Evaluation of state of circulation in radiation injury using impedance plethysmography.
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.
Radiation injury results from transfer of energy from radioactive source to the patient. This energy transfer can be caused by either sub-atomic particles like electron, proton, neutron or electro-magnetic ionising radiations like X-rays or Gamma rays. Radiation exposure may be partial involving hands, feet, legs and face or it may be complete involving the whole body. Most of the patients get partial exposure and have history of mishandling industrial radiography sources.
The earliest damage seen in radiation injury is transistory erythema which comes immediately after exposure and is due to dilatation of capillaries resulting from histamine like substances released by injured cells. This is followed 2-3 weeks later by fixed erythema, which is much deeper and more prolonged than the transient erythema. If the dose of radiation received by the patient is more than 5000 rad, epilation, dry and moist desquamation and ultimately necrosis of epidermis results.
Radiation burns are sometimes deceptive on superficial appearance as damage to important organs in subcutaneous tissue, nerve endings, hair follicles, sweat glands and endothelium of blood vessels may not be obvious. Among these the injury to the endothelium, of blood vessels is most serious. It produces endarteritis obliterens, leading to necrosis of overlying tissues which continues to progress for several months.
It is, therefore, very important to evaluate the status of blood circulation in patients with radiation injury. Conventionally thermography and vasular scintigraphy are employed for this purpose. These techniques give precise information about the blood circulation during the initial period after the injury. However, their sensitivity at later stage is not sufficient to detect decreased blood circulation caused by endarteritis obliterens.
We have carried out impedance plethysmographic (IPG) study of the digits in some patients with history of radiation injury. In this paper, we present IPG observations and their comparison with thermographic and scintigraphic findings.
Fifteen normal subjects in the age group of 20-35 years and seven patients with history of radiation injury were subjected to this study. All the seven patients were from industrial radiography units of private companies and were referred to Bhabha Atomic Research Centre for radiation dose measurement as well as management. Five of these patients (SS, SH, PKS, PGK and PMJ) were trained radiographers and two were casual workers (PAR and KM). Radiation burn was caused by Co-60 in five of them (PAR, SS, SH, PKS and PGK) and by Ir-192 in the remaining two (KM and PMJ).
During the follow up studies (1 to 4 years after the burn) in these patients, thinning of epidermis of the skin in digits was noticed and at this stage they were referred to Non-invasive Vascular Laboratory, King Edward Memorial Hospital, for PG investigation.
Impedance plethysmograms of both the upper extremities were first recorded in all the subjects in the manner described elsewhere to rule out possibility of peripheral arterial occlusive disease at proximal level and then IPG of digits were recorded in bipolar electrode configuration as follows. Current electrodes were applied 2 cm apart around the digit under investigation and the same were used as sensing electrodes. IPG of all the digits were recorded with patient in supine as well as on hyper-abduction with patient in sitting position.
Blood flow index (BFI) and differential pulse arrival time (DPAT) were computed from the IPG data for all the locations. The control values of these parameters for digits were found to be 1.50 0.35 and 17.5 2.5 respectively. IPG diagnosis was made as follows:
1. BFI at wrist in either of the upper extremity indicated possibility of arterial occlusion proximally and the diagnosis was made as described elsewhere in this volume .
2. BFI at wrist and in a digit in supine as well as on hyper-abduction with DPAT 20 ms suggested arterial occlusion in the digit.
3. BFI less than 1.15 in a digit in supine as well as on hyper- abduction with DPAT less than or equal to 15 ms indicated narrowing of the artery in the digit.
Figure 1 depicts IPG waveforms recorded from a patient (VAR-22M) with the history of handling 30 curie Cobalt60 source on 11.4.85. He was referred to BARC for management on 6.5.85. On clinical examination, he presented with swelling and blackish discolouration of thumb, index and middle finger in the left hand and blackish discolouration of palmer surface in the right hand. Next day the skin of thumb and index finger ulcerated. His burns healed by second week of June 1985. He was followed up in November 1986 and thinning of epidermis of the skin in left thumb and left index finger was noted. IPG study carried out on 18 November 1986 showed decrease in blood flow in all the digits in left hand and thumb and little finger in the right hand, without evidence of an arterial occlusion.
Comparison of IPG observations with Thermography in remaining patients showed that digits recording BE less than 0.80 by IPG were observed to be hypothermic by Thermography. Digits recording BM between 0.80 and 1.15 showed no discernible change in Thermography, though clinically thinning of epidermis was noted in some cases (SS, SH and KM), during follow up studies. This comparison, therefore, suggested that IPG could detect the decrease in blood flow at early stages before it was evident either clinically or by Thermography. Thus IPG was not only helpful in the diagnosis but also in planning the correct mode of therapy.
The authors are thankful to Dr SM Sharma, Associate Director, Medical Group, Bhabha Atomic Research Centre, Dr (Mrs) Usha Desai, Head, Medical Division, BARC and Dr (Mrs) Pragna Pai, Dean, Seth GS Medical College and KEM Hospital for encouraging us and to Mr SP Agarwal Scientific Officer, DRP, BARC, for his valuable help and suggestions