Search

Purpose: We hypothesized that adults with type 1 diabetes mellitus (T1DM) would exhibit impaired heart rate variability (HRV), QT interval, T-wave amplitude, and baroreflex sensitivity (BRS) when compared with healthy controls. In addition, we hypothesized that acute hypoglycemia would result in further adverse changes in measures of autonomic and cardiovascular function. Methods: A single 180-min hyperinsulinemic (2 mU/kg TBW/min), hypoglycemic (~3.3 umol/mL) clamp was completed in 10 healthy adults and 13 adults with T1DM. Counterregulatory hormones were assessed and measures of heart rate (electrocardiogram) and blood pressure (intra-arterial catheter or finger photoplethysmography) were analyzed at baseline and during the hypoglycemic clamp for measures of HRV, QT interval, T-wave amplitude, and spontaneous cardiac BRS (sCBRS). Results: Baseline measures of HRV, sCBRS, and T-wave amplitude were blunted in adults with T1DM when compared with healthy controls. Hypoglycemia resulted in significant reductions in HRV, sCBRS, and T-wave amplitude and prolonged QT intervals; these changes were not different between adults with T1DM and healthy controls. Conclusions: Results from the current study show that adults with T1DM exhibit impaired autonomic and cardiovascular function. Additionally, novel findings highlight an effect of acute hypoglycemia to further reduce measures of autonomic and cardiovascular function similarly between adults with T1DM and healthy controls. These results suggest that acute hypoglycemia may worsen impairments in autonomic and cardiovascular control in patients with T1DM, thus increasing the risk of ventricular arrhythmias and cardiovascular mortality. [ABSTRACT FROM AUTHOR]

Stellate ganglionectomy (SGx) was used to assess the contribution of cardiac sympathetic nerves to neurogenic hypertension in deoxycorticosterone (DOCA)–salt treated rats. Experiments were conducted in two substrains of Sprague–Dawley (SD) rats since previous studies reported bradycardia in Charles River-SD (CR-SD) rats and tachycardia in SASCO-SD (SA-SD) rats with DOCA treatment suggesting different underlying neural mechanisms. Uninephrectomized male rats underwent SGx or SHAM surgery and were instrumented for telemetric monitoring of mean arterial pressure (MAP) and heart rate (HR). After recovery, 0.9% saline solution and DOCA (50mg) were administered. Baseline MAP (Days 0–5 average) after SGx in CR-SD rats (96±2mmHg; n=7) was not significantly different (p=0.08) than CR-SD SHAM rats (103±3mmHg; n=9); however, there was a significantly lower HR during the baseline period (377±7 vs. 432±7bpm, p<0.05) in SGx rats. In SA-SD rats baseline MAP was not different between SGx and SHAM rats and HR was lower in SGx rats (428±8 vs. 371±5bpm, p<0.05). After DOCA treatment in both substrains, MAP and HR were elevated similarly in SHAM and SGx groups showing minimal impact in both groups of SGx on hypertension development. However, overall MAP in SA-SD SHAM rats reached a significantly higher level (155±10mmHg vs 135±5mmHg, p<0.05) than that observed in CR-SD SHAM rats demonstrating that the magnitude of hypertensive response to DOCA–salt treatment varies between substrains. In conclusion, removal of cardiac sympathetic nerves did not alter the development or maintenance of DOCA–salt hypertension in SD rats. [ABSTRACT FROM AUTHOR]

New Findings What is the central question of this study? Activation of the carotid body chemoreceptors with hypoxia alters baroreceptor-mediated responses in humans. We aimed to examine whether this relationship can be translated to other chemoreceptor stimuli (i.e. hypoglycaemia)., What is the main finding and its importance? We show that hypoglycaemia-mediated changes in heart rate variability and baroreflex sensitivity cannot be attributed exclusively to the carotid chemoreceptors; however, the chemoreceptors play a role in resetting the baroreflex working range during hypoglycaemia. These results provide a potential mechanism for impaired glycaemic control and increased risk of cardiac arrhythmias in patients with carotid chemoreceptor overactivity (i.e. sleep apnoea)., Activation of the carotid body chemoreceptors with hypoxia alters baroreceptor-mediated responses. We aimed to examine whether this relationship can be translated to other chemoreceptor stimuli (i.e. hypoglycaemia) by testing the following hypotheses: (i) activation of the carotid body chemoreceptors with hypoglycaemia would reduce spontaneous cardiac baroreflex sensitivity (sCBRS) in healthy humans; and (ii) desensitization of the carotid chemoreceptors with hyperoxia would restore sCBRS to baseline levels during hypoglycaemia. Ten young healthy adults completed two 180 min hyperinsulinaemic [2 mU (kg fat-free mass)−1 min−1], hypoglycaemic (∼3.2 μmol ml−1) clamps, separated by at least 1 week and randomized to normoxia (arterial partial pressure of O2, 122 ± 10 mmHg) or hyperoxia (arterial partial pressure of O2, 424 ± 123 mmHg; to blunt activation of the carotid body glomus cells). Changes in heart rate, blood pressure, plasma catecholamines, heart rate variability (HRV) and sCBRS were assessed. During hypoglycaemia, HRV and sCBRS were reduced ( P < 0.05) and the baroreflex working range was shifted to higher heart rates. When hyperoxia was superimposed on hypoglycaemia, there was a greater reduction in blood pressure and a blunted rise in heart rate when compared with normoxic conditions ( P < 0.05); however, there was no detectable effect of hyperoxia on sCBRS or HRV during hypoglycaemia ( P > 0.05). In summary, hypoglycaemia-mediated changes in HRV and sCBRS cannot be attributed exclusively to the carotid chemoreceptors; however, the chemoreceptors appear to play a role in resetting the baroreflex working range during hypoglycaemia. [ABSTRACT FROM AUTHOR]

Purpose: Primary palmar-plantar hyperhidrosis is the condition of excessive sweating of the hands and feet. For severe and medically refractory cases, endoscopic thoracic sympathotomy (ETS) is a bilateral ganglion-sparing disconnection between the stellate and T2 ganglion in an effort to minimize compensatory hyperhidrosis. The purpose of this study was to determine the effect of ETS on cardiac autonomic function. Methods: Participants in this study were 22 otherwise healthy hyperhidrosis patients with 17 returning 1-12 months after surgery. Heart rate (HR) and blood pressure were collected at rest and during sequential nitroprusside/phenylephrine infusion (modified Oxford). To determine change in cardiac autonomic function, heart rate variability indices of RMSSD, LF and HF (log, nu) power were calculated. Sequential baroreflex sensitivity was also calculated. Results: After surgery, resting HR on standardized ECG tended to be lower and reached significance during the modified Oxford baseline ( p < 0.001). HRV changed significantly between assessments with an increase in HF (nu) and decrease in LF (nu) and LF (log) spectral ranges ( p < 0.05), while the increase in RMSSD was marginally significant ( p < 0.06). Compared with matched controls, HRV indices were significantly different before surgery, but similar after surgery. No change was detected in resting sequential baroreflex sensitivity, baroslope obtained by modified Oxford or QTc interval. Conclusions: We conclude that ETS changes cardiac autonomic modulation of HR to levels similar to controls. Despite the minimally destructive nature of ETS, effects on HRV are consistent with previously reported post-sympathectomy blunting of exaggerated sympathetic control associated with hyperhidrosis. No significant changes in the baroreflex indices suggest that ETS did not significantly affect blood pressure regulation. [ABSTRACT FROM AUTHOR]

Purpose: We studied patients with palmar hyperhidrosis before and after endoscopic thoracic sympathotomy (ETS) to determine the effect of chronic sympathetic denervation on (1) forearm blood flow (FBF) response to mental stress and (2) exercise tolerance. Methods and results: Twenty-two healthy patients were evaluated before ETS, and 17 returned after surgery (11 F; 19-32 years). We measured heart rate (HR; 12 lead), blood pressure, and FBF (plethysmography, ml dl min). Supine HR tended to decrease after ETS (69 ± 10 vs. 66 ± 6, p = 0.2). Mental stress FBF was recorded during baseline, 3-min Stroop color word test, and 2-min recovery. Mental stress responses were unaffected by ETS. However, during post-mental stress recovery period, ETS resulted in a significant elevation in FBF (2 ± 1 vs. 3 ± 1), FVC (3 ± 1 vs. 4 ± 2), and a decrease in FVR (52 ± 22 vs. 32 ± 16, p < 0.01 for all). ETS resulted in a reduction in pre-exercise seated baseline HR (94 ± 2.5 beats/min preoperatively vs. 84 ± 4.3 beats/min postoperatively, p < 0.05), maximal HR response to cycle exercise, and exercise systolic blood pressure (172 ± 5.2 mmHg pre-op vs. 158 ± 5.9 mmHg post-op, p < 0.05) but not mean or diastolic pressure. VOmax and exercise duration determined by cycle ergometry was unchanged. Conclusions: Functional evidence of upper limb denervation is observed during the FBF recovery period from mental stress and hemodynamic alterations associated with upright cycle exercise. However, the sustained exercise capacity suggests modest clinical consequences. [ABSTRACT FROM AUTHOR]

Slow deep breathing (SDB) has a therapeutic effect on autonomic tone. Our previous studies suggested that coupling of the cardiovascular to the respiratory system mediates plasticity expressed in sympathetic nerve activity. We hypothesized that SDB evokes short-term plasticity of cardiorespiratory coupling (CRC). We analyzed respiratory frequency (fR), heart rate and its variability (HR&HRV), the power spectral density (PSD) of blood pressure (BP) and the ventilatory pattern before, during, and after a 20-min epoch of SDB. During SDB, CRC and the relative PSD of BP at fR increased; mean arterial pressure decreased; but HR varied; increasing ( n = 3), or decreasing ( n = 2) or remaining the same ( n = 5). After SDB, short-term plasticity was not apparent for the group but for individuals differences existed between baseline and recovery periods. We conclude that a repeated practice, like pranayama, may strengthen CRC and evoke short-term plasticity effectively in a subset of individuals. [ABSTRACT FROM AUTHOR]