Corrected formula for estimating peripheral blood flow by impedance plethysmography.

In this paper, the limitations of the conventional formula for the computation of peripheral blood flow from impedance plethysmograms are highlighted, and a correction to the formula is suggested. A conductivity cell experiment is described to show the dependence of the value of the blood flow index (BFI), obtained from the conventional formula, on the mean resistivity of the cell. It is also shown that the value of the corrected BFI is independent of the mean resistivity. Anomalies observed in the amplitude of systolic waves in impedance plethysmograms of patients with oedema are explained.

Effect of pulmonary circulation on vector impedance cardiogram.

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.

Diagnosis of peripheral arterial occlusive diseases using impedance plethysmography.

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 plethysmographic observations in thoracic outlet syndrome.

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.

Diagnosis of venous disorders using impedance plethysmography.

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.

Diagnosis of aortic occlusive diseases using impedance plethysmography.

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.