Local Hemodynamic Conditions Associated with Focal Changes in the Intracranial Aneurysm Wall

BACKGROUND AND PURPOSE

Aneurysm hemodynamics has been associated with wall histology and inflammation. We investigated associations between local hemodynamics and focal wall changes visible intraoperatively.

MATERIALS AND METHODS

Computational fluid dynamics models were constructed from 3D images of 65 aneurysms treated surgically. Aneurysm regions with different visual appearances were identified in intraoperative videos: 1) "atherosclerotic" (yellow), 2) "hyperplastic" (white), 3) "thin" (red), 4) rupture site, and 5) "normal" (similar to parent artery), They were marked on 3D reconstructions. Regional hemodynamics was characterized by the following: wall shear stress, oscillatory shear index, relative residence time, wall shear stress gradient and divergence, gradient oscillatory number, and dynamic pressure; these were compared using the Mann-Whitney test.

RESULTS

Hyperplastic regions had lower average wall shear stress (P = .005) and pressure (P = .009) than normal regions. Flow conditions in atherosclerotic and hyperplastic regions were similar but had higher average relative residence time (P = .03) and oscillatory shear index (P = .04) than thin regions. Hyperplastic regions also had a higher average gradient oscillatory number (P = .002) than thin regions. Thin regions had lower average relative residence time (P < .001), oscillatory shear index (P = .006), and gradient oscillatory number (P < .001) than normal regions, and higher average wall shear stress (P = .006) and pressure (P = .009) than hyperplastic regions. Thin regions tended to be aligned with the flow stream, while atherosclerotic and hyperplastic regions tended to be aligned with recirculation zones.

CONCLUSIONS

Local hemodynamics is associated with visible focal wall changes. Slow swirling flow with low and oscillatory wall shear stress was associated with atherosclerotic and hyperplastic changes. High flow conditions prevalent in regions near the flow impingement site characterized by higher and less oscillatory wall shear stress were associated with local "thinning" of the wall.

[Principles of revascularization in treatment of giant intracranial aneurysms]

During recent decades extra-intracranial and intra-intracranial bypasses have deserved high interest among neurosurgeon, especially in management of giant cerebral aneurysms. Development of microsurgery and neuroanesthesiological techniques, advances in neuroradiology and neurophysiology prerequisite improvement of revascularization surgery. Evolution of competitive endovascular methods pushes the surgeons to improve microneurosurgical technique of revascularization and elaboration of new approaches to management of intracranial aneurysms. In this review we discuss principles of surgery of cerebrovascular bypasses in management of giant aneurysms applied in our clinic.

Post-Traumatic Frontal and Parieto-Occipital Extradural Haematomas: a Retrospective Analysis of 41 Patients and Review of the Literature

The purpose of this study was to analyse the differences between patients with frontal (FEDH) or parieto-occipital (POEDH) epidural haematomas and evaluate possible statistically significant prognostic factors.

In this retrospective study of a group of 41 patients with a FEDH (17) or POEDH (24 individuals), the authors analysed the influence of gender, age, type of injury, clinical presentation, Glasgow coma scale (GCS) score on admission, radiological findings, and time interval from trauma to surgery on outcomes. A good recovery and moderate disability were considered a “good” or “favourable outcome”, whereas severe disability, a vegetative state or death was a “poor outcome”.

In the POEDH subgroup, a higher GCS score on admission and a younger age were statistically significant prognostic factors for a better outcome (p=0.006, rs=0.702). In the subgroup of patients with FEDHs, the results were not significant. However, patients with FEDHs more frequently had “good outcomes” than members of the POEDH subgroup (88.2 vs. 70.9%). Children (≤ 18 years old) constituted a smaller portion of the POEDH subgroup (12.5%) than those in the FEDH subgroup (41.2%). The evaluation of time intervals between the accident and surgery (≤ 24 h vs. > 24 h) showed no significant influence on outcomes in any of the studied subgroups. However, patients undergoing surgery within 24 h of their injury had a less favourable GCS score on admission than those operated on more than 24 h after their injury. Subacute and chronic clinical courses predominated in patients with a FEDH (10/17 FEDH vs. 11/22 POEDH). Different accompanying intradural lesions occurred in 12 patients of the POEDH subgroup, but only in 2 of the FEDH subgroup (50 vs. 11.8%). However, the presence of such lesions did not significantly deteriorate surgical outcomes in either of the subgroups.

Microsurgical technique for previously coiled aneurysms

Since the introduction of Guglielmi detachable coils to treat intracranial aneurysms in 1991, the number of patients undergoing endovascular coiling has continuously risen as well as the number of those residual and recurrent previously coiled aneurysms that necessitate a microsurgical occlusion. Between July 1995 and August 2009 we retrospectively analyzed 81 patients with 82 previously coiled aneurysms treated microsurgically at two Finnish Neurosurgical University Hospitals, Helsinki and Kuopio. Fifty-eight aneurysms (71%) were located at anterior circulation and 24 (29%) at posterior circulation. Fifteen patients were operated on within the first month (early surgery) after coiling, whereas 66 were treated later (late surgery). Complete or partial removal of coils during surgery may facilitate clipping, but is significantly (P<0.001) more difficult to accomplish in late surgery. Removal of coils may also increase the chance for poor outcome. Chance of poor outcome increased also with intraoperative aneurysm rupture, size of the aneurysm and posterior circulation location. Good clinical outcome, three months after surgery, was achieved in 71 patients (88%); four patients were severely disabled, and six patients died (three of them due to poor clinical condition). Complete microsurgical occlusion of the residual previously coiled aneurysm is a high-risk procedure in large and giant aneurysms, and these patients should be referred to a dedicated neurovascular center to minimize surgical complications. Bypass procedures may be the best option for demanding growing lesions, especially those in posterior circulation.

Trimethoprim prophylaxis of acute exacerbations in chronic obstructive pulmonary diseases

A double-blind randomized trial was carried out to study the efficacy and tolerance of trimethoprim with a daily single dose of 300 mg in long-term prophylaxis of acute exacerbations of chronic obstructive pulmonary diseases (COPD). The patients, 13 in the trimethoprim group and 11 in the placebo group, were followed up at fixed intervals and checked for respiratory functions and haematological parameters for six months. The number of exacerbations were significantly lower than during the previous winter in both groups: 0.6 compared to 3.8 in the trimethoprim group, and 0.6 to 3.0 in the placebo group. Tolerance of trimethoprim was good and did not differ from that of placebo. The necessity of double-blind trials in evaluating the prophylactic value of antibiotics in COPD is emphasized, since the exacerbations are also dependent on many unknown factors. There were no statistically significant differences in blood counts of folate levels.

Citalopram controls phobic symptoms in patients with panic disorder: randomized controlled trial

OBJECTIVE

To examine the effects of long-term treatment with citalopram or clomipramine on subjective phobic symptoms in patients with panic disorder.

DESIGN

Double-blind, parallel-group, five-arm study.

PATIENTS

Patients aged 18 to 65 years with panic disorder (DMS-III-R diagnosis) and with no major depressive symptoms.

INTERVENTIONS

Four hundred and seventy-five patients were randomized to 8 weeks of treatment with either citalopram (10 to 15 mg per day; 20 to 30 mg per day; or 40 to 60 mg per day), clomipramine (60 to 90 mg per day) or placebo. Two hundred and seventy-nine patients continued treatment after the 8-week acute phase.

OUTCOME MEASURES

Phobic symptoms were assessed using the Phobia Scale and the Symptom Checklist's (SCL-90) phobia-related factors.

RESULTS

At all dosages, citalopram was more efficacious than placebo, with 20 to 30 mg generally being the most effective dosage. Citalopram (20 to 30 mg) generally decreased phobic symptoms significantly more than placebo after Month 3. Interpersonal sensitivity decreased when measured on the respective SCL-90 sub-scale. Alleviation of phobic symptoms generally continued to increase towards the end of the treatment. The effect of clomipramine was not as consistent.

CONCLUSIONS

All active treatment groups, especially the group receiving 20 to 30 mg per day of citalopram, effectively controlled phobic symptoms in patients with panic disorder. Long-term treatment with citalopram further decreased phobic symptoms.

Smoking and cognitive deficits in schizophrenia: a pilot study

The cross-sectional study assessed the associations among smoking status, number of cigarettes smoked per day, and psychiatric symptoms in 88 chronic schizophrenic outpatients with a stable psychic condition. Among the 49 smokers, the number of cigarettes smoked per day was associated with the severity of cognitive symptoms of the Positive and Negative Syndrome Scale. The authors suggest that smoking may alleviate cognitive deficits in schizophrenia by increasing dopaminergic neurotransmission in the prefrontal areas of the brain.

Effect of smoking on neuroleptics in schizophrenia

OBJECTIVE

The effect of smoking on daily doses and plasma levels of neuroleptics prescribed for schizophrenic patients was studied.

METHODS

90 outpatients with schizophrenic disorder (DSM-III-R) who were on a stable regimen of psychotropic medication and showed a stable clinical state were included in a double-blind placebo-controlled trial. Data were collected and blood tests taken at the baseline interview. The plasma levels were obtained for 52 patients.

RESULTS

Daily neuroleptic doses converted to chlorpromazine equivalents correlated significantly (r = 0.436) with the plasma levels of their unmetabolised fractions. The neuroleptic doses increased with age in smokers, while in nonsmokers they decreased. Neither sex, age nor smoking had a significant association with the neuroleptic plasma levels.

CONCLUSIONS

Smoking seems to lead to increased neuroleptic dosages in postmenopausal schizophrenics by increasing hepatic metabolism and renal excretion of the drugs and possibly enhancing dopamine release. It is also possible that older smoking patients form a selected group of heavy smoker and they, therefore, need exceptionally high neuroleptic doses.

Citalopram causes no significant alterations in plasma neuroleptic levels in schizophrenic patients

Steady-state plasma concentrations of commonly used neuroleptic drugs were measured in 90 schizophrenic patients before and after adding placebo or citalopram (40 mg/day) to their treatment regimen. Plasma concentrations of citalopram and its main metabolite, desmethylcitalopram, were also measured. In addition, patients with exceptionally high neuroleptic levels or an increase in adverse effects during the 12-week study period were evaluated for their debrisoquine/sparteine hydroxylase (CYP2D6) genotype, an enzyme responsible for oxidative metabolism of several neuroleptics and selective serotonin re-uptake inhibitors. There were no significant changes in plasma concentrations of haloperidol, chlorpromazine, zuclopenthixol, levomepromazine, thioridazine or perphenazine during the study. Plasma concentrations of citalopram and desmethylcitalopram were well within the levels reported previously with monotherapy, and remained stable throughout the study. None of the 15 patients analysed for the CYP2D6 genotype was a poor metabolizer. It is concluded that clinically important pharmacokinetic drug interactions do not play a crucial role when citalopram is used as an augmentation therapy in neuroleptic-treated schizophrenic patients.

Citalopram as an adjuvant in schizophrenia: further evidence for a serotonergic dimension in schizophrenia

There is increasing evidence suggesting that symptoms of depression and anxiety may also be associated with serotonergic dysfunction in schizophrenic patients. The effect of the adjuvant selective serotonin reuptake inhibitor citalopram was assessed regarding the symptom dimensions of schizophrenia measured with the Positive and Negative Syndrome Scale (PANSS) and with the Hamilton Rating Scale for Depression (HRSD). Citalopram alleviated symptoms of the depression/anxiety dimension of the PANSS, but not the symptoms of the four other PANSS domains or depressive symptoms measured with the HRSD. The results support the hypothesis of a serotonergic dimension in schizophrenia.

Citalopram as an adjuvant in chronic schizophrenia: a double-blind placebo-controlled study

The effects of citalopram--the most selective serotonin reuptake inhibitor on the market--on psychopathological symptoms were studied in chronic schizophrenic patients on a stable regimen of neuroleptic medication. Outpatients suffering from schizophrenic disorder (DSM-III-R) with Positive and Negative Symptom Scale (PANSS) scores higher than 50 were included in a double-blind placebo-controlled add-on study. The daily dose of citalopram was 20 mg in the first week and 40 mg for the remaining period. A total of 90 patients (45 patients receiving citalopram and 45 receiving placebo) completed the 12-week trial. There were no changes in neuroleptic plasma levels during the trial. There was a significant decrease in total PANNS scores during the trial, although no statistically significant differences between the citalopram group and the placebo group were revealed. The number of responders in terms of severity of illness (CGI) was higher and the increase in subjective well-being (VAS) was greater in patients on citalopram than in those receiving placebo. There were no significant differences in the occurrence of side-effects. It is concluded that, in chronic schizophrenic out-patients, citalopram has no clear effect on the psychopathological symptoms; it may improve the general clinical condition, and it appears to increase the subjective well-being of these patients. Citalopram appears to be safe when used to treat schizophrenic patients who are receiving concomitant neuroleptic treatment.

Prediction of positive placebo response among chronic schizophrenic outpatients

We undertook this study to determine whether predictors of positive placebo response in chronic schizophrenic outpatients could be identified. Twelve placebo responders and 33 placebo nonresponders who participated in a parallel-group, double-blind, 12-week clinical drug trial were compared. No significant differences between the groups were found with regard to 16 anamnestic and symptom variables. To investigate further which variables at baseline predicted positive placebo response, a stepwise linear regression model was created. Of the seven variables entered into the model, only high scores in the positive domain of the Positive and Negative Syndrome Scale (delusions, unusual thought content, grandiosity, and suspiciousness/persecution) at baseline predicted significantly positive placebo response (p = .0047). Because the onset of placebo response was gradual, the authors hypothesize that placebo response in chronic schizophrenia consists mainly of two ingredients: nonspecific psychotherapeutic effect caused by the several assessments carried out during the study, and regression toward the mean.

Citalopram, a selective serotonin reuptake inhibitor, in the treatment of aggression in schizophrenia

The aim of this double-blind cross-over study was to investigate whether treatment with the selective serotonin reuptake inhibitor, citalopram reduces aggressiveness in chronically violent schizophrenic inpatients. Initially 19 patients were enrolled into this double-blind cross-over study in which the patients were treated for 24 weeks with placebo and 24 weeks with citalopram (20-60 mg/day) as a supplement to their previous neuroleptic medication. Fourteen patients completed the entire study, but sufficient data on 15 patients could be used in the end-point analysis of efficacy. Psychiatric assessments (Brief Psychiatric Rating Scale, Clinical Global Impression Scale for Severity of Illness, Social Dysfunction and Aggression Scale and the Global Aggression Scale) and side effects (UKU Side Effect Scale) were recorded at baseline and 4 times during both periods. Aggressive incidents (Staff Observation Aggression Scale) were recorded throughout the study. During citalopram treatment, the frequency of aggressive incidents was significantly lower and the mental state did not deteriorate. Patients either experienced no side effects or else side effects were equally mild during both periods.

Aspoxicillin versus piperacillin in severe abdominal infections--a comparative phase III study

We compared aspoxicillin, a new broad-spectrum penicillin derivative, with piperacillin in severe abdominal infection. Aspoxicillin 4 g administered tds (n = 52) or piperacillin 4 g qds (n = 53) usually as monotherapy were randomly given to patients suffering from perforated appendicitis, acute cholecystitis, ulcer or colon perforation, or intra-abdominal abscess. Blood, tissue and exudate cultures were obtained when applicable for pathogen identification and susceptibility testing. The efficacy rates were similar in the two study groups. Of the 50 evaluable aspoxicillin patients 45 (90%) were considered as treatment responders compared with 48 patients out of 53 (91%) in the piperacillin group (NS). The 95% confidence interval for the efficacy difference was -12% to +11% thus showing no difference between the two drugs. Both drugs were generally well tolerated and no serious drug-related adverse events were noted. However, five patients died because of their illness and one patient had a fatal myocardial infarction. In conclusion, aspoxicillin 4 g tds was shown to be equal to piperacillin 4 g qds in severe abdominal infections.

Citalopram in patients with unsatisfactory response to neuroleptics: an open follow-up study

There is clinical evidence that antidepressants have beneficial effects on certain symptom clusters of psychotic patients. Specific serotonin reuptake inhibitors like citalopram provide a new possibility to selectively influence brain neurotransmission. We studied the effects of citalopram (20-60 mg daily) in 36 psychotic or borderline patients receiving neuroleptic treatment without satisfactory response. Particular attention was paid to negative symptomatology, anxiety, and impulsiveness. 22 of the patients (65%) were assessed to react to citalopram treatment in a clinically significant manner. Initially, the responders tended to have higher scores in withdrawal-retardation, anxious-depression, and hostile-suspiciousness factors of the Brief Psychiatric Rating Scale (BPRS), with a lower degree of thinking disturbances. In the responder group, a significant decline in all symptom clusters was recorded. The mean decrease was 38% in Clinical Global Impression (CGI) and BPRS scales. The most prominent change (52%) was seen in hostile-suspiciousness factor of the BPRS inventory. In light of the positive results achieved in this open-label trial, controlled trials with patients not responding satisfactorily to neuroleptics are warranted.

Multiple-dose pharmacokinetic study with a slow-release carbamazepine preparation

The pharmacokinetics, clinical efficacy and side effects of carbamazepine (CBZ) in the steady-state condition were studied using a slow-release preparation (SR), Neurotol Slow, and a conventional preparation (C), Tegretol. Eighteen adult epileptic patients under CBZ therapy were evaluated in this single-blind, randomized cross-over study. The previous daily CBZ dose was kept unchanged and divided into 2 daily doses during two 2 week study periods. At the end of each period blood samples were drawn at frequent intervals for 12 h after the administration of the morning CBZ dose. Serum concentrations of unchanged CBZ and its main metabolite, carbamazepine-10,11-epoxide (CBZE), were determined by HPLC. Peak concentrations of CBZ and CBZE were significantly lower, and the time-lapse before CBZ reached its peak was significantly longer during SR treatment. The fluctuations in serum CBZ and CBZE were significantly lower during SR treatment. There was no significant difference in bioavailability between the 2 preparations. The number of epileptic seizures was 31 during SR and 57 during C treatment. Side effects were more common during C treatment. The occurrence of dizziness was significantly lower with SR treatment than with C treatment. We conclude that greater stability in serum CBZ and CBZE concentrations can be obtained by using an SR of CBZ, without reducing the bioavailability of the drug.

Effect of ibopamine on the failing heart at rest and during isometric exercise: a noninvasive study

Eleven patients suffering from heart failure were treated with oral ibopamine, a di-isobutyric ester of N-methyldopamine, 100 mg three times a day for 1 week and 200 mg three times a day for 3 weeks. Therapy was discontinued by one patient because of tachycardia. Left ventricular performance was evaluated with echocardiography and systolic time intervals at rest and after 3 minutes of isometric exercise using a handgrip. Six of 10 patients completing the study were in New York Heart Association (NYHA) functional class III, 2 in class IV, and 2 in class II. All patients, except one who remained stable in class II, improved their subjective condition by one functional class during 4 weeks of therapy (p less than 0.01). There were no changes in heart rate, blood pressure, rate-pressure product, cardiac index, or total peripheral vascular resistance. The left ventricular end-systolic diameter decreased after four weeks from 71.2 +/- 12.7 (SD) to 65.9 +/- 13.0 mm (p less than 0.001); the left ventricular end-diastolic diameter did not change. The ejection fraction increased from 26 +/- 8 to 32 +/- 9% (p less than 0.01). Afterload, that is, left ventricular circumferential systolic wall stress, declined as a result of decreased systolic diameter. Systolic time intervals did not vary. There were no changes due to ibopamine during isometric exercise probably owing to increased beta-adrenergic stimulation induced by the handgrip. Neither urine volume nor body weight changed. Side effects were mild except for tachycardia of one patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of dosing frequency of carbamazepine with a slow-release preparation

The occurrence of side effects and epileptic seizures and the pharmacokinetics of carbamazepine (CBZ) and carbamazepine-10,11-epoxide were studied using a slow-release CBZ preparation, Neurotol slow, and a conventional CBZ preparation, Tegretol. The study was an open, randomized cross-over trial, with a 2 week study period for each preparation. Tegretol was given 3 times and Neurotol slow twice a day. The earlier CBZ dose was kept unchanged. The initial sample consisted of 24 adult epileptic patients receiving CBZ treatment of whom 20 patients were evaluable. The fluctuation in serum CBZ concentrations did not differ significantly between the 2 treatment periods, even though the interdose interval of Neurotol slow was 4 h longer than that of Tegretol. The switch-over from conventional CBZ to the slow-release formulation did not seem to alter the efficacy and side effects of CBZ. By using Neurotol slow instead of a conventional CBZ preparation, Tegretol, it is evidently possible to reduce the dosing frequency from 3 times a day to twice daily administrations.

The effect of nifedipine on plasma lipids in patients with essential hypertension

The effect of nifedipine on plasma lipids given over a period of one month to 14 patients with essential hypertension was studied. There were no significant changes in the concentrations of plasma total cholesterol, LDL cholesterol, VLDL cholesterol, HDL cholesterol and triglycerides during treatment. Nifedipine appears to be preferable to diuretic agents and to beta-blockers without ISA as nifedipine has no untoward effects on lipid metabolism.

Alpha and beta adrenergic control of contraction force of perch heart (Perca fluviatilis) in vitro

Noradrenaline showed a negative inotropic effect on the isolated electrically triggered atrium of the perch. The effect was stronger at lower temperature and was antagonized by an alpha adrenergic blocker, phentolamine. The inotropic effect of adrenaline was dependent on incubation temperature. The effect was negative at 15 C but biphasic at 24 C, where with increasing adrenaline concentration a positive inotropic effect was followed by negative inotropy. Phentolamine not only antagonized the negative inotropic effect of adrenaline at 15 degrees C but changed it to positive. This positive inotropic effect was antagonized by a beta adrenergic blocker, propranolol. On the triggered ventricular strip adrenaline had no effect at 6 or 15 C, but increased contraction force at 24 C. It can be suggested that in the perch heart atrium there is an activity balance of alpha and beta receptors, which mediate the negative and positive inotropic control, respectively. As in higher vertebrates, alpha adrenergic activation decreases and beta activation increases by agonists in the following order: noradrenaline, adrenaline and isoprenaline. The balance changes towards increased beta activity when temperature rises.

Membrane potential oscillations in enzymatically isolated rat myocardial cells

Enzymatical isolation was used for preparation of single myocardial cells, contractions of which were mainly of slow phasic type but normal fast contractions also occurred. Membrane potential (MP) changes of these cells were measured by conventional microelectrode techniques. Initial MP level of these cells varied between -60 to -90 mV (74.4 +/- 1.9). In the majority of the cells the MP rapidly dropped to -20 to -40 mV and continued to decline while oscillating. In some cells MP recovered from -20 to -40 back to a more negative potential, and the MP oscillation was strongest (up to 20 mV) between -30 to -50 mV. In about 3% of the impalements the MPs did not degenerate at all, but stayed at initial values for several minutes. The MP oscillations were dependent on the MP level and connected to the slow phasic contractions. In connection to the normal fast contractions, two types of action potentials (AP) could be registered. Near -50 mV the cells often generated slow APs of duration 200-400 ms and dV/dt less than 3 V/s but at higher MP level normal fast APs up to 120 mV (100-300 ms and dV/dt greater than 40 V/s) were generated. The slow phasic contractions were never connected to either type of AP.

Characterization of contractions in mechanically and enzymatically isolated myocardial cells from the rat heart ventricles

Single spontaneously beating myocardial cells were prepared by mechanical or enzymatical isolation. Using a TV camera and videotape recorder, beating parameters were characterized in different buffer solutions in regard to temperature and integrity of sarcolemma, which was tested by ability of cells to exclude a vital stain, Evans blue. The mechanically disaggregated cells were totally permeable to this stain, but about 60% of the enzymatically isolated myocytes were able to exclude the stain. The myocytes prepared in the presence of calcium were most tolerant to physiological concentration of calcium. Contractions were mainly of phasic type where the velocity of contraction wave was very slow (50-330 microns/s). The velocity was not correlated to the beat rate. Temperature dependence of the velocity was positively correlated with the integrity of sarcolemma. Beat rate was inversely related to the integrity of sarcolemma being slowest in calcium tolerant enzymatically isolated cells. Beat rate of calcium sensitive myocytes was higher but unstable and the temperature dependence of the rate was steeply reduced and even reversed during the incubation. Some calcium tolerant myocytes generated occasionally an electric type of contraction which came in bursts and was characterized by synchronous sarcomere shortening without any contraction wave.

Characterization of contractions in mechanically disaggregated myocardial cells from the rat

Myocardial cell groups, mechanically disaggregated from the rat heart, beat spontaneously in a medium which resembles intracellular fluid. The cells, initially functioning in an uncoordinated way, i.e. each cell in its own rhythm, gradually become coordinated as a function of time. After 90 min of incubation at 15 degrees C all the cell groups were functioning in a coordinated way. The initiation of coordination was temperature-dependent. Lowering the temperature from 15 degrees C to 10 degrees C significantly delays the coordination, only 75% of the cell groups being coordinated after 90 min. The contraction wave in coordinated cell groups was very slow; 90 +/- 7 micrometers/s at 20 degrees C, 100 +/- 6 micrometers/s at 30 degrees C and 100 +/- 7 micrometers/s at 35 degrees C. The velocity of contraction waves was not significantly temperature-dependent, suggesting a neonenzymatical type of propagation. It also seems too slow to be an electrical event. Apparently the contraction waves are propagated by diffusion of Ca2+. The addition of caffeine to the medium hastened the coordination of contractions, but Na-azide strongly inhibited it. The results indicate that the sarcoplasmic reticulum functions in the coordination of contractions, probably by releasing Ca2+ for the activation of the myofilaments.