Internal jugular vein response to Valsalva maneuver
We frequently use inferior vena cava POCUS to estimate right atrial pressure. Internal jugular vein (IJV) ultrasound can also be used for this purpose. In spontaneously breathing patients, IJV size/cross sectional area increases with valsalva maneuver secondary to an increase in right atrial pressure. Venous compliance is high at low pressures and low at high pressures, and the relationship between intravenous pressure and volume is characterized by a curvilinear shape as shown below. As such, you can expect that the change in IJV size would be more prominent when a normal person performs valsalva as opposed to a patient with increased right atrial pressure (e.g., heart failure).
In one study including 67 patients undergoing right heart catheterization, an increase in right IJV cross sectional area (CSA) more than 17% during Valsalva effectively ruled out elevated RAP. In the same study, less than 17% increase in R IJV CSA with Valsalva predicted elevated RAP (≥12 mmHg) with 90% sensitivity and 74% specificity. One can also use anteroposterior diameter of IJV in transverse plane, but CSA is expected to be more accurate as the vein is not an exact circle/oval. Regardless, its not a bad thing to get a rough idea. For example, in a study using jugular venous distensibility ratio, that is the ratio between maximum diameter (during Valsalva maneuver) and rest diameter of the vein, patients with a high ratio (>1.6 [= more distensible]) had a low median RAP of 4 mmHg.
Following image demonstrates increase in IJV size in a person with normal RAP. CSA increased by more than 100% (not a perfect along-the-wall trace but conveys the point).
Following images were obtained from patients with heart failure and elevated right atrial pressure. Note that the IJV size barely changes with Valsalva.
We can take advantage of this property of IJV for safe cannulation, when placing a central line or dialysis catheter. For example, some patients (especially those who are volume depleted) may have collapsed IJV and performing valsalva increases its size, making it easier to insert the needle. Below is a nice illustration. In addition, good response of IJV to valsalva may also be used to rule out significant central vein stenosis when performing vein mapping prior to placing an AV fistula.
One problem with IJV POCUS in general is that it is very much susceptible to transducer pressure. If the operator’s hand is not stabilized properly, wrong measurements can be obtained; particularly problematic during follow up exams to see whether the RAP is improving. Below images demonstrate the effect of compression on the vein diameter.
In addition, not all the patients will be able to effectively perform valsalva maneuver. In general, the maneuver is expected to create a certain level of intrapleural pressure. In research settings, it can be estimated by the intra-oral pressure measured through a mouthpiece tubing attached to a manometer. Intra-oral pressure equal to 40 mmHg/54 cm of water is the standard. Moreover, the strain should be maintained for a certain period (typically 15-20 seconds). Obviously in real life, it is difficult to standardize or measure the effort of individual patients.
Also note that Valsalva can be used to aid cannulation of femoral vein similar to that of IJV. In fact, one study in healthy volunteers found that there was a relatively greater increase in femoral vein diameter with Valsalva compared to IJV.
Fun fact: Valsalva maneuver was named after Antonio Maria Valsalva, an Italian anatomist who used it to expel pus from the middle ear in the pre-antibiotic era.