Subglottic pressure and the control of phonation by the echolocating bat,Eptesicus

Abstract

1. The respiratory dynamics of phonation, particularly the relationship between subglottic pressure and the sound pressure level (SPL), frequency and duration of vocalizations by nine bats (Eptesicus fuscus) is described. 2. Subglottic pressure rises to about 30 or 40 cm H2O immediately prior to emission of a single FM pulse or group of pulses, respectively, and drops 5 to 20 cm H2O during the course of each pulse (Fig. 2). 3. The maximum SPL of the echolocative pulse is positively correlated with the magnitude of the subglottic pressure at the onset of phonation in eight bats. The unusually high subglottic pressure in bats is an adaptation for the production of high intensity orientation pulses, thus increasing the range of echolocation. 4. The maximum SPL was proportional to the subglottic pressure at the pulse onset raised to a power which ranged from a mean of 0.4 to 1.36 for individualEptesicus (Fig. 3 and Table 1). The approximately linear relationship between sound pressure level and onset subglottic pressure in several bats suggests the vocal tract has a minimal effect on pulse intensity. 5. Within a given vocalization, upward sweeping FM is usually associated with either constant or increasing subglottic pressure (Figs. 4 and 5), but the absolute value of the subglottic pressure at pulse onset is correlated with the initial frequency of vocalization in only four of these bats (Table 2). 6. Subglottic pressure drops most rapidly during short pulses, but during long vocalizations (exceeding 20 ms) it attains a minimum rate of decline of about 0.2 cm H2O/ms (Fig. 6 and Table 2), which may be determined by the maximum glottal resistance at which phonation can occur. 7. The relatively non-compliant lung ofEptesicus (mean static compliance = 0.021 ±0.002 ml/cm H2O) may be an adaptation for the production of the unusually high subglottic pressures needed to produce high intensity echolocative pulses.