Decreased cardiopulmonary baroreflex sensitivity in Chagas' heart disease (original) (raw)

Onset of mild lower body negative pressure induces transient change in mean arterial pressure in humans

European Journal of Applied Physiology, 2002

Mild (0 to -20 mmHg) lower body negative pressure (LBNP) has traditionally been considered to elicit reflex responses mediated by cardiopulmonary baroreceptors only, without any arterial baroreflex involvement. Mild LBNP has therefore frequently been used to study the influence of cardiopulmonary baroreceptors on the human circulatory system. In a previous study we found that mean arterial pressure (MAP) was transiently but strongly affected by rapid (0.3 s) onset and release of -20 mmHg LBNP. In the present study we tested whether MAP is also transiently affected by slow onset and release of -20 mmHg LBNP. A group of 12 subjects participated in this study, which was approved by the local Ethics Committee. Heart rate, stroke volume, cardiac output, MAP, total peripheral resistance, acral and non-acral skin blood flow, and blood flow velocity in the brachial artery were continuously recorded during the pre-LBNP period, during LBNP and during the post-LBNP period. The LBNP was gradually applied and released over a 15 s period. The main finding was that MAP was transiently but strongly affected by the gradual onset of LBNP as mild as -20 mmHg. During onset of LBNP MAP was significantly (P=0.003) lower than MAP in the pre-LBNP period. This shows that not only the cardiopulmonary baroreceptors but also the arterial baroreceptors must be activated during mild LBNP.

Lower Body Negative Pressure: Physiological Effects, Applications, and Implementation

Physiological Reviews, 2019

This review presents lower body negative pressure (LBNP) as a unique tool to investigate the physiology of integrated systemic compensatory responses to altered hemodynamic patterns during conditions of central hypovolemia in humans. An early review published in Physiological Reviews over 40 yr ago (Wolthuis et al. Physiol Rev 54: 566-595, 1974) focused on the use of LBNP as a tool to study effects of central hypovolemia, while more than a decade ago a review appeared that focused on LBNP as a model of hemorrhagic shock (Cooke et al.

Effect of parasympathetic impairment on the haemodynamic response to handgrip in Chagas's heart disease

Heart, 1986

Haemodynamic responses to. sustained isometric exercise (handgrip at 30% of maximum voluntary capacity) were studied in 10 patients with Chagas's cardiopathy without previous or current heart failure. Five of the patients (group 1) had profound impairment of parasympathetic control of heart rate. They had no tachycardia in response to intravenous administration of atropine and no bradycardia during phase IV of the Valsalva manoeuvre. The other five (group 2) showed normal vagal regulation of heart rate, as judged by chronotropic responses to these tests.

Paradoxical Vasodilation During Lower Body Negative Pressure in Patients with Vasodepressor Carotid Sinus Syndrome

Journal of The American Geriatrics Society, 2003

OBJECTIVES: To elucidate the pathophysiological mechanism of the vasodepressor form (VD) of carotid sinus syndrome (CSS) by maneuvers designed to induce generalized sympathetic activation after baroreceptor unloading (lower body negative pressure, LBNP) or direct peripheral adrenoreceptor stimulation via local administration of norepinephrine (NA).DESIGN: Subjects were identified with VD of CSS through diagnostic testing.SETTING: Research laboratory.PARTICIPANTS: Eleven young controls (YC) (mean age ± standard error of mean = 22.8 ± 0.7), eight elderly controls (EC) (72.6 ± 0.6), and eight elderly patients with VD (78.7 ± 1.7).MEASUREMENTS: Forearm arterial blood flow (FABF) was measured in the left and right arms by venous occlusion plethysmography. Measurements were performed during baseline conditions, LBNP (−20 mmHg), and intra-arterial NA infusion in the left brachial artery at three progressively increasing rates (60, 120, and 240 pmol/min).RESULTS: During LBNP, FABF significantly decreased in YC (baseline 3.61 ± 0.30 vs −20 mmHg 2.96 ± 0.24 mL/100 g/min, P = .030) and EC (4.05 ± 0.74 vs 3.69 ± 0.65 mL/100 g/min, P = .033) but increased in elderly patients with VD (3.65 ± 0.60 vs 4.54 ± 0.80 mL/100 g/min, P = .020). During NA infusion, a significant forearm vasoconstriction occurred in YC (FABF left:right ratio 1.00 ± 0.05 at baseline; 0.81 ± 0.08 at 60 pmol/min, P = .034; 0.81 ± 0.05 at 120 pmol/min, P < .001; 0.72 ± 0.04 at 240 pmol/min, P < .001), whereas no significant FABF changes were observed in EC (1.04 ± 0.06; 0.96 ± 0.07, P = .655; 0.89 ± 0.10, P = .401; 0.94 ± 0.10, P = .590) or elderly patients with VD (1.04 ± 0.06; 1.16 ±0 .10, P = .117; 1.04 ± 0.08, P = .602; 1.11 ± 0.10, P = .305).CONCLUSION: VD of CSS is associated with a paradoxical vasodilatation during LBNP and an impairment of peripheral α-adrenergic responsiveness, which may be age-related.

The effects of lower body negative pressure on baroreceptor responses in humans

Experimental Physiology, 1990

In healthy human subjects the immediate responses of pulse interval and the steady-state responses of arterial blood pressure and cardiac output to changes in carotid sinus transmural pressure were determined before and during the application of a subatmospheric pressure to the lower part of the body. Increases in carotid sinus transmural pressure, effected by applications of subatmospheric pressure to the neck (neck suction) resulted in prolongation of pulse interval and decrease in blood pressure; opposite responses were obtained to application of a positive pressure (neck pressure). Application of lower body negative pressure resulted in a decrease in pulse interval (heart rate increase) but little change in blood pressure. During lower body negative pressure, the responses of pulse interval to neck pressure were reduced but those to neck suction were unaffected; the responses of blood pressure to neck suction were enhanced but those to neck pressure were unaffected. From experiments in which cardiac output was also determined, it was seen that lower body negative pressure reduced cardiac output, increased calculated total body vascular resistance and augmented the resistance response to neck suction although not to neck pressure. These results are compatible with the view that application of lower body negative pressure does not change the sensitivity of the baroreceptor reflex and that the changes in the responses are due to non-linearities of the stimulus-response curves.

Aortic distensibility is reduced during intense lower body negative pressure and is related to low frequency power of systolic blood pressure

European Journal of Applied Physiology, 2012

As sympathetic activity approximately doubles during intense lower body negative pressure (LBNP) of-60 mmHg or greater, we examined the relationship between surrogate markers of sympathetic activation and central arterial distensibility during severe LBNP. Eight participants were exposed to progressive 8-min stages of LBNP of increasing intensity (-20,-40,-60, and-80 mmHg), while recording carotid-femoral pulse wave velocity (cPWV), stroke volume (SV), heart rate, and beatby-beat blood pressure. The spectral power of low frequency oscillations in SBP (SBP LF) was used as a surrogate indicator of sympathetically modulated vasomotor modulation. Total arterial compliance (C) was calculated as C = SV/pulse pressure. Both cPWV and C were compared between baseline, 50 % of the maximally tolerated LBNP stage (LBNP 50), and the maximum fully tolerated stage of LBNP (LBNP max). No change in mean arterial pressure (MAP) occurred over LBNP. An increase in cPWV (6.5 ± 2.2; 7.2 ± 1.4; 9.0 ± 2.5 m/s; P = 0.004) occurred during LBNP max. Over progressive LBNP, SBP LF increased (8.5 ± 4.6; 9.3 ± 5.8; 16.1 ± 12.9 mmHg 2 ; P = 0.04) and C decreased significantly (18.3 ± 6.8; 14.3 ± 4.1; 11.6 ± 4.8 ml/mmHg 9 10; P = 0.03). The mean correlation (r) between cPWV and SBP LF was 0.9 ± 0.03 (95 % CI 0.79-0.99). Severe LBNP increased central stiffness and reduced total arterial compliance. It appears that increased sympathetic vasomotor tone during LBNP is associated with reduced aortic distensibility in the absence of changes in MAP.