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Biomedical subjects

P K Khanna

Publications and source records attributed to P K Khanna.

At least 19 recordsLinked to original sources
PubMed2006

Direct synthesis of nanocrystalline silver from the reaction between silver carboxylates and n-trioctylphosphine.

Neat n-Trioctylphosphine (TOP) has been used for the first ever time for reduction of silver nitrate and silver carboxylates (citrate, oleate, and myristate) under mild thermal reaction conditions. UV-visible absorption measurements of re-dispersible silver particles that were obtained by reduction of silver myristrate (product-IV) and silver nitrate (product-I) showed surface plasmon resonance absorption peak at 400 nm. The powder XRD pattern of fcc zero-valent silver resulted in diameters in the range of about 25-30 nm. TEM analysis showed particle diameter similar to that was observed by the XRD. FTIR spectroscopy revealed that the organics from the carboxylate group are retained by the nano-particles in case of product-IV however, presence of TOP is observed in product-I. It is found that when silver nitrate is reduced by TOP, spherical silver nano-particles with poor redispersity are formed but extended heating results in formation of long silver rods of micrometer size however, the re-dispersible nano-particles are easily formed when silver carboxylates are reduced by TOP.

Carboxylic Acids↗
PubMed2006

Tuned optical properties of in-situ synthesized m-nitroaniline doped Ag/PVA nano-composites.

Meta-nitroaniline (m-NA) doped silver/poly(vinylalcohol) (Ag/PVA) nanocomposites are prepared via in-situ reduction of silver salt by employing hydrazine hydrate (HH) in order to study the effect of the NLO active m-NA on the optical properties of nanoparticles of silver in the colloidal as well as self supported film form. Reduction of silver salt in aqueous alcoholic PVA with HH is done first followed by doping of the reaction mixture with m-NA. The UV-Visible absorption spectra show peak at about 400 nm for Ag nanoparticles due to surface plasmon resonance phenomenon, which gets blue shifted with the change in m-NA concentration. The Second Harmonic Generation (SHG) studies show improvement in intensity with increasing m-NA concentration up to a saturation point (approximately 2.52 wt% with respect to PVA). Further increase in m-NA concentration leads to decrease in SHG intensity. The solutions and the films are characterized by photoluminescence (PL), FTIR spectroscopy, XRD, SEM, TEM, and thermal analysis. m-NA doped composites showed better PL efficiency. SEM of the nanocomposite film shows uniform distribution of particles within the film. The particle size as shown by TEM is found to be less than 10 nm.

Aniline Compounds↗
PubMed1977

Effect of positive acceleration (+gz) on electrocardiogram of subjects with vasoregulatory abnormality.

ST-T wave changes in the electrocardiogram detected during routine examination and aggravated by erect posture, hyperventilation, and exercise in apparently healthy young individuals have been termed vasoregulatory abnormalities. No evidence of ischaemic heart disease has been found in such subjects. Ten young healthy air crew with vasoregulatory abnormalities were subjected to maximal exercise on treadmill and procedure repeated after 120 mg propranolol daily for 3 days. After one week, they were subjected to a stress of positive acceleration (+gz) in a human centrifuge at 2-5 g and 3-5 g for 15 seconds each at a constant rate of rise of 0-1 g/s and the electrocardiogram was monitored during and in the post-acceleration phase. The procedure was repeated after propranolol 120 mg daily for 3 days. The stress of positive acceleration resulted in pronounced prominence of P waves and inversion of T waves (as has been reported in normal subjects) with minimal ST depression in the electrocardiogram. ST segment depression during exercise, at heart rates corresponding to those achieved during peak centrifuge runs, was significantly more pronounced. The ST, P, and T wave changes were returned to normal after propranolol. It is concluded that minimal ST segment depression after stress of positive acceleration as compared with conspicuous ST segment depression during exercise at corresponding heart rates, and their normalisation after propranolol, rules out ischaemia as an aetiological factor in subjects with vasoregulatory abnormalities.

Acceleration↗
PubMed1976

Exercise in an hypoxic environment as a screening test for ischaemic heart disease.

Submaximal and maximal exercise testing have been used to predict coronary events but these tests do not give reliable information regarding employability of subjects with abnormal electrocardiogram. In 30 subjects with stabilized ischaemic heart disease (Group A) and 70 subjects with abnormal resting electrocardiogram (Group B), resting electrocardiograms--at ground level and at a simulated height of 4592 m (15000 ft)--after 40-min exposures were recorded. The double Master's two-step exercise test (DM) was performed at ground level as well as at stimulated height (DMH). In the ischaemic group, exercise combined with hypoxia did not yield better results than exercise alone; but among the asymptomatic subjects, exercise in an hypoxic environment gave significantly better results than exercise alone (p less than 0.005) or hypoxia alone (p less than 0.01). Those with negative responses to the test have been employed on strenous duties, including employment at high altitude for the last 3 years. None of them have manifested any objective or subjective evidence of ischaemic heart disease. DM exercise testing in an hypoxic environment is a reliable method to assess subjects with abnormal electrocardiogram and evaluate their functional status.

Adult↗
PubMed1975

Effect of submaximal exercise on fibrinolytic activity in ischaemic heart disease.

Fibrinolytic activity and platelet adhesiveness are normal in cases of angina pectoris and healed myocardial infarction, whereas fibrinolytic activity is diminished in acute myocardial infarction. Exercise increases fibrinolytic activity in normal people but the effect on it of submaximal exercise in patients with ischaemic heart disease is not known. Resting platelet adhesiveness and fibrinolytic activity were determined in 20 patients suffering from ischaemic heart disease and eight healthy controls. Both groups were then subjected to submaximal exercise on a motor-driven treadmill. The ST segment of the electrocardiogram and the heart rate were monitored during exercise by an on-line digital computer. Fibrinolytic activity determinations were repeated immediately after exercise. There was a significant increase in fibrinolytic response in both groups but it was significantly less in the ischaemic groups (36-2%) compared with the controls (55-9%) (P less than 0-01). The ST segment depression was 2-3 mm in the ischaemic group and 0-52 mm in controls--also a significant difference (P less than 0-01). There was no correlation, however, between the ST change and the fibrinolytic response. A diminished response in the ischaemic group may favour their predisposition to thrombotic episodes.

Adult↗