Decrease In Pulse Amplitude Research Articles

Effects of noise on some autonomic system activities.

Experiments were conducted on the effects of various expected noise conditions upon autonomic system activity in men during rest and work (bicycle ergometer). Skin temperature and heart rate were not appreciably, if at all, affected by any of the noises. Wide-band, predominantly low-frequency noise, at a level of 92 dB, A-weighted, generally caused a decrease in pulse amplitude (indicative of constriction of peripheral blood vessels) during either work or rest, whereas an equally intense one-third octave band of random noise, center frequency of 3150 Hz, had no appreciable effect on pulse amplitude. Repeated exposures to the wide-band noise showed some adaptation or habituation of the pulse amplitude response during conditions of either work or rest. The results were the same for fast rise time (impulsive) bursts of wide-band noise as for bursts with slow, gradual onsets. Rapid interruptions of wide-band noise caused less of a decrease in average pulse amplitude than did uninterrupted noise. It is suggested that constriction of peripheral blood vessels in response to expected intense low-frequency or wide-band noises is more related to auditory, reflexive protective mechanisms than to autonomic system responses generally considered to be stressful to the organism.

Peripheral Vasoconstriction In The Rat In Response To Sound: II. Dependence On Rate Of Change Of Sound Level

Vasoconstrictions elicited by sound were studied in the non-anaesthetized rat. Arterial pulsations in the tail were recorded by a non-invasive technique. On slightly heating the animal, the tail vessels became dilated. An 80 dB SPL noise burst caused a decrease in pulse amplitude, usually to less than 10% of the pre-stimulus value. It was found that 4 s bursts of 80 dB SPL noise with rise times 1, 10, or 100 ms were equally efficient in producing vasoconstriction. If the rise time was longer, 1 s, the vasconstriction was significantly smaller. It was pointed out that the feedback control of the stimulus noise provided by the acoustic middle ear reflex would contribute to enhancing rapid variations in sound level, and thereby form part of a physiological explanation for the present findings.

Cuff pressure oscillations in the measurement of relative blood pressure.

ABSTRACTThe continuous relative blood pressure measure obtained with a partially‐inflated arm blood‐pressure cuff operates under the same principle as the oscillometric method of blood pressure determination. In psychophysiological studies the rise in blood pressure seen, for example, in response to an emotion‐evoking question, produces a rise in cuff pressure, along with any of three pulse‐amplitude changes: a decrease, no change, or an increase. These seemingly paradoxical responses which accompany an increase in blood pressure may be explained by considering the relationship of cuff pressure to the cuff pressure for maximum oscillations. Experiments were conducted in which cuff pressure and its oscillations were recorded. Indications of an increase in blood pressure, and the pulse‐amplitude changes resulting there from, were obtained at different cuff pressures in the same subject. The results confirm the hypothesis that with cuff pressure below the point of maximum oscillation, an increase in blood pressure results in a decrease in pulse amplitude. With a cuff pressure just above the point of maximum oscillations, an increase in blood pressure results in an increase in pulse amplitude.

Electromagnetic pulse interaction with mammalian cranial structures.

The transmitted field strengths in homogeneous spherical models of human and animal heads are determined as a function of time and position, using frequency analytic techniques for an impinging pulse of Gaussian character. A relaxation process and constant conductivity are assumed for the electrical behavior of brain matter. The constant conductivity process predicts continued decrease in pulse amplitude as it advances in the head starting from the leading surface; however, the relaxation process predicts reduction only from the surface to the center. Moreover, it appears that the transmitted pulse in a spherical model of the head is always related to the time derivative of the incident radiation. Numerical results indicate that the transmitted pulse amplitude is quite small and can be estimated using the constant conductivity model.

Ion conductance changes associated with spike adaptation in the rapidly adapting stretch receptor of the crayfish.

The time course of the repetitive impulse discharges has been investigated for two high intensities of maintained depolarizing currents, 30 nA and 50 nA, for which the receptor adaptation was complete within 70 msec. The changes in sodium and potassium conductance associated with the decline in spike activity have been analyzed at different instances of time by interrupting in successive experiments the various action potentials in the pulse trains either at the early phase by holding the potential at about -60 mV and recording the inward current (upstroke-gNa) or by evaluating the delayed outward current flowing as the result of a depolarizing voltage pulse which at the end of the action potential re-increased the membrane potential by mV (after potentialgK). At the higher current intensity of 50 nA the discharge frequency was increased, while larger reductions in upstroke-gNa and after potential-gK during receptor adaptation became apparent. The progressive decrease in pulse amplitude from 99 mV to 63 or 55 mV is paralleled by a gradual reduction in upstroke-gNa from 97 mmho/cm-2 to 37 or 27.5 mmho/cm-2 and in after potential-gK from 11.5 mmho/cm-2 to about 7 mmho/cm-2. When under a stimulus of 30 nA the sodium conductance decreases to an average value of 37 mmho/cm-2 only a distorted spike can be elicited, while the spike activity was completely suppressed at upstroke-gNa equals 27.5 mmho/cm-2 was essentially the same under both conditions. The results have been interpreted in terms of the model for impulse generation formulated by Michaelis and Chaplain (1973). According to the model both sodium and potassium inactivation reduce the pulse amplitude. However, while Na-inactivation reduces the frequency of impulse discharge, the K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation ensures a constancy of the information-carrying parameter, i.e. the average impulse density.

DEEP‐HOLE GEOPHONE STUDY IN GARVIN COUNTY, OKLAHOMA

The results of a seismic well survey made with calibrated recording equipment are presented. This survey differed from the conventional type in that a geophone which could be locked to the wall of the bore hole was used, thereby providing reliable amplitude data and permitting reflections to be recorded at depth. Consequently it was possible to observe the true shape and amplitude of the seismic pulses, both initial and reflected, over the major portion of their travel paths. Quantitative data were obtained on such factors as decrease of pulse amplitude with depth, location of reflecting horizons, and magnitude of reflection coefficients.