Cardiogenic Oscillations
Many members have noted their flow rate seems to have oscillations, especially in the expiratory phase. These oscillations should not be a cause for concern and are basically an echo of hearth rate as described in detail below. These oscillations are frequently seen in polysomnograph (PSG) charts, but we frequently see them in CPAP flow rate charts in OSCAR.
From the American Thoracic Society:
Cardioballistic artifact is a normal physiologic occurrence that may be seen in the airflow signal, nasal pressure and esophageal pressure-monitoring channels, chest or abdominal belts, and EEG channels. It is most often observed during exhalation and during central apneic events. The mechanisms of transmission of cardiogenic oscillations in the airflow channel or other respiratory channels have been debated. The observation that voluntary upper airway obstruction uniformly results in loss of cardiac oscillations led to the theory that they may be an indicator of upper airway patency, with the idea that changes in intrathoracic pressure produced with each heartbeat result in movement of air through the patent upper airway. However, during sleep, such oscillations over-imposed on airway signals have been observed in the presence of directly visualized upper airway occlusion and in an animal model with complete anatomical separation of the upper airway, lending to the belief that these oscillations occur irrespective of the airway patency. In such cases, intra- and extra-thoracic mechanisms have been hypothesized. For the former, it is believed that the heartbeat displaces air from the intrathoracic cavity causing a pressure wave that bounces against the occlusion. For the latter, pulses in the vessels above the site of obstruction, especially those located relatively superficially within the tissues of the upper airway may cause a similar pulse wave. One further speculation is that transmission of cardiogenic oscillations to the airflow signal may be influenced by the degree of respiratory muscle tone. When there is high muscle tone during respiratory effort, the transmission of the pulse wave is diminished.
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