The blood flow and vascular responses in dynamically exercising skeletal muscles evoked by combination of cold stimulation and voluntary apnea in humans.

PURPOSE

We evaluated (1) the combined effects of cold stimulation and voluntary breath holding (apnea) on heart rate, blood pressure, blood flow and vascular responses in dynamically exercising muscles in humans, and (2) if some interactions exist between cold stimulation and apnea on the cardiovascular responses.

METHODS

Nine males and 1 female performed three trials entailing a dynamic two-legged knee extension exercise at a constant workload that elicited heart rates around 100 beats min. During the trials the participants performed either: (1) immersed their right hand into ice water maintained at 4 °C (cold pressor test; CPT); (2) performed maximal-duration apnea; and (3) performed a combination of CPT and apnea. Leg blood flow (LBF) and cardiac output (CO) were measured simultaneously using two Doppler ultrasound systems.

RESULTS

CPT induced a rise in mean arterial pressure (MAP) (P < 0.05) but had no significant effect on CO or exercising leg vascular conductance (LVC). Apnea evoked large pressor responses, bradycardia and decreases in CO, LBF and LVC (all P < 0.05). The increase in MAP induced by combined CPT and apnea was smaller than the sum of those induced separately by CPT or apnea (P < 0.05). Combined CPT and apnea decreased LBF and LVC to a similar extent as apnea alone.

CONCLUSION

Addition of local cold stimulation to apnea does not enhance pressor responses or vasoconstriction within active muscles. This suggests that maximum voluntary apnea evokes massive vasoconstriction, even within exercising muscles, which cannot be enhanced by additional sympathetic stimulation.