Cardiovascular Effects of Drugs and Exercise
by Brendan Gabriel
Drugs that act on the cardiovascular system are usually prescribed for patients with chronic hypertension, tachycardia, angina, atherosclerosis and arrhythmias among others. The main drugs that are used are Calcium channel blockers(CCB), Beta Blockers, diuretics and ACE inhibitors.
Beta blockers are used to treat hypertension arrhythmia, angina in the cardiovascular system. They block the action of part of the sympathetic nervous system. Non-selective beta blockers (that act on B1-heart receptors and B2-airway receptors), decrease HR, force of heart contraction and decreased muscle vasodilation during exercise. Cardio-selective(act mostly on B1 receptors) beta blockers have been shown to lower exercise HR but often not significantly.
The effects of exercise and beta blockers on HR are shown in this study: During a 10-min treadmill exercise, cardiovascular characteristics were taken. A Betaxolol( a selective beta blocker) group and a placebo group showed no significant difference, but timolol(a non-selective beta blocker) showed a significant difference (P<0.05). ( Atkins et al. 1985). However Joyner et al. (1986) found that CO and HR reduced significantly in both selective and non-selective beta blockers (P<0.05).
Because beta Blockers act against the sympathetic NS during exercise, overall exercise capacity is usually decreased when taking beta blockers, (van Baak et al., 1987)
Diuretics have been used mainly to treat hypertension. Act by preventing the reabsorption of water and electrolytes, thus reducing BP. During aerobic exercise diuretics have mainly negative effects, including: loss of blood plasma volume(PV) and electrolytes. The loss of fluid in the blood causes decrease BP and increased HR, which decrease the body’s ability to perform exercise, this will lead to a decrease in overall V02 max. Claremont et al. (1976) showed that as a result of diuresis, PV decreased 15.3% (SE +/- 1.3), while heart rates during exercise increased 20-25 beats/min, during 2 hours of cycling in healthy subjects.
ACE inhibitors work by blocking the action of angiotensin, and are also used to treat hypertension. Harrap et al. (1990) found that a 4-week period of ACE inhibitor treatment in young spontaneously hypertensive rats , was enough to prevent full phenotype expression of the hypertensive gene.
ACE inhibitors have diuretic actions on the kidneys but they also increase vasorelaxation which can be used to reduce hypertension. The diuretic action of ACE inhibitors has the same effect on exercise as the diuretics that have been looked at above. However , the vasorelaxation that occurs when taking ACE inhibitors causes a large drop in BP. Gundersen et al. (1994) found that after 12-weeks treatment with ramipril( an ACE inhibitor), BP was significantly reduced(P<0.05).
BP is the main change ACE inhibitors cause in the body; however this does not appear to make a significant change in exercise capacity (Gundersen et al. 1994).
CCB are also used to treat hypertension, they work by blocking the entry of Ca into cardiac and smooth muscle cells, this lowers the rate and force of contraction of these muscles. CCB have quite a wide range of actions depending on the type. They usually induce a less severe reduction in HR compared to Beta blockers. However they are often used in conjunction with beta blockers. Agostoni et al. (1986) showed that CCB have no significant effect on exercise capability compared with a placebo in patients with congestive heart failure.
In Summary, most drugs that act on the cardiovascular system either reduce HR, contractility or BP. A large reduction is HR during rest and exercise can cause a significant reduction in exercise capacity, this is the problem with beta blockers. Diuretics dehydrate the blood and this causes a reduction in V02max. ACE inhibitors and CCB, have a lesser effect on exercise, and are well used alongside exercise programmes for patients.
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Exercise Capacity and Metabolic Effects During Exercise, Int J Sports Med; 08: 342-347 DOI: 10.1055/s-2008-1025681