{"id":2805,"date":"2024-03-06T23:08:36","date_gmt":"2024-03-06T12:08:36","guid":{"rendered":"https:\/\/pro.blister-prevention.com\/?p=2805"},"modified":"2024-03-06T23:18:34","modified_gmt":"2024-03-06T12:18:34","slug":"hashmi-heel-blister-study","status":"publish","type":"post","link":"https:\/\/pro.blister-prevention.com\/office-hours\/hashmi-heel-blister-study\/","title":{"rendered":"Discussion of Hashmi (2013) Experimental Heel Blister Study"},"content":{"rendered":"\n

Thank you for joining me on this episode of Blister Prevention Office Hours. We’re going to be looking at the Hashmi et al (2013)<\/a> study today, all about posterior heel blisters. I had intended to look at this in greater detail last month, but it just morphed into its own presentation. So now we’re going to be talking about this paper. If you didn’t catch last month\u2019s episode<\/a>, I highly recommend you take a look because it was a really good discussion about posterior heel blisters and all the relevant factors. We had a good look at the relative motion scenarios at heel lift and heel strike; had a quick look at research; and we delved into quite some depth on how the prevention’s work. So if you are here to look at what works as a blister prevention for the posterior heel, then definitely head back to last month’s episode and watch that.<\/p>\n\n\n\n

What we\u2019ll cover<\/h2>\n\n\n\n

So yeah, we’re going to look at the Hashmi research. We\u2019ll look at the aims, the methods and all of the findings and implications. This paper is titled: The formation of friction blisters on the foot: the development of a laboratory-based blister creation model, and it was in Skin Research and Technology<\/a>. It was by Farina Hashmi, Barry Richards, Saeed Forghany and Chris Nester. What they did was they produced blisters on the posterior heel with this jig; I’m going to explain this in more detail in a moment.<\/p>\n\n\n\n

Aims<\/h2>\n\n\n\n

So the aims were twofold. What they wanted to do was have a look at how digital infrared thermographic imaging correlated with the contact method of temperature measurement, which was just a normal thermometer basically where it’s actually touching the skin to get the measurement. And also to describe the temperature changes before, during and after blister formation.<\/p>\n\n\n\n

This is what a digital infrared thermographic imaging camera looks like. I got this picture off eBay – you can buy this for $200AUD. This isn\u2019t the exact model they used but it would have been this kind of camera which produces this kind of image. And this is an example of the images that they were able to produce, before, during and after blister formation indicating temperatures and temperature change.<\/p>\n\n\n\n

\"digital
Digital infrared thermographic imaging camera<\/figcaption><\/figure>\n\n\n\n

Methods<\/h2>\n\n\n\n

There were 30 subjects and they had this load application mechanism (LAM) set up which looks fantastic. It’s a spring operated rotating load applicator with a curved surface covered with textured rubber providing a high frictional interface with the skin. So basically as that applicator moved up and down, because of the high friction level, it would grab the skin so the skin moved with it, thereby creating the shear deformation in the soft tissues between skin surface and bone. And temperature readings were taken before, during and after blister creation.<\/p>\n\n\n\n

How much did this load applicator move? It moved 15mm (1.5cm). It seems like a lot. But the reason they used that amount was they found in an unpublished pilot study that that’s how much the foot moves relative to the shoe at heel strike. Being unpublished, we couldn’t take a bit of a look at it in more detail, but I think this needs verification. I’m not doubting that it’s true. But I have a feeling that most podiatrists wouldn’t be comfortable with the fact that the heel moves relative to the shoe 1.5cm with each step. Presumably there’s a bit of heel fat pad compression that’s responsible for that. But how much is the foot moving up relative to the shoe at heel lift? Because presumably what goes up must come down. So that would be a tidy little experiment for someone who’s got some slow motion high speed video to actually replicate and publish.<\/p>\n\n\n\n

The loading cycle:<\/strong> So the load applicator was operated at a rate of 120 passes per minute. So it went up and down for two minutes and that speed was chosen to replicate fast walking. And so the load was applied for two minutes and then there was a one minute break so they could take the temperature recordings, and also to inspect the skin to see whether a blister had formed, because that was the endpoint of the load application.<\/p>\n\n\n\n

Temperatures were recorded every three minutes during the load\/rest cycles until blister formation. And every three minutes for the 30 minutes post blister formation. The subjects remained standing and had those measurements taken every three minutes. And then for the next five hours, the temperature was measured every hour, and the participants were allowed to leave the room at this stage. They just weren\u2019t able to wear shoes on any of these areas of their foot.<\/p>\n\n\n\n

Endpoint:<\/strong> As I mentioned, the endpoint of the loading was the initiation of the blister injury and that was determined by skin inspection. They were looking for a blanched area of skin within an erythematous inflamed area of skin, and a visible pleat of epidermis lifted from the underlying dermis. So that’s what it looks like when a blister first forms and hasn’t yet had a chance to fill with fluid.<\/p>\n\n\n\n

Findings and implications<\/h2>\n\n\n\n

So let’s get to the meat of this discussion. We’re going to talk about the researchers findings and the implications of this research.<\/p>\n\n\n\n

Clinical signs:<\/strong> First of all, there was a consistent pattern of clinical signs that was redness initially. They termed this a hot spot. It\u2019s probably not that important, but is a hotspot a clinical sign or is it a subjective symptom? I think a lot of people (our patients) use the term hotspot as a symptom rather than something that they see. But as I said, it\u2019s not important to this discussion. So these clinical signs were initial redness, blanching of the skin in response to load, and the appearance of a small pleat of epidermis that subsequently filled with fluid. It takes up to two hours to fill with fluid, but is usually filled in around an hour; iIt’s not full of fluid straight away.<\/p>\n\n\n\n

Symptoms:<\/strong> A consistent pattern of symptoms were described. That is, an initial rubbing sensation, followed by a stinging sensation, which then subsided until a sharp pain felt, heralding the initiation of a blister. This is in line with other descriptions surrounding blister formation.<\/p>\n\n\n\n

Time to blister: <\/strong>Time to blister varied greatly in this study. It was between four and 32 minutes. The authors speculated this variation could be due to surface hydration. Definitely, different people will sweat at different rates over that time. But it could just be the intrinsic resilience to shear strain over that time. Everyone’s skin and subcutaneous tissue can deal with repetitive shear load a bit better or less so than others. And if we look at the other experimental blister research papers, we can see that there is this vast range of time to blister. Sulzberger et al<\/a>, who produced blisters on the palms, found it took from three minutes to over 50 minutes of loading. Some people still hadn’t blistered after 50 minutes. And Naylor<\/a>, who produced blisters on the anterior shins back in 1955 found it took between 27 and 138 load applications for blistering to occur. So there’s a big difference between subjects.<\/p>\n\n\n\n

Temperature recordings:<\/strong> Remembering that the researchers were looking to see if there is a correlation between the contact and the non-contact forms of temperature measurement; they found that there was good correlation. The degrees Celsius wasn’t exactly the same but the changes all correlated very well. So the good thing about this is it supports the use of a non-contact way of measuring temperature which obviously has advantages because when you apply a thermometer to the skin that could cause a change in skin temperature. Plus there’s the need for contact, so there is time involved. So yeah, the non-contact method has many advantages.<\/p>\n\n\n\n

Temperature change: <\/strong>Temperatures increased from baseline to blister formation. Then, once the blister formed and the load was no longer applied, temperature reduced. Looking at that in a bit more detail.
Baseline to blister formation:<\/p>\n\n\n\n