Finding natural frequency of animals lung I'm currently trying to get my research paper but I still can't wrap my head around how can you measure natural frequency of lungs for example. I've tried searching countless article and journal but it seems that most of the subject are material like concrete etc.
I need help to better understand how to start, The detail about this are I'm currently assigned to measure the natural frequency of animal lungs
I can understand the basic principle like when the object are, let sat concrete or some other solid object But my understanding are currently lacking about biological object.
I need help, thanks
 A: A good starting point could be clarifying what is meant by natural frequency here, which will likely define how to study and analyze this problem. At least three possibilities come to mind:

*

*Breathing rate = The frequency of breathing. This could be studied by recording the lung activity using available sensors. This will give something like electrocardiogram, which is nearly periodic. One can then calculate the number of cycles per unit time, which would give us frequency, or one can use more sophisticated methods based on Fourier analysis.

*Nonlinear oscillations lungs and heart are routinely modeled using nonlinear equations, in which case the problem may be that of determining the parameters of this equations and the frequency of oscillations, including the natural frequency (see more below). There exist vast literature on the subject.

*Natural frequency of an oscillator in physics natural frequency usually means a rather specific meaning - the own frequency of an oscillator, when no energy is pumped into it (why may also mean no damping). If, e.g., we take an equation of a linear oscillator: $$\ddot{x}(t)+\gamma\dot{x}(t)+\omega_0^2x(t)=f\cos(\Omega t)
$$
here $\omega_0$ is called natural frequency, $\Omega$ is the frequency of the driving force, and $\gamma$ is the damping coefficient. The forced oscillations occur at frequency $\Omega$, which is not the natural frequency. If there is no driving force, the oscillatiosn will have frequency $\omega = \sqrt{\omega_0^2-\gamma^2/4}$ rather than frequency $\omega_0$. Moreover, if $\gamma/2>\omega_0$, we will not have oscillations at all.

The non-linear models mentioned above are empirical, however one cannot be sure that lungs or hear would perform periodic motion, if their muscles do not contract. The oscillations due to the contraction of muscles are however seem more like forced oscillations - they certainly would not exist without constantly pumping the energy into the system. Thus, I am not sure that lungs can be called an oscillator and be assigned a natural frequency in physical sense. At best they are viewed as an overdamped oscillator, with undefined natural frequency. As an analogy one could consider a bicycle air-pump - it certainly performs oscillations when the air is being pumped, but it would not oscillate, unless somebody keeps moving it. If it is pushed and left to itself, it will stop pumping before completing even one cycle - i.e., no oscillations.
A: As you breathe, your lungs fill and empty, fill and empty. This is periodic (Up to a point. E.G. Assume a resting animal.) and has a frequency. Breaths/minute might be determined by how much oxygen is needed and lung capacity. The animal might breathe, wait a bit, and breathe again.
I am guessing, but the natural frequency might be the frequency if the animal just drew breath after breath with no pauses.
Suppose you take a breath and relax. It takes time for the air to whoosh out. In part, this might be determined by the diameter of your throat and mouth. In part you use muscles to expand your lungs. When you relax, it takes time for the muscles to allow the chest to contract. Or perhaps it just takes time for body parts that were lifted to fall back.
You probably can figure out similar reasons for the length of time it takes to draw a breath.
