Phono 



EKG 



Rl Hfort 



listocardiographic recording. Finally, 

 the natural frequency of the entire 

 system should be as low as possible — 

 0.3 Hz or less is mandatory. These 

 four requirements imply that the ideal 

 Beg system is one in which subject 

 and bed tloat as a unit in space. 



Several ingenious systems, some 

 simple, some complex, have been 

 assembled to accomplish the above 

 requirements. Beds have been con- 

 structed from aluminum and canvas, 

 styrofoam. balsa, or aluminum honey- 



comb, and suspended by wires or 

 floated on mercury or air. The sim- 

 plest and original bed is based on the 

 pendulum, and was the type used in 

 this stud\ . The Beg bed was the same 

 stretcher used to weigh Gigi (Figure 2). 

 The stretcher was constructed from 

 canvas and two 20-fool heavy wall, 

 galvanized steel pipes 3 inches in 

 diameter. The total weight of 227 kg 

 may seem large to most ballisto- 

 cardiographers. but Gigi's weight at 

 the time was 4..'i00 kg. and the whale: 



Figure 1. — Examples of normal ballistocardio- 

 graphic tracings in man. From top to bottom 

 are recorded acceleration (A), velocity (V). 

 and displacement (D). In addition, the EKG 

 and the major events of the cardiac cycle are 

 given as reference points. (From Scarborough 

 et al.. Am. J. Cardiol. 2:613-641. 1958.) 



bed ratio of 20; 1 was more than 

 adequate. Six ropes supported the 

 poles, four at the ends, each 13 feet 

 in length, and two in the middle. A 

 board inserted between the two middle 

 ropes prevented injury to the animal. 

 The six ropes were suspended by a 

 single cable from a crane. During the 

 recording the cable was 7'/2 meters 

 from pulley to hook, giving a natural 

 frequency of about 0.18 Hz. The 

 crane was part of a truck hoist, which 

 was ideal for isolation from ground 

 because of the pneumatic lift and 

 the rubber tires. 



Most of the water was drained from 

 Gigi's tank to reduce her mobility and 

 to enhance our own. She was reluctant 

 to lie on the bed. and had to be coaxed. 

 The coaxing process took 45 minutes. 

 Once on the bed. she became surpris- 

 ingly quiet, which was fortunate, 

 since she could easil\ have demolished 

 our fragile accelerometer. One re- 

 adjustment of the relative position of 

 whale and bed was required to level 

 the bed. 



Acceleration was transduced in 

 the head-foot direction with an 

 Endevco' piezo-resistive accelerometer 

 clamped to one of the steel poles with 

 a large C clamp. The accelerometer 

 was calibrated with a pendulum, ac- 

 cording to the method of Moss (1961). 

 Lead two of the ECG was recorded 

 using 4 inch 18 g spinal needles. All 

 electrical cables were supported by a 

 rope stretched across the tank. A 60 Hz 

 passive notch filter and a .^d Hz 

 low pass Butterworth filter were used 

 on both the ECG and Beg to eliminate 

 unwanted noise and at the same time 

 preserve timing relations. Data were 

 recorded on a Hewlett-Packard oscil- 

 loscope and an Ampex FM tape rec- 

 order. 



'Use of trade names in this publication does 

 not imply endorsement of commercial products 

 by \he National f^arine Fisheries Service. 



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