Changes in heart rate during breathing interrupted by recurrent apneas in humans

Heart rate varies with breathing patterns, especially in sleep apnea. To assess the effects on heart rate of recurrent apneas interrupting tidal breathing, we studied five normal awake male subjects. These subjects voluntarily changed their breathing pattern from regular tidal breathing to tidal breathing interrupted by breath holding at end expiration. This recurrent apneic breathing pattern did not change mean heart rate but increased its variance significantly. In addition, the variations in heart rate formed a cyclic pattern of oscillation with a mean cycle length identical to both arterial O₂ saturation [Sa(O₂)] (R = 0.95; P < 0.01) and ventilation (R = 0.92; P < 0.01). Cyclic changes in either Sa(O₂) or ventilation reproduced the oscillatory patterns of heart rate seen with tidal breathing interrupted by multiple apneas, but the amplitude of the variance in heart rate was smaller. Finally, preventing the cyclic declines in Sa(O₂) with supplemental O₂ did not significantly alter the heart rate changes seen in tidal breathing interrupted by apneas.