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Biomedical subjects

B Krishnan

Publications and source records attributed to B Krishnan.

At least 55 records · Page 3Linked to original sources
PubMed1992

Effect of physical training on breathing pattern during progressive exercise.

It has been suggested that physical training causes a slower, deeper breathing pattern at a given level of ventilation, but there is no convincing evidence to support this. We examined breathing pattern during maximal incremental exercise on a cycle ergometer in 7 males before and after 3-4 weeks of cycle endurance training (TRAINING), and in 6 males before and after a similar period of unaltered physical activity (CONTROL); all subjects were healthy and previously sedentary. After physical training there was a significant increase in peak oxygen uptake, and significant reductions in carbon dioxide output, heart rate (fHR) and minute ventilation (VI) at submaximal workloads; peak VI was significantly increased whereas peak fHR was unchanged. At matched VI levels (moderate, moderately-high, high) the TRAINING subjects' breathing pattern was not significantly altered; there was a power of at least 80% to detect a significant (> 0.30 L) increase in tidal volume (P < 0.05) at moderately high and high ventilation levels. There was no change in the CONTROL subjects' maximal exercise performance, or breathing pattern at matched VI levels, over the same period. Short-term, activity-specific physical training does not significantly affect the breathing pattern adopted by normal humans during progressive exercise.

Adult↗
PubMed1992

False aneuploidy in benign tumors with a high lymphocyte content: a study of Warthin's tumor and benign thymoma.

The quality of results of flow cytometric DNA content analysis of formalin-fixed, paraffin-embedded tissue may be affected by a number of preanalytical variables. We performed flow cytometric DNA content analysis on two types of benign tumors to investigate the effect of a prominent lymphocytic component: Warthin's tumor (N = 20) and benign thymoma (N = 8). Malignant tumors (N = 23) were included as DNA aneuploid controls. All tissues studied were archival material processed using Hedley's technique either without prolonged rehydration in water (day 0 samples) or with 24- or 48-hour rehydration (day 1 and day 2 samples, respectively). Image cytometric DNA ploidy analysis was also performed on most cases. Eight cases (40%) of Warthin's tumor and five cases (63%) of benign thymoma showed either hyperdiploid peaks or marked asymmetry on the day 0 DNA histograms; nine of the malignant tumors were aneuploid. The DNA histogram abnormalities of the benign tumors could be gated out by excluding the lymphocyte nuclei. None of the DNA indices of the benign tumors corresponded with expected deviations based on published chromosomal studies. All of the DNA histogram abnormalities of the benign tumors disappeared and/or fused with the main peaks on the day 1 or day 2 samples, except for one case of benign thymoma. All the DNA aneuploid peaks on the malignant tumors persisted with prolonged rehydration. Image cytometric DNA analysis showed a diploid pattern in all benign tumors. We conclude that a high lymphocyte content may be a cause of false aneuploidy in these benign tumors. Furthermore, the degree of rehydration appears to be an important factor in achieving optimum fluorochrome staining of DNA.

Adenolymphoma↗
PubMed1992

Inspiratory muscle weakness and dyspnea in chronic heart failure.

Dyspnea is a common, disabling symptom in chronic heart failure, yet the underlying mechanisms remain unknown. The respiratory muscle pump is composed of skeletal muscles whose strength directly influences the pump's performance. Respiratory muscle weakness is important in the dyspnea experienced by some patients with pulmonary disease; however, the role of the respiratory muscle pump in the dyspnea of chronic heart failure has not previously been examined. To assess respiratory muscle strength and its relation to dyspnea during daily activity, we measured maximum inspiratory and expiratory mouth pressures as indices of respiratory muscle strength and the baseline dyspnea index in nine stable, chronic cardiac pump failure patients who had no evidence of primary lung disease, and in nine age- and sex-matched healthy control subjects. The chronic heart failure patients, when compared with their matched control subjects, had reduced inspiratory and expiratory muscle strength, and both inspiratory and expiratory muscle strength were significantly correlated with dyspnea during daily activity (r2 = 0.80, p = 0.001 and r2 = 0.45, p = 0.05, respectively). Inspiratory muscle strength accounted for all of the variance in dyspnea that was correlated with respiratory muscle strength when the relative contributions of inspiratory and expiratory muscle strength were examined. There was no correlation between lung volumes or spirometry and dyspnea in the heart failure patients. These findings indicate that patients with stable chronic heart failure have inspiratory and expiratory muscle weakness and further suggest that the respiratory muscle pump significantly contributes to the dyspnea during the activities of daily living.

Activities of Daily Living↗
PubMed1991

Determination of DNA cleavage specificity by esperamicins.

The esperamicins are members of a class of potent antitumor antibiotics that contain stained diacetylenic ring systems capable of forming DNA-cleaving diradicals upon reaction with thiols. Here we show that the diacetylenic ring core itself determines the sequence specificity for scission of duplex DNA): esperamicin A1, and three products of hydrolysis of the glycon, esperamicins C, D, and E, are found to retain a common sequence preference. The sugar residues exert a strong influence on the cleavage efficiency, presumably by interacting nonspecifically with DNA. The presence of a branch in the DNA is found locally to inhibit scission by esperamicins, and this effect is shown to be due to the core also.

Aminoglycosides↗
PubMed1989

AT2433-A1, AT2433-A2, AT2433-B1 and AT2433-B2 novel antitumor compounds produced by Actinomadura melliaura. II. Structure determination.

The chemical structures of AT2433-A1 (2), AT2433-A2 (3), AT2433-B1 (4) and AT2433-B2 (5) were elucidated by degradation and spectroscopic studies. Compounds 2-5 are disaccharides closely related to rebeccamycin. The aglycone in 2 and 3 was determined to be 6-N-methyl-11-chloro-5H-indolo[2,3-a]pyrolo[3,4-c]carbazole and in 4 and 5 it was determined to be 6-N-methyl-5H-indolo[2,3-a]pyrolo[3,4-c]carbazole. Compounds 2 and 4 are 4-N"-methyl analogs of 3 and 5.

Aminoglycosides↗
PubMed1988

Aluminum toxicity to the brain.

The association between elevated brain aluminum levels and Alzheimer's disease (AD) is examined and critically reviewed. We found elevated aluminum levels in the brains of patients with AD (greater than 4 micrograms/g dry wt.) compared with normal subjects (approximately 1.5 micrograms/g dry wt.). Nine laboratories from different geographical regions have confirmed this finding. Two laboratories did not find any differences between AD and control brains. This discrepancy is traced to differences in sample sizes used for the aluminum assay and the sample selection criteria. It is found that it is essential to use small sizes (approximately 10 mg dry wt.) and to ensure that control brains do not contain neurofibrillary tangles (NFT) and that AD brains do. The exact pathogenic role of aluminum in AD is, as yet, unclear. It is the only element (other than calcium, which non-specifically accumulates at all degenerating tissue sites) that is found in elevated concentrations in NFTs. It is found elevated at four loci in the brain, i.e. the DNA-containing structures of the nucleus, the protein moities of NFTs, the amyloid cores of senile plaques and cerebral ferritin. The evidence thus far indicates that aluminum is toxic to the brain and it is probable that it has a pathogenic role in Alzheimer's disease.

Aluminum↗
PubMed1988

Proton magnetic relaxation studies in normal and cancerous breast tissues.

Proton magnetic resonance (PMR) relaxation times were measured for dissected malignant and normal tissue derived from breast cancer patients. Relaxation time measurements (T1, T2) were carried out at a RF frequency of 20 MHz and at a temperature of 27 degrees C with a Brucker PC 120 NMR Process analyser. The tissue types were confirmed by histopathological examination. In general T1 values were found to be longer for malignant tissues as compared to normal tissues which is in agreement with the earlier observations. The measured T2 values do not exhibit the malignant tissues above. The percentage of water content was also measured in both normal and malignant tissue and was found to be considerably larger in tumour tissue as compared to normal tissue. These results are discussed on the basis of two fraction fast exchange models of water molecules and confirm that PMR relaxation time measurement plays an important role in the differentiation of cancerous tissues from that of normal.

Breast↗
PubMed1981

Delayed sternal closure following open-heart operation.

Between June, 1976, and December, 1980, 29 patients underwent delayed sternal closure at the Newark Beth Israel Medical Center. The indications were enlarged heart with tamponade when the mediastinum was closed, poor lung compliance, hemodynamic instability due to intractable arrhythmias or coagulopathy, and presence of a mediastinal assist device. Following an open-heart procedure, the retrosternal space may no longer accommodate the heart and approximation of the sternum will produce hypotension and elevation of right and left end-diastolic pressures. In such instances, only the skin is closed and between one to four days later, the wound is closed in a routine manner. There are several advantages of the procedure: hemodynamic stability; quick access to the heart for massage or evacuation of clots; and possibility of removing an intraaortic balloon in the ascending aorta without leaving a large Dacron tube. Of the 29 patients treated, 19 were long-term survivors and only 1 patient had a minor superficial wound infection. Although it is not recommended that this procedure be utilized routinely or indiscriminately, its judicious use will add flexibility in the management of selected and difficult cases.

Adult↗