The beta blockers effect in the VO 2peak is very controversial in the literature , with some studies presenting decrease and others no alteration The main explanations for these discrepancies between studies are the methodological differences, especially concerning the population studied and the type of beta blocker used.
Defining Recovery Thresholds
Thus, the decrease in VO 2peak with the use of beta blockers has been reported, especially in healthy and trained individuals as well as with the use of non-selective beta blockers 8,9. When the beta blocker decreases the VO 2peak , this reduction has been mainly attributed to the medication effect, reducing the HR max and, consequently, the maximum cardiac output 14,16, In fact, previous studies 14,16,18,20 have demonstrated increase of maximum systolic volume with the use of beta blocker, which was attributed to the increase of the pre-load promoted by this medication and by the longer time of ventricular filling.
Additionally, increase in oxygen consumption by the muscles has also been reported, explaining hence the increase of arteriovenous difference of O 2 14,18, It is possible that these adaptations are higher in sedentary individuals, since the trained ones already presented these variables maximum systolic volume and maximum arteriovenous difference increased by chronic training 9 , which may make the medication effect more difficult. These aspects may explain why atenolol did not harm the aerobic power in sedentary patients, as happens in trained subjects 9.
This response is similar to the observed in other studies 18,21 which did not report alteration of lactate threshold with the use of beta blockers, despite the lactate concentration during the exercise be decreased with the use of atenolol The fact the use of atenolol does not affect the HR max and VO 2peak percentages in which the VT were reached in sedentary hypertensive patients, supports the current recommendation of aerobic exercise intensity prescription based on the same HR max percentage for hypertensive subjects, regardless of the use of selective beta blockers.
In other words, physical training may be prescribed in the same percentage of the HR max as long as this HR is determined by a maximum test performed with the use of the beta blocker. It is known that high levels of systolic BP in patients with hypertension may increase the risk of rupture of pre-existent aneurysm 22 , high HR values may increase the risk of arrhythmia in prone individuals 23 and high values of rate pressure product HR x systolic BP represent increase of cardiac work, which increases the risk of heart attack in cardiac hypertensive patients 2.
Thus, as in this study, atenolol reduced the HR, systolic BP values and consequently, of the rate pressure product for the same exercise intensity AT and RCP , it is possible to say that its use reduced the cardiovascular risk during performance of the aerobic exercise in these patients.
This study presents some limitations. The number of subjects investigated was small, but similar to other studies which identified reduction of VO 2 with the beta blocker 14,15,21 , which suggests that this small number was not responsible for the absence of atenolol effect in the aerobic fitness and ventilator thresholds. Another aspect to be considered is that, despite having included men and women, the differences between sexes were not assessed. However, there are suggestions in the literature 24 that the responses to exercise and to atenolol are not different between men and women.
All patients received the same dose, which may have resulted in different levels of blockade.
Another aspect which may be raised is the short time of beta blocked used four weeks. Nonetheless, as the efficiency of this blockage has been verified by the reduction of cardiac sympathetic modulation, this period was sufficient for the medication to have its effect. An important limitation is the fact that the treatments were not applied in a random manner, which may have influenced the results, leading to better performance in the second test due to adaptation to the testing.
However, as the VO 2 response did not change with atenolol, it is not probable that this influence had occurred. These results support the recommendation that training intensity may be determined at the same percentage HR max obtained in a maximum test in sedentary hypertensive patients who received or not atenolol. American College Sports Medicine. ACSM's Guidelines for exercise testing and prescription. American College of Sports Medicine position stand. Exercise and hypertension. Med Sci Sports Exerc ; Effect of exercise on blood pressure control in hypertensive patients. Eur J Cardiovasc Prev Rehabil ; Barueri: Manole, The effect of antihypertensive medicantions on exercise performance: a review.
Tesch PA. Exercise performance and beta-blockade. Sports Med ; Van Baak MA. Beta-adrenoceptor blockade and exercise.
Keywords - thresholds of recovery
An update. Wasserman K. Principles of exercise testing and interpretation. Task Force. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation ; Direct and indirect blood pressure during exercise.
Chest ; Effects of beta-adrenergic blockade on the cardiac response to maximal and submaximal exercise in man. J Clin Invest ; The effects of betaadrenoceptor blockade on factors affecting exercise tolerance in normal men.
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Br J Clin Pharmacol ; Exercise performance during captopril and atenolol treatment in hypertensive patients. Effect of atenolol or prazosin on maximal exercise performance in hypertensive joggers.
Am J Med ; The effect of long-term beta-adrenergic receptor blockade on the oxygen delivery and extraction relationship in patients with coronary artery disease. J Cardiopulm Rehabil Prev ; Effect of beta1 selective adrenoceptor blockade on physiological response to exercise. Br Heart J ; Hemodynamic response to graded exercise after chronic beta-adrenergic blockade. J Appl Physiol ; The AON components continue to check the status of the resource and try to recover it at intervals defined in the control file.
The components of AON do much more than issue commands and recover a resource. Figure 1 illustrates a basic example of AON recovery logic. Figure 1. Automation Failure Logic. AON intercepts this message and begins recovery actions for the resource.
You can set automation completely off for a resource or schedule times when automation does not occur. You can set three threshold levels: infrequent, frequent, and critical.
At the infrequent or frequent threshold levels, AON notifies operators to give them the opportunity to proactively investigate resource failures. When the number of failures exceeds the critical threshold, AON notifies operators and stops further recovery attempts to prevent reiterative, unproductive automation. For all types of failed resources, AON monitors resource recovery at the intervals specified in the control file.
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