Changes in linear dynamics of cerebrovascular system after severe traumatic brain injury

Universität des Saarlandes, Saarbrücken, Saarland, Germany
Stroke (Impact Factor: 6.02). 05/2003; 34(5):1197-202. DOI: 10.1161/01.STR.0000068409.81859.C5
Source: PubMed

ABSTRACT We sought to describe the dynamic changes in the cerebrovascular system after traumatic brain injury by transfer function estimation and coherence.
In 42 healthy volunteers (mean+/-SD age, 37+/-17 years; range, 17 to 65 years), spontaneous fluctuations of middle cerebral artery blood flow velocity and of finger blood pressure (BP) were simultaneously recorded over a period of 10 minutes under normocapnic and hypocapnic conditions to generate normative spectra of coherence, phase shift, and gain over the frequency range of 0 to 0.25 Hz. Similar recordings were performed in 24 patients with severe traumatic brain injury (Glasgow Coma Scale score <or=8; mean+/-SD age, 50+/-20 years) serially on days 1, 3, 5, and 8 after trauma. Cranial perfusion pressure was kept at >70 mm Hg. Each blood flow velocity/BP recording was related to the presence or absence of middle cerebral artery territory brain parenchyma lesions on cranial CT performed within a close time frame.
In controls, hypocapnia decreased coherence (0.0 to 0.20 Hz), increased phase shift (0.0 to 0.17 Hz), and decreased gain in the frequency range of 0.0 to 0.11 Hz but increased gain at frequencies of 0.20 to 0.25 Hz (P<0.01 for all frequency ranges reported). In patients with traumatic brain injury, 102 investigations were possible. Compared with controls, coherence was increased in the frequency range <0.03 Hz and between 0.13 and 0.25 Hz in both normocapnia and hypocapnia, irrespective of the CT findings. Gain was unchanged in normocapnia and in the absence of a CT lesion. Gain was decreased in hypocapnia at frequencies >0.12 Hz irrespective of the presence/absence of a CT lesion. Phase shift decreased rapidly between 0.06 and 0.13 Hz under hypocapnic conditions and under normocapnic conditions in the presence of a CT lesion (P< 0.01).
Use of spontaneous fluctuations of blood flow velocity and BP to assess the cerebrovascular system dynamically requires consideration of the Paco2 level. In different conditions, including severe traumatic brain injury, the cerebrovascular system behaves linearly only in parts of the investigated frequency range.

Download full-text


Available from: Martin Müller, Jan 20, 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Acute hypoxia directly causes cerebral arteriole vasodilation and also stimulates peripheral chemoreceptors to change autonomic neural activity. These changes may alter cerebral vascular modulation. We therefore hypothesized that dynamic cerebral autoregulation would be altered during acute exposure to hypoxia. Fifteen healthy men were examined under normoxic (21%) and hypoxic conditions. Oxygen concentrations were decreased in stepwise fashion to 19%, 17%, and 15%, for 10 mins at each level. Mean blood pressure (MBP) in the radial artery was measured via tonometry, and cerebral blood flow velocity (CBFV) in the middle cerebral artery was measured by transcranial Doppler ultrasonography. Dynamic cerebral autoregulation was assessed by spectral and transfer function analysis of beat-by-beat changes in MBP and CBFV. Arterial oxygen saturation decreased significantly during hypoxia, while end-tidal CO2 and respiratory rate were unchanged, as was steady-state CBFV. With 15% O2, very-low-frequency power of MBP and CBFV variability increased significantly by 185% and 282%, respectively. Moreover, transfer function coherence (21% O2, 0.46+/-0.04; 15% O2, 0.64+/-0.04; P=0.028) and gain (21% O2, 0.61+/-0.05 cm/secs/mm Hg; 15% O2, 0.86+/-0.08 cm/secs/mm Hg; P=0.035) in the very-low-frequency range increased significantly by 53% and 48% with 15% O2, respectively. However, these indices were unchanged in low- and high-frequency ranges. Acute hypoxia thus increases arterial pressure oscillations and dependence of cerebral blood flow (CBF) fluctuations on blood pressure oscillations, resulting in apparent increases in CBF fluctuations in the very-low-frequency range. Hypoxia may thus impair dynamic cerebral autoregulation in this range. However, these changes were significant only with hypoxia at 15% O2, suggesting a possible threshold for such changes.
    Journal of Cerebral Blood Flow & Metabolism 05/2007; 27(4):776-84. DOI:10.1038/sj.jcbfm.9600384 · 5.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The objective of the study was to test the hypothesis that dynamic cerebral pressure-autoregulation is associated with the outcome of patients with severe head injury and to derive optimal criteria for future studies on the predictive value of autoregulation indices. Repeated measurements were performed on 32 patients with severe head injury. Arterial blood pressure (ABP) was measured continuously with an intravascular catheter, intracranial pressure (ICP) was recorded with a subdural semiconductor transducer and cerebral blood flow velocity (CBFV) was measured with Doppler ultrasound in the middle cerebral artery. Transfer function analysis was performed on mean beat-to-beat values, using ABP or CBFV as input variables and CBFV or ICP as the output variables. A dynamic index of autoregulation (ARI) ranging between 0 and 9 was extracted from the CBFV step response for a change in ABP. No significant differences between survivors and non-survivors were found due to mean values of ICP, ABP, CPP, CBFV, pCO2, GCS, age or heart rate. The transfer functions between ABP-ICP and CBFV-ICP did not show any significant differences either. The median [lower, upper quartiles] ARI was significantly lower for non-survivors compared with survivors [4.8 (0.0, 5.9) v. 6.9 (5.9, 7.4), p= 0.004]. The correlation between ARI and GOS was also significant (r=0.464, p=0.011). Cohen's coefficient was optimal for a threshold of ARI= 5.86 (kappa 0.51, p=0.0036), leading to a sensitivity for death of 75%, specificity=76.5%, odds ratio =9.75 and overall precision = 75.8%. The difference in ARI values between survivors and non-survivors persisted when results were adjusted for GCS (p = 0.028). A similar analysis for the Marshall CT scale did not reach significance (p = 0.072). A logistic regression analysis confirmed that apart from the ARI, no other variables had a significant contribution to predict outcome. In this group of patients, death following severe head injury could not be explained by traditional indices of risk, but was strongly correlated to indices of dynamic cerebral pressure-autoregulation extracted by means of transfer function analysis. Future studies using a prospective design are needed to validate the predictive value of the ARI index, as estimated by transfer function analysis, in relation to death and other unfavourable outcomes.
    British Journal of Neurosurgery 11/2004; 18(5):471-9. DOI:10.1080/02688690400012343 · 0.95 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Migraine is considered a disorder of the autonomic nervous system. We used the frequency analysis of dynamic cerebral autoregulation to assess whether blood flow regulation disturbances can be found at the frequencies at which sympathetic and parasympathetic activity is present. We measured simultaneously mean arterial blood pressure (BP) and the mean blood velocity (V) in the middle cerebral artery using transcranial Doppler ultrasound in 33 healthy controls (mean age+/-SD; 36+/-13 years) and in 22 patients with migraine (mean age; 39+/-7 years). Apart from assessing spectral power density for BP and V, we calculated the transfer function parameters gain, phase, and coherence at the frequency range between 0.0 and 0.25 Hz. Compared with the controls, the spectral power density of BP and V exhibited a maximum magnitude of 10(26) in the migraine patients, whereas the maximum magnitude of BP and V in the controls was 10(-3). Coherence showed no difference between patients and controls. Gain between BP and V increased in the controls >0.01 Hz but was approximately 0 or negative in the migraine patients over the whole frequency range (P<0.01). The usually observed phase lead of V against BP was absent in the migraine patients in whom BP leaded V over nearly the whole frequency range (P<0.01). In terms of phase and gain, dynamic cerebral autoregulation is completely different in migraine patients compared with healthy subjects. Insofar, this can be interpreted as a lack of sympathetic and parasympathetic control of cerebral blood flow.
    Stroke 09/2005; 36(9):1886-90. DOI:10.1161/01.STR.0000177886.94134.92 · 6.02 Impact Factor