|
The Valsalva manoeuvre carries the name of Antonio Maria Valsalva, the 17th. Century physician and anatomist from Bologna, whose principal scientific interest was the human ear. He described the Eustachian tube and a manoeuvre to test its patency. This consisted of forcibly exhaling against closed lips and pinched nose, forcing air into the middle ear if the tube was open. This manoeuvre with slight modifications can be used as a test of cardiac function and autonomic nervous control of the heart or to ‘clear’ the ears (equalize pressure) when external pressure increases, as in diving or aviation. Figure 1. Blood pressure (systolic and diastolic) and pulse rate during a normal response to Valsalva’s manoeuvre. Forty millimeter mercury pressure is applied at 5 seconds and relieved at 20 seconds. 1.Initial pressure rise: On application of expiratory force, pressure rises inside the chest forcing blood out. This causes a transient rise in blood pressure. 2.Reduced venous return and compensation: Return of blood to the heart is impeded by the pressure inside the chest. The output of the heart is reduced, the blood pressure falls. This occurs from 5 to about 14 seconds in the illustration. The fall in blood pressure reflexly causes blood vessels to constrict with some rise in pressure(15 to 20 seconds. This compensation can be quite marked with pressure returning to near or even above normal, but the cardiac output and blood flow to the body remains low. During this time the pulse rate increases. 3. Pressure release: The pressure on the chest is released, allowing the aorta to expand again, causing a further initial slight fall in pressure. (20 to 23 seconds). Venous blood can once more enter the chest and the heart, cardiac output begins to increase. 4. Return of cardiac output: Blood return to the heart is enhanced by the effect of entry of blood which had been dammed back, causing a rapid increase in cardiac output and of blood pressure (24 seconds on). The pressure usually rises above normal before returning to a normal level. With return of blood pressure, the pulse rate returns towards normal. Deviation from this response pattern signifies either abnormal heart function or abnormal autonomic nervous control of the heart. Straining, blowing against resistance as in blowing up balloons has a Valsalva effect and the fall in blood pressure can result in dizziness and even fainting. It has been suggested that straining at stool because of constipation can cause diverticulosis, a disease of the large bowel, because the straining causes ‘blowouts’ along the colon. There is no evidence for this. The increased pressure in the abdomen is applied to the outside of the colon and cannot account for the diverticula or blowouts. The relation between diverticuar disease (diverticulosis/diverticulitis) and constipation is probably the result of propulsive forces acting on the colonic contents against resistance of hard faeces, which causes weaker patches of the colon wall to blow out and form the diverticula.
| ||||||||
|
| |||||||||
 |
|
| |