Obstructive Sleep Apnoea / Hypopnoea Syndrome (OSAHS) is associated with obstruction of the upper airway and occurs as a result of repeated closure of the upper airway during sleep, either by anatomical or patho-physiological factors. During these episodes, the diaphragm and chest muscles involved in breathing work actively to re-open the occluded airway and suck air into the lungs. The aim of this study is to clinically investigate the changes in inspiratory and expiratory total air when a mandibular repositioning appliance (MRA) was used for the treatment of OSAHS and to suggest possible improvement in research technology when using the MRA. A twenty three OSAHS white Caucasian male patients were randomly selected and evaluated against twenty three non-apnoeic subjects matched for race and sex from Fife region, Scotland. Anthropometric comparison is done for the body mass index (BMI) and the percentage of predicted neck circumference (PPNC). Rhinomanometer tests were used for the OSAHS patients and control before wearing the appliance and for the OSAHS group before and after wearing the MRA. Significant improvements of inspiratory and expiratory total air have resulted. MRA is useful alternative or adjunct to the use of Continuous Positive Airway Pressure (CPAP) devices in selected patients with snoring and mild to moderate (OSAHS).