**2. History**

The history of ICPwf is centuries-old. For understanding, it is necessary to go back to the year 1783, after researcher Alexander Monro [1], who started studies of intracranial structures. His work was later completed by George Kellie [2], giving rise to the Monro-Kellie doctrine. This doctrine showed that the volume of intracranial components (blood, CSF and brain tissue) and the bone box that contains them is fixed. The volume of these components needs to be under balance, if there is an increase in one, the others need to compensate by reducing their volumes. Thus, intracranial hypertension (ICH) emerges when this compensation ceases to happen [3]. The stiffness of the skull was later challenged by the work of Sérgio Mascarenhas in 2012 [4].

Angelo Mosso, at the end of the 19th century, presented results showing the influence of brain activity on its blood flow. For the first time, it was possible to observe the brain pulses, through a system that captured these pulses and recorded them on paper. These figures can be seen in Zago's manuscript [5]. Many years later these pulses were related to ICP and CSF [6].

Langfitt [7] brought an important contribution showing the mathematical hypothesis for the relationship between ICP and intracranial volume, making it easier to understand the importance of intracranial compliance (ICC=V/ P) in critical care. Marmarou [8] in 1975 added to the pressure-volume curve the information about the increase in the amplitude of ICPwf as the mean value of ICP increases, and demonstrated that ICPwf contains unique information on intracranial contents, this data has already proven useful in several diseases such as stroke, hydrocephalus, idiopathic intracranial hypertension and brain injuries. It is important for gathering information on cerebrovascular hemodynamics and also of the cerebrospinal compensatory system. In 1983, Cardoso [9] showed that with the increase in ICP, in addition to the increase in the amplitude of its pulse, there was also a change in its configuration, as morphology became pyramidal with an increase in amplitude in the middle region of the pulse. Cardoso also shows the ICPwf configuration: P1 - systolic peak, P2 - tidal wave and P3 - venous return (explained in detail below).

Hu [10], understanding the possibility of using ICPwf as information to aid in diagnosis, created an algorithm called MOCAIP (Morphological Clustering and Analysis of Continuous Intracranial Pressure). This software is able to turn the waveform into numbers to facilitate the interpretation of the medical team. Nucci [11], in 2016, presented results of a software to calculate ICPwf parameters and clusters of waveforms for different stages of pathology.

Ballestero [12] and Bollela [13], in 2017, presented studies with hydrocephalus and meningitis respectively, that showed the applicability of a new noninvasive sensor to monitor the ICPwf, in the Ballestero study the ICPwf was analyzed through the relationship between the amplitude of the P2 and P1 pulses.

ICPwf is an important information, increasingly disseminated among physicians. New methods and analyses facilitate the use of this parameter, which is useful and disseminating over clinical institutions. The next chapters will provide more details and clinical applications of ICPwf.

**3**

damage [19, 20].

**Figure 1.**

*Intracranial Pressure Waveform: History, Fundamentals and Applications in Brain Injuries*

ICP is determined by the intracranial components volumes, as the brain tissue, the vascular or cerebral blood flow (CBF) and cerebrospinal fluid (CSF) [14, 15], and relations between them in a semi-rigid skull box, the Monroe-Kellie doctrine. Each cardiac beat corresponds to an ICP waveform composed of three peaks; arterial pulsation- P1, cerebral venous flow, secondary to autoregulation-derived cyclic fluctuations of arterial blood volume, reflecting intracranial compliance- P2, and

These cardiac-derived pulsatile signals are overlapped in time domain with the respiratory cycle, with influence in the cerebral venous pulsation by means of intrathoracic pressure generated by breathing, disclosed as slow waves [16] (**Figure 1b**). Moreover, ventilation plays a direct and remarkable role over CBF [17]. Thus, ICP is influenced by many physiological factors from extra and intracranial compartments. Moreover, factors as age, body posture, time of day as well as the clinical condition also are considerable variables, although in absence of disturbances, mean ICP is kept mostly within a range between 7 and 15 mmHg for adults, 3 and

There is an existing volume of reserve in the brain which is around 60–80 mL in young persons and approximately 100–140 mL in geriatric population, because of ongoing cerebral atrophy with age. However, in normal conditions and for short time observations, the brain volume is typically static, with mean ICP varying mainly according to the CBF and the balance between production and absorption or outflow of the CSF. The relation observed between these intracranial components is named intracranial compliance (ICC). Compensatory mechanisms exist to maintain intracranial volume homeostasis by extrusion of the CSF or venous blood, in order to preserve ICC, otherwise, these efforts may be insufficient in pathological conditions (i.e. traumatic brain injury) with intracranial hypertension (ICH) and ICC impairment producing primary or secondary brain tissue

*(a) One single arterial pulse transmitted to the intracranial compartment, with three peaks observed; systolic peak (P1), tidal peak (P2) and aortic valve closure peak (P3). (b) Respiratory slow waves overlapping cardiac* 

Langfitt et al. characterized the transmission of pressure across the intracranial compartments as the intracranial elastance curve, observing an exponential behavior between ICP and intracranial volume [21], from a stable ICP vs. volume relation until

6 mmHg in children, and between 1.5 and 6 mmHg in term infants [18].

**3. Intracranial pressure- waveform pathophysiology**

*DOI: http://dx.doi.org/10.5772/intechopen.94077*

the aortic valve closure- P3 (**Figure 1a**).

*intracranial pulses spectrum (from Hall et al. [16]).*

**3.1 Waveform components**

*Intracranial Pressure Waveform: History, Fundamentals and Applications in Brain Injuries DOI: http://dx.doi.org/10.5772/intechopen.94077*
