Comparison of the effects of exercise and posture on the baroreflex in man

Pickering, Thomas G.; Gribbin, B.; Petersen, E. Strange; Cunningham, D. J.; Sleight, Peter

doi:10.1093/cvr/5.4.582

Cited by 40 publications

(27 citation statements)

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“…Discrepancies may arise from the use of different methods for the assessment of the reflex sensitivity [43][44][45]. By using the transfer function gain between cardiac interval and blood pressure, orthostatic stress resulted in decreases in sensitivity, a finding that is consistent with other studies [15,46]; however, there was no significant difference between the groups of subjects. Thus, we suggest that at least the cardiac component of the baroreflex does not play an important role in the development of syncope, as also proposed by others [45].…”

Section: Autonomic Function In Subjects During Orthostatic Stresssupporting

confidence: 72%

Spectral and cross-spectral autoregressive analysis of cardiovascular variables in subjects with different degrees of orthostatic tolerance

Gulli

Wight

Hainsworth

et al. 2001

Clinical Autonomic Research

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The mechanisms leading to vasovagal syncope are still unclear. A simple discriminating test for the identification of syncopeprone subjects is not presently available. Fifty-two subjects had a stepwise orthostatic test with 60 ~ tilt and -20 and -40 mm Hg lower-body negative pressure before the appearance of impending syncope symptoms. Spectral and cross-spectral analyses of heart period and systolic pressure time series were performed to estimate the power of the high-frequency (= 0.25 Hz) and low-frequency (= 0.1 Hz) oscillations, the coherence between heart period and systolic pressure, and the mean low-frequency and high-frequency central frequency, phase shift, and transfer fimction at maximal coherence. According to time to presyncope, the 52 subjects were divided into two groups: 25 with normal orthostatic tolerance, and 27 with poor orthostatic tolerance. In the supine positions, the mean central low-frequency was significantly lower in poortolerance group than in normal-tolerance group, discriminating poor from normal orthostatic tolerance with 80% specificity and 83% sensitivity, and was significantly correlated to time to presyncope. In the 2 to 3 minutes preceding syncope, subjects with poor orthostatic tolerance had less tachycardia, lower low-frequency power of systolic pressure, higher respiratory frequency, and a less negative phase shift in highfrequency range. In presyncope, sympathetic activation is reduced in subjects with poor orthostatic tolerance. In addition, the higher breathing frequency and the smaller negativity of phase shift in high-frequency range, which may indicate an inadequate engagement of the baroreflex, suggest a causal role of respiration in the development of syncope. Supine central values of low frequency may be proposed as a valuable clinical index of orthostatic intolerance. Received April 20, 2000; accepted as revised February 22, 2001Vasovagal, or neurocardiogenic, syncope is a sudden onset ofhypotension often associated with bradycardia and sometimes asystole, and leads to a short period of loss of consciousness that is usually followed by a rapid and complete recovery. Although the actual trigger mechanisms for the attack are still debated, it is now well established that there is an inappropriate change in autonomic nervous activity consisting of sympathetic withdrawal and often an increase in vagal efferent discharge [1,2]. Vasodilatation is the dominant syncope-initiating effect because prevention of bradycardia by administration of atropine or by cardiac pacing does not usually prevent the hypotension [3,4].Vasovagal attacks are associated with decreased cardiac filling and can be reproduced in a laboratory by applying a sufficiently severe orthostatic stress. Sometimes, a period of passive head-up tilting alone can induce the attacks [5], but often it is necessary to increase the stress by combining it with a vasodilator, such as isoproterenol [6] or nitrate [7], or by combining head-up tilting with suction applied to the lower body [8]. However, it may not alw...

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Section: Autonomic Function In Subjects During Orthostatic Stresssupporting

confidence: 72%

Spectral and cross-spectral autoregressive analysis of cardiovascular variables in subjects with different degrees of orthostatic tolerance

Gulli

Wight

Hainsworth

et al. 2001

Clinical Autonomic Research

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“…BRS has been reported to be lower in the standing position compared to supine [24] and this was confirmed in our study. Both IDDM patients and control subjects had lower BRS on standing.…”

Section: Discussionsupporting

confidence: 90%

Assessment of baroreceptor-cardiac reflex sensitivity using time domain analysis in patients with IDDM and the relation to left ventricular mass index

et al. 1996

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Summary Autonomic dysfunction in insulin-dependent diabetic (IDDM) patients has been associated with abnormalities of left ventricular function and an increased risk of sudden death. A group of 30 patients with IDDM and 30 age, sex and blood pressure matched control subjects underwent traditional tests of autonomic function. In addition, baroreceptor-cardiac reflex sensitivity (BRS) was assessed using time domain (sequence) analysis of systolic blood pressure and pulse interval data recorded non-invasively using the Finapres beat-to-beat blood pressure recording system. 'Up BRS' sequences-increases in systolic blood pressure associated with lengthening of R-R interval, and 'down BRS' sequences-decreases in systolic blood pressure associated with shortening of R-R interval were identified and BRS calculated from the regression of systolic blood pressure on R-R interval for all sequences. We also assessed heart rate variability using power spectral analysis and, after expressing components of the spectrum in normalised units, assessed sympathovagal balance from the ratio of low to high frequency powers. IDDM subjects underwent 2-D echocardiography to assess left ventricular mass index. Standard tests of autonomic function revealed no differences between IDDM patients and control subjects, but dramatic reductions in baroreceptor-cardiac reflex sensitivity were detected in IDDM patients. 'Up BRS' when supine was 11.2 ± 1.5 ms/mmHg (mean ± SEM) compared with 20.4 ± 1.95 in control subjects (p < 0.003) and when standing was 4.1 ± 1.9 vs 7.6 ± 2.7 ms/mmHg (p < 0.001). Down BRS when supine was 11.5 ± 1.2 vs 22 ± 2.6 (p < 0.001) and standing was 4.4 ± 1.9 vs 7.3 ± 2.5 ms/ mmHg (p < 0.003). There were significant relations between impairment of the baroreflex and duration of diabetes (p < 0.001) and poor glycaemic control (p < 0.001). From a fast Fourier transformation of supine heart rate data and using a band width of 0.05-0.15 Hz as low-frequency and 0.2-0.35 Hz as high frequency total spectral power of R-R interval variability was significantly reduced in the IDDM group for both low-frequency (473 ± 62.8 vs 746.6 ± 77.6 ms 2 p = 0.002) and high frequency bands 125.2 ± 12.9 vs 459.3 ± 89.8 ms 2 p < 0.0001. When the absolute powers were expressed in normalised units the ratio of low frequency to high frequency power (a measure of sympathovagal balance) was significantly increased in the IDDM group (2.9 ± 0.53 vs 4.6 ± 0.55, p < 0.002 supine: 3.8 ± 0.49 vs 6.6 ± 0.55, p < 0.001 standing). Thus, time domain analysis of baroreceptor-cardiac reflex sensitivity detects autonomic dysfunction more frequently in IDDM patients than conventional tests. Impaired BRS is associated with an increased left ventricular mass index and this abnormality may have a role in the increased incidence of sudden death seen in young IDDM patients. [Diabetologia (1996[Diabetologia ( ) 39: 1385[Diabetologia ( -1391

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“…Our observation of the parallel changes of TS and BRS gains in response to orthostasis further supports their common mechanism. Reduction of the baroreflex gain in upright posture was already noticed by Pickering et al [19], using the Oxford method. In subsequent studies, the same trend was confirmed using spontaneous BRS techniques [10,23].…”

Section: Discussionmentioning

confidence: 52%

Spontaneous baroreflex sensitivity and heart rate turbulence parameters: parallel responses to orthostasis

et al. 2008

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Premature ventricular contractions (PVC-s) induce baroreflex mediated arterial pressure and heart rate fluctuations. PVC-related RR interval fluctuations detected on Holter ECG recordings could be characterized by the heart rate turbulence (HRT) parameters, including early post-extrasystolic acceleration, described by turbulence onset, and late deceleration, described by turbulence slope (TS). We have determined the increasing and decreasing spontaneous baroreflex sequence sensitivity (up- and down-BRS) parameters in supine and in upright position in 12 patients with VVI pacemaker while in sinus rhythm. Five-five premature ventricular pacemaker extrastmuli were also applied in both body positions and HRT parameters were calculated. Up- and down-BRS values showed a very close relationship with TS both in the supine (R = 0.94, P < 0.001 and R = 0.92, P < 0.001, respectively), and upright position (R = 0.96, P < 0.001, and R = 0.94, P < 0.001, respectively). The BRS indices decreased significantly upon tilting, which was paralleled by a significant decrease in TS (from 21.6 to 13.9 ms/cycle, P = 0.02). Our findings confirm the close association between TS and spontaneous BRS indices. The relationship is further supported by the similar postural behavior of these parameters. Our results suggest that the confounding effect of posture should be considered when analyzing Holter recordings.

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Comparison of the effects of exercise and posture on the baroreflex in man

Cited by 40 publications

References 0 publications

Spectral and cross-spectral autoregressive analysis of cardiovascular variables in subjects with different degrees of orthostatic tolerance

Spectral and cross-spectral autoregressive analysis of cardiovascular variables in subjects with different degrees of orthostatic tolerance

Assessment of baroreceptor-cardiac reflex sensitivity using time domain analysis in patients with IDDM and the relation to left ventricular mass index

Spontaneous baroreflex sensitivity and heart rate turbulence parameters: parallel responses to orthostasis

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