Abstracf--The behavior of the oscillating limiter is sbown to be characterized by an equation which, d e r certain cooditiols, is equivalent to that pertaining to a 6rst-order phase-locked loop.Both the first-order phase-locked loop (PLL) and the oscillating limiter (OL) have already been widely discussed. The literature is so extensive,

The measurement of sound transmission in human lungs has shown promise to reveal, by noninvasive methods, information about the structure of peripheral airways and lung tissue. The paper gives a detailed explanation of the instrumentation and testing methods developed to measure sound transmission through human lungs and thoracic structures in the 5-20 kHz frequency range and describes in detail experiments comparing the acoustic lung transmission patterns of four different subject groups. The experimental results are compared with those predicted by an acoustical model of sound transmission through lung parenchyma.

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A transducer system is described that permits noninvasive recordings of the pressure-vs-time arterial profile at any palpable site on the body. A thin (30 microns) piezoelectric polymer film of polyvinylidene fluoride serves as the active element and as the mechanical coupler to the skin. The system has high frequency response and a low frequency cut-off of 0.16 Hz. The active element and its support provides a good mechanical impedance match with the skin. The transducer housing resembles a thick wrist watch and is strapped in place. The complete system is designed to record as many as four simultaneous profiles on a subject. Comparisons of the noninvasive transducer records with records taken with an indwelling catheter indicate congruence of the two signals and the first and second derivatives of the two signals, both when the transducer is applied directly to the skin and when a layer of fat is interposed between the skin and the transducer. The system provides a simple atraumatic means of periodically screening and/or monitoring cardiovascular changes in large populations of subjects and would provide a means of tracking changes induced by therapeutic programs.

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The impulse response of the pulmonary system has been measured by exciting the system with wideband acoustic noise introduced through the mouth. The transmitted sound is detected using microphones placed on the patient's back at appropriate locations. A specially designed analog correlator is used to obtain the impulse response of the pulmonary system through cross-correlation techniques. Uniquely characteristic responses have been obtained from smoking and nonsmoking patient groups.