Diagnosis of aortic occlusive diseases using impedance plethysmography.

AK Deshpande, GD Jindal, IP Babu, SN Nerurkar, MD Kelkar, GB Parulkar 
 Dept. of Medicine, Grant Medical College, Bombay, Maharashtra.

Correspondence Address:
A K Deshpande
Dept. of Medicine, Grant Medical College, Bombay, Maharashtra.

Full Text

::   Introduction

Parulkar et a1[4] exteneded the use of dZ/dt waveform for the estimation of peripheral blood flow using impedance plethysmography (IPG). They introduced several new lead configurations for assessment of blood flow in different segments of the upper and lower extremities. This method has distinct advantages over the conventional venous occlusion method as it yielded sufficient information for the clinician to plan mode of therapy in patient with peripheral arterial occlusive diseases[2],[3]. We have extended this method for investigating patients suspected of aortic occlusive diseases (AOD). In this paper we present comparison between impedance plethysmographic and aortographic observations in 57 patients suspected of AOD and highlight the use of impedance plethysmographic technique in the non-invasive diagnosis of aortic occlusions.

::   Material and method

Impedance plethysmographic investigation was carried out in all the patients at Non-invasive Vascular Laboratory, Dept. of Cardiovasc and Thoracic Surgery, KEM Hospital or Isotope Unit, JJ Hospital, Mumbai, using BARC made impedance plethysmograph system[1]. Fifty-seven patients (41 males, 16 females) in the age group of 8 to 65 years, who presented at various surgical OPDs of K. E. M. Hospital and J. J. Hospital were subjected to this study. Aortography was carried out at Radiology Department of K. E. M. Hospital in 56 patients and digital subtraction angiography was performed at National Hospital in the remaining patient.

Impedance Plethysmographic investigation was carried out in the manner described by Bhuta et al[1] and values of blood flow index (BFI) and differential pulse arrival time (DPAT) were calculated. The control values of BM were taken to be 1.80 + 0.35 and 1.50 + 0.30 for upper and lower extremities respectively and those of DPAT were taken to be 30 + 2.5 ms for upper arm, 20 + 2.5 ms for elbow, 25 + 2.5 ms for wrist, 75 + 5 ms for thigh, 35 + 5 ms for knee and 40 + 5 ms for ankle, based on the past experience of authors[2],[3],[4]. The values of BM and DPAT in a patient used to make the IPG diagnosis were as follows:

1. Bilateral marked decrease in the value of BFI (<0.60) with increase in value of DPAT at thigh location represented an aortic occlusion.

2. Bilateral moderate decrease in the value of BFI (0.60
3. Bilateral mild decrease in BFI (0.90
4. A bifed systolic wave of decreased amplitude recorded from thigh location was suggestive of multiple aortic occlusions probably due to aorto-arteritis.

5. An increased amplitude of systolic wave in the IPG waveform, recorded from neck location in a patient satisfying condition' with increased BFI in one or both the upper extremities suggested coarctation of aorta.

6. Further decrease in the value of BFI with changes in the value of DPAT at distal locations in the extremities represented poor patency of distal arteries.

::   Results

[Table:1] summarises the IPG observations in all the 57 patients subjected to this study. Five patients with normal values of BFI and DPAT at thigh location bilaterally were found to have normal aortograms, thus corroborating the IPG observations.

Nine patients with moderately decreased values of BM and normal values of DPAT at thigh but increased value of DPAT at knee were diagnosed as bilateral aorto-iliac block by IPG. Aortogram in these patients confirmed Leriche's syndrome in 7 patients and saddle emboli at aortic bifurcation in remaining 2 patients.

Eighteen patients recording mildly decreased values of BFI and significantly decreased values of DPAT at thigh (see [Figure:1]) were diagnosed as cases of atherosclerotic narrowing of the aorta. The average and standard deviation values of DPAT in this group were observed to be 48 ms and 10ms respectively and were significantly different from that of control subjects with probability of error of 1%. IPG diagnosis was confirmed by aortography in all the 18 patients.

Twenty-five patients recording markedly decreased values of BFI and significantly increased values of DPAT at thigh were diagnosed as cases of aortic occlusion. The average and standard deviation values of DPAT in these cases were 103 ms and 10 ms respectively and were significantly different from that of control subjects at 1% level of confidence. Eight patients in this group recorded bifed systolic wave in the IPG waveforms at thigh (see [Figure:2]) and were confirmed as cases of aorto-arteritis by angiography. Fourteen patients in this group recording increased value of BFI at neck (see [Figure:3]) were found to have coarctation (of descending aorta in 3 and of aortic arch in 11) by aortogrphy. Interestingly, BFI was observed to be increased in upper extremities bilaterally in 3 patients and unilaterally in 11 patients respectively. Remaining 3 patients in this group showed thrombotic occlusion on aortography.

::   Discussion

Excellent correlation between IPG observations and aortographic findings in patients with aortic occlusions is evident from the above observations. The level of occlusion has fairly well been indicated by IPG in cases of aortic coarctation and Leriche's syndrome. However, in remaining cases the level could not he indicated by IPG due to limitation of the technique itself. This limitation can possibly be overcome by recording normalised dZ/dt (Z.dZ/dt) waveform which is more sensitive than dZ/dt waveform.

::   Acknowledgments

The authors are thankful to Research Society - Grant Medical College and JJ Hospital, Research Society-Seth GS Medical College and King Edward Memorial Hospital and Indian Council of Medical Research, New Delhi, for providing funds from time to time for this study. The authors are also thankful to Dr SK Ganeriwal, Dean, Grant Medical College and JJ Hospital, Mumbai for giving continuous encouragement for this study.

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