Hemodynamic response

By far, the most widely used model in calculating hemodynamic response is based on the classic Beer-Lambert law. The Beer-Lambert law is derived from solution to radiation transport equation under several simplifying assumptions [91]. It describes a linear relationship between absorbance, A, of light through a medium and wavelength dependent extinction coefficient, e(A). This relationship is given by Equation (1) 

3 Homogeneous change of parameters of interest within each volume 

For non-scattering media, following the classical Beer-Lambert law, L is equal to the distance between source and detector, denoted as d. For scattering media Equation (1) can be rewritten as 

1The term optical window denotes the spectral range where a low absorption by chro-mophores allow for significant penetration of light. 

Oxy- and deoxy-hemoglobins are mainly of interest because they are related to the regional cerebral blood flow (rCBF). The focal change in rCBF determines the activation state. The term activation usually refers to the focal increase in rCBF whereas a decrease is called deactivation [78]. With the dual wavelength approach, one can derive two simultaneous equations to be solved for each of the two chromophore concentration changes. To this end, Equation (4) is split into two parts, separating the contributions from HbO and Hb. Equation (4) is then, rewritten as 

---

Winship IR, Plaa N, Murphy TH (2007) Rapid astrocyte calcium signals correlate with neuronal activity and onset of the hemodynamic response in vivo. J Neurosci 27 6268-6272 Wu MM, Buchanan J, Luik RM, Lewis RS (2006) Ca store depletion causes STIMl to accumulate in ER regions closely associated with the plasma membrane. J Cell Biol 174 803-813 Wyss-Coray T (2006) Inflammation in Alzheimer disease driving force, bystander or beneficial response Nat Med 12 1005-1015... 

Dobutamine is a /Jj- and / -receptor agonist with some oq-agonist effects. The net vascular effect is usually vasodilation. It has a potent inotropic effect without producing a significant change in heart rate. Initial doses of 2.5 to 5 mcg/kg/min can be increased progressively to 20 mcg/kg/min on the basis of clinical and hemodynamic responses. 

Sookoian, S. etal., A1166C angiotensin II type 1 receptor gene polymorphism may predict hemodynamic response to losartan in patients with cirrhosis and portal hypertension, Am. J. Gastroenterol., 100, 636, 2005. 

The acquisition of neuronal response using noninvasive NIR spectroscopy is less well-known than the slower hemodynamic response. However, there is a great deal of potential for its development and verification via comparison with other modalities such as event-related potentials (ERP) [32]. The origins of optically sensing this fast signal (usually known as intrinsic optical signal or IOS for short) can be traced back to Cohen [14]. Cohen showed that neuronal activity elicits a fast... 

Adult subject studies can be divided into two broad categories response to basic sensory stimulation and response to more complex cognitive tasks. Recently, there have also been reports applying the NIR spectroscopy to brain computer interface research [18] and studyinh the correlation of hemodynamic response to computational cognitive models [94]. 

Cognitive Tests. Schroeter et. al. studied hemodynamic responses to classic Stroop task where mismatch in words spelling out various colors [93]. The task consisted of two rows and were asked to decide whether the color of the top row of letter corresponded with the bottom row spelling out a color. Three types of stimuli were presented, (1) neutral, where top row consisted of X s, (2) congruent, where top row... 

A preference of hemodynamic response is mainly due to better contrast-to-noise ratio and the ease of comparability with fMRI BOLD response which is inversely related to changes in Hb, over measurement of neuronal activity. However, measurement of the fast neuronal response can potentially benefit NIR methods by addressing the inherent pitfalls of MBLL assumptions in slow response measurements. Fast response, aside from being a direct measurement of neuronal activity, also has the potential to provide better spatial resolution. 

J. H. Meek, M. Firbank, C. E. Elwell, J. Atkinson, O. Braddick, and J. S. Wyatt. Regional hemodynamic responses to visual stimulation in awake infants. Pediatric Research, 43 840-843, 1998. 

Concomitant illness Use caution in patients with diseases or conditions that could affect metabolism or hemodynamic responses. 

Since propofol does not depress the hemodynamic response to laryngoscopy and intubation, its use may permit wide swings in blood pressure at the time of induction of anesthesia. Propofol should be used with utmost caution in patients with cardiac disease. 

O. Smithies, B.H. Koller, T.M. Coffman, Coagulation defects and altered hemodynamic responses in mice lacking receptors for thromboxane A2,J. Clin. Invest. 102(1998) 1994. 

Penney DG. Acute carbon monoxide poisoning animal model A review. Toxicology 1990 62 123. Penny DG. A review Hemodynamic response to carbon monoxide. Environ Health Perspect 1988 77 121. Rocco TP, Fang JC. Pharmacological treatment of heart failure. In Brunton L, Lazo J, Parker K, eds. 

Edwards N, Blyton DM, Kirjavainen TT, Sullivan CE. Hemodynamic responses to obstructive respiratory events during sleep are augmented in women with preeclampsia. Am J Hypertens 2001 14(11 pt 1) 1090-1095. 

Nelesen RA, Yu H, Ziegler MG, Mills PJ, Clausen JL, Dimsdale JE (2001) Continuous positive airway pressure normalizes cardiac autonomic and hemodynamic responses to a laboratory stressor in apneic patients. Chest 119 1092-1101... 

Winship, I.R, Plaa, N., and Murphy, T. H. (2007). Rapid astrocyte calcium signals correlate with neuronal activity and onset of the hemodynamic response in vivo. J. Neurosci. 27, 6268-6272. 

Tregellas JR, Davalos DB, Rojas DC, Waldo MC, Gibson L, et al. 2007. Increased hemodynamic response in the hippocampus, thalamus and prefrontal cortex during abnormal sensory gating in schizophrenia. Schizophr Res 92 262-272. 

Barch DM, Mathews JR, Buckner RL, Maccotta L, Csernansky JG, et al. 2003. Hemodynamic responses in visual, motor, and somatosensory cortices in schizophrenia. Neuroimage 20 1884-1893. 

Renshaw PF, Yurgelun-Todd DA, Cohen BM. 1994. Greater hemodynamic response to photic stimulation in schizophrenic patients An echo planar MRI study. Am J Psychiatry 151 1493-1495. 

The concept of the neurovascular unit —a funcdonal endty comprising neurons, asdocytes, smooth muscle cells and endothelial cells— has now emerged and it is appreciated that this coordinated unit plays a key role in the hemodynamic response to alteradons in brain funcdon and acdvity. Disrup-don of this regulatory network occurs after sdoke and it is now believed that efforts at neuroprotecdon should target the endre unit, not just neurons (del Zoppo, 2006). 

Lee, S.S., Hadengue, A., Moreau, R., Sayegh, R., Hillon, R, Lebrec, D. Postprandial hemodynamic response in patients with cirrhosis. Hepatology 1988 8 647-651... 

Bandl, J.-C., Garcia-Pagan, J.C., Escorsell, A., Francois, E., Molthlnho, E., Rodes, J., Bosch, J. Effects of propranolol on the hepatic hemodynamic response to physical exercise in patients with cirrhosis. Hepatology 1998 28 677-682... 

Scott RP, Savarese JJ, Ali HH, et al. Atracurium clinical strategies for preventing histamine release and attenuating the hemodynamic response. Anesthesiology 1984 61 A287. 

---