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Neurology India, Vol. 53, No. 1, January-March, 2005, pp. 51-54 Original Article The effects of hematocrit and age on transcranial Doppler measurements in patients with recent ischemic stroke Isikay CananTogay, Uzuner Nevzat, Gücüyener Demet, Özdemir Gazi Department of Neurology, Ankara University School of Medicine Code Number: ni05012 Abstract BACKGROUND: The effects of age and hematocrit on transcranial Doppler (TCD) velocities have not been evaluated in a large patient group with recent ischemic stroke. Key Words: Transcranial Doppler, hematocrit, stroke Introduction Transcranial Doppler (TCD) is a non-invasive, safe and easy method to measure blood flow velocities (BFV) in the basal cerebral arteries. It is widely used for the evaluation of patients with ischemic stroke, subarachnoid hemorrhage and sickle cell anemia. However, TCD measurements can be significantly affected by some individual and physiological factors. The major hemodynamic factors determining BFV in the basal cerebral arteries are the length and cross-sectional area of the vessel, pressure gradient along a vessel, and viscosity of the blood.[1] Other factors associated with cerebral BFV include age and sex of the subject,[2],[3] partial pressure of oxygen and carbon dioxide,[4],[5] body temperature,[6] and some physiological changes, such as sleeping or awakening and exercise.[7],[8]Previous reports demonstrated that age was associated with decreasing flow velocities and increasing pulsatility indices.[2],[3],[4],[9],[10] An average decline of 0.3-0.5% per year in the mean flow velocities (MFV) was suggested in the individuals between 20-70 years of age.[11] Hematocrit is the major determinant of blood viscosity, and cerebral blood flow was shown to be inversely correlated with the hematocrit level.[12],[13] These studies were followed by others performed with TCD in small patient groups.[1],[9],[14] The correlation of TCD parameters with hematocrit concentration has not been evaluated previously in a population with recent stroke. The aim of this study was to assess the influence of hematocrit level and age on TCD measurements in a larger group of patients with ischemic stroke or other non-vascular neurological disorders. Materials and Methods Complete data of the patients who were referred to the Neurovascular Laboratory between January 1996 and September 2001 were reviewed retrospectively (n:1500). Patients with complete TCD examination that was consisted of BFV in all basal brain vessels and performed on the day of performing blood tests were selected. Patients with evidence of cerebrovascular stenosis or intracranial hemorrhage, those with impaired consciousness, and those with known hematological disorders, heart failure, chronic obstructive pulmonary disease or other pulmonary diseases by history or physical examination were excluded. Patients with a significant difference (>50%) of flow velocities between two sides were also excluded. There were 862 records remaining for evaluation. A total of 638 patients were excluded due to missing data, incomplete evaluation and fulfillment of exclusion criteria.General epidemiological features, diagnoses, blood counts, and all imaging studies available in the patient records were reviewed. TCD examinations were performed in the Neurovascular Laboratory by the same author (Uzuner N, MD, Professor of Neurology), using 2-MHz pulsed-wave Doppler transducer and TCD scanner (DWL Multidop X4, TCD8 software). The average values for peak systolic (PSV), end diastolic (EDV) and mean flow velocities (MFV), pulsatility indices (PI) (peak velocity minus diastolic velocity divided by mean velocity), and systolic/diastolic (S/D) ratios in the middle cerebral arteries (insonated through the temporal window at a depth of 35-55 mm) were recorded. Patients were divided into two subgroups; Group 1 consisted of patients with recent ischemic stroke and Group 2 comprised patients with epilepsy, syncope, peripheral vertigo, demyelinative disease, and those with miscellaneous neurological symptoms or signs (ocular motor paresis, facial pain, ptosis etc.) but no defined diagnosis. We used Student′s t and Mann-Whitney U tests to compare age, TCD measurements and hematocrit levels between the two groups and sexes. Pearson′s and Spearman′s coefficients of correlations were used to determine the association between hematocrit, age and TCD parameters. P<0.05 was accepted as statistically significant. Results Among 862 patients (mean age, 57±16 years; range, 17 to 95 years), 413 were women (mean age, 53±17 years) and 449 were men (mean age, 60±13 years). Men were significantly older than women (P<0.001). Neurological diagnoses of the patients are shown in [Table - 1]. Ischemic stroke was the primary indication for neurovascular examination and was documented in 551 patients (64%). Hypertension, diabetes mellitus and smoking were present in 40.8%, 15.3% and 14.8% patients, respectively.Laboratory data and TCD measurements including the average values of PSV, EDV, MFV, PI levels and S/D ratios in the middle cerebral arteries (MCA) are shown in [Table - 2]. PSV and MFV were highly correlated (r=0.93, P<0.001), and MFV was inversely correlated with PI values (r=-0.45, P<0.001). PSV and MFV in the MCA were higher in women (P<0.001), while hematocrit concentrations were significantly lower in women compared to men (P<0.001) [Table - 2]. There was no significant association between age and hematocrit. The patients aged over 60 years had significantly lower flow velocities and higher PI values in the MCA compared to those who were younger in age (P<0.001) [Table - 2]. Age, TCD measurements, and hematocrit concentrations in the two groups are shown in [Table - 2]. The hematocrit concentration was not significantly different between the two groups. PI values were significantly higher in Group 1, while MFV were lower in Group 1 than in Group 2 (P<0.001). Statistical analyses revealed that MFV in the MCA has a weak inverse relation with hematocrit level (rho=-0.18), and a modest inverse relation with age (rho=-0.43) (both P<0.001). Age demonstrated a positive correlation with PI level in the MCA (rho=+0.55) (P<0.001). The inverse correlation between MFV and age was more notable in Group 2 (rho=-0.59) compared to Group 1 (rho=-0.33). MFV were also more influenced by hematocrit concentration in Group 2 (rho=-0.30) than in Group 1 (rho=-0.12). Pulsatility index and S/D were not significantly influenced by hematocrit level (P=0.09). By linear regression analysis, MFV in the MCA was 102.12+(-1.06xHct) and 88.22+(-0.54xAge) for patients in Group 2 (P<0.001) [Figure - 1], [Figure - 2]. Discussion The women in our study population had significantly lower hematocrit levels, which was the probable cause of increased flow velocities compared with men. It is important to note that there was no significant association between age and hematocrit.In this study, BFV were inversely related with age, and distal resistance was higher in the older individuals (>60 years of age) than those aged <60 years. Age was the only variable that demonstrated a significant correlation to PI, and the strongest inter-individual velocity predictor that was independent of hematocrit concentration. These results are in concordance with the study of Macko et al showing an inverse relation between age and MCA velocities, and a positive correlation of age to PI.[4] Lower MFV and higher PI level in Group 1 can also be explained with the higher mean age of the patients in this group. A relation between blood viscosity and TCD velocities in the MCA was also reported in previous studies but in smaller patient groups.[1],[9],[14],[15],[16],[17] Brass et al evaluated the effects of hematocrit on TCD-measured BFV in the MCA of 45 patients and showed higher flow velocities in patients with lower hematocrit levels (r=-0.71).[1] Ameriso et al evaluated 42 healthy volunteers and reported a modest inverse relationship between hematocrit level and TCD measured-MFV in the MCA (r=-0.42).[9] Fiermonte et al showed that TCD velocities in patients with polycythemia vera increased significantly after pharmacological and/or phlebotomic treatment.[14] The inverse relation of BFV with hematocrit can be best explained with the relation of hematocrit to blood viscosity and arterial oxygen content.[9] In this study, a modest inverse correlation was found between hematocrit level and TCD velocities in patients with non-vascular neurological disorders. However, TCD velocities in patients with a recent ischemic stroke were not affected by hematocrit significantly. The relation of TCD velocities with age was also more notable in patients with non-vascular neurological disorders than the others. We think that the lesser impact of hematocrit level and age on TCD velocities in patients with a recent ischemic stroke may be due to impaired autoregulation of the cerebral vessels. Transcranial Doppler of the basal cerebral arteries is widely used to evaluate the patients with subarachnoid hemorrhage, sickle cell anemia, and intracranial hypertension. TCD analysis in these patients may become challenging if they have significant anemia or polycythemia. Increased TCD velocities compatible with moderate to severe vasospasm might be mimicked by significant anemia. On the other hand, normal flow velocities in patients with polycythemia can be interpreted falsely negative. Our observations indicate that corrections of TCD velocities may be required for elderly patients and for patients with significant anemia or polycythemia. However, a similar correction does not seem to be necessary in patients with ischemic stroke. References
Copyright 2005 - Neurology India The following images related to this document are available:Photo images[ni05012t1.jpg] [ni05012t2.jpg] [ni05012f2.jpg] [ni05012f1.jpg] |
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