Suppression of savanna ants alters invertebrate composition and influences key ecosystem processes.

In almost every ecosystem, ants (Hymenoptera: Formicidae) are the dominant terrestrial invertebrate group. Their functional value was highlighted by Wilson (1987) who famously declared that invertebrates are the "little things that run the world." However, while it is generally accepted that ants fulfil important functions, few studies have tested these assumptions and demonstrated what happens in their absence. We report on a novel large-scale field experiment in undisturbed savanna habitat where we examined how ants influence the abundance of other invertebrate taxa in the system, and affect the key processes of decomposition and herbivory. Our experiment demonstrated that ants suppressed the abundance and activity of beetles, millipedes, and termites, and also influenced decomposition rates and levels of herbivory. Our study is the first to show that top-down control of termites by ants can have important ecosystem consequences. Further studies are needed to elucidate the effects ant communities have on other aspects of the ecosystem (e.g., soils, nutrient cycling, the microbial community) and how their relative importance for ecosystem function varies among ecosystem types (e.g., savanna vs. forest).

Outcome of an exercise to notify patients treated by an obstetrician/gynaecologist infected with HIV-1.

Experience with hepatitis B suggests that the risk of HIV transmission from a health care worker infected with HIV to a patient will be greatest during major surgical procedures. The number of patients worldwide who are known to have undergone such procedures, been notified, and subsequently tested is still too small to be confident that the risk of HIV transmission in these circumstances is negligible. We describe a patient notification exercise, undertaken in the United Kingdom in 1991. Attempts were made to contact 1217 patients, in three health districts (A, B, and C), who had undergone surgical procedures performed by an obstetrician/gynaecologist who was infected with HIV. The exercise aimed to offer the patients reassurance, counselling and--if they wished--HIV testing. One thousand one hundred and forty-two patients (94%) were contacted, and all 520 who elected to be tested were negative for anti-HIV. The proportion of identified patients tested was 63% in district A, 35% in district B, and 61% in district C. Surgical procedures were classified retrospectively according to the likely risk (none, possible, or high) of exposure to the doctor's blood and, therefore, risk of HIV transmission. One hundred and ninety-five of those tested had undergone a procedure that carried a high risk of exposure; 179 had undergone a procedure thought to carry no risk. Patients in districts A and C who had undergone a procedure that carried a high risk of exposure were more likely to be tested than those who had not; 206 patients overall had undergone procedures that carried a high risk of exposure but were not subsequently tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Low affinity heparin is an antithrombotic agent.

We have investigated the antithrombotic activities and haemorrhagic side effects of a low affinity heparin (LAH). In the rabbit thrombosis model using activated human serum as the thrombogenic challenge, the effect of LAH on 10' and 20' stasis was studied. At 10' stasis, 150 micrograms/kg of LAH reduced thrombus formation by 67% and total prevention was achieved at 500 micrograms/kg. At 20' stasis, 150 micrograms/kg was totally ineffective, 500 micrograms/kg was partially effective and 1000 micrograms/kg was required to achieve complete prevention of thrombosis. Mean peak circulatory level following infusion of 500 micrograms/kg of LAH was found to be 1.6 micrograms/ml by heparin cofactor II based assay and 0.13 iu/ml by anti-factor Xa assay. Thrombin generation tests of the same post injection samples showed an 80% reduction in thrombin production when compared with pre-injection samples. At 2.5 mg/kg, the mean bleeding time ratio (challenge:control) measured in the rabbit ear template model was 1.25 (cf saline control 0.88). Compared with results from previous studies on unfractionated heparin and dermatan sulphate, LAH is approximately 6 times less effective than UFH but 5 times more potent than dermatan sulphate. Since the mean bleeding time for UFH at 2.5 mg/kg was previously found to increase nearly two fold over the control value, LAH may present a lesser haemorrhagic risk than UFH. These data suggest that LAH is more effective in directly preventing venous thrombosis than dermatan sulphate. Although LAH is not as effective as UFH on a weight basis in the impairment of thrombogenesis, it may carry significantly lower bleeding risk.

Severe obesity: effects on foot mechanics during walking.

The purpose of our study was to determine the effects of severe obesity on the foot mechanics of adult females. Twenty-nine adult females between the ages of 20 and 48 years volunteered as subjects for this investigation. The subjects were separated into a severely obese (O) group (body mass index = 41.14 +/- 2.61; N = 16) and a normal weight control group (body mass index = 20.84 +/- 0.47; N = 13). A Locam camera (100 Hz) positioned perpendicular to the subjects' posterior aspect was used to film the rearfoot movement of the subjects during the final 15 sec of a 10 min treadmill walk. The O group had a significantly greater touchdown angle (P = .05), more total eversion range of motion (P = .001), and a faster maximum eversion velocity (P < .001). Moreover, analysis of dynamic foot angles indicated that the O group had significantly (P = .003) more forefoot abduction. Finally, anthropometric data revealed statistically different (P < .001) Q angle measurements between the O and control groups. The results of this study suggest that severely obese females have significantly greater rearfoot motion, foot angle, and Q angle values than normal weight females.

Multiple unipolar lead electrocardiographic monitoring during exercise in severe coronary artery disease: a comparison with bipolar lead monitoring.

A system of 21-lead electrocardiography was used to assess 21 patients with severe angina during and after exercise using on-line computerised ST segment analysis. A direct comparison was made between the results obtained from 18 unipolar precordial leads and those from bipolar leads CM5 and CC5. Treadmill exercise was performed 48 hr prior to cardiac catheterization, which revealed luminal narrowing of at least 70% in one or more major coronary arteries in all cases. In all cases the ST depression exceeded 1 mm in both CM5 and CC5 at the peak of exercise. The magnitude of ST depression was greater in the bipolar leads in 75% of cases and in the remaining 25% the greatest peak ST depression occurred in a single unipolar lead. There was no correlation between the magnitude of ST depression and the number of coronary vessels involved. Isopotential surface mapping in the anterior, lateral and inferior projections from the unipolar leads at each stage of exercise failed to show a correlation between the area or distribution of ST segment change and the number or anatomical location of the vessels involved. It was not possible to show that the multiple-lead system could differentiate the site and severity of coronary artery disease in these patients with angina. The multiple-lead system was cumbersome and time-consuming in application and therefore cannot be recommended for routine exercise testing.

Diagnostic value of thyrotrophin releasing hormone tests in elderly patients with atrial fibrillation.

A prospective study was carried out to compare clinical and biochemical thyroid states with responses of thyroid stimulating hormone (TSH) to thyrotrophin releasing hormone (TRH) in elderly patients with either atrial fibrillation (n = 75; mean age (SD) 79.3 (6.0) years) or sinus rhythm (n = 73; mean age 78.4 (5.6) years) admitted consecutively to the department of geriatric medicine. No patient in either group had symptoms or signs of hyperthyroidism. Overall, the TSH responses to TRH did not differ significantly between the two groups. Ten (13%) of the patients with atrial fibrillation (of whom four had raised thyroid hormone concentrations) and five (7%) of the patients with sinus rhythm showed no TSH response to TRH while 26% of each group (20 and 19 patients, respectively) showed a much reduced response. Only one of 13 patients with apparently isolated atrial fibrillation showed no TSH response to TRH, and none of these 13 patients was hyperthyroid. In particular, three patients (two with atrial fibrillation and one with sinus rhythm) who showed no TSH response to TRH at presentation exhibited a return of TSH response to TRH at follow up six weeks later. In conclusion, reduced or absent TSH responses to TRH are common in sick elderly patients whether they have atrial fibrillation or sinus rhythm and whether they are euthyroid or hyperthyroid biochemically. An absence of response is therefore an uncertain marker of hyperthyroidism in these groups of patients, and diagnosis and ablative treatment should be based at least on the presence of raised circulating free triiodothyronine or free thyroxine concentrations, or both.

Circadian rhythm of blood pressure in patients dependent on ventricular demand pacemakers.

The reported circadian rhythm of blood pressure variability with a rise in pressure before awakening has been the subject of controversy. Previous studies have suggested that since heart rate continues to fall before awakening while blood pressure is rising these physiological variables are subject to different control mechanisms. To evaluate further the dissociation of heart rate and blood pressure changes in a group of patients with a fixed heart rate, 11 patients who were dependent on ventricular demand pacemakers underwent intra-arterial ambulatory blood pressure monitoring. Nine aged matched control subjects followed the same protocol. Circadian curves plotted from pooled hourly mean data showed that despite a fixed heart rate the circadian pattern persisted, although attenuated, with blood pressure rising several hours before its rapid rise on awakening. Physiological testing showed that despite a fixed heart rate systolic blood pressure rose in response to bicycle exercise, there was a postural fall in the blood pressure on tilting and a modified Valsalva response. There was considerable beat to beat variability resulting presumably from asychronous pacing. Hour to hour changes did not contribute to the differences between the two groups and were not responsible for attenuation of the circadian rhythm. It is concluded that blood pressure and heart rate control mechanisms may be dissociated, particularly in the period before awakening.

Changes of Q wave amplitude during exercise for the prediction of coronary artery disease.

We have examined the changes of Q wave amplitude during exercise in 156 patients with chest pain with a view to improving the accuracy of stress testing for the diagnosis of coronary artery disease. Coronary arteriography showed significant disease in 127 patients and normal arteries or minimal disease in 29. The Q wave amplitude was measured in lead CM5 from the computer-derived average of 25 consecutive beats immediately before and at the peak of maximal treadmill exercise. The amplitude was greater in the normal subjects at rest and increased with exercise, but the reverse occurred in those with coronary disease. Using the criterion of decrease or no change of Q wave amplitude during exercise as indicating a positive test, the discriminative capacity of Q wave changes was equivalent to that of ST segment depression and was maintained when patients with myocardial infarction were excluded. Using either an abnormal Q wave or ST segment response to exercise improved the test's sensitivity with a loss of specificity but no change of predictive value. In 42% of patients with coronary disease when both the Q wave and ST segment exercise responses were abnormal coronary disease was predicted with an accuracy of 91%. Analysis of subgroups of patients with coronary artery disease suggested a possible explanation for the observed changes in Q wave amplitude, measurement of which can improve the stress test's accuracy for predicting obstructive coronary artery disease.

Evaluation of verapamil and high dose nifedipine in patients with chronic stable angina with objective methods.

The efficacy and safety of verapamil and nifedipine were objectively assessed in patients with chronic stable angina. Twenty four patients entered a double blind randomized cross over trial of nifedipine (10 mg thrice daily) and placebo. In this dosage nifedipine did not show any significant change in exercise duration and the variables obtained using computer assisted exercise testing when compared to placebo. The next stage consisted of another double blind randomized cross over trial comparing the effects of verapamil (120 mg thrice daily) and nifedipine (20 mg thrice daily) with an initial placebo run-in period in 32 patients. At this dose level nifedipine showed a definite and significant improvement in all the objective variables; however an increase in side effects was observed resulting in withdrawal of the drug in seven patients. A common problem was tachycardia precipitating angina after nifedipine ingestion. On the other hand verapamil produced a marked improvement in exercise tolerance and other variables as compared to placebo and nifedipine, was well tolerated and produced a mild bradycardia. This study clearly indicates that verapamil is distinctly superior to nifedipine in efficacy side effects and safety in patients with chronic stable angina. This may be attributable to the differential effect on heart rates induced by these drugs.

Double-blind randomized crossover trial of verapamil and propranolol in chronic stable angina.

Propranolol (240 mg daily) and verapamil (360 mg daily) were objectively compared for their respective efficacy in the treatment of chronic stable angina pectoris. Twenty-two patients were studied in a randomized placebo controlled, double-blind crossover trial with 4 weeks on each active drug treatment. Multistage treadmill exercise with computer-assisted ECG analysis was performed after 2 weeks on placebo and at the end of each 4-week active drug treatment. The mean exercise time to produce angina was 5.5 minutes (SEM +/- 0.4 minutes) on placebo and this increased to 7.8 (+/- 0.5) minutes on propranolol and 9.1 (+/- 0.5) minutes on verapamil. The improvement in exercise time of verapamil over propranolol was statistically significant (p less than 0.01). Ten patients became free of angina with verapamil and four with propranolol. Resting and maximal exercise heart rates were significantly reduced by propranolol; verapamil did not reduce the maximal heart rate but reduced the resting heart rate slightly. However, the heart rate increase per minute of exercise was significantly diminished (p less than 0.001). ST segment changes showed improvement with both drugs despite marked differences in heart rate profile. The overall efficacy of the slow calcium channel blocker, verapamil, compares favorably with that of a standard beta-adrenoreceptor blocking drug (propranolol), thus providing a new perspective in the management of angina pectoris. These two classes of drugs seem to act by different mechanisms and it is suggested that if patients are resistant or intolerant to one of these drugs, the other can be used to yield a beneficial response.

Simultaneous recording of continuous arterial pressure, heart rate, and ST segment in ambulant patients with stable angina pectoris.

Simultaneous and accurate recording of arterial blood pressure and ST segment changes is fraught with technical difficulties. We have developed a new system to enable accurate reproduction of the electrocardiogram and intra-arterial blood pressure, using a transducer/perfusion unit conventionally used to study hypertensive subjects, linked to a frequency modulated tape recorder. Detailed methods of digital analysis have been developed to process the data. This system has been used to study 22 patients with arteriographically proven severe obstructive coronary artery disease who suffered frequent attacks of angina. Control data from quantified dynamic exercise in the laboratory were used for comparison with the effects of normal daily activities outside the hospital and to test the hypothesis that "double product" (heart rate X systolic blood pressure) is relevant to the onset of angina in such patients. The most important finding was that both angina and asymptomatic episodes of ST segment depression were invariably accompanied by an increase in heart rate, whereas there was considerable variation in blood pressure changes ranging from an increase to a substantial fall. This suggests that heart rate changes are more important in determining ischaemic episodes than blood pressure. Furthermore, the "double product" was not reproducible during repeated episodes of angina and asymptomatic ischaemia and did not appear to have an important role in the pathogenesis of intermittent myocardial ischaemia in this group of patients.

Alpha-adrenoreceptor blockade with indoramin in hypertension.

We have evaluated the effects of indoramin, an alpha-adrenoreceptor blocking drug, used as sole therapy in a group of 27 patients with essential hypertension. Blood pressure and heart rate were measured continuously over prolonged ambulatory periods using an established invasive technique before and after six weeks of therapy. The protocol was randomised, double-blind, and with double-dummy placebo control. A standardised programme of physiological stress testing was also performed during each study. Placebo produced no appreciable change in the levels or patterns of blood pressure over 24-h periods, but indoramin produced a significant reduction, which was particularly marked during the night. Physiological testing did not reveal any postural hypotension, and the response to dynamic and isometric exercise was modified in level but not in degree of change. There were many unwanted effects, which may limit the clinical value of this drug.

Rationale for the choice of calcium antagonists in chronic stable angina. An objective double-blind placebo-controlled comparison of nifedipine and verapamil.

The effectiveness and safety of verapamil, nifedipine, and placebo in patients with chronic stable angina pectoris were evaluated and compared in two double-blind randomized crossover trials. In the first study, nifedipine (10 mg 3 times daily) was compared with placebo in 24 patients with chronic effort-related angina pectoris; no significant differences in exercise performance were observed with nifedipine compared with placebo. In the second study, the effects of verapamil (120 mg 3 times daily), nifedipine (20 mg 3 times daily), and placebo were compared in 32 patients with chronic stable angina using a double-blind crossover study design. Compared with placebo, both nifedipine and verapamil prolonged exercise duration (5.7 +/- 0.3 minutes with placebo, 7.9 +/- 0.5 minutes with nifedipine [p less than 0.001], and 10.0 +/- 0.7 minutes with verapamil [p less than 0.001]), but the improvement with verapamil was greater than that seen with nifedipine (p less than 0.01). Seven patients had increasing angina with nifedipine, none did with verapamil; the exacerbation of angina during nifedipine therapy appeared related to our observation that, compared with placebo, patients receiving nifedipine had higher heart rates, while patients receiving verapamil had slower heart rates. This study indicates that, at the doses used, verapamil was more effective and better tolerated than nifedipine in patients with chronic stable angina pectoris.

Calcium channel blockade as primary therapy for stable angina pectoris. A double-blind placebo-controlled comparison of verapamil and propranolol.

The effectiveness and safety of the beta-adrenergic blocking agent propranolol and the calcium channel antagonist verapamil were compared in 22 patients with chronic stable angina pectoris using a double-blind randomized placebo-controlled crossover protocol. The double-blind phase was preceded by a 2 week single-blind placebo period, followed by randomization to either 4 weeks' therapy with verapamil, 360 mg/day, or propranolol, 240 mg/day, followed by crossover to the other drug. Both verapamil and propranolol increased exercise tolerance (5.5 +/- 0.4 minutes with placebo, 7.8 +/- 0.5 minutes with propranolol [p less than 0.001], and 9.1 +/- 0.5 minutes with verapamil [p less than 0.001]), but the increase with verapamil was significantly greater (p less than 0.01). Both drugs prolonged the exercise duration to 1 mm S-T depression (3.3 +/- 0.4 minutes with placebo, 5.7 +/- 0.5 minutes with propranolol [p less than 0.001] and 5.5 +/- 0.6 minutes with verapamil [p less than 0.001]); the degree of improvement was similar with both active drugs. Both drugs decreased the resting heart rate (76 +/- 3 beats/min with placebo, 56 +/- 2 beats/min with propranolol [p less than 0.001], and 71 +/- 3 beats/min with verapamil [p less than 0.01]), but the heart rate decreased more with propranolol than with verapamil (p less than 0.001). Neither drug produced significant adverse reactions. This study, along with 8 similar double-blind placebo-controlled randomized investigations which have compared verapamil with propranolol, indicate that verapamil is as effective and safe as propranolol in relieving symptoms and improving exercise tolerance in patients with chronic stable angina pectoris and may be considered a first-line therapeutic agent in patients with ischemic heart disease.

Randomized double-blind comparison of verapamil and nifedipine in chronic stable angina.

A randomized double-blind crossover trial was performed in 32 patients with chronic stable angina to compare the antianginal actions of verapamil (120 mg 3 times daily) and nifedipine (20 mg 3 times daily). Efficacy was assessed using objective end points obtained by computer-assisted exercise testing and 24 hour ambulatory monitoring for S-T segment shift. Twenty-eight patients completed the trial. The mean exercise time to produce angina improved from 5.7 +/- 0.3 minutes (mean +/- standard error of the mean) in patients on placebo, to 7.9 +/- 0.5 minutes in those on nifedipine and 10.0 +/- 0.7 minutes in those on verapamil. Similar improvement was seen in all other objective variables. Generally verapamil produced mild bradycardia and nifedipine mild tachycardia. Four patients complained of palpitations and angina after ingestion of nifedipine and were identified by ambulatory monitoring to have tachycardia and persistent S-T depression. These opposite effects on heart rate may explain the differences in efficacy between these 2 potent calcium ion antagonists.