T2緩和時間を指標とした15％最大筋力時の手関節伸展運動筋の解析

骨格筋緩和時間(T1, T2)を指標としたMRI法は，表面筋電図法，超音波法に加え新しい骨格筋の運動分析法として注目されている．本研究では，物を把持するなど日常生活で重要な手関節伸展運動について検討した．健常人8名を被験者とし，最大等尺性収縮筋力の15％の等張性収縮運動の前後でのT2強調画像とT2の変化，および運動後25分の回復を測定した．測定筋は，短橈側手根伸筋，総指伸筋，小指伸筋，円回内筋，尺側手根伸筋，深指屈筋，浅指屈筋，尺側手根屈筋，橈側手根屈筋，腕橈骨筋とした．運動後T2強調画像から活動筋を弁別した．短橈側手根伸筋，総指伸筋，小指伸筋にT2の延長を認めた（P＜0.01）．その後，緩やかに短縮したが，短橈側手根伸筋と総指伸筋では25分後までT2の延長を認めた．尺側手根伸筋，円回内筋は延長傾向を認めたが，有意ではなかった．主動筋の短橈側手根伸筋に対して，総指伸筋，小指伸筋に協同作用としての活動が確認できた．屈筋群である尺側手根屈筋，橈側手根屈筋，深指屈筋，浅指屈筋，腕橈骨筋は非活動であった．以上より，T2を指標としたMRI法により手関節運動筋の運動解析が可能であることが示された

Roles of Keber's valve and foot chamber for foot manipulation in the mussel Nodularia douglasiae

In order to analyse the roles of Keber's valve for foot manipulation in the mussel Nodularia douglasiae, the anatomy and haemolymph flow in the cardiovascular system were detected by magnetic resonance imaging. The superficial layer of the foot was covered by a dense muscle layer, which extended to the dorsal side and connected with the shell. This closed space, the foot chamber, had an inlet (anterior aorta) and an outlet (Keber's valve). At rest, in the beginning of the systolic phase, flows in the anterior aorta and the pedal artery increased, followed by the pedal and visceral sinuses. Then these flows ceased at the end of the systolic phase, followed by inflow to the ventricle in the diastolic phase; therefore, the compliance of the foot chamber is low enough to transfer pressure pulses to the visceral sinus. Extension of the foot started with relaxation of the foot muscle, so the compliance of the foot chamber increased. Then, Keber's valve closed so that the haemolymph filled the foot haemocoel. Retraction of the foot is initiated by the opening of Keber's valve. Judging from these results Keber's valve and the foot chamber are essential for circulation at rest, foot extension and retraction. This article has an associated First Person interview with the first author of the paper

A portable infrared photoplethysmograph: heartbeat of Mytilus galloprovincialis analyzed by MRI and application to Bathymodiolus septemdierum

Infrared photoplethysmogram (IR-PPG) and magnetic resonance image (MRI) of the Mytilus galloprovincialis heart were obtained simultaneously. Heart rate was varied by changing temperature, aerial exposure and hypoxia. Higher heart rates (35-20 beat min−1) were usually observed at 20°C under the aerobic condition, and typical IR-PPG represented a single peak (peak v). The upward and downward slopes of the peak v corresponded to the filling and contracting of the ventricle, respectively. A double-peak IR-PPG was observed in a wide range of heart rates (5 to 35 beats min−1) under various conditions. The initial peak v corresponded to the filling of the ventricle, and the origin of the second peak (v’) varied with the heart rate. A flat IR-PPG with a noise-level represented cardiac arrest. Although large movement of the shells and the foot caused slow waves or a baseline drift of the IR-PPG, the heart rate can be calculated from the v-v interval. Based on these results, we assembled a portable IR-PPG recording system, and measured the heartbeats of Bathymodiolus septemdierum (Mytilidae) for 24 h on a research vessel just after sampling from the deep sea, showing that IR-PPG is a noninvasive, economical, robust method that can be used in field experiments