. The correct view is : during exercise, there is sympathetic stimulation plus adrenalin release 4 rise ot contractility ot heart muscle -> more empt

unrained persons are concerned. The correct view is : during exercise, there is sympathetic stimulation plus adrenalin release 4 rise ot contractility ot heart muscle -> more emptying ot the heart during systole, i.e the end sys­tolic volume becomes less than normal rise in stroke Volume [In trained athletes the picture is perhaps ditterent. In them, the heart rate rises less, heart is enlarged and rise in stroke volume plays a greater role. In them, Starlings law ot heart is an important tactor. ] The heart rate rise is also due to the (1) sympathetic stimulation and (n) adrenalin secretion. (iii) In addition, the reduction ot vagal tone also helps to develop tachycardia. In severe exercise, (iV) the rising body temperature, and (V) lactic acidosis also contribute to it.Cause ot sympathetic stimulation During exercise probably many tactors help to stimulate the sympathetic nervous system. Further, the stimulated sympathetic stimulates, in turn, suprarenal medulla to secrete adrenalin. Question is, what causes the sympathetic stimulation ? The precise picture is not clear. However, some tacts are known; (i) area 4 ot Broadmann, in cerebral cortex. (i.e. the motor cortex tig. 10A. 1. 1. A), when stimulated (as it must be in physical exercise), causes some sympathetic stimulation. These sympathetic stimulation, probably, mostly result in vasodilatation ot muscle vessels, (i.e. the vasodilator sympathetic fibers are stimulated), and have been described again later in this chapter. In short they play strong roles in muscle vaso dilatation but not in cardiac output increment, (n) in the peripheral muscles and pints, there are receptors, which when stimulated, cause retlex sympathetic stimulation. Muscular exercise, because it produces movements ot the joints, cause these receptors to be stimulated; (iii) in sports tournaments (or when an animal sees an approaching enemy), the excitement may cause sympathetic stimulation even betore the actual work has begun. (This however is unlikely to occur when non exciting routine jobs are being done). It should be clear that although there is sympathetic activity and adrenalin secretion, the diastohc blood pressure (DBP) usually faills during exercise; the explanation tor this has been given later. Peripheral Circulatory Changes The blood pressure The systolic blood pressure (SBP) rises as a rule, the diastohc blood pressure (DBP) usually talls and the mean blood pressure (MBP) does not usually change much but may fall in some cases. The pulse pressure rises sharply. Expla­nation: The SBP depends more on the cardiac output and as the GO rises the SBP also rises. The DBF is more dependent on the peripheral resistance. During muscular exercise, the peripheral resistance (PR) talls, so the DBP also talls usually. The changes mentioned above are seen in isotonic exercises (running/jogging etc.) where the active muscles are allowed to shorten. In isometric exercises (eg. working with a bulworker) where the muscles contract, but do not shorten, both the SBP & the DBP (and hence the MBP also) rise sharply. Hence isometric exercises like pushing a stationary car can be dangerous in an elderly man. Causes ot the tall ot the PR This can now receive attention. During muscular exercise, great circulatory readjustments occur. This includes a vaso dilatation in the skeletal muscles (and in some other regions, see later) and vaso constriction in other organs (see later). As the skeletal muscles account tor about 40% ot the body weight, a generalized vaso dilatation in them, even where the intensity ot the dilatation is slight, causes great reduction ot PR. The blood vessels ot the muscles are compressed while the muscles are contracting, producing a temporary ishcemia but a heavy vaso dilatation (which cancels the ettects due to the compression during contraction) occurs during relaxation. But in isometric contraction the sustained compression leads to rise ot BP (both SBP & DBP). Changes in regional circulation (1) Coronary: The coronary circulation increases and in very heavy exercise the increase may be manifold. Increase (= coronary vaso dilatation) is principally due to local O2 lack caused by the exercise (recall,. O2 lack in the myocardium is the most powerful coronary vasodilator). It should be understood that sympathetic stimulation causes coronary