A quantitative framework for analyzing epicardial activation patterns during ventricular fibrillation

Few techniques have been developed for deriving quantitative measures of activation patterns during ventricular fibrillation (VF). Such measures have many potential applications, for example, assessing the effects of time, drugs, or electrical interventions. We have developed a new framework for quantifying VF patterns as mapped from an array of ≈500 unipolar electrodes. Individual activation wavefronts are isolated from one another using an algorithm that groups together adjacent active electrogram samples (dV/dt <−0.5 V/sec). Contacts between wavefronts are detected; these include fractionations, in which a single wavefront breaks into multiple wavefronts, and collisions, in which multiple wavefronts coalesce to form a new wavefront. The timing and contact relationships between wavefronts are summarized as a directed graph. From this model of the VF episode, we derive several parameters: number of wavefronts number of fractionations, number of collisions, mean wavefront size, mean area swept out, and mean duration. As an example of this analysis, we computed these parameters in six open-chest pigs at 5, 10, 15, and 20 sec after electrical induction of VF. The number of wavefronts and the number of collisions decreased, whereas the mean wavefront size and mean area swept out increased during this period. These results are consistent with previous studies showing a recovery of organization during the first minute of VF.     

Genetic relatedness and virulence gene profiles of Escherichia coli strains isolated from septicaemic and uroseptic patients

We investigated the relationship between clonality and virulence factors (VFs) of a collection of Escherichia coli strains isolated from septicaemic and uroseptic patients with respect to their origin of translocation. Forty septicaemic and 30 uroseptic strains of E. coli were tested for their phylogenetic groupings, genetic relatedness using randomly amplified polymorphic DNA (RAPD), biochemical fingerprinting method (biochemical phenotypes [BPTs]), adherence to HT-29 cells and the presence of 56 E. coli VF genes. Strains belonging to phylogenetic groups B2 and D constituted 93% of all strains. Fifty-four (77%) strains belonged to two major BPT/RAPD clusters (A and B), with cluster A carrying significantly (P = 0.0099) more uroseptic strains. The degree of adhesion to HT-29 cells of uroseptic strains was significantly (P = 0.0012) greater than that of septicaemic strains. Of the 56 VF genes tested, pap genes was the only group that were found significantly (P < 0.0001) more often among uroseptic isolates. Phylogenetic group B2 contained a significantly higher number of strains carrying pap genes than those in group D. We conclude that uroseptic E. coli are clonally different from septicaemic strains, carry more pap genes and predominantly adhere more to the HT-29 cell model of the gut.     

Circadian period and the timing of melatonin onset in men and women: predictors of sleep during the weekend and in the laboratory

Sleep complaints and irregular sleep patterns, such as curtailed sleep during workdays and longer and later sleep during weekends, are common. It is often implied that differences in circadian period and in entrained phase contribute to these patterns, but few data are available. We assessed parameters of the circadian rhythm of melatonin at baseline and in a forced desynchrony protocol in 35 participants (18 women) with no sleep disorders. Circadian period varied between 23 h 50 min and 24 h 31 min, and correlated positively (n = 31, r_s = 0.43, P = 0.017) with the timing of the melatonin rhythm relative to habitual bedtime. The phase of the melatonin rhythm correlated with the Insomnia Severity Index (n = 35, r_s = 0.47, P = 0.004). Self‐reported time in bed during free days also correlated with the timing of the melatonin rhythm (n = 35, r_s = 0.43, P = 0.01) as well as with the circadian period (n = 31, r_s = 0.47, P = 0.007), such that individuals with a more delayed melatonin rhythm or a longer circadian period reported longer sleep during the weekend. The increase in time in bed during the free days correlated positively with circadian period (n = 31, r_s = 0.54, P = 0.002). Polysomnographically assessed latency to persistent sleep (n = 34, r_s = 0.48, P = 0.004) correlated with the timing of the melatonin rhythm when participants were sleeping at their habitual bedtimes in the laboratory. This correlation was significantly stronger in women than in men (Z = 2.38, P = 0.017). The findings show that individual differences in circadian period and phase of the melatonin rhythm associate with differences in sleep, and suggest that individuals with a long circadian period may be at risk of developing sleep problems.     

Morphometric analysis of molars in a Middle Pleistocene population shows a mosaic of ‘modern’ and Neanderthal features

Previous studies of upper first molar (M¹) crown shape have shown significant differences between Homo sapiens and Homo neanderthalensis that were already present in the European Middle Pleistocene populations, including the large dental sample from Atapuerca‐Sima de los Huesos (SH). Analysis of other M¹ features such as the total crown base area, cusp proportions, cusp angles and occlusal polygon have confirmed the differences between both lineages, becoming a useful tool for the taxonomic assignment of isolated teeth from Late Pleistocene sites. However, until now the pattern of expression of these variables has not been known for the SH sample. This fossil sample, the largest collection from the European Middle Pleistocene, is generally interpreted as being from the direct ancestors of Neanderthals, and thus is a reference sample for assessing the origin of the Neanderthal morphologies. Surprisingly, our study reveals that SH M¹s present a unique mosaic of H. neanderthalensis and H. sapiens features. Regarding the cusp angles and the relative occlusal polygon area, SH matches the H. neanderthalensis pattern. However, regarding the total crown base area and relative cusps size, SH M¹s are similar to H. sapiens, with a small crown area, a strong hypocone reduction and a protocone enlargement, although the protocone expansion in SH is significantly larger than in any other group studied. The SH dental sample calls into question the uniqueness of some so‐called modern traits. Our study also sounds a note of caution on the use of M¹ occlusal morphology for the alpha taxonomy of isolated M¹s.     

Cardiac release of histamine after ventricular fibrillation and defibrillation during insertion of implantable cardioverter defibrillators (ICD)

Histamine has inotropic, chronotropic, arrhythmogenic, and vasoactive effects, and is released from the heart in ischaemia-reperfusion injury. The effect of ventricular fibrillation (VF) and defibrillation (DEF) on histamine release was investigated in 9 anaesthetized patients undergoing transvenous implantation of ICD. Concomitant arterial and coronary sinus (CS) blood samples were drawn before induction of VF (duration 20 seconds), immediately after, and 2 and 5min after DEF (18–24 Joules). Basal arterial histamine was 2.5±6nmol/1, and did not increase after VF. The histamine level in CS was 1.1±0.2nmol/1 before VF (p < 0.008 compared to arterial), and increased to 2.5 ± 0.6 nmol/1 immediately after (p < 0.045 compared to basal), to 3 ± 1.1 nmol/1 2 min after (p < 0.45), and to 2.4 ± 0.8 nmol/1 5min after VF. In the basal state there was an uptake of histamine across the coronary circulation. After VF/DEF the level of histamine increased in coronary venous blood, suggesting cardiac release of histamine.     

L-thyroxine increases susceptibility of adult rats to low K+-induced ventricular fibrillation, and sinus rhythm restoration in old rats

Hypokalaemia increases the risk for life-threatening arrhythmias; however, data about interaction with thyroid status are lacking. The aim of this study was to investigate vulnerability of l-thyroxine (T(4))-treated adult and old rats to low K(+)-induced ventricular fibrillation (VF) as well as the ability of the heart to recover sinus rhythm. The experiments were performed on isolated heart preparations using the heart of 4- and 20-month-old female Wistar rats without and with feeding with T(4) 50 microg (100 g day)(-1) over a period of 2 weeks. Perfusion of the isolated heart with oxygenated Krebs-Henseleit solution at constant pressure was followed by perfusion with K(+)-deficient solution until occurrence of VF (< 10 min). After 2 min of sustained VF, the heart was perfused with normal solution for 10 min, during which sinus rhythm was restored. ECG, left ventricular pressure (LVP) and coronary flow were continuously monitored. The results showed that compared with untreated rats, the onset of low K(+)-induced ventricular premature beats was delayed and their number was significantly decreased in both T(4)-treated groups. Nevertheless, VF occurred earlier in T(4)-treated than in non-treated adult rats (6.78 +/- 0.28 vs. 9.59 +/- 0.55 min, P < 0.05), whereas the difference was not significant in aged animals. Furthermore, sinus rhythm appeared earlier in old T(4)-treated rats compared with non-treated rats (7.18 +/- 0.57 vs. 8.94 +/- 0.64 min, P < 0.05), whereas in adult hearts it set in at practically the same time regardless of treatment. In conclusion, our results indicate that administration of a pharmacological dose of T(4) can increase the risk of low K(+)-induced VF in adult but not in old animals; in the latter it even facilitated restoration of sinus rhythm. Moreover, enhanced mechanical function was observed in both adult and old T(4)-treated hearts.     

基于联合熵的室性心动过速与室颤识别

对心电信号进行分析,是医学临床上检测和诊断心脏功能的重要手段。室性心动过速(VT)和心室纤颤(VF)是威胁人类生命的严重的心脏疾病。本文应用联合熵方法分析正常心跳信号(NSR)、VT和VF信号的动力学复杂性信息。将动力学符号统计理论以及替代数据的概念融入其中,通过计算原始时间序列和其替代时间序列之间的联合熵值,来量化序列的动力学复杂性。经过对实际心率数据的计算机分析,证明了联合熵方法的合理性。根据联合熵值的不同对NSR、VT和VF信号进行区分,取得了令人满意的效果。     

Effects of grasping force magnitude on the coordination of digit forces in multi-finger prehension

The study addresses three main questions: (1) Does the magnitude of the grasping force affect the prehension synergies, i.e., conjoint changes of finger forces and moments? (2) Do individual finger forces scale with the total grasping forces (‘scale-invariance hypothesis’)? (3) How specification of the grasping force magnitude affects the inverse optimization of digit forces. Subjects (n = 7) grasped with minimal force an instrumented handle and maintained it at rest in the air. Then, the subjects doubled the initial grasping force. The forces and moments exerted by individual digits were recorded with six-component sensors. External torques that the subjects should resist (9 in total) varied among the trials from 0 to 0.46 Nm both in clockwise and counterclockwise directions. After the force doubling, the moments of the normal forces (M ⁿ) increased in the pronation effort tasks (PR-tasks) and decreased in the supination effort tasks (SU-tasks). The changes in the moments of the tangential forces (M ^t) were opposite to the M ⁿ changes; the moments increased in the SU-tasks and decreased in the PR-tasks. The opposite effects of force doubling on the M ^ts in the SU-tasks and PR-tasks were a consequence of the unidirectional changes of the thumb tangential forces: in all the tasks the contribution of the thumb tangential force to the total tangential force increased after the grasping force doubling (and the total contribution of the four fingers decreased). The decrease of the virtual finger (VF) tangential force was mainly due to the decrease of the index finger force (VF is an imagined finger that exerts the same force and moment as all the fingers together). In the non-zero torque tasks the individual finger forces did not scale proportionally with the grasping force, the sharing percentage of the individual finger forces in the VF normal force changed with the grasping force increase. The root mean square differences between the actual finger sharing percentages in the VF force and the sharing percentages predicted from optimization procedures in which different cost functions were used were in all cases smaller after the doubling than before the doubling. Hence the answers to the three questions formulated above are: (1) the alteration of the grasping force magnitude induces complex coordinated changes of all digit forces and moments; (2) the scale invariance hypothesis is confirmed only for the zero-torque tasks and rejected for the non-zero tasks, and (3) the specification of the grasping force magnitude at the level of twice the initial grasping force—which essentially restricts the control task to the object tilt prevention—improves the accuracy of the employed optimization procedures.     

Pathological analysis of myocardial cell under ventricular tachycardia and fibrillation based on symbolic dynamics

Ventricular fibrillation (VF) is one of the most serious malignant arrhythmias usually resulting from immediate degeneration of ventricular tachycardia (VT). In order to analyse the nonlinear dynamics of the cardiac micro-mechanism under VT and VF rhythm, at the cellular level, myocardial cell action potentials are investigated under different rhythm, normal sinus rhythm, VT and VF. On the basis of nonlinear chaotic theory and symbolic dynamics, we put forward new definitions, complexity rate, etc, and obtained some useful properties for cellular electrophysiological analysis. The results of the experiments and computation show that the myocardial cellular signals under VT and VF rhythm are different kinds of chaotic signals in that the cardiac chaos attractor under VF is higher than that under VT. The analytical complexity theory has been promising in the clinical application.     

Plasticity of antimicrobial and phagocytic programs in human macrophages

Macrophage (MΦ) polarization is triggered during the innate immune response to defend against microbial pathogens, but can also contribute to disease pathogenesis. In a previous study, we found that interleukin-15 (IL-15) -derived classically activated macrophages (M1 MΦ) have enhanced antimicrobial activity, whereas IL-10-derived alternatively activated macrophages (M2 MΦ) were highly phagocytic but lacked antimicrobial activity. Given that the ability to modulate MΦ polarization from M2 MΦ to M1 MΦ may promote a more effective immune response to infection, we investigated the plasticity of these MΦ programs. Addition of IL-10 to M1 MΦ induced M2-like MΦ, but IL-15 had little effect on M2 MΦ. We determined the set of immune receptors that are present on M2 MΦ, elucidating two candidates for inducing plasticity of M2 MΦ, Toll-like receptor 1 (TLR1) and interferonγ (IFN-γ) receptor 1. Stimulation of M2 MΦ with TLR2/1 ligand (TLR2/1L) or IFN-γ alone was not sufficient to alter M2 MΦ phenotype or function. However, co-addition of TLR2/1L and IFN-γ re-educated M2 MΦ towards the M1 MΦ phenotype, with a decrease in the phagocytosis of lipids and mycobacteria, as well as recovery of the vitamin-D-dependent antimicrobial pathway compared with M2 MΦ maintained in polarizing conditions. Similarly, treatment of M2 MΦ with both TLR2/1L and anti-IL-10 neutralizing antibodies led to polarization to the M1-like MΦ phenotype and function. Together, our data demonstrate an approach to induce MΦ plasticity that provides the potential for re-educating MΦ function in human mycobacterial disease to promote host defense and limit pathogenesis.     

Sex differences in adolescents’ cardiac reactivity and recovery under acute stress: The importance of nonlinear measures

How well adolescents can self-regulate in the face of stressors has considerable implications for long-term well-being and risk of psychopathology. This study investigated sex differences in adolescents’ cardiac reactivity and recovery during a stressful task. Measures of cardiac variability (linear) and complexity (nonlinear) were obtained from N = 92 adolescents, 41 males (M age = 13.28, SD = 0.69; BMI = 21.9) and 51 females (M age = 13.36, SD = 0.67; BMI = 21.5). The adolescents underwent the Trier Social Stress Test, consisting of five conditions: baseline, anticipation, social exposure, math task, and recovery. Repeated measures ANOVAs revealed that female in comparison to male adolescents showed lower cardiac complexity revealed by higher short-term scaling exponent at baseline (p = .006) and math (p = .013) and lower entropy at exposure (p = .013) and math (p = .012). A marginal between-groups effect was found for Higuchi's fractal dimension, F(1, 90) = 3.67, p = .059, η_p² = .041, with females showing lower fractal dimension than males in math (p = .037). Linear measures did not reveal sex-related differences. Results suggest that adolescent females show lower cardiac complexity during stress. These findings support the importance of nonlinear cardiac measures for understanding cardiac reactivity during stress. Further research is needed to test the hypothesis that cardiac complexity is useful to detect an increased risk of emotional disorders, disorders that are more prevalent in women.     

Is the circadian core temperature rhythm of juvenile rats due to a periodic blockade of thermoregulatory thermogenesis?

Previous studies have demonstrated an endogenous circadian rhythm of core temperature (T _c) in suckling-age rat pups. Our aim was to establish whether the low and irregular T _c at the beginning of the light phase is caused by a temporary blockade of thermoregulatory thermogenesis. We therefore isolated and artificially fed 10-day-old pups for 30 h at five ambient temperatures (T _a), ranging from thermoneutrality to severe cold loading, while continuously recording T _c and metabolic rate (MR). During the maximum phase of the T _c rhythm MR increased linearily with decreasing T _a — to as much as 260% of the daily mean MR at thermoneutrality (TNMR) — so that T _c decreased less than 1°C with increasing cold load. During the minimum phase, the MR at all but the lowest T _a fell to, or even below, the TNMR and the amplitude of the T _c rhythm increased from 2 to 5°C with increasing cold load. Under the most severe cold load, however, a further decrease of the minimum T _c was prevented by an increase of MR to 135% of the TNMR. Supplementing the continuously fed synthetic milk with noradrenaline (1.2 mg kg^–1 h^–1) during the minimum phase of the T _c rhythm increased MR upto 290% of the TNMR. The loose regulation of T _c during the minimum phase of the juvenile circadian T _c rhythm is thus not caused by a peripheral impairment of thermogenic capacitiy at the beginning of the light phase.     

Dipole moment ofin vivo and isolated perfused rabbit hearts

We have measured magnitude and location of heart dipole moment during QRS in 46 New Zealand white rabbits. The spatial magnitude curve had one to three peaks. Mean values were M₁=80±10 μA-cm (N=5) pointing to right anterior and caudal, M₂=260±15 μA-cm (N=42) directed slightly to left of due anterior and caudal, and M₃=236±9 μA-cm (N=43) pointing towards left posterior and cephalad. The mean thorax resistivity was 250 ohm-cm. For 23 rabbits, M₂/M₃>1 and for 16 rabbits, M₂/M₃<1. Mean times of occurrence of the three peaks were 5.8, 11.2, and 19.6 ms, respectively. Spatial magnitude curves for hearts perfused at the center of a sphere showed usually one major peak at about 19 ms. Locuscardiograms ofin vivo hearts were also measured. By comparing M values forin vivo and isolated hearts, we found that M₁ values agreed closely but mean M₂ measured from the heartsin vivo was 2.5 times that for the isolated hearts, and M₃ forin vivo hearts was about two-thirds that for isolated hearts. We relate these differences to the effects of intracardiac blood and lungs on the measured dipole moment. A preliminary report of this work was given inAdvances in Electrocardiology, Proceedings XIth International Congress on Electrocardiology, P. d'Alche, ed. Caen, France, 1985, pp. 39–41 This project was supported by Grant No. HL 19486 (BCH) and by Research Career Award HL K6 1932 (CVN) from the National Heart, Lung and Blood Institute, U.S. Public, Health Service     

Influence of head-down bed rest on the circadian rhythms of hormones and electrolytes involved in hydroelectrolytic regulation

We investigated in six men the impact of a 17-day head-down bed rest (HDBR) on the circadian rhythms of the hormones and electrolytes involved in hydroelectrolytic regulation. This HDBR study was designed to mimic an actual spaceflight. Urine samples were collected at each voiding before, during and after HDBR. Urinary excretion of aldosterone, arginine vasopressin (AVP), cyclic guanosine monophosphate (cGMP), cortisol, electrolytes (Na⁺ and K⁺) and creatinine were determined. HDBR resulted in a significant reduction of body mass (P<0.01) and of caloric intake [mean (SEM) 2,778 (37) kcal·24 h^–1 to 2,450 (36) kcal·24 h^–1, where 1 kcal·h^–1=1.163 J·s^–1; P<0.01]. There was a significant increase in diastolic blood pressure [71.8 (0.7) mmHg vs 75.6 (0.91) mmHg], with no significant changes in either systolic blood pressure or heart rate. The nocturnal hormonal decrease of aldosterone was clearly evident only before and after HDBR, but the day/night difference did not appear during HDBR. The rhythm of K⁺ excretion was unchanged during HDBR, whereas for Na⁺ excretion, a large decrease was shown during the night as compared to the day. The circadian rhythm of cortisol persisted. These data suggest that exposure to a 17-day HDBR could induce an exaggeration of the amplitude of the Na⁺ rhythm and abolition of the aldosterone rhythm. Electronic Publication     

Histamine release from serosal mast cells by intermediate products of arachidonic acid metabolism

In the present paper we report the results of experiments carried out to measure the release of histamine from isolated rat mast cells during the metabolic activation of arachidonic acid. Arachidonic acid (10^–8–10^–4 M) and the terminal products (10^–6 M) of the arachidonic acid pathways were devoid of any significant histamine releasing properties. A substantial amount of histamine was released from rat mast cells by low concentrations of arachidonic acid during incubation with prostanoid generating systems, such as guinea-pig lung microsomes, rat serosal macrophages and polymorphonuclear cells and prostaglandin-H-synthase from calf seminal vesicles. The release of histamine was not accompanied by a leakage of lactate dehydrogenase and was blocked byd-mannitol and by lipoxygenase and cyclo-oxygenase pathway inhibitors. The data are consistent with the hypothesis that free radical derivatives of arachidonic acid, originating from hydroperoxy fatty acids, are generated during catalysis, causing mast cell histamine release.     

Pathological analysis of myocardial cell under ventricular tachycardia and fibrillation based on symbolic dynamics.

Ventricular fibrillation (VF) is one of the most serious malignant arrhythmias usually resulting from immediate degeneration of ventricular tachycardia (VT). In order to analyse the nonlinear dynamics of the cardiac micro-mechanism under VT and VT rhythm, at the cellular level, myocardial cell action potentials are investigated under different rhythm, normal sinus rhythm, VT and VT. On the basis of nonlinear chaotic theory and symbolic dynamics, we put forward new definitions, complexity rate, etc, and obtained some useful properties for cellular electrophysiological analysis. The results of the experiments and computation show that the myocardial cellular signals under VT and VF rhythm are different kinds of chaotic signals in that the cardiac chaos attractor under VF is higher than that under VT. The analytical complexity theory has been promising in the clinical application.     

Repeatability of Dietary Patterns Derived Using α-Priori and α-Posterior Methods

We aimed to examine the repeatability of dietary patterns derived using α-priori and α-posterior techniques. During 2008, 500 participants were enrolled and asked to fill-in a food frequency questionnaire twice. The Mediterranean dietary pattern was α-priori assessed by the MedDietScore, while principal components analysis (PCA) and cluster analysis (CA) were used as the α-posterior techniques. Results revealed that the overall MedDietScore was similar between the two recordings (M = 28, SD = 3.7 vs. M = 28, SD = 3.8). Although PCA revealed 13 patterns in each record (60% of explained variability), the food items characterizing each pattern were varying through the two recordings. According to CA, three clusters were revealed from both records. The α-posterior methods should be used with caution, while the α-priori approach leads to more robust results.     

Behavioural clusters characteristic of cardiovascular reactivity profiles relate to poorer health outcomes

Objectives

Blunted cardiovascular reactivity is associated with a distinct behavioural profile of greater exposure to early life adversity, coupled with higher levels of behavioural disengagement and symptoms of depression. The present study sought to extend on this work by investigating if behavioural clusters with distinct patterns of reactivity were related to health and behavioural outcomes at baseline and at a 4-year follow-up.

Methods

Hierarchical cluster analyses were conducted using longitudinal data drawn from the Midlife Development in the United States (MIDUS 2) Biomarker Project and the MIDUS 3 follow-up 4 years later. During MIDUS, 2 participants (N = 513) underwent a standardized stress testing protocol and had their blood pressure and heart rate monitored throughout. In addition, hierarchical cluster analyses were conducted on responses from measures of early life adversity, behavioural disengagement and depression. Binary logistic regressions were conducted to determine whether cluster membership was related to health and behavioural outcomes which were taken at both time points.

Results

Three behavioural clusters emerged with statistically different blood pressure reactivity patterns. The cluster characterized by greater exposure to early life adversity, higher levels of behavioural disengagement and depressive symptoms, had relatively lower blood pressure reactivity patterns compared with both the exaggerated reactivity cluster and the cluster similar to the sample mean. In fully adjusted models, this cluster was associated with hypertension (p = .050) and depressed affect (p = .033), while Cluster 1 characteristic of an exaggerated blood pressure reactivity profile was associated with depressed affect (p < .001). Cluster membership did not significantly predict future health status.

Conclusion

This study extends research on behavioural clusters characteristic of reactivity profiles to demonstrate how they relate to health and behavioural outcomes during MIDUS 2.     

Die γ-induzierte copolymerisation von vinylfluorid und vinylidenfluorid

The ⁶⁰Co-γ-induced copolymerization of vinyl fluoride (VF) and vinylidene fluoride (VF₂) was investigated for the polymerization temperatures 273 K, 253 K, and 233 K. The dependency of the over-all reaction rate and the over-all activation energy on the composition of the monomer feed is evaluated. The copolymerization parameters were determined as r₁=5,23 and r₂=0,06 (VF?M₁). The change of over-all reaction rate with monomer feed is discussed. By means of a mathematical treatment of the kinetical behaviour of non-steady-state reactions, which was modified for the case of copolymerization, the influence of termination and propagation on the over-all reaction rate was determined separately.     

The clustering and morphology of chondrocytes in normal and mildly degenerate human femoral head cartilage studied by confocal laser scanning microscopy

Chondrocytes are the major cell type present in hyaline cartilage and they play a crucial role in maintaining the mechanical resilience of the tissue through a balance of the synthesis and breakdown of extracellular matrix macromolecules. Histological assessment of cartilage suggests that articular chondrocytes in situ typically occur singly and demonstrate a rounded/elliptical morphology. However, there are suggestions that their grouping and fine shape is more complex and that these change with cartilage degeneration as occurs in osteoarthritis. In the present study we have used confocal laser scanning microscopy and fluorescently labelled in situ human chondrocytes and advanced imaging software to visualise chondrocyte clustering and detailed morphology within grade‐0 (non‐degenerate) and grade‐1 (mildly degenerate) cartilage from human femoral heads. Graded human cartilage explants were incubated with 5‐chloromethylfluorescein diacetate and propidium iodide to identify the morphology and viability, respectively, of in situ chondrocytes within superficial, mid‐ and deep zones. In grade‐0 cartilage, the analysis of confocal microscope images showed that although the majority of chondrocytes were single and morphologically normal, clusters (i.e. three or more chondrocytes within the enclosed lacunar space) were occasionally observed in the superficial zone, and 15–25% of the cell population exhibited at least one cytoplasmic process of ~ 5 μm in length. With degeneration, cluster number increased (~ 50%) but not significantly; however, the number of cells/cluster (P < 0.001) and the percentage of cells forming clusters increased (P = 0.0013). In the superficial zone but not the mid‐ or deep zones, the volume of clusters and average volume of chondrocytes in clusters increased (P < 0.001 and P < 0.05, respectively). The percentage of chondrocytes with processes, the number of processes/cell and the length of processes/cell increased in the superficial zone of grade‐1 cartilage (P = 0.0098, P = 0.02 and P < 0.001, respectively). Processes were categorised based on length (L0 – no cytoplasmic processes; L1 < 5 μm; 5 < L2 ≤ 10 μm; 10 < L3 ≤ 15 μm; L4 > 15 μm). With cartilage degeneration, for chondrocytes in all zones, there was a significant decrease (P = 0.015) in the percentage of chondrocytes with ‘normal’ morphology (i.e. L0), with no change in the percentage of cells with L1 processes; however, there were significant increases in the other categories. In grade‐0 cartilage, chondrocyte clustering and morphological abnormalities occurred and with degeneration these were exacerbated, particularly in the superficial zone. Chondrocyte clustering and abnormal morphology are associated with aberrant matrix metabolism, suggesting that these early changes to chondrocyte properties may be associated with cartilage degeneration.