Spontaneous baroreflex sensitivity: towards an ideal index of cardiovascular risk

Rosiglitazone improves insulin sensitivity and baroreflex gain in rats with diet-induced obesity

Obesity decreases baroreflex gain (BRG); however, the mechanisms are unknown. We tested the hypothesis that impaired BRG is related to the concurrent insulin resistance, and, therefore, BRG would be improved after treatment with the insulin-sensitizing drug rosiglitazone. Male rats fed a high-fat diet diverged into obesity-prone (OP) and obesity-resistant (OR) groups after 2 weeks. Then, OP and OR rats, as well as control (CON) rats fed a standard diet, were treated daily for 2 to 3 weeks with rosiglitazone (3 or 6 mg/kg) or its vehicle by gavage. Compared with OR and CON rats, conscious OP rats exhibited reductions in BRG (OP, 2.9 ± 0.1 bpm/mm Hg; OR, 4.0 ± 0.2 bpm/mm Hg; CON, 3.9 ± 0.2 bpm/mm Hg; P < 0.05) and insulin sensitivity (hyperinsulinemic euglycemic clamp; OP, 6.8 ± 0.9 mg/kg · min; OR, 22.2 ± 1.2 mg/kg · min; CON, 17.7 ± 0.8 mg/kg · min; P < 0.05), which were well correlated (r(2) = 0.49; P < 0.01). In OP rats, rosiglitazone dose-dependently improved (P < 0.05) insulin sensitivity (12.8 ± 0.6 mg/kg · min at 3 mg/kg; 16.0 ± 1.5 mg/kg · min at 6 mg/kg) and BRG (3.8 ± 0.4 bpm/mm Hg at 3 mg/kg; 5.3 ± 0.7 bpm/mm Hg at 6 mg/kg). However, 6 mg/kg rosiglitazone also increased BRG in OR rats without increasing insulin sensitivity, disrupted the correlation between BRG and insulin sensitivity (r(2) = 0.08), and, in OP and OR rats, elevated BRG relative to insulin sensitivity (analysis of covariance; P < 0.05). Moreover, in OP rats, stimulation of the aortic depressor nerve, to activate central baroreflex pathways, elicited markedly reduced decreases in heart rate and arterial pressure, but these responses were not improved by rosiglitazone. In conclusion, diet-induced obesity impairs BRG via a central mechanism that is related to the concurrent insulin resistance. Rosiglitazone normalizes BRG, but not by improving brain baroreflex processing or insulin sensitivity.

The role of carotid plaque echogenicity in baroreflex sensitivity

OBJECTIVE

The baroreflex sensitivity is impaired in patients with carotid atherosclerosis. The purpose of our study was to assess the impact of carotid plaque echogenicity on the baroreflex function in patients with significant carotid atherosclerosis, who have not undergone carotid surgery.

METHOD

Spontaneous baroreflex sensitivity (sBRS) was estimated in 45 patients with at least a severe carotid stenosis (70%-99%). sBRS calculation was performed noninvasively, with the spontaneous sequence method, based on indirectly estimated central blood pressures from radial recordings. This method failed in three patients due to poor-quality recordings, and eventually 42 patients were evaluated. After carotid duplex examination, carotid plaque echogenicity was graded from 1 to 4 according to Gray-Weale classification and the patients were divided into two groups: the echolucent group (grades 1 and 2) and the echogenic group (grades 3 and 4).

RESULTS

Sixteen patients (38%) and 26 patients (62%) were included in the echolucent and echogenic group, respectively. Diabetes mellitus was observed more frequently among echolucent plaques (χ(2) = 8.0; P < .004), while those plaques were also more commonly symptomatic compared with echogenic atheromas (χ(2) = 8.5; P < .003). Systolic arterial pressure, diastolic arterial pressure, and heart rate were similar in the two groups. Nevertheless, the mean value of baroreflex sensitivity was found to be significantly lower in the echogenic group (2.96 ms/mm Hg) compared with the echolucent one (5.0 ms/mm Hg), (F [1, 42] = 10.1; P < .003).

CONCLUSIONS

These findings suggest that echogenic plaques are associated with reduced baroreflex function compared with echolucent ones. Further investigation is warranted to define whether such an sBRS impairment could be responsible for cardiovascular morbidity associated with echogenic plaques.

Impaired baroreflex gain during pregnancy in conscious rats: role of brain insulin

Pregnancy impairs baroreflex gain, but the mechanism is incompletely understood. To test the hypothesis that reductions in brain insulin contribute, we determined whether pregnant rats exhibit lower cerebrospinal fluid (CSF) insulin concentrations and whether intracerebroventricular infusion of insulin normalizes gain of baroreflex control of heart rate in conscious pregnant rats. CSF insulin was lower in pregnant (68 ± 21 pg/mL) compared to virgin (169 ± 25 pg/mL) rats (P < 0.05). Pregnancy reduced baroreflex gain (pregnant 2.4 ± 0.2 bpm/mm Hg, virgin 4.6 ± 0.3 bpm/mm Hg; P < 0.0001) and the maximum heart rate elicited by hypotension (pregnant 455 ± 15 bpm, virgin 507 ± 12 bpm; P = 0.01). Infusion of insulin (100 μU/min) intracerebroventricularly increased baroreflex gain in pregnant (2.4 ± 0.4 to 3.9 ± 0.5 bpm/mm Hg; P < 0.01) but not virgin (4.6 ± 0.4 to 4.2 ± 0.4 bpm/mm Hg; NS) rats. Maximum heart rate was not altered by intracerebroventricular insulin in either group. Interestingly, while in pregnant rats the baroreflex was unchanged by intracerebroventricular infusion of the artificial CSF vehicle, in virgin rats, vehicle infusion lowered baroreflex gain (4.7 ± 0.3 to 3.9 ± 0.3 bpm/mm Hg; P < 0.05) and the maximum baroreflex heart rate (495 ± 19 to 444 ± 21 bpm; P < 0.05). These data support the hypothesis that brain insulin is required to support optimal baroreflex function and that a decrease in brain insulin contributes to the fall in baroreflex gain during pregnancy.

EVAluation of the prognostic value of BARoreflex sensitivity in hypertensive patients: the EVABAR study

AIMS

The prognostic value of baroreflex sensitivity in hypertensive patients has not much been studied.

METHOD

A cohort of 451 hypertensive patients without cardiovascular history was studied for an average of 6.2 +/- 2.8 years follow-up. Each patient had a baroreflex sensitivity measurement by the sequence method, which is represented by the slope of up-sequences (systolic blood pressure+/pulse interval+) and down-sequences (systolic blood pressure-/pulse interval-) of spontaneous fluctuations in systolic blood pressure and pulse interval.

RESULTS

During the follow-up, there were 20 deaths from any cause and 30 patients presented a major adverse cardiovascular event. Deaths and major adverse cardiovascular events were associated with a reduction in baroreflex sensitivity (systolic blood pressure+/pulse interval+ and systolic blood pressure-/pulse interval-). In multivariate analysis, the reduction in baroreflex sensitivity systolic blood pressure+/pulse interval+ was associated with an increased risk of deaths from any cause (Odds ratio 1.23; 95% confidence interval 1.02-1.67, P = 0.04). A baroreflex sensitivity systolic blood pressure+/pulse interval+ under 4.5 ms/mmHg was associated with a 2.5-increased relative risk of major adverse cardiovascular event (95% confidence interval 1.11-5.93, P = 0.03). However, multivariate analysis showed that baroreflex sensitivity systolic blood pressure-/pulse interval- was not associated either with death or major adverse cardiovascular events.

CONCLUSIONS

Reduction in baroreflex sensitivity marked by a reduction in vagal reflexes is an independent marker of the risk of mortality and major adverse cardiovascular events in hypertensive patients.