Linkage of hiccup with heartbeat

We explored a possible link between the cardiac cycle and the timing of rec urrent hiccups in 10 patients with chronic, intractable hiccups. Recordings made during daytime naps in a sleep laboratory included sleep state; elect rocardiogram; and respiration by means of a thermistor to detect airflow, b ands around the rib cage and abdomen to assess expansion, and a bipolar sur face electrode electromyogram over parasternal intercostal muscles. Hiccups could be detected on the abdominal bands and the parasternal electromyogra m. The time of occurrence of each hiccup and each R wave in a continuous tr acing of 100 or more hiccups were recorded and analyzed together with semiq uantitive estimates of the phase of hiccup respiration. Whereas the hiccup rate ranged from approximately one-third to one-eighth of heart rate and wa s more variable than heart rate, hiccups showed a tendency, stronger in som e subjects than others, to occur in midsystole. Variation in R-wave-R-wave (R-R) interval in association with hiccups was found in five patients. In t hree of these patients, hiccups were synchronized with respiration so that the cyclic change in R-R interval posthiccup could be explained as sinus ar rhythmia, but, in two patients, the hiccups were not synchronized with resp iration, so that hiccups are most likely responsible for the variation in h eart rate. Also, the variation of R-R interval with hiccups suggests that t here is some phasic autonomic efferent activity associated with hiccups.