Robert J. Bryg

Effect of passive tilt on sympathetic and parasympathetic components of heart rate variability in normal subjects

Decreased heart rate (HR) variability has been shown to be an independent predictor of poor outcome after acute myocardial infarction. Presumably, both reduced parasympathetic activity and increased sympathetic activity contribute to this observed HR variability response. To elucidate the physiologic contributions of the sympathetic and parasympathetic nervous systems to HR variability, the effect of passive head-up tilt (+70 degrees) was investigated on 4 indexes of HR variability in 17 healthy subjects. The standard deviation of the mean of 512 consecutive RR intervals, a traditional marker of HR variability and a purported index of cardiac parasympathetic neural tone, was compared with the mean difference of 512 consecutive RR intervals, with the maximal expiratory RR interval to minimal inspiratory RR interval ratio (respiratory RR ratio) and with the low- and high-frequency components of the power spectrum of 512 consecutive RR intervals. Passive tilt produced a nonsignificant decrease in the standard deviation of RR intervals. There was, however, a highly significant decrease in the mean difference of consecutive RR intervals and the high-frequency component of the RR-interval spectrum. Both the respiratory RR ratio and the low-frequency component of the RR-interval spectrum increased with tilt. It was concluded that the mean difference of consecutive RR intervals and the high-frequency component of the RR-interval spectrum are potentially superior indexes of pure parasympathetic neural tone and may be preferable for future use in cardiovascular studies of autonomic dysfunction.

Effects of transdermal scopolamine on heart rate variability in normal subjects

A decrease in cardiac parasympathetic tone is a recognized finding in patients with ischemic heart disease, sudden cardiac death and heart failure, correlating closely with disease severity and overall survival. To study the clinical potential of vagomimetic intervention, the effect of transdermal scopolamine on fluctuations in heart rate was studied in 32 healthy adult subjects using both time-domain (mean RR interval, standard deviation of the mean RR interval, mean of the differences between consecutive RR intervals) and frequency-domain measures (spectrum analysis of 128 consecutive RR intervals) of heart rate variability. After an exposure of 24 hours, transdermal scopolamine resulted in a significant increase in all indexes tested. The increase was most pronounced in the 0.25-Hz respiratory peak of the RR interval power spectrum, compatible with a strong vagomimetic mode of action of transdermal scopolamine. Results indicate that transdermal scopolamine may have potential merit as a selective vagotonic agent in certain patients with myocardial infarction, heart failure or ventricular arrhythmias.

Effect of pregnancy on pressure gradient in mitral stenosis.

Abstract Mitral stenosis is one of the leading cardiovascular diseases in young women. While pulmonary artery pressures during pregnancy have been shown to increase, 1 the serial changes in transmitral pressure gradients with pregnancy have not been previously reported. With the recent advent of Doppler echocardiography, 2,3 it has become possible to noninvasively assess mitral valve flow during pregnancy. We report the progressive increase in transmitral gradient from early pregnancy in 2 women.

Reassessment of the association between gastrointestinal arteriovenous malformations and aortic stenosis

PURPOSE AND PATIENTS AND METHODSnThe purported association between aortic stenosis and gastrointestinal arteriovenous malformations (AVMs) has not been rigorously evaluated. The diagnosis of aortic stenosis in most the prior studies has been based on clinical examination. We therefore utilized two-dimensional and Doppler echocardiography to document the presence or absence of aortic stenosis in 29 men with gastrointestinal AVMs documented by endoscopy.nnnRESULTSnOf the 29 patients studied, 22 (76 percent) had ejection systolic murmurs and 18 (62 percent) had echocardiographic evidence of aortic sclerosis. However, none of the patients had any evidence of aortic stenosis as assessed by Doppler echocardiography.nnnCONCLUSIONnAlthough previous case reports and retrospective studies have suggested an association between gastrointestinal AVMs and aortic stenosis, our study does not support this association and suggests the need for a prospective trial.

Impact of arrhythmias on heart rate variability-strategies to deal with imperfect clinical data

By introducing differing degrees and quality of ectopic beats into clinical data files, the considerable impact of arrhythmias on heart rate variability is demonstrated. Arrhythmias can be removed by either of three approaches proposed, each having variable fidelity with respect to restoring time and frequency domain indices of heart rate variability. Methods devised for the correction of the RR-interval time series substitute the ectopy associated RR-intervals by either a constant RR-interval, identical to the last normal value prior to the ectopic beat (Method I), by the mean value of the total sum of ectopy-associated RR-intervals (Method II) or by values generated by cubic splining and interpolation over the duration of the arrhythmia (Method III). It is shown that splining with interpolation is the overall best technique of overcoming undesired segments in data files with complex arrhythmias. The other techniques, however, have their own merits, particularly when only little ectopy is present.<<ETX>>

The effect of controlled respiration on parameters of heart rate variability

To assess whether controlling the respiratory rate affects the various parameters of heart rate variability in normal subjects, 26 healthy young subjects were studied with spontaneous and controlled respiration at 15 breaths/minute. The mean, standard deviation, and mean of the differences of consecutive RR intervals (MSD msec), the absolute power of the mayer wave sinus arrhythmia (0.05-0.15 Hz) (MWSA) and respiratory sinus arrhythmia (0.16-0.35 Hz) (RSA), and ratio of MWSA (%MSWA) and RSA (%RSA) to total power were calculated. A decrease is demonstrated in the SD and MWSA with controlled respiration which shows a decrease in the sympathetic function. There is no change in the parasympathetic system, with no change in either MSD or RSA. The ratios %MWSA and %RSA, however, change because of changes in the total power of the power spectrum.<<ETX>>

Relation of changes in hemodynamics to Doppler parameters of aortic and mitral flow in patients with congestive heart failure

We determined the relationship between the acute hemodynamic response and the Doppler-derived indices of aortic and mitral flow after a phosphodiesterase inhibitor and dobutamine. The relationships between the percent change of invasively measured stroke volume (SV), stroke work (SW) and systemic vascular resistance (SVR) and Doppler-derived aortic flow peak velocity, flow velocity integral and peak aortic acceleration were evaluated

Incidence and Mechanisms of Doppler-Detected Aortic Regurgitation in Dilated Cardiomyopathy

Patients with dilated cardiomyopathy have been noted to have aortic regurgitation by Doppler echocardiography. To determine what the incidence of aortic regurgitation is in this population and its possible mechanism, we performed a retrospective study of patients referred to the echocardiography laboratory. From the echocardiographic database, 1,131 echocardiograms were identified with global left ventricular dysfunction

Transdermal scopolamine increases heart rate variability by selective parasympathetic stimulation

Summary form only given. It was hypothesized that the transdermal application of low-dose scopolamine using the unique therapeutic system Transderm Scop would selectively augment parasympathetic cardiac reflex activity and increase heart rate variability. The authors tested several indices of heart rate variability in 31 healthy adults (age: 31+or-7 years) after 234 hours of exposure to one patch of transdermal scopolamine. It was confirmed that transdermal scopolamine markedly increases heart rate variability in healthy human adults. Power spectrum analysis of R-R intervals appears to be a very sensitive measure of changes occurring within the autonomic nervous system. Changes in the power of the 0.25-Hz band, in particular, reliably indicate changes in parasympathetic nervous system activity. Transdermal scopolamine thus holds promise as a therapeutic intervention for selectively enhancing abnormally decreased vagal tone in patients after myocardial infarction, whose reduced heart rate variability may be restored to normal.<<ETX>>