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ORIGINAL ARTICLE
Year : 2005  |  Volume : 53  |  Issue : 1  |  Page : 51-54

The effects of hematocrit and age on transcranial Doppler measurements in patients with recent ischemic stroke


1 Department of Neurology, Ankara University School of Medicine, Turkey
2 Osmangazi University School of Medicine, Turkey

Date of Acceptance01-Dec-2004

Correspondence Address:
Canan Togay Isikay
Ankara Tip Fakultesi, Ibni Sina Hastanesi, 6. kat 06100 Ankara
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.15055

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 » 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. AIM: This study assessed the effects of age and hematocrit on TCD measurements in patients with recent ischemic stroke compared to patients with non-vascular diseases. SETTINGS AND DESIGN: University Hospital, retrospective study. MATERIALS AND METHODS: TCD records and data files of 862 consecutive patients (mean age, 57±16 years) with various neurological diagnoses were reviewed retrospectively. The peak systolic, end diastolic and mean flow velocities (FV), systolic/diastolic ratios and pulsatility indices (PI) in the middle cerebral arteries were averaged and the effect of age and hematocrit values on these TCD values was studied. Independent samples t test, Pearson's coefficients of correlation, and linear regression test were used for statistical analysis. RESULTS: Among 862 patients, 413 were women (mean age, 53±17 years) and 449 were men (mean age, 60±13 years). Peak systolic and mean FV were higher and hematocrit concentration was lower in women compared to men (P<0.001). The relation of TCD velocities with age and hematocrit was more remarkable in the group of patients with non-vascular neurological disorders. PI values demonstrated a significant correlation to age (r=+0.47) (P<0.001), but did not change significantly with hematocrit level. CONCLUSIONS: It should be remembered that blood FV measured by TCD may be significantly affected by age and hematocrit level. However, there seems to be no significant association between TCD velocities and hematocrit in patients with a recent ischemic stroke.


Keywords: Transcranial Doppler, hematocrit, stroke


How to cite this article:
Isikay CT, Uzuner N, Gucuyener D, Ozdemir G. The effects of hematocrit and age on transcranial Doppler measurements in patients with recent ischemic stroke. Neurol India 2005;53:51-4

How to cite this URL:
Isikay CT, Uzuner N, Gucuyener D, Ozdemir G. The effects of hematocrit and age on transcranial Doppler measurements in patients with recent ischemic stroke. Neurol India [serial online] 2005 [cited 2020 Jan 25];53:51-4. Available from: http://www.neurologyindia.com/text.asp?2005/53/1/51/15055



 » Introduction Top


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 Top


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 Top


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 Top


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 Top

1.Brass LM, Pavlakis SG, DeVivo D, Piomelli S, Mohr JP. Transcranial Doppler measurements of the middle cerebral artery. Effect of Hematocrit. Stroke 1988;19:1466-9.  Back to cited text no. 1  [PUBMED]  
2.Grolimund P, Seiler RW. Age dependence of the flow velocity in the basal arteries: A transcranial Doppler ultrasound study. Ultrasound Med Biol 1988;14:191-8.  Back to cited text no. 2    
3.Vriens EM, Kraaier V, Musbach M, Wieneke GH, Van Huffelen AC. Transcranial pulsed Doppler measurements of blood velocity in the middle cerebral artery: Reference values at rest and during hyperventilation in healthy volunteers in relation to age and sex. Ultrasound Med Biol 1989;15:1-8.  Back to cited text no. 3  [PUBMED]  
4.Macko RF, Ameriso SF, Akmal M, Paganini-Hill A, Mohler JG, Massry SG, et al. Arterial oxygen content and age are determinants of middle cerebral artery blood flow velocity. Stroke 1993;24:1025-8.  Back to cited text no. 4  [PUBMED]  
5.Brown MM, Wade JPH, Marshall J. Fundamental importance of arterial oxygen content in the determination of cerebral blood flow in man. Brain 1985;108:81-93.  Back to cited text no. 5    
6.Doering TJ, Brix J, Schneider B, Rimpler M. Cerebral hemodynamics and cerebral metabolism during cold and warm stress. Am J Phys Med Rehab 1996;75:408-15.  Back to cited text no. 6  [PUBMED]  
7.Kuboyama T, Hori A, Sato T, Mikami T, Yamaki T, Ueda S. Changes in cerebral blood flow velocity in healthy young men during overnight sleep and while awake. Electroencephalography and Clin Neurophysiol 1997;102:125-31.  Back to cited text no. 7  [PUBMED]  
8.Klingelhofer J, Hajak G, Matzander G, Schulz-Varszegi M, Sander D, Ruther E, et al. Dynamics of cerebral blood flow velocities during normal human sleep. Clin Neurol Neurosurg 1995;97:142-8.  Back to cited text no. 8  [PUBMED]  [FULLTEXT]
9.Ameriso SF, Paganini-Hill A, Meiselman HJ, Fisher M. Correlates of middle cerebral artery blood velocity in the elderly. Stroke 1990;21:1579-83.  Back to cited text no. 9  [PUBMED]  
10.Arnolds BJ, von Reutern GM. Transcranial Doppler sonography. Examination technique and normal reference values. Ultrasound Med Biol 1986;12:115-23.  Back to cited text no. 10  [PUBMED]  
11.Tong DC, Albers GW. Normal values. In: Babikian VL, Wechsler LR, Toole JF, editors. Transcranial Doppler Ultrasonography. Butterworth Heinemann, 2nd Ed. New York: Raven Press; 1999. p. 34.  Back to cited text no. 11    
12.Hudak ML, Koehler RC, Rosenberg AA, Traystman RJ, Jones MD. Effect of hematocrit on cerebral blood flow. Am J Physiol 1986;251:H63-70.  Back to cited text no. 12    
13.Massih J, Tang YL, Hudak ML, Koehler RC, Traystman RJ, Jones MD Jr. Effect of hematocrit on cerebral blood flow with induced polycythemia. J Appl Physiol 1987;62:1090-6.  Back to cited text no. 13    
14.Fiermonte G, Aloe SMA, Latagliata R, Petti MC, Giacomini P. Polycythaemia vera and cerebral blood flow: A preliminary study with transcranial Doppler. J Int Med 1993;234:599-602.  Back to cited text no. 14    
15.Ameriso SF, Meiselman H, Saraj A, Fisher M. The effect of hemorheologic factors on middle cerebral artery blood flow velocity in young individuals. J Neuroimaging 1992;2:16-8.  Back to cited text no. 15    
16.Sohn YH, Kim GW, Kim JS. Do hematocrit and serum fibrinogen influence transcranial Doppler measurements? J Korean Med Sci 1997;12:405-8.  Back to cited text no. 16  [PUBMED]  [FULLTEXT]
17.Schuurman PR, Albrecht KW. Intraoperative changes of transcranial Doppler velocity: Relation to arterial oxygen content and whole-blood viscosity. Ultrasound Med Biol 1999;25:151-4.  Back to cited text no. 17  [PUBMED]  [FULLTEXT]


Figures

[Figure - 1], [Figure - 2]

Tables

[Table - 1], [Table - 2]

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