Masking release at 4 kHz in harbor porpoises (Phocoena phocoena) associated with sinusoidal amplitude-modulated masking noise.

Acoustic masking reduces the efficiency of communication, prey detection, and predator avoidance in marine mammals. Most underwater sounds fluctuate in amplitude. The ability of harbor porpoises (Phocoena phocoena) to detect sounds in amplitude-varying masking noise was examined. A psychophysical technique evaluated hearing thresholds of three harbor porpoises for 500-2000 ms tonal sweeps (3.9-4.1 kHz), presented concurrently with sinusoidal amplitude-modulated (SAM) or unmodulated Gaussian noise bands centered at 4 kHz. Masking was assessed in relation to signal duration and masker level, amplitude modulation rate (1, 2, 5, 10, 20, 40, 80, and 90 Hz), modulation depth (50%, 75%, and 100%) and bandwidth (1/3 or 1 octave). Masking release (MR) due to SAM was assessed by comparing thresholds in modulated and unmodulated maskers. Masked thresholds were affected by SAM rate with the lowest thresholds (i.e., largest MR was 14.5 dB) being observed for SAM rates between 1 and 5 Hz at higher masker levels. Increasing the signal duration from 500-2000 ms increased MR by 3.3 dB. Masker bandwidth and depth of modulation had no substantial effect on MR. The results are discussed with respect to MR resulting from envelope variation and the impact of noise in the environment.

Effect of pile-driving sounds on harbor seal (Phoca vitulina) hearing.

Seals exposed to intense sounds may suffer hearing loss. After exposure to playbacks of broadband pile-driving sounds, the temporary hearing threshold shift (TTS) of two harbor seals was quantified at 4 and 8 kHz (frequencies of the highest TTS) with a psychoacoustic technique. The pile-driving sounds had: a 127 ms pulse duration, 2760 strikes per h, a 1.3 s inter-pulse interval, a ∼9.5% duty cycle, and an average received single-strike unweighted sound exposure level (SELss) of 151 dB re 1 µPa2s. Exposure durations were 180 and 360 min [cumulative sound exposure level (SELcum): 190 and 193 dB re 1 µPa2s]. Control sessions were conducted under low ambient noise. TTS only occurred after 360 min exposures (mean TTS: seal 02, 1-4 min after sound stopped: 3.9 dB at 4 kHz and 2.4 dB at 8 kHz; seal 01, 12-16 min after sound stopped: 2.8 dB at 4 kHz and 2.6 dB at 8 kHz). Hearing recovered within 60 min post-exposure. The TTSs were small, due to the small amount of sound energy to which the seals were exposed. Biological TTS onset SELcum for the pile-driving sounds used in this study is around 192 dB re 1 µPa2s (for mean received SELss of 151 dB re 1 µPa and a duty cycle of ∼9.5%).

Flow Induced Microvascular Network Formation of Therapeutic Relevant Arteriovenous (AV) Loop-Based Constructs in Response to Ionizing Radiation.

BACKGROUND The arteriovenous (AV) loop model enables axial vascularization to gain a functional microcirculatory system in tissue engineering constructs in vivo. These constructs might replace surgical flaps for the treatment of complex wounds in the future. Today, free flaps are often exposed to high-dose radiation after defect coverage, according to guideline-oriented treatment plans. Vascular response of AV loop-based constructs has not been evaluated after radiation, although it is of particular importance. It is further unclear whether the interposed venous AV loop graft is crucial for the induction of angiogenesis. MATERIAL AND METHODS We exposed the grafted vein to a single radiation dose of 2 Gy prior to loop construction to alter intrinsic and angio-inductive properties specifically within the graft. Vessel loops were embedded in a fibrin-filled chamber for 15 days and radiation-induced effects on flow-mediated vascularization were assessed by micro-CT and two-dimensional histological analysis. RESULTS Vessel amount was significantly impaired when an irradiated vein graft was used for AV loop construction. However, vessel growth and differentiation were still present. In contrast to vessel density, which was homogeneously diminished in constructs containing irradiated veins, vessel diameter was primarily decreased in the more peripheral regions. CONCLUSIONS Vascular luminal sprouts were significantly diminished in irradiated venous grafts, suggesting that the interposing vein constitutes a vital part of the AV loop model and is essential to initiate flow-mediate angiogenesis. These results add to the current understanding of AV loop-based neovascularization and suggest clinical implications for patients requiring combined AV loop-based tissue transfer and adjuvant radiotherapy.

Pile driving playback sounds and temporary threshold shift in harbor porpoises (Phocoena phocoena): Effect of exposure duration.

High intensity underwater sounds may cause temporary hearing threshold shifts (TTSs) in harbor porpoises, the magnitude of which may depend on the exposure duration. After exposure to playbacks of pile driving sounds, TTSs in two porpoises were quantified at 4 and 8 kHz with a psychophysical technique. At 8 kHz, the pile driving sounds caused the highest TTS. Pile driving sounds had the following: pulse duration 124 ms, rate 2760 strikes/h, inter-pulse interval 1.3 s, duty cycle ∼9.5%, average received single-strike unweighted broadband sound exposure level (SELss) 145 dB re 1 µPa(2)s, exposure duration range 15-360 min (cumulative SEL range: 173-187 dB re 1 µPa(2)s). Control sessions were also carried out. Mean TTS (1-4 min after sound exposure stopped in one porpoise, and 12-16 min in the other animal) increased from 0 dB after 15 min exposure to 5 dB after 360 min exposure. Recovery occurred within 60 min post-exposure. For the signal duration, sound pressure level (SPL), and duty cycle used, the TTS onset SELcum is estimated to be around 175 dB re 1 µPa(2)s. The small increase in TTS between 15 and 360 min exposures is due to the small amount of sound energy per unit of time to which the porpoises were exposed [average (over time) broadband SPL ∼144 dB re 1 µPa].

Hearing thresholds of a harbor porpoise (Phocoena phocoena) for narrow-band sweeps.

The hearing sensitivity of a 2-yr-old male harbor porpoise was measured using a standard psycho-acoustic technique under low ambient noise conditions. Auditory sensitivity was measured for narrow-band 1 s sweeps (center frequencies: 0.125-150 kHz). The audiogram was U-shaped; range of best hearing (within 10 dB of maximum sensitivity) was from 13 to ∼140 kHz. Maximum sensitivity (threshold: ∼39 dB re 1 µPa) occurred at 125 kHz at the peak frequency of echolocation pulses produced by harbor porpoises. Reduced sensitivity occurred at 32 and 63 kHz. Sensitivity fell by ∼10 dB per octave below 16 kHz and declined sharply above 125 kHz. Apart from this individual's ca. 10 dB higher sensitivity at 0.250 kHz, ca. 10 dB lower sensitivity at 32 kHz, and ca. 59 dB lower sensitivity at 150 kHz, his audiogram is similar to that of two harbor porpoises tested previously with a similar psycho-acoustic technique.

Flow increase is decisive to initiate angiogenesis in veins exposed to altered hemodynamics.

Exposing a vein to altered hemodynamics by creating an arteriovenous (AV) shunt evokes considerable vessel formation that may be of therapeutic potential. However, it is unclear whether the introduction of oscillatory flow and/or flow increase is decisive. To distinguish between these mechanical stimuli we grafted a femoral vein into the arterial flow pathway of the contralateral limb in rats creating an arterioarterial (AA) loop (n = 7). Alternatively, we connected the femoral artery and vein using the vein graft, whereby we created an AV-loop (n = 27). Vessel loops were embedded in a fibrin filled chamber and blood flow was measured by means of flow probes immediately after surgery (day 0) and 15 days after loop creation. On day 15, animals were sacrificed and angiogenesis was evaluated using µCT and histological analysis. Mean flow increased from 0.5 to 2.4 mL/min and was elevated throughout the cardiac cycle at day 0 in AV-loops whereas, as expected, it remained unchanged in AA-loops. Flow in AV-loops decreased with time, and was at day 15 not different from untreated femoral vessels or AA-loop grafts. Pulsatile flow oscillations were similar in AV-and AA-loops at day 0. The flow amplitude amounted to ~1.3 mL/min which was comparable to values in untreated arteries. Flow amplitude remained constant in AA-loops, whereas it decreased in AV-loops (day 15: 0.4 mL/min). A large number of newly formed vessels were present in AV-loops at day 15 arising from the grafted vein. In marked contrast, angiogenesis originating from the grafted vein was absent in AA-loops. We conclude that exposure to substantially increased flow is required to initiate angiogenesis in grafted veins, whereas selective enhancement of pulsatile flow is unable to do so. This suggests that indeed flow and most likely wall shear stress is decisive to initiate formation of vessels in this hemodynamically driven angiogenesis model.

High flow conditions increase connexin43 expression in a rat arteriovenous and angioinductive loop model.

Gap junctions are involved in vascular growth and their expression pattern is modulated in response to hemodynamic conditions. They are clusters of intercellular channels formed by connexins (Cx) of which four subtypes are expressed in the cardiovascular system, namely Cx37, Cx40, Cx43 and Cx45. We hypothesize that high flow conditions affect vascular expression of Cx in vivo. To test this hypothesis, flow hemodynamics and subsequent changes in vascular expression of Cx were studied in an angioinductive rat arteriovenous (AV) loop model. Fifteen days after interposition of a femoral vein graft between femoral artery and vein encased in a fibrin-filled chamber strong neovascularization was evident that emerged predominantly from the graft. Blood flow through the grafted vessel was enhanced ∼4.5-fold accompanied by increased pulsatility exceeding arterial levels. Whereas Cx43 protein expression in the femoral vein is negligible at physiologic flow conditions as judged by immunostaining its expression was enhanced in the endothelium of the venous graft exposed to these hemodynamic changes for 5 days. This was most likely due to enhanced transcription since Cx43 mRNA increased likewise, whereas Cx37 mRNA expression remained unaffected and Cx40 mRNA was reduced. Although enhanced Cx43 expression in regions of high flow in vivo has already been demonstrated, the arteriovenous graft used in the present study provides a reliable model to verify an association between Cx43 expression and high flow conditions in vivo that was selective for this Cx. We conclude that enhancement of blood flow and its oscillation possibly associated with the transition from laminar to more turbulent flow induces Cx43 expression in a vein serving as an AV loop. It is tempting to speculate that this upregulation is involved in the vessel formation occuring in this model as Cx43 was suggested to be involved in angiogenesis.