Rhodopsin in plasma from patients with diabetic retinopathy - development and validation of digital ELISA by Single Molecule Array (Simoa) technology.

BACKGROUND: Diabetic retinopathy (DR) is the most frequent cause of blindness among younger adults in the western world. No blood biomarkers exist to detect DR. Hypothetically, Rhodopsin concentrations in blood has been suggested as an early marker for retinal damage. The aim of this study was therefore to develop and validate a Rhodopsin assay by employing digital ELISA technology, and to investigate whether Rhodopsin concentrations in diabetes patients with DR are elevated compared with diabetes patients without DR. METHODS: A digital ELISA assay using a Simoa HD-1 Analyzer (Quanterix©, Lexington, MA 02421, USA) was developed and validated and applied on a cohort of diabetes patients characterised with (n=466) and without (n=144) DR. RESULTS: The Rhodopsin assay demonstrated a LOD of 0.26ng/l, a LLOQ of 3ng/l and a linear measuring range from 3 to 2500ng/l. Total CV% was 32%, 23%, 19% and 17% respectively at the following Rhodopsin concentrations: 1, 3, 5 and 13ng/l. Recovery was 17%, 34%, 51% and 55% respectively at Rhodopsin concentrations of 2, 10, 50 and 250ng/l. There was no statistically significant difference in the plasma concentration of Rhodopsin between the diabetes patients with or without DR, but significantly increased number of DR patients having concentrations above the LOD. CONCLUSION: We developed and validated a digital ELISA method for quantification of Rhodopsin in plasma but found no statistically significant difference in the plasma concentration of Rhodopsin between diabetes patients with DR compared to diabetes patients without DR, though significantly more DR patients had values above the LOD.

Noise levels of closing sounds in vivo are equal for different bileaflet mechanical heart valves.

BACKGROUND AND AIM OF THE STUDY: Patients with mechanical heart valves must endure the valve's closing sounds for the rest of their life. Sound pressure levels (SPLs) recorded show wide patient-to-patient variation, even for the same type of valve. The variation was attributed to body constitution variability and differences in hemodynamic status. It was hypothesized that aortic mechanical valves generate closing clicks which correlate in magnitude with hemodynamic parameters, such as the rate of relaxation of the left ventricle (dp/dt) and potential energy stored in the aortic windkessel. METHODS: Three different aortic mechanical heart valves were investigated in a porcine model (n = 9), namely St. Jude Medical, CarboMedics and ATS. Closing sounds were measured with a microphone placed in a portable anechoic chamber 10 cm above the exposed heart. Left ventricular pressure (LVP) and cardiac output were also measured. Different hemodynamic conditions were produced by intravenous infusion of isotonic saline and dobutamine. Volume regulation and atrial pacing were also applied. RESULTS: Different hemodynamic situations were established (cardiac output, 1.2-6.5 l/min; heart rate, 99-171 bpm). The measured mean SPLs were 49.5-53.9 dB(A), and there were no statistically significant differences in noise between the valves (p = 0.8; one-way ANOVA). Likewise, only a weak relationship was identified between different hemodynamic parameters and the SPLs recorded. CONCLUSION: The SPLs of the investigated bileaflet mechanical heart valves did not differ significantly. Moreover, the SPL was only weakly related to LVP during closure and estimated stroke work.

Differential tension between secondary and primary mitral chordae in an acute in-vivo porcine model.

BACKGROUND AND AIM OF THE STUDY: Chordae tendineae may be instrumental for valvular-ventricular interaction, i.e. the reciprocal exchange of force between the left ventricular myocardium and the mitral apparatus. Chordae tendineae are divided into primary leading edge chordae and secondary belly chordae, and differences in thickness and distribution may reflect different functions of the two types. Primary chordae may be fundamental for leading edge control and for correct leaflet coaptation, while secondary chordae may act as the main mediators of valvular-ventricular interaction. It was postulated that tension in secondary chordae of the anterior leaflet is greater than in the primary chordae. The study aim was to investigate the distribution of chordae tendineae tension in the porcine mitral valve in vivo. METHODS: During extracorporeal bypass, miniature chordal force transducers were implanted on four chordae in 23 Danish Landrace pigs. Chordae tendineae tension was recorded online in the open-chest condition with spontaneous circulation in three different hemodynamic conditions: baseline with no intervention; partial aortic occlusion; and during dobutamine infusion. RESULTS: Systolic tension in secondary chordae under baseline conditions was significantly higher than in primary chordae (0.7 N versus 0.2 N, respectively). No significant impact on this distribution by changing the hemodynamic condition could be identified. CONCLUSION: Chordal tension is distributed towards the secondary chordae, with a tension more than three-fold that in the primary counterpart. The magnitude of chordal tension seems to be determined primarily by ventricular pressure. This finding supports the hypothesis that secondary chordae are more important mediators of the valvular-ventricular interaction than are primary chordae.