Monitoring Airflow through the Nose and Mouth



  

Polysomnography generally includes monitoring of the patient's airflow through the nose and mouth, blood pressure, electrocardiographic activity, blood oxygen level, brain wave pattern, eye movement, and the movement of respiratory muscle and limbs.

Flow Volume Loop

  

Flow is volume per unit time

Upper Airway Obstruction

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IMPACT OF SLEEP ON BREATHING 1

     "Sleep is not a homogenous phenomenon but rather consists of two distinct states, referred to as non-rapid eye movement ( non-REM ) or rapid eye movement (REM).  The two states are distinguished by a combination of behavioral and electrographic criteria. Non-REM sleep consists of four stages that are thought to represent progressively deeper sleep, with deeper stages N3 being referred to as slow-wave sleep. REM sleep, during which dreaming occurs, is characterized by intense cerebral metabolic activity and central nervous system excitation, despite which incoming sensory information and outgoing motor activity are actively inhibited. In the normal adult, non-REM sleep and REM sleep alternate cyclically, with periods of REM sleep lasting 10 to 20 minutes and occurring 90 to 120 minutes.

    Non-REM sleep and REM sleep have several important physiologic influences on breathing, particularly on respiratory drive, stability, and ventilatory mechanics. Overall respiratory drive is decreased during non-REM sleep, owing to loss of the stimulatory effect of wakefulness on breathing and to a reduction in chemosensitivity. As a result, during stages 1 and 2 of non-REM sleep, as the central nervous system state fluctuates between awake and asleep, there is a fluctuation in respiratory drive that predisposes to periodic breathing. Once slow wave sleep is fully established, nonchemical respiratory inputs are minimized, and breathing is regulated by the metabolic respiratory control system. Under these conditions, overall respiratory drive is usually stable but less than during wakefulness. As a result, minute volume of ventilation is reduced by 1 to 2 liters/min compared with wakefulness, arterial PCO2 is increased  by 2 to 8 mm Hg., and arterial PO2 is decreased by 5 to 10 mm Hg..

    During REM sleep, respiratory drive is often irregular, ventilatory responses to chemical and mechanical respiratory stimuli may be transiently reduced or abolished, and short periods of central apnea lasting 10 to 20 seconds are relatively common. In addition, intercostal and accessory muscle activity is reduced coincident with the generalized inhibition of skeletal muscle tone characteristic of this state. As a result, thoracoabdominal coupling may be diminished, resulting in further decreases in ventilation, and functional residual capacity may be further reduced. The influences of non-REM and REM sleep on respiratory drive and muscle activity are exerted on the muscles of the upper airway in addition to those of the chest wall. Therefore, upper airway resistance is increased during non-REM sleep compared with wakefulness, and increased even more  during REM sleep.

    The physiologic impact of sleep on breathing is of little consequences in health people. In patients with disturbances of respiratory structure or function, however, the imposition of these sleep-related changes on the underlying disturbance may have important clinical consequences."

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CPAP: May Be One Solution for Obstructive Sleep Apnea

     

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"Pulmonary" or

Lung Function Tests 2 Lung function tests (also called pulmonary function tests, or PFTs) evaluate how well your lungs work. The tests determine how much air your lungs can hold, how quickly you can move air in and out of your lungs, and how well your lungs put oxygen into and remove carbon dioxide from your blood. The tests can diagnose lung diseases, measure the severity of lung problems, and check to see how well treatment for a lung disease is working. Other tests such as residual volume, gas diffusion tests, body plethysmography, inhalation challenge tests, and exercise stress tests may also be done to determine lung function.

Spirometry is the first lung function test done. It measures how much and how quickly you can move air out of your lungs. For this test, you breathe into a mouthpiece attached to a recording device (spirometer). The information collected by the spirometer may be printed out on a chart called a spirogram.

The more common lung function values measured with spirometry are:

  • Forced vital capacity (FVC). This measures the amount of air you can exhale with force after you inhale as deeply as possible.
  • Forced expiratory volume (FEV). This measures the amount of air you can exhale with force in one breath. The amount of air you exhale may be measured at 1 second (FEV1), 2 seconds (FEV2), or 3 seconds (FEV3). FEV1 divided by FVC can also be determined.
  • Forced expiratory flow 25% to 75%. This measures the air flow halfway through an exhale (FVC).
  • Peak expiratory flow (PEF). This measures how quickly you can exhale. It is usually measured at the same time as your forced vital capacity (FVC).
  • Maximum voluntary ventilation (MVV). This measures the greatest amount of air you can breathe in and out during one minute.
  • Slow vital capacity (SVC). This measures the amount of air you can slowly exhale after you inhale as deeply as possible.
  • Total lung capacity (TLC). This measures the amount of air in your lungs after you inhale as deeply as possible.
  • Functional residual capacity (FRC). This measures the amount of air in your lungs at the end of a normal exhaled breath.
  • Expiratory reserve volume (ERV). This measures the difference between the amount of air in your lungs after a normal exhale (FRC) and the amount after you exhale with force (RV).
Gas diffusion tests Gas diffusion tests measure the amount of oxygen and other gases that cross the lungs' air sacs (alveoli) per minute. These tests evaluate how well gases are being absorbed into your blood from your lungs. Gas diffusion tests include:

  • Arterial blood gases, which determine the amount of oxygen and carbon dioxide in your bloodstream.
  • Carbon monoxide diffusing capacity (also called transfer factor, or TF), which measures how well your lungs transfer a small amount of carbon monoxide (CO) into the blood. Two different methods are used for this test. If the single-breath or breath-holding method is used, you will take a breath of air containing a very small amount of carbon monoxide from a container while measurements are taken. In the steady-state method, you will breathe air containing a very small amount of carbon monoxide from a container. The amount of carbon monoxide in the breath you exhale is then measured. Diffusing capacity provides an estimate of how well a gas is able to move from your lungs into your blood.
Footnotes:

1 - "Textbook of Respiratory Medicine - Mason, Broaddus, Murray, Nadel : Volume 2"

2 - " WebMD website"

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