Mechanisms Underlying Exaggerated Metaboreflex Activation in Prehypertensive Men

Augmented Hemodynamic Responses in Obese Young Men during Dynamic Exercise: Role of the Muscle Metaboreflex

Studies found that cardiovascular responses to exercise are enhanced in individuals with obesity and are associated with a greater cardiac output (CO) response compared to normal weight controls. However, the mechanisms underlying these altered responses during dynamic exercise are not clear. We investigated whether the cardiovascular responses mediated by the muscle metaboreflex (MMR) activation are augmented in obese men during both static and dynamic exercise. Twenty males (10 obese (OG) and 10 non-obese (NOG)) were studied. Changes in CO, mean arterial pressure (MAP), and total vascular conductance (TVC) were compared between the two groups during dynamic handgrip exercise (DHE), post-exercise muscular ischemia (PEMI), and dynamic exercise corresponding to 40%, 60% and 80% workloads. Subjects completed 2 min of DHE at 30% of MVC, followed by 2 min of PEMI. MAP, CO, and TVC responses to DHE and dynamic exercise were significantly higher in OG, whereas there were no differences during PEMI. Increases in CO and MAP during mild to heavy dynamic exercise were seen in both groups, but the changes in these variables were greater in the OG. There were no significant differences in TVC between the two groups. Compared to NOG, the augmented blood pressure response to DHE and dynamic exercise in OG was associated with a greater increase in CO. Thus, the augmented CO and MAP responses were not associated with the activation of the MMR. Consequently, additional factors specific to obesity, such as the mechanoreflex, may have been involved.

Effects of combined histamine H1 and H2 receptor blockade on hemodynamic responses to dynamic exercise in males with high-normal blood pressure

While postexercise hypotension is associated with histamine H₁ and H₂ receptor-mediated postexercise vasodilation, effects of histaminergic vasodilation on blood pressure (BP) in response to dynamic exercise are not known. Thus, in 20 recreationally active male participants (10 normotensive and 10 with high-normal BP) we examined the effects of histamine H₁ and H₂ receptor blockade on cardiac output (CO), mean atrial pressure (MAP), aortic stiffness (AoStiff), and total vascular conductance (TVC) at rest and during progressive cycling exercise. Compared with the normotensive group, MAP, CO, and AoStiff were higher in the high-normal group before and after the blockade at rest, while TVC was similar. At the 40% workload, the blockade significantly increased MAP in both groups, while no difference was found in the TVC. CO was higher in the high-normal group than the normotensive group in both conditions. At the 60% workload, the blockade substantially increased MAP and decreased TVC in the normotensive group, while there were no changes in the high-normal group. A similar CO response pattern was observed at the 60% workload. These findings suggest that the mechanism eliciting an exaggerated BP response to exercise in the high-normal group may be partially due to the inability of histamine receptors. Novelty Males with high-normal BP had an exaggerated BP response to exercise. The overactive BP response is known due to an increase in peripheral vasoconstriction. Increase in peripheral vasoconstriction is partially due to inability of histamine receptors.

Effects of aerobic exercise intensity on ambulatory blood pressure and vascular responses in resistant hypertension: a crossover trial

BACKGROUND

Resistant hypertension often exposes patients to poor blood pressure (BP) control, resulting in clinical vulnerability, possible need for device-based procedures (denervation) and increased therapy costs. Regular exercise markedly benefits patients with hypertension, including resistant patients. However, little is known about short-term exercise effects in resistant hypertension.

OBJECTIVE

To evaluate acute hemodynamic effects of exercise in resistant hypertension.

METHOD

After maximal exercise testing, 20 patients (54.0 ± 5.7 years, 30.2 ± 4.9 kg/m) with resistant hypertension participated in three crossover interventions, in random order, and on separate days: control (45' of rest), and light intensity and moderate intensity (45' of aerobic exercise at 50 and 75% of maximum heart rate, respectively). Ambulatory BP, forearm blood flow (with subsequent calculation of vascular resistance), and reactive hyperemia were measured before and after interventions trough venous occlusion plethysmography.

RESULTS

Compared with control, both exercise intensities reduced ambulatory systolic pressure over 5 h (light: -7.7 ± 2.4 mmHg and moderate: -9.4 ± 2.8 mmHg, P < 0.01), whereas only light intensity reduced diastolic pressure (-5.7 ± 2.2 mmHg, P < 0.01). Light intensity also lowered systolic and diastolic pressures over 10-h daytime (-3.8 ± 1.3 and -4.0 ± 1.3 mmHg, respectively, P < 0.02), night-time (-6.0 ± 2.4 and -6.1 ± 1.6 mmHg, respectively, P < 0.05), and diastolic pressure over 19 h (-4.8 ± 1.2 mmHg, P < 0.01). Forearm blood flow changed (decreased) compared with baseline only at 50 min after light intensity (P < 0.05). After the control and light intensity sessions, vascular resistance increased at the end of 1 h, and after moderate intensity, it decreased only at the moment (∼2 min) immediately after intervention (P < 0.05).

CONCLUSION

A single session of light or moderate aerobic exercise acutely reduces ambulatory BP in resistant hypertension, although benefits persist longer following light intensity.

Metaboreflex activation delays heart rate recovery after aerobic exercise in never-treated hypertensive men

KEY POINTS

Recent evidence indicates that metaboreflex regulates heart rate recovery after exercise (HRR). An increased metaboreflex activity during the post-exercise period might help to explain the reduced HRR observed in hypertensive subjects. Using lower limb circulatory occlusion, the present study showed that metaboreflex activation during the post-exercise period delayed HRR in never-treated hypertensive men compared to normotensives. These findings may be relevant for understanding the physiological mechanisms associated with autonomic dysfunction in hypertensive men.

ABSTRACT

Muscle metaboreflex influences heart rate (HR) regulation after aerobic exercise. Therefore, increased metaboreflex sensitivity may help to explain the delayed HR recovery (HRR) reported in hypertension. The present study assessed and compared the effect of metaboreflex activation after exercise on HRR, cardiac baroreflex sensitivity (cBRS) and heart rate variability (HRV) in normotensive (NT) and hypertensive (HT) men. Twenty-three never-treated HT and 25 NT men randomly underwent two-cycle ergometer exercise sessions (30 min, 70% V̇O2 peak ) followed by 5 min of inactive recovery performed with (occlusion) or without (control) leg circulatory occlusion (bilateral thigh cuffs inflated to a suprasystolic pressure). HRR was assessed via HR reduction after 30, 60 and 300 s of recovery (HRR30s, HRR60s and HRR300s), as well as by the analysis of short- and long-term time constants of HRR. cBRS was assessed by sequence technique and HRV by the root mean square residual and the root mean square of successive differences between adjacent RR intervals on subsequent 30 s segments. Data were analysed using two- and three-way ANOVA. HRR60s and cBRS were significant and similarly reduced in both groups in the occlusion compared to the control session (combined values: 20 ± 10 vs. 26 ± 9 beats min-1 and 2.1 ± 1.2 vs. 3.2 ± 2.4 ms mmHg-1 , respectively, P < 0.05). HRR300s and HRV were also reduced in the occlusion session, although these reductions were significantly greater in HT compared to NT (-16 ± 11 vs. -8 ± 15 beats min-1 for HRR300s, P < 0.05). The results support the role of metaboreflex in HRR and suggest that increased metaboreflex sensitivity may partially explain the delayed HRR observed in HT men.

Acute resistance exercise with blood flow restriction in elderly hypertensive women: haemodynamic, rating of perceived exertion and blood lactate

PURPOSE

This study aimed to compare haemodynamic, rating of perceived exertion and blood lactate responses during resistance exercise with blood flow restriction (BFR) compared with traditional high-intensity resistance exercise in hypertensive older women.

METHODS

Eighteen hypertensive women (age = 67·0 ± 1·7 years.) undertook three random sessions: (i) three sets; 10 repetitions; 20% of one repetition maximum (1RM) with BFR; (ii) three sets; 10 repetitions; 65% of 1RM; without BFR; and (iii) no-exercise with BFR. The exercise sessions were performed on knee extension equipment.

RESULTS

Systolic (SBP) and diastolic blood pressure (DBP), heart rate (HR), stroke volume (SV) and cardiac output (CO) were significantly higher (P<0·05) in all sets of exercise sessions than the control. No statistically significant differences were detected between exercise sessions. However, SBP, DBP and systemic vascular resistance were higher (P<0·05) and SV and CO were lower (P<0·05) during the rest intervals in the session with BFR. The perceived exertion was significantly higher (P<0·01) in the 1st (4·8 ± 0·4 versus 3·1 ± 0·3), 2nd (7·3 ± 0·4 versus 5·7 ± 0·4) and 3rd sets (8·6 ± 0·5 versus 7·5 ± 0·4) of the traditional high-intensity resistance exercise compared with the exercise with BFR. Blood lactate was higher (P<0·05) in the traditional high-intensity resistance exercise (6·2 ± 0·7 mmol) than in the exercise with BFR (4·5 ± 0·4 mmol).

CONCLUSION

In comparison with high-intensity resistance exercise, low-intensity resistance exercise with BFR can elicit: (i) same haemodynamic values during exercise; (ii) lower rating of perceived exertion; (iii) lower blood lactate; (iv) higher haemodynamic demand during the rest intervals.

Attenuated muscle metaboreflex-induced pressor response during postexercise muscle ischemia in renovascular hypertension

During dynamic exercise, muscle metaboreflex activation (MMA; induced via partial hindlimb ischemia) markedly increases mean arterial pressure (MAP), and MAP is sustained when the ischemia is maintained following the cessation of exercise (postexercise muscle ischemia, PEMI). We previously reported that the sustained pressor response during PEMI in normal individuals is driven by a sustained increase in cardiac output (CO) with no peripheral vasoconstriction. However, we have recently shown that the rise in CO with MMA is significantly blunted in hypertension (HTN). The mechanisms sustaining the pressor response during PEMI in HTN are unknown. In six chronically instrumented canines, hemodynamic responses were observed during rest, mild exercise (3.2 km/h), MMA, and PEMI in the same animals before and after the induction of HTN [Goldblatt two kidney, one clip (2K1C)]. In controls, MAP, CO and HR increased with MMA (+52 ± 6 mmHg, +2.1 ± 0.3 l/min, and +37 ± 7 beats per minute). After induction of HTN, MAP at rest increased from 97 ± 3 to 130 ± 4 mmHg, and the metaboreflex responses were markedly attenuated (+32 ± 5 mmHg, +0.6 ± 0.2 l/min, and +11 ± 3 bpm). During PEMI in HTN, HR and CO were not sustained, and MAP fell to normal recovery levels. We conclude that the attenuated metaboreflex-induced HR, CO, and MAP responses are not sustained during PEMI in HTN.