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Cardiac vagal tone withdrawal in conscious treated hypertensive patients and normal healthy controls during baroreceptor unloading and baroreceptors loading

      The autonomic response to blood pressure determined by baroreflex mechanism depends on the loading /unloading state of baroreceptors (Rushmer, 1976). Autonomic dysfunction occurs in patients with hypertension. We investigated the cardiac vagal tone (CVT) response to baroreceptor unloading during phase IIi of Valsalva’s maneuver (VM) and baroreceptors loading during isometric handgrip test (IHGT). Methods: Autonomic monitoring was performed on 23 age match subjects; 12 hypertensive males (mean ± SD; 45 ± 14.4 years) and 11 (3 females, 8 males) controls (35.6 ± 9.7 y). The study was ethically approved and informed consent was obtained. Non-invasive, beat-by-beat measurements of arterial blood pressures (BPs), CVT in units of a linear vagal scale (LVS) and cardiac sensitivity to baroreflex (CSB) were performed using the Neuroscope system (Medifit instruments Ltd, UK) (Julu et al, 2001). Measurements were taken during recline position for baseline and during VM and IHGT. Statistical analysis was performed using paired student’s test. Results: Baseline values in HTN patients were: (mean ± SD); BPs (mmHg): SBP 152.6 ± 19.9, DBP 69.4 ± 14.8, MAP 97.1 ± 15.6, HR 74.3 beats.min-1, CVT 4.6 ± 3.6in the linear vagal scale (LVS), CSB 4.04 ± 3.1 ms.mmHg1. In control subjects: SBP 122.2 ± 11.7, DBP 63.4 ± 9.2, MAP 82.9 ± 9.7, HR 75.8 ± 7.7, CVT 5.8 ± 4.6, CSB 6.5 ± 4.6. During VM the CVT dropped from 11.2 ± 4.7 to 6.4 ± 3.2 (p < 0.05); and during IHGT CVT dropped from 6.6 ± 2 to 3.4 ± 2.7 (p < 0.05). Patients with HTN showed similar significant CVT withdrawal. The drop was continuous till the end of the test. Conclusion: The study demonstrates continuous CVT withdrawal during baroreceptors unloading and loading in control and HTN subjects. The identical response could reflect the integrity of the central mechanism in both groups.
      • 1.
        Rushmer R.F (1976). Structure and Function of the Cardiovascular System, 2nd ed. Philadelphia: W. B. Sanders Company.
      • 2.
        Julu P.O.O, Kerr A.M, Apartopoulos F, Al-Rawas S, Witt Engerström I, Engerström L, Jamal G.A and Hansen S (2001). Characterisation of breathing and associated central dysfunction in the Rett disorder. Archives of Disease in Childhood 85, 29-37.
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