ABSTRACT
Anal valve movement and abdominal sternal movement were photographed with a ciné camera during normal ventilation to obtain a correlation between the two parameters.
As the sterna are raised (expiration) the anal valve opens to about one third of its maximum. At peak sternal movement the anal valve opens fully and these events mark the transition between expiration and inspiration. The anal valve finally closes towards the end of inspiration.
The narrow aperture of the anal valve during expiration, coupled with the increase in pressure in the branchial chamber, causes the expired water to be forced well clear of the anus. Conversely, the wide aperture during inspiration and the small negative pressure in the branchial chamber ensure that water is drawn in from close to the animal, and so there is minimal mixing of expired water with inspired.
The relationships between water flow, anal valve movement, branchial chamber pressure, sternal movement, pleural strain, and activity in certain expiratory and inspiratory muscles are discussed.
