Eucapnic voluntary hyperventilation test decreases exhaled nitric oxide level in children.

Background: Exhaled nitric oxide (FeNO) measurements and eucapnic voluntary hyperventilation (EVH) tests have been used as diagnostic tools for asthma. Data on the impact of hyperventilation on the level of FeNO are limited.

Aim: We aimed to evaluate whether EVH tests affect the level of FeNO in children aged 10-16 years.

Cut-off values to evaluate exercise-induced asthma in eucapnic voluntary hyperventilation test for children.

Background And Aim: The eucapnic voluntary hyperventilation (EVH) testing is a diagnostic tool for diagnostics of exercise-induced bronchoconstriction; while the testing has become more common among children, data on the test's feasibility among children remain limited. Our aim was to investigate EVH testing feasibility among children, diagnostic testing cut-off values, and which factors affect testing outcomes.

Methods: We recruited 134 patients aged 10-16 years with a history of exercise-induced dyspnoea and 100 healthy control children to undergo 6-min EVH testing.

Alterations in heart rate variability in patients with peripheral arterial disease requiring surgical revascularization have limited association with postoperative major adverse cardiovascular and cerebrovascular events.

Objective: Obstructive sleep apnea (OSA) is common in peripheral arterial disease (PAD) and associates with high mortality after surgery. Since abnormal heart rate variability (HRV) is predictive of postoperative complications, we investigated the relations of HRV with PAD, OSA and major adverse cardiovascular and cerebrovascular events (MACCE).

Materials And Methods: Seventy-five patients (67±9 years) scheduled for sub-inguinal revascularization and 15 controls (63±6 years) underwent polysomnography and HRV analyses.

Eucapnic voluntary hyperventilation test in children.

Background: In children, exercise-induced dyspnea is a common symptom that can be due to dysfunctional breathing. EVH test has bee used especially in elite athletes as bronchoprovocation test. Currently, there are only few studies on the EVH test.

Automated Detection of Atrial Fibrillation Based on Time-Frequency Analysis of Seismocardiograms.

In this paper, a novel method to detect atrial fibrillation (AFib) from a seismocardiogram (SCG) is presented. The proposed method is based on linear classification of the spectral entropy and a heart rate variability index computed from the SCG. The performance of the developed algorithm is demonstrated on data gathered from 13 patients in clinical setting.

Respiratory modulation of human autonomic function: long-term neuroplasticity in space.

Key Points: We studied healthy astronauts before, during and after the Neurolab Space Shuttle mission with controlled breathing and apnoea, to identify autonomic changes that might contribute to postflight orthostatic intolerance. Measurements included the electrocardiogram, finger photoplethysmographic arterial pressure, respiratory carbon dioxide levels, tidal volume and peroneal nerve muscle sympathetic activity. Arterial pressure fell and then rose in space, and drifted back to preflight levels after return to Earth.

Respiratory modulation of human autonomic function on Earth.

Key Points: We studied healthy supine astronauts on Earth with electrocardiogram, non-invasive arterial pressure, respiratory carbon dioxide concentrations, breathing depth and sympathetic nerve recordings. The null hypotheses were that heart beat interval fluctuations at usual breathing frequencies are baroreflex mediated, that they persist during apnoea, and that autonomic responses to apnoea result from changes of chemoreceptor, baroreceptor or lung stretch receptor inputs. R-R interval fluctuations at usual breathing frequencies are unlikely to be baroreflex mediated, and disappear during apnoea.

Human hair in the identification of cocaine abuse with cantilever-enhanced photoacoustic spectroscopy and principal component analysis.

In this study, a novel approach combining different techniques, including Fourier transform infrared (FT-IR) spectroscopy, photoacoustic spectroscopy (PAS) with an interferometric cantilever microphone, and principal component analysis (PCA) along with a proper data preprocessing procedure, have been used in the investigation of hair samples for cocaine abuse. Hair fibers from cocaine-overdose patients have been measured using a simple procedure involving cantilever-enhanced photoacoustic Fourier transform infrared spectroscopy. In addition, a reference group of hair samples from subjects with no cocaine abuse has been measured.

Baroreflex physiology studied in healthy subjects with very infrequent muscle sympathetic bursts.

Because it is likely that, in healthy human subjects, baroreflex mechanisms operate continuously, independent of experimental interventions, we asked the question, In what ways might study of unprovoked, very infrequent muscle sympathetic bursts inform baroreflex physiology? We closely examined arterial pressure and R-R interval responses of 11 supine healthy young subjects to arterial pressure ramps triggered by large isolated muscle sympathetic bursts. We triggered data collection sweeps on the beginnings of sympathetic bursts and plotted changes of arterial pressure (finger volume clamp or intra-arterial) and R-R intervals occurring before as well as after the sympathetic triggers. We estimated baroreflex gain from regression of R-R intervals on systolic pressures after sympathetic bursts and from the transfer function between cross-spectra of systolic pressure and R-R intervals at low frequencies.

Delta entropy of heart rate variability along with deepening anesthesia.

Background: Conventional time and frequency domain measures of heart rate variability (HRV) are strongly influenced by anesthetic drugs, and are therefore not able to detect subtle changes in HRV, even during light anesthesia. Approximate entropy of R-R intervals is an HRV measure that has a tendency to decrease during anesthesia, but it is severely compromised by low-frequency variations of the signal. However, the negative effect of the low-frequency variations can be eliminated by differentiating the R-R interval tachogram before analysis.

Muscle sympathetic nerve activity during intense lower body negative pressure to presyncope in humans.

Activation of sympathetic efferent traffic is essential to maintaining adequate arterial pressures during reductions of central blood volume. Sympathetic baroreflex gain may be reduced, and muscle sympathetic firing characteristics altered with head-up tilt just before presyncope in humans. Volume redistributions with lower body negative pressure (LBNP) are similar to those that occur during haemorrhage, but limited data exist describing arterial pressure-muscle sympathetic nerve activity (MSNA) relationships during intense LBNP.

Cardiac repolarization and striatal dopamine transporter function are interrelated.

Objective: In Parkinson's disease, striatal dopamine transporter (DAT) binding and cardiac sympathetic function are disturbed. In addition, heart rate (HR)-corrected cardiac repolarisation time (QTc interval), which is partly under autonomic control, is prolonged. Whether there is physiological coupling between striatal DAT binding and QTc time (QTc-DAT relation) is not known.

Rapid prediction of trauma patient survival by analysis of heart rate complexity: impact of reducing data set size.

Heart rate complexity (HRC) is an emerging "new vital sign" for critically ill and injured patients. Traditionally, 800-beat data sets have been used to calculate HRC variables, thus limiting their practical use in an emergency. We sought to investigate whether data set reductions diminish the use of HRC to predict mortality in prehospital trauma patients.

Heart-rate complexity for prediction of prehospital lifesaving interventions in trauma patients.

Background: Traditional vital signs often fail to identify critically injured patients soon enough to permit timely intervention. To improve our ability to forecast the need for prehospital lifesaving interventions (LSIs), we applied heart-rate complexity (HRC) analysis to the electrocardiogram (ECG) of patients en route to trauma centers.

Methods: Analysis of ECG and clinical data from 374 patients en route by helicopter to three urban Level I trauma centers was conducted.

Assessment of cardiovascular regulation after burns by nonlinear analysis of the electrocardiogram.

Critical illness and hypovolemia are associated with loss of complexity of the R-to-R interval (RRI) of the electrocardiogram, whereas recovery is characterized by restoration thereof. Our goal was to investigate the dynamics of RRI complexity in burn patients. We hypothesized that the postburn period is associated with a state of low RRI complexity, and that successful resuscitation restores it.

Prehospital loss of R-to-R interval complexity is associated with mortality in trauma patients.

Background: To improve our ability to identify physiologic deterioration caused by critical injury, we applied nonlinear analysis to the R-to-R interval (RRI) of the electrocardiogram of prehospital trauma patients.

Methods: Ectopy-free, 800-beat sections of electrocardiogram from 31 patients were identified. Twenty patients survived (S) and 11 died (NonS) after hospital admission.

The role of heart rate variability in risk stratification for adverse postoperative cardiac events.

There is growing evidence of a strong association between the compromised autonomic nervous system and sudden cardiac death. Heart rate variability (HRV) measures are widely used to measure alterations in the autonomic nervous system. Several studies with cardiac patients show that decreased HRV as well as baroreceptor dysfunction are more powerful predictors for sudden cardiac death than established clinical predictors such as left ventricular ejection fraction.

Sympathetic nerve activity and heart rate variability during severe hemorrhagic shock in sheep.

Introduction: In this study we explored direct and indirect measures of autonomic nervous system function, as well as changes in cardiovascular complexity, during hemorrhagic shock (HS).

Methods: HS was induced in anesthetized sheep (n=8) by removing 40 ml/kg of blood in four 10 ml/kg steps over 40 min. Resuscitation was performed with lactated Ringer's and re-infusion of shed blood.

Effects of cellular phone use on ear canal temperature measured by NTC thermistors.

The earlier studies using phantom models and human subjects concerning warming effects during cellular phone use have been controversial, partly because radiofrequency (RF) exposures have been variable. In this randomized, double-blind, placebo-controlled crossover trial, 30 healthy subjects were submitted to 900 MHz (2W) and 1800 MHz (1W) cellular phone RF exposure, and to sham exposure in separate study sessions. Temperature signals were recorded continuously in both ear canals before, during and after the 35-min RF exposure and the 35-min sham exposure sessions.

Comparison of methods for editing of ectopic beats in measurements of short-term non-linear heart rate dynamics.

Non-linear heart rate (HR) dynamics characterizes the fractal properties and complexity of the variations in HR. Ventricular and supraventricular ectopic beats might introduce a mathematical artefact to the analyses on sinus rhythm. We therefore evaluated the effects of different editing practices for ectopic beats such that 753 40-min ECG recordings were (i) not edited for the ectopic beats, or the ectopic beats were edited with (ii) an interpolation or with (iii) a deletion method before the analyses of non-linear HR dynamics.

Loss of complexity characterizes the heart rate response to experimental hemorrhagic shock in swine.

Objective: To improve our ability to identify physiologic deterioration caused by critical illness, we applied nonlinear and frequency-domain analytical methods to R-to-R interval (RRI) and systolic arterial pressure (SAP) time series during hemorrhagic shock.

Design: Prospective, randomized, controlled trial.

Setting: Animal laboratory of a government research institute.

Estimation of cardiac output in a pharmacological trial using a simple method based on arterial blood pressure signal waveform: a comparison with pulmonary thermodilution and echocardiographic methods.

Objective: Cardiac output (CO) has traditionally been measured using invasive techniques, which involve an element of risk. Thus, a reliable less-invasive method for determining CO would be very valuable for research use. We tested whether simple analysis of the arterial pulse waveform, not requiring large-vessel catheterisation or expensive equipment, could provide an estimate of CO that is accurate enough for pharmacological studies.

Stochastic model for heart-rate fluctuations.

A normal human heart rate shows complex fluctuations in time, which is natural, because the heart rate is controlled by a large number of different feedback control loops. These unpredictable fluctuations have been shown to display fractal dynamics, long-term correlations, and 1/f noise. These characterizations are statistical and they have been widely studied and used, but much less is known about the detailed time evolution (dynamics) of the heart-rate control mechanism.

Analysis of rapid heart rate variability in the assessment of anticholinergic drug effects in humans.

Anticholinergic agents have widespread therapeutic indications in clinical medicine. In addition, certain other drug groups-such as neuroleptics, antidepressants and antihistamines-possess distinct anticholinergic properties that reduce tolerance and compliance. Especially in patients with heart disease, attention should be paid to cardiac anticholinergic drug effects.