Search

To the Editor: The manuscript by Drs. Sato and Robbins ([3][1]) presents a new method for determining average flow profiles. The resulting average flow profiles are compared with those obtained with our method ([2][2]). It is noteworthy that the method of flow profile analysis we used was first

The effects of gas density on the frequency responses of four pressure transducers were determined at gas densities from 1.2 to 25.0 g/l. Transducers tested included three sensitive differential types used with pneumotachographs to measure respiratory flow (Validyne DP-45 and DP-103; Medistor P-11) and a transducer commonly used to measure esophageal pressure (Statham P23Dd). Three different responses were obtained. The Validyne DP-103 was overdamped and its response was essentially independent of gas density. The frequency response of this transducer is adequate for use with quiet breathing only. The Validyne DP-45 and Medistor P-11 responses were underdamped. The resonant peaks of these transducers decreased markedly in frequency as the gas density increased. The Statham P23Dd was also underdamped; however, its resonant frequency increased as gas density increased. An esophageal balloon did not alter the frequency response characteristics of this tubing-transducer system. Both increases in length and decreases in diameter of connecting tubing reduced the frequency of resonant peaks of underdamped pressure transducers.

The regular involuntary inspiratory muscle contractions that occur in normal conscious men during breath holding were quantified by means of the waves of intrathoracic pressure that they produced. A stream of cool air circulated through the nose and mouth reproducibly inhibited the contractions. The degree of inhibition increased with increasing nasal flow in the range of normal resting respiratory flow and with lower temperature of circulating gas. The effect depended on the phase of respiration in which flow occurred and was abolished by local anesthesia of the nose and pharynx. The results demonstrate that the upper airway contains flow-sensitive receptors, the discharge of which can have a marked influence on respiration.

Vagal influence on inspiratory motor output was assessed in 20 normal subjects and in 12 patients with respiratory disorders under enflurane anethesia using the method of airway occlusion. The change in inspiratory duration during occlusion (delta TI) was measured from mechanical parameters (respiratory flow and tracheal pressure). In eight of the subjects, however, the effect of occlusion and augmentation of tidal volume was further evaluated from diaphragmatic electromyogram. In normal subjects delta TI (mechanical) averaged 0.15 s (range -0.1 to +0.77 s) and correlated with the duration of inspiration during occlusion. Electromyographic observations indicated that the change in neural TI exceeds the change in mechanical TI by approximately 0.2 s and that augmentation of tidal volume shortens TI with no apparent volume threshold. There was a tendency for vagal influence to be higher with restrictive lung disease and lower with obstructive airway disease. These observations indicate that a majority of humans display a significant vagal influence on TI in the spontaneous tidal volume range under anesthesia.

When the whole body is exposed to sinusoidal variations of ambient pressure (delta Pam) at very low frequencies (f), the resulting compression and expansion of alveolar gas is almost entirely achieved by gas flow through the airways (Vaw). As a consequence thoracic gas volume (TGV) may be computed from the imaginary part (Im) of the delta Pam/Vaw relationship: TGV = PB/[2 pi f X Im(delta Pam/Vaw)], where PB is barometric minus alveolar water vapor pressure. The method was tested in 35 normal subjects and compared with body plethysmography. The subjects sat in a chamber connected to a large-stroke-volume reciprocating pump that brought about pressure swings of 40 cmH2O at 0.05 Hz. delta Pam and Vaw were digitally processed by fast Fourier transform to extract the low-frequency component from the much larger respiratory flow. Total lung capacities (TLC) obtained by ambient pressure changes and by plethylsmography were highly correlated (r = 0.959, p less than 0.001) and not significantly different (6.96 +/- 1.38 l vs. 6.99 +/- 1.38). TLC obtained by ambient pressure changes were not influenced by lowering the frequency to 0.03 Hz, adding an external resistance at the mouth, or increasing abdominal gas volume. We conclude that the method is practical and in agreement with body plethysmography in normal subjects.

Measurements of flow resistance of various components of the respiratory system were measured in adult male subjects in the sitting position. Nasal resistance is the largest single component being nearly one-half the total and two-thirds of the airway resistance during nose breathing. It is highly nonlinear, and shows much variability. During mouth breathing upper airway resistance (mouth, pharynx, glottis, larynx and upper trachea) is also markedly nonlinear, and accounts for one-third the total airway resistance. Lower airway resistance is approximately linear up to flows of 2 liters/sec. Pulmonary tissue resistance is low as reported in this study. Chest wall resistance is nearly linear up to flow rates of 2 liters/sec and accounts for slightly less than half the total respiratory resistance during mouth breathing and 10–19% during nasal breathing. larynx; airways; chest wall; nose Submitted on December 16, 1963

Trans-pulmonary pressure, respiratory flow, and tidal volume of seven normal subjects were measured at rest and during treadmill exercise on the level at a speed of 1.5 mph. Pulmonary compliance remained unchanged during exercise. Nonelastic resistance showed an insignificant increase (0.9—1.4 cm H2O per liter per sec). Examination of other parameters which may affect compliance were made. Functional residual capacity decreased 120—200 ml during exercise, tidal volume doubled, and respiratory frequency increased 43.5%, yet none of these factors affected the lung compliance. The phenomenon of “second wind” was experienced by four of the subjects, and nothing was observed to explain its occurrence during exercise. exercise second wind; change in functional residual capacity during exercise; effect of functional residual capacity on compliance; effect of tidal volume on compliance during exercise; effect of respiratory frequency on compliance Submitted on January 15, 1965