lung volumes in giraffes -- dinosaur megaherbivore inferences?
Graham Mitchell & J.D. Skinner, 2011. Lung volumes in giraffes, Giraffa camelopardalis. Comparative Biochemistry & Physiology A158(1):72-78. ABSTRACT. We have measured lung mass and trachea dimensions in 46 giraffes of both genders ranging in body mass from 147 kg to 1441 kg, calculated static and dynamic lung volumes, and developed allometric equations that relate changes in them to growth. We found that relative lung mass is 0.6 ± 0.2% of body mass which is significantly less than it is in other mammals (1.1 ± 0.1%). Total lung volume is significantly smaller (46.2 ± 5.9 mL kg－1) than in similar sized mammals (75.0 ± 2.1 mL kg－1). The lung volume:body mass ratio decreases during growth rather than increase as it does in other mammals. Tracheal diameter is significantly narrower than in similar sized mammals but dead space volume (2.9 ± 0.5 mL kg－1) is larger than in similar sized mammals (2.4 ± 0.1 mL kg－1). Our calculations suggest that tidal volume (10.5 ± 0.2 mL kg－1) is increased compared to that in other mammals(10.0 ± 0.2 mL kg－1) so that the dead space:tidal volume ratio is the same as in other mammals. Calculated Functional Residual Capacity is smaller than predicted (53.4 ± 3.5 vs 33.7 ± 0.6 mL kg－1) as is Expiratory Reserve Volume (47.4 ± 2.6vs 27.2 ± 1.0 mL kg－1, but Residual Volume (6.0 ± 0.4 mL kg－1) is the same as in other similar sized mammals (6.0 ± 0.9 mL kg－1. Our calculations suggest that Inspiratory Reserve Volume is significantly reduced in size (11.6 ± 1.6 vs 3.8 ± 2.4 mL kg－1), and, if so, the capacity to increase tidal volume is limited. Calculated dynamic lung volumes were the same as in similar sized mammals. We have concluded that giraffe morphology has resulted in lung volumes that are significantly different to that of similar sized mammals, but these changes do not compromise ventilatory capacity.