FETAL HICCUPS IN THE BABOON

Bouts of hiccuping are recognized by pregnant women as distinct episod ic movements of their fetuses. Ultrasound imaging of these fetuses has documented the occurrence of hiccups from early gestation through par turition. This study provides a systematic characterization of prenata l hiccuping in the fetal baboon (Papio species). Tracheal fluid pressu re was recorded from II chronically instrumented fetal baboons for 21. 5 +/- 7.3 consecutive days (mean +/- SD) Over a range in gestation fro m 124 to 164 days (term 175 days). In an initial review of pressure re cordings by visual inspection, hiccups were recognized as distinctive high-amplitude fluctuations in tracheal pressure that were readily dis criminated from fetal breaths. Automated techniques were then develope d and validated to detect hiccups and summarize their features. The me an hiccup amplitude was 23.0 +/- 3.1 mmHg, inspiratory time was 0.26 /- 0.03 s, and expiratory time was 0.27 +/- 0.02 s. Each of these feat ures discriminated hiccups from breaths (P < 0.001). Hiccuping inciden ce (1.8 +/- 0.4% of time), rate (26.2 +/- 6.2 min(-1)), bout duration (4.3 +/- 0.8 min), and the interval between bouts (3.35 +/- 0.60 h) we re also different (P < 0.01) from breathing. These features of hiccups remained relatively constant over the latter third of gestation with the exception of an increase in duration of the expiratory time interv al (r = 0.54, P < 0.01). Despite their vigorous nature, bouts of hiccu ping were not associated with transitions in behavioral state. Moreove r, the features of hiccups were not differentiated by state. Bouts of hiccuping recurred in a cyclic fashion, on average every 3-4 h. The du ration of bouts had a diurnal rhythmicity (r = 0.59, P < 0.005), with longer bouts at night than during the day. It is concluded that the me chanisms generating hiccups are largely distinct from those that regul ate fetal breathing and that the characteristics of hiccups and bouts of hiccuping are similar across primate species.