{"id":1308,"date":"2019-01-05T18:12:28","date_gmt":"2019-01-05T17:12:28","guid":{"rendered":"http:\/\/www.josephcaruana.co.uk\/diving\/?p=1308"},"modified":"2019-01-10T12:17:48","modified_gmt":"2019-01-10T11:17:48","slug":"a-comparison-of-ce-test-data-for-two-closed-circuit-rebreathers","status":"publish","type":"post","link":"https:\/\/www.josephcaruana.co.uk\/diving\/2019\/01\/05\/a-comparison-of-ce-test-data-for-two-closed-circuit-rebreathers\/","title":{"rendered":"A Comparison of CE Test Data for two Closed Circuit Rebreathers"},"content":{"rendered":"

This post provides a comparison of some available CE-testing data on the breathing characteristics of two rebreathers currently on the market: the JJ-CCR and X-CCR. \u00a0The comparison was carried out mostly for my own interest, but I decided to post it here in case it might be of interest to others as well. \u00a0(The code was written in Python 3.5.2 and all plots produced with matplotlib.)<\/p>\n

Firstly, a few words of note.<\/p>\n

The configuration of the two rebreathers is different. \u00a0To mention but two examples: the JJ uses an axial canister whereas the X-CCR uses a radial one, and the JJ is fitted with a DSV whereas the X-CCR uses a BOV. \u00a0The available CE test data are for the units set up as per the above respective configurations.<\/p>\n

The CE testing documentation for the JJ states that tests were carried out at a pitch angle of 74o<\/sup>\u00a0(with the exception of the testing of\u00a0hydrostatic imbalance vs. pitch angle, of course, because in that case the pitch angle needs<\/em> to be varied since that is precisely what is being tested. \u00a0Tests of the X-CCR were presented at pitch angles of 0o<\/sup> (i.e. “in trim”) and 90o<\/sup> (i.e. vertically upright). \u00a0The reader should note that in some cases, a perfect, direct comparison of the two units is not possible due to the different pitch angles at which data were collected for each respective unit. \u00a0This should be borne in mind throughout.<\/p>\n

Tests at 100m using trimix were carried out using a similar (but slightly different) mix for each unit. \u00a0In the case of the JJ it was 11\/65 whereas for the X-CCR a (slightly less dense) mix of 10\/70 was used.<\/p>\n

In each of the below figures, I have included the EN14143 threshold in red. \u00a0You do not want to approach or (worse) exceed the threshold. \u00a0Exceeding the established threshold compromises the ability to obtain CE certification. \u00a0The further away the data lie from this threshold, the better.<\/p>\n

WORK OF BREATHING<\/strong><\/span><\/p>\n

As the name implies, work of breathing denotes the amount of work required to breathe. \u00a0When we draw in a breath, our muscles cause our lungs to expand, and if this process encounters any resistance, the work required to expand the lungs will be higher.<\/p>\n

Work of breathing (WOB) is described via the simple equation: WOB=0.5+0.03\u00d7RMV, where RMV stands for Respiratory Minute Volume. \u00a0The latter simply means the volume of gas inhaled (or exhaled) per minute. \u00a0The higher the RMV, the higher the WOB.<\/p>\n

Basing on the available data, both at 40m (using air) and 100m (using trimix), the WOB for the JJ and the X-CCR is virtually identical, with the JJ\u2019s figures (at 74o<\/sup>) running approximately between the X-CCR\u2019s 0o<\/sup> and 90o<\/sup> tests.\u00a0<\/span><\/p>\n

If<\/i> the performance between the two units were identical, this would kind of be expected, since 74o<\/sup> sits between the other two angles (0o<\/sup> and 90o<\/sup>).\u00a0 <\/span>However, it is very important to note that one cannot comment further basing on this plot; a perfect comparison cannot be drawn from this plot since the pitch angles at which the tests for the two respective units were carried out are different<\/strong>. \u00a0A more direct comparison can be made when considering the next test: hydrostatic imbalance.<\/strong><\/span><\/p>\n

\"\"<\/p>\n

 <\/p>\n

\"\"<\/p>\n


\nHYDROSTATIC IMBALANCE<\/strong><\/span><\/p>\n

The counterlungs (CLs) are rarely located at the exact same depth as the diver’s lungs; this means that there will be a difference between the ambient pressure acting upon the CLs and that acting upon the diver’s lungs. \u00a0This results in the diver breathing at lower or higher volumes, which\u00a0they will attempt to resist via muscle tensioning.<\/p>\n

For example, in the case of a back-mounted configuration, the CLs lie atop the diver’s back, which means that when the diver is swimming in trim, the ambient pressure on the CLs will be lower than that acting upon the diver’s lungs, simply because the CLs are located higher up in the water column (i.e. they are positioned at a shallower depth). \u00a0As a result, drawing in a breath will encounter some resistance (negative imbalance) such that breathing is performed at lower volume and inhalation feels difficult.<\/p>\n

On the other hand, for a chest-mounted configuration, the CLs lie at greater depth, so the pressure on them is higher than on the diver’s lungs. \u00a0In this case, the inverse occurs: drawing in a breath will feel easier (as it is easier for gas to move from higher pressure to lower pressure) and breathing is performed at higher volume, but exhalation feels more difficult (as this time round the diver is pushing gas out against a pressure gradient).<\/p>\n

The hydrostatic imbalance test measures this difference in pressure, and the test is typically carried out with respect to the suprasternal notch. The CE test involves two test cases:<\/p>\n

(1) Maintaining the same roll angle but varying the pitch angle.
\n(2) Maintaining the same pitch angle but varying the roll angle.<\/p>\n