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Perceived exertion and gas exchange after calcium and beta-blockade in atrial fibrillation
Insights
Minute ventilation (VE) is the most reliable indicator of perceived exertion during exercise in patients with atrial fibrillation, regardless of beta-adrenergic or calcium channel blockade. This finding is crucial for exercise prescription and monitoring.
Area of Science:
- Cardiology
- Exercise Physiology
- Pharmacology
Background:
- Chronic atrial fibrillation affects exercise capacity and perceived exertion.
- Beta-adrenergic and calcium channel blockers are commonly used to manage atrial fibrillation.
- Understanding factors influencing perceived exertion is vital for safe and effective exercise interventions.
Purpose of the Study:
- To investigate the relationship between various physiological parameters and ratings of perceived exertion (RPE) during exercise in patients with atrial fibrillation.
- To determine how beta-adrenergic and calcium channel blockade affect these relationships.
- To identify the most reliable physiological correlate of RPE in this patient population.
Main Methods:
- Nine male patients with chronic atrial fibrillation underwent maximal exercise testing.
- Testing was performed under placebo, celiprolol (beta-blocker), and diltiazem (calcium channel blocker) conditions.
- Physiological variables including heart rate (HR), blood pressure (BP), oxygen uptake (VO2), minute ventilation (VE), and carbon dioxide production (VCO2) were measured at rest and during exercise.
Main Results:
- Both celiprolol and diltiazem significantly reduced HR and BP compared to placebo, with more pronounced effects during beta-blockade.
- RPE was significantly correlated with HR during placebo and diltiazem therapy but not during beta-blockade.
- The relationship between RPE and VO2, VE, and VCO2 remained consistent across all treatment conditions, suggesting VE is a robust correlate of RPE.
Conclusions:
- Minute ventilation (VE) is a more consistent and reliable indicator of perceived exertion during exercise in patients with atrial fibrillation, compared to HR, VO2, or VCO2.
- The presence of atrial fibrillation and beta-adrenergic blockade can alter the association between RPE and HR.
- These findings have implications for exercise prescription and monitoring in patients with atrial fibrillation undergoing pharmacologic therapy.
Abstract:
Nine male patients (mean age 65 yr) with chronic atrial fibrillation underwent maximal exercise testing during placebo, beta-adrenergic (celiprolol, 600 mg), or calcium (diltiazem, 30 or 60 mg four times daily) channel blockade. The results were analyzed to determine which factors most closely related to ratings of perceived exertion (RPE) during exercise. Heart rate (HR), blood pressure (BP), oxygen uptake (VO2), minute ventilation (VE), and carbon dioxide production (VCO2) were evaluated at rest, 3.0 mph/0% grade, the gas exchange anaerobic threshold (ATge), 80% of placebo maximal O2 uptake, and maximal exercise. Both beta-adrenergic and calcium channel blockade significantly reduced heart rate and systolic blood pressure relative to placebo; these effects were more profound during beta-adrenergic blockade and as exercise progressed. Correlation coefficients and estimates of slope were derived for changes in RPE during exercise vs. changes in HR, VO2, VE, and VCO2 during the three treatments (r = 0.76 to 0.92, P less than 0.001). Although RPE was significantly correlated with HR during placebo and diltiazem therapy (r = 0.45, P less than 0.01), this was not the case during beta-adrenergic blockade (r = 0.31, NS). Slope of the regression lines between RPE and VO2, VE, and VCO2 did not differ between the three treatments. Slope of the regression lines between RPE and HR differed only during calcium channel blockade. Because the presence of atrial fibrillation and beta-adrenergic blockade altered the associations between RPE, VO2, and HR, these results suggest that VE is more closely related to RPE than the other parameters.