SLEEP DISORDERS AND DIAGNOSTIC WORKUP

Sleep is a very complex, a diverse amalgam of behavioral and physiological phenomena which are repeated cyclically with a homeostatic and a circadian regulation. During sleep, disorders can occur in the brain electrical activity and in the somatic and autonomic nervous system.
For a long time sleep was considered a passive phenomenon, necessary for the proper functioning of the central nervous system, but since that time further studies have demonstrated the involvement of active phenomena in regulating the alternation of sleep and wakefulness.
Sleep is therefore an important a biological variable, and, as such, may be source, or point of convergence, of many pathological conditions; it has been determined that the irregularity and instability of sleep-wake cycle can quantitatively and qualitatively alter the psycho-physical status of a person.
In recent decades, Sleep Medicine, has gradually transformed into a self directed multi-disciplinary field, and has produced a body of approximately ninety clinical conditions, collected in the new International Classification of Sleep Disorders (ICSD 2005), and divided into six main clinical categories: insomnia, respiratory sleep disorders, hypersomnia of central origin, circadian rhythm disorders, parasomnias and sleep related movement disorders..
Today the considerable technological advances allow evaluation and the study of these changes using highly specialized materials and methods, and permit the healthcare professional to adjust the complexity of the diagnostic tools to the specific clinical diagnostic needs.
The ideal diagnostic tool for the simultaneous electro-neurophysiologic recording of many physiologic and pathologic parameters is polysomnography (PSG) that not only allows evaluating sleep disturbances, but also paroxysmal disturbances in wakefulness (excessive daytime sleepiness, movement disorders, etc.).
There are actually several types of systems applicable to the study of sleep and its disorders which according to national and international guidelines can be categorized into four levels, based on the complexity of the examination.

Standard Polysomnography is at the highest category of complexity level, as it involves the acquisition of electro-encephalographic (EEG) activity to enable the staging of sleep in connection with electro-oculographic (EOG), electro-myographic (EMG) derivations and cardio-respiratory signal detection.
The key feature of this type of examination is that it is performed under direct supervision by skilled personnel in a sleep laboratory, which can monitor on a continuous basis the adequacy of the technical path, the patient's behavior and his cooperation, and intervene to correct, document or interpret the signals.
At a second level we have a dynamic portable polysomnography system for home application which is comparable to the Standard Polysomnography for acquisition of biological parameters, but without technician supervision.

At the third level we have cardio-respiratory monitoring, which allows the recording of cardio-respiratory signals up to eight channels:
- Oxygen Saturation
- Heart rate
- Plethysmographic curve
- Nose cannula air flow sensor
- Thoracic-respiratory activity
- Abdominal respiratory activity
- Snoring
- Body position
- Effect of treatment with CPAP,
and a reduced type with no less than four channels (Oxygen Saturation, body position, snoring, airflow), which indirectly allows the identification of respiratory events through pulse oxymetry. In both cases, the examination is performed at home without assistance of technical staff.
At the fourth level is placed a simple monitoring of one or two channels, such as oxymetry, which monitors the oxyhemoglobin saturation in a given period of time.
The type of monitoring to be conducted is chosen on a clinical basis, evaluating signs and symptoms; in general, highly suggestive symptoms simplify the choice.
It must be borne in mind that you can use the term "polysomnographic evaluation, only if you are recording EEG, through which you can analyze the sleep stages.
The parameters detected with each equipment can be either bioelectrical or not. The former can be detected through the direct interposition of electrodes on the skin of the patient (EEG, EOG, EMG, ECG); for non-electrical signals, however, you can use special transducers or dedicated instruments.
The application of sensors must meet specific criteria set out in national and international guidelines, in order to obtain good quality data that are reliable and easily interpretable.
The International Federation of EEG and Clinical Neurophysiology has outlined a 10-20 International Measuring System (SI 10-20) to standardize the placement of cortical electrodes. This system requires drawing ideal lines starting from special anatomical landmarks, in antero-posterior and coronal-lateral directions.
The electro-oculogram necessary to identify movements of the eyes is detected using the difference of potentials between the cornea (positive) and retina (negative); one electrodes is placed 1 cm above the outer part of the right eye; a second electrode is placed 1 cm below the outer part of the left eye, cross referenced to each other to detect both, vertical and horizontal movements.
For the acquisition of EMG, electrodes are placed on the skin overlaying the selected muscle. For sleep scoring is necessary to record the activity of the mylohyoid muscle, which is useful for the recognition of the different sleep phases and to identify the atonic state during REM phase, the two electrodes must be placed in the sub mental region at a distance of 2 cm off the midline, with a third reference electrode placed at the center of the chin.
The ECG activity has a signal with high potential, available from almost any region of the body; conventionally the D2 derivation is used because it yields the best morphology, which involves placing an electrode on the clavicle and the other on the right axillary line left at the seventh intercostal space.
Special devices are used to detect non-electrical activities.
The oro-nasal flow is monitored with thermistors / thermocouples or airflow sensors cannulae, which detect changes in temperature or in air flow during the inspiratory and expiratory acts.
Thoracic and abdominal activities are acquired with transducers with piezoelectric crystal sensors or inductive plethysmographic bands; chest bands should be applied on mammary line and the abdominal band on the umbilical line.
The sound is recorded through a microphone applied to the skin that covers the larynx or the trachea.
When there is need to correlate the type of respiratory events to the type of decubitus, the patient’s position can be recorded with appropriate transducers applied at the level of the sternum.
The oxygen saturation, which is the important index in determining the severity of a patient apnea is detectable by a digital oxymeter probe consisting of a light emitter and a photo receiver, which processes the light signal in relation to the amount of bound hemoglobin in the blood.

CONCLUSIONS
The high prevalence of sleep related disorders highlights the importance of implementing diagnostic and therapeutic targets, with the aim of reducing the social dimensions of the problem and curb the risk of progression of cardiovascular, metabolic, cognitive, and systemic pathologies, that are strongly influenced by sleep.
Sleep is not just resting. Sleep is life!