Spontaneous baroreflex sensitivity after coronary artery bypass graft surgery as a function of gender and age

The effects of low-volume high-intensity interval versus moderate intensity continuous training on heart rate variability, and hemodynamic and echocardiography indices in men after coronary artery bypass grafting: A randomized clinical trial study

BACKGROUND

Heart rate variability (HRV) declines after coronary artery bypass grafting (CABG). The purpose of this study was to evaluate the effect of low-volume high-intensity interval training (LV-HIIT) and moderate-intensity continuous training (MICT) on HRV as well as, hemodynamic and echocardiography indices.

METHODS

Forty-two men after CABG (55.12 ± 3.97 years) were randomly assigned into LV-HIIT, MICT, and control (CTL) groups. The exercise training in LV-HIIT consisted of 2-minute interval at 85-95 percent of maximal heart rate (HRmax), 2-minute interval at 50% of HRmax and 40-minute interval at 70% of HRmax in MICT for three sessions in a week, for 6-weeks. HRV parameters were evaluated by 24-hour Holter electrocardiography (ECG) recording, and echocardiography parameters at baseline and end of intervention were measured in all 3 groups.

RESULTS

At the end of the intervention, left ventricular ejection fraction (LVEF) significantly increased in LV-HIIT group (58.53 ± 7.26 percent) compared with MICT (52.26 ± 7.91 percent) and CTL (49.68 ± 7.27 percent) groups (P < 0.001). Furthermore, mean R-R interval, root mean square successive difference (RMSSD) of R-R interval, and standard deviation of R-R interval (SDRR) in LV-HIIT group considerably increased compared with MICT group (P < 0.001). High-frequency power (HF) significantly increased in LV-HIIT and MICT groups compared with CTL group (P < 0.001). On the other hand, low frequency (LF) and LF/HF ratio significantly decreased in LV-HIIT group in comparison with MICT group (P < 0.010).

CONCLUSION

These results suggest that LV-HIIT has a greater effect on improvement of cardiac autonomic activities by increasing R-R interval, SDRR, RMSSD, and HF, and decreasing LF and LF/HF ratio in patients after CABG.

Influence of D,L-sotalol on baroreflex sensitivity response to posture following coronary artery bypass graft surgery in men and women

Low baroreflex sensitivity (BRS) following coronary artery bypass graft (CABG) surgery increases the risk of sympathetically mediated cardiac arrhythmias. To reduce this risk, D,L-sotalol, a nonselective β-adrenergic receptor antagonist (Class II) and an antiarrhythmic (Class III), is prescribed postoperatively. However, its effect on BRS has not been reported. The purpose of this study was to characterize the influence of D,L-sotalol on BRS measures in supine and standing postures 4 days following CABG surgery. BRS was measured in 27 men and 10 women receiving D,L-sotalol and compared with archival data for 21 men and 10 women obtained prior to the routine administration of D,L-sotalol. In the latter (control) group, 61% had BRS of less than 3 ms/mmHg in the supine posture and 74% in the standing posture compared to 42% with less than 3 ms/mmHg in the supine posture and 65% in the standing posture in the D,L-sotalol group. Men in the D,L-sotalol group showed higher R-R interval and BRS in both supine and standing postures compared with controls. Women in the D,L-sotalol group had higher R-R interval in the supine posture. The higher BRS in men not only reduces the risk of arrhythmias after CABG surgery but may also allow a more rapid circulatory response to the standing posture, thereby decreasing the risk of syncope.

Heart rate variability response to standing in men and women receiving d,l-sotalol following coronary artery bypass graft surgery

Heart rate variability (HRV), a quantitative marker of autonomic control of heart rate (HR), declines in men and women following coronary artery bypass graft (CABG) surgery. Although d,l-sotalol is prescribed following CABG surgery primarily for its antiarrhythmic effect, its effects on HRV have not been reported; the β-adrenergic antagonist effect of d,l-sotalol may attenuate sympathetically mediated HR and blood pressure (BP) responses to standing, resulting in postural hypotension. In this study, the HRV response to standing 4 days following CABG surgery in men and women prescribed d,l-sotalol was measured to examine the influence of d,l-sotalol on previously reported HRV responses, taking age and gender into consideration. Participants included 28 men and 10 women who completed testing in supine and standing postures; all had received low-dose d,l-sotalol daily since the first postoperative day. Data included continuous electrocardiograph recording of R-R interval for 10 min in each posture. Participants showed significant effects of standing on the autonomic modulation of HR, as seen by a decrease in parasympathetic indices and R-R interval and an increase in BP. In men, standing decreased parasympathetic modulation and increased the sympathetic nervous system indicator, but previously reported age effects were not seen. In women, standing decreased low frequency power and R-R interval and increased BP, with older women having a smaller increase in BP, suggesting an attenuated response. The differential autonomic nervous system modulation of HR as a function of gender and age after CABG surgery may be attenuated by d,l-sotalol.

Cyclohexanone contamination from extracorporeal circuits impairs cardiovascular function

Extracorporeal circulation provides critical life support in the face of cardiopulmonary or renal failure, but it also introduces a host of unique morbidities characterized by edema formation, cardiac insufficiency, autonomic dysfunction, and altered vasomotor function. We tested the hypothesis that cyclohexanone (CHX), a solvent used in production of extracorporeal circuits and intravenous (IV) bags, leaches into the contained fluids and can replicate these clinical morbidities. Crystalloid fluid samples from circuits and IV bags were analyzed by gas chromatography-mass spectrometry to provide a range of clinical CHX exposure levels, revealing CHX contamination of sampled fluids (9.63-3,694 microg/l). In vivo rat studies were conducted (n = 49) to investigate the effects of a bolus IV infusion of CHX vs. saline alone on cardiovascular function, baroreflex responsiveness, and edema formation. Cardiovascular function was evaluated by cardiac output, heart rate, stroke volume, vascular resistance, arterial pressure, and ventricular contractility. Baroreflex function was assessed by mean femoral arterial pressure responses to bilateral carotid occlusion. Edema formation was assessed by the ratio of wet to dry organ weights for lungs, liver, kidneys, and skin. CHX infusion led to systemic hypotension; pulmonary hypertension; depressed contractility, heart rate, stroke volume, and cardiac output; and elevated vascular resistance (P < 0.05). Mean arterial pressure responsiveness to carotid occlusion was dampened after CHX infusion (from +17.25 +/- 1.8 to +5.61 +/- 3.2 mmHg; P < 0.05). CHX infusion led to significantly higher wet-to-dry weight ratios vs. saline only (3.8 +/- 0.06 vs. 3.5 +/- 0.05; P < 0.05). CHX can reproduce clinical cardiovascular, neurological, and edema morbidities associated with extracorporeal circulatory treatment.

Depression of cardiovascular autonomic function is more pronounced after mitral valve surgery: evidence for direct trauma

The analysis of baroreflex sensitivity (BRS) and heart rate variability (HRV) leads to additional insights into patients' prognosis after cardiovascular events. The following study was performed to assess the differences in the post-operative recovery of autonomic regulation after mitral valve (MV) and aortic valve (AV) surgery with a heart-lung machine. Among the 43 consecutive male patients enrolled in a prospective study, 26 underwent isolated AV surgery and 17 isolated MV surgery. Blood pressure as well as ECG signals were recorded the day before, 24 hours after and one week after surgery. BRS was calculated according to the dual sequence method, and HRV was calculated using standard linear as well as nonlinear parameters. There were no major differences between the two groups in the pre-operative values. At 24 hours a comparable depression of HRV and BRS in both groups was observed, while at 7 days there was partial recovery in AV patients, which was absent in MV patients: p(AV versus MV)<0.001. While the response of the autonomic system to surgery is similar in AV and MV patients, there is obviously a decreased ability to recover in MV patients, probably attributed to traumatic lesions of the autonomic nervous system by opening the atria. Ongoing research is required for further clarification of the pathophysiology of this phenomenon and to establish strategies to restore autonomic function.

Effects of low-intensity exercise conditioning on blood pressure, heart rate, and autonomic modulation of heart rate in men and women with hypertension

Untreated hypertension increases cardiovascular risk 2-fold to 3-fold, leading to serious cardiovascular problems that include left ventricular hypertrophy, stroke, ischemic heart disease, myocardial infarction, vascular disease, renal disease, and death. Exercise conditioning is recommended as one of the initial treatments for hypertension. The purpose of this pretest-posttest study was to quantify the effects of a 12-week home-based low-intensity exercise conditioning (walking) program in hypertensive men and women on systolic and diastolic blood pressure, heart rate, and autonomic modulation of heart rate. A total of 20 mildly hypertensive men and women who were assigned to a structured exercise (walking) program were compared with a control group of 20 nonexercising mildly hypertensive participants. Electrocardiographic heart rate and R-R interval data and beat-by-beat arterial blood pressure data were collected continuously for 10 min with participants in the supine and standing postures and during low-intensity steady-state exercise. The results show that systolic and diastolic blood pressure and R-R interval decreased and spontaneous baroreflex sensitivity increased in the exercise group. The decline in blood pressure was significant statistically and clinically. The increase in spontaneous baroreflex sensitivity indicates that the ability of the cardiovascular system to respond rapidly to changing stimuli improved after the 12-week walking protocol. The low-intensity exercise conditioning program achieved a training effect in this population.

Maternal Heart Rate Variability and Fetal Behavior in Hypertensive and Normotensive Pregnancies

The relation between maternal heart rate variability (HRV) and fetal behavior was examined in hypertensive and normotensive pregnant women. A total of 40 mother—fetal pairs (n = 20 normotensive mothers; n = 20 hypertensive mothers) at 33—41 weeks' gestation were observed using a standardized procedure lasting approximately 50 min. It included the following measurements: maternal beat-by-beat arterial blood pressure and HRV; spontaneous fetal heart rate (HR), body and breathing movements; and an estimate of amniotic fluid volume. The women in the hypertensive group had higher average body mass index (BMI) (33.7 vs. 28.8 kg/m2) than the normotensive group. In the normotensive group, there was no association between maternal HRV and fetal gestational age, HR, body or breathing movements. In the hypertensive group, maternal HRV measures of low-frequency, high-frequency, and total power were associated with fetal gestational age; also, there was an association between maternal autonomic modulation of HR and fetal spontaneous HR. These findings suggest that the maternal autonomic system influences fetal cardiac function in pregnancies complicated by hypertension.

Effects of endotracheal tube suctioning on arterial oxygen tension and heart rate variability

The purpose of this study was to examine the autonomic mechanisms underlying changes in heart rate (HR) and systolic blood pressure (SBP) responses to endotracheal tube (ETT) suctioning and to compare the open versus closed methods of ETT suctioning on these measures and on arterial oxygen tension. Eighteen orally intubated participants, 33 to 82 years of age (M = 60 years), were randomized for the order of suctioning method. Arterial oxygen tension (PaO2) was measured before suctioning and 30 s and 5 min following suctioning. Beat-to-beat HR and arterial blood pressure data were collected for 10-min periods before and after suctioning. HR and SBP measures were analyzed before suctioning and 1 min and 5 min following suctioning. Although there were no significant effects of ETT suctioning on the autonomic mechanisms of HR modulation and no significant differences between the two methods of suctioning, ETT suctioning resulted in an increase in HR, SBP, and PaO2. However, there was a decrease in the parasympathetic nervous system indicator of HR variability (HRV) following open suctioning. All patients in this study maintained a PaO2 level 80 mm Hg, which may account for our lack of significant autonomic changes. This suggests that hyperoxygenation with 100% oxygen for a minimum of 1 min (or 20 breaths), as delivered by preoxygenation modes available on most microprocessor ventilators, should be the method of choice for all hyperoxygenation procedures to avoid a decrease in PaO2 following suctioning.

Heart rate variability following coronary artery bypass graft surgery as a function of recovery time, posture, and exercise

This study examined the claim made by Niemela et al. (1992) that the decline in heart rate variability after coronary artery bypass graft surgery is irreversible. We tested six women and 16 men six and 12 weeks postoperative in three postures: in the supine position, in the standing position, and during low-intensity steady-state exercise. Beat-by-beat arterial blood pressure and electrocardiographic R–R interval data were collected continuously for 10 min in each condition. R–R interval data were analyzed with spectral analysis; baroreflex data were analyzed using the sequence method. Our results show that the indices of parasympathetic modulation improved over time, as seen by an | increased spontaneous baroreflex sensitivity and parasympathetic indicator, that both indices were affected by posture, and that spontaneous baroreflex sensitivity was also affected by low-intensity exercise. The effects of posture are consistent with attenuated responses of healthy older subjects to orthostatic stress. Similarly, the effects of low-intensity exercise are consistent with findings in healthy subjects. We found that spontaneous baroreflex sensitivity declined during exercise, whereas, in healthy subjects, this is maintained during low-intensity steady-state exercise. Our results of significant functional recovery between six and 12 weeks postoperative suggest that at least some of the autonomic dysfunction following surgery is temporary. Previously, no such duration of study has lasted longer than four or six weeks following cardiac surgery, which may not have been long enough to show significant functional restoration in heart rate variability.Key words: heart rate variability, spontaneous baroreflex sensitivity, CABG surgery, posture, exercise.