Search results for "Chronotropic"

Polyunsaturated fatty acids in cultured cardiomyocytes : effect on physiology and beta-adrenoceptor function

1992

This study was carried out to investigate the influence of the membrane fatty acid composition on the basal electrical and contractile activities and the response to beta-adrenergic stimulation of rat cardiac muscle cells in culture. Cells were grown for 3 days in a conventional serum culture medium and then incubated for 24 h in synthetic media containing either n-6 or n-3 as the sole source of polyunsaturated fatty acids (PUFA). The n-6/n-3 ratio in the phospholipids was 0.9 in the n-3 cells and 13.1 in the n-6 cells compared with 6.3 in controls cells. Such modifications did not alter action potentials and the main parameters related to contraction, although shortening was slightly acce…

Study on the histamine-like activity of guanfacine

1990

Abstract The effects of guanfacine have been studied on guinea-pig isolated atria and diethylstilboestrol-treated rat isolated uterus to determine whether it possesses histamine-like activity. Guanfacine produced a concentration-dependent negative chronotropic effect which was not modified by ranitidine (0.1 μM). In rat isolated uterus contracted by KCl, clonidine (5–5000 μM) produced concentration-dependent relaxation which was blocked by ranitidine (0.1 μM), but guanfacine only produced relaxation at high concentrations (100–1000 μM), and this was not affected by ranitidine (0.1 μM). It is concluded that guanfacine, unlike clonidine, does not produce effects due to activation of H2-recept…

Effects of the Phosphodiesterase Inhibitor Enoximone on the Autonomic Innervation of the Isolated Heart

1989

Enoximone is a selective inhibitor of a low Km, cyclic AMP-specific type of phosphodiesterase (PDE III). In guinea pig and chicken atria, enoximone (0.1-100 mumol/L) caused a weak increase in the force of contraction. The heart rate was slightly enhanced or was unchanged (chicken). Enoximone (30 mumol/L) also failed to shift the concentration-response curves for the positive inotropic and chronotropic effects of norepinephrine in guinea pig atria. Under almost the same conditions, enoximone and the nonselective PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX) markedly potentiated the forskolin-induced mobilization of choline from phospholipids. The concentrations of IBMX (100 mumol/L) and o…

Ouabain enhances release of acetylcholine in the heart evoked by unilateral vagal stimulation.

1986

The aim of the study was to elucidate peripheral effects of ouabain on the parasympathetic innervation of the heart, effects that could contribute to the experimentally and clinically well established “vagal effect of cardiac glycosides”. The experiments were carried out with ouabain concentrations of 3×10−7 and 10−6 mol/l, which were considered “therapeutic”, as they increased force of contraction and did not elicit arrhythmias in incubated chicken atria. In atrial preparations of chickens and guinea-pigs the negative chronotropic and inotropic effects of acetylcholine (ACh) were not altered by 3×10−7 mol/l ouabain. Resting efflux of ACh from perfused chicken hearts was increased by ouabai…

Selection of blood pressure signal for baroreflex analysis

2020

This study aims to evaluate the strength of the causal coupling among systolic, mean and diastolic blood pressure (SBP, MBP and DBP) with heart period (RR interval) (evaluating cardiac chronotropic baroreflex arm) and peripheral vascular resistance (PVR) (evaluating vascular resistance baroreflex arm) in frequency domain using partial spectral decomposition method. We recorded beat-to-beat RR, SBP, MBP and DBP and PVR values in 39 volunteers during supine rest and head-up tilt. Our results showed that during supine rest the most dominant causal coupling was from DBP to RR in both low and high frequency bands and significantly decreased during orthostasis. The strength of spectral couplings …

Heart rate response and functional capacity in patients with chronic heart failure with preserved ejection fraction

2018

Aims The mechanisms of exercise intolerance in heart failure with preserved ejection fraction (HFpEF) are not yet elucidated. Chronotropic incompetence has emerged as a potential mechanism. We aimed to evaluate whether heart rate (HR) response to exercise is associated to functional capacity in patients with symptomatic HFpEF. Methods and results We prospectively studied 74 HFpEF patients [35.1% New York Heart Association Class III, 53% female, age (mean ± standard deviation) 72.5 ± 9.1 years, and 59.5% atrial fibrillation]. Functional performance was assessed by peak oxygen consumption (peak VO2 ). The mean (standard deviation) peak VO2 was 10 ± 2.8 mL/min/kg. The following chronotropic pa…

Chronotropic Incompetence Predicts Distance Walked in Six-Minute Walk Test in Heart Failure With Preserved Ejection Fraction

2020

Heart rate response and functional capacity in patients with chronic heart failure with preserved ejection fraction

2018

Aims: The mechanisms of exercise intolerance in heart failure with preserved ejection fraction (HFpEF) are not yet elucidated. Chronotropic incompetence has emerged as a potential mechanism. We aimed to evaluate whether heart rate (HR) response to exercise is associated to functional capacity in patients with symptomatic HFpEF. Methods and results We prospectively studied 74 HFpEF patients [35.1% New York Heart Association Class III, 53% fe- male, age (mean ± standard deviation) 72.5 ± 9.1 years, and 59.5% atrial fi brillation]. Functional performance was assessed by peak oxygen consumption (peak VO 2 ). The mean (standard deviation) peak VO 2 was 10 ± 2.8 mL/min/kg. The following chronotro…

Beta‐blockers withdrawal in patients with heart failure with preserved ejection fraction and chronotropic incompetence: Effect on functional capacity…

2020

Abstract Background The pathophysiology of heart failure with preserved ejection fraction (HFpEF) is complex and multifactorial. Chronotropic incompetence (ChI) has emerged as a crucial pathophysiological mechanism. Beta‐blockers, drugs with negative chronotropic effects, are commonly used in HFpEF, although current evidence does not support its routine use in these patients. Hypothesis We postulate beta‐blockers may have deleterious effects in HFpEF and ChI. This work aims to evaluate the short‐term effect of beta‐blockers withdrawal on functional capacity assessed by the maximal oxygen uptake (peakVO2) in patients with HFpEF and ChI. Methods This is a prospective, crossover, randomized (1…

Acetylcholine overflow from isolated perfused hearts of various species in the absence of cholinesterase inhibition

1977

1. The content of acetylcholine in the tissue and effluent of isolated hearts of various birds and mammals was determined in the absence of inhibition of cholinesterase. 2. Stimulation of both vagus nerves for 15 min at 20 Hz caused marked negative chronotropic effects in all species. Spontaneous or stimulation-induced overflow of acetylcholine into the effluents was not detected in mammals. In the avian heart, the order of spontaneous overflow was: duck = chicken > pigeon, whereas the order of evoked overflow was: chicken > pigeon > duck. The acetylcholine overflow from the cat heart was below the limit of estimation (3 pmol g−1 min−1). In the chicken heart, the evoked overflow per min (28…