Gregory J. Gates

Changes in heart rate variability after adenotonsillectomy in children with obstructive sleep apnea.

BACKGROUND Obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular morbidity and mortality, and increased sympathetic activity is considered to be a causative link in this association. Higher levels of sympathetic activity have been reported in children with OSAS. Sympathetic predominance is indicated on heart rate variability (HRV) analysis by increased heart rate (HR) and a higher ratio of low-frequency to high-frequency band power (LF/HF). Improvement in OSAS after adenotonsillectomy (AT) in children with OSAS could, therefore, be associated with reduced HR and reduced LF/HF. METHODS Changes in HR and time and frequency components of HRV were retrospectively analyzed in 2-min epochs free of respiratory events during light, deep, and rapid-eye-movement (REM) sleep in children with OSAS who underwent polysomnography before and after AT. RESULTS Eighteen children with OSAS, aged 4.9 ± 2.4 years (mean ± SD) were studied. After AT, the apnea-hypopnea index decreased from 31.9 ± 24.8 events/h to 4.1 ± 3.7 events/h. The HR decreased after AT in all stages of sleep (99.8 ± 16.9 beats/min to 80.7 ± 12.9 beats/min [light sleep]; 100.2 ± 15.4 beats/min to 80.5 ± 12.4 beats/min [deep sleep)]; and 106.9 ± 16.4 beats/min to 87.0 ± 12.1 beats/min [REM sleep]), as did the LF/HF (1.6 ± 2.7 to 0.6 ± 0.5 [light sleep]; 1.2 ± 1.6 to 0.5 ± 0.6 [deep sleep]; and 3.0 ± 5.4 to 1.4 ± 1.7 [REM sleep]). CONCLUSIONS The proportion of sympathetic activity of the autonomic nervous system declines in children with OSAS after AT in association with improvement in sleep-disordered breathing.

Impact of intermittent hypoxia on long-term facilitation of minute ventilation and heart rate variability in men and women: Do sex differences exist?

Following exposure to intermittent hypoxia, respiratory motor activity and sympathetic nervous system activity may persist above baseline levels for over an hour. The present investigation was designed to determine whether sustained increases in minute ventilation and sympathovagal (S/V) balance, in addition to sustained depression of parasympathetic nervous system activity (PNSA), were greater in men compared with women following exposure to intermittent hypoxia. Fifteen healthy men and women matched for age, race, and body mass index were exposed to eight 4-min episodes of hypoxia during sustained hypercapnia followed by a 15-min end-recovery period. The magnitude of the increase in minute ventilation during the end-recovery period, compared with baseline, was similar in men and women (men, 1.52 +/- 0.03; women, 1.57 +/- 0.02 fraction of baseline; P < 0.0001). In contrast, depression of PNSA and increases in S/V balance were evident during the end-recovery period, compared with baseline, in men (PNSA, 0.66 +/- 0.06 fraction of baseline, P < 0.0001; S/V balance, 2.8 +/- 0.7 fraction of baseline, P < 0.03) but not in women (PNSA, 1.27 +/- 0.19 fraction of baseline, P = 0.3; S/V balance, 1.8 +/- 0.6 fraction of baseline, P = 0.2). We conclude that a sustained increase in minute ventilation, which is indicative of long-term facilitation, is evident in both men and women following exposure to intermittent hypoxia and that this response is independent of sex. In contrast, sustained alterations in autonomic nervous system activity were evident in men but not in women.

The effect of ventilation on spectral analysis of heart rate and blood pressure variability during exercise.

Heart rate variability (HRV) and systolic blood pressure variability (BPV) during incremental exercise at 50, 75, and 100% of previously determined ventilatory threshold (VT) were compared to that of resting controlled breathing (CB) in 12 healthy subjects. CB was matched with exercise-associated respiratory rate, tidal volume, and end-tidal CO(2) for all stages of exercise. Power in the low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, >0.15-0.4 Hz) for HRV and BPV were calculated, using time-frequency domain analysis, from beat-to-beat ECG and non-invasive radial artery blood pressure, respectively. During CB absolute and normalized power in the LF and HF of HRV and BPV were not significantly changed from baseline to maximal breathing. Conversely, during exercise HRV, LF and HF power significantly decreased from baseline to 100% VT while BPV, LF and HF power significantly increased for the same period. These findings suggest that the increases in ventilation associated with incremental exercise do not significantly affect spectral analysis of cardiovascular autonomic modulation in healthy subjects.

Reducing patient radiation dosage during pediatric SVT ablations using an "ALARA" radiation reduction protocol in the modern fluoroscopic era.

Ablation for supraventricular tachycardia (SVT) relies upon fluoroscopy (fluoro), which exposes the patient and staff to ionizing radiation. The objective of this work was to present a new “ALARA—As Low As Reasonably Achievable” protocol with alterations to fluoroscopic x‐ray parameters to reduce dose without an electroanatomical (EAM) approach.

The Acute Effects of Acupuncture Upon Autonomic Balance in Healthy Subjects

Restoration of the sympathovagal (S/V) balance, involving a lowering of sympathetic and/or an augmentation of vagal modulation or a combination of both is associated with improvements in cardiovascular morbidity and mortality. To determine whether acupuncture exerts a favorable influence upon resting blood pressure and sympathovagal balance, a single-blind cross-over investigation was used to study the acute effects of acupuncture on S/V balance in normal healthy subjects. The ANOVA revealed a significant lowering of the sympathovagal balance (LF:HF) during rest for the acupuncture treatment from pre (4 +/- 2 nu) to post (2.2 +/- 1.8 nu)(p < 0.05). No such change was seen during sham treatment. The ANOVA revealed significant differences in systolic blood pressures during rest (114 +/- 4 vs. 108 +/- 3 mmHg) for the acupuncture treatment (p < 0.05). No significance was found during the sham treatment. The ANOVA failed to reveal any significant improvements in sympathovagal balance during the sustained isometric contraction. The clinical significance of these findings appears to suggest that acupuncture treatment might be beneficial in lowering blood pressure at rest. Furthermore, the lowering of the blood pressure might be in part due to a lowering of the sympathovagal balance. These findings are of importance since acupuncture treatments are non-pharmacological and have no known detrimental side-effects. This investigation employed healthy volunteers, yet acupuncture has been found to have more potent effects in animal models of hypertension and or in the presence of an autonomic imbalance.

Sympathetic drive is modulated by central chemoreceptor activation.

To determine the effects of central chemoreceptor stimulation upon sympathetic modulation while minimizing baroreceptor influences, we performed a single-blind, counter-balanced, placebo-controlled trial of a modified hypercapnic/hyperoxic rebreathe protocol stimulus to activate the central chemoreflex. Muscle sympathetic nerve activity (MSNA), heart rate, blood pressure, and ventilation were recorded dynamically as subjects transitioned from a hypocapnia to hypercapnia state. The stages of data recording were defined as hyperventilation (HyV), pre-threshold (PreT) and post-threshold (PostT), with threshold being defined as the point of non-linear deviation in ventilation. The changes in MSNA (-4.2+/-52.4 arbitrary units (AU) vs. 245.0+/-84.0AU) and burst count (-0.1+/-0.7 bursts/segment vs. 2.5+/-1.7 bursts/segment) were significantly different between control and rebreathe for the HyV to PreT step. There was also a significant difference for PreT to PostT for total MSNA (3.9+/-65.4AU vs. 183.7+/-104.2AU). In a hypercapnic/hyperoxic state, the central chemoreceptors modulate sympathetic activity below the chemoreflex threshold independently of the baroreceptors, possibly contributing to basal autonomic/sympathetic tone. Central chemoreceptors also appear to play a significant role in sympathetic modulation after the threshold.

Heart rate variability in non-apneic snorers and controls before and after continuous positive airway pressure

BackgroundWe hypothesized that sympathetic nervous system activity (SNSA) is increased and parasympathetic nervous system activity (PNSA) is decreased during non-rapid eye movement (NREM) sleep in non-apneic, otherwise healthy, snoring individuals compared to control. Moreover, we hypothesized that these alterations in snoring individuals would be more evident during non-snoring than snoring when compared to control.MethodsTo test these hypotheses, heart rate variability was used to measure PNSA and SNSA in 11 normotensive non-apneic snorers and 12 control subjects before and 7-days after adapting to nasal continuous positive airway pressure (nCPAP).ResultsOur results showed that SNSA was increased and PNSA was decreased in non-apneic snorers during NREM compared to control. However, these changes were only evident during the study in which snoring was eliminated with nCPAP. Conversely, during periods of snoring SNSA and PNSA were similar to measures obtained from the control group. Additionally, within the control group, SNSA and PNSA did not vary before and after nCPAP application.ConclusionOur findings suggest that long-lasting alterations in autonomic function may exist in snoring subjects that are otherwise healthy. Moreover, we speculate that because of competing inputs (i.e. inhibitory versus excitatory inputs) to the autonomic nervous system during snoring, the full impact of snoring on autonomic function is most evident during non-snoring periods.

Novel method of signal analysis for ablation of Wolff-Parkinson-White syndrome

BACKGROUND Identification of the site of successful radiofrequency catheter ablation (RFCA) for Wolff-Parkinson-White (WPW) syndrome may be subjective. OBJECTIVE The purpose of this study was to develop an automated signal analysis program to predict a successful ablation site. METHODS Patients who underwent successful RFCA for WPW from 2008- 2010 at our center were analyzed. Inclusion criteria were age <21 years, loss of preexcitation in <5 seconds, and sustained success at 3 months. Exclusion criteria were congenital heart disease and pacing during RFCA. The standard recording system signal was filtered into low frequency (LF 0-≤0.02 Hz) and high frequency (HF >0.02-≤0.45 Hz). Software identified the beginning of the HF signal, LF and R-wave peaks, LF/HF signal amplitude, and area under the HF/LF signals. Successful and unsuccessful (radiofrequency energy applied without accessory pathway block) signals were compared. RESULTS Thirty patients were analyzed; 16 had both successful and unsuccessful signals, and 14 had a successful ablation with 1 radiofrequency application. Mean age was 13.7 ± 3.1 years, weight 54.9 ± 22.4 kg, and time to accessory pathway ablation 1.7 ± 1.4 seconds. Significant differences were found between successful and unsuccessful signals in area under HF signal, LF amplitude, LF to R time, HF ratio, and HF area × HF ratio. A receiver operating curve of HF area × HF ratio produced an area under the curve of 0.89. An HF area × HF ratio of 3.1 distinguished successful from unsuccessful signals with 100% specificity and 81% sensitivity. CONCLUSION Automated signal analysis retrospectively differentiated successful from unsuccessful signals in patients undergoing RFCA for WPW. This software may improve the safety and efficacy of RFCA in children.

The effect of chemoreceptor stimulation upon muscle sympathetic nerve activity.

The aim of this investigation was to quantify the combined peripheral and central chemoreceptor contribution to sympathetic outflow above (post) and below (pre) the chemoreceptor ventilatory threshold (CVT). We measured muscle sympathetic nerve activity (MSNA) in seven subjects during hypoxic/hypercapnic and room air rebreathe protocols. Comparisons were made using a repeated measures analysis of variance with two within subject factors. One factor contained three levels--hyperventilation, pre-CVT, and post-CVT. The other factor contained two levels--rebreathe and control. Total MSNA increased from hyperventilation to pre-CVT to post-CVT in the rebreathe trial (385.7+/-95.9, 592.4+/-155.7, 882.0+/-235.4 au/15s respectively) and remained constant in the control trial (433.0+/-189.3, 409.1+/-183.4, 406.1+/-161.4 au/15s respectively). Ventilation increased in the rebreathe trial only. Heart rate and blood pressure did not change in either trial. These data suggest that the chemoreceptors significantly contribute to the modulation of sympathetic outflow.

Improving ECG Services at a Children’s Hospital: Implementation of a Digital ECG System

Background. The use of digital ECG software and services is becoming common. We hypothesized that the introduction of a completely digital ECG system would increase the volume of ECGs interpreted at our childrens hospital. Methods. As part of a hospital wide quality improvement initiative, a digital ECG service (MUSE, GE) was implemented at the Childrens Hospital at Montefiore in June 2012. The total volume of ECGs performed in the first 6 months of the digital ECG era was compared to 18 months of the predigital era. Predigital and postdigital data were compared via t-tests. Results. The mean ECGs interpreted per month were 53 ± 16 in the predigital era and 216 ± 37 in the postdigital era (p < 0.001), a fourfold increase in ECG volume after introduction of the digital system. There was no significant change in inpatient or outpatient service volume during that time. The mean billing time decreased from 21 ± 27 days in the postdigital era to 12 ± 5 days in the postdigital era (p < 0.001). Conclusion. Implementation of a digital ECG system increased the volume of ECGs officially interpreted and reported.