Instrumentation

Nasal pressure decreases during inspiration and increases during expiration. In nasal pressure monitoring a nasal cannula is connected to a pressure-sensitive transducer, which measures this pressure difference.

Nasal pressure monitoring is more sensitive than thermal devices in detecting airflow limitation and hypopneas, With increased upper airway resistance the nasal pressure monitor will register a plateu indicating a flow limitation.

Disadvantage : cannot be used to measure airflow in mouth breathers and in patients with nasal obstruction. For this reason, nasal pressure transducers are not used to score apneas.

An oronasal thermal device ( thermistor or thermocouple) placed between the nose and mouthis commonly used to monitor airflow by detecting changes in temperature ( cool air flows

during inspiration and warm air flows during expiration). A thermistor consisting of wires records changes in electrical resistance, and thermocouples consisting of dissimilar metals

( e.g. , copper and constantan).

Used to score apneas.

Temperature of thermal device must be below body temperature to sense the temperature difference between expired and inspired air.

These devises must therefore not be in contact with the skin. Because of this, they are easily displaced, causing false changes in airflow.

Although snoring can be monitored by placing a miniature microphone on the patient´s neck, there is no accepted grading system to quantify the intensity of this parameter. In practice the technologist´s notations as the study is being recorded, as well as the polysomnographer´s review of the audio as the study is being read, provide a better estimation of the degree of snoring. It is often worthwhile to describe the relationship of position to snoring, especially if the patient´s study shows merely primary snoring.

measures changes in thoracoabdominal cross-sectional areas, and the sum of these 2 compartments is proportional to airflow. Inductance refers to resistance to current flow.

Transducers across the chest and abdomen detect changes in the cross- sectional areas of the thorax and abdomen during breathing. These belts are prone to dislodgement during the night by patient movement, causing inaccuracy in measurements of the respiratory effort.

Piezoelectric strain gauges are used to record thoracic and abdominal and thus respiratory movements. These belts consists of a crystal that emits an electrical signal in response to changes in length or pressure. For all these devices 1 belt is placed around the chest and another one is placed around the abdomen, which allows detection of the paradoxical movements indicating upper airway OSA.

For standard PSG these constitute the " effort channels".

For AASm not accurate for representation of respiratory effort.

The technique is a specialized procedure and is not used in standard PSG labs. Esophageal pH is monitored by asking patients to swallow a pH probe. Recording the output using a DC amplifier detects nocturnal gastroesophageal reflux disease, which may be mistaken for sleep apnea or nocturnal angina because the patient may wake up choking or have severe chest pain as a result of acid eructation.

Arterial oxygen saturation (Sao2) during sleep is routinely measured on PSG´s noninvasively by finger pulse oximetry.

Patients with OSA may have respiratory event-related recurrent desaturations with a return of SaO2 to baseline at the termination of the event, although the cumulative burden of these events may cause the patient´sSaO2 to be below 90 % for more than 10% of total sleep time ( resp. event-related hypoxemia).

On the other hand , patients with alveolar hypoventilation caused by primary pulmonary, neuromuscular, or skeletal pathological conditions may have low baseline oxygen saturation, with worsening in the supine position or in REM sleep.

detects expired carbon dioxide level, which closely approximates intra-alveolar CO2. Capnography detects both airflow and the partial pressure of CO2 in alveoli, which is useful for evaluating OSA, sleep hypoventilation, and underlying pulmonary disease.

Should be used in children with suspected OSA.

an essential parameter to measure , because many patients have sleep-disordered breathing that is exclusive to or worse in the supine position. Clinicians also strive to capture supine sleep, especially supine REM sleep, during CPAP studies to ensure that a pressure under consideration is optimal. The most reliable technique to record position is actual visual analysis by the technologist on the night of the study, as well as during the scoring session.

monitors body movements and other activities continuously for days,weeks or even months.

Principle : increased movements ( indicated by black bars in the actigraph) are seen during wakefulness in contrast to markedly decreased movements or no movements ( indicating by white bars interrupting the black bars) during sleep

Indication :

• may be useful adjunct to history, physical examination, and sleep logs in patients with insomnia, including paradoxical sleep ( sleep state misperception) and inadequate sleep hygiene, and circadian rhythm sleep disorders
  
• may be a useful to document rest-activity patterns during modified portable sleep apnea testing.
• useful to document rest - activity patterns over days and weeks when a sleep log is not able to provide such data.

• Nyquist Theory
  
• Aliasing
  
• Sampling Rate