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COPYRIGHT LAW - REPRODUCTION PROHIBITED UNLESS 
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Peter F. Kelly, D.P.M., F.A.C.F.A.S.  *
  
Diplomate, American Board of Podiatric Surgery  
Fellow, American College of Foot and Ankle Surgeons  


PERIPHERAL VASCULAR DISEASE:  A PRACTICAL 
MONITORING METHOD

Published in Two Parts

PART ONE:   DISCUSSION OF VASCULAR ASSESSMENT  


*This work resulted in receipt of the Angiology Award, Pannsylvania 
College of Podiatric Medicine, 1986


ABSTRACT
 
     Until this time, no simple noninvasive method of calculating and 
monitoring calibrated parameters of blood perfusion has existed.

	The first section of this paper discusses various methods of 
diagnosing circulatory deficiencies and uses the example of intermittent 
claudication, for it is a frequently encountered symptom of circulatory 
inadequacy.   

     The second section of this paper will introduce mathematical 
fundamentals which show a practical method of calibrating circulatory 
velocity and flow studies.  With this the practitioner of Podiatric 
Medicine or Surgery is better prepared to monitor blood flow through 
the extremities with increased accuracy. 


INTRODUCTION
 
     Intermittent claudication is oftentimes the first clinical symptom of 
arterial insufficiency in the legs.  It is usually easily diagnosed from the 
specific localization of clinical symptoms.  Claudication is observed as 
pain and/or cramping in the muscles of locomotion of patients who, after 
walking or exercising, experience pain in a muscle group which forces 
the individual to stop activity temporarily until the circulation restores 
nutrients and clears out products of metabolism.(1,2)
 
     A clinical diagnosis of intermittent claudication may be performed 
with relative ease.  Some of the brief routines described below only 
emphasize how simple it may be to make more adequate the history and 
physical exam by adding this important vascular parameter.  The 
implications of this problem are serious enough in an otherwise 
uncompromised circulation, but become increasingly important in the 
diabetic and patient suffering from peripheral vascular disease.(2,3)
 
     Claudication is also an important indicator of a progressive vascular 
diseases which may lead to the loss of a limb.  Because of that grave and 
realistic prognosis, and the occasional elusive symptoms sometimes 
elicited by intermittent claudication, it seems obvious that it would be 
valuable for the  practitioner to find a most reliable  method  to gauge 
the patient's vascular status during the initial evaluation and subsequent 
follow up.
 
     The Podiatrist, by knowing accurately blood flow to the foot, is able 
to administer more precise dosages of medication for the compromised 
area. Current vascular research has suggested parameters which may be 
of clinical significance in determining the status and extent of disease, 
where the practitioner will be able to make measurements of vascular 
flow and resistence non-invasively, non-occlusively.  The practitioner 
will also bypass the unreliabilities of auscultation, and by calibrating the 
existing Doppler unit, be able to directly measure blood flow and 
peripheral resistance.  Advances in these techniques of Doppler 
ultrasound allows measurement not only of systolic blood pressure and 
blood flow quite accurately, but now of vascular resistance.  The 
significance of measuring vascular resistance is that the clinician would 
measure directly the decreased perfusion to the tissues.(7,14) 

     Many clinical tests which have merit, but also certain drawbacks, will 
be discussed. 
 

THEORY OF ISCHEMIA
 
     Intermittent claudication is ultimately caused by a decrease in 
perfusion resulting in ischemia and pain.  Peripheral vascular disease, 
vasospastic syndromes, arterial entrapment, hypoxemia of severe anemia 
or severe muscular work loads contribute to claudication.  The resulting 
pain is a result of the inadequate clearing of metabolic acids, 
prostaglandins, bradykinins, histamines, and other elements from fuscle 
tissue.  A unique characteristic of patients with intermittent claudication 
is an increased lactate to pyruvate ratio, not only during and after 
exercise, but also before.
 
     Claudication is also distinguished histochemically by recruitment of 
type two (anaerobic, white) muscle fibers at the expense of type one 
(aerobic, red) fibers.  Certain enzyme changes are seen in each of the 
muscle types, such as increased succinate dehydrogenase activity to 
further adapt the cell to the decrease in nutrients.(4)  More severely 
ischemic muscle does not adapt, but will display fiber atrophy resulting 
from capillary losses, which indicate a disuse phenomena.(5,6) 
 

CLINICAL TESTING OF VASCULAR DISEASE
 
     Common clinical methods for diagnosing intermittent claudication 
include treadmill walking tests, stepping tests, the Ankle-Arm Ischemic 
Index and brachial-ankle pressure gradients, knee bends or toe rises 
(with segmental plethysmography) and venous occlusion 
plethysmography.  Non-invasive diagnostic methods include ultrasonic 
arteriography, thermography, and capillary plethysmography. 

     Arteriography is an invasive technique and usually only considered in 
the preoperative examination for patients undergoing vascular surgery.  
Thus, by preference of the physician, the diagnosis of occlusive vascular 
disease is made by the clinical tools and	non-invasive diagnostic 
methods.  Oftentimes the treadmill evaluation is used to evaluate 
claudication distance because of its practicality. 

     The treadmill evaluation readily demonstrates the characteristics of 
claudication and directly informs the doctor whether his therapy is 
beneficial.  However, no speed or degree of treadmill slope standards 
exist since investigators adapt both of those parameters to the 
possibilities of the patient.  The evaluation is subjective since the 
endpoint of the test is influenced partly by the patient's feelings which 
may be variable from day to day.  Normal conditions of walking are not 
duplicated, and patients who are physically handicapped, or have 
chronic obstructive pulmonary disease or cardiovascular disease may not 
be able to participate.  Thus another method of evaluation is necessary to 
insure uniform results and participation.(7) 

     Treadmill walking tests using Doppler determination of pressures at 
the ankle are commonly used as a basis for management and assessment 
of therapy for intermittent claudication.  Total walking time is 
reproducible, however, the time of pain onset is still unreliable.  
Additionally, a single walking test is an inadequate assessment of 
claudication.(8) 

     The Arm-Ankle Pressure gradient is the systolic pressure gradient 
between upper arm level and ankle level, and is an indirect measurement 
of the amount of arteriosclerosis from heart level to ankle level.  In 
normal subjects there is no fall in systolic pressure between upper arm 
and ankle level, and therefore any fall in pressure may reflect structural 
changes in the wall of arteries.  The pressure gradient has been shown to 
increase with increasing numbers of cardiovascular risk factors; 
therefore, it has been concluded that the pressure gradient may be used 
to measure the degree of arteriosclerosis between heart and ankle.(9) 

     Problems with this method relate to the wide ranges of extremity 
blood flow, which may be a result of changes in sympathetic activity.  
Baker and Dix found a considerable variation in a survey of their 
patients with clinically stable arterial insufficiency, so the method is not 
reliable from a clinical standpoint.(10) 

     Plethysmography can be a helpful diagnostic aid if the segments 
measured (such as the ankle) are calibrated using standard pressures of a 
blood pressure cuff.  This is usually set according to the preference of 
the individual vascular laboratory and is said to be very accurate in 
differentiating between normal and abnormal.  Because of the substantial 
number of false positives (up to 20 per cent), it is recommended that this 
technique should not be used alone, but in conjunction with systolic 
blood pressure measurements using the Doppler Ultrasound.  The 
Doppler Ultrasound reduces the false positive results to nearly zero.(7, 
11) 

     Venous occlusion plethysmography determines the amount of blood 
flowing through a limb using two techniques.  Inflating a blood pressure 
cuff at the base of the limb between systolic and diastolic blood pressure 
occludes venous outflow but not arterial inflow.  Thus blood is pooled in 
the limb and the volume increase may be measured.  The rate of blood 
flow of the large vessels may also be determined. 

     A variation of the technique is to inflate the cuff to a suprasystolic 
pressure for a given time causing circulatory arrest and accumulation of 
metabolites, mimicking the physiology of intermittent claudication.  
After release of this pressure a reactive hyperemia occurs and this 
resulting plethysmography curve will provide information about 
restrictive vascular lesions.  Normal definitions and limits are 
established by the individual vascular laboratory.(7, 12) 

     A well established technique convenient to the clinician is Segmental 
Oscillometry performed at rest and after exercise.  Oscillations are 
recorded at rest at the level of the thigh, calf, ankle, and dorsal and 
plantar aspects of the foot.  Measurements at the ankle before and after 
exercising, the patient having perfomed a set number of deep knee bends 
and toe rises, provides information about lesions at the iliac level and 
femoral artery respectively.  This technique is quite useful with regard to 
such lesions, however, the results obtained can be misunderstood as 
being able to provide more information than is possible.(7) 

     Another vascular tracing technique, but less invasive than 
arteriography, is measuring isotope clearance from the muscles of the 
calf and the thigh.  This provides information as to whether a stenotic 
lesion greater or lesser than 70 per cent exists.  Compared to 
arteriography, isotope clearance is not quite as accurate, nor is the 
resolution of anatomical information as high.  The main advantage of 
isotope clearance is that it is less invasive and also provides information 
in a three dimensional scale.(13) 

     Ultrasonic arteriography can be used to construct a picture of blood 
vessels using echography.  Frequently it is used to detect areas which 
form potential emboli.  Diameters of vessels may be found, and 
occlusive lesions may be pinpointed in the larger vessels.  With the 
application of the Doppler principle, ultrasonic arteriography converts 
into a functional scan since Doppler frequency shifts correspond to 
fluctuations in flow.(7) 
 

RECENT DEVELOPMENTS IN VASCULAR ASSESSMENT
 
     Recently the clinical applicability of Poiseuille's law involving 
resistance and blood flow has been utilized.  The Poiseuille law states 
that the "pressure drop along a rigid tube having constant diameter 
relates proportionately to flow and resistance".  Poiseuille discovered 
that resistance was proportional to the length and area of the tube, and 
the viscosity of the fluid, and by basic physics showed that the pressure 
drop was also dependent upon velocity. 

     Of primary concern to the physician, regarding peripheral vascular 
disease, is whether sufficient amounts of blood are getting to and 
flowing through a given part.  Until now a physician's only method of 
assessing a patient's vascular status was by measuring blood pressure and 
comparing this value to accepted norms:  This approach erroneously 
assumes that pressure is a good indicator of flow.  Some specialists 
relate excessive pressure to the increased work load of the heart as well 
as increased resistance in the circulation.  Since pressure readings can 
have such different interpretations, these measurements seem to be 
limited in value. 

     Instead, by using the Poiseuille equation, flow and resistance are 
determined directly, and one can also determine pressure.  Validation of 
the Poiseuille equation gives the medical community an opportunity to 
establish vascular grading systems based upon pressure, flow, and 
resistance.  These grading systems should allow easy comparison for 
future vascular assessment of the patient. 

     Recent investigators have also identified a need for non-occlusive  
measurement of blood pressure.  The occlusive cuff method is inaccurate 
due to differences in the sizes of cuff bladders and longitudinal motion 
of arm tissue.  The problem with Korotkoff sounds is that they cannot be 
heard at low levels of pressure and are masked in a high noise 
environment.  Korotkoff sounds are also inaudible in infants, or in adults 
in shock.  Auscultation is of little value in the measurement of arterial 
status of patients and, in addition, tells nothing about blood flow through 
the part.
 
     It has been concluded that using an occlusive cuff with a Doppler 
Ultrasound flowmeter was a more sensitive method for taking blood 
pressure than by indirect sphygmomanometry, using Korotkoff 
sounds.(14) 

     Although arteriography is still necessary for defining structural 
lesions, Doppler studies have been found to agree with arteriography in 
83 of the 84 arterial segments examined.  It was also concluded that 
ultrasound diagnosis and radiographic evaluation levels were 
comparable.(15)  Similarly it has been demonstrated that Doppler shift 
sensors surpass sphygmomanometry methods by being able to measure 
diastolic and systolic endpoints in shock states, in infants, as well as in a 
high noise environment.(14)
 
     Korotkoff sounds are only generated during the opening of an artery 
but not during its closure, whereas distinctive Doppler-shift signals are 
detected during both events.  In addition, Doppler-shifted ultrasound 
signals are easily obtained from blood vessels, even in atherosclerotic 
patients.  For the aforementioned reasons, it is clear that Doppler 
instrumentation is the most precise method to non-invasively and non-
occlusively determine velocity.(14)
 
     Flow and resistance represent the best indicators of vascular status in 
the lower extremity; this is because claudication results from a decrease 
in circulation through a given area, such that nutrients cannot flow into 
the area, and metabolic wastes, kinins, and other products build up, 
causing pain.  By applying Poiseuille's law, the physician can directly 
measure the amount of blood flow to an area, and by noting the degree 
of resistance in that part, one can determine how well the body part is 
being perfused. 
 

SUMMARY 
     Various methods of diagnosing intermittent claudication have been 
discussed.  None are completely advantageous in comparison, and each 
presents unique faults.  Within the larger setting of diagnosing 
circulatory deficiencies, the example of intermittent claudication has 
been used.  In the next section a simplified method of calculating 
parameters of blood perfusion will be presented so that the practitioner 
might be able to increase his accuracy in monitoring blood flow through 
the extremities.