am a 22 year old with asthma and a pacemaker. When I exert myself my oxygen goes to 80 and my hear rate to 160's or more. What can cause low oxygen with excertion? I am currenly seeing some specialiast at a university hospital. but they havent got to the bottom of it or not.
they have ruled out a shunt.
2007-02-08 14:40:03 · 1 answers · asked by owned by a siberian husky 4 in Health ➔ Diseases & Conditions ➔ Respiratory Diseases
If at 22, you have an implanted pacer, you have a COMPLEX medical problem, and trying to characterize it for us with a short paragraph question is obviously extremely insufficient information!
Nevertheless, if you're saturating 80% on exertion and your doc's have "ruled out a shunt", the answer is...
YOU STILL HAVE A SHUNT!
The concept of a shunt, in this setting, is that somehow unoxygenated blood is bypassing the lung tissue and arriving back into the left heart to mix with the oxygenated blood, where it is then pumped to the body in a mixed form. If by echocardiography, they have ruled out an INTRACARDIAC shunt, they have only proven that this ONE TYPE of shunt isn't occurring. A "right to left shunt" in the heart would be what they could best rule out by echo.
Intrapulmonary shunting is a much more difficult assessment. Sometimes the answer is that there are regions of the lung that are being poorly oxygenated, either because they are blocked off, or because the patient is too weak to expand them fully with each breath. Fortunately for us, most lungs are smart. They self regulate their blood flow so that regions which are not participating in oxygen exchange are shut down and blood doesn't tend to flow into them. If blood DOES flow into these regions then it can flow all the way past the lung and still be saturated only as much as the venous side. If this blood rejoins the rest of the blood coming back from oxygen-exchanging regions in the lung, the result is a mixed saturation level averaging out somwhere between the high point of the best saturated blood and the low point of the blood flowing through the unoxygenated lung tissue. This is a form of "intrapulmonary shunt".
There is a study called a "V/Q scan" to evaluate for exactly this. It involves inhaling and exhaling radio-labeled gas in front of a gamma camera (radiation detector) and then also undergoing an x-ray study of the pulmonary blood vessels. If there are regions of the lung that are not participating in gas exchange, then the blood vessels to those areas should be shut down. If they're not, you've got the diagnosis.
Sometimes the intrapulmonary shunt isn't subtle at all. I saw a man recently who had a massive intrapulmonary vascular malformation. Basically, he has a huge nest of abnormal blood vessels in his lung which allow flow of unoxygenated blood past his lungs! We caught that finding by accident on a CT scan when we were trying to figure out why he wasn't getting better.
Seek, and you shall find!
I hope that helps. Good luck!
If you figure it out, let me know... I'm curious!!
2007-02-08 15:03:10 · answer #1 · answered by bellydoc 4 · 3⤊ 0⤋