The central clinical features of this case include dysauto-nomia, parkinsonism, and abnormalities in respiratory control. Unlike previous reports, in this patient, the medulla was morphologically intact. Instead, there was a widespread neuropathy, as well as the classic pathologic findings of Shy-Drager. The moderate abnormalities in respiratory mechanics do not, by themselves, explain the presence of hypercapnic respiratory failure. Although there was evidence of phrenic and intercostal nerve pathologic conditions, the preservation of vital capacity with changes in posture, the lack of paradoxic thoracoabdominal movements, and the presence of substantial maximal inspiratory and expiratory pressures are indications of neuromuscular apparatus sufficient to provide an adequate minute ventilation gas exchange.

Correlation of findings of respiratory abnormalities during sleep with findings at autopsy can be approached through the concept of feedback control in the respiratory system (Fig 3), where abnormalities in respiration are considered to result from functional instabilities inherent in the organization of respiratory rate and rhythm. The patient did show significant physiologic evidence for absence of chemosensi-tive feedback control to the central respiratory generator. Patients with selective defects in afferent feedback, such as seen in bilateral anterior cordotomy for relief of pain, exhibit respiratory irregularities during sleep, occasionally leading to respiratory failure and death. In addition, this patient had significant peripheral nerve disease. This presumably could have involved feedback control from tendon organs and muscle spindles in the muscles and structures of the chest wall. Absence of nonchemical feedback control from these and other sensory nerves might also have contributed to the abnormalities in respiratory control during sleep. read only
We speculate that the behavior of respiration present during sleep in this patient results from an absence of feedback control which in turn uncovers or promotes periodic behavior of respiration. One possibility is that absence of afferent feedback allows oscillatory patterns from other brain centers to influence central respiratory drive centers. Alternatively, the absence of afferent information or of autonomic efferent activity could amplify oscillations of the respiratory controller because of an inability to maintain lung volume or cardiovascular homeostasis.

Figure 3. A schematic diagram of the respiratory control system as it might pertain to this case.

Figure 3. A schematic diagram of the respiratory control system as it might pertain to this case.