Background: Taking a bath sometimes poses a risk for subjects with chronic cardiopulmonary\ndisorders, due to the thermal effect and water pressure on his/her body.\nThe ECG measurement would be helpful for the early recognition of abnormal cardiac\nbeats and respiratory conditions. This paper describes a new attempt to improve on\nprevious bathtub ECG measurement techniques that had electrodes placed inside the\nbathtub that were intrusive to the subjectsâ�� bathing experience. This study is concerned\nwith the initial development of a method to measure an electrocardiogram (ECG)\nthrough tap water without conscious awareness of the presence of electrodes that are\nplaced outside the bathtub wall.\nMethods: A configuration of capacitive coupling electrodes placed outside the bathtub\nwas designed so that the electrodes could be hidden. The capacitive coupling was\nmade from the electrodes to the water through the bathtub wall. Two electrodes with\nan active shielding amplifier covered further by an electromagnetic shield were fixed\nto the outside surface of the bathtub wall, near the batherâ��s right scapula and left foot.\nThe potential difference between these two electrodes, similar to the bipolar lead-II\nECG, was amplified to obtain raw signals inclusive of ECG/QRS components. Respiration\nintervals were also derived from ECG/RR intervals. Comparison experiments between\nthis bathtub method and conventional direct methods with spot-electrodes and a\nchest-band sensor were made using 10 healthy male volunteers (22.2 �± 0.98 years).\nResults: The ECG signal was detectable through tap water as well as water with differing\nconductivity resulting from mixing bathwater additives with the water. ECG signals\nand respiration curves derived from ECG/RR intervals were successfully obtained in all\nsubjects. The intervals of the ECG/RR and respiration obtained by the bathtub system\nand by the direct method were respectively agreed well with each other.\nConclusion: The ECG signal, in particular ECG/QRS components, were successfully\ndetected utilizing capacitive coupling electrodes placed outside the bathtub wall. Also,\nthe ECG/RR and respiration intervals were determined with reasonable accuracy as\ncompared with the conventional direct methods.
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