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.
Wheeler et al and Johnston et al introduced application of venous occlusion principle in impedance plethysmography (IPG) for the diagnosis of deep vein thrombosis (DVT) and the plethysmograms thus obtained were named as occlusive impedance phlebograms (OIP). It was possible to cornpute venous capacitance (VC) and maximum venous outflow (MVO) from these phlebograms and sensitivity of these parameters was found to be 96%, 50% and 38% for the diagnosis of acute proximal vein thrombosis, popliteal vein thrombosis and calf vein thrombosis respectively. However, for the diagnosis of chronic DVT, sensitivity of OIP varied between 18 and 80%.
With an objective to improve the diagnostic yield of impedance plethysmography in chronic deep vein thrombosis, Dewoolkar et al and Suraokar et al employed Parulkar's method of recording dZ/dt waveform from various locations in the lower extremities. The data thus obtained was found to be helpful in the diagnosis of superficial venous incompetence and chronic deep vein thrombosis,. Out of 800 patients investigated using this procedure at Non-invasive Vascular Laboratory, K. E. M. Hospital, one hundred and forty-one patients had subsequently undergone venography. In this paper we present venographic correlation of on-line impedance plethysmographic and occlusive impedance phlebographic observations in these 141 patients.
Ninty-two male and forty-nine female subjects in the age group of 10 to 75 years were subjected to this study. The clinical examination in these patients revealed pain in 45, calf tenderness in 17, varicosity in 62, oedema in 81, varicose dermatitis in 17 and varicose ulcers in 23 subjects. Homan's sign was found positive in only 10 of these subjects. Impedance plethysmography and occlusive impedance phlebography were carried out at Non-invasive Vascular Laboratory, King Edward Memorial Hospital, following the procedure described elsewhere in this volume. IPG parameters namely blood flow index (BFI), differential pulse arrival time (DPAT) and pulse termination time (PTT) and DIP parameters namely venous capacitance and maximum venous outflow were derived from IPG and OIP data respectively,. In addition, a new parameter, namely coefficient of venous stasis (CVS), was obtained by dividing value of BFI at a location in elevated position by that in supine position. The control values of these parameters are given in [Table - 1].
The IPG and OIP data obtained in a subject was first analysed to rule out any possibility of peripheral arterial occlusive disease using the criteria of Jindal et al and then was interpreted for the diagnosis of venous disorders as follows:
1. The value of either BFI, DPAT, PTT, VC or MVO was said to be significantly decreased (or increased) if it was either one standard deviation less (or more) than the control value or 20% less (or more) than the corresponding value in the opposite extremity.
2. The value of CVS more than 1.24, 1.04 and 1.22 at knee, calf and ankle locations respectively with BFI (elevated) within normal limits suggested primary superficial venous incompetence.
3. The value of CVS more than 1.24, 1.04 and 1.22 at knee, calf and ankle locations respectively with significant decrease in the value of BM (elevated) was suggestive of venous stasis caused by deep vein thrombosis. Increase in PTT at all the locations confirmed this diagnosis.
4. Marked increase in the value of CVS with BFI (elevated) significantly decreased indicated secondary varicosity as a consequence of deep vein thrombosis.
5. Significant decrease in the value of BFI (supine) with CVS within normal limits gave partial evidence of acute deep vein thrombosis, subject to confirmation by DIP observations.
6. Unilateral decrease in the value of VC and MVO gave sufficient evidence for the diagnosis of deep vein thrombosis, however bilateral decrease was considered non-specific.
7. Marked decrease in the value of Zo as well as BFI (supine) and BFI (elevated) indicated accumulation of extra-vascular water in the legs. However, in such a case, it was not possible to detect deep vein thrombosis.
8. Significant increase in BFI (supine) as well as BFI (elevated) and also in PTT suggested arterio-venous (A-V) malformation or fistula.
Bilateral venography in 46 patients, unilateral venography in 90 patients and arteriography and venography both in 5 patients were performed at Radiology Department, King Edward Memorial Hospital, Mumbai, using standard procedure. The IPG diagnosis was then compared with angiographic findings for the validity of the same as described in the following section.
[Table - 2] gives the comparison between IPG observations and angiographic findings. As can be seen from the Table the IPG diagnosis is true positive, false positive, false negative and true negative in 26, 4, 14 and 30 limbs respectively for primary varicosity. This yielded a sensitivity of 65% and specificity of 88.2% of IPG technique in the diagnosis of primary superficial venous incompetence. Similarly IPG diagnosis is true positive, false positive, false negative and true negative in 80, 6, 23 and 24 limbs respectively for deep vein thrombossis, this includes 10 limbs (Sr. No. 2 in the Table) having IPG diagnosis based on OIP observations alone as true positive. This leads to sensitivity of 77.7% and specificity of 85% of IPG in the diagnosis of DVT.
[Figure - 1] illustrates the IPG and OIP data and [Figure - 2] gives venogram in a patient with deep vein thrombosis in the left leg. Similarly Figure 3 depicts the IPG and OIP waveforms in a patient with bilateral DVT. Figure 4 shows similar data in a patient with A-V malformation, which are obviously different from those of [Figure - 1] and [Figure - 3].
False positive diagnosis of DVI was observed in two patients with paired popliteal veins and paired superfical femoral veins respectively (Sr. No. 8 in [Table - 2]). This P. probably indicates that paired veins are haemodynamically less competent than the single vein, which is corroborated by the clinical impression in these patients.
We have observed that IPG and 0IP observations are inconclusive in patients having lymphangitis, nephrotic syndrome or congestive cardiac failure. The IPG data is so modified by lymphangitis or nephrotic syndrome that evidence of DVT is suppressed. However, in congestive cardiac failure, the IPG and OIP manifestations are very much like that of DVT and may lead to false positive diagnosis of DVT.
To conclude IPG offers a simple, non-invasive, non-dextrous and low cost technique in the diagnosis of venous disorders. Furthermore it offers an excellent method in posttherapeutic assessment of patients, as it can be repeated any number of times on a given patient without causing any harm or discomfort to the patient.
The authors gratefully acknowledge financial support from Indian Council of Medical Research, New Delhi and Research Society, Seth GS Medical College and King Edward Memorial Hospital, Mumbai for carrying out clinical studies. The authors are thankful to Shri MK Gupta, Assoc. Director, E & I Group, BARC, Shri BR Bairi, Head. Electronics Division, BARC, and Shri KR Gopalakrishnan, Head, Nuclear Instruments Section, BARC for giving us encouragement. The authors are also thankful to Dr. Alka Deshpande, Assoc. Prof., Dept. of Medicine, JJ Hospital, Dr. MD Kelkar, Ex. Head, Dept. of Radiology, King Edward Memorial Hospital and Shri SP Agrawal Scientific Officer, DRP, BARC, for giving valuable suggestions in planning this study and analysing the results.