Hello Readers:
PFOs and PFOs
As is true of many things in life, there are PFOs and PFOs. While the incidence in the general population is the same for men [26.8%] and women [27.6%], and the number of PFOs decreases with age [determined by autopsy]. In contrast, the diameter of the opening increases with age, as determined at autopsy.
In the general population, these are associated with “paradoxical stroke.” This describes stoke in the absence of factors such are plaque in the carotid arteries or clots coming from the left side of heart. Most of what we know about PFO and stroke come from studies from outside the diving community.
At NASA, we found that a test subject that had many Doppler bubbles following decompression but did not arterialize these bubbles when he was seated in then upright position. He did arterialize bubbles during a PFO test when he was recumbent. We hypothesized this difference was possibly the result of blood flow difference when recumbent or because of Coanda-effect flow patterns from the legs [bubbles were from the legs] and the eustacian valve.
Reference: Powell, MR, KV Kumar, WT Norfleet, and J Waligora, B Butler. Arterial bubbles with saline contrast via patent foramen ovale but not with hypobaric decompression. Aviation, Space Environ. Med., 66, 273-275, (1995).
Valsalva’s Maneuver
Valsalva’s maneuver, as most divers know, consists of a big inspiration, a breathe hold with force [with the glottis closed for about ten seconds], and a quick release of pressure. One transesophageal echo (TEE) ultrasound study showed that, of those with a PFO, 92% demonstrated a shunt with the maneuver or coughing and 57% had a shunt at rest [no pressure/released needed]. The TEE study did not show an age dependence on size of number.
There are actually many maneuvers that mimic Valsalva’s and can result in arterialization – as I mentioned several postings [days] before. They masquerade as common actions. These can easily be performed by divers and no thought is given. These concern anything that involves short, breath holding and straining. These events have been implicated in transient global amnesia [TGA], a type of paradoxical stroke. In patients with global amnesia in whom Valsalva-like activities immediately preceded the onset of TGA, frequency of PFO was 55%, and 47% of these reported a precipitating activity (e.g., lifting heavy furniture, digging out the roots of a tree, strenuous defecation, filling a concrete mixer, and pumping bicycle tires) immediately before the TGA occurred. Clearly, CNS DCS could occur when divers climb ladders onto the boat with their dive gear, lift tanks and other gear following a dive or otherwise “huff and puff about.” An unknown event to most divers is coughing. That’s right! This is quite hypothetical, but under the wrong circumstances, DCS might result. Normally this does not occur or divers would be dropping like flies.
Reference: Klötzsch C, Sliwka U, Berlit P, Noth J. An increased frequency of patent foramen ovale in patients with transient global amnesia. Analysis of 53 consecutive patients. Arch Neurol. 1996 Jun;53(6):504-8.
Some Recommendations
[1] Be certain to avoid Valsalva-like maneuvers.
[2] Unless the circumstances warrant it, do not have the PFO closed. Closure might be necessary for a commercial diver but not a recreational one. Recreational divers can make many variations in their dive program.
The complications from closure can be serious and are many-fold greater that a reoccurrence of DCS.
Dr Deco :doctor:
