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Respiratory sinus arrhythmia (RSA) is heart rate variability in synchrony with respiration, by which the R-R interval on an ECG is shortened during inspiration and prolonged during expiration. Although RSA has been used as an index of cardiac vagal function, it is also a physiologic phenomenon reflecting respiratory-circulatory interactions universally observed among vertebrates. Previous studies have shown that the efficiency of pulmonary gas exchange is improved by RSA, suggesting that RSA may play an active physiologic role. The matched timing of alveolar ventilation and its perfusion with RSA within each respiratory cycle could save energy expenditure by suppressing unnecessary heartbeats during expiration and ineffective ventilation during the ebb of perfusion. Furthermore, evidence has accumulated of a possible dissociation between RSA and vagal control of that heart rate, suggesting differential controls between the respiratory modulation of cardiac vagal outflow and cardiac vagal tone. RSA or heart rate variability in synchrony with respiration is a biological phenomenon, which may have a positive influence on gas exchange at the level of the lung via efficient ventilation/perfusion matching. [ABSTRACT FROM AUTHOR]

Aims: To evaluate the effect of considerably high left ventricular filling pressure with mitral regurgitation on mitral annular velocity during early diastole.Subjects: Two hundred and forty-three patients who underwent cardiac catheterization for evaluation of chest pain.Methods: Mitral annular velocity during early diastole was measured by colour M-mode tissue Doppler imaging. Patients were divided into the following three groups according to the cardiac catheterization data. Group A (n=147): patients having left ventricular relaxation time constant τ<46 ms and left ventricular end-systolic volume index <38 ml m−2; group B (n=88): patients having τ≥46 ms and/or end-systolic volume index ≥38 ml m−2; group C (n=8): patients having mean pulmonary capillary wedge pressure ≥16 mmHg in addition to τ≥46 ms and end-systolic volume index ≥38 ml m−2.Results: Mitral annular velocity during early diastole was significantly less in group B (4·8±1·4 cm s−1) than in group A (7·7±1·9 cm s−1). However, there was no significant difference between groups A and C (8·3±0·8 cm s−1). A transmitral E/A >1·0 was observed in 12/147 patients of group A, 10/88 of group B, and 8/8 of group C. The incidence of ≥Sellers' grade II mitral regurgitation was higher in group C than the others.Conclusions: A paradoxically faster mitral annular velocity during early diastole is found in patients having left ventricular dysfunction with moderate to severe mitral regurgitation and considerably high left ventricular filling pressure. Attention should be paid to an interpretation of mitral annular velocity during early diastole regarding left ventricular early diastolic performance in patients having mitral regurgitation with an E/A >1·0 in their transmitral flow. Copyright 2002 The European Society of Cardiology. Published by Elsevier Science Ltd. All rights reserved. [ABSTRACT FROM AUTHOR]

Study Objectives: We examined whether autonomic functions assessed by heart rate variability (HRV) during standardized head-up tilt testing (HUTT) predict risk for death in stable patients with coronary artery disease (CAD).Design and Setting: Retrospective cohort study in medium-sized university general hospital.Measurements and Results: In a cohort of 250 patients with CAD who were undergoing elective coronary angiography, we analyzed HRV during standardized HUTT under paced breathing with discontinuation of treatment with all medications. During a subsequent mean follow-up period of 99 months, there were 13 cardiac deaths and 12 noncardiac deaths. Cox regression analysis adjusted for cardiovascular risks revealed that increased postural change (supine to upright) in the power of low-frequency component (LF) power predicted an increased risk for cardiac death (relative risk [per 1-ln ms(2) increment], 4.36; 95% confidence interval, 1.64 to 11.6), while neither the high-frequency component nor its response to HUTT predicted any form of death. When the patients were trichotomized by the level of postural LF change (large drop, < or = - 0.6 ln[ms(2)]; small drop and rise, > 0 ln[ms(2)]), the three groups did not differ in terms of clinical features or CAD severity at baseline or coronary interventions during the follow-up period; however, the 8-year cardiac mortality rates were 0%, 6%, and 12%, respectively (p = 0.008 [log rank test]). Additionally, the difference was enhanced when analyzed excluding 64 patients who had been treated with a beta-blocker during the follow-up period (0%, 7%, and 15%, respectively; p = 0.006 [log rank test]).Conclusions: The postural response of HRV predicts the risk for death in patients with CAD. Postural LF increase (LF rise), in particular, is an independent risk factor for cardiac death. [ABSTRACT FROM AUTHOR]

Abstract Background The extent of clinical exposure needed to ensure quality care has not been well determined during internal medicine training. We aimed to determine the association between clinical exposure (number of cases seen), self- reports of clinical competence, and type of institution (predictor variables) and quality of care (outcome variable) as measured by clinical vignettes. Methods Cross-sectional study using univariate and multivariate linear analyses in 11 teaching hospitals in Japan. Participants were physicians-in-training in internal medicine departments. Main outcome measure was standardized t-scores (quality of care) derived from responses to five clinical vignettes. Results Of the 375 eligible participants, 263 (70.1%) completed the vignettes. Most were in their first (57.8%) and second year (28.5%) of training; on average, the participants were 1.8 years (range = 1–8) after graduation. Two thirds of the participants (68.8%) worked in university-affiliated teaching hospitals. The median number of cases seen was 210 (range = 10–11400). Greater exposure to cases (p = 0.0005), higher self-reports of clinical competence (p = 0.0095), and type of institution (p < 0.0001) were significantly associated with higher quality of care, using a multivariate linear model and adjusting for the remaining factors. Quality of care rapidly increased for the first 100 to 200 cases seen and tapered thereafter. Conclusion The amount of clinical exposure and levels of self-reports of clinical competence, not years after graduation, were positively associated with quality of care, adjusting for the remaining factors. The learning curve tapered after about 200 cases.

Abstract Background Due to its easy applicability, pulse wave has been proposed as a surrogate of electrocardiogram (ECG) for the analysis of heart rate variability (HRV). However, its smoother waveform precludes accurate measurement of pulse-to-pulse interval by fiducial-point algorithms. Here we report a pulse frequency demodulation (PFDM) technique as a method for extracting instantaneous pulse rate function directly from pulse wave signal and its usefulness for assessing pulse rate variability (PRV). Methods Simulated pulse wave signals with known pulse interval functions and actual pulse wave signals obtained from 30 subjects with a trans-dermal pulse wave device were analyzed by PFDM. The results were compared with heart rate and HRV assessed from simultaneously recorded ECG. Results Analysis of simulated data revealed that the PFDM faithfully demodulates source interval function with preserving the frequency characteristics of the function, even when the intervals fluctuate rapidly over a wide range and when the signals include fluctuations in pulse height and baseline. Analysis of actual data revealed that individual means of low and high frequency components of PRV showed good agreement with those of HRV (intraclass correlation coefficient, 0.997 and 0.981, respectively). Conclusion The PFDM of pulse wave signal provides a reliable assessment of PRV. Given the popularity of pulse wave equipments, PFDM may open new ways to the studies of long-term assessment of cardiovascular variability and dynamics.