Exaggerated Inspiratory Muscle Metaboreflex in Arterial Hypertension

Older hypertensive patients (HTN) experience abnormal cardiovascular responses to exercise mediated in part by alterations in the metabolically sensitive component of the exercise pressor reflex (metaboreflex) from contracting muscle. High inspiratory muscle work and the concomitant accumulation of metabolites elicit activation of neural afferents resulting in increases in mean arterial pressure (MAP) (i.e., inspiratory muscle metaboreflex). It is unknown if HTN patients exhibit exaggerated cardiovascular responses to inspiratory muscle metaboreflex activation. PURPOSE: To investigate the effect of high-intensity inspiratory resistive breathing (to activate the inspiratory muscle metaboreflex) on cardiovascular responses in HTN compared to age-matched controls (CTL). We hypothesized that time to task failure during the high-intensity inspiratory resistive breathing task (IRBT) would be less for HTN than CTL. Further, we hypothesized that HTN during the high-intensity IRBT would have greater increases in MAP than CTL. METHODS: HTN (n = 8; 69 ± 8 yrs; 29 ± 4 kg/m2) and CTL (n = 9; 70 ± 7 yrs; 28 ± 4 kg/m2) performed an IRBT at 60% of their maximal inspiratory pressure until task failure. During the IRBTs, the breathing frequency was 20 breaths/min with a 50% duty cycle. At rest and during the IRBTs, mean arterial pressure (MAP, via finger photoplethysmography) and mouth pressure were continuously measured. RESULTS: Maximal inspiratory pressure was not different between groups (HTN: 91 ± 29 vs. CTL: 99 ± 29 cmH2O, p = 0.57). During the 60% IRBT, time to task failure was not different between HTN and CTL (HTN: 537 ± 385 vs. CTL: 518 ± 397 s, p = 0.81). MAP was not different between groups at rest (HTN: 98 ± 10 vs. CTL: 90 ± 5 mmHg) (p = 0.16) but was higher in HTN than CTL at task failure (HTN: 116 ± 13 vs. CTL: 100 ± 11 mmHg) (p < 0.01). The change in MAP from rest to task failure was greater in HTN than CTL (HTN: 19 ± 8 vs. CTL: 10 ± 7 mmHg, p = 0.03). HR was not different between groups at rest or task failure during the 60% IRBT (both, p > 0.43). The increase in HR from rest to task failure was not different between groups (HTN: 13 ± 8 vs. CTL: 17 ± 8 beats/min, p = 0.35). CONCLUSION: These data suggest that inspiratory muscle metaboreflex activation elicits an exaggerated cardiovascular response in older hypertensive patients compared to healthy adults.