Methods: On averaging continuous raw data

We now have the luxury (compared to the good old days) of continuously monitoring data during a study protocol. For example, one can acquire continuous beat-to-beat measurements of middle cerebral blood flow velocity (MCA V) during 5, 30, 180 minutes or even more.

When you start a new study, you may want to analyze your raw data:

1) using the same method described in that interesting paper you just read or,

2) as it has always been done in your lab.

So, at the end of data collection, you sit in front of your raw data which now need to be averaged. What’s your game plan ?

If you compare two 10-minute conditions (baseline and drug infusion; under steady-state for the last 5 min), you get your data averaged over the last 5 seconds of steady-state? 15 seconds ? 60 seconds? 180 seconds ? Why? Also, is it protocol-depend? Why?


Methods: Monitoring cerebral blood flow velocity with transcranial Doppler: hand-held vs. frame-held probe

When I was introduced to cerebrovascular physiology a couple years ago, the first piece of equipment I’ve worked with was transcranial Doppler. After having learned the technique to search flow velocity in the middle cerebral artery, the following was pretty clear to me: 1) a good quality Doppler signal was critical for subsequent interpretation and, 2) you first use a hand-held probe to search for the artery of interest and then switch to a frame-held probe (see figure below) to monitor, usually for a continuous period of time (for example, continuous infusion of vasopressors or endurance exercise), blood flow velocity.


That frame-held probe is appealing since, among other things, you need to keep the same angle of insonation throughout the study protocol in order to have reliable blood flow velocity data (because there is no way to know that angle of insonation with transcranial Doppler) especially in situations where the head is moving during data acquisition.

So, in the beginning of my training, the utilization of a frame-held probe was the way to go in cerebrovascular research since I had only worked with healthy volunteers/patients without head injuries…but what about these individuals for whom these head frames are most likely not tolerated ? Could we use hand-held probes and still be confident in our data acquisition ? What about stability and reliability of hand-held probes?

The main objective of an interesting study recently published by Saeed et al. was to compare cerebral blood flow velocity and cerebral autoregulation using a hand-held vs. frame-held probe.

Cerebral blood flow velocity (in the middle cerebral artery) was thus monitored with a frame-held probe or held in position by one investigator for 5 minutes (for each method) in 11 heatlhy volunteer. Hemodynamics was also monitored and cerebral autoregulation calculated for each period. These measurements were repeating in a subsequent visit. A total of 3 frame-held and 2 hand-held measurements were performed on both left and right sides at each visit.

The main findings of this study were:

1) no significant differences in cerebral blood flow velocity and cerebral autoregulation between the methods;
2) no significant difference between repeated measures on separate days for both cerebral blood flow velocity and cerebral autoregulation.
As highlighted by the authors:

(…) this is the first study to report that HH measurements of CBFv and ARI estimates are not statistically different from FH, which has important implications for bedside estimates of CBFv and ARI, particularly in traumatic brain injury (TBI) patients and neonates, where CBFv and ARI measurements form an important part of clinical assessment.

(HH: Hand-held; CBFv: cerebral blood flow velocity; ARI: cerebral autoregulation; FH: frame-held)

These results are very interesting and promising if one wants to investigate cerebral blood flow velocity with transcranial Doppler in patients who cannot tolerate a head frame. However, we have to note that a short period of recording was investigated in this study. It will be important to replicate this protocol with longer recording periods.


Saeed NP, Panerai RB, Robinson TG. Are hand-held TCD measurements acceptable for estimates of CBFv? Ultrasound Med Biol 2012 38(10):1839-44

Going for the jugular !

No, I didn’t start ultimate fighting…

No, I didn’t receive a bad review for my last submitted paper…

No, I’m not preparing myself for a science debate…

No, I haven’t been scooped by another research group…

No, I’m not writing a letter to the editor…

I’m working on a research protocol! I would really need to get access to the internal jugular vein of my subjects. During my postdoc, I worked in a lab interested in cerebral metabolism and perfusion in humans and the internal jugular vein was catheterized everyday! I have thus been involved in a couple of those studies during my stay over there and published interesting results. I’m now working in Quebec city and I’m aware of only one lab in Canada that puts lines in the jugular vein.

I would be mostly interested in jugular venous oxygen saturation. Since I’m working presently on the impact of vasopressors on cerebral perfusion and oxygenation, I consider that measure very important since technology such as near-infrared spectroscopy (used to non-invasively study frontal lobe oxygenation) has its limitations…

I hope to be able to convince the Ethics committee…

Then, I hope to be able to convince the subjects!

Any volunteers??