Frequency analysis of time-varying elastance model of the left ventricle

Zadeh's transfer function method for linear time-variable systems is used to apply frequency-domain analysis to a periodically time-varying elastance model of the left ventricle. Left ventricular pressure computed from the system function of the time-varying elastance and the phasors of aortic flow shows a typical waveform of the measured ventricular pressure.     

Protective effect of melatonin on myocardial infarction

The dose- and time dependence of melatonin and the effective window of melatonin administration were determined in a mouse model of myocardial infarction. When mouse hearts were subjected to 60 min of occlusion of the left anterior descending artery (LAD) followed by 4 h of reperfusion, melatonin pretreatment for 30 min significantly reduced the infarct size/risk area. The most effective dose was found to be 150 microg/kg intraperitoneally, and the effective period of protection lasted up to 2 h after melatonin administration. Melatonin administration 45 min after LAD ligation or right before reperfusion was as effective as administration 30 min before ligation; however, melatonin administered after the release of occlusion was not protective. Melatonin's effect was still present in mice deficient for the Mel1a melatonin receptor. 8-Methoxy-2-propionamidotetralin, a melatonin receptor agonist with no antioxidant activity, offered no protection, suggesting a lack of involvement of melatonin receptors. Finally, the effects of melatonin were similar in rats and mice. Our results demonstrate that melatonin is an effective cardioprotective agent when administered either before or during coronary occlusion at a very low dose.     

The functional effect of soybean extract and isolated isoflavone on myocardial infarction and ventricular dysfunction: The soybean extract on myocardial infarction

BackgroundMyocardial infarction is a public health problem. Functional food is an alternative treatment for cardiovascular diseases.ObjectiveThe objective was to analyze the functional and anatomopathological post-myocardial-infarction effects of soybean extract (SE) and isoflavone (IF).MethodsMyocardial infarction was induced in adult Wistar rats. After 5 days, an echocardiogram was performed to determine heart rate (HR), ejection fraction (EF), systolic volume (LVESV) and diastolic volume (LVEDV). Animals with ventricular dysfunction (EF<45%) were selected for study. The animals were divided into three groups: control (n=14), SE (n=15) and IF (n=12). The IF group received 120 mg/kg/day isolated IF, and the SE group received 12.52 g/day. After 30 days, a new echocardiogram was performed. A histological exam was carried out to determine the collagen. Activity of biochemical markers [arginase, lactate dehydrogenase (LDH) and malate dehydrogenase] was measured.ResultsThe animals of the control, IF and SE groups showed a reduction in EF after the infarction (P=.432, P=.017 and P=.320, respectively). An increase of LVESV and LVEDV was observed in all groups (P=.009, P=.001 and P=.140; and P=.003, P=.008 and P=.205, respectively). A reduction of HR was found in the SE group (P=.020). There was a greater activity of LDH in the SE group. A smaller quantity of mature collagen was found in the region proximal to the myocardial infarction in the SE group.ConclusionA protective effect in the SE group was observed 30 days after the myocardial infarction.     

The effect of dietary supplementation of fish oil on experimental myocardial infarction

The effect of altering the abundance of precursors and inhibitors of prostaglandin formation by dietary supplements of fish oil was investigated in dogs with experimentally induced myocardial infarction. Prior to induction, 10 male mongrel dogs were fed standard dog chow supplemented with 25% of the total calories as menhaden oil for 36 to 45 days. The fatty acid composition of the lipids in plasma and platelets changed to reflect the increased intake of polyunsaturated fatty acids of the n-3 type. Thrombosis and subsequent infarction was induced by electrical stimulation of the left circumflex coronary artery of ambulatory dogs that were monitored by telemetry. Upon stimulation of control animals, the frequency of ectopic beats rose from less than 10% at the beginning to about 80% after 19 hours. In contrast, the oil-fed dogs maintained a more normal ECG pattern, showing less than 30% ectopic beats after 19 hours. In these animals, the size of infarction (measured by formazan formation) was 3% of the left ventricle compared to 25% in the control animals. The results suggest that dietary supplementation with fish oil may be beneficial in reducing myocardial damage associated with coronary artery thrombosis.     

The protective effect of peony extract on acute myocardial infarction in rats

To investigate the protective effects, and the mechanisms involved, of an extract of the medicinal herb radix paeoniae rubra (PE) on cardiovascular disease, acute myocardial infarction (AMI) was induced by ligation of the left coronary artery in Sprague Dawley rats. Animals were randomly divided into six groups: control, sham-operated, AMI, AMI + PE low dose, AMI + PE high dose, and AMI + positive control. Myocardial enzymes, cytokines, oxidative stress, blood coagulation times, a marker for early stage apoptosis, caspase-3 activity, and expression levels of bax, bcl-2 and fas in isolated primary cardiomyocytes were examined. In contrast with control and sham groups, significant increases in the following parameters were measured in the blood of AMI group animals: activities of cardiac enzymes including glutamic oxaloacetic transaminase, creatine kinase, creatine kinase-MB, lactate dehydrogenase, α-hydroxybutyric dehydrogenase, and levels of IL-10, TNFα, and lipid peroxidation. Under the same conditions, superoxide dismutase activity, thrombin time and activated partial thromboplastin time decreased significantly. PE showed a dose-dependent protection against AMI-induced alterations in cardiac enzymes, cytokines, oxidative stress, and coagulation. In AMI cardiomyocytes, compared with control and sham groups, the left ventricular end-diastolic pressure, early stage apoptosis, caspase-3 activity and expression levels of bax, bcl-2 and fas significantly increased, while the ratio bcl-2/bax decreased. PE showed dose-dependent protection. These results suggest that PE is an effective agent for protecting against AMI; possible mechanisms may include the regulation of cardiac enzymes, cytokines, oxidative stress, coagulation and apoptosis.     

Coronary flow reserve and the J curve relation between diastolic blood pressure and myocardial infarction.

The results of several large studies of hypertension and follow up studies on insured people have indicated that the lower the blood pressure the better for longevity. These studies excluded subjects with overt ischaemia. More recently long term studies of hypertension that included patients with more severe forms of hypertension and did not exclude those with overt ischaemia have shown a J shaped relation between diastolic blood pressure during treatment and myocardial infarction; the lowest point (the J point) was at a diastolic blood pressure (phase V) between 85 and 90 mm Hg. The J curve seems to be independent of treatment, pulse pressure, and the degree of fall in diastolic blood pressure and is unlikely to be caused by poor left ventricular function. The most probable explanation is that subjects who have severe stenosis of the coronary artery as well as hypertension have a poor coronary flow reserve, which makes the myocardium vulnerable to coronary perfusion pressures that are tolerated by patients without ischaemia, particularly at high heart rates. An optimal diastolic blood pressure (phase V) for such patients is about 85 mm Hg, though particular caution is appropriate when treating very old patients (84 and over) and patients aged 60-79 who have isolated systolic hypertension.     

The psychological and social effects of myocardial infarction on wives.

Eighty-two wives of men suffering a first myocardial infarction were interviewed while their husbands were in hospital, and again two months and a year after they went home. The wives had substantial and persistent psychological symptoms, and the husbands'' illness had continuing effects on their work, leisure and social activities, and family life and marriage, their psychosocial disability being comparable to that of the patients. Measures of psychosocial adjustment before the illness and the quality of the marriage and of family life were good predictors of outcome for the wives. The women had a major role in the patients'' readjustment during convalescence, and their attitudes and behaviour as well as the general quality of family life were important determinants of the rate and extent of the patients'' recovery. The wives of patients with myocardial infarction should have more practical help and advice during the hospital period, and the whole family should be given advice and help throughout the convalescence.     

The bimodal quasi-static and dynamic elastance of the murine lung.

The double sigmoidal nature of the mouse pressure-volume (PV) curve is well recognized but largely ignored. This study systematically examined the effect of inflating the mouse lung to 40 cm H2O transrespiratory pressure (Prs) in vivo. Adult BALB/c mice were anesthetized, tracheostomized, and mechanically ventilated. Thoracic gas volume was calculated using plethysmography and electrical stimulation of the intercostal muscles. Lung mechanics were tracked during inflation-deflation maneuvers using a modification of the forced oscillation technique. Inflation beyond 20 cm H2O caused a shift in subsequent PV curves with an increase in slope of the inflation limb and an increase in lung volume at 20 cm H2O. There was an overall decrease in tissue elastance and a fundamental change in its volume dependence. This apparent "softening" of the lung could be recovered by partial degassing of the lung or applying a negative transrespiratory pressure such that lung volume decreased below functional residual capacity. Allowing the lung to spontaneously recover revealed that the lung required approximately 1 h of mechanical ventilation to return to the original state. We propose a number of possible mechanisms for these observations and suggest that they are most likely explained by the unfolding of alveolar septa and the subsequent redistribution of the fluid lining the alveoli at high transrespiratory pressure.