Giammario Spadacini

Effects of controlled breathing, mental activity and mental stress with or without verbalization on heart rate variability

OBJECTIVES To assess whether talking or reading (silently or aloud) could affect heart rate variability (HRV) and to what extent these changes require a simultaneous recording of respiratory activity to be correctly interpreted. BACKGROUND Sympathetic predominance in the power spectrum obtained from short- and long-term HRV recordings predicts a poor prognosis in a number of cardiac diseases. Heart rate variability is often recorded without measuring respiration; slow breaths might artefactually increase low frequency power in RR interval (RR) and falsely mimic sympathetic activation. METHODS In 12 healthy volunteers we evaluated the effect of free talking and reading, silently and aloud, on respiration, RR and blood pressure (BP). We also compared spontaneous breathing to controlled breathing and mental arithmetic, silent or aloud. The power in the so called low- (LF) and high-frequency (HF) bands in RR and BP was obtained from autoregressive power spectrum analysis. RESULTS Compared with spontaneous breathing, reading silently increased the speed of breathing (p < 0.05), decreased mean RR and RR variability and increased BP. Reading aloud, free talking and mental arithmetic aloud shifted the respiratory frequency into the LF band, thus increasing LF% and decreasing HF% to a similar degree in both RR and respiration, with decrease in mean RR but with minor differences in crude RR variability. CONCLUSIONS Simple mental and verbal activities markedly affect HRV through changes in respiratory frequency. This possibility should be taken into account when analyzing HRV without simultaneous acquisition and analysis of respiration.

Effect of breathing rate on oxygen saturation and exercise performance in chronic heart failure

BACKGROUND In chronic heart failure (CHF), impaired pulmonary function can independently contribute to oxygen desaturation and reduced physical activity. We investigated the effect of breathing rate on oxygen saturation and other respiratory indices. METHODS Arterial oxygen saturation (SaO2) and respiratory indices were recorded during spontaneous breathing (baseline) and during controlled breathing at 15, six, and three breaths per min in 50 patients with CHF and in 11 healthy volunteers (controls). 15 patients with CHF were randomly allocated 1 month of respiratory training to decrease their respiratory rate to six breaths per min. Respiratory indices were recorded before training, at the end of training, and 1 month after training. FINDINGS During spontaneous breathing, mean SaO2 was lower in CHF patients than in controls (91-4% [SD 0.4] vs 95.4% [0.2], p<0.001). Controlled breathing increased SaO2 at all breathing rates in patients with CHF. Compared with baseline, minute ventilation increased at 15 breaths per min (+45.9% [9.8], p<0.01), did not change at six breaths per min, and decreased at three breaths per min (-40.3% [4.8], p<0.001). In the nine CHF patients who had 1 month of respiratory training, resting SaO2 increased from 92.5% (0.3) at baseline to 93.2% (0.4) (p<0.05), their breathing rate per min decreased from 13.4 (1.5) to 7.6 (1.9) (p<0.001), peak oxygen consumption increased from 1157 (83) to 1368 (110) L/min (p<0.05), exercise time increased from 583 (29) to 615 (23) min/s (p<0.05), and perception of dyspnoea reduced from a score of 19.0 (0.4) to 17.3 (0.9) on the Borg scale (p<0.05). There were no changes in the respiratory indices in the patients who did not have respiratory training. INTERPRETATION Slowing respiratory rate reduces dyspnoea and improves both resting pulmonary gas exchange and exercise performance in patients with CHF.

Demonstrable cardiac reinnervation after human heart transplantation by carotid baroreflex modulation of RR interval.

BACKGROUND After heart transplantation, respiration-synchronous fluctuations (0.18 to 0.35 Hz, high frequency [HF]) in RR interval may result from atrial stretch caused by changes in venous return, but slower fluctuations (0.03 to 0.15 Hz, low frequency [LF]) not due to respiration suggest reinnervation. In normal subjects, sinusoidal neck suction selectively stimulates carotid baroreceptors and causes reflex oscillations of RR interval. METHODS AND RESULTS To evaluate the presence of reinnervation, we measured the power of RR-LF and RR-HF in 26 heart transplant recipients and 16 control subjects before and during sinusoidal neck suction at 0.1 Hz and 0.20 Hz (similar to but distinct from that of controlled respiration, 0.25 Hz) and before and during administration of atropine or beta-blocker (esmolol hydrochloride) by spectral analysis. All transplant recipients showed small respiratory HF fluctuations. Nonrespiratory LF fluctuations were present in 13 of 26 transplant recipients and increased with months since transplantation (r = .53, P < .01). HF neck suction induced a 0.20-Hz component in all 16 control subjects and none of the 26 transplant subjects. LF neck suction increased RR-LF (from 0.73 +/- 0.20 to 1.30 +/- 0.26 ln ms2, P < .001), similar to but less than in control subjects (from 6.12 +/- 0.21 to 8.27 +/- 0.21 ln ms2, P < .001). Atropine reduced all fluctuations in control subjects and blocked the HF increase caused by 0.20-Hz neck suction but not the LF increase during 0.10-Hz stimulation. Neck suction-induced changes in LF fluctuations persisted after administration of atropine in transplant recipients but were attenuated by esmolol hydrochloride, suggesting sympathetic rather than vagal reinnervation. CONCLUSIONS The presence of baroreceptor-induced RR oscillations is evidence of functional, although incomplete, autonomic reinnervation.

Radiofrequency catheter ablation of concealed accessory pathways in two dogs with symptomatic atrioventricular reciprocating tachycardia

BACKGROUND Radiofrequency catheter ablation (RFCA) is widely used as a curative therapeutic strategy in human beings with paroxysmal supraventricular tachycardia (SVT), but rarely applied in animals. This report describes successful RFCA of atrioventricular accessory pathways (AP) in two dogs with episodic weakness caused by frequent paroxysms of supraventricular tachycardia. METHODS AND RESULTS Invasive electrophysiological studies (EPS) identified two APs in the 1st dog (right postero-septal, right posterior), and one in the 2nd dog (right posterior). Programmed electrical stimulation demonstrated that all APs had only retrograde unidirectional conduction, and played a role to maintain inducible atrioventricular reciprocating tachycardia (AVRT). The bypass tracts were successfully eliminated with RFCA, with consequent prevention of AVRT induction during post-ablation EPS. At 8months follow-up, the dogs were asymptomatic, and no reoccurrence of tachycardia was seen. CONCLUSION Concealed APs responsible for AVRT and accompanied symptoms may be safely eliminated using RFCA in dogs.

Peripheral arterial vascular function at altitude: sea-level natives versus Himalayan high-altitude natives.

Objectives Regulation of the vascular system may limit physical performance and contribute to adaptation to high altitude. We evaluated vascular function in 10 Himalayan high-altitude natives and 10 recently acclimatized sea-level natives at an altitude of 5050 m. Methods We registered electrocardiogram, blood flow velocity in the common femoral artery, and blood pressure in the radial artery using non-invasive methods under baseline conditions, and during maximal vasodilation after 2 min leg occlusion. Vascular mechanics were characterized by estimating pulse wave velocity and input impedance. Results Pulse wave velocity and parameters of input impedance did not differ between groups under baseline conditions. In the post-ischemic period, the ratio between maximal hyperemic and baseline blood flow velocity was significantly higher in the high-altitude than in the sea-level natives (5.7 ± 2.5 versus 3.8 ± 1.2, P < 0.05). The leg vascular resistance decreased in the post-occlusive period without differences between groups. Characteristic impedance decreased in the post-ischemic period by about one third of the baseline level without differences between groups. The post-ischemic decrease of input impedance modulus was more marked in the high-altitude than in the sea-level natives at low frequencies (28 ± 12 versus 6.4 ± 20% at 2 Hz, P < 0.01). Conclusions Our results demonstrate a superior ability to increase blood flow velocity as a response to muscular ischemia in high-altitude natives compared to sea-level natives. This phenomenon may be associated with a more effective coupling between blood pressure and blood flow which is probably caused by differences in conduit vessel function.

Successful Selective Ablation of Fast Atrioventricular Node Pathway by Cryothermal Energy Application

This paper reports the experience of successful cryoablation of fast atrioventricular nodal pathway in a patient with recurrent atrioventricular nodal reentrant tachycardia after previous unsuccessful attempts of slow pathway ablation. Slow formation of a permanent lesion by cryothermal energy application allowed precise modulation of atrioventricular nodal conduction until the endpoints of complete fast pathway ablation were met with long‐term cure of the arrhythmia.

Radiofrequency catheter ablation of atypical atrial flutter in dogs

Five dogs were presented to our institution for fatigue caused by an incessant supraventricular tachycardia. In all dogs, an ECG on admission showed a narrow QRS complex tachycardia with a median ventricular cycle length of 220 ms (range 180-360 ms), and a positive atrial depolarization identifiable in the ST segment following the previous QRS complex. There was a 1:1 atrioventricular conduction ratio in all but one dog, which presented with 2:1 atrioventricular block. Electrophysiologic studies identified the underlying arrhythmogenic mechanism as a right atrial macro-reentrant tachycardia with two distinct isthmic areas: right septal (RS) in three dogs and right atrial free wall (RAFW) in two dogs. Linear radiofrequency catheter ablation was performed during tachycardia in all dogs at the identified isthmic area, which acutely blocked the macroreentrant circuit. At 18-month follow-up, 3 dogs (1 with RAFW isthmus and 2 with RS isthmus) showed no recurrence of the arrhythmia on Holter monitoring. One dog with RS isthmus showed recurrence of the supraventricular tachycardia 15 days post-ablation, and 1 dog with RAFW isthmus presented with persistent atrial fibrillation 2 months post-ablation.

Effects of breathing control on cardiocirculatory modulation in Caucasian lowlanders and Himalayan Sherpas

Abstract This study was performed to investigate the influence of breathing control on the autonomic cardiac regulation at high altitude in adapted and non-adapted awake subjects. We recorded electrocardiogram and pulse oximetry in 14 short-term acclimatized lowlanders and 14 Himalayan Sherpas during resting conditions at an altitude of 5,050 m. Spectrum analysis was performed on synchronized 15 min periods of R-R intervals and the oxygen saturation of arterial blood (SaO2). Despite mean SaO2 being similar in lowlanders and Himalayan Sherpas [78.5 (SD 7.0)% compared to 79.4 (SD5.8)%, respectively], fluctuations in SaO2 were significantly increased in lowlanders compared to Sherpas, thus indicating an unstable regulation of respiration control in lowlanders. Regression analysis demonstrated a significant relationship between spectrum power of SaO2 and the relative power of R-R intervals in the frequency band between 0.01 and 0.08 Hz in lowlanders, but not in Sherpas. Our results demonstrate differences in respiratory and autonomic cardiac control between non-adapted lowlanders and Himalayan high-altitude residents and indicate that unstable breathing control during chronic hypobaric hypoxia is significantly correlated with the autonomic cardiocirculatory regulation.

Persistence of baroreceptor control of cerebral blood flow velocity at a simulated altitude of 5000 m.

Objective To assess the effects of acute exposure to simulated high altitude on baroreflex control of mean cerebral blood flow velocity (MCFV). Patients and methods We compared beat-to-beat changes in RR interval, arterial blood pressure, mean MCFV (by transcranial Doppler velocimetry in the middle cerebral artery), end-tidal CO2, oxygen saturation and respiration in 19 healthy subjects at baseline (Albuquerque, 1779 m), after acute exposure to simulated high altitude in a hypobaric chamber (barometric pressure as at 5000 m) and during oxygen administration (to achieve 100% oxygen saturation) at the same barometric pressure (HOX). Baroreflex control on each signal was assessed by univariate and bivariate power spectral analysis performed on time series obtained during controlled (15 breaths/min) breathing, before and during baroreflex modulation induced by 0.1-Hz sinusoidal neck suction. Results At baseline, neck suction was able to induce a clear increase in low-frequency power in MCFV (P < 0.001) as well as in RR and blood pressure. At high altitude, MCFV, as well as RR and blood pressure, was still able to respond to neck suction (all P < 0.001), compared to controlled breathing alone, despite marked decreases in end-tidal CO2 and oxygen saturation at high altitude. A similar response was obtained at HOX. Phase delay analysis excluded a passive transmission of low-frequency oscillations from arterial pressure to cerebral circulation. Conclusions During acute exposure to high altitude, cerebral blood flow is still modulated by the autonomic nervous system through the baroreflex, whose sensitivity is not affected by changes in CO2 and oxygen saturation levels.

Power Spectral Changes of Spontaneous Beat‐to‐Beat Variability of the RT Interval in Patients with Coronary Artery Disease

Objective: This study sought to evaluate the spontaneous beat‐to‐beat variability of the RT interval (RTV) as a marker of autonomic balance at the ventricle in patients with coronary artery disease (CAD), as heart rate variability (HRV) primarily reflects sympathovagal interactions at the sinus node.