It is a matter of common observation that in many conditions, notably cardiac arrhythmias, the sphygmomanometer will often detect the fact that in a given heart the beats may vary in strength, some strong beats pushing through to the artery at the wrist, though the pressure of the manometer cuff is sufficient to cut off all those that are weak or of average power. The arrhythmia of mitral stenosis when auricular fibrillation has set in is a good example. In the hypertension of chronic nephritis or of arteriosclerosis, the same phenomenon may be encountered.
When the systolic pressure is being tested in a patient in whom an alternating pulse is present, a manometer pressure may be reached that cuts off every other beat—the weaker beat—thus halving the rate of the pulse at the wrist. Increasing the pressure on the brachial artery, by still further inflation of the cuff, of course