 Physiological changes which occur during valsalva maneuver is one of the techniques used in clinics for various things for example assessment of autonomic functions then for the diagnosis of murmurs. So what is this valsalva maneuver and what are the physiological changes which occur during valsalva maneuver? Valsalva maneuver is basically forced expiration which is performed with closed glottis. So air is basically not moving outside of the lungs but due to forced expiration there is increase in the intrathoracic pressure. So when we do forced expiration what happens that the person breathes into a manometer and he maintains this forced expiration for some time and while breathing in a manometer so that during forced expiration he is able to maintain a certain pressure. So that is an indication that he is continuing the valsalva maneuver. Now this is a technique used as a test but physiologically these valsalva maneuver kind of physiological changes occur during various events for example straining during defecation then during cuffing and also lifting heavy weight. So all these physiological activities also cause valsalva maneuver like changes because during these activities there is forced expiration which is happening. So this valsalva maneuver basically has four phases that is first is the start of the maneuver okay so onset of a strain when he has just started the expiration then he will continue the valsalva maneuver for some time then stop of the maneuver that is release of the strain and after stopping. So we see the physiological changes that occur during these four phases and most important among these is during continuing of the valsalva maneuver and after stopping the valsalva maneuver. So what happens that as the person starts the onset of the strain with the start of the strain there is increase in intratheurastic pressure and for very minimal time there is increase in blood pressure. So this start of the strain represents the mechanical effect which the intratheurastic pressure is happening on the blood pressure. So basically adding on the intratheurastic pressure to the aortic pressure occurs so increase in blood pressure and again this mechanical effect happens during stopping of the procedures. So at that particular moment with decrease in the intratheurastic pressure there is decrease in the blood pressure. On the other hand when the person is continuing the procedure due to increase intratheurastic pressure actually there is decrease in the preload. Because increase intratheurastic pressure collapses the veins and that is why decrease in preload occurs. And decrease in preload what will happen there will be decrease in cardiac output decrease in cardiac output there will be decrease in blood pressure and this decreased blood pressure is actually sensed by baroreceptors initiating the baroreflex causing increase in heart rate and increase in blood pressure. On the other hand after stopping what happens the opposite events occur that is the intratour acid pressure returns back to normal. So there is increase in preload, increase in cardiac output, increase blood pressure and baroreflex brings about the opposite events. So here you just remember that the start and the stop of the valsalva manoeuvre has mechanical effects and where we are studying the physiology in the second phase during the continuing of the procedure and after stopping of the procedure that is the fourth phase. So let us see this effects on blood pressure and heart rate in a diagrammatic manner. So here three graphs are shown. First graph you see this is the time okay x axis is the time where this box is showing the, this part is the start of the manoeuvre okay and here the manoeuvre is continuing and this is the stop of the manoeuvre and you see the intratour acid pressure is represented on the y axis. So with the start of the manoeuvre the intratour acid pressure is increasing. So what is the effect of this on blood pressure and heart rate? So here I have already marked the 1, 2, 3, 4 that is the phases of the valsalva manoeuvre. So this is the first phase start, second, third phase and after this continues the fourth phase accordingly I have also marked these in the BP graph. So again x axis represents the time okay so here it is the manoeuvre is started at around 10 seconds. So this represents the baseline right. So we will see blood pressure and heart rate graph with each phase of the valsalva manoeuvre. So let us see first phase. So here when the manoeuvre is starting what we see due to the mechanical effect there is increase in blood pressure. This top red line shows us the stolic blood pressure and this bottom red line shows the diastolic blood pressure. So both are rising during the start of the manoeuvre and as blood pressure rises the baroreflex kicks in right. So we see decrease in the heart rate only for very small time. We are not interested in this mechanical effect what we are interested in the physiological effects. So what is happening in phase 2? You see that as the intratour acid pressure is maintained because of decreased preload blood pressure is decreasing right. So both systolic and diastolic blood pressure are falling and due to baroreflex because of the pollen BP baroreceptors are stimulated less there is activation of the sympathetic system inhibition of the parasympathetic system and heart rate actually increases. So this portion is due to baroreflex. Then third phase again the mechanical effect what will happen? You see that as the intratour acid pressure falls there is little bit fall in blood pressure. Here little bit rise you are seeing because due to baroreflex the BP starts correcting right and with the stoppage of the balsalva manoeuvre BP falls due to the mechanical effect. Then fourth part, fourth part is that after stoppage what will happen? There will be increase in preload, increased preload will cause increase in the cardiac output and increase in the blood pressure. So here again what you are seeing is the manifestation of the physiological changes which are occurring and this increased BP is detected by the baroreceptors which in turn cause decrease in the heart rate. So this is balsalva manoeuvre and the physiological changes which occur during balsalva manoeuvre. Now for autonomic function testing we calculate a balsalva ratio. What is that? That is the ratio between longest RR interval and the shortest RR interval. Now this longest RR interval will occur when the heart rate decreases because the intermediate interval is basically increasing and that is why the heart rate is decreasing and this shortest RR interval will occur when there is increased heart rate. So tell me which phases are we going to take this longest RR interval and shortest RR interval when are they going to occur? You see heart rate decrease is occurring in the fourth phase and heart rate increase is occurring in the second phase. So longest RR interval in fourth phase we take and shortest RR interval in the second phase we take and that ratio is taken as balsalva ratio and normally this ratio is less than 1.21. So this ratio is an indicator of parasympathetic activity. Why parasympathetic activity and not sympathetic activity? See whenever in autonomic function test we are talking about heart rate then we are referring to parasympathetic changes. Why? Sympathetic system also causes changes in heart rate? True. But the effect of parasympathetic system on heart rate is extremely fast. It is the beat to beat changes which occur in heart rate that is due to parasympathetic activity. On the other hand sympathetic system the changes occur little late. Well this is because of the mechanism of action. Parasympathetic action happens directly via the ion channels. It causes the opening of the ion channels and there is instant changes in the heart rate. However sympathetic system the norepinephrine which is released acts via metabotropic receptors which take little time to act. So in autonomic function testing valsalva manoeuvre when we are looking at we are basically looking at the parasympathetic activity. Fine. With this now let us move on to the applications of the valsalva manoeuvre. So what are its application? As I told you one is assessment of the autonomic function test. So that is for parasympathetic activity and if there is autonomic abnormality disautonomia that is reflected in the valsalva ratio. Valsalva ratio is going to increase. Then it is also used for heart failure assessment. So the heart rate changes which we are talking that don't occur in case of heart failure. Then it is also used for termination of certain arrhythmias especially parapsysmal supraventricular tachycardia because what we are seeing that in phase 4 there is increase in parasympathetic activity and this increase parasympathetic activity not only reduces the heart rate but it also reduces the conduction of the impulse. So one of the application of valsalva manoeuvre is PSVT termination and then there are certain murmurs which can be exaggerated or decreased during the valsalva manoeuvre. So these are the various applications of the valsalva manoeuvre. Thanks for watching the video. If you liked it do press the like button, share the video with others and don't forget to subscribe to the channel Physiology Open. Thank you.