Going to the movies can make all the difference.

The upper airway is a complex structure (see Fig. 1). It is a conduit to life, facilitating the basic requirements of breathing and swallowing, as well as higher functions such as speech. Understanding the factors which control the muscles of the upper airway is therefore of major importance, especially so since collapse of the upper airway during sleep is relatively common. Obstructive sleep apnoea (OSA) is the third most common respiratory disorder, after asthma and chronic obstructive airway disease. Moreover the long-term consequences of severe OSA syndrome are considerable. Daytime sleepiness impairs social function and increases accident risk. The cardiovascular risks are also increased with a 10-years predicted occurrence of stroke of 14%, and 23% for myocardial infarction (Kiely & McNicholas, 2000). Figure 1 T1-weighted, magnetic resonance image in a healthy subject Thirty years ago Remmers et al. published their seminal paper on the ‘pathogenesis of upper airway occlusion during sleep’ (Remmers et al. 1978). The study examined the relationship between the genioglossal electomyogram (EMG) and pharyngeal pressure, and concluded that airway occlusion occurred when the negative pharyngeal pressure exceeded the genioglossus force; the so called ‘balance of forces’. This theory led to a multitude of studies measuring upper airway muscle activation, specifically the muscles of the soft palate and the genioglossus EMG, with the assumption that these are the key muscles for controlling upper airway patency, and that EMG activation is related to muscle stiffening. In this issue of The Journal of Physiology (Cheng et al. 2008) point out that, ‘EMG does not necessarily translate into muscle motion, and the exact mechanism by which the airway is kept patent by the genioglossus is unknown’. Accordingly the EMG may not be the best methodology to capture the functional significance of genioglossal activation, not least because it is a complex structure with multiple fibre directions; indeed few studies have attempted to map the activity of the whole muscle (Eastwood et al. 2003). Cheng et al. (2008) report a technique that provides a method of quantifying the activity of the entire genioglossus muscle. The methodology also allows visualization within the muscle, while providing a high temporal resolution to capture within-breath movements. The technique also advances other imaging modalities, such as endoscopic imaging, which provide information on changes in the size of the airway lumen rather than the surrounding tissues. Cheng et al. have employed fast spoiled gradient echo imaging techniques to reveal how MRI tagging is deformed with tissue motion. Application of this technique to the measurement of genioglossus activity in humans required the ability to monitor breathing with MRI compatible techniques, the development of non-cardiac gated tagging techniques, and the capacity to obtain multiple within breath scans per subject, while analysis of the images involved adaptation of harmonic phase methodology. By combining all these elements the authors have produced a series of great movies illustrating the complexity of the genioglossus activity throughout the respiratory cycle. Watching these movies it is easy to see how a picture is worth a thousand words. However, the value of the images would be limited if there was no way of quantifying the muscle movement seen. It is therefore important to note that authors have also been able to measure the lateral and anterior–posterior displacement of the tongue throughout the respiratory cycle; allowing within- and between-subject comparisons. These data demonstrate that the tongue retains a constant volume throughout the respiratory cycle, albeit redistributed during contraction or compression. To say that the methodology used influences the answers obtained may be an obvious statement when referring to this paper. By developing new methods of visualizing and quantifying genioglossus activity, the authors have opened up the possibility of further understanding the physiological principles of how the upper airway remains patent during the respiratory cycle; how the activity may change under pathological conditions such as those which occur in OSA. Above all the paper illustrates the value of an interdisciplinary approach to produce technological advances that allow new ways of investigating physiology.