16 research outputs found
Altered Baroreflex-Mediated Cardiovascular Responses to Acute Hypotension in Heart Failure Patients Compared to Healthy Adults
Patients with heart failure (HF) exhibit baroreflex dysfunction, which is associated with increased morbidity and mortality. Orthostatic hypotension, a decrease in blood pressure (BP) upon standing, is a condition that often occurs in HF, and may be linked with altered baroreflex responsiveness in this population. However, data on baroreflex-mediated cardiovascular responses to acute hypotension in HF patients are limited. Therefore, 8 HF patients (7 men; mean±SEM 65±3y; ejection fraction 30.5±3.1%) and 7 healthy control (CON) adults (6 men; 65±2y) underwent 7.5 minutes of unilateral lower-limb ischemia via inflation of a thigh cuff on one leg to non-pharmacologically induce acute hypotension upon cuff deflation. Beat-to-beat systolic BP, diastolic BP, and mean arterial BP (MAP; photoplethysmographic finger cuff) and heart rate (HR; electrocardiogram) were recorded continuously before, during, and after cuff inflation. Statistical analysis involved independent-samples t-tests. Baseline values were not different between groups (systolic BP: 128±8 vs. 128±4mmHg; diastolic BP: 73±3 vs. 82±5mmHg; MAP: 90±3 vs. 97±4mmHg; HR: 62±2 vs. 56±2b.min-1 for HF and CON, respectively; P\u3e0.05). The magnitude of the induced decrease in MAP was similar in both groups (HF -11±1 vs. CON -12±2mmHg; P\u3e0.05). However, the time-to-peak MAP decrease was significantly longer in HF compared to CON (HF 11±2 vs. CON 6±1s; PP\u3e0.05). However, the time-to-peak HR increase was longer in HF compared to CON (HF 9±1 vs. CON 6±1s; PP\u3e0.05). However, the time-to-peak HR increase was longer in HF compared to CON (HF 9±1 vs. CON 6±1s;
Endurance training attenuates the increase in peripheral chemoreflex sensitivity with intermittent hypoxia
Muscle mechanoreflex activation via passive calf stretch causes renal vasoconstriction in healthy humans
Rapid adjustments to autonomic control of cardiac rhythm at the onset of isometric exercise in healthy young adults
Abstract Sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) influences on cardiac rhythm at the onset of exercise, a time of rapid autonomic adjustments, are clinically important areas of investigation. Continuous wavelet transform (CWT) involves timeâfrequencyâbased heart rate variability (HRV) analysis allowing investigation of autonomic influences on cardiac rhythm during short durations of exercise. Therefore, the purpose of this study was to characterize SNS and PNS influences on cardiac rhythm at the onset of isometric exercise in healthy young adults. CWT analysis was retrospectively applied to RâR interval data (electrocardiogram) previously collected from 14 healthy young adults (26â±â2âyears) who performed 30âs, oneâlegged, isometric, calf exercise at 70% maximal voluntary contraction (MVC; 70% MVC trial) or rested (0% MVC trial). Absolute and normalized lowâfrequency (aLF, nLF; 0.04â0.15âHz) and highâfrequency (aHF, nHF; 0.15â0.4 Hz) bands and LF/HF were used to analyze one 30âs baseline period and six 5âs time windows during the 30âs exercise (70% MVC) or rest (0% MVC). Statistical analysis involved twoâway analysis of variance with postâhoc analysis. aHF, aLF, LF/HF, nHF, and nLF displayed a trialâtime interaction (all pââ€â0.027). In the 70% compared to the 0% MVC trial, aHF and nHF were lower after 5â30âs (all pââ€â0.040), aLF was lower after 20â30âs (all pââ€â0.011) and LF/HF and nLF were higher after 5â20âs (all pââ€â0.045). These results indicate the reduction of the PNS influence on cardiac rhythm begins sooner than the augmentation of the SNS influence at the onset of isometric exercise in healthy young adults
Healthy older humans exhibit augmented carotid-cardiac baroreflex sensitivity with aspirin during muscle mechanoreflex and metaboreflex activation
Local adenosine receptor blockade accentuates the sympathetic responses to fatiguing exercise
The role adenosine plays in evoking the exercise pressor reflex in humans remains controversial. We hypothesized that localized forearm adenosine receptor blockade would attenuate muscle sympathetic nerve activity (MSNA) responses to fatiguing handgrip exercise in humans. Blood pressure (Finometer), heart rate, and MSNA from the peroneal nerve were assessed in 11 healthy young volunteers during fatiguing isometric handgrip, postexercise circulatory occlusion (PECO), and passive muscle stretch during PECO. The protocol was performed before and after adenosine receptor blockade by local infusion of 40 mg aminophylline in saline via forearm Bier block (regional intravenous anesthesia). In the second experiment, the same amount of saline was infused via the Bier block. After aminophylline, the MSNA and blood pressure responses to fatiguing handgrip, PECO, and passive stretch (all P < 0.05) were significantly greater than during the control condition. Saline Bier block had no similar effects on the MSNA and blood pressure responses. These data suggest that adenosine receptor antagonism in the exercising muscles may accentuate sympathetic activation during fatiguing exercise