Biomedical subjects

Y C Tzeng

Publications and source records attributed to Y C Tzeng.

7 recordsLinked to original sources

PubMed2007

Effects of hypercapnia and hypoxemia on respiratory sinus arrhythmia in conscious humans during spontaneous respiration.

Normally, at rest, the amplitude of respiratory sinus arrhythmia (RSA) appears to correlate with cardiac vagal tone. However, recent studies showed that, under stress, RSA dissociates from vagal tone, indicating that separate mechanisms might regulate phasic and tonic vagal activity. This dissociation has been linked to the hypothesis that RSA improves pulmonary gas exchange through preferential distribution of heartbeats in inspiration. We examined the effects of hypercapnia and mild hypoxemia on RSA-vagal dissociation in relation to heartbeat distribution throughout the respiratory cycle in 12 volunteers. We found that hypercapnia, but not hypoxemia, was associated with significant increases in heart rate (HR), tidal volume, and RSA amplitude. The RSA amplitude increase remained statistically significant after adjustment for respiratory rate, tidal volume, and HR. Moreover, the RSA amplitude increase was associated with a paradoxical rise in HR and decrease in low-frequency-to-high-frequency mean amplitude ratio derived from spectral analysis, which is consistent with RSA-vagal dissociation. Although hypercapnia was associated with a significant increase in the percentage of heartbeats during inspiration, this association was largely secondary to increases in the inspiratory period-to-respiratory period ratio, rather than RSA amplitude. Additional model analyses of RSA were consistent with the experimental data. Heartbeat distribution did not change during hypoxemia. These results support the concept of RSA-vagal dissociation during hypercapnia; however, the putative role of RSA in optimizing pulmonary perfusion matching requires further experimental validation.

Adolescent↗

PubMed2006

Mechanism of cardioventilatory coupling: insights from cardiac pacing, vagotomy, and sinoaortic denervation in the anesthetized rat.

Cardioventilatory coupling (CVC), a temporal alignment between the heartbeat and inspiratory activity, is a major determinant of breath-to-breath variation in observed respiratory rate (f(o)). The cardiac-trigger hypothesis attributes this to adjustments of respiratory timing by baroreceptor afferent impulses to the central respiratory pattern generator. A mathematical model of this hypothesis indicates that apparent CVC in graphical plots of ECG R wave vs. inspiratory time is dependent on the heart rate (HR), the rate of the intrinsic respiratory oscillator (f(i)), and the strength of the hypothetical cardiovascular afferent impulse. Failure to account for HR and f(i) may explain the inconsistent results from previous attempts to identify the neural pathways involved in CVC. Cognizant of these interactions, we factored in the HR-to-f(i) ratio in our examination of the role of the vagus nerve and arterial baroreceptors in CVC by cardiac pacing 29 anesthetized Sprague-Dawley rats and incrementally changing the HR. With the assumption of a relatively constant f(i), CVC could be examined across a range of HR-to-f(o) ratios before and after vagotomy, sinoaortic denervation, and vagotomy + sinoaortic denervation. We confirmed the relation between CVC, HR-to-f(o) ratio, and breath-to-breath respiratory period variability and demonstrated the loss of these relations after baroreceptor elimination. Sham experiments (n = 8) showed that these changes were not due to surgical stress. Our data support the notion that inspiratory timing can be influenced by cardiac afferent activity. We conclude that the putative cardiovascular input arises from the arterial baroreceptors and that the vagus nerve is not critical for CVC.

Algorithms↗

PubMed2005

Effect of automatic external defibrillator audio prompts on cardiopulmonary resuscitation performance.

OBJECTIVES: To determine the effectiveness of the cardiopulmonary resuscitation (CPR) audio prompts in an automatic external defibrillator in 24 lay subjects, before and after CPR training. METHODS: Untrained subjects were asked to perform CPR on a manikin with and without the assistance of audio prompts. All subjects were then trained in CPR, and retested them eight weeks later. RESULTS: Untrained subjects who performed CPR first without audio prompts performed poorly, with only (mean (SD)) 24.5% (32%) of compressions at the correct site and depth, a mean compression rate of 52 (31) per minute, and with 15% (32%) of ventilatory attempts adequate. Repeat performance by this group with audio prompts resulted in significant improvements in compression rate (91(12), p = 0.0002, paired t test), and percentage of correct ventilations (47% (40%), p = 0.01 paired t test), but not in the percentage correct compressions (23% (29%)). Those who performed CPR first with audio prompts performed significantly better in compression rate (87 (19), p = 003, unpaired t test), and the percentage of correct ventilations (51 (34), p = 0.003 unpaired t test), but not in the percentage of correct compressions (18 (27)) than those without audio prompts. After training, CPR performance was significantly better than before training, but there was no difference in performance with or without audio prompts, although 73% of subjects commented that they felt more comfortable performing CPR with audio prompts. CONCLUSIONS: For untrained subjects, the quality of CPR may be improved by using this device, while for trained subjects the willingness to perform CPR may be increased.

Adult↗

PubMed2004

Fractal characteristics of breath to breath timing in sleeping infants.

We examined interbreath interval (IBI) time series of 19 term infants during active and quiet sleep for fractal properties using Fano factor analysis. For each time series we calculated the fractal exponent (alpha), comparing alpha for the original time series with two forms of surrogate data, a temporally independent surrogate set and an autoregressive surrogate set. alpha values were normally distributed between 0.79 and -0.22, and did not differ with sleep state. The fractal characteristics of the original time series were not retained in the temporally independent surrogate time series indicating that the distribution of intervals alone was not fractal, but were retained using autoregressive surrogates with an order of 10, suggesting that the fractal properties of the IBI time series were related to correlations between successive breaths. These observations suggest that some of the respiratory variability that occurs during sleep in infants, which in the past has been regarded as stochastic noise, may be the product of deterministic processes.

Factor Analysis, Statistical↗

PubMed2003

Inspiratory coupling to cardiac activity and to somatic afferent nerve stimulation in the anaesthetised rat.

We examined the ability of somatic afferent nerve stimulation to entrain inspiratory onset in the anaesthetized spontaneously breathing rat, and compared features of this stimulus-ventilatory coupling to entrainment of inspiratory onset by cardiac activity. In 14 rats prior to stimulation, we commonly observed a constant temporal alignment between ECG R waves and inspiratory onset (cardioventilatory coupling). Stimulation of a hamstring nerve at rates close to the heart rate also caused coupling (a constant stimulus to inspiratory onset interval), although this was highly dependent upon frequency of stimulation, with small changes in frequency causing a loss of coupling. In experiments where stimuli were given at constant intervals after ECG R waves, we observed no augmentation of coupling. Our results indicate that both cardiac and somatic afferent nerve activity is able to entrain inspiratory onset. We have suggested that coupling causes respiratory frequency to increase, and it is possible that this is a general mechanism whereby non-respiratory afferents act as stimulants or pacemakers to respiratory rhythm. The role of non-respiratory activity in initiating inspiration needs to be more fully recognised and studied.

Anesthesia↗

PubMed2003

Quantal ventilatory variability during spontaneous breathing anaesthesia.

BACKGROUND: Cardioventilatory coupling is the triggering of inspiratory onset by preceding cardiac activity. We have observed two forms of coupling with a bimodal ('quantal') variation of respiratory period. METHODS: We investigated the variables of inspiratory duration (TI), expiratory duration (TE), and tidal volume (VT) where respiratory period variation was bimodal. In 25 anaesthetized spontaneously breathing subjects we took 11 samples of recording where the variation of respiratory period was quantal. RESULTS: In eight of these epochs the variation in respiratory period was associated with fluctuations in the number of heart beats per breath (entrainment ratio) with a constant time interval between inspiration and the immediately preceding heart beat (coupling interval), which we define as pattern II coupling. During pattern II coupling, the quantal variations in respiratory period were entirely caused by variation in TE, with no associated changes in either TI or VT. The other three epochs with quantal variations in respiratory period were observed in pattern III coupling, where an alternating fluctuation in both entrainment ratio and coupling interval occurs. During pattern III coupling, quantal fluctuations were observed in TE, TI, and VT. IMPLICATIONS: Cross correlation analysis suggested that when pattern III was present, TI was dependent upon the preceding TE, which differs markedly from traditional views on the interaction between inspiratory and expiratory duration. VT was linearly related to TI, and so could also be determined by the preceding TE during this type of coupling.

Adult↗

PubMed2003

Cardioventilatory coupling in resting human subjects.

In 48 conscious resting subjects we examined the temporal coupling of heart beat timing and the onset of inspiration (cardioventilatory coupling), and the relationship between coupling and spectral indices of autonomic function. Using the proportional Shannon entropy (SH(alpha)) of the RI(-1) interval (interval between inspiration and the preceding ECG R wave) as a measure of coupling we detected statistically significant coupling in 32 of the 48 subjects. This was confirmed by visual inspection of time series plots of RI intervals, in which coupling was evident as horizontal banding. Coupling resulted in a significant preference for whole number heart rate/respiratory frequency ratios. The strongest coupling was associated with low ventilatory frequency and high heart rate variability in the high (0.15-0.40 Hz) and low (0.04-0.15 Hz) frequency ranges, but was not related to blood pressure variability, or to a spectral measure of baroreflex sensitivity (alpha-index, low frequency range). There was no difference in coupling strength between males and females. We have previously described cardioventilatory coupling in spontaneously breathing anaesthetised subjects. The current study extends those observations by demonstrating that the qualitative features of coupling seen during anaesthesia are also observed in the conscious state. We conclude that the role of coupling in normal physiological respiratory control needs to be more widely explored.

Adolescent↗