Using TCD for Valsalva

We use Valsalva’s maneuver at various places –

Although he was mainly concerned with bad ears, he somehow seems to have created a fold in the colon as well: Antonio Maria Valsalva (* 17. Juni 1666 in Imola; † 2. Februar 1723 in Bologna)
  1. to elicit certain cardiac murmurs (such as the one of HOCM)
  2. to slow down the heart rate for a diagnostic window in supraventricular tachycardia
  3. to quantify damage to the autonomic nervous system (as in small fibre neuropathy)
  4. to provoke a right-left-shunt in PFO testing

If you are not careful, you can even invoke Valsalva’s accidentally when you really want to determine cerebrovascular reserve.

In yesterday’s session we derived the four phases of the Valsalva reaction from the rudiments of what we should remember about cardiovascular physiology, in particular the baroreflex (carotid sinus), Bainbridge reflex and the role that the sympathetic and parasympathetic nervous system play as mediators of tachycardia/hypertension.

We then went on to examine the role of various practical parameters in the Valsalva maneuver, such as the depth of the initial inhalation, the length of straining (phase II) and the straining pressure, using transcranial doppler and an ecg to monitor the heart rate and blood pressure changes. In my experiences, TCD is still the best way to measure changes in blood pressure continuously if you don’t have an arterial line and cannot afford a Finapres device. But you have to make sure that you do not extend the straining phase too much (otherwise CO2 increases and you get an increase in flow), so I only use 10 seconds instead of the usual 15 seconds that are recommended (this publication seems to show that this is still ok).

We also discussed the inherent difficulties in defining normal values for autonomous nervous system examinations because of the wide variation in base vagal tone, reactivity, hydration and more.



Bainbridge vs Bezold-Jarisch reflex – who wins in neurocardiogenic syncope?

The original tracing of the bainbridge reflex
The original tracing of the bainbridge reflex

About a century ago, Bainbridge described his reflex (if not under that name), namely increase of heart rate provoked by increased venous return. Although it has long been debated how big a role it plays in human vs. canine physiology, it is the physiologic foundation for respiratory arrhythmia, the effect of metronomic breathing on heart rate (as measured during autonomic testing) and many more phenomena.

In neurocardiogenic syncope it might play a role in the final bradycardic phase, but more likely is that it is far overtaken by yet another physiologic (and similarly controversial) reflex named after Bezold and Jarisch.

If all that confuses you, then take a look at this recent anesthesiologic article.