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Study of physiological variability is an upcoming area of research having manifold clinical applications. Considerable work has been done on heart rate variability and blood pressure variability during the past four decades. Electronics division, Bhabha Atomic Research Centre, has developed an instrument called medical analyzer, which can be used to study several variabilities simultaneously. This instrument has been used to collect data from control subjects and patients with established diagnosis. The data has been analyzed with the help of a software package developed for this purpose and has been found to be consistent with expected manifestations of the disease on the autonomic nervous system. The description of the software package and results of the study are briefly described in this paper. [ABSTRACT FROM AUTHOR]

Radial Pulse forms the most basic and essential physical sign in clinical medicine. The paper proposes the application of crisp and fuzzy clustering algorithms under supervised and unsupervised learning scenarios for identifying non-trivial regularities and relationships of the radial pulse patterns obtained by using the Impedance Plethysmographic technique. The objective of our paper is to unearth the hidden patterns to capture the physiological variabilities from the arterial pulse for clinical analysis, thus providing a very useful tool for disease characterization. A variety of fuzzy algorithms including Gustafson-Kessel (GK) and Gath-Geva (GG)have been intensively tested over a diverse group of subjects and over 4855 data sets. Exhaustive testing over the data set show that about 80 % of the patterns are successfully classified thus providing promising results. A Rank Index of 0.7739 is obtained under supervised learning, which provides an excellent conformity of our process with the results of plethysmographic experts. A correlation of the patterns with the diseases of heart, liver and lungs is judiciously performed.

Seven patients with history of radiation burn were subjected to impedance plethysmographic investigation at Non-invasive Vascular Laboratory, K. E. M. Hospital. Impedance plethysmograms were recorded from various locations in both the upper extremities in supine and digits of both the hands in supine as well as on hyper-abduction in sitting position. Control values of blood flow index (BFI) and differential pulse arrival time (DPAT) were derived from similar data in 15 normal subjects. It was observed that digits having thinning of epidermis of skin recorded marked decrease in values of BFI and significant change in value of DPAT and these observations correlated well with thermography and vascular scintigraphy. Digits recording significant decrease in BFI, which were clinically normal, were found to have changes in the skin during follow up examination. Thus IPG provided a sensitive modality for detecting ischaemia in early stages in patients with history of radiation injury.

Vector impedance cardiograms in horizontal lead configuration [VICG(H)] were recorded in 34 normal subjects, 18 patients with mitral stenosis, 9 patients with mitral regurgitation, 14 patients with aortic regurgitation and 13 patients with non- cyanotic septal disorders. Data in normal subjects revealed that most of the phase reversal points in VICG(H) waveform did not coincide with those of conventional impedance cardiogram. The shape of VICG(H) waveform and values of VICG indices were observed to be markedly affected in patients having significant alteration in the pulmonary circulation and the changes observed were specific of the type of the disorder. The results of the study suggested that right side of the heart had dominant contribution in generation of VICG(H) waveform.

Impedance plethysmograms were recorded from thoracic region in 254 normal subjects, 183 patients with coronary artery disease, 391 patients with valvular heart disease and 107 patients with congenital septal disorder. The data in 18 normal subjects and 55 patients showed that basal impedance decreases markedly during exercise in patients with ischaemic heart disease. Estimation of cardiac index by this technique in a group of 99 normal subjects has been observed to be more consistent than that of the stroke volume. Estimation of systolic time index from impedance plethysmograms in 34 normal subjects has been shown to be as reliable as that from electrocardiogram, phonocardiogram and carotid pulse tracing. Changes in the shape of plethysmographic waveform produced by valvular and congenital heart diseases are briefly described and the role of this technique in screening cardiac patients has been highlighted.

Forty patients with symptoms of neuro-vascular compression in the upper extremities were subjected to impedance plethysmographic study using Parulkar's method. Two patients recorded decreased blood flow (BFI) in supine position and were diagnosed as having partial occlusion at subclavian level. Sixteen of the patients recorded decreased BFI on 90 degrees abduction and hyper-abduction. Twelve of these patients had radiological evidence of anomalous cervicle ribs. In remaining four patients extrinsic impression on the subclavian artery due to fibrous deposits was confirmed by arteriography. Remaining 22 patients recorded normal impedance plethysmograms. Impedance plethysmography thus provided a non-invasive modality for confirmation of vascular compression in thoracic outlet syndrome.

Impedance plethysmographic observations have been compared with arteriographic findings in 216 patients with peripheral arterial occlusive diseases. Impedance plethysmographic diagnosis in these patients was obtained by Parulkar's method without apriori knowledge of arteriographic diagnosis. But for minor discrepancy in the anatomical location of the block in few patients, impedance plethysmographic observations correlated very well with arteriographic findings. Impedance plethysmographic diagnosis was found to be correct in 312, wrong in 53, false negative in 8 limbs respectively, yielding a sensitivity of 97.5% and specificity of 98.1% of this technique.

Impedance plethysmography (IPG) was carried out in one hundred and forty-one patients suspected of venous disorders using Parulkar's method. In these patients occlusive impedance phlebography (OIP) and venography were also carried out using standard procedures. Comparison of IPG and OIP observations with venographic findings revealed sensitivity of these methods to be 65% and 77.7% in the diagnosis of primary varicosity of veins and chronic deep vein thrombosis respectively with a specificity of 85%. Occlusive impedance phlebograms showing unilateral decrease in OIP parameters were observed to be sufficiently diagnostic. IPG observations in 5 patients with arterio-venous malformation were observed to be different from those in patients with deep vein thrombosis.

Impedance Plethysmography technique has been discussed with explanation of two compartment model and parallel conductor theory for the estimation of peripheral blood flow and stroke volume. Various methods for signal enhancement to facilitate computation of blood flow are briefly described. Source of error in the estimation of peripheral blood flow is identified and the correction has been suggested.

This paper describes the basic methods for measurement of body impedance, electrodes and their configuration, and the measuring instrument with its limitations. A microcomputer assisted impedance plethysmograph system, developed at BARC and different lead configurations for impedance plethysmographic investigation are also described. Typical impedance plethysmographic waveforms recorded from a normal subject and measurement of their amplitude and various time intervals are illustrated.

Impedance plethysmographic observations have been correlated with aortographic observations in 57 patients suspected of aortic occlusive diseases. Aortic occlusions have been characterised by marked decrease in blood flow index and significant increase in differential pulse arrival time at thigh level bilaterally. Atherosclerotic affection of the aorta has been featured by a bilateral decrease in the value of blood flow index as well as differential pulse arrival time at thigh level. Leriche's syndrome, however, has been found to decrease the blood flow index moderately at thigh in both the legs without any significant change in differential pulse arrival time. Aortography in all the patients has confirmed the diagnosis made by impedance plethysmography.

A review of investigations into the origin of impedance plethysmographic waveform is presented in this article. Attempts made by several investigators in the comparison of impedance plethysmographic estimations of peripheral blood flow with that obtained by standard methods are briefly described. Investigations indicating the negligible contribution from contact impedance at body electrode interface are highlighted. Temporal correlation of impedance plethysmographic waveform recorded from thorax with various important events of the cardiac cycle is summarised and various hypotheses on the genesis of this waveform are presented.

Quantitative electromyographic (QEMG) data recorded with two levels of threshold for the apparatus are compared. Using a fixed fraction of a subject's maximum effort the data are shown to be independent of sex, age and the strength of the muscles. The diagnostic yield of such a method is shown to be better with 50 muV threshold for analysis than with 100 muV, in cases of muscle disorders such as Duchenne muscular dystrophy and polymyositis. However, in cases of neurogenic lesions due to anterior horn cell disease the diagnostic yield remains the same with both thresholds.