Cuff Test Research Articles

Continuous cerebral autoregulation monitoring by improved cross-correlation analysis: comparison with the cuff deflation test

To improve the cross-correlation method for noninvasive, continuous monitoring of cerebral autoregulation, to evaluate this method in humans with intact and impaired autoregulatory capacity, and to compare it to the cuff deflation test. Prospective study in the intensive care unit of a university hospital. Fourteen patients with severe head injury, six patients with subarachnoid hemorrhage, and nine healthy volunteers. Middle cerebral artery flow velocities and arterial blood pressure were monitored continuously. Aaslid's thigh cuff tests were performed and results were scored using Tiecks' model for autoregulation index. Data were then collected without any patient manipulation. The mean time delay between slow spontaneous oscillations of blood pressure and middle cerebral artery flow velocity was calculated by cross-correlation analysis. Data are expressed as median (lower/upper quartile). Healthy subjects had a higher autoregulation index than patients, 5.0 (5.0/5.5) vs. 3.3 (2.0/4.5). Slow oscillations of blood pressure and middle cerebral artery flow velocity showed a time delay of -2.0 s (-2.7/-1.7) in healthy subjects but were almost synchronal in patients, -0.07 s (-0.5/0.45). Inter-method agreement in diagnosing an intact or impaired cerebral autoregulation was obtained in 108 of 147 examinations of autoregulation (73.5%) and was considered moderate. Cross-correlation analysis may serve as a simple, noninvasive, and continuous measure of cerebral autoregulation. The time delay of -2.0[Symbol: see text]s in healthy subjects is in good agreement with other studies. Short-term autoregulation tests and monitoring techniques based on slow spontaneous oscillations should not be used interchangeably.

Predicting the Outcome of Prostatectomy Using Noninvasive Bladder Pressure and Urine Flow Measurements

ObjectivesTo determine whether categorisation of bladder outlet obstruction (BOO) using measurements of bladder pressure and urine flow obtained by a novel noninvasive medical device (the penile cuff test) improves prediction of outcome from endoscopic prostatectomy (TURP). MethodsA consecutive cohort of 208 men undergoing TURP following standard assessment in our institution was recruited, and 179 (86%) completed the protocol. Each subject underwent a penile cuff test prior to surgery; outcome was assessed by change in IPSS at 4 mo. The proportion of men with good outcome (>50% reduction in IPSS) was compared according to categorisation by noninvasive bladder pressure and urine flow measurements. ResultsThe cuff test was completed by 93% of men with 2% experiencing an adverse event. Men categorised as having BOO by the test (37% of total) had an 87% chance of a good outcome from TURP (p<0.01), whilst of those deemed not obstructed (19% of total) 56% experienced good outcome (p<0.01). For the remaining men not categorised in these two groups, 77% had good outcome, which was identical to the result of the cohort as a whole (77%, p=NS). ConclusionsUrodynamic categorisation using measurements obtained by the noninvasive penile cuff test improves prediction of outcome for men with LUTS undergoing TURP. This finding together with the ease and acceptability of the test suggest its suitability for office-based clinical use to assist men and their physicians in the selection for surgical treatment for relief of LUTS.

EFFECTS OF ENALAPRIL ON ENDOTHELIUM FUNCTION IN PATIENTS WITH ISCHEMIC HEART DISEASE

Aim. To study endothelium vasomotor function (EF) in patients with ischemic heart disease (IHD) and the influence of angiotensin converting enzyme inhibitor enalapril (Enam, Dr .Reddy’s, India) on it. Material and methods. 87 patients were examined totally. 49 patients were suffering from IHD: 18 patients were younger than 60 years old and 31 patients were older . The combination of arterial hypertension (HT) and IHD were registered in 38 patients: 18 patients were below and 20 patients were above 60 years old. All patients additionally to basic IHD therapy took enalapril in dose 2,5-30 mg/daily during 12 weeks. Before the beginning and in the end of treatment cuff test, test with nitroglycerine, bicycle exercise test and Holter monitoring were made, the thickness of intima-media complex of carotid artery and the level of endothelin-1 in blood plasma were defined. Results. EF disorders were shown in IHD, maximal disorders were determined in patients with combination of IHD and HT. EF disorders were also more expressive in patients of elder group. Enalapril restored of cuff tests results, nitroglycerine tests results, reduced a number of myocardial ischemia episodes and provided target blood pressure in 60, 5% patients with HT. Conclusion. Enalapril improves endothelium vasomotor function, endothelium reaction on nitroglycerine and clinical course of IHD and HT.

COMPARISON OF EFFECTS OF ENALAPRIL AND UNCONTROLLED ANTIHYPERTENSIVE THERAPY ON INSULIN RESISTANCE, ENDOTHELIUM FUNCTION, MARKERS OF INFLAMMATION AND PLATELET ACTIVITY IN PATIENTS WITH METABOLIC SYNDROME

Aim. To assess influence of enalapril and uncontrolled antihypertensive therapy on insulin resistance, endothelium function, markers of inflammation, and platelet activity in patients with metabolic syndrome (MS). Material and methods. 41 patients with MS (21 women and 20 men, aged 58±2 years) were included into open parallel controlled study. MS was defined according to III report of USA Educational Program on cholesterol (2001). Patients were divided into 2 groups. Patients of the 1st group received enalapril (Enam, Dr. Reddy’s) 10 mg daily with further dose titration to 20 mg daily. Patients of the 2nd group continued receiving the same antihypertensive therapy as before (15% - inhibitors of angiotensin converting enzymes, 15% - в-blockers, 15% - diuretics, and 20% of patients - combined therapy). Study duration was 12 weeks. Results. Therapy with enalapril during 3 months resulted into significant decrease in systolic and diastolic blood pressure (BP) by 13 and 9% respectively. BP level decreased insignificantly (by 4,5 and 2% respectively) in controlled group. Ratio of plasma concentration of glucose to insulin in the 1st group increased by 14% before glucose load, and by 25% (p&lt;0,05) 2 hours after peroral glucose load, while in the 2nd group decrease in these figures was noted by 12 and 5% respectively. This shows that treatment with enalapril, unlike uncontrolled antihypertensive therapy, lead to decrease in insulin resistance. Cuff test revealed significant increase in growth of brachial artery diameter in the group of patients, who received enalapril (12% before treatment, and 17% after treatment). Regular antihypertensive therapy didn’t change this parameter significantly (13 and 13,8% respectively). C-reactive protein level decreased by 48% (p&lt;0,05) in the 1st group. Insignificant increase of this marker’s level was observed in the 2nd group. Platelet functional activity in both groups didn’t change significantly. Conclusion. Together with strong antihypertensive effect, enalapril monotherapy is more efficient than regular antihypertensive therapy in reducing insulin resistance and chronic subclinical inflammation, as well as it has priority in improving endothelium depending vasodilatation.

Evaluierung verschiedener Messprotokolle für die Leg-cuff-Methode zur Messung der dynamischen zerebralen Autoregulation

Aaslid's leg cuff method is a well validated technique to measure dynamic cerebral autoregulation. In the literature different protocols to choose cuff pressure have been described. The aim of this study is to find a technique as accurate as possible without un-necessary inconvenience for the patient. The leg cuff test with bilateral cuffs was performed on 10 young healthy volunteers with three different protocols (cuff pressure at systolic level, doppler controlled and 30 mmHg above systolic level). For each examination the autoregulation index invented by Tiecks and Mahony was calculated. Statistical modelling of correlated data was done with Generalized Estimating Equations. The choice of the protocol influences the quality of the actual autoregulation test. The most reliable protocol is also the most inconvenient one for the patient. We found no systematic bias of the protocol on the autoregulation index, but the relation between induced blood pressure drop and resulting autoregulation index was close to statistical significance. For the leg cuff test with bilateral cuffs in awake patients we recommend to apply the protocol proposed by Tiecks. Additional report of the magnitude of induced blood pressure drop would be helpful to improve the results' comparability.

NONINVASIVE ASSESSMENT OF BLADDER CONTRACTILITY IN MEN

Preoperative assessment of detrusor function by pressure flow study (PFS) improves outcome from prostatectomy but is invasive and uncomfortable for the patient. We report on a large scale validation of a novel noninvasive assessment of detrusor contractility. A flexible cuff placed around the penis was inflated automatically during voiding until flow interruption. Cuff pressure at interruption (pcuff.int) reflects isovolumetric bladder pressure (pves.isv), a measure of detrusor contractility. For comparison 151 symptomatic men performed the cuff test with simultaneous PFS monitoring. Test/retest agreement was assessed in 91 subjects who performed a cuff test without PFS on 2 occasions. For the 117 (77%) subjects with an acceptable cuff pressure flow trace, Bland Altman analysis showed that pcuff.int overestimated pves.isv by a mean (s.d.) of 16.4 (27.5) cm H2O, predominantly due to the cuff being positioned below the bladder. For test/retest analysis 52 (57%) of the men who were able to attend twice provided acceptable cuff data on both occasions with a mean (s.d.) difference in pcuff.int of -3.3 (32.0) cm H2O, improving to 0.0 (20.3) cm H2O in a subgroup of 39 subjects who voided more than 150 ml. On questionnaire assessment 121 (80%) subjects preferred the cuff test to PFS. The cuff test gives a valid and reproducible estimate of isovolumetric bladder pressure in a manner acceptable to patients, although test failure and variability of agreement require improvement. The test may be of value in the assessment of urinary symptoms and may aid in patient selection for prostatectomy.

Inter-observer agreement in the estimation of bladder pressure using a penile cuff.

Objective data are useful in quantifying a patient's lower urinary tract symptoms (LUTS). We are investigating the use of an inflatable penile cuff to obstruct flow progressively during voiding, and thereby determine the pressure p(cuff,int) at which flow is interrupted. The aim of this study was to determine the agreement between experienced observers in their estimates of p(cuff,int). We recorded 486 cuff inflation cycles during 142 voids from 42 subjects recruited from urology out-patient's and prostate assessment clinics. Each inflation cycle was assessed independently by three experienced observers, a total of 1,458 ratings. According to our standard assessment procedure, the observers (i) indicated whether the inflation should be analyzed, (ii) estimated p(cuff,int) for those inflation cycles judged suitable for analysis, and (iii) discarded measurements that were clearly inconsistent with others from the same voiding cycle. Overall, 689 of the 1,458 ratings (45%) were excluded, with just 4% of all ratings discarded for inconsistency. For 385 of the 486 inflation cycles (79%) there was complete agreement that the cycle should or should not be analyzed. Thereafter, for the 262 inflation cycles analyzed by two or three observers, the overall SD error in measurements of p(cuff,int) was 4.6 cm H(2)O. We conclude that there is good agreement between experienced observers in their interpretation of data from the cuff test. For practical purposes, there is no need for multiple observers in the clinical application of the cuff method.

A review of the special tests associated with shoulder examination. Part I: the rotator cuff tests.

Careful examination of the shoulder is an essential component in forming a diagnosis of problems in this area. A number of tests have been described that are claimed to improve diagnostic accuracy by specifically examining one component of the shoulder complex. Many of these tests are eponymous, and there is confusion about not only how to perform them but also what conclusion to draw from the results. This article attempts to clarify the tests used to examine the rotator cuff by presenting them as described by the original authors with the additional aim of providing a source for those wishing to refresh their knowledge without the need to refer to the original source material.

Peak Systolic Velocity Doppler Index Reflects Most Appropriately the Dynamic Time Course of Intact Cerebral Autoregulation

Background: Transcranial Doppler sonography measures blood flow velocity in basal cerebral vessels with high accuracy and time resolution. Dynamic blood flow tests were used to investigate functional integrity of the cerebral autoregulation (CA) mechanism. It is known from cortical activation studies that velocity indices differ in their appropriateness to measure changes in blood flow velocity. We aimed to compare the peak systolic, enddiastolic and time-averaged mean flow velocity indices for their use in measuring the effectiveness of the CA mechanism. Methods: We performed the leg cuff test to induce in 15 healthy volunteers (aged 24.8 ± 0.4 years, 9 males) CA due to a sudden arterial blood pressure decrease. Data from the middle and posterior cerebral arteries were measured continuously with transcranial Doppler ultrasound, and the arterial blood pressure with a noninvasive photoplethysmographic method. After transforming all variables to relative changes, velocity-pressure diagrams were calculated for each velocity-pressure index. Additionally, we calculated the autoregulation index. Results: The step decrease in arterial blood pressure resulted in an initial drop, which is followed by a rapid recovery of cerebral blood flow velocity. The autoregulation index was 5.5 ± 1. Efficacy of CA is illustrated more accurately by peak systolic velocity-pressure curves, which lie continuously above a passive velocity-pressure relationship assuming CA to be absent. Conclusions: Our data show peak systolic blood flow velocity index to be most accurate for measuring effectiveness of the dynamic CA mechanism. No differences in the CA were found between the vascular territory of the middle and posterior cerebral arteries.

Cerebral Autoregulation in Middle Cerebral Artery Territory Precedes That of Posterior Cerebral Artery in Human Cortex

Objective: Cerebral autoregulation tends to compensate changes in arterial blood pressure. This mechanism of cerebral blood flow regulation appears to be insufficient in orthostatic dysregulation in which mainly vertebrobasilar symptoms occur. To investigate this hypothesis, we compared cerebral autoregulation in the vascular territory of the carotic and vertebrobasilar vessel system using a leg cuff test to induce a drop in cerebral perfusion pressure. Methods: We measured blood flow velocity in 10 healthy young volunteers (aged 26.7 ± 0.3 years, 7 male) simultaneously in the middle and posterior cerebral artery with transcranial Doppler sonography. A leg cuff test was used to induce a sudden decrease in arterial blood pressure. Arterial blood pressure was measured with a non-invasive photoplethysmographic method. The averaged relative blood flow velocity changes due to the pressure step were compared between both vessel territories. Results: After cuff release systolic (diastolic) blood flow velocity increased with a latency of 1.1 ± 0.3 s (1.8 ± 0.4 s). Due to a smaller decrease and identical time courses cerebral blood flow velocity recovery in the posterior cerebral artery precedes blood flow recovery in the middle cerebral artery by 0.9 ± 0.3 s. Discussion: Cerebral autoregulation in the carotid and vertebrobasilar system does not differ in the time course of the blood flow velocity recovery. Due to a smaller decrease in blood flow velocity recovery in the posterior cerebral artery precedes recovery in the middle cerebral artery by nearly 1 s.

The influence of nitroglycerin and prostaglandin E1 on dynamic cerebral autoregulation in adult patients during propofol and fentanyl anaesthesia.

We investigated dynamic cerebral autoregulation in 24 normocapnic adult patients during propofol and fentanyl anaesthesia. Hypotension was induced, to a mean arterial pressure (MAP) of 60-65 mmHg, using nitroglycerin or prostaglandin E1. Time-averaged mean cerebral blood flow velocity in the right middle cerebral artery was measured continuously using transcranial Doppler sonography. Dynamic autoregulatory response was activated by a sudden decrease in MAP following release of bilateral thigh cuffs (thigh cuff test) and evaluated as a dynamic rate of autoregulation (dRoR in % x s(-1)). The cuff test was repeated to obtain two values of dRoR during baseline and during induced hypotension; the data were then averaged. The mean value of dRoR during baseline and during induced hypotension was 14.2 (2.9) and 14.2 (1.6) % x s(-1), respectively, in the nitroglycerin group, and 14.6 (2.6) and 14.4 (2.4) % x s(-1), in the prostaglandin E1 group. We were unable to demonstrate significant between- or within-group differences in dRoR. Thus, we conclude that nitroglycerin and prostaglandin E1 do not attenuate dynamic cerebral autoregulation.

The influence of nitroglycerin and prostaglandin E1 on dynamic cerebral autoregulation in adult patients during propofol and fentanyl anaesthesia*

We investigated dynamic cerebral autoregulation in 24 normocapnic adult patients during propofol and fentanyl anaesthesia. Hypotension was induced, to a mean arterial pressure (MAP) of 60–65 mmHg, using nitroglycerin or prostaglandin E1. Time‐averaged mean cerebral blood flow velocity in the right middle cerebral artery was measured continuously using transcranial Doppler sonography. Dynamic autoregulatory response was activated by a sudden decrease in MAP following release of bilateral thigh cuffs (thigh cuff test) and evaluated as a dynamic rate of autoregulation (dRoR in %.s−1). The cuff test was repeated to obtain two values of dRoR during baseline and during induced hypotension; the data were then averaged. The mean value of dRoR during baseline and during induced hypotension was 14.2 (2.9) and 14.2 (1.6) %.s−1, respectively, in the nitroglycerin group, and 14.6 (2.6) and 14.4 (2.4) %.s−1, in the prostaglandin E1 group. We were unable to demonstrate significant between‐ or within‐group differences in dRoR. Thus, we conclude that nitroglycerin and prostaglandin E1 do not attenuate dynamic cerebral autoregulation.

ANTERIOR SUPERIOR INSTABILITY WITH ROTATOR CUFF TEARING: SLAC LESION

Anterosuperior instability of the shoulder may occur from a variety of pathologic lesions. We describe a specific entity, the SLAC (superior labrum, anterior cuff) lesion that involves an association of anterior-superior labral tear with a partial supraspinatus tear. We retrospectively isolated a group of 40 patients with this lesion. The presenting complaints, physical examination findings, surgical findings, and results were isolated. Overhead activities were the most common etiology; load and shift instability testing and whipple rotator cuff testing were the most common physical examination findings. Surgical repair was successful in 37 of the 40 patients. The SLAC lesion is a definable clinical entity with predictable history, examination, surgical pathology, and satisfactory results from surgery.

Cerebral blood flow velocity response to induced and spontaneous sudden changes in arterial blood pressure

The influence of different types of maneuvers that can induce sudden changes of arterial blood pressure (ABP) on the cerebral blood flow velocity (CBFV) response was studied in 56 normal subjects (mean age 62 yr, range 23-80). ABP was recorded in the finger with a Finapres device, and bilateral recordings of CBFV were performed with Doppler ultrasound of the middle cerebral arteries. Recordings were performed at rest (baseline) and during the thigh cuff test, lower body negative pressure, cold pressor test, hand grip, and Valsalva maneuver. From baseline recordings, positive and negative spontaneous transients were also selected. Stability of PCO2 was monitored with transcutaneous measurements. Dynamic autoregulatory index (ARI), impulse, and step responses were obtained for 1-min segments of data for the eight conditions by fitting a mathematical model to the ABP-CBFV baseline and transient data (Aaslid's model) and by the Wiener-Laguerre moving-average method. Impulse responses were similar for the right- and left-side recordings, and their temporal pattern was not influenced by type of maneuver. Step responses showed a sudden rise at time 0 and then started to fall back to their original level, indicating an active autoregulation. ARI was also independent of the type of maneuver, giving an overall mean of 4.7 +/- 2.9 (n = 602 recordings). Amplitudes of the impulse and step responses, however, were significantly influenced by type of maneuver and were highly correlated with the resistance-area product before the sudden change in ABP (r = -0.93, P < 0.0004). These results suggest that amplitude of the CBFV step response is sensitive to the point of operation of the instantaneous ABP-CBFV relationship, which can be shifted by different maneuvers. Various degrees of sympathetic nervous system activation resulting from different ABP-stimulating maneuvers were not reflected by CBFV dynamic autoregulatory responses within the physiological range of ABP.

Neurovascular coupling and cerebral autoregulation can be described in terms of a control system

Neurovascular coupling and cerebral autoregulation are important and fast mechanisms for maintaining an adequate blood supply to the brain. It was suggested that both mechanisms follow a common control system. The aim of our study was to describe neurovascular coupling and cerebral autoregulation in mathematical terms of a control system and to test the aforementioned hypothesis. We analyzed the input-output dynamics of neurovascular coupling (flicker light test) and cerebral autoregulation (leg cuff test) in terms of a control system, and compared both systems. A transcranial Doppler device was used to measure continuously the blood flow velocity changes in young healthy volunteers who lacked vascular risk factors. For both tests, a control system model with only four parameters was sufficient to allow the vascular reaction to be described in all (rate time, undamped natural angular frequency, attenuation, gain). All parameters were identical for both control systems, except for gain, which is not directly comparable because, in the flicker light test, input function was not measured but assumed as a unit step function in each volunteer. This new method permits description of the regulation of cerebral blood flow using a control loop with four parameters. For the first time, these parameters allowed a demonstration that cerebral autoregulation and neurovascular coupling could be governed by the same control system. (E-mail: Manfred.Kaps@Neuro.med.uni-Giessen.de)

Anterior superior instability with rotator cuff tearing: slac lesion

Anterosuperior instability of the shoulder may occur from a variety of pathologic lesions. We describe a specific entity, the SLAC (Superior labrum, anterior cuff) lesion that involves an association of anterior-superior labral tear with a partial supraspinatus tear. We retrospectively isolated a group of 40 patients with this lesion. The presenting complaints, physical examination findings, surgical findings, and results were isolated. Overhead activities were the most common etiology; load and shift instability testing and whipple rotator cuff testing were the most common physical examination findings. Surgical repair was successful in 37 of the 40 patients. The SLAC lesion is a definable clinical entity with predictable history: examination, surgical pathology, and satisfactory results from surgery.

The continuous assessment of cerebrovascular reactivity: a validation of the method in healthy volunteers.

Using transcranial Doppler ultrasonography, we investigated the moving correlation between slow waves in arterial blood pressure (ABP) and blood flow velocity (FV) at different levels of cerebrovascular vasodilation provoked by changing PETCO2. Fourteen healthy volunteers were examined. The FV in middle cerebral arteries, PETCO2, and ABP were recorded during normocapnia, hypercapnia, and hypocapnia. The moving correlation coefficients between ABP and mean FV (FVm) or systolic FV (FVs) during spontaneous fluctuations in ABP were calculated for 3-min epochs and averaged for each investigation, thus yielding the mean index (Mx) and systolic index (Sx). As a reference method, Aaslid's cuff tests were performed to obtain the rate of regulation (RoR). RoR, Mx, and Sx significantly depended on PETCO2 (analysis of variance, P < 0.00001). At high PETCO2, cerebrovascular reactivity was disturbed as reflected in RoR values of < 0.17/s for all volunteers and increased values of Mx (> 0.4 in 86% of volunteers) and Sx (> 0.2 in 79% of volunteers). Overall, there was a reasonably good correlation of both Mx and Sx with RoR (R2 = 0.65 and 0.58, respectively). Indices derived from the correlation between spontaneous fluctuations of blood flow velocity wave form and arterial blood pressure may be used for the noninvasive continuous monitoring of cerebrovascular reactivity.

The Continuous Assessment of Cerebrovascular Reactivity: A Validation of the Method in Healthy Volunteers

Using transcranial Doppler ultrasonography, we investigated the moving correlation between slow waves in arterial blood pressure (ABP) and blood flow velocity (FV) at different levels of cerebrovascular vasodilation provoked by changing PETCO2. Fourteen healthy volunteers were examined. The FV in middle cerebral arteries, PETCO2, and ABP were recorded during normocapnia, hypercapnia, and hypocapnia. The moving correlation coefficients between ABP and mean FV (FVm) or systolic FV (FVs) during spontaneous fluctuations in ABP were calculated for 3-min epochs and averaged for each investigation, thus yielding the mean index (Mx) and systolic index (Sx). As a reference method, Aaslid’s cuff tests were performed to obtain the rate of regulation (RoR). RoR, Mx, and Sx significantly depended on PETCO2 (analysis of variance, P< 0.00001). At high PETCO2, cerebrovascular reactivity was disturbed as reflected in RoR values of <0.17/s for all volunteers and increased values of Mx (>0.4 in 86% of volunteers) and Sx (>0.2 in 79% of volunteers). Overall, there was a reasonably good correlation of both Mx and Sx with RoR (R2 = 0.65 and 0.58, respectively). Implications Indices derived from the correlation between spontaneous fluctuations of blood flow velocity wave form and arterial blood pressure may be used for the noninvasive continuous monitoring of cerebrovascular reactivity.

Linear and nonlinear analysis of human dynamic cerebral autoregulation.

The linear dynamic relationship between systemic arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) was studied by time- and frequency-domain analysis methods. A nonlinear moving-average approach was also implemented using Volterra-Wiener kernels. In 47 normal subjects, ABP was measured with Finapres and CBFV was recorded with Doppler ultrasound in both middle cerebral arteries at rest in the supine position and also during ABP drops induced by the sudden deflation of thigh cuffs. Impulse response functions estimated by Fourier transfer function analysis, a second-order mathematical model proposed by Tiecks, and the linear kernel of the Volterra-Wiener moving-average representation provided reconstructed velocity model responses, for the same segment of data, with significant correlations to CBFV recordings corresponding to r = 0.52 +/- 0.19, 0.53 +/- 0.16, and 0.67 +/- 0.12 (mean +/- SD), respectively. The correlation coefficient for the linear plus quadratic kernels was 0.82 +/- 0.08, significantly superior to that for the linear models (P < 10(-6)). The supine linear impulse responses were also used to predict the velocity transient of a different baseline segment of data and of the thigh cuff velocity response with significant correlations. In both cases, the three linear methods provided equivalent model performances, but the correlation coefficient for the nonlinear model dropped to 0.26 +/- 0.25 for the baseline test set of data and to 0.21 +/- 0.42 for the thigh cuff data. Whereas it is possible to model dynamic cerebral autoregulation in humans with different linear methods, in the supine position a second-order nonlinear component contributes significantly to improve model accuracy for the same segment of data used to estimate model parameters, but it cannot be automatically extended to represent the nonlinear component of velocity responses of different segments of data or transient changes induced by the thigh cuff test.

Assessment of cerebral autoregulation using carotid artery compression.

A simple method of testing cerebral autoregulation by observing transcranial Doppler changes in middle cerebral artery flow velocity (FV) during a brief ipsilateral carotid artery compression (the transient hyperemic response test) was studied in 11 normal healthy volunteers. The aim of this study was to assess the reliability of the method and to compare derived autoregulatory indices with those of a standard noninvasive test of autoregulation, Aaslid's leg-cuff test. Volunteers were subjected to repeated carotid compressions and leg-cuff tests at different levels of CO2. Hypercapnia was induced using inhalation of a mixture of 5% CO2 in air. Hypocapnia was induced by moderate hyperventilation. To assess the influence of the duration of carotid compression, a series of carotid compressions lasting 3, 4, 5, 7, and 9 seconds were performed in random sequence. Monitored parameters included ipsilateral FV, end-tidal CO2, and arterial blood pressure. The transient hyperemic response ratio (THRR), calculated as the maximum increase of FV divided by baseline values after release of the carotid compression, was taken as the autoregulation index. This index was compared with the rate of autoregulation index derived from the leg-cuff test. Both tests were significantly associated with end-tidal CO2 (ANOVA, P < .000001 for both carotid compression and cuff test). There was a linear correlation between THRR and autoregulation index (r = .86). However, the reproducibility of the THRR was more consistent than for the autoregulation index from single tests (13% versus 46%, respectively; P < .0001). Although the influence of the duration of carotid compression on THRR values was significant for carotid compressions lasting up to 5 seconds, there was no relation to the relative magnitude of FV drop during the compression. Brief (> 5 seconds) carotid artery compression provides an index of cerebral autoregulation that is reproducible and is affected by CO2 tension in a fashion similar to autoregulatory indices derived from a standard leg-cuff test. The simplicity of the method provides a potentially useful addition to other noninvasive autoregulation tests for clinical assessments, particularly when repeated measurements are required.