“…and a great big soul that’s driving.” (Mary Chapin Carpenter.)
An infrared laser can delicately pace the beating of a quail embryo’s heart, the first time the technique has been shown to work with an intact heart and without causing damage.
Full story over at Physics World. (edit to add: also picked up by Medicalphysicsweb.)
UPDATE: Nicholas Smith at Osaka University, whose team first demonstrated in 2008 how ultrashort laser pulses could induce contractions in cardiac muscle cells and so took a big step towards possible optical pacemaking, kindly sent me some thoughts on this topic.
He confirms that, although much is understood about the fine details of cardiac activity, there is still plenty of uncertainty left. The US team in the new study think that thermal effects generated by the laser could be the key to why it initiates a heartbeat, but other factors could be in the mix too.
“It’s well known that the equations describing membrane equilibrium are temperature dependent, and if all ion channels across the whole heart (such as sodium channels, but potentially others) suddenly undergo a transient change in permeability, then that could kick the heart into beating at the periodicity of the laser irradiation,” Smith says. But equally, “the new work uses a wavelength of 1.875 microns, which can be absorbed with reasonably high efficiency. So perhaps it’s the wavelength which is most significant, allowing low-power irradiation to have efficient interaction with the sample.”
Assuming that you start with the right wavelength, and around 2 microns seems to work, then it could be just a matter of supplying the right amount of total intensity at the right time, gated so as to generate a pacemaker signal. This perhaps need not be from a laser at all. As Smith notes, laser diodes are already fairly compact, but if you could generate sufficient power from an LED at 1.875 microns, you might be able to produce an implanted pacemaker using an LED instead.
The topic is formidably complex, though.
“One of the main barriers to knowing what’s going on is that you are looking at a fairly indirect connection between laser light and effect,” says Smith. “In our research, we observed (and expected) that laser light would cause muscle cell contraction, but the interaction is a multi-step process: light irradiation, followed by 2-photon absorption, then generation of excited and reactive species along with heat, leading to various changes in cell structure and permeability, affecting the calcium levels in the cell – and then contraction.
“In the new work by Jenkins et al it’s probably slightly simpler, due to the single-photon absorption, but there are many stages involved and some of them are nearly impossible to monitor properly. This is the main barrier to understanding what happens. We made good headway into following how the light affects the cell, but the complexity in the interaction chain means it’s hard to isolate and identify each step.”