Good exercise capacity at hospital discharge predicts recovery of baroreflex sensitivity after myocardial infarction

Mild obstructive sleep apnea does not modulate baroreflex sensitivity in adult patients

BACKGROUND

Obstructive sleep apnea (OSA) is a chronic and progressive disease. OSA is associated with increased cardiovascular morbidity and mortality, the risk being more frequently encountered with severe degrees of OSA. Increased sympathetic activation and impaired cardiac autonomic control as reflected by depressed baroreceptor reflex sensitivity (BRS) are possible mechanisms involved in the cardiovascular complications of OSA. However, it is not known at what stage of OSA that changes in BRS appear. The aim of this study was to evaluate BRS in patients with mild OSA.

METHODS

The study population consisted of 81 overweight patients with mild OSA and 46 body weight-matched non-OSA subjects. BRS, apnea-hypopnea index, body mass index, and metabolic parameters were assessed. The phenylephrine test was used to measure BRS.

RESULTS

Patients in the OSA group were slightly but significantly older than the non-OSA population (50.3±9.3 years vs 45.7±11.1 years, P=0.02). Body mass index, percentage body fat, blood pressure, fasting glucose, insulin, and lipid levels did not differ between the OSA patients and non-OSA subjects. Absolute BRS values in patients with mild OSA and non-OSA subjects (9.97±6.70 ms/mmHg vs 10.51±7.16 ms/mmHg, P=0.67) and BRS values proportional to age-related and sex-related reference values (91.4%±22.7% vs 92.2%±21.8%, P=0.84) did not differ from each other. BRS <50% of the sex-specific reference value was found in 6% of patients with mild OSA and in 2% of non-OSA subjects (P=0.29).

CONCLUSION

Patients with mild OSA did not show evidence of disturbed BRS in comparison with weight-matched non-OSA controls.

Effect of beta blockade with and without sympathomimetic activity (ISA) on sympathovagal balance and baroreflex sensitivity

Beta blockers increase heart rate variability (HRV) and improve survival in coronary artery disease (CAD). The benefit of beta blockers with intrinsic sympathomimetic activity (ISA) in CAD still remains a matter of debate, and their effect on HRV has not yet been investigated. Therefore, we measured HRV, systolic blood pressure variability (BPV) and baroreflex sensitivity (BRS) under propranolol (PROP, without ISA, 160 mg q.d.), pindolol (PIN, with potent ISA, 15 mg q.d.) and placebo (PLA, q.d.) in 30 healthy subjects, aged 21-39 years, during controlled frequency breathing (0.30 Hz) in supine and tilt positions. PROP increased HRV in the high-frequency (0.15-0.40 Hz) band (PROP 7.4 +/- 1.0; PLA 6.9 +/- 1.4; PIN 6.8 +/- 1.0 ln MI2; P = 0.003), decreased BPV in the low-frequency band (at 0.1 Hz, Mayer waves) (PROP 0.6 +/- 0.7; PLA 1.3 +/- 1.1; PIN 1.2 +/- 1.2 ln mmHg2; P = 0.001) and enhanced BRS (PROP 14.6 +/- 9.5; PLA 8.0 +/- 6.8; PIN 8.7 +/- 6.8 ms mmHg-1; P = 0.001) in the supine position. After passive tilt, PROP decreased HRV in the low-frequency band (PROP 6.1 +/- 0.9; PLA 6.5 +/- 1.1; PIN 6.9 +/- 0.7 ln MI2; P < 0.001) and decreased Mayer waves (PROP 1.8 +/- 0.8; PLA 2.4 +/- 1.0; PIN 2.7 +/- 0.8 ln mm Hg2; P < 0.001). PIN increased the low-frequency HRV response, which is induced by passive tilt (PIN + 0.9 +/- 1.0; PLA + 0.3 +/- 1.3, PROP + 0.3 +/- 1.0 ln MI2; P = 0.026). Our results prove that beta-adrenergic blockade with potent ISA does not increase HRV, has no beneficial effect on autonomic balance and even exaggerates sympathetic responses to passive tilt.

The effect of a very low-calorie diet-induced weight loss on the severity of obstructive sleep apnoea and autonomic nervous function in obese patients with obstructive sleep apnoea syndrome

The aim of this study was to examine the effect of a very low-calorie diet (VLCD)-induced weight loss on the severity of obstructive sleep apnoea (OSA), blood pressure and cardiac autonomic regulation in obese patients with obstructive sleep apnoea syndrome (OSAS). A total of 15 overweight patients (14 men and one woman, body weight 114 +/- 20 kg, age 52 +/- 9 years, range 39-67 years) with OSAS were studied prospectively. They were advised to follow a 2.51-3.35 MJ (600-800 kcal) diet daily for a 3-month period. In the beginning of the study, the patients underwent nocturnal sleep studies, autonomic function tests and 24-h electrocardiograph (ECG) recording. In addition, 15 age-matched, normal-weight subjects were studied. They underwent the Valsalva test, the deep-breathing test and assessment of heart rate variability at rest. The sleep studies and autonomic function tests were repeated after the weight loss period. There was a significant reduction in weight (114 +/- 20 kg to 105 +/- 21 kg, P < 0.001), the weight loss being 9.2 +/- 4.0 kg (range 2.3-19.5 kg). This was associated with a significant improvement in the oxygen desaturation index (ODI4) during sleep (31 +/- 20-19 +/- 18, P < 0.001). Before the weight loss the OSAS patients had significantly higher blood pressure (150 +/- 18 vs. 134 +/- 20, P < 0.05, for systolic blood pressure, 98 +/- 10 vs. 85 +/- 13, P < 0.05, for diastolic blood pressure) and heart rate (67 +/- 10 beats min-1 vs. 60 +/- 13, P < 0.05) at rest than the control group. They had also lower baroreflex sensitivity (4.7 +/- 2.8 ms mmHg-1 vs. 10.8 +/- 7.1 ms mmHg-1, P < 0.01). During the weight reduction, the blood pressure declined significantly, and the baroreflex sensitivity increased by 49%. In conclusion, our experience shows that weight loss with VLCD is an effective treatment for OSAS. Weight loss improved significantly sleep apnoea and had favourable effects on blood pressure and baroreflex sensitivity that may have prognostic implications.