Effect of age and repeated hyperbaric oxygen treatments on vagal tone.

OBJECTIVES: To evaluate the influence of repeated hyperbaric oxygen (HBO2) exposures and age on vagal response to hyperbaric oxygenation, and to evaluate the timing of changes in vagal activity during the treatments. STUDY DESIGN: Open, controlled, non-randomized study. METHODS: Heart rate variability of 23 patients with chronic osteomyelitis or radionecrosis of the jaw or reconstructive surgery of the facial region was studied during repeated treatments. During each treatment, the patients were exposed to HBO2 at 2.5 ATA and heart rate variability was measured using power spectral analysis before compression, three times at 2.5 ATA and during and after decompression. The patients were grouped according to age (Cut-off point 50 years). Statistical analysis was carried out using analysis of variance for repeated measurements. RESULTS: Repeated exposures did not change vagal response to hyperbaric oxygenation. Vagal activity measured by HF power increased significantly in both age groups during the HBO2 exposures but there were no significant difference between the groups in the response. However, the level of HF power was significantly higher in the subjects under 50 years old. Significant differences between consecutive measurements were related to pressure changes. CONCLUSIONS: Repeated therapeutic HBO2exposures are not causing permanent changes in vagal control of the heart. Vagal responsiveness to hyperbaric hyperoxia is preserved in advanced age.

Epidural infusion of bupivacaine and fentanyl reduces perioperative myocardial ischaemia in elderly patients with hip fracture--a randomized controlled trial.

BACKGROUND: Perioperative myocardial ischaemia is an important risk factor for cardiac morbidity and mortality after noncardiac surgery. The impact of analgesic management on the incidence and severity of cardiac ischemia was studied in 77 elderly patients undergoing surgical treatment of traumatic hip fracture. METHODS: After hospital admission and written consent, patients were randomised to conventional analgesic regimen (intramuscular oxycodone, OPI group) or continuous epidural infusion of bupivacaine/fentanyl (EPI group). The analgesic regimens were started preoperatively. Patients were operated under spinal anaesthesia and the treatments were continued three days postoperatively. ECG was continuously recorded. ST segment depression of > or = 0.1 mV or elevation of > or = 0.2 mV lasting > or = 1 min were considered as ischaemic episodes. Nocturnal arterial oxygen saturation (SaO2) was recorded perioperatively, and subjective pain was assessed every morning using a visual analogue scale (VAS). RESULTS: Fifty-nine (OPI 30, EPI 29) patients were evaluable for efficacy. Thirteen patients (43%) in the OPI and 12 patients (41%) in the EPI group had ischaemic episodes (NS). However, significantly more patients in the OPI group had ischaemic episodes during the surgery (8 vs. 0 in the EPI group, P=0.005). The median (quartal deviation) total ischaemic burden (i.e. integral of ST-change vs. time) in patients with ischaemic episodes was ten times larger in the OPI group (340 [342] mm x min) compared with the EPI group (30 [36] mm x min) (P=0.002). There were no significant differences between the groups in average heart rates or in heart rates at the start of ischaemic episodes or in maximal heart rates during the attacks. Average nocturnal SaO2 was similar in the two groups and there were no differences in the number of hypoxaemic (SaO2<90%) episodes. Preoperatively there were no differences in subjective pain, but postoperative and average perioperative VAS scores for pain were almost 40% lower in the EPI group (P=0.006). Perioperative myocardial infarctions were not detected. CONCLUSIONS: Continuous epidural bupivacaine/fentanyl analgesic regimen, started preoperatively, reduces the amount of myocardial ischaemia in elderly patients with hip fracture.

Hyperbaric oxygen increases parasympathetic activity in professional divers.

The role of autonomic nervous system in hyperoxic bradycardia was evaluated by using the power-spectral analysis of heart-rate variability (HRV). Ten professional divers went through two hyperbaric hyperoxic experiments: (1) hyperbaric oxygen (HBO), 100% oxygen at 2.5 ATA, (2) hyperbaric air (HBAIR), O(2) 21% at 2.5 ATA. Four-minute traces of ECG were registered and subjected to power-spectral analysis. Cardiac conduction parameters were evaluated by a diagnostic 12-lead ECG and arrhythmias by a continuous 3-lead ECG. Statistical analysis was made using analysis of variance for repeated measurements. Heart rate decreased (P < 0. 001), but the response was similar during both treatments (P=0.14). Total power increased significantly more during HBO than HBAIR (P=0.003). High-frequency (HF) power (P < 0.001), Hayano's index (P=0.001) and normalized units of HF power (P=0.002) increased and LF/HF index (P < 0.001) decreased more during HBO than HBAIR. There were no changes in cardiac conduction or incidence of arrhythmias. In conclusion, 100% oxygen at 2.5 ATA caused marked increase in parasympathetic tone compared with 21% oxygen at 2.5 ATA.

Correlation properties and complexity of perioperative RR-interval dynamics in coronary artery bypass surgery patients.

BACKGROUND: Dynamic measures of heart rate variability (HRV) may uncover abnormalities that are not easily detectable with traditional time and frequency domain measures. The purpose of this study was to characterize changes in RR-interval dynamics in the immediate postoperative phase of coronary artery bypass graft (CABG) surgery using traditional and selected newer dynamic measures of HRV. METHODS: Continuous 24-h electrocardiograph recordings were performed in 40 elective CABG surgery patients up to 72 h postoperatively. In one half of the patients, Holter recordings were initiated 12-40 h before the surgery. Time and frequency domain measures of HRV were assessed. The dynamic measures included a quantitative and visual analysis of Poincaré plots, measurement of short- and intermediate-term fractal-like scaling exponents (alpha1 and alpha2), the slope (beta) of the power-law regression line of RR-interval dynamics, and approximate entropy. RESULTS: The SD of RR intervals (P < 0.001) and the ultra-low-, very-low-, low-, and high-frequency power (P < 0.01, P < 0.001, P < 0.001, P < 0.01, respectively) measures in the first postoperative 24 h decreased from the preoperative values. Analysis of Poincaré plots revealed increased randomness in beat-to-beat heart rate behavior demonstrated by an increase in the ratio between short-term and long-term HRV (P < 0.001) after CABG. Average scaling exponent alpha1 of the 3 postoperative days decreased significantly after CABG (from 1.22 +/- 0.15 to 0.85 +/- 0.20, P < 0.001), indicating increased randomness of short-term heart rate dynamics (i.e., loss of fractal-like heart rate dynamics). Reduced scaling exponent alpha1 of the first postoperative 24 h was the best HRV measure in differentiating between the patients that had normal ( 48 h, n = 7) intensive care unit stay (0.85 +/- 0.17 vs. 0.68 +/- 0.18; P < 0.05). In stepwise multivariate logistic regression analysis including typical clinical predictors, alpha1 was the most significant independent predictor (P < 0.05) of long intensive care unit stay. None of the preoperative HRV measures were able to predict prolonged intensive care unit stays. CONCLUSIONS: In the selected group of patients studied, a decrease in overall HRV was associated with altered nonlinear heart rate dynamics after CABG surgery. Current results suggest that a more random short-term heart rate behavior may be associated with a complicated clinical course. Analysis of fractal-like dynamics of heart rate may provide new perspectives in detecting abnormal cardiovascular function after CABG.

Heart rate variability in healthy volunteers during normobaric and hyperbaric hyperoxia.

Inhaled supranormal partial pressure of oxygen induces bradycardia and peripheral vasoconstriction. The exact mechanism of the decreasing heart rate is not clear, but the autonomic nervous system is partly involved. In the present study the role of the autonomic nervous system in hyperoxic bradycardia was evaluated by using the power spectral analysis of heart rate variability. Ten healthy volunteers participated in four experiments: (i) hyperbaric oxygen treatment (100% oxygen at 2.5 ATA), (ii) hyperbaric air treatment (O2 21% at 2.5 ATA), (iii) oxygen treatment at normal pressure (100% O2, 1 ATA) and (iv) air breathing at normal pressure (21% O2, 1 ATA). During the experiments, ECG was registered and subjected to power spectral analysis. The volunteers rated their perception of temperature, ear discomfort, sweating and excitement on a visual analogue scale. Statistical comparison of the results of the four trials was conducted with a two-way ANOVA for repeated measurements. Heart rate decreased during all interventions, but there were no statistically significant differences between the sessions. High frequency variability of heart rate variability and Hayano's index of HF power increased and LF/HF ratio decreased with increasing partial pressure of oxygen. Our results suggest, that normobaric and hyperbaric hyperoxia increase parasympathetic influence in the regulation of the heart.