determined using the proposed method are quite different from those obtained using the g-t-g displacement: it has a smaller toe zone and a stress-hardening transition, over which the tendon stiffness increases dramatically with the increasing strain. The tendon stiffness measured by using the g-t-g displacement method may underestimate the actual mechanical properties of tendon by approximately 43%.