Methodology

Polysomnographic techniques are described in detail elsewhere (28). To assess whether upper airway narrowing is a contributing

Figure 5. Relation of daytime PaCO2 to "respiratory muscle strength" (RMS = arithmetic mean of Pimax and Pemax) in 33 patients with "uncomplicated" chronic myopathy (closed circles, regression lines) and 14 patients with myopathy plus chronic lung disease (open circles). Note that in uncomplicated myopathy, PaCO2 is reduced (< 40 mm Hg) in most patients with mild weakness and is likely to be elevated only when RMS < 40% predicted. Reprinted by permission from Reference 19.

Figure 6. Relation of daytime PaCO2 to VC in 37 patients with uncomplicated chronic myopathy (closed circles, regression line) and 16 with myopathy plus chronic lung disease (open circles). Reprinted by permission from Reference 19.

cause of apneas or hypopneas may require use of a supraglottic or esophageal pressure sensor. Interpretation of recordings obtained by inductance plethysmography or other devices that measure rib cage and abdominal expansion is problematic in patients with quadriplegic or diaphragm paralysis. It is essential to check the polarity of the tracings and to compare phase relations awake and asleep.

Reliability of the devices for monitoring PCO2 in sleep is currently doubtful and requires more study.

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