The Measurement of Respiratory Volumes and Flows on Two Captive West Indian Manatees (Trichechus manatus)
Barbara Kirkpatrick; Debborah E. Colber; Elizabeth A.C. Newton; Charles Manire
The specific goal of this project was to measure a living manatee's average breath size, flow rate, and vital capacity. Many researchers have estimated lung volumes and flow rates using necropsied animals, but results have not been verified with data obtained from behavioral research with live animals.
Respiratory measurements were obtained from two captive manatees housed at Mote Marine Laboratory, Hugh and Buffett. These animals had already been trained for several husbandry and research behaviors. Obtainment of in-situ spirometry was completed by operant conditioning of both animals to breathe into a standard resuscitator mask typically used with adult humans. Once the manatees were trained to breathe into the mask, the mask was connected to a spirometer (Spirometrics Flowmate LTE). A total of 725 breaths were measured. Vital capacity or breath size (VC), inspiratory vital capacity (IVC), peak expiratory flow (PEF), peak inspiratory flow (PIF), and expiratory time (Texp) were measured with each maneuver. In the first segment of the study, the manatees were reinforced for all breaths captured by the spiromete. In the second segment of the study a threshold of five liters (L) was set for a minimum effort. In the third segment of the study, a stair step method of reinforcement was used in attempts to obtain maximal effort and therefore, a true vital capacity.
Basic descriptive statistics: the mean, median, maximum and minimum were computed for each subject in each of the three training segments. These data then were plotted against time to examine trends. Tables 1 and 2 show basic descriptive statistics, mean, median, maximum and minimum values for each subject in each of the training segments.
Segment 1 was considered a training exercise allowing the animals and their trainers to become adept at performing and measuring VC. With the trainers, the primary experience learned was proper technique to apply the mask over the manatee nostrils to prevent any air leak and not cover a nostril. Segment l's data are not considered representative of a typical breath.
Based on the continued upward slope of a line in Figure 1, it does not appear that a true vital capacity was obtained. However, some interesting parallels with human data were seen. In humans, vital capacity is 10-15 ml/kg, based on ideal body weight. Values for the manatees found in this study were similar when adjusted for body weight.
Other parameters worth noting include the similarity found in the expiratory flow rates between the two animals in segment three. Flow rates were high and these findings are consistent with the anatomical structure of the manatee lung. Manatees have reinforced airways down to the bronchioles giving the support needed for high flows. In addition, expiratory times are very short, usually 1-2 seconds.
This study has established a technique to measure in-situ lung capacity parameters on captive manatees. Further studies are indicated to determine true vital capacity of the West Indian manatee.
This work was supported by a grant from the Florida Manatee Trust Fund. The authors wish to thank the dedicated manatee training team, Wendi Fellner, Joe Gaspard, Brandi Littlefield, Mike Kress, and Jann Warfield with this effort. Thanks also to Gordon B. Bauer for his collegial discussions during this project.