Central, mixed and obstructive sleep apnea patient Clinical scenario: A 57-year-old male with a history of TMJ, bruxism and arthritis is not on any daily medications but takes a daily multivitamin and Tylenol PM as needed. In April, 2008, a sleep study was completed and the following information was provided about the patient: Sleep parameters Diagnostic study Sleep efficiency 84.9% Apnea-hypopnea index (episodes/hr) 27.5 Central apnea index (episodes/hr) 5.6 Obstructive apnea index (episodes/hr) 1.1 Hypopnea index (episodes/hr) 18.4 Mixed apnea index (episodes/hr) 2.4 The above data indicated that the patient had mild-to-moderate sleep apnea with a mixture of both obstructive and central events. He was sent home on a CPAP therapy of 9 cm H 2 0. The patient returned to the sleep center due to increased complaints of Excess Daytime Sleepiness (EDS) and morning headaches. A repeat study was ordered and the following information was found: CPAP study Clinical applications guide 33
Early in the night, during a CPAP titration, the patient was not on enough CPAP to eliminate obstructive hypopneas. The obstructive nature of the hypopneas was suggested by snoring (see Micro channel) and the peak-plateau inspiratory flow pattern (red arrow, and shown in detail in the next figure). Thoracic-abdominal paradox could also be used to indicate obstruction, but the thoracic channel had cardioballistic and other artifacts that made it hard to interpret. A close up of the cardioballistic artifact is shown below on the THO channel. An example of inspiratory flow limitation is indicated by the red arrow. Most of the breaths in this one-minute tracing are flow limited. Flow-limited breaths have a peak-plateau or scooped out inspiratory flow pattern. In the breath marked by the arrow, there is an initial peak in inspiratory flow, then a relative flattening, followed sometimes by a secondary peak at the end of inspiration (zero flow is marked with the dashed line). This type of inspiratory flow pattern is specific for upper airway obstruction. 34 BiPAP autosv Advanced System One
Thoracic-abdominal paradox could also be used to indicate upper airway obstruction. However, cardioballistic artifact in the thoracic belt made this difficult to identify in this patient. Note that each heart beat can be seen in the thoracic (THO) channel. Regardless, it is clear that PAP was not adequate and needs to be increased to treat the obstructive apneas and hypopneas. Clinical applications guide 35
Later in the night, CPAP at 8 cm H 2 O appeared to eliminate upper airway obstruction. There was no snoring, flow limitation, or thoracic-abdominal paradox (the cardioballistic artifact improved). Central apneas became apparent. The patient had CPAP-emergent central apneas in which central apneas seemed to emerge from obstructive hypopneas/apneas when CPAP was administered. The cause of these central apneas was not clear but may have involved instability in the ventilatory control feedback loop or volume feedback from mechanoreceptors in the lung. Upon completion of the CPAP study, the following was documented: Sleep parameters Titration study Sleep efficiency 88.7% Apnea-hypopnea index (episodes/hr) 22.7 Central apnea index (episodes/hr) 10.6 Obstructive apnea index (episodes/hr) 0.4 Hypopnea index (episodes/hr) 11.7 Mixed apnea index (episodes/hr) 0 36 BiPAP autosv Advanced System One
BiPAP autosv Advanced System One titration Since patient was previously on an auto CPAP device and having recurrent symptoms of a sleep disorder with an elevated central apnea count, the physician tried the patient on a BiPAP autosv Advanced System One device. Prior to the biocalibrations, the patient is drifting off to sleep and having sleep-onset central apneas. This is a common occurrence as patients transition from awake drive-to-breathe to a chemical drive-to-breathe. BiPAP autosv Advanced System One is detecting the central apneas and administering breaths. These ventilatortriggered breaths are recognized by the downward spike in the PatPress channel. Clinical applications guide 37
This is a nice example of how the BiPAP autosv Advanced System One works. During the biocalibration procedure, the patient was asked to hold his breath. After 4.5 seconds of apnea, the ventilator provided a ventilatortriggered breath. Note that there was no resulting inspiratory flow (downward arrow) because the glottis is closed. Then the patient exhaled (upward arrow) and another ventilator-triggered breath was given. This time, the airway was open and there was high flow. The next breath was patient-triggered and only received half the inspiratory support as the previous breath. 38 BiPAP autosv Advanced System One
Once the patient is asleep, BiPAP autosv Advanced System One helps to produce stable, regular breathing. Notice the variation in inspiratory pressure (PatPress channel). The EPAP is 5 cm H 2 O. The patient has a stable and regular flow pattern (CFLOW) without central apneas. In this five-minute tracing, there are no ventilator-triggered breaths however, there are many pressure support-triggered breaths supporting the patient while he sleeps. Clinical applications guide 39
There are ventilator-triggered breaths in the first portion of this figure (indicated by downward spike in PatPress channel). BiPAP autosv Advanced System One was preventing long expiratory pauses and central apneas. The middle and last portions of the figure were patient-triggered breaths with progressively decreasing inspiratory pressure; the patient is taking over more control of respiration. The flow rate is stable without pauses, apneas, or variations. Upon completion of the BiPAP autosv Advanced System One study, the following parameters were found: Sleep parameters BiPAP autosv study Sleep efficiency 93.7% Apnea-hypopnea index (episodes/hr) 6.4 Central apnea index (episodes/hr) 2 Obstructive apnea index (episodes/hr) 8 Hypopnea index (episodes/hr) 2.8 Mixed apnea index (episodes/hr) 0 40 BiPAP autosv Advanced System One