Hemodynamic responses to neuromuscular electrical stimulation and to metaboreflex activation.

BACKGROUND: Metabolites produced during muscle exercise can sensitize types III and IV fibers, which account for increasing blood pressure (BP) and vascular resistance in non-exercising limbs, as well as for redistributing the blood flow to active muscles; reflex response is called metaboreflex. Neuromuscular electrical stimulation (NMES) induces greater local muscle metabolic demand than voluntary isometric contractions. Metabolic accumulation is essential to activate muscle metaboreflex; thus, the hypothesis of the current study is that one NMES session can induce metaboreflex with different hemodynamic responses in upper and lower limbs. Objective - to investigate whether one acute NMES session could activate metaboreflex by inducing different hemodynamic responses between arms and legs. METHODS: Twenty (20) healthy subjects (mean age = 47.7±9.4 years, 13 women, mean body mass index = 26 ± 3 kg/m2) participated in this randomized crossover study. All participants were subjected to two NMES interventions, one in the upper limbs (UPL) and the other in the lower limbs (LL). Mean blood pressure (MBP), blood flow (BF) and vascular resistance (VR) were used to selectively evaluate metaboreflex responses at baseline, during NMES interventions, and recovery periods with, and without, postexercise circulatory occlusion (PECO+ and PECO-, respectively) through the area under the curve (AUC) in VR. RESULTS: MBP increased by 13% during UPL interventions and only remained high during PECO+. Changes in MBP were not observed in LL, although BF in the contralateral leg has decreased by 14% during PECO+ protocol. Muscle metaboreflex activation (AUC differences in VR between PECO+ and PECO-) was not different between UPL and LL (P=0.655). CONCLUSIONS: Acute NMES session has induced similar metaboreflex activation in both arms and legs, although hemodynamic responses differed between interventions.

Increased Maximal Expiratory Pressure, Abdominal and Thoracic Respiratory Expansibility in Healthy Yoga Practitioners Compared to Healthy Sedentary Individuals

Abstract Background Increasing thoracic expansion is effective at reducing blood pressure in hypertensive subjects. Yoga prescribes many respiratory techniques with a growing number of practitioners. However, very little is known whether sedentary or yoga practitioners show measurable differences in their respiratory patterns. Objective This study aims to demonstrate differences between healthy sedentary individuals and healthy yoga practitioners regarding maximal respiratory pressures and thoracic and abdominal respiratory expansibility. Methods Maximal inspiratory and expiratory pressures (MIP and MEP, respectively) were evaluated by manovacuometry, while respiratory expansion was assessed by the cirtometry of abdominal (CA), thoracic xiphoidal (CTX), and thoracic axillary (CTA) circumferences at rest (end expiratory moment) and at full inspiration in healthy sedentary individuals (SED) and yoga practitioners (YOGA). A delta derived from rest and full inspiration measures (ΔCA, ΔCTX, and ΔCTA, respectively), followed by a percentage of each item (ΔCA/CA, ΔCTX/CTX, and ΔCTA/CTA) was then calculated. Groups were compared by means of an unpaired Student's t-test, with a significance level p < 0.05. Results All respiratory expansion measures were significantly higher in in the YOGA group. A significantly higher MEP (cmH2O) was also detected in yoga practitioners: SED 89.3 ± 19.3 and YOGA 114.7 ± 24.8 ( p = 0.007), along with decreased heart rate at rest (bpm): SED 84±6 and YOGA 74±15 ( p = 0.001). Conclusions Yoga practitioners have shown greater thoracic and abdominal expansion and increased MEP, when compared to healthy sedentary individuals, as well as significantly lower heart rates at rest and body mass index (BMI). However, whether or not these findings are related to respiratory patterns is uncertain.

Optimization of Vagal Stimulation Protocol Based on Spontaneous Breathing Rate.

Controlled breathing maneuver is being widely applied for cardiovascular autonomic control evaluation and cardiac vagal activation through reduction of breathing rate (BR). However, this maneuver presented contradictory results depending on the protocol and the chosen BR. These variations may be related to the individual intrinsic profile baseline sympathetic tonus, as described before by others. In this study, we evaluated the effect of controlled breathing maneuver on cardiovascular autonomic control in 26 healthy subjects allocated into two protocols: (1) controlled breathing in three different rates (10, 15, and 20 breaths/min) and (2) controlled breathing in rates normalized by the individual spontaneous breathing rate (SBR) at 100, 80, 70, and 50%. Our results showed autonomic responses favorable to vagal modulation with the lower BR maneuvers. Nevertheless, while this activation was variable using the standard protocol, all participants of the normalized protocol demonstrated an increase of vagal modulation at 80% BR (HFnu 80 = 67.5% vs. 48.2%, p < 0.0001). These results suggest that controlled breathing protocols to induce vagal activation should consider the SBR, being limited to values moderately lower than the baseline.

Continuous positive airway pressure reduces blood pressure in patients with obstructive sleep apnea; a systematic review and meta-analysis with 1000 patients.

BACKGROUND: Obstructive sleep apnea (OSA) may lead to the development of hypertension and therapy with continuous positive airway pressure (CPAP) can promote reduction in blood pressure. OBJECTIVE: The objective of this study is to review systematically the effects of CPAP on blood pressure in patients with OSA. METHODS: The search was conducted in the following databases, from their beginning until February 2013: MEDLINE, Embase, Cochrane CENTRAL, Lilacs and PEDro. In addition, a manual search was performed on references of published studies. Randomized clinical trials (RCTs) that used CPAP compared with placebo CPAP or subtherapeutic CPAP for treatment of patients with OSA and that evaluated office SBP and DBP and 24-h ambulatory blood pressure were selected. RESULTS: Sixteen RCTs were included among 3409 publications, totaling 1166 patients. The use of CPAP resulted in reductions in office SBP [-3.20  mmHg; 95% confidence interval (CI) -4.67 to -1.72] and DBP (-2.87  mmHg; 95% CI -5.18 to -0.55); in night-time SBP (-4.92  mmHg; 95% CI -8.70 to -1.14); in mean 24-h blood pressure (-3.56  mmHg; 95% CI -6.79 to -0.33), mean night-time blood pressure (-2.56  mmHg; 95% CI -4.43 to -0.68) and 24-h DBP (-3.46  mmHg; 95% CI -6.75 to -0.17). However, no significant change was observed in daytime SBP (-0.74  mmHg; 95% CI -3.90 to 2.41) and daytime DBP (-1.86  mmHg; 95% CI -4.55 to 0.83). CONCLUSION: Treatment with CPAP promoted significantly but small reductions in blood pressure in individuals with OSA. Further studies should be performed to evaluate the effects of long-term CPAP and the impact on cardiovascular risk.