Abstract
BACKGROUND: In a previous article we reported the time that hiccups stop as the instant when CO(2) levels in both expiratory gas (EtCO(2)) and inspiratory gas (InspCO(2)) reach approximately 50 mmHg. To support our findings, in this article we aim to clarify the precise values of the CO(2) level in arterial blood (PaCO(2)) and venous blood (PvCO(2)) during plastic bag rebreathing. METHODS: A healthy male volunteer was asked to perform a rebreathing experiment using a 20 L air-filled plastic bag. During the experiment, his blood oxygen saturation level (SpO(2)), EtCO(2) and InspCO(2) were measured until the volunteer gave up. PaCO(2) and PvCO(2) were measured at the following four points: P(0), when the rebreathing started; P(1), when both EtCO(2) and InspCO(2) indicated the same value; P(2), when both reached 50 mmHg; and P(3), when SpO(2) dropped to 90%. RESULTS: InspCO(2) increased from the beginning and showed the same value as EtCO(2) at P(1). PaCO(2) at P(1) was almost the same value as both InspCO(2) and EtCO(2). After P(1), InspCO(2), EtCO(2) and PaCO(2) increased at the same rate, and at P(2), they reached the level of PvCO(2). After P(2), all four markers continued to show the same value as they gradually increased. CONCLUSIONS: Creating conditions inside the body in which PaCO(2) increases to the same level as PvCO(2) will stop hiccups consistently. Although other physiological pathways to stop hiccups may exist, for a successful outcome it is important that the balance of power between the cerebellum and the medulla is drastically altered.