Ophthalmic artery flow reversal and pressure reducing carotid stenosis

Abstract

Background

In the United States (US), 80,000 strokes annually are attributed to carotid stenosis among the 140,000,000 people over age 40 years old. More than 300,000 people in the US have severe carotid stenosis. Most of those people have normal cerebral perfusion pressure to each portion of the brain because the circle of Willis (coW) provides collateral connection between the basilar artery and the two carotid arteries. In those cases, a reduction in flow through one carotid artery does not affect brain perfusion. However, about 75,000 people with severe carotid stenosis also have a disconnected coW resulting in a pressure reducing carotid stenosis and regional reduced cerebral perfusion pressure. Currently, in standard medical care, every carotid stenosis is treated aggressively without considering whether the coW is connected. Currently, the 240,000 patients reporting transient ischemic attack (TIA) and 550,000 additional patients suffering unheralded stroke are evaluated for carotid artery stenosis after the event resulting in 160,000 carotid stenoses diagnosed. Fewer than 10,000 strokes are prevented annually by 104,000 carotid revascularizations by endarterectomy or stent. Carotid stenosis contributes to 40,000 cases of cognitive impairment and dementia. The United States Preventive Services Task Force (USPSTF) recommends against carotid stenosis screening, although patients might benefit from medical treatment for atherosclerotic artery stenosis. A complete ultrasonic cerebral arterial examination in specialty care includes Doppler measurements from carotid, ophthalmic, and cerebral arteries. Could ophthalmic artery (OA) direction measurement alone in primary care be used for effective screening for pressure reducing carotid stenosis? The aim of this analysis is to determine whether OA flow reversal (OAr) is a specific marker of pressure reducing carotid stenosis indicating elevated risk of preventable stroke and/or cognitive deficit.

Methods

This analysis of 21,106 cerebro-arterial examinations compared simple measurements [OA flow direction, carotid bruit (CBr) auscultation, bilateral arm blood pressure (BP)] to carotid artery Doppler measurements [peak systolic velocity (PSV) greater than 230 cm/s, or occlusion].

Results

OAr had a 12.5% sensitivity for carotid stenosis, 43.9% sensitivity for carotid occlusion, and 99.4% specificity for carotid obstruction.

Conclusions

The purpose of the carotid artery examination is to predict whether therapy will provide benefit to the patient. Doppler detection of OAr can be a primary care screening method for pressure reducing carotid obstruction with high specificity that might discover some of the 1% of people who have pressure reducing carotid stenosis. These people might benefit from anti-atherosclerotic medical therapy in primary care. With 6 months of medical treatment, OAr might normalize to forward flow indicating improved cerebral perfusion pressure. In addition, 2% of people have carotid occlusion. These people might be at risk for stroke during systemic hypotension. They might be spared cerebral dysfunction by more careful BP control in primary care or during surgery.

Highlight box.

Key findings

• Detection of ophthalmic artery (OA) flow reversal is an easily performed, quick procedure that identifies patients who might benefit from anti-atherosclerotic treatment and careful blood pressure control in primary care.

What is known and what is new?

• Patients with severe carotid stenosis have a projected 11% chance of stroke in 5 years if the carotid stenosis is not treated, but treatment reduces this risk by half. Patient with OA flow abnormality have a 12.5% chance of stroke in 2 years if not treated. Modern anti-atherosclerotic medical care can reduce the severity of carotid artery stenosis with a few months of treatment, and might be as effective in reducing stroke as anatomic carotid revascularization by endarterectomy or stent.

• Although OA flow direction measurement was first reported half a century ago as part of a comprehensive cerebrovascular examination, the test was not widely adopted or advocated. In this report, the detection of flow reversal is linked to middle cerebral hypotension rather than anatomic carotid stenosis severity as a simple specific measurement.

What is the implication, and what should change now?

• A complete cerebrovascular examination should include bilateral OA Doppler waveform analysis.

• Screening for OA flow reversal in primary care followed by anti-atherosclerosis treatment might prevent 100,000 strokes per year in the United States and improve cognition in some of the 10,000,000 with impairment.

Introduction

Anatomic carotid stenosis verified by X-ray contrast angiography is a risk factor for stroke. Asymptomatic patients with significant carotid stenosis [>60 percent diameter reduction (%DR)] in the asymptomatic carotid artery surgery (ACAS) study (1) had a 5%/2-year chance of any ipsilateral stroke and a 2.5%/2-year chance of severe ipsilateral stroke if treated with the regular anti-atherosclerotic medical care recommended in 1987. In the ACAS study, patients were qualified for recruitment by measuring ophthalmic artery (OA) pressure using OPG-Gee (oculoplethysmography by the method of William Gee) (2) to detect OA hypotension (20 mmHg below normal) or by carotid artery duplex Doppler high velocity measurements indicating stenosis. The stenosis was verified after recruitment by X-ray contrast angiography. The rate of stroke in these ACAS patients is similar to the overall rate of stroke in patients reported a decade earlier by Kartchner and McRae (3). In patients referred to their clinic for carotid artery evaluation, the patients who did not receive carotid endarterectomy were followed for an average of 2 years. The stroke incidence in these patients was less than 1.9% overall, but in those patients with both ipsilateral carotid bruit (CBr) and a greater than 20 mS eye pulse delay [OPG-KM (oculoplethysmography by Mark Kartchner & Lorin McRae)], the 2-year stroke incidence was 12.5% (Table 1). In patients without the combination of both bruit and eye pulse delay, the stroke rate was less than 0.9% per year.

Table 1. Twenty-four-month stroke incidence in survivors without carotid endarterectomy (3).

Followed for average 24 months	Pulse delay oculoplethysmography		Population
	Normal	>20 mS delay
Carotid phono-angiography
Normal	11/677 (1.6)	2/91 (2.2)	13/768 (1.7)
Bruit	2/77 (2.6)	6/48 (12.5)	8/125 (6.4)
Population	13/754 (1.7)	8/139 (5.8)

Data are presented as n/total (%).

The eye is supplied by the OA, a branch if the distal internal carotid artery (ICA) junction with the middle cerebral artery (MCA) which supplies the motor and sensory cortices of the brain. The pulse delay indicates regional cerebral hypotension of the brain in the ipsilateral MCA territory. The normal pulse transit time from the common carotid artery (CCA) to the supra-orbital artery (SOA) is 40 mS, increasing linearly as the ICA stenosis becomes severe to 90 mS at ICA occlusion (4).

The current standard practice in primary care for the prevention of stroke in patients over age 40 years old is: (I) provide advice on healthy living; and (II) measure systemic blood pressure (BP) as a vital sign on clinic visit. Treat hypertension medically when systolic BP (SBP) is found to be greater than 140 mmHg (5). When initial stroke-like symptoms are reported, evaluate the patient for cause, including examination for ICA stenosis. The result is: 240,000 people report a transient ischemic attack (TIA) each year; 80,000 of those cases progress to stroke; an additional 530,000 people suffer unheralded stroke. More than 160,000 people die each year of stroke, and 200,000 are disabled at 6 months after stroke; 100,000 are disabled for the remainder of life (6). About 20% of these strokes are attributable to carotid artery stenosis. Many of the carotid strokes can be prevented by in-time identification and treatment of carotid stenosis.

Patients with severe ICA stenosis without stroke symptoms might suffer from cognitive deficit or dementia (7,8), especially if the circle of Willis (coW) is disconnected (9). The dementia might be improved by treating the carotid stenosis (10,11).

Screening the ICA with ultrasonic Doppler velocimetry in a “high risk” population of elderly patients with hypertension, diabetes, coronary artery disease, and/or family history of stroke found a 7.4% prevalence of ICA peak systolic velocity (PSV) exceeding 120 cm/s (12). Screening for carotid stenosis with ultrasonic Duplex Doppler velocimetry is not recommended by the United States Preventive Services Task Force (USPSTF) (13). Screening for carotid stenosis is cost-effective if the screening cost is low and the specificity of the screening method is high (14).

The purpose of this analysis is to determine whether simple diagnostic measurements that can be performed at minimal cost in primary care can identify patients who might benefit from anti-atherosclerotic medical therapy provided in primary care. The diagnostic measurements are: bilateral arm BP, CBr auscultation, and ultrasonic Doppler measurement of OA flow direction. These measurements can be done quickly during the collection of vital signs such as BP, body temperature, and body weight. The OA direction test provides similar information to the OA pulse delay [OPG-KM (3)] test in Table 1. Because the OA Doppler test only requires contact with the closed eyelid rather than with the exposed eyeball [OPG-Gee (2) and OPG-KM (3)], the test is much more easily performed and evaluated. For patients with abnormal findings, the measurements can be repeated after 6 months (15) or 24 months (16) of medical therapy to determine whether the measurements have normalized. If the abnormal measurement persists, the patient can be referred to specialty care.

Methods

This analysis included 21,106 cerebrovascular ultrasonic Doppler examinations between January 1, 2014 and May 31, 2024 at Pacific Vascular, Inc. (Bothell, WA, USA), an employee-owned vascular testing organization in Washington state. All examinations were requested by referring physicians based on clinical indications. The examinations were conducted in nine laboratories in western Washington state using Toshiba/Canon duplex/Doppler ultrasound systems. Pacific vascular provided anonymized records of the examinations for this analysis. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study (STUDY00023700) was evaluated by the University of Washington Institutional Review Board (WCG IRB Institution #55014) for research involving human subjects. The UWIRB has determined that this analysis does not involve “human subjects” as defined by federal regulations. It does not require exempt status, IRB review, or informed consent.

Each carotid Doppler examination includes measurements from five anatomic locations: two from the CCA proximal to the carotid bifurcation, three from the ICA distal to the carotid bifurcation, all spaced at about 2 cm intervals (17). The highest PSV from the three ICA locations (proximal ICA, middle ICA, and distal ICA) were used to estimate the stenosis Venturi pressure depression (18) and Bernoulli pressure drop (19,20) with the equation: ∆p (mmHg) = 4 × [V (m/s)]².

The ICA was classified as severely stenotic if the highest ICA PSV exceeded 230 cm/s (21,22) or occluded if the ICA velocity measurements were less than 10 cm/s. OA velocity direction was measured with trans-orbital Doppler (23,24) and classified as OA normal forward flow (OAf) or OA flow reversal (OAr). Arm systolic BPs (SBPs) were measured bilaterally by the Doppler method (25).

These measurements are divided into three types: (I) bilateral arm BP that can be performed in primary care with existing equipment; (II) OA flow direction that could be performed in primary care with low-cost instrumentation and minimal examiner training; and (III) carotid artery velocity measurement that requires specialized equipment and highly trained/certified examiners in a specialty clinic.

Statistical analysis

Anonymized results of each clinical examination were provided on separate line in an Excel spreadsheet including continuous variables, categorical variables, and text variables. Some continuous variables, such as age in years, were converted into categories, such as decades; other continuous variables were displayed as cumulative distribution functions and/or as binary categories (normal/abnormal) above or below a clinically accepted threshold.

Results

The average age of the 21,106 patient examinations is 70.3±12.6 years old (Figure 1), 51.7% female. The majority of the patients (97.5%) are older than 40 years. The prevalence of arterial disease indicators in patients younger than 40 years is near zero and in patients older than 40 years the prevalence ranges between 1% and 15% increasing with each decade of age (Figure 1).

Figure 1.

Age distribution of patients and prevalence of arterial disease findings by decade. Ages 20 to 29 years: 3/140 cervical bruit and 3/140 ICA occlusion. Ages 30 to 39 years: 4/360 cervical bruit, 1/360 ICA occlusion, and 3/360 OAr. Ages 100 to 104 years: 1/20 ArmBPdiff. ArmBPdiff, arm blood pressure difference; ICA, internal carotid artery; OAr, ophthalmic artery flow reversal; PSV, peak systolic velocity.

Although the patients in this report referred for clinical indications spanned nearly 100 years from age 20 to 
104 years old, 95% of the patients were between the ages of 40 and 91 years old.

Cumulative distribution plots of indicators of pressure reducing ICA stenosis (Figure 2) show that both the findings of OA flow delayed and OAr are strongly associated with the highest ICA PSV >230 cm/s.

Figure 2.

Cumulative distribution of the highest ICA PSV for OA waveform type. The number of examination sides in each category is indicated below the label. The left vertical axis is the PSV measured with ultrasonic Doppler. The right vertical axis is the Bernoulli pressure drop across the ICA stenosis computed from the highest ICA PSV. ∆p (mmHg) = 4 × [V (m/s)]². (Left) Cumulative distribution for all ICAs with flow for sides with OA: OAr, OAd, or OAf. (Right) For each ICA velocity (vertical axis), difference between percentile for OAf, OAr, or OAd percentiles. Horizontal line at 230 cm/s is the commonly accepted ICA Doppler diagnostic criterion for 70%DR stenosis (21,22). %DR, percent diameter reduction; ICA, internal carotid artery; OA, ophthalmic artery; OAd, ophthalmic artery flow delayed; OAf, ophthalmic artery normal forward flow; OAr, ophthalmic artery flow reversal; PSV, peak systolic velocity.

PSV in the ICA greater than 230 cm/s is considered to be the most accurate Doppler criterion for a >70%DR ICA stenosis (21,22). Of the screening tests evaluated, including detecting OAr, listening for CBr, and measuring the difference in SBP between the right and left arm (∆SBP >20 mmHg), the finding of OAr is the most sensitive and specific for stenosis. The sensitivity of these tests is not sufficient for diagnostic purposes, but the specificity indicates few false-positive results, which is important for a screening test in an asymptomatic population (Table 2).

Table 2. Summary of sensitivity and specificity of screening tests.

Test	Stenosis >230 cm/s (%)			Occlusion <10 cm/s (%)			Obstruction (%)		Test positive (%)	Stenosis yield (%)	Occlusion yield (%)
	Sens	Spec		Sens	Spec		Sens	Spec
OAr	12.5	98.1		43.9	98.3		18.2	99.4	3.2	1.5	1.5
ABPD	6.9	98.0		5.0	97.5		6.3	98.0	2.6	0.8	0.2
Bruit	9.9	95.4		3.5	94.7		8.5	95.3	5.3	1.2	0.1
3-test	26.8	92.0		48.3	91.1		30.3	93.2	10.2	3.2	1.7

“Stenosis” means either right or left side ICA PSV >230 cm/s. “Occlusion” means either right or left side ICA PSV <10 cm/s. “Obstruction” is either stenosis or occlusion on either side. “Stenosis yield” is the number of potentially treatable ICA stenosis cases found by the method. “Occlusion yield” is the percentage of cases found that might have severe MCA hypotension when systemic BP is lowered or when changing from supine to upright. “ABPD” means difference between arm SBP >20 mmHg. “Bruit” means a systolic bruit heard with a stethoscope on either side of the neck just under the jaw. “3-test” means at least one test (OAr, ABPD, and/or Bruit) is abnormal. BP, blood pressure; ICA, internal carotid artery; MCA, middle cerebral artery; OAr, ophthalmic artery flow reversal; PSV, peak systolic velocity; SBP, systolic blood pressure; Sens, sensitivity; Spec, specificity.

Systemic BP is correlated with the prevalence of atherosclerosis. A comparison of the prevalence of ICA stenosis and occlusion between five SBP bands (Figure 3) indicates that the prevalence of ICA occlusion increases from 2.6% to 4% across the ranges of SBP, and the prevalence of severe ICA stenosis increases from 7.5% to 16.5% across the same ranges. The relationship is not obvious from a correlation of individual examinations between brachial SBP and stenotic carotid velocity. R²=0.01; slope =0.4 (cm/s)/(mmHg).

Figure 3.

Percent of cases within five BP ranges with carotid obstruction. Below the BP range limits indicated are the percentages of examinations within that range (highest of left or right SBP reported): 97% of examinations report SBP between 100 mmHg (1%ile) and 200 mmHg (98%ile). Orange: examination sides with severe ICA stenosis (>230 cm/s =21 mmHg Bernoulli pressure drop). Blue: examination sides with ICA occlusion (PSV <10 mmHg). BP, blood pressure; ICA, internal carotid artery; PSV, peak systolic velocity; SBP, systolic blood pressure.

Discussion

Preventable carotid ischemic stroke can occur from three causes:

1. Critically low MCA territory perfusion pressure <55 mmHg (26) due to a pressure reducing carotid stenosis when systemic BP is reduced, particularly when the patient is upright which reduces the cerebral perfusion pressure by an additional 30 mmHg compared to supine due to the hydrostatic elevation effect. If the low pressure is due to a carotid stenosis combined with a disconnected coW, these patients will exhibit impaired cerebrovascular flow reserve when the MCA velocity is measured with transcranial Doppler (TCD) during a 30-second breath hold to induce hypercapnia and cerebral vasodilation. These are the patients likely to have OAr when sitting upright.

2. The release of atheroemboli from a carotid atheroma due to intrastenotic Venturi pressure depression causing local paradoxical pulsation (18,27) and induced inflation of the vasa vasorum resulting in atheroma rupture (28,29), or the disruption of the atheroma when the longitudinal force of the Bernoulli pressure drop across the stenosis (30,31) exceeds the mechanical strength of the atheroma (30). The inflated vasa vasorum can be detected with ultrasound B-mode imaging as reduced gray scale median (GSM) within the atheroma or detected with magnetic resonance imaging (MRI) as “intraplaque hemorrhage”.

3. The release of thromboemboli from thrombus formed in an ulceration of a carotid atheroma after the rupture of the fibrous cap (32-34). Ultrasound B-mode imaging, X-ray contrast angiography, and MRI anatomic imaging can be used to identify a disrupted atheroma surface leaving an ulceration. Emboli passing through the MCA can be identified by TCD monitoring over a period of hours looking for the passage of unusual, strong ultrasound scatterers in the Doppler waveform. Although the source of these emboli might be the ulceration of a carotid atheroma, often they originate as thrombus in veins of the legs passing from the right heart to the left heart via a patent foramen ovale (PFO) (25% prevalence) or originate as thrombus in chambers of the left heart associated with atrial fibrillation or a previous ventricular infarct from coronary artery obstruction.

The purpose of the carotid artery examination is not to determine the size, composition, or shape of the ICA atheroma or the residual lumen diameter, and it is to predict whether therapy will provide benefit to the patient, either by reducing the chance of stroke or by improving cerebral function. Low BP in some cerebral arteries and restricted flow reserve to respond to the need for perfusion increases is likely to result in chronic regional cortical dysfunction as well as an increased chance of cerebral infarction.

Although the annual chance of stroke in elderly people is less than 1/1,000, the chance of impaired cognition is 1/20. Some impaired cognition is due to pressure reducing atherosclerotic stenosis in the extracranial or cerebral arteries, which can be improved by anti-atherosclerotic medical treatment. Convenient noninvasive quantitative measurements can be used to detect pressure reducing carotid stenosis and to monitor changes to enhance patient compliance with treatment.

In this report, the sensitivity of the three tests combined (OAr, CBr, arm-arm BP difference) to detect treatable pressure reducing carotid stenosis was only 30.3%; that value is low, compared to the expectation that a diagnostic test will have both a sensitivity and a specificity greater than 80% (35). The specificity for all three tests for treatable ICA stenosis cases and for ICA occlusion cases requiring caution is near 92%. In current medical practice, the positive predictive value of carotid contrast X-ray angiography predicting the chance of any stroke in 2 years in the ACAS study patients treated with medical care is (52/834 × 100% = 6.2%) (1). When considering the prevention of disabling stroke, some estimates report that 40 endarterectomies are needed to prevent one disabling stroke (36) [number needed to treat (NNT) =40].

Anti-atherosclerotic medical treatment (such as treatment with statins), which became popular after the ACAS trial is currently considered by some to be an effective alternative to anatomic carotid revascularization by CEA or STENT with equivalent long-term outcomes for the patient (37-39). Anatomic revascularization with stent was introduced after the ACAS trial. Stent revascularization has been shown to have outcomes equivalent to CEA by the Carotid Revascularization Endarterectomy vs. Stent (CREST) randomized trial (40).

Although elevated BP is correlated with atherosclerotic stenosis, the correlation does not prove that high BP causes atherosclerosis or that a pressure reducing atherosclerotic stenosis causes high BP. Pressure reducing renal artery stenosis is a recognized treatable cause of renovascular hypertension. An atheroma in the carotid bulb might affect the performance of baroreceptors at the carotid bulb. The group of examinations tabulated for this analysis is likely affected by survivorship bias: people with an isolated ICA because of missing segments of the coW, if the ICA becomes occluded, are likely to have a fatal ischemic stroke.

The OA continuous wave (CW) Doppler examination was described in 1974 in a pioneering work by Merrill Spencer, Jack Reid, and associates (23). OA Doppler has been used since then as part of the routine carotid examination protocol in cerebrovascular laboratories following the tradition of that CW Doppler mapping work. The carotid examination method invented by Gene Strandness, Don Baker, and Jack Reid in 1974 (41,42) combined carotid ultrasound B-mode imaging with pulsed Doppler and spectral waveform analysis. The laboratories following that tradition have not adopted OA measurements in that protocol. The OA direction measurement can be easily added to the conventional carotid duplex scan using the 5 MHz scan head commonly used for carotid examination (43). The ideal ultrasound frequency for Doppler of the OA is5 MHz balancing the exponential attenuation of ultrasound transmission through the eye with the Rayleigh scattering of ultrasound by OA blood. The measurement requires only 2 minutes of additional examination time. This examination is easy to learn (44,45). With a simple application specific ultrasonic directional Doppler, the OA examination could easily become part of the vital sign measurement protocol requiring no more skill or time than measuring BP or body weight. Although the number of cases of OAr indicating “clinically important” carotid artery stenosis in people over age 65 years is about 1% (46), so a primary care practice would find only a few cases of OAr per year, the finding has the potential to have high beneficial impact on the cases found.

In 2021, the USPSTF recommended against screening for carotid artery stenosis using ultrasonic carotid duplex scanning followed by confirmatory contrast X-ray angiography and carotid endarterectomy if justified (13,47). The United Kingdom National Screening Committee (UKNSC) and the European guidelines are similar (48,49). The USPSTF determined that screening for carotid stenosis resulted in more morbidity than not screening. The USPSTF recommendations strive to identify carotid stenosis anatomic severity and then speculate about the risk of embolization, rather than to identify cases of limited brain flow reserve plus those at highest risk of atheroemboli from carotid atheroma rupture. We recommend an alternative approach: (I) screening patients in primary care for OAr; (II) in cases with OAr, recommend a trial of medical therapy; (III) triage patients with persistent OAr to the conventional ultrasound evaluation; and (IV) anatomic treatment of persistent severe carotid stenosis. Neither the USPSTF recommendations nor this report considers cellular emboli or thromboemboli from the heart or paradoxical thromboemboli originating in the leg veins then crossing to the arterial system via a PFO.

In addition to the brain, other tissues rely on an adequate arterial pressure supply to allow the local regulation of perfusion as needed. In leg arteries, the measurement of the arterial supply pressure is easy with a BP cuff around the ankle; the measurement of individual pressures of the cerebral arteries is more difficult because they are encased within the incompressible skull. But the physiological principles are similar. In the lower extremity, two stages of arterial obstruction are considered: (I) exercise-induced hypotension leading to painful claudication; and (II) resting critical limb ischemia leading to tissue loss. These conditions are most often evaluated by measuring ankle BP at rest and after hyperemic flow is induced. Exercise can increase muscle flow by more than 10 times resting flow (50). Low ankle BP is most often caused by severe atherosclerotic stenosis of the femoral artery. Because the clinical consequences are obvious and the arterial pressure at the ankle is easily measured, the management of femoral artery stenosis rarely depends on the imaging measurement of %DR stenosis or evaluation of the content of the obstructing atheroma. In contrast, management of ICA stenosis usually depends on %DR. The presence or absence of collateral supply via the coW bypassing the ICA stenosis is rarely considered. OPG-Gee (2) based on ophthalmodynamometry has been used to directly measure the OA pressure and infer the distal ICA and MCA pressure. OPG-KM (3) has also been used to infer MCA hypotension, following untreated patients for subsequent stroke. Hyperemia-induced cerebral flow reserve is sometimes used for additional information about cerebral flow (51), but cerebral vasodilation by inducing hypercapnia increases flow by less than two times (52). The atheroma content is frequently evaluated by MRI tissue analysis (53), ultrasound echogenicity analysis (54) including intravascular contrast enhancement (55), or X-ray shadow analysis (56). We postulate that MCA hypotension can be easily evaluated by detecting OAr to identify patients at risk of cerebral dysfunction who can benefit from treatment.

Conclusions

OAr is an easily and quickly performed examination with high specificity for identifying ICA obstruction. Wide adoption of this measurement might serve to identify those patients most likely to benefit from carotid stenosis therapy by medical or surgical methods. The measurement is suitable for screening patients in primary care who might suffer from reversible vascular dementia due to MCA hypotension. Patients with regional MCA hypotension from arterial stenosis might become symptomatic when the systemic BP is reduced, or even when changing from supine to upright.

Limitations

The OA examinations in this report were conducted with specialized Doppler instruments by sonographers certified to perform these examinations. Patients in this data set were referred for testing based on clinical indications; thus, these patients are not representative of the general population or general elderly population. Perhaps these methods can be adopted in primary care by examiners with brief training and simple instruments to reduce the rate of stroke in the elderly population.

The Venturi/Bernoulli pressure drop computed values reported here are likely to be higher than the actual pressure drop present across the arterial stenosis. This report has used the carotid Doppler velocity measurements obtained at acute examination angles between the ultrasound beam and the direction of ICA flow (as is common practice in peripheral artery diagnosis), then adjusted for the angle of acquisition as viewed on the ultrasound image by the examiner. The adjustment achieved by dividing the measured value by the cosine of the examination angle often doubles the numeric value (1/cos60 =2). A factor of 2 in the Doppler equation results in a factor of 4 in computed pressure reduction (velocity squared). Because of normal helical laminar flow and turbulent flow in arteries, this “Doppler equation” method always results in higher velocities than the velocity component parallel to the artery axis upon which the Bernoulli equation was validated in patients (57,58). Of course, the pressure reduction in an arterial stenosis cannot be greater than the pressure available from the heart according to the Torricelli principle. The OA flow direction is not affected by this “Doppler angle” problem because the OA is interrogated at nearly zero degrees, parallel to the axis of the OA.

Multivariate analysis (59) was not used in this study with risk parameters for stroke such as: (I) contrast X-ray angiographic severity; (II) post-symptom X-ray angiographic atheroma irregularity (ulceration remaining after an embolic event); and (III) the nature and frequency of recent stroke-like events to predict risk of stroke: because the intent of this endeavor is to identify and treat patients before the first clinical event using simple direct indicators of regional cerebral ischemic/hypotensive risk. The noninvasive measures reported here can be effectively used individually and can easily be evaluated and repeated to encourage patients to comply with prevention programs (60) and also to evaluate medical treatment effectiveness in primary care.

Recommendations

1. Conventional duplex Doppler examinations should include waveforms from the OA noting the direction of flow as an indicator of periorbital collateral flow (61).

2. Measurement of OA flow direction should be added to the vital signs protocol for every patient over the age of 60 years old to identify those cases who likely have low BP in the MCA putting them at risk for impaired cognition and at risk for ischemic stroke. The examination can be done with a CW directional Doppler (62) with a directional display. Acquiring an instrument to perform the OA Doppler examination can also be useful for other patients in primary care. An instrument with a Doppler spectral waveform display is also useful for managing pre-eclampsia in pregnancy (63) and might be useful for managing patients with sickle cell disease (64).

3. Assessment of CBr is useful focusing at the highest level of the neck and the duration of the bruit sound (65) as well as the frequency (66) because a higher frequency indicates a smaller residual lumen diameter (500 Hz indicates 1 mm lumen diameter) (67,68).

4. Carotid Doppler stenosis reports should include a pulse oximetry measurement as a convenient indication of hypercapnia (69) which causes cerebral vasodilation and increased carotid artery velocities (70).

5. Carotid Doppler stenosis reports should include a note about cardiac arrhythmia because after a prolonged pause in ventricular contraction, the high cardiac ejection stroke volume causes a single high SBP pulse resulting in high carotid velocities putting excess mechanical strain (32) on any obstructing atheroma.

Supplementary

The article’s supplementary files as

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study (STUDY00023700) was evaluated by the University of Washington Institutional Review Board (WCG IRB Institution #55014) for research involving human subjects. The UWIRB has determined that this analysis does not involve “human subjects” as defined by federal regulations. It does not require exempt status, IRB review, or informed consent.

Data Sharing Statement

Available at https://atm.amegroups.com/article/view/10.21037/atm-25-66/dss

atm-13-05-54-dss.pdf ^{(75KB, pdf)}

DOI: 10.21037/atm-25-66