Effect of Age on Sex Differences in the Inspiratory Muscle Metaboreflex

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Sex differences exist in the cardiovascular consequences of the inspiratory muscle metaboreflex in young adults. However, it is unknown if these sex differences are present in older adults. PURPOSE: To determine the effect of age on sex differences in the cardiovascular consequences of the inspiratory muscle metaboreflex. We hypothesized that, compared to their younger counterparts, older men and women would exhibit greater 1) increases in mean arterial pressure (MAP) and limb vascular resistance (LVR) and 2) decreases in limb blood flow (QL). We also hypothesized that the inspiratory muscle metaboreflex-induced cardiovascular responses would not be different between older men and women. METHODS: Sixteen young (8 men, 8 women; 18-24 yr) and older (8 men, 8 women; 60-73 yr) adults were recruited for this study. Subjects performed inspiratory resistive breathing tasks (IRBTs) at 2% and 65% of their maximal inspiratory pressure. During the IRBTs, breathing frequency was 20 breaths min-1 with a 50% duty cycle. At rest and during the IRBTs, MAP was measured via automated oscillometry, QL was measured via Doppler ultrasound, and LVR was calculated. End tidal CO2 remained at baseline levels during the IRBTs. EMG was recorded on the leg to ensure no muscle contraction occurred. RESULTS: The 65% IRBT led to significantly greater increases in MAP from baseline in OW (15.9±8.1 mmHg) compared to YW (6.9±1.4 mmHg), but not (p>0.05) between OM (12.3±5.7 mmHg) and YM (10.8±5.7 mmHg). OW (-20.2±7.2 %) had greater (p<0.05) decreases in QL from baseline compared to YW (-9.4±10.2 %), but no differences (p>0.05) were present between OM (-22.8±9.7 %) and YM (-22.7±11.3 %) during the 65% IRBT. The 65% IRBT led to greater (p<0.05) increases in LVR in OW (48.2±25.5 %) compared to YW (19.7±15.0 %), but no differences (p>0.05) existed among OM (54.4±17.8 %) and YM (47.1±23.3 %). No differences (p>0.05) were present in MAP, QL, or LVR between OM and OW. The 2% IRBT resulted in no changes (p>0.05) in MAP, QL, or LVR across time or among groups. CONCLUSIONS: These data suggest older women compared to younger women exhibit greater inspiratory muscle metaboreflex-induced cardiovascular consequences, while there were no differences between older and younger men. Lastly, sex differences in the inspiratory muscle metaboreflex are not present in older adults.