Oxygen metabolism after cardiac arrest: Patterns and associations with survival.

Aim: Whether changes in oxygen metabolism, as measured by oxygen consumption (VO2), carbon dioxide production (VCO2) and the respiratory exchange ratio (RER), are associated with survival after cardiac arrest is poorly understood. In this prospective observational study, we investigated the association between VO2, VCO2, and RER in the initial 12 and 24 h after return of spontaneous circulation (ROSC) and survival to hospital discharge. Methods: Adults with ROSC after cardiac arrest, admitted to the intensive care unit, requiring mechanical ventilation and treated with targeted temperature management were included. VO2 and VCO2 were measured continuously for 24 h after ROSC, using a noninvasive anesthesia monitor. Area under the curve for VO2, VCO2 & RER was calculated using all available values over 12 and 24 h after ROSC. Using logistic regression, we evaluated the relationship between these metabolic variables and survival to hospital discharge. Analyses were adjusted for temperature, vasopressors, and neuromuscular blockade. Results: Sixty four patients were included. Mean age was 64 ± 16 years, and 59% were women. There was no significant association between the area under the curve of VO2 or VCO2 and survival. A higher RER in the initial 12 h was associated with better survival (aOR = 3.97, 95% CI [1.01,15.6], p = 0.048). Survival was lower in those with median RER < 0.7 in the initial 12 h compared with those with a median RER ≥ 0.7 (25% vs 67%, p = 0.011). Conclusion: Higher RER in the initial 12 h was associated with survival after cardiac arrest. The etiology of unusually low RERs in this patient population remains unclear.

Effects of Exercise Testing and Cardiac Rehabilitation in Patients with Coronary Heart Disease on Fear and Self-Efficacy of Exercise: A Pilot Study.

BACKGROUND: Exercise fear and low exercise self-efficacy are common in patients attending cardiac rehabilitation (CR). This study tested whether exercise prescription methods influence exercise fear and exercise self-efficacy. We hypothesized that the use of graded exercise testing (GXT) with a target heart rate range exercise prescription, relative to standard exercise prescription using rating of perceived exertion (RPE), would produce greater reductions in exercise fear and increase self-efficacy during CR. METHOD: Patients in CR (N = 32) were randomized to an exercise prescription using either RPE or a target heart rate range. Exercise fear and self-efficacy were assessed with questionnaires at three time points: baseline; after the GXT in target heart rate range group; and at session 6 for the RPE group and CR completion. Items were scored on a five-point Likert-type scale with higher mean scores reflecting higher fear of exercise and higher self-efficacy. To analyze mean differences, a mixed effects analysis was run. RESULTS: There were no significant changes in exercise self-efficacy between baseline and discharge from CR; these were not statistically significant (mean differences baseline - 0.63; end - 0.27 (p = 0.13)). Similarly, there was no change in fear between groups (baseline 0.30; end 0.51 (p = 0.37)). CONCLUSION: Patients in the RPE and target heart rate groups had non-significant changes in exercise self-efficacy over the course of CR. Contrary to our hypothesis, the use of GXT and target heart rate range did not reduce fear, and we noted sustained or increases in fear of exercise among patients with elevated baseline fear. A more targeted psychological intervention seems warranted to reduce exercise fear and self-efficacy in CR.

Semi-supervised exercise training program more effective for individuals with postural orthostatic tachycardia syndrome in randomized controlled trial.

PURPOSE: Exercise like any medication requires the correct dose; to be effective the appropriate frequency, duration, and intensity are necessary. This study aimed to assess if a semi-supervised exercise training (ET) program would be more effective at improving aerobic fitness (VO2PEAK), exercise tolerance, and symptoms in individuals with postural orthostatic tachycardia syndrome (POTS) compared to the standard of care (SOC). METHODS: Subjects were randomized to either the ET or SOC groups (n 26 vs. 23; age 33 ± 11 vs. 37 ± 10 years; VO2PEAK 66 ± 15 vs. 62 ± 15% predicted, ET vs. SOC respectively, p > 0.05). Composite Autonomic Symptom Score (COMPASS 31), 10 min stand test, and cardiopulmonary exercise test were performed at baseline and following 12 weeks. The ET group received an exercise consultation and eight semi-supervised in-person or virtual exercise sessions. RESULTS: The ET group demonstrated a greater improvement in VO2PEAK, higher or longer tolerance for baseline peak workload, and more often had a delayed symptom onset with exercise than the SOC group (ΔVO2PEAK 3.4 vs. - 0.2 mL/min/kg, p < 0.0001, ΔWorkload 19 ± 17 vs. 0 ± 10 W; Workload time 63 ± 29 vs. 22 ± 30 s; onset-delay 80% vs. 30%, p < 0.05). Individuals in the ET group reported a significant improvement in orthostatic intolerance domain score (p = 0.02), but there was not a significant difference in the improvement in total COMPASS score (- 11.38 vs. - 6.49, p = 0.09). CONCLUSION: Exercise training was more effective with greater improvements in aerobic fitness, orthostatic symptoms, and exercise tolerance for individuals with POTS when intensity and progression were personalized and delivered with minimal supervision compared to the SOC.

Comparison of Ratings of Perceived Exertion and Target Heart Rate-Based Exercise Prescription in Cardiac Rehabilitation: A RANDOMIZED CONTROLLED PILOT STUDY.

PURPOSE: Although ratings of perceived exertion (RPE) are widely used to guide exercise intensity in cardiac rehabilitation (CR), it is unclear whether target heart rate ranges (THRRs) can be implemented in CR programs that predominantly use RPE and what impact this has on changes in exercise capacity. METHODS: We conducted a three-group pilot randomized control trial (#NCT03925493) comparing RPE of 3-4 on the 10-point modified Borg scale, 60-80% of heart rate reserve (HRR) with heart rate (HR) monitored by telemetry, or 60-80% of HRR with a personal HR monitor (HRM) for high-fidelity adherence to THRR. Primary outcomes were protocol fidelity and feasibility. Secondary outcomes included exercise HR, RPE, and changes in functional exercise capacity. RESULTS: Of 48 participants randomized, four patients dropped out, 20 stopped prematurely (COVID-19 pandemic), and 24 completed the protocol. Adherence to THRR was high regardless of HRM, and patients attended a median (IQR) of 33 (23, 36) sessions with no difference between groups. After randomization, HR increased by 1 ± 6, 6 ± 5, and 10 ± 9 bpm ( P = .02); RPE (average score 3.0 ± 0.05) was unchanged, and functional exercise capacity increased by 1.0 ± 1.0, 1.9 ± 1.5, 2.0 ± 1.3 workload METs (effect size between groups, ηp2 = 0.11, P = .20) for the RPE, THRR, and THRR + HRM groups, respectively. CONCLUSIONS: We successfully implemented THRR in an all-RPE CR program without needing an HRM. Patients randomized to THRR had higher exercise HR but similar RPE ratings. The THRR may be preferable to RPE in CR populations for cardiorespiratory fitness gains, but this needs confirmation in an adequately powered trial.