Respiratory Therapy - Time Constant

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[mattcanfield]

I like to use the time constant to help set T-low on APRV. We use it to see how long it takes the lungs to deflate, and in APRV, we don't want that derecruitment to happen, so making sure we set our T-low appropriately. Hope this makes sense and helps. Great video and content as always! Am looking forward to learning more in the comments as well.

[bibinthomas]

Its to understand the diseases affiliated with it. Low time constant means pneumonia IRDS ARDS pulm edema... And high means asthma bronchitis and emphysema. The knowledge of time constants help with the understanding of these diseases

[jackiekraft]

I am attending CCBC in Baltimore Maryland. I’m in second semester. We were told time constant was the time it takes the lungs to fill to 60% or it’s filling capacity. As far as why we need to know it- idk. Lol

[_OtherAdam_]

Currently in my first semester of RT school. Were currently calculating it with TC = RAW x CL
My instructor and book defines it as the time in seconds necessary to inflate a particular lung region to about 60% of its potential filling capacity

Example: A time constant necessary to deliver 98% of a set volume if RAW is 2.5cmH2O/L/Sec and the CL is 0.1L/cmH2O.

2.5cmH2O/L/Sec X 0.1L/cmH2O = 0.25 = 25%
we know 4TC = 98%
0.25 X 4 = 1 second (This is the answer)

Idk why the definition in my book says "seconds necessary to inflate to about 60%". When this question clearly states that were calculating for 98% volume.
Im having a tough time with this one so correct me if I'm wrong. Also the way you explained it did help me understand it better. Thank you!

[lisaholguin]

I am learning about it currently. egans 12 edition pg 240 but super confused on it

[shaquandarollins]

First yr student here, just had a lecture and was looking for better understanding. So far just as you said Increased Raw or CL requires more time to inflate and vice versa Decreased Raw and CL requires less time to inflate. TC defined as the time lung units require to fill and empty. Calculated as TC = Raw x Cst

[NicholasTXTV]

I’m being taught about time constant and their factors to know how long it’s take to fill up the lung units as well as “fast lung units” and “slow lung units” why? I don’t know some questions were just on the quiz

[cordyjackson]

My class is being taught time constants in relation to Insp time and exp time. This is for mechanical vent and how and why to set I time and E time for patients with obstructive pulmonary disease versus restrictive pulmonary disease

[staceymartinez]

We were taught that if and alveoli is not able to recoil back into place it will have a longer time constant than an alveoli that has a thicker and will not stretch or is less compliance resulting in a shorter time constant.

[daividplummer]

We are learning it as part of our CRAP class. We’re covering ventilation and it comes in to play exactly how your describing it. If you’re ventilating normal compliance then TC= 0.1 seconds. 1TC moves 63% of lung volume and 2TC=86% 3TC=95% 4TC=98% 5TC=100%. Apparently 3TC’s is the most you can hope for in the clinical environment. When your patients have high compliance high airway resistance or low compliance.
This calculated by (compliance=VT/delta P)x(Raw=pip-Pplat/flow). Liters and cmh2o cancel and your left with seconds.
The RRT who commented about the inspiratory hold is how our teacher taught us, this will give you your pressure gradients in the airways and chest wall.
It’s in Egans chapter 11 page 241 of the 11th edition.
But how you describe it is exactly how I understand it’s meant to be used. It’s about understanding a patient with high compliance and high airway resistance needs a longer I:E ratio and a patient with low compliance moves air quickly and achieves smaller volume.
I’m pretty confused by it because it’s hard to fully apply it without having been around a ventilator yet, so some aspects are hard to picture. But the learning of the formulas and learning about the pressure volume curves are very helpful to understand how difficult these patients are working to move air in and out.
Sorry, long response I’m still digesting it for sure. Your post was pretty spot on from what I know about it. Thanks for the honesty and braking it down well for not having used it. I’m in Maine first semester.
Class is awesome so far glad I’ve finally got some education for some of this stuff been following you for a while but a lot of the content was over my head and still is really. Thanks

[stefanoagnolin]

Hi I'm a pediatric intensivist (M.D.) currently working in Italy where there is no respiratory therapist (the figure as intended in th U.S. does not exit unfortunately). I've been studing mechanical ventilation in children and newborn for the last 5 years. I've completed residency in 2023. I've attended a pre-congress course about IMV during EPSNIC 2022 in Barcellona hold by dr. Medina (great physician working in Spain) and He talked a lot about time constant. We calculate TC as Raw x Cst. TC x 5 is necessary to fill 100% of lung capacity.. is it right?

[sarahmartin]

We are learning about time constants in my program (Butte college in Northern California) I would have to say the same thing Stacy commented which is that alveoli that are not able to recoil back into place will have a longer time constant and vice versa. Love your videos by the way

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Respiratory Coach

[brycee]

Being taught in my critical care paramedic class. Not really understanding it or the reasons behind it.

[didib]

In cardiopulmonary renal physiology we have been talking about it as it relates to compliance elasticity and exercise physiology.

[shimashudwan]

It use in anaesthesia to calculate percentage or gas concentration in the circuit

[Uniquemade_]

I just want to say Thank you for your videos. I've been watching your videos for a couple of months. Very informative, I appreciate you for taking time to actually create videos for the future Rts and even current Rts. This means a lot. I finished my boards yesterday and I am officially a RRT, of course with your help. Learning never stops in this field, I will continue to watch your videos and ask any questions that I may have. Thank you, love ya! #Fan

[LolitasCrafts]

We have been taught exactly what and how you explained it. However, I’m on my third semester doing ICU clinicals and have not yet heard an RT mention time constants at all either. But I’ll make sure to ask on my next clinical, now I’m curious too.

[pyt]

with decreased inspiratory time the fraction of the tidal volume delivered to lung units with long time constant will decrease that is all the tidal volume will go to faster lung units
This will have the effect of decreasing dynamic compliance
in addition to airway resistance this factor contributes to the frequency dependence of dynamic compliance that is dynamic compliance becomes lower with increasing respiratory rates

[aimgm]

There is some relation between time constant and atrial kick/ atrial systole of the cardiac cycle.
Narrow valves in mitral stenosis increase the time constant due to increased resistance. I didnt understand that.. that's why l came upon your video.
If anyone knows, pls let me know

[raspberry]

Thank you for the video. I'm in 1st year med school and we learned that TC = resistance x compliance. I'm kind of struggling to understand how someone with low compliance finishes inflating their lungs quicker (aka small time constant) given that the alveoli are stiff, therefore, you need more time to inflate them... thank you in advance!