Obstructive sleep apnoea (OSA) and metabolic syndrome (MetS) independently increases muscular sympathetic nervous activity (MSNA). Unknown is whether OSA has an additive effect on MSNA in patients with MetS. We tested the hypothesis that: OSA would have an additive effect on MSNA in patients with MetS. In addition, we studied whether the increase in MSNA in patients with MetS is associated with alteration in arterial baroreflex sensitivity (BRS). Twenty four patients with MetS diagnosed according ATP-III were divided in two groups:
MetS+OSA (n=14) and
MetS (n=10).
They were matched for age, body mass index, waist circumference, and metabolic profile: OSA was defined by an apnoea/hypopnoea index (AHI)>15 events/hour by polysonography. MSNA was recorded directly from the peroneal nerve using the technique of microneurography. Blood pressure (BP) was monitored on a beat-by-beat basis (Finapress) and heart rate by ECG. BRS was analyzed by spontaneous BP and heart rate fluctuations. AHI was higher (42±9 vs. 7±1 events/h,
P
=0.0001) and minimum oxygen saturation lower (77±2 vs. 87±1 %,
P
=0.001) in MetS+OSA patients. Patients MetS+OSA had higher MSNA (55±3 vs. 43±2 bursts/100 beats,
P
=0.01) and systolic BP (158±4 vs.144±3 mmHg,
P
=0.01) when compared with patients with MetS without OSA. Further analysis showed that AHI and minimum oxygen saturation have significant correlation with MSNA (r=0.65;
P
=0.001 and r=−0.48;
P
=0.017, respectively). Patients with MetS+OSA had lower BRS for increases (7.8±0.9
vs.
13.4 ± 1.4 msec/mmHg,
P
=0.01) and decreases (7.2±0.9
vs.
13.2 ± 2.0 msec/mmHg,
P
=0.03) in blood pressure than patients with MetS without OSA. MSNA significantly correlated with BRS during spontaneous increases in blood pressure (r=−0.56,
P
=0.01). OSA exacerbates MSNA in patients with MetS. In addition, the augmented MSNA in patients with MetS+OSA is associated with reduced BRS. These findings suggest that OSA increases the risk for cardiovascular disease in patients with MetS.
Highs and lows of sympathetic neurocardiovascular transduction: influence of altitude acclimatization and adaptation