[Cardiorespiratory effects of heliox using a model of upper airway obstruction]

Heliox is a mixture of Oxygen and Helium. The low density of Helium allows this mixture to flow in a laminar pattern where oxygen, nitrogen or air flow would be turbulent. Therefore the force necessary to move a volume of gas (e.g. Heliox) is greatly reduced in comparison to a turbulent gas flow. In a respiratory loading experiment we investigated the effects which Heliox exerts on hemodynamic as well respiratory variables. 10 volunteers were breathing spontaneously and through three different endotracheal (ET-) tubes (ID 4.0, 4.5, 5.0 mm). The subjects were switched from room air to Heliox and differences in the variables heart rate (HR), blood pressure (BP), stroke volume (SV), stroke index (SI), peripheral vascular resistance (TPRI) and left ventricular work index (LVWI) were measured. Furthermore the (PhAng) between abdomen and thorax was detected using respiratory inductance plethysmography (n=2) and the sense of dyspnoe under the different conditions was assessed by the use of a dyspnea score (DS). The means of BP, SV, SI, TPRI and LVWI did not significantly differ between the resting and the different loading conditions irrespective of the gas that was used. The variability of hemodynamic measures was significant larger during loaded vs. unloaded breathing. Heliox could significantly reduce this degree of variability. In two subjects Heliox could also significantly reduce the PhAng as well as DS. Heliox showed effects on hemodynamic as well as respiratory and subjective variables. These effects can be interpreted as a reduction of the extent of pressure variations in the intrapleural space leading to less impact on hemodynamic variables while breathing Heliox vs. room air in a resistive loading experiment. In the future the combined measurement of hemodynmic variables as well as non-invasive assessment of respiration might shed new light on cardio-respiratory interaction and effects of Heliox during airway obstruction.