Research Review: The Respiratory System

During these increasingly uncertain times, some of us including a few fellow Redditors have been wondering how vibration affects our respiratory system.

PLEASE NOTE: Although promising, the research discussed in this article is not currently recommended by medical professionals for Covid-19 specific symptoms. If you are feeling ill or are experiencing respiratory issues, please consult with a medical professional on your best course of action.

There are many studies examining the effects of vibration on our respiratory system with a particular focus on cystic fibrosis and chronic obstructive pulmonary disease. Various metrics including peak expiratory flow rate and the rheology (state of flow) of bronchial mucus were used in understanding the effects of the treatment on the natural cleaning process of the lungs. One of the current largest fears about Covid-19 is that in the worst case scenario it can cause pneumonia or “an outpouring of inflammatory material [fluid and inflammatory cells] into the lungs.” (Graham Readfearn, 2020).

So let’s delve more specifically into what modifying the rheology (flow of matter) of a fluid actually means. Mucus is used in the lungs as a layer of defence from foreign particles. It is also a 'thixotropic' non-Newtonian fluid “whose mechanical properties are altered in accordance with the intensity and frequency of the force applied to it” (Alcântara et al., 2014). Have you ever seen videos of people putting non-Newtonian fluid on a subwoofer? These fluids are typically 'shear-thickening' vs. 'thixotropic', so think of the fluid in our lungs as the OPPOSITE of that; with thixotropic fluid the higher the intensity over time, the thinner the liquid becomes (Science Learning Hub, 2010). It is hypothesized that due to this thinning property of mucus, our lungs have an easier time expelling it: “we believe the acoustic vibrations.. and the lower frequency higher amplitude flexing.. help to prevent “sticking” of the gel layer to the top of the cilia, allowing them to beat freely” (Cantin et al., 2006).

The speculation into what frequencies work best details a broad range of anywhere between 3hz to 90hz. This primarily has to do with resonant frequencies. A resonant frequency like the natural frequency of our lungs will be the most efficient at absorbing mechanical force and as a result should be the most effective at reaching/affecting the fluid inside. Some of you may also know of resonance through videos of people breaking wine glasses with their voice but fear not! The amount of sound required to cause damage to tissue lies somewhere between 180-190db which would take an incredible amount of energy to produce (Cudahy, 2002).

So why isn't there just one prescribed optimal frequency? It’s important to note that the natural resonance of an object changes based on factors like tension and mass which ultimately determine its wavelength. For example the larger one’s lungs, the lower the resonant frequency. There’s also another type of resonance known as the Helmholtz air resonance of a cavity demonstrated by when we blow air into the neck of a bottle and hear a clear note in return. Both types are efficient means of a system absorbing the energy you put in, just like pushing a swing at its optimal point (at the end of the back-swing/front-swing). So in the current literature we have multiple different devices targeting different frequencies to achieve the same goal. But what do we know specifically about vibroacoustic therapy’s effects on the lungs?

According to Cantin et al., low frequency sound stimulation via a transducer can be “as safe and as effective as conventional chest physiotherapy in inducing airway clearance in patients with Cystic Fibrosis”. So will bass help treat the specific symptoms of Covid-19? While we can’t say for sure as we still need a dedicated study on the topic, we can say that based on the current research we certainly think it's possible!

We hope everyone is staying healthy, respecting their local guidelines for social distancing, and know that together we’ll get through this!

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