Dynamic alterations in cerebral hemodynamics measured by portable near-infrared spectroscopy in orthostatic hypotension and intolerance, 2023

Abstract
Background
We aimed to evaluate dynamic alterations in cerebral total hemoglobin concentration (HbT) in individuals with orthostatic hypotension (OH) and orthostatic intolerance (OI) symptoms using a portable NIRS system.

Methods
Participants comprised 238 individuals (mean age, 47.9 years) without a history of cardiovascular, neurodegenerative, or cerebrovascular diseases, including those with unexplained OI symptoms and healthy volunteers. Participants were categorized by the presence of OH based on the supine-to-stand blood pressure (BP) drop and OI symptoms using on OH questionnaires: classic OH (OH-BP), OH symptoms alone (OH-Sx), and control groups. Random case-control matching sets were constructed, resulting in 16 OH-BP and 69 OH-Sx-control sets. The time-derivative of HbT change in the prefrontal cortex during the squat-to-stand maneuver was measured using a portable near-infrared spectroscopy system.

Results
There were no differences in demographics, baseline BP, and heart rate among matched sets. The peak-time of maximum slope variation in HbT change, indicating the recovery rate and speed of cerebral blood volume (CBV) change, was significantly longer in OH-Sx and OH-BP groups than in the control group under transition to a standing position after squatting. In the OH-BP subgrouping, the peak-time of maximum slope variation in HbT change was significantly longer only in OH-BP with OI symptoms, but did not differ between OH-BP without OI symptoms and controls.

Conclusions
Our results suggest that OH and OI symptoms are associated with dynamic alterations in cerebral HbT. Regardless of the severity of the postural BP drop, OI symptoms are associated with prolonged CBV recovery.

https://academic.oup.com/ajh/advance-article-abstract/doi/10.1093/ajh/hpad025/7076096?login=false

 

Interesting.

It would be good to have this study done with pwME.

 

Yes, and it could be used as a biomarker to start a diagnostic process.

 

There are a couple of other papers posted under the nirs tag. I think sit-stand demonstration of cerebral tissue oxygenation / Hb would be a good objective marker and expect it would be positive in many patients. (I did this informally on myself in Nov 21).

 

I can feel clearly when the blood drains away from the head during certain movements. And also how good it feels when certain exercises improve blood flow to the brain. Alternating between sitting and standing is a good way to provoke low blood flow to the brain but not the only problematic movement. It also happens when walking stairs, or manipulating things on the floor, standing or sitting too long. And the opposite can happen too: too much blood flowing into the brain during for example the yoga pose called the candle (and less extreme ones too, like merely resting the lower body at too high an elevated position). It's a bit like a partially filled bottle: the liquid has room to move around and will follow gravity, whereas in a filled bottle it does not. The question is, does it have too much room because there is not enough liquid, or does it have too much room because the container fails too constrict properly?

 

I experience decreased CBF after I drink coffee. I have to be very careful when I stand up too fast after lying down.

 

When I stand for a few minutes I start to feel weak, lightheaded, and uncoordinated. It's more difficult to think/brain foggy/headache increases etc.

On another thread I said I walk about 15 to 30 minutes while shopping. That's broken up with rests. And, I have trouble doing the walking even with breaks.

When I lay down my head clears almost immediately. An in office Nasa Lean type test, and a Holter monitor test both proved I have POTS.

 

Hi @SNT Gatchaman

How did you do this test?

Thanks in advance for your answer.

 

Emphasising this was very informal. At the time we were looking at coagulation parameters (eg TEG) and venous oxygen saturations etc. This was earlier on in my "journey of discovery" when I thought microclots might well be front and centre rather than a downstream putative marker of hypercoagulability. Anyhow, my ICU specialist colleague suggested grabbing one of these machines from the stock room (it was outside operating theatre hours and there was a row of them on standby) and attached the sensor to my forehead. Usually you do both left and right sides, we just did right. Basically this was like in-service training for device familiarisation so wasn't a weird thing for us to do. For the simple measurement it's similar to putting a pulse oximeter on your finger or wearing a smart watch. The aspect that makes this device more expensive/clever is that it can sense through the skull into the superficial portion of the frontal lobe. I think you can interrogate liver quite easily as well. It's used in cardiac and liver transplant surgery.

I simply laid supine on the floor and got a resting reading, then slowly stood up. Usual POTSy heart rate elevation, which was worse than now at that point in my illness. The %oxygenated dropped by 10% in under 30 seconds. My colleague said this basically shouldn't move, which I took as given, seeing as they were familiar, but I don't think we double-checked with them as control at the time. Caveat is that the sensor we used wasn't spec'ed for my body size, though I don't have a genetically thicker frontal bone or increased scalp fat, so we didn't fuss too much at the time.

While still definitely present, my POTS is symptomatically better 16 months on, so it would be interesting to repeat.

I view this similar to peripheral venous oxygenation saturations. It's a relatively simple test but not widely available. I think if there were an actual desire to look at things properly, it would be an easy "ah, actually all tests are clearly not normal." This might be specific to LC or simply earlier in disease course. There are point-of-care venous oxygen saturation meters that are around NZD $15K and the NIRS would be $60-80K I'm guessing. They were developed from sports science but lower cost devices in development would be very useful beyond the OR/ICU environment, eg in management of out-of-hospital cardiac arrest.

See Near-Infrared Spectroscopy Assessments of Regional Cerebral Oxygen Saturation for the Prediction of Clinical Outcomes in Patients With Cardiac Arrest: A Review of Clinical Impact, Evolution, and Future Directions (2020)

---
Off topic, but the other device development I'm interested in for us is lactate bio-sensing, which again derives from sports science. The type that could be useful would be a multi-array microneedle similar to continuous capillary glucose monitors, but they're trying to do non-invasive versions via infrared or sweat. The latter would work for athletes but not for us.

See —
Continuous Lactate Monitoring System Based on Percutaneous Microneedle Array (2022)
Lactate Biosensing for Reliable On-Body Sweat Analysis (2021)

 

The whole "I need to sit down if you want to talk to me" is also a big clue in this. It's already difficult for me to pay attention to a single thing, but when I'm standing, I'm only executing steps I planned in advance and I cannot have a conversation or figure anything out standing upright.

I need to sit down if someone wants to talk to me, otherwise all I can do is nod and wave, and maybe retain some of it. I can say a few words that somehow make sense if it's only been a few seconds, but my ability to think drops by the second until I'm sitting down.

One frustrating consequence of this is that I can't be blocked when I walk. If someone blocks my path I have to either sit down or just go around them as if they're not there. I can't just stand still when I'm only executing pre-planned steps. Sometimes I walk just for the stretching, on autopilot, but if I'm walking somewhere or to do something, I can't be interrupted or I have to start over.

The difference between laying down and standing up is just so massive, and the growing symptoms are really similar to altitude sickness. It's such a loss that this area of research is still at a glacial pace, even with plenty of objective data to work with. It could be so transformative.

Brains need blood. Less blood is bad for brains. This isn't hard. I don't understand how any of this is hard, dots don't ever get easier to connect than this. It's even as simple as the blood belonging in the body, not outside, which took a surprisingly long while to figure out for such a smart group of people.

 

@rvallee

Yup, what you described is my most disabling issue. It starts to ameliorate after 6pm. I'm so much less disabled in the evenings. Why is that?

 

I know that state of only being able to listen to another person talking to me and responding with yes or no, and not being capable of properly expressing myself or thinking.

It's just another manifestation of poor blood flow to the brain.

 

Exactly! Even while sitting down conversations can be hard (depends on how I'm feeling, the topic, so many factors). But it's impossible while standing up.

Pre-pandemic, when I went to stores more often, I had the hardest time with those employees who greet you when you come in and/or ask if they can help you find something. I had to get out my folding stool, sit down, and then ask what they said.

They were always quite surprised that I sat down to ask them to repeat what they said. They probably thought I had hearing problems vs. brain problems.

I knew generally what they had said but I just could not make a sentence and respond while standing up.