Characteristics of Vibration that Alter Cardiovascular Parameters in Mice

Abstract

We hypothesized that short-term exposure of mice to vibration within a frequency range thought to be near the resonant frequency range of mouse tissue and at an acceleration of 0 to 1 m/s(2) would alter heart rate (HR) and mean arterial pressure (MAP). We used radiotelemetry to evaluate the cardiovascular response to vibration in C57BL/6 and CD1 male mice exposed to vertical vibration of various frequencies and accelerations. MAP was consistently increased above baseline values at an acceleration near 1 m/s(2) and a frequency of 90 Hz in both strains, and HR was increased also in C57BL/6 mice. In addition, MAP increased at 80 Hz in individual mice of both strains. When both strains were analyzed together, mean MAP and HR were increased at 90 Hz at 1 m/s(2), and HR was increased at 80 Hz at 1 m/s(2). No consistent change in MAP or HR occurred when mice were exposed to frequencies below 80 Hz or above 90 Hz. The increase in MAP and HR occurred only when the mice had conscious awareness of the vibration, given that these changes did not occur when anesthetized mice were exposed to vibration. Tested vibration acceleration levels lower than 0.75 m/s(2) did not increase MAP or HR at 80 or 90 Hz, suggesting that a relatively high level of vibration is necessary to increase these parameters. These data are important to establish the harmful frequencies and accelerations of environmental vibration that should be minimized or avoided in mouse facilities.

Figure 1.

Diagram of the vibration system.

Figure 2.

Diagram of the protocol for data recording. Telemetric MAP and HR were recorded (gray boxes) for 30 s without vibration and then with vibration for 4 min 30 s, during which acceleration increased from 0 to 1.45 m/s². A 30-min recovery period was included after each frequency tested to ensure that the MAP and HR either remained or had returned to baseline levels. NV, no vibration.

Figure 3.

MAP changes during vibration of 30 to 110 Hz resulting from increasing acceleration within each frequency in C57BL/6 and CD1 mice. (A) Representative C57BL/6 mouse. The hatched bar along the y axis shows the range of MAP that was recorded for 30 s in mice without vibration. The black vertical arrow designates the approximate point on the x axis at which the acceleration reached specified values. The maximal acceleration at 90 Hz was 1.45 m/s² at 300 s. (B) The bar graph demonstrates that both C57BL/6 and CD1 mice had increased (*, P ≤ 0.05 compared with baseline) MAP at 90 Hz but not at other frequencies.

Figure 4.

(A) MAP and (B) HR changes in C57BL/6 and CD1 mice combined (n = 6) during vibration of 30 to 110 Hz resulting from increasing acceleration within each frequency. MAP and HR were significantly (*, P ≤ 0.05 compared with baseline) increased at 90 Hz; HR was increased at 80 Hz also. HR at 30 and 70 Hz increased very briefly in one mouse but immediately returned to baseline.

Figure 5.

HR changes during vibration of 30 to 110 Hz resulting from increasing acceleration within each frequency in C57BL/6 and CD1 mice. (A) Representative C57BL/6 mouse. The hatched bar along the y axis shows the range of MAP that was recorded for 30 s in mice without vibration. The black vertical arrow designates the approximate point on the x axis at which the acceleration reached specified values. The maximal acceleration at 90 Hz was 1.45 m/s² at 300 s. (B) The bar graph demonstrates that C57BL/6 mice had increased (P ≤ 0.05) HR at 90 Hz but not at other frequencies. CD1 mice did not have increased HR at any frequency. The 70- and 80-Hz frequencies significantly increased HR in CD1 mice, but the increases were not sustained during vibration exposure.

Figure 6.

MAP and HR changes at 80 and 90 Hz when C57BL/6 and CD1 mice combined (n = 6) mice were exposed to the sound of the vibration table and not the vibration. The sound generated by the vibration table at these frequencies and 1 m/s² did not cause an increase in MAP or HR.

Figure 7.

(A) MAP and (B) HR in C57BL/6 and CD1 mice combined (n = 6) exposed to 30 to 70 Hz of vibration with constant acceleration (1 m/s²). The hatched bar along the y axis shows the average range of HR or MAP that was recorded for 30 s in mice without vibration.

Figure 8.

(A) MAP and (B) HR at various frequencies and 1 m/s² constant vibration in anesthetized C57BL/6 and CD1 combined mice. The hatched bar along the y axis shows the average range of HR or MAP that was recorded for 30 s in mice without vibration. There was no increase in MAP or HR at any frequency during anesthesia. The baseline MAP and HR are lower than control levels at some frequencies, likely because of varying depths of anesthesia.

Figure 9.

The minimal acceleration necessary to cause an increase in (A) MAP and (B) HR in C57Bl/6 and CD1 mice combined. The minimal acceleration necessary to cause an increase was 0.75 m/s² at 90 Hz.