CoNIC Challenge: Pushing the frontiers of nuclear detection, segmentation, classification and counting

Nuclear detection, segmentation and morphometric profiling are essential in helping us further understand the relationship between histology and patient outcome. To drive innovation in this area, we setup a community-wide challenge using the largest available dataset of its kind to assess nuclear segmentation and cellular composition. Our challenge, named CoNIC, stimulated the development of reproducible algorithms for cellular recognition with real-time result inspection on public leaderboards. We conducted an extensive post-challenge analysis based on the top-performing models using 1,658 whole-slide images of colon tissue. With around 700 million detected nuclei per model, associated features were used for dysplasia grading and survival analysis, where we demonstrated that the challenge's improvement over the previous state-of-the-art led to significant boosts in downstream performance. Our findings also suggest that eosinophils and neutrophils play an important role in the tumour microevironment. We release challenge models and WSI-level results to foster the development of further methods for biomarker discovery.

Learning from Alfred Wegener's pioneering field observations in West Greenland after a century of climate change

The cryosphere in Greenland is currently undergoing strong changes. While remote sensing improves our understanding of spatial and temporal changes across scales, particularly our knowledge of conditions during the pre-satellite era is fragmented. Therefore, high-quality field data from that period can be particularly valuable to better understand changes of the cryosphere in Greenland at climate time scales. At Graz University, the last work-place of Alfred Wegener we have access to the extensive expedition results from their epic 1929-1931 expedition to Greenland. The expedition coincides with the warmest phase of the Arctic early twentieth century warm period. We present an overview of the main findings of the Wegener expedition archive and set it into context with further monitoring activities that occurred since, as well as the results from reanalysis products and satellite imagery. We find that firn temperatures have increased significantly, while snow and firn densities and have remained similar or decreased since. Local conditions at the Qaamarujup Sermia have changed strongly, with a reduction in length of more than 2 km, in thickness by up to 120 m and a rise in terminus position of approximately 300 m. The elevation of the snow line of the years 1929 and 1930 was similar to the one from the extreme years 2012 and 2019. Compared to the satellite era, we find that during the time of the Wegener expedition fjord ice extent was smaller in early spring and larger in late spring. We demonstrate that a well-documented snapshot of archival data can provide a local and regional context for contemporary climate change and that it can serve as the basis for process-based studies on the atmospheric drivers of glacier changes.

The Cell Tracking Challenge: 10 years of objective benchmarking

The Cell Tracking Challenge is an ongoing benchmarking initiative that has become a reference in cell segmentation and tracking algorithm development. Here, we present a significant number of improvements introduced in the challenge since our 2017 report. These include the creation of a new segmentation-only benchmark, the enrichment of the dataset repository with new datasets that increase its diversity and complexity, and the creation of a silver standard reference corpus based on the most competitive results, which will be of particular interest for data-hungry deep learning-based strategies. Furthermore, we present the up-to-date cell segmentation and tracking leaderboards, an in-depth analysis of the relationship between the performance of the state-of-the-art methods and the properties of the datasets and annotations, and two novel, insightful studies about the generalizability and the reusability of top-performing methods. These studies provide critical practical conclusions for both developers and users of traditional and machine learning-based cell segmentation and tracking algorithms.

A graph-based cell tracking algorithm with few manually tunable parameters and automated segmentation error correction

Automatic cell segmentation and tracking enables to gain quantitative insights into the processes driving cell migration. To investigate new data with minimal manual effort, cell tracking algorithms should be easy to apply and reduce manual curation time by providing automatic correction of segmentation errors. Current cell tracking algorithms, however, are either easy to apply to new data sets but lack automatic segmentation error correction, or have a vast set of parameters that needs either manual tuning or annotated data for parameter tuning. In this work, we propose a tracking algorithm with only few manually tunable parameters and automatic segmentation error correction. Moreover, no training data is needed. We compare the performance of our approach to three well-performing tracking algorithms from the Cell Tracking Challenge on data sets with simulated, degraded segmentation—including false negatives, over- and under-segmentation errors. Our tracking algorithm can correct false negatives, over- and under-segmentation errors as well as a mixture of the aforementioned segmentation errors. On data sets with under-segmentation errors or a mixture of segmentation errors our approach performs best. Moreover, without requiring additional manual tuning, our approach ranks several times in the top 3 on the 6^th edition of the Cell Tracking Challenge.

Cell segmentation and tracking using CNN-based distance predictions and a graph-based matching strategy

The accurate segmentation and tracking of cells in microscopy image sequences is an important task in biomedical research, e.g., for studying the development of tissues, organs or entire organisms. However, the segmentation of touching cells in images with a low signal-to-noise-ratio is still a challenging problem. In this paper, we present a method for the segmentation of touching cells in microscopy images. By using a novel representation of cell borders, inspired by distance maps, our method is capable to utilize not only touching cells but also close cells in the training process. Furthermore, this representation is notably robust to annotation errors and shows promising results for the segmentation of microscopy images containing in the training data underrepresented or not included cell types. For the prediction of the proposed neighbor distances, an adapted U-Net convolutional neural network (CNN) with two decoder paths is used. In addition, we adapt a graph-based cell tracking algorithm to evaluate our proposed method on the task of cell tracking. The adapted tracking algorithm includes a movement estimation in the cost function to re-link tracks with missing segmentation masks over a short sequence of frames. Our combined tracking by detection method has proven its potential in the IEEE ISBI 2020 Cell Tracking Challenge (http://celltrackingchallenge.net/) where we achieved as team KIT-Sch-GE multiple top three rankings including two top performances using a single segmentation model for the diverse data sets.

EmbryoMiner: A new framework for interactive knowledge discovery in large-scale cell tracking data of developing embryos

State-of-the-art light-sheet and confocal microscopes allow recording of entire embryos in 3D and over time (3D+t) for many hours. Fluorescently labeled structures can be segmented and tracked automatically in these terabyte-scale 3D+t images, resulting in thousands of cell migration trajectories that provide detailed insights to large-scale tissue reorganization at the cellular level. Here we present EmbryoMiner, a new interactive open-source framework suitable for in-depth analyses and comparisons of entire embryos, including an extensive set of trajectory features. Starting at the whole-embryo level, the framework can be used to iteratively focus on a region of interest within the embryo, to investigate and test specific trajectory-based hypotheses and to extract quantitative features from the isolated trajectories. Thus, the new framework provides a valuable new way to quantitatively compare corresponding anatomical regions in different embryos that were manually selected based on biological prior knowledge. As a proof of concept, we analyzed 3D+t light-sheet microscopy images of zebrafish embryos, showcasing potential user applications that can be performed using the new framework.

Sensors and Control Concept of Walking “Johnnie”

One key problem to achieve a dynamically stable walking motion with biped robots is to measure and control the actual state of the robot with respect to its environment. Dynamically stable walking on unstructured terrain and fast walking can only be achieved with an orientation sensor. The control system of the biped robot “Johnnie” is designed such that the orientation of the upper body is controlled throughout all phases of the gait pattern. Furthermore, a sophisticated measurement and control of the foot torques has been implemented. In this way, the interaction forces and torques between robot and environment are controlled and tilting of the foot is avoided.

[Histological diagnostics of enucleated eyes]

Enucleated eyeglobes represent a challenge for the pathologist, as their appraisal requires specific ophthalmological knowledge. Part 1 of this CME article dealt with macroscopic findings in eyeglobes, in order to facilitate adequate cutting planes to retrieve pathologies histologically. Part 2 which is presented here teaches basic histology of eye-specific tissues (e.g., cornea, anterior chamber angle, retina, and optic nerve). Theses structures show typical changes in blinded eyes. Knowledge of these changes, together with awareness of fundamental ophthalmic disease entities and surgical strategies (see part 1), will many times allow to deduce the pathophysiology that finally culminated in blindness and enucleation. Disease entities more closely discussed in this article include corneal ulcers, rubeotic secondary glaucomas, and chronic degenerative retinal diseases.

[Histological workup of enucleated eyes]

The appraisal of enucleated eyes presents a particular challenge to pathologists. In German-speaking countries, this task has mostly been in the hands of ophthalmologists. It requires particular ophthalmologic knowledge including nosology, implants, surgical procedures, and nomenclature. This CME article teaches the basics needed for pathologic appraisal of enucleated eyes. The first part focusses on the macroscopic evaluation and describes the exterior and interior of the eye. Competent interpretation of the macroscopic findings is crucial to identify adequate cutting planes for histology. Anatomic landmarks on the globe's exterior and common section planes are described. Diseases that typically lead to enucleation will be explained in detail and illustrated with images. In the second part of this article, a histologic description of eye-specific tissue types is provided.

[Malignant melanoma of the conjunctiva]

BACKGROUND

Malignant melanoma of the conjunctiva is a rare tumour. Early disease stages may be difficult to distinguish from benign lesions such as pigmented nevi or primary acquired melanosis. We describe the therapeutic procedure and histological findings in two patients and review the epidemiology and pathogenesis of malignant conjunctival melanoma. Two female patients (84 and 85 years old, respectively) presented with a pigmented tumor close to the limbus with surrounding conjunctival pigmentation and involvement of the cornea.

RESULTS

Following complete excision of the tumour, conjunctival malignant melanoma arising from primary acquired melanosis was diagnosed histologically. Subsequent treatment with mitomycin C eye drops was initiated. There was no recurrence of the tumor within the follow-up period (24 and 6 months).

DISCUSSION

Patients with primary acquired melanosis need to be reviewed on a regular basis to detect malignant transformation at an early stage.

A novel siRNA-lipoplex technology for RNA interference in the mouse vascular endothelium

For the application of RNA interference (RNAi) in vivo the functional delivery of short interfering RNAs (siRNAs) is still the major obstacle. Therefore, delivery technologies need to be established for the systemic application of RNAi in vivo. Here we report uptake, biodistribution and in vivo efficacy of siRNA molecules formulated into siRNA-lipoplexes. The applied formulation is based on complex formation of positively charged liposomes, a mixture of cationic and fusogenic lipids complexed with the negatively charged siRNA. We determined by fluorescence microscopy the temporal and spatial distribution of fluorescently labeled siRNA-lipoplexes, the body clearance and endothelial cell type specific uptake after single intravenous injection. Furthermore, by using siRNA molecules for targeting endothelia-specifically expressed genes, such as CD31 and Tie2, we were able to demonstrate downregulation of the corresponding mRNA and protein in vivo. Taken together, we show the applicability of this non-viral delivery technology for inducing RNAi in the vasculature of mice after systemic application.

RNA interference in the mouse vascular endothelium by systemic administration of siRNA-lipoplexes for cancer therapy

RNA interference (RNAi) entails the potential for novel therapeutic strategies through the silencing of disease-causing genes in vivo. However, recent studies have raised an issue regarding applicable routes of administration for small interfering RNA (siRNA) molecules as therapeutics. In this study, we demonstrate that liposomally formulated siRNA molecules, the so-called siRNA-lipoplexes, but not naked siRNAs, are delivered to the tumor endothelial cells in vivo by microscopy. In addition, functional intracellular delivery of formulated siRNA targeting the tumor suppressor PTEN is shown in endothelial cells of the liver and tumor. Finally, the therapeutic potential of systemically administered siRNA(CD31)-lipoplexes is established by inhibition of tumor growth in two different xenograft mouse models. Our findings corroborate the applicability of this liposomal siRNA delivery technology for inducing RNAi to modulate gene expression levels in angiogenesis-dependent processes. In addition, our results advocate CD31 as a promising therapeutic target for antiangiogenic intervention. Therefore, our study provides a basis for the development of antiangiogenic cancer therapies based on RNAi.

[Atomic force microscope (AFM). A nanomanipulator for biophysical studies of stereocilia of the cochlear hair cells]

OBJECTIVES

Studies of the mechanoelectrical sensor system of the hair cell bundle in the cochlea require a manipulation device that enables controlled force application and movement of individual stereocilia in the nanometer range.

METHODS

In our atomic force microscope (AFM) setup, the scan is directly controlled in an upright differential interference contrast (DIC) infrared video microscope with a water immersion objective and in the measured AFM image. Here we present studies on hair cells of the mammalian cochlea.

RESULTS AND CONCLUSIONS

The resulting images revealed the tips of individual stereocilia of living sensory cells of the organ of Corti and the typical shape of the ciliary bundle. Scanning electron-microscopic (SEM) images of the identical hair bundles obtained after AFM investigation demonstrated that up to four AFM manipulations on the same cell did not cause obvious damage to the surface morphology of the stereocilia.

Kinetic tremor in a reach-to-grasp movement in Parkinson's disease

The aim of this study was to quantify the tremor of the hand during a natural movement (kinetic tremor) in tremor-dominant parkinsonian patients (n = 13). We used a three-dimensional camera system to kinematically analyze rest and kinetic tremors in an unrestrained reach-to-grasp movement, and additional tremor recordings were performed under standard postural and rest conditions using electromyography and accelerometry. The standard analysis showed a highly synchronized tremor with similar frequencies at rest and in sustained postural tasks, with and without loading. A kinematic recording was used to compare rest and action conditions. A strong inhibition of the resting tremor was present at the onset of the movement and reached its peak during deceleration. A kinetic tremor of low amplitude was present in most of the parkinsonian patients, but its occurrence was confined mainly to the terminal periods of the movement. The frequency of kinetic tremor was significantly higher than that at rest, before the onset of the movement in Parkinson's disease, as determined by the kinematic analysis (mean, 5.5 Hz vs 6.5 Hz; p <0.01). Our results confirm similarities between the tremor at rest and the oscillations during a sustained postural task in classic parkinsonian tremor. In contrast to this stable tremor, which seems to be generated by basal ganglia oscillators, a different pathophysiology of oscillations during motion must be considered. The kinetic tremor is most likely related to an enhancement of the physiologic tremor in the terminal phase of the reach-to-grasp movement.

Essential tremor and cerebellar dysfunction clinical and kinematic analysis of intention tremor

The cerebellum is assumed to play a major role in the pathophysiology of essential tremor (ET). As intention tremor is considered one of the classical features of cerebellar disease, we have assessed a large group of patients with ET for the semiology of the tremor and have performed objective quantitative analysis of a grasping movement in patients with ET, cerebellar disease and a normal control group. We found 25% of the patients to have a moderate or severe kinetic tremor with clear-cut features of a classical intention tremor. Another 33% of the patients had a mild intentional component of their kinetic tremor. Patients with intention tremor (ET(IT)) did not differ from those with predominant postural tremor (ET(PT)) with respect to alcohol sensitivity of the tremor and the frequency of a family history. ET(IT) patients were older and more often showed head and trunk involvement. The onset of this intention tremor has been assessed retrospectively. It was found to begin at a randomly distributed time interval after the onset of the postural tremor, but older patients had a shorter time to development of intention tremor. Quantitative accelerometry of postural tremor showed similar tremor frequencies in both patient groups, but ET(IT) patients had a slightly larger tremor amplitude. Quantitative analysis of a grasping movement using an infrared-camera system was performed in two subgroups of the patients with ET(PT) and ET(IT) and control groups with cerebellar disease or normal subjects. The intention tremor could be quantified objectively as an increased amplitude of curvature during the deceleration and target phase of the movement. The amplitude measurements of intention tremor were clearly abnormal and of comparable magnitude for ET(PT) and cerebellar disease. Additionally, the patients with ET(IT) had a significantly slowed grasping movement during the deceleration and target period. Hypermetria was significantly increased for the patients with ET(IT) and cerebellar disease. We conclude that intention tremor is a feature of ET. ET(IT) patients have abnormalities of their upper limb function compatible with cerebellar disease. This suggests that patients with more advanced ET show abnormalities of cerebellar functions.

Cation permeation and blockade of ROMK1, a cloned renal potassium channel

ROMK1 is an inwardly rectifying K+ channel cloned from the outer medulla of rat kidney. We have determined the permeation and blocking characteristics for several monovalent cations in ROMK1 when expressed in Xenopus oocytes, using the two-electrode voltage-clamp technique. The selectivity sequence for monovalent cations as determined by reversal potential changes under bi-ionic conditions was K+ > Rb+ > Cs+ = NH4+ >> Na+ = Li+. The conductivity for the two permeant ions K+ and Rb+ was a saturable function of the external concentration, with Km values of 11.5 +/- 1.3 mmol l-1 (n = 19) and 47.3 +/- 4.8 mmol l-1 (n = 19), respectively. With mixtures of K+ and Rb+, the conductance ratio [Rb]/[K+Rb] was varied between 0 and 1. ROMK1 was blocked by both Cs+ and Ba2+ in a concentration- and voltage-dependent manner. The electrical distance (delta) at which Ba2+ and Cs+ blocked the channel was 0.41 and 0.69, respectively, suggesting that these two ions block at different sites within the pore. Taken together with previous reports, the results indicate that ROMK1 has a multi-ion pore, and that the N-terminus contributes to the pore structure.

Short-term hemodynamic, anti-ischemic, and antianginal effects of pirsidomine, a new sydnonimine

Pirsidomine is a new sydnonimine compound in clinical development. As a prodrug, it is transformed into a nitric oxide-releasing metabolite in vivo. In animal tests there were no signs of tolerance with repeated administration. The short-term effects of 10, 20, and 40 mg of the drug on pulmonary hemodynamics and ischemic parameters were examined at rest and during exercise in a double-blind, randomized, placebo-controlled study. The study included 48 patients with documented coronary artery disease and exercise-induced ST-segment depression. Compared with the baseline test, there was a reduction of diastolic pulmonary artery pressure with pirsidomine at rest (placebo: -0.4 +/- 0.5 mm Hg; 10 mg: - 1.5 +/- 2.4 mm Hg; 20 mg: - 1.4 +/- 1.1 mm Hg; 40 mg: - 2.3 +/- 1.3 mm Hg [p < 0.05 ]) and at the highest comparable workload (placebo: -2.8 +/- 1.9 mm Hg; 10 mg: -7.3 +/- 6.8 mm Hg; 20 mg: -8.4 +/- 7.9 mm Hg [p <0.05]; 40 mg: -13.8 +/- 7.1 mm Hg [p <0.05]). ST-segment depression decreased at the highest comparable workload (placebo: -0.33 +/- 0.49 mm; 10 mg: -1.33 +/- 1.37 mm [p <0.05]; 20 mg: -1.33 +/- 0.83 mm [p <0.05]; 40 mg: -1.96 +/- 0.86 mm [p <0.05]) and total exercise time increased (placebo: 15 +/- 48 s; 10 mg: 98 +/- 126 s; 20 mg: 165 +/- 251 s [p <0.05]; 40 mg: 155 +/- 174 s [p <0.05]). Of 40 patients who complained of angina pectoris symptoms in the baseline test, 15 became free of angina pectoris with pirsidomine. Compared with placebo, blood pressure, heart rate during exercise, and cardiac output during exercise showed no significant change. Plasma concentration response relations of the metabolite revealed concentrations that caused a half-maximum effect of 6 ng/ml, 13 ng/ml, 20 ng/ml, and 28 ng/ml in reduction of ST-segment depression, reduction of diastolic pulmonary artery pressure, relief of angina pectoris symptoms, and an increase in exercise duration, respectively. Thus, pirsidomine is an effective anti-ischemic and antianginal agent. A significant preload reduction was obtained with plasma metabolite concentrations lower than those necessary to achieve a satisfactory antianginal effect.

Double-blind comparison of antihypertensive treatment with ramipril and piretanide, given alone or in combination

In a double-blind, randomized, multicenter trial, we compared the efficacy and safety of the fixed combination of 5 mg ramipril and 6 mg piretanide and the respective component monotherapies in hypertensive patients [supine diastolic blood pressure (DBP) 100-114 mm Hg]. After a single-blind run-in period on placebo, 611 patients were randomized to ramipril (n = 209), piretanide (n = 201), or the combination therapy (n = 201). At randomization, the three groups had the same characteristics (51% men, age 55 +/- 10 years, BP 165 +/- 18/104 +/- 6 mm Hg). At 4 weeks, BP decreased more with combined therapy than with monotherapy. As compared with piretanide monotherapy, the gain in the antihypertensive effect in the supine position averaged 2.1 mm Hg [90% confidence interval (CI) -0.8-5.0 mm Hg; p = 0.07] systolic BP (SBP) and 1.9 mm Hg (CI 0.3-3.5 mm Hg, p = 0.02) DBP and, as compared with ramipril monotherapy, these differences were 4.2 mm Hg (CI 1.3-7.0 mm Hg, p = 0.008) and 2.0 mm Hg (CI 0.5-3.6 mm Hg, p = 0.009). The incidence of adverse events (AE) and the changes in biochemical measurements were similar in the three treatment groups with the exception of spontaneously reported polyuria and serum uric acid concentration. Polyuria was reported more frequently (p < 0.001) with piretanide therapy (n = 23) and combined therapy (n = 19) than with ramipril therapy (n = 1).(ABSTRACT TRUNCATED AT 250 WORDS)

Properties and regulation of pH-dependent cation channels in the apical membrane of cultured proximal tubule cells

The established opossum kidney (OK) cell line serves as a model system for ion and substrate transport in the renal proximal tubule. Previous experiments on OK cells revealed a channel-mediated Na+ conductance which is regulated by intracellular pH (pHi). In this study we report on patch clamp experiments determining the properties and pHi dependence of a cation channel located in the apical membrane. This channel is selective for sodium over chloride but discriminates poorly between the monovalent cations Na+,K+,Li+ and Cs+. Its open probability (P(o)) rises at depolarising membrane potentials. Under normal conditions the channel is inactive in the cell-attached patch mode and is activated upon excision. However, after excision the channel usually runs down within 30-90 s which cannot be overcome by either altering the Ca(2+)-concentration (10(-3) mol/l, 10(-6) mol/l, Ca(2+)-free) or adding 1 mmol/l Mg-ATP to the bath solution. In the cell-attached patch mode the channel could be activated by decreasing pHi from pH 7.4 to pH 6.5, by either the ammonium prepulse technique or the nigericin K+ method, in more than 50% of the experiments performed. In the renal proximal tubule such a non-selective cation channel would constitute a functional Na+ channel and might therefore support Na+ reabsorption especially during the intracellular acidification due to hormonal inhibition of the Na+/H+ exchanger.

Pharmacokinetics and pharmacodynamics of ramipril and piretanide administered alone and in combination

The pharmacokinetics and pharmacodynamics of single oral doses of 5 mg ramipril and 6 mg piretanide administered separately and in combination were determined in a single blind, randomised, 3-period cross-over study in 24 healthy male volunteers. The peak plasma concentrations of ramipril and ramiprilat increased slightly (from 11.9 to 14.8 ng/ml, and from 6.39 to 8.96 ng/ml, respectively) as did the area under the plasma concentration-time curve of ramipril (0-4 h) and ramiprilat (0-24 h) (from 15.8 to 19.8 ng.ml-1.h, and from 63.4 to 74.6 ng.ml-1.h, respectively). The urinary excretion of ramiprilat also rose (from 6.82 to 7.73% of dose) following simultaneous treatment with piretanide. These effects were probably due to reduced first-pass metabolism of ramipril/ramiprilat to inactive metabolites. The blood pressure lowering effect, the time course of inhibition of ACE activity in plasma and the concentration-response relationship for the inhibition of plasma ACE activity were not affected by piretanide. The peak plasma concentration of piretanide was somewhat reduced (from 285 to 244 ng/ml) following simultaneous treatment with ramipril. No other pharmacokinetic parameter was affected. Piretanide increased urine flow, and sodium, chloride and potassium excretion, especially during the first 2 hours following administration. These pharmacodynamic parameters were not affected by ramipril. Thus, simultaneous administration of single oral doses of ramipril and piretanide caused modest changes in the peak and average plasma concentrations of both drugs, which did not lead to detectable alterations in the pharmacodynamic parameters measured in healthy volunteers.

Usefulness of piretanide plus ramipril for systemic hypertension: a multicenter trial

To test the dose responses of piretanide, ramipril, and their combination in patients with essential hypertension, a prospective, randomized, double-blind, placebo-controlled trial was conducted in 480 patients. Twelve separate groups were studied: placebo, piretanide 3 mg, piretanide 6 mg, ramipril 2.5 mg, ramipril 5 mg, ramipril 10 mg, and their combinations, as single daily morning doses. Patients were randomized after a 2-week run-in period without drugs; treatment was given for 6 weeks. A dose response compared with placebo was found for both drugs; the combination was more effective than either drug alone. Piretanide 6 mg, combined with ramipril 5 mg, provided optimal blood pressure reduction. Self-reported adverse effects of both drugs and their combinations did not exceed those reported for placebo. A surface analysis suggested that piretanide primarily reduced systolic blood pressure, whereas ramipril was more effective in reducing diastolic blood pressure. The data attest to a combined efficacy of piretanide and ramipril in decreasing arterial blood pressure.

[Determination of duration of action of beta blockers with Holter-ECG registration]

Duration of Action of Betaadrenergic Blockers Determined with Holter-ECG in Healthy Volunteers In phase I, the duration of action of betaadrenergic blockers is usually determined from the reduction of exercise induced tachycardia. In this randomized placebocontrolled doubleblind trial, however, ambulatory 24-h heart rate monitoring was used in 12 healthy volunteers to evaluate the duration of action of the new cardioselective and vasodilating betaadrenergic blocker ridazolol (CAS413). After the control periods as well as after prospectively defined hours the following mean values of heart rate were obtained: Ridazolol: Control 65.2, 12 h 69.6, 16 h 64.9, 24 h 74.0 beasts/min, placebo: Control 64.8, 12 h 78.5, 16 h 69.7, 24 h 73.5 beats/min. Differences after 12 h were statistically significant and would have been significant after 16 h with more volunteers. Additional explorative analysis with adjustment of significance levels for multiple analysis resulted in significant effects from 2 to 14 h. It was not useful, however, to calculate the time of maximal and half-maximal effects because of the large individual variation. Holter-monitoring of spontaneous heart rate in volunteers provides a rapid orientation on the duration of action of betaadrenergic blockers. The method allows to fix prospectively reasonable times of evaluation in efficacy trials in patients with coronary artery disease.