Some Effects of Respiratory Frequency on Pulmonary Mechanics*

Abstract

In 1956 Otis and co-workers (1) compared the behavior of a single pulmonary pathway to an electrical circuit consisting of a capacitor and resistor in series with a sinusoidally varying voltage source. In a pulmonary pathway driven by a sinusoidally varying pressure, the resultant flow curve is also a sine wave and leads the pressure curve by an amount 9, which is determined by the relationship, O= tank ( 1/27rfRC), [1] where 9 is the phase angle in degrees between the pressure and flow curves, f is the frequency in cycles per second, R is resistance in centimeters of water per liter per second, and C is compliance in liters per centimeter of water. The product RC is the time constant and at any given frequency determines the phase angle of the system. A sinusoidally driven system of multiple parallel pathways can be considered as a single pathway only if the time constants of the individual pathways are the same. With different time constants, the effective resistance and compliance of the system will decrease with increasing frequency.Otis and co-workers observed a constant pulmonary compliance (CL) at frequencies of 10 to 120 respirations per minute in three normal subjects. Two of these subjects breathed a histamine aerosol and at 120 respirations per decreasing CL following epinephrine as compared with values before epinephrine. One patient with emphysema showed marked fall of CL over the range of 20 to 55 respirations per minute. Defares and Donleben (2) reported a small percentage of normal subjects with frequency dependent pulmonary compliance. Frank, Mead, and Ferris (3) studied nine healthy elderly adults at increasing frequencies and consistently found small decreases in CL. Others (1, 4, 5) have demonstrated constant CL in normal subjects with increasing frequency.Although the chest wall and lungs moving together determine the characteristics of the total respiratory system, the effect of respiratory frequency on total thoracic and chest wall mechanics has not been extensively studied. This study was undertaken to evaluate total thoracic, pulmonary, and chest wall compliance, resistance, and impedance as a function of frequency in normal subjects. MethodsThe subjects sat in a body plethysmograph with the head protruding through a rubber neckpiece. The plethysmograph was constructed of 1-inch plywood and measured 20 X 26 X 34 inches on the inside. Sinusoidally varying plethysmograph pressures were produced by a 16-inch diameter piston driven by an electric motor at a frequency of 10 to 130 cycles per minute. The piston stroke was adjusted to produce peak to peak plethysmograph pressures of 20 to 40 cm H20. The plethysmograph pressure was measured by a Statham PM5TC strain gauge. The esophageal pressure was measured by a 15-cm long thin wall balloon attached to a 50-cm long polyethylene tube with internal diameter of 0.070 inch.The tube was passed through the nares for a distance of 35 cm and inflated with 1 ml of air. The balloon was attached to one side of a Statham PM5TC differential strain gauge ...

Pulmonary mechanics by spectral analysis of forced random noise.

“…This variability could be due to different respiratory flows at the time of measurement or variability of upper airway area. f,, in the normal subjects was uniformly higher (P < 0.001) during inspiration compared to FRC (Table III) (16,50). A similar discrepancy was noted by DuBois et al (3) who attributed it to the failure of the lungs and chest wall to behave as a single, lumped system.…”

“…Mead (11) considered the airways to be expanding structures in parallel with the air spaces, and using a two-compartment parallel model, showed that time-constant differences between the airways and the parenchyma caused frequency dependence of compliance and resistance. The fall in resistance and compliance predicted for normal subjects by Mead's model is too small to be apparent in measurements made at practical breathing frequencies, although there have been several reports of frequency-dependent compliance occurring in normal subjects (49)(50)(51). As peripheral airway resistance is increased, the time-constant differences between the airways and parenchyma become more prominent, and can account for most of the frequency-dependent behavior observed in diseased lungs without having to invoke a generalized distribution of peripheral time-constant discrepancies.…”

Frequency dependence of compliance as a test for obstruction in the small airways

“…Previous reports on measurements of CGY. (l) as a function of frequency in "normal" subjects have noted several subjects whose lungs were frequency dependent (13,15,16). As Ingram and Schilder (13) point out in their series, the subjects who had frequency dependence were all cigarette smokers, and it is possible that they had disease in their small airways.…”

Dynamics of Respiration during Rapid Rate Mechanical Ventilation in Anesthetized and Paralyzed Rabbits

“…The compliance and resistance of the lungs have been shown to decrease as a function of ventilatory rate in normal subjects (2,6), and especially in subjects with obstructive lung disease (1, 3). Such rate-dependency ofcompliance and resistance may be explained by differences in the distribution offlow caused by either regional heterogeneities within the lungs (1, 4) or by the conducting airways acting as a "shunt" compliance in parallel with the peripheral airways (22).…”

“…The resistance of the endotracheal tube was determined by fitting the pressure difference across the tube (calculated as the difference between the pressure proximal to the endotracheal tube and the tracheal pressure) to a similar equation in which the elastic term (DoVIC) was eliminated (8). The compliance of the chest wall (Cw ) was calculated from the compliances of the respiratory system (C RS ) and lungs (Cd as: (2) assuming that chest wall and lungs were dynamically in series (15). Eight breaths were analyzed for each ventilatory rate.…”