Nocturnal physiological and biochemical changes in sudden unexplained death syndrome: a preliminary report of a case control study.

Sudden nocturnal deaths among "healthy" workers in Southeast Asia have been termed "sudden unexplained nocturnal death syndrome (SUNDS)" or "sudden unexplained death syndrome (SUDS)". The pathogenesis is still unknown. The paucity of publications on nocturnal monitoring and scientific data stimulated us to perform this study, which included biochemical tests and physiological monitoring during the night in 11 males north-eastern Thai workers. Group 1 (G1) consisted of 5 subjects with neither a previous history of near-SUDS (NSUDS) nor a familial history of SUDS (FHSUDS). Group 2 (G2) consisted of 6 subjects with a family history of either SUDS or NSUDS. Two subjects in G2 presented with NSUDS. Two-day nocturnal monitoring included blood sugar, electrolytes, and respiratory parameters. 24-hour Holter ECGs were monitored for 2 days. The subjects underwent exercise stress tests on the 2nd day of this study. Significant nocturnal hypoxia was more common in G2 than G1 and this abnormality was aggravated by exercise. There were no significant findings in sleep apnea (apnea indices) or in nocturnal biochemical changes, eg blood sugar, electrolytes, thiamine. The recordings of the Holter-ECGs were within normal limits in both groups. We conclude that nocturnal hypoxia might be the primary abnormality in SUDS, and this abnormality was aggravated by the day-time exercise. The cause of nocturnal hypoxia requires further studies.