Vagal blockade suppresses the phase I heart rate response but not the phase I cardiac output response at exercise onset in humans

Purpose We tested the vagal withdrawal concept for heart rate (HR) and cardiac output (CO) kinetics upon moderate exercise onset, by analysing the effects of vagal blockade on cardiovascular kinetics in humans. We hypothesized that, under atropine, the φ1 amplitude (A1) for HR would reduce to nil, whereas the A1 for CO would still be positive, due to the sudden increase in stroke volume (SV) at exercise onset. Methods On nine young non-smoking men, during 0–80 W exercise transients of 5-min duration on the cycle ergometer, preceded by 5-min rest, we continuously recorded HR, CO, SV and oxygen uptake (˙O2) upright and supine, in control condition and after full vagal blockade with atropine. Kinetics were analysed with the double exponential model, wherein we computed the amplitudes (A) and time constants (τ) of phase 1 (φ1) and phase 2 (φ2). Results In atropine versus control, A1 for HR was strongly reduced and fell to 0 bpm in seven out of nine subjects for HR was practically suppressed by atropine in them. The A1 for CO was lower in atropine, but not reduced to nil. Thus, SV only determined A1 for CO in atropine. A2 did not differ between control and atropine. No effect on τ1 and τ2 was found. These patterns were independent of posture. Conclusion The results are fully compatible with the tested hypothesis. They provide the first direct demonstration that vagal blockade, while suppressing HR φ1, did not affect φ1 of CO

Testing the vagal withdrawal hypothesis during light exercise under autonomic blockade: a heart rate variability study

Introduction. We performed the first analysis of heart rate variability (HRV) at rest and exercise under full autonomic blockade on the same subjects, to test the conjecture that vagal tone withdrawal occurs at exercise onset. We hypothesized that, between rest and exercise: i) no differences in total power (PTOT) under parasympathetic blockade; ii) a PTOT fall under β1-sympathetic blockade; iii) no differences in PTOT under blockade of both ANS branches. Methods. 7 males (24±3 years) performed 5-min cycling (80W) supine, preceded by 5-min rest during control and with administration of atropine, metoprolol and atropine+metoprolol (double blockade). Heart rate and arterial blood pressure were continuously recorded. HRV and blood pressure variability were determined by power spectral analysis, and baroreflex sensitivity (BRS) by the sequence method. Results. At rest, PTOT and the powers of low (LF) and high (HF) frequency components of HRV were dramatically decreased in atropine and double blockade compared to control and metoprolol, with no effects on LF/HF ratio and on the normalised LF (LFnu) and HF (HFnu). At exercise, patterns were the same as at rest. Comparing exercise to rest, PTOT varied as hypothesized. For SAP and DAP, resting PTOT was the same in all conditions. At exercise, in all conditions, PTOT was lower than in control. BRS decreased under atropine and double blockade at rest, under control and metoprolol during exercise. Conclusions. The results support the hypothesis that vagal suppression determined disappearance of HRV during exercise

Dynamics of cardiovascular and baroreflex readjustments during a light-to-moderate exercise transient in humans

We hypothesised that, during a light-to-moderate exercise transient, compared to an equivalent rest-to-exercise transient, (1) a further baroreflex sensitivity (BRS) decrease would be slower, (2) no rapid heart rate (HR) response would occur, and (3) the rapid cardiac output (CO) response would have a smaller amplitude (A1). Hence, we analysed the dynamics of arterial baroreflexes and the HR and CO kinetics during rest-to-50 W (0-50 W) and 50-to-100 W (50-100 W) exercise transients

Higher nicotinic receptor availability in the cingulo-insular network is associated with lower cardiac parasympathetic tone

The dorsal anterior cingulate cortex (dACC) and the anterior insula (AI) constitute the salience network and form as well the major cortical components of the central autonomic nervous system. These two cortical regions have the highest density in α4β2 nicotinic acetylcholine receptors (nAChRs) within the whole cortex.The aim of the study was to test the association between nAChRs density/availability in the salience network and the heart rate variability in humans. We selected subjects from a previous positron emission tomography (PET) imaging study in epilepsy with 18F-FA-85380, a specific marker for α4β2 nAChRs, including 10 healthy controls, 10 patients with nonlesional focal epilepsy and 8 patients with idiopathic generalized epilepsy. Participants underwent a 10 min-resting electrocardiogram as they were lying still in a semi-supine position while watching an emotionally neutral video. We tested the association between parasympathetic tone and the regional brain nAChR availability, as measured by 18F-F-A-85380 binding potential (BP), using linear regression. We observed an association between higher nAChRs availability in the bilateral dACC and the right dorsal AI/frontal operculum and a lower parasympathetic tone, without significant effect of the clinical group on this relation. Our study is the first one to show a neurochemical correlate to the parasympathetic role of the anterior cingulate cortex and the AI. The nicotinic system, which plays a major role in the peripheral autonomic nervous system intervening both in the parasympathetic and sympathetic chains, seems also to play a role in the central autonomic nervous system

Dynamics of the RR-interval versus blood pressure relationship at exercise onset in humans

PURPOSE: The dynamics of the postulated phenomenon of exercise baroreflex resetting is poorly understood, but can be investigated using closed-loop procedures. To shed light on some mechanisms and temporal relationships participating in the resetting process, we studied the time course of the relationship between the R-R interval (RRi) and arterial pressure with a closed-loop approach. METHODS: On ten young volunteers at rest and during light exercise in supine and upright position, we continuously determined, on single-beat basis, RRi (electrocardiography), and arterial pressure (non-invasive finger pressure cuff). From pulse pressure profiles, we determined cardiac output (CO) by Modelflow, computed mean arterial pressure (MAP), and calculated total peripheral resistance (TPR). RESULTS: At exercise start, RRi was lower than in quiet rest. As exercise started, MAP fell to a minimum (MAPm) of 72.8 ± 9.6 mmHg upright and 73.9 ± 6.2 supine, while RRi dropped. The initial RRi versus MAP relationship was linear, with flatter slope than resting baroreflex sensitivity, in both postures. TPR fell and CO increased. After MAPm, RRi and MAP varied in opposite direction toward exercise steady state, with further CO increase. CONCLUSION: These results suggest that, initially, the MAP fall was corrected by a RRi reduction along a baroreflex curve, with lower sensitivity than at rest, but eventually in the same pressure range as at rest. After attainment of MAPm, a second phase started, where the postulated baroreflex resetting might have occurred. In conclusion, the change in baroreflex sensitivity and the resetting process are distinct phenomena, under different control systems

Effects of gravitational acceleration on cardiovascular autonomic control in resting humans

Previous studies of cardiovascular responses in hypergravity suggest increased sympathetic regulation. The analysis of spontaneous heart rate variability (HRV) parameters and spontaneous baroreflex sensitivity (BRS) informs on the reciprocal balance of parasympathetic and sympathetic regulations at rest. This paper was aimed at determining the effects of gravitational acceleration (a g) on HRV and BRS. METHODS: Eleven healthy subjects (age 26.6 ± 6.1) were studied in a human centrifuge at four a g levels (1, 1.5, 2 and 2.5 g) during 5-min sessions at rest. We evaluated spontaneous variability of R-R interval (RR), and of systolic and diastolic blood pressure (SAP and DAP, respectively), by power spectral analysis, and BRS by the sequence method, using the BRSanalysis(®) software. RESULTS: At 2.5 g, compared to 1 g, (1) the total power (P TOT) and the powers of LF and HF components of HRV were lower, while the LF/HF ratio was higher; (2) normalized units for LF and HF did not changed significantly; (3) the P TOT, LF and HF powers of SAP were higher; (4) the P TOT and LF power of DAP were higher; and (5) BRS was decreased. CONCLUSIONS: These results do not agree with the notion of sympathetic up-regulation supported by the increase in HR and DAP (tonic indices), and of SAP and DAP LF powers (oscillatory indices). The P TOT reduction leads to speculate that only the sympathetic branch of the ANS might have been active during elevated a g exposure. The vascular response occurred in a condition of massive baroreceptive unloadin

Effects of gravitational acceleration on cardiovascular autonomic control in resting humans

Purpose: Previous studies of cardiovascular responses in hypergravity suggest increased sympathetic regulation. The analysis of spontaneous heart rate variability (HRV) parameters and spontaneous baroreflex sensitivity (BRS) informs on the reciprocal balance of parasympathetic and sympathetic regulations at rest. This paper was aimed at determining the effects of gravitational acceleration (a g) on HRV and BRS. Methods: Eleven healthy subjects (age 26.6±6.1) were studied in a human centrifuge at four a g levels (1, 1.5, 2 and 2.5g) during 5-min sessions at rest. We evaluated spontaneous variability of R-R interval (RR), and of systolic and diastolic blood pressure (SAP and DAP, respectively), by power spectral analysis, and BRS by the sequence method, using the BRSanalysis® software. Results: At 2.5g, compared to 1g, (1) the total power (P TOT) and the powers of LF and HF components of HRV were lower, while the LF/HF ratio was higher; (2) normalized units for LF and HF did not changed significantly; (3) the P TOT, LF and HF powers of SAP were higher; (4) the P TOT and LF power of DAP were higher; and (5) BRS was decreased. Conclusions: These results do not agree with the notion of sympathetic up-regulation supported by the increase in HR and DAP (tonic indices), and of SAP and DAP LF powers (oscillatory indices). The P TOT reduction leads to speculate that only the sympathetic branch of the ANS might have been active during elevated a g exposure. The vascular response occurred in a condition of massive baroreceptive unloading

Heart rate variability and baroreflex sensitivity in bilateral lung transplant recipients

7The effects of lung afferents denervation on cardiovascular regulation can be assessed on bilateral lung transplantation patients. The high-frequency component of heart rate variability is known to be synchronous with breathing frequency. Then, if heart beat is neurally modulated by breathing frequency, we may expect disappearance of high frequency of heart rate variability in bilateral lung transplantation patients. On 11 patients and 11 matching healthy controls, we measured R-R interval (electrocardiography), blood pressure (Portapres® ) and breathing frequency (ultrasonic device) in supine rest, during 10-min free breathing, 10-min cadenced breathing (0·25 Hz) and 5-min handgrip. We analysed heart rate variability and spontaneous variability of arterial blood pressure, by power spectral analysis, and baroreflex sensitivity, by the sequence method. Concerning heart rate variability, with respect to controls, transplant recipients had lower total power and lower low- and high-frequency power. The low-frequency/high-frequency ratio was higher. Concerning systolic, diastolic and mean arterial pressure variability, transplant recipients had lower total power (only for cadenced breathing), low frequency and low-frequency/high-frequency ratio during free and cadenced breathing. Baroreflex sensitivity was decreased. Denervated lungs induced strong heart rate variability reduction. The higher low-frequency/high-frequency ratio suggested that the total power drop was mostly due to high frequency. These results support the hypothesis that neural modulation from lung afferents contributes to the high frequency of heart rate variability.nonenoneFontolliet, T; Gianella, P; Pichot, V; Barthelemy, JC; Gasche-Soccal, P; Ferretti, G; Lador, F;Fontolliet, T; Gianella, P; Pichot, V; Barthelemy, Jc; Gasche-Soccal, P; Ferretti, G; Lador,