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Baroreflex control of muscle sympathetic nerve activity: a nonpharmacological measure of baroreflex sensitivity.

ABSTRACT: The sensitivity of baroreflex control of sympathetic nerve activity (SNA) represents the responsiveness of SNA to changes in blood pressure. In a slightly different analysis, the baroreflex threshold measures the probability of whether a sympathetic burst will occur at a given diastolic blood pressure. We hypothesized that baroreflex threshold analysis could be used to estimate the sensitivity of the sympathetic baroreflex measured by the pharmacological modified Oxford test. We compared four measures of sympathetic baroreflex sensitivity in 25 young healthy participants: the "gold standard" modified Oxford analysis (nitroprusside and phenylephrine), nonbinned spontaneous baroreflex analysis, binned spontaneous baroreflex analysis, and threshold analysis. The latter three were performed during a quiet baseline period before pharmacological intervention. The modified Oxford baroreflex sensitivity was significantly related to the threshold slope (r = 0.71, P < 0.05) but not to the binned (1 mmHg bins) and the nonbinned spontaneous baroreflex sensitivity (r = 0.22 and 0.36, respectively, P > 0.05), which included burst area. The threshold analysis was also performed during the modified Oxford manipulation. Interestingly, we found that the threshold analysis results were not altered by the vasoactive drugs infused for the modified Oxford. We conclude that the noninvasive threshold analysis technique can be used as an indicator of muscle SNA baroreflex sensitivity as assessed by the modified Oxford technique. Furthermore, the modified Oxford method does not appear to alter the properties of the baroreflex.

SUBMITTER: Hart EC

PROVIDER: S-EPMC2838548 | biostudies-literature | 2010 Mar

REPOSITORIES: biostudies-literature

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Baroreflex control of muscle sympathetic nerve activity: a nonpharmacological measure of baroreflex sensitivity.

Hart Emma C EC Joyner Michael J MJ Wallin B Gunnar BG Karlsson Tomas T Curry Timothy B TB Charkoudian Nisha N

American journal of physiology. Heart and circulatory physiology 20091211 3

The sensitivity of baroreflex control of sympathetic nerve activity (SNA) represents the responsiveness of SNA to changes in blood pressure. In a slightly different analysis, the baroreflex threshold measures the probability of whether a sympathetic burst will occur at a given diastolic blood pressure. We hypothesized that baroreflex threshold analysis could be used to estimate the sensitivity of the sympathetic baroreflex measured by the pharmacological modified Oxford test. We compared four me ...[more]

PMID: 20008270

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Project description:Patients with posttraumatic stress disorder (PTSD) have elevated sympathetic nervous system reactivity and impaired sympathetic and cardiovagal baroreflex sensitivity (BRS). Device-guided slow breathing (DGB) has been shown to lower blood pressure (BP) and sympathetic activity in other patient populations. We hypothesized that DGB acutely lowers BP, heart rate (HR), and improves BRS in PTSD. In 23 prehypertensive veterans with PTSD, we measured continuous BP, ECG, and muscle sympathetic nerve activity (MSNA) at rest and during 15 min of DGB at 5 breaths/min ( n = 13) or identical sham device breathing at normal rates of 14 breaths/min (sham; n = 10). Sympathetic and cardiovagal BRS was quantified using pharmacological manipulation of BP via the modified Oxford technique at baseline and during the last 5 min of DGB or sham. There was a significant reduction in systolic BP (by -9 ± 2 mmHg, P < 0.001), diastolic BP (by -3 ± 1 mmHg, P = 0.019), mean arterial pressure (by -4 ± 1 mmHg, P = 0.002), and MSNA burst frequency (by -7.8 ± 2.1 bursts/min, P = 0.004) with DGB but no significant change in HR ( P > 0.05). Within the sham group, there was no significant change in diastolic BP, mean arterial pressure, HR, or MSNA burst frequency, but there was a small but significant decrease in systolic BP ( P = 0.034) and MSNA burst incidence ( P = 0.033). Sympathetic BRS increased significantly in the DGB group (-1.08 ± 0.25 to -2.29 ± 0.24 bursts·100 heart beats-1·mmHg-1, P = 0.014) but decreased in the sham group (-1.58 ± 0.34 to -0.82 ± 0.28 bursts·100 heart beats-1·mmHg-1, P = 0.025) (time × device, P = 0.001). There was no significant difference in the change in cardiovagal BRS between the groups (time × device, P = 0.496). DGB acutely lowers BP and MSNA and improves sympathetic but not cardiovagal BRS in prehypertensive veterans with PTSD. NEW & NOTEWORTHY Posttraumatic stress disorder is characterized by augmented sympathetic reactivity, impaired baroreflex sensitivity, and an increased risk for developing hypertension and cardiovascular disease. This is the first study to examine the potential beneficial effects of device-guided slow breathing on hemodynamics, sympathetic activity, and arterial baroreflex sensitivity in prehypertensive veterans with posttraumatic stress disorder.

Project description:What is the central question of this study? Does ageing influence the respiratory-related bursting of muscle sympathetic nerve activity (MSNA) and the association between the rhythmic fluctuations in MSNA and blood pressure (Traube-Hering waves) that occur with respiration? What is the main finding and its importance? Despite the age-related elevation in MSNA, the cyclical inhibition of MSNA during respiration is similar between young and older individuals. Furthermore, central respiratory-sympathetic coupling plays a role in the generation of Traube-Hering waves in both young and older humans. Healthy ageing and alterations in respiratory-sympathetic coupling have been independently linked with heightened sympathetic neural vasoconstrictor activity. We investigated how age influences the respiratory-related modulation of muscle sympathetic nerve activity (MSNA) and the association between the rhythmic fluctuations in MSNA and blood pressure that occur with respiration (Traube-Hering waves; THW). Ten young (22 ± 2 years; mean ± SD) and 10 older healthy men (58 ± 6 years) were studied while resting supine and breathing spontaneously. MSNA, blood pressure and respiration were recorded simultaneously. Resting values were ascertained and respiratory cycle-triggered averaging of MSNA and blood pressure measurements performed. The MSNA burst incidence was higher in older individuals [22.7 ± 9.2 versus 42.2 ± 13.7 bursts (100 heart beats)(-1), P < 0.05], and was reduced to a similar extent in the inspiratory to postinspiratory period in young and older subjects (by ∼ 25% compared with mid- to late expiration). A similar attenuation of MSNA burst frequency (in bursts per minute), amplitude and total activity (burst frequency × mean burst amplitude) was also observed in the inspiratory to postinspiratory period in both groups. A significant positive correlation between respiratory-related MSNA and the magnitude of Traube-Hering waves was observed in all young (100%) and most older subjects (80%). These data suggest that the strength of the cyclical inhibition of MSNA during respiration is similar between young and older individuals; thus, alterations in respiratory-sympathetic coupling appear not to contribute to the age-related elevation in MSNA. Furthermore, central respiratory-sympathetic coupling plays a role in the generation of Traube-Hering waves in both healthy young and older humans.

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Baroreflex control of muscle sympathetic nerve activity: a nonpharmacological measure of baroreflex sensitivity.

Publications

Baroreflex control of muscle sympathetic nerve activity: a nonpharmacological measure of baroreflex sensitivity.

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