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No worries! The frequency-dependant blockade is attributed to the fact that local anaesthetics only block the sodium channels when they are in their 'open' configuration. So nerves which fire more rapidly will have a greater degree of open sodium channels and therefore be blocked to a greater extent. See this great summary from LITFL: www.bjaed.org/article/S2058-5349(19)30152-0/fulltext

Thank you. It is clear to some extent. We can explain the anti arrhythmic property of lignocaine with this concept.i e during tachyarrhythmia nerve fibers fire more rapidly which will keep more sodium channels in opened state, allowing more lignocaine to bind and block the nerve. And in case of chronic pain there will be continuous firing of concerned nerve, such nerve get blocked more intensively. But... How can we apply this concept to spinal anaesthesia and nerve blocks where there is no rapid firing of nerves as there is no surgical stimulus? Still we are getting block. How? If there is no firing of nerve fibre,I.e when sodium channels are in resting phase, can't we block nerve fibre? Am I missing any primary concept? I am eagerly waiting for your reply... Thank you.

As Fowler’s method is measuring the Nitrogen washout, by definition, a VC breathe is necessary not just inspiratory capacity.

@@lien3212 what I mean is, when person exhales tidal volume, at that point,his expiratory reserve volume would still remain there in the lungs.And Vital capacity by definition includes inspiratory capacity and expiratory reserve volume. So person needs to inhale inspiratory capacity which will become his vital capacity by mixing with the expiratory reserve volume which is already there.

@@rajeevkaparthi190 ahh, i think you misunderstood. Fowlers measures nitrogen washout AND closing volume. Inspiratory capacity breath cannot be used to measure CV as lung is at FRC at the end of expiration.

Thank you.vital capacity means,there should be nothing in the lungs except residual volume.In the video at 2.00 min it was said, patient is asked to breathe in to his vital capacity at the end of normal tidal volume, at FRC. How can you breathe vital capacity if the FRC is already left in the lungs. Either you should ask him to breathe out till the residual volume or you ask him to take full inspiratory capacity. But how can you say that it is vital capacity when the lung is already filled partially with FRC., I need clarification as nowhere I could find the answer. I am sorry if I am troubling you. Thank you .

@@rajeevkaparthi190 From my understanding, at the end of tidal breathing, one has ERV + RV left in lungs (i.e. FRC). A VC breath from that point means max inhalation (to IRV) followed by max exhalation to RV (remember you can never breathe out RV due to small airways collapse hence CV). Fowlers method starts at the end of normal tidal breathing when one takes a VC breath of 100% oxygen- this ensures any N2 measurement from the exhaled breath is what was in the lungs. Does this make sense?

Great to hear!

Nitrogen is present throughout lungs during the respiratory cycle (assuming the patient is breathing air). At the start of the test, a single breath of 100% oxygen is taken. When the patient starts to exhale, it will be gas from the anatomical dead space which leaves first. This hasn't mixed with any of the existing gas within the lungs (by definition) and so contains no nitrogen. As exhalation continues, we begin to see a contribution from the non-dead space volume. This contains nitrogen from breathing air BEFORE the single breath of 100% oxygen was taken. Hope that helps

Thanks for letting me know. Volume issue resolved in the link above

All feedback welcome. Feel free to dig into the weeds of this topic: www.sajaa.co.za/index.php/sajaa/article/download/2528/2824

Glad it was helpful. Here is an excellent paper from Cruickshank describing principles behind the derivation: watermark.silverchair.com/mkh008.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAA00wggNJBgkqhkiG9w0BBwagggM6MIIDNgIBADCCAy8GCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMZZBgGfeKmar8i9pRAgEQgIIDACcOfX6UtI25NCaqnQvS9vt0cIHB47suZO9jF7tUpnP12KmN-SG8_IgkuV9GwC82UmVhx0XQCYUh6FcW5khheI3sy_SXkyeIOyOIDdLeFfoOMvqyNmCQUVR69ZFJ5TXlXM3auXO52kK9zhXJdPJsdmQZSSqNWimyPk1GwwW47MH9fCHy7WegMrZqtHtB9clW5ldItRIgHh-hFlJxAoUqQuFplGXsPcmoJJPDX6SpWKd_aHayWxrZD4LjBmnUlPotZYIxCRgtnGk5u-gHwIs21WN-Hobpi2ds670Ad8TO9gLWx30g7OhDu9kgnxk9JsFY0um9EWCaQ6UoT7KASXxFyP1V5M0lriOjtjDn7t4HnILxlxJQsUhqXbkowxWpwjj4T6902weFtoe_KB5WH0c-RdPQh42N5aPZ6-4Q_ILVVblsqn6Cev9qPyJ_JgnUh7weKet6jfNb0DHQC48y29kffh5kvbRu9Ijd-tqJsWsruus04b4gIDANSnKWyHlCWW1i4L0yObIx60qPICyc1jWHKg5oafzdPS3vaxaDTC9XDw34WiH3OojN3K5jAQgRfs2tzCp8kLofTVvSON7zrbbpZZ1jdK3IOmYITa8ojf53LnUMZJeRH8LVRU8Fca1kMELwKqQI6DJKw3LwC3GOeYgD-aeya4ejiZWYQwZT8y1fqj0N3PJWvDE3pbmBQJxXnjgWKJp8aIfK2ycMyUctwZOTa0-T3dgSYPZLFh80aAP1wpCooSPDisute0PvsJcmTrtNnO9c0Acq85U0pMoZmJIJvQSWkr6I_vByBWGike_2oYWSIyOdInUEPr2l_5hRlngD7rpN5keEA4BLfQL_gjJbFuSkp7C-1hYnT2Y8XzMZ3sH3AVAKyOdE78KV1vjMeYRjYRP6AxOIkmtQCdnbsDt5jAh80-SyYUbmNHBvU0zlOx0Tn1_ATgL5sVcIUzYpMWqTIx0VV7PGOxAqcCpzpOhWOfVGffqESgRWU5oi18Dr_jAm7mmzk8sHDlzuyu3eqWRtHQ

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Thanks for your comments. Spread the word!

Thanks!

Glad you found it useful!

This is a wonderful book by Chambers which formed the basis of my revision for the FRCA. www.cambridgebookshop.co.uk/products/basic-physiology-for-anaesthetists?variant=42184468857071&currency=GBP&gad_source=1

Danke schön! Glad you found it helpful. West's book is an absolute masterpiece - definitely worth investing the time to go through it.

Thanks for the feedback - glad you found it useful!

Thanks for your comment and glad you found it useful! It's a very similar argument for the shunt equation in terms of conservation of mass.

Glad it was helpful!

Glad it was helpful!

Coming soon!

You're welcome. The terms In(1/2) and -In2 are equivalent. It's because of the quotient rule: ln(a/b) = In(a) - In(b) In this case, a is 1 and b is 2 So In(1/2) = In1 - In2 Since In1 = 0, you're just left with -In2. Hope that helps.