Heart-rate variability effects of beta-adrenoceptor agonists (xamoterol, prenalterol, and salbutamol) assessed nonlinearly with scatterplots and sequence methods

"In-House" Data on the Outside-A Mobile Health Approach

Mobile health (mHealth) technologies have the potential to capture dense patient data on the background of real-life behavior. Merck & Co., Inc. (Kenilworth, NJ), in collaboration with Koneksa Health, conducted a phase I clinical trial to validate cardiovascular mHealth technologies for concordance with traditional approaches and to establish sensitivity to detect effects of pharmacological intervention. This two-part study enrolled 18 healthy male subjects. Part I, a 5-day study, compared mHealth measures of heart rate (HR) and blood pressure (BP) to those from traditional methods. Hypotheses of similarity, in the clinic and at home, were tested individually for HR, systolic BP, and diastolic BP, at a 2-sided 0.05 alpha level, with a prespecified criterion for similarity being the percentage differences between the 2 measurements within 15%. Part II, a 7-day, 3-period randomized balanced crossover study, evaluated the mHealth technology's ability to detect effects of bisoprolol and salbutamol. Hypotheses that the changes from baseline in HR were greater in the bisoprolol (reduction in HR) and salbutamol (increase in HR) groups compared with no treatment were tested, at a 1-sided 0.05 alpha level. Linear mixed-effects models, Pearson's correlation coefficients, summary statistics, and exploratory plots were applied to analyze the data. The mHealth measures of HR and BP were demonstrated to be similar to those from traditional methods, and sensitive to changes in cardiovascular parameters induced by bisoprolol and salbutamol.

Heart Rate Variability Analysis: Higuchi and Katz’s Fractal Dimensions in Subjects with Type 1 Diabetes Mellitus

Background and aims: Statistical markers are valuable when assessing physiological status over periods of time and in certain disease states. We assess if type 1 diabetes mellitus promote modification in the autonomic nervous system using the main two types of algorithms to estimate a Fractal Dimension: Higuchi and Katz.

Material and methods: 46 adults were divided into two equal groups. The autonomic evaluation consisted of recording heart rate variability (HRV) for 30 minutes in supine position in absence of any other stimuli. Fractal dimensions ought then able to determine which series of interbeat intervals are derived from diabetics’ or not. We then equated results to observe which assessment gave the greatest significance by One-way analysis of variance (ANOVA1), Kruskal-Wallis technique and Cohen’s d effect sizes.

Results: Katz’s fractal dimension is the most robust algorithm when assisted by a cubic spline interpolation (6 Hz) to increase the number of samples in the dataset. This was categorical after two tests for normality; then, ANOVA1, Kruskal-Wallis and Cohen’s d effect sizes (p≈0.01 and Cohen’s d=0.814143 –medium effect size).

Conclusion: Diabetes significantly reduced the chaotic response as measured by Katz’s fractal dimension. Katz’s fractal dimension is a viable statistical marker for subjects with type 1 diabetes mellitus.

Anesthetic considerations for patients with acute cervical spinal cord injury

Anesthesiologists work to prevent or minimize secondary injury of the nervous system and improve the outcome of medical procedures. To this end, anesthesiologists must have a thorough understanding of pathophysiology and optimize their skills and equipment to make an anesthesia plan. Anesthesiologists should conduct careful physical examinations of patients and consider neuroprotection at preoperative interviews, consider cervical spinal cord movement and compression during airway management, and suggest awake fiberoptic bronchoscope intubation for stable patients and direct laryngoscopy with manual in-line immobilization in emergency situations. During induction, anesthesiologists should avoid hypotension and depolarizing muscle relaxants. Mean artery pressure should be maintained within 85-90 mmHg (1 mmHg = 0.133 kPa; vasoactive drug selection and fluid management). Normal arterial carbon dioxide pressure and normal blood glucose levels should be maintained. Intraoperative neurophysiological monitoring is a useful option. Anesthesiologists should be attentive to postoperative respiratory insufficiency (carefully considering postoperative extubation), thrombus, and infection. In conclusion, anesthesiologists should carefully plan the treatment of patients with acute cervical spinal cord injuries to protect the nervous system and improve patient outcome.

Autonomic dysfunction in patients with chronic obstructive pulmonary disease (COPD)

It has been recognized that chronic obstructive pulmonary disease (COPD) is a systemic disease which has been shown to negatively affect the cardiovascular and autonomic nerve system. The complexity of the physiologic basis by which autonomic dysfunction occurs in patients with COPD is considerable and the knowledge in this field remains elementary. The purpose of this review is to provide an overview of important potential mechanisms which might affect the autonomic nervous system in patients with COPD. This review aims to summarize the basic research in the field of autonomic dysfunction in patients with COPD. In COPD patients the activity of sympathetic nerves may be affected by recurrent hypoxemia, hypercapnia, increased intrathoracic pressure swings due to airway obstruction, increased respiratory effort, systemic inflammation and the use of betasympathomimetics. Furthermore, experimental findings suggest that autonomic dysfunction characterized by a predominance of sympathetic activity can significantly modulate further inflammatory reactions. The exact relationship between autonomic dysfunction and health status in COPD remains to be elucidated. Treatment aimed to restore the sympathovagal balance towards a reduction of resting sympathetic activity may modulate the inflammatory state, and possibly contributes to improved health status in COPD.

Short-term effects of inhaled salbutamol on autonomic cardiovascular control in healthy subjects: a placebo-controlled study

AIMS

To investigate short-term effects of inhaled salbutamol on haemodynamic changes and cardiovascular autonomic control.

METHODS

A randomized, single-blinded, placebo-controlled study of 0.2 mg of inhaled salbutamol was conducted on 12 healthy nonsmoking volunteers with a mean age of 24 +/- 2 years at two different testing sessions. Non-invasively obtained continuous haemodynamic measurements of cardiac output, beat-to-beat arterial blood pressure, and total peripheral resistance were recorded prior to and for a total of 120 min after inhalation of the respective study drug. Continuous cardiovascular autonomic tone was recorded using power spectral analysis of heart rate and blood pressure variability. Spontaneous baroreceptor activity was assessed by the sequence method.

RESULTS

There were no significant changes in any of the baseline parameters between the different testing sessions. Inhalation of salbutamol caused a significant increase in cardiac output from 6.7 +/- 1.3 to 7.7 +/- 1.4 l min(-1) (P < 0.05), and a decrease in total peripheral resistance from 1076 +/- 192 to 905 +/- 172 dyne s(-1) cm(-5) (P < 0.05) within 15 min after inhalation. Moreover, salbutamol significantly increased sympathetically mediated low-frequency heart rate variability (P < 0.01), whereas parasympathetically mediated high-frequency heart rate variability decreased (P < 0.01). All changes persisted for approximately 30 min and were fully reversible at 120 min. There were no significant changes in systolic blood pressure variability or spontaneous baroreceptor activity.

CONCLUSIONS

Inhalation of therapeutic doses of salbutamol in healthy subjects resulted in significant haemodynamic changes and a shift of sympathovagal balance towards increased sympathetic tone in the absence of baroreceptor activation.

Beta1-adrenergic receptors maintain fetal heart rate and survival

Beta-adrenergic receptor (betaAR) activation has been shown to maintain heart rate during hypoxia and to rescue the fetus from the fetal lethality that occurs in the absence of norepinephrine. This study examines whether the same subtype of betaAR is responsible for survival and heart rate regulation. It also investigates which betaARs are located on the early fetal heart and whether they can be directly activated during hypoxia. Cultured E12.5 mouse fetuses were treated with subtype-specific betaAR antagonists to pharmacologically block betaARs during a hypoxic insult. Hypoxia alone reduced heart rate by 35-40% compared to prehypoxic levels. During hypoxia, heart rate was further reduced by 31% in the presence of a beta(1)AR antagonist, CGP20712A, at 100 nM, but not with a beta2 (ICI118551)- or a beta3 (SR59230A)-specific antagonist at 100 nM. Survival in utero was also mediated by beta1ARs. A beta1 partial agonist, xamoterol, rescued 74% of catecholamine-deficient (tyrosine-hydroxylase-null) pups to birth, a survival rate equivalent to that with a nonspecific betaAR agonist, isoproterenol (87%). Receptor autoradiography showed that beta1ARs were only found on the mouse heart at E12.5, while beta2ARs were localized to the liver and vasculature. To determine if the response to hypoxia was intrinsic to the heart, isolated fetal hearts were incubated under hypoxic conditions in the presence of a betaAR agonist. Heart rate was reduced to 25-30% by hypoxia alone, but was restored to 63% of prehypoxic levels with 100 nM isoproterenol. Restoration was completely prevented if beta1ARs were blocked with CGP20712A at 300 nM, a concentration that blocks beta1ARs, but not beta2- or beta3ARs. Our results demonstrate that beta1ARs are located on the heart of early fetal mice and that beta1AR stimulation maintains fetal heart rate during hypoxia and mediates survival in vivo.

Heart rate variability in young patients with diabetes mellitus and healthy subjects explored by Poincaré and sequence plots

Autonomic neuropathy is a common complication of the diabetes mellitus (DM). The significance of its early diagnosis is very high because the mortality of the patients with this complication is elevated. Considering the effort to apply new mathematical methods to cardiac dysregulation diagnosis, the major aim of the study was to ascertain which of the new heart rate variability (HRV) parameters are different in young patients with DM type 1 compared with control group. The next aim was to assess the HRV changes during prolonged (40 min) supine rest. The heart rate was continuously recorded during supine rest in 17 young patients with DM type 1 (10 women, 7 men) aged 22.4 +/- 1.0 years (mean +/- SEM). The control group consisted of 17 healthy matched probands. The HRV (time/frequency domains, Poincare and sequence plots, sample entropy) was analysed in two intervals - T1 starting at fifth minute and T2 starting at 30th minute of supine rest. The major results of our study are: the reduced Poincare plot pattern measures in the young DM group; the lower percentage of points in the third quadrant of sequence plot (this parameter was not correlated with the mean heart rate) and significant changes in HRV during supine rest in DM group (in contrast to control subjects). In conclusion, HRV parameters based on nonlinear dynamics were able to distinguish cardiac dysregulation in young patients with DM from the control group. The percentage of points in the third quadrant of sequence plot provides information that is not dependent on mean heart rate. Poincare and sequence plots, together with the rate of HRV changes during supine rest, can provide clinically relevant information usable in diagnosis of the cardiac dysregulation.

High-frequency modulation of heart rate variability during exercise in patients with COPD

STUDY OBJECTIVES

To evaluate cardiac autonomic modulation in patients with COPD during peak exercise.

METHODS

Fifty-three patients with COPD (mean FEV(1), 35% predicted [SD, 11% predicted]; mean PaO(2), 68 mm Hg [SD, 11 mm Hg]; mean PaCO(2), 40 mm Hg [SD, 7 mm Hg]; mean age, 61 years [SD, 10 years]; 26 women and 27 men) and 14 healthy control subjects aged 60 years (SD, 8 years) [seven women and seven men] were studied at rest and during ramped bicycle ergometry to their volitional peak. Patients were not receiving autonomic medications other than inhaled beta-agonist agents and/or anticholinergic agents. Control subjects were not receiving any medications. Cardiac autonomic modulation was assessed via time-frequency analysis (Wigner-Ville) of ECG-derived heart rate variability as the power in the low-frequency (LF) band (ie, 0.04 to 0.15 Hz) and the high-frequency (HF) band (ie, > 0.15 to 0.4 Hz) averaged from > 3 min at rest and minutes 2 through 5 of their exercise period.

RESULTS

Patients with COPD had a significantly increased mean, ln-transformed HF band from rest to peak exercise (9.9 ms(2) [SD, 1.4 ms(2)] vs 10.7 ms(2) [SD, 1.4 ms(2)], respectively; p < 0.01), while the HF band was unchanged for the control group (10.7 ms(2) [SD, 1.5 ms(2)] vs 10.4 ms(2) [1.3 ms(2)], respectively; difference not significant). The mean ln-transformed LF band was significantly increased from rest to peak exercise in patients with COPD (10.9 ms(2) [SD, 1.5 ms(2)] vs 11.5 ms(2) [SD, 1.4 ms(2)], respectively; p < 0.01) and in control subjects (10.9 ms(2) [SD, 1.5 ms(2)] vs 11.5 ms(2) [SD, 1.3 ms(2)], respectively; p < 0.01). The mean LF/HF ratio was significantly decreased from rest to peak exercise in patients with COPD (3.1 [SD, 1.5] vs 2.5 [SD, 1.0], respectively; p < 0.01) and was increased in control subjects (1.9 [SD, 0.8] vs 2.4 [1.0], respectively; p < 0.01). When expressed in normalized units ([absolute power of the components]/[total power - very low frequency power] x 100), the HF band was again significantly greater during peak exercise than at rest in the patients with COPD and was unchanged during peak exercise for the control group. Autonomic changes were not significantly correlated with age, gender, body mass index, spirometry, lung volumes, resting gas exchange, or oxygen saturation during exercise.

CONCLUSION

These data suggest that, in contrast to control subjects, the balance of sympathetic to parasympathetic cardiac modulation decreases in patients with COPD during maximal volitional exercise.

On- and off-responses of heart rate to exercise - relations to heart rate variability

During physical exercise, heart rate (HR) increases by parasympathetic withdrawal and increase of sympathetic activity to the heart. HR variability (HRV) in time and frequency domains provides information about autonomic control of the cardiovascular system. Non-linear analysis using the Poincaré plot method is able to reveal supplementary information about cardiac autonomic control. The aim of this study was to determine the association between HRV parameters, the initial increase of HR at the onset of exercise (on-response) and HR decrease in the recovery phase after acute exercise (off-response). HR was continuously monitored in 17 healthy male subjects (mean age: 20.3 +/- 0.2 (SEM) years) at rest (25 min supine; 5 min standing), during exercise (8 min of step test at 70% of maximal power output) and in the recovery phase (30 min supine). HRV analysis in time and frequency domains and evaluation of the Poincaré plot measures (length, widths) were performed on selected segments of HR time series. HR on- and off-responses were quantified using an exponential curve fitting technique. The time constants T(on) and T(off), representing the rate of on- and off-responses to exercise, were computed. Postexercise HRV indices and time constant of on-response - T(on) - to exercise were negatively correlated. From preexercise HRV indices, only Poincaré plot parameters were correlated with T(on). No correlation between HRV indices and parameters of off-response was found. In conclusion, preexercise HRV parameters are not closely correlated with the rate of cardioacceleration at the onset of exercise and cannot predict the rate of HR recovery. On the other hand, postexercise HRV parameters are related to the rate of initial adjustment of HR to exercise referring to the importance of rapid HR on-response for a faster recovery after exercise.

Developmental changes in heart rate variability during exposure to prolonged hypercapnia in piglets

The hypothesis that hypercapnia-induced differences in heart rate variability (HRV) would emerge during early maturation was tested using a developing porcine model. Piglets were randomly assigned to either exposed (10% CO2 for 1 h) or control (100% O2) conditions, and then to one of three study groups: (a) 5-8 days old, (b) 13-15 days old, (c) 26-34 days old. Experiments were performed on pairs of age-and litter-matched animals that were anesthetized, paralyzed, and artificially ventilated. HRV was evaluated using power spectral analysis, SD of differences between successive RR intervals, and cardiac interval analysis. Statistical comparisons of simultaneously studied animals were made at baseline, 15 and 55 min after onset of hypercapnia, and 2 h after offset of hypercapnia. Our analyses revealed that only HRV of 26-34-day-old animals differed significantly from values of control animals. Cardiac intervals of those animals were distributed in such a manner that hypercapnia likely elicited coactivation of sympathetic and parasympathetic systems. Comparison of the distribution of cardiac intervals for other animals showed that 5-8-day-old animals had high frequency of balanced intervals at baseline that remained so during hypercapnia. Given that such coactivation may be neuroprotective, the paucity of balanced intervals in 13-15-day-old animals could mean that the end of the second postnatal week is associated with increased vulnerability.

Low-level inotropic stimulation with type III phosphodiesterase inhibitors in patients with advanced symptomatic chronic heart failure receiving beta-blocking agents

beta-blocking agents are now well established as a cornerstone therapy in mild to moderate heart failure. Patients with more advanced heart failure depend on adrenergic activation to maintain adequate myocardial function. This leads to significant difficulties in using beta-blockers in advanced or severe heart failure. In addition, recent data indicate that adrenergic withdrawal might be detrimental in some of these patients. In higher doses, positive inotropic agents have been shown to increase mortality when used alone in subsets with advanced heart failure. Preliminary data suggest that the combination of low-dose phosphodiesterase inhibitors and a beta-blocker may be better tolerated and does not appear to be associated with the adverse effects of either therapy used alone. We discuss the theoretic underpinning of this approach and the supportive clinical data.