Testing limits to airflow perturbation device (APD) measurements

Background  

The Airflow Perturbation Device (APD) is a lightweight, portable device that can be used to measure total respiratory resistance as well as inhalation and exhalation resistances. There is a need to determine limits to the accuracy of APD measurements for different conditions likely to occur: leaks around the mouthpiece, use of an oronasal mask, and the addition of resistance in the respiratory system. Also, there is a need for resistance measurements in patients who are ventilated.     

Effect of aspirin on nasal resistance to airflow.

The effect of aspirin on nasal resistance to airflow was investigated by rhinomanometry in 25 healthy subjects before and after ingestion of aspirin or vitamin C in a double blind crossover trial. Aspirin caused a significant increase in nasal resistance compared with vitamin C. The effect of aspirin may be due to its inhibition of the synthesis of prostaglandins.     

Response of nasal blood flow to neurohormones as measured by laser-Doppler velocimetry

Laser-Doppler velocimetry (LDV) has been adapted to measure nasal blood flow (NBF) in the mucosa of human volunteers. Resting NBF was 42.4 +/- 2.1 ml X 100 g-1 X min-1 in 19 nonatopic subjects and 37.9 +/- 1.7 ml X 100 g-1 X min-1 in 24 atopic subjects. Topical saline, but not water, reduced ipsilateral NBF by 15.4 +/- 6.6% (n = 22) without affecting contralateral NBF. Administration of 60 microgram of oxymetazoline reduced NBF by 26.5% (n = 28), whereas 120 microgram resulted in a 54.3% reduction. Phenylephrine produced a dose-related reduction in NBF with an ID50 (dose producing 50% reduction) of 1,456 microgram. Methacholine (0.006 to 12 mg) had no significant effect on NBF when studied alone or after oxymetazoline pretreatment. Therefore, LDV can be employed to monitor NBF, which has been found to be sensitive to alpha-adrenergic, but not cholinergic, stimulation.     

An improved device for posterior rhinomanometry to measure nasal resistance

Rhinomanometry is a method for measuring nasal resistance for the purpose of providing an objective evaluation of nasal patency. Posterior rhinomanometry is accomplished without the use of a mask, thus allowing the patient to breathe naturally. Here, we report on the improvements we have made to the existing posterior rhinomanometry system. In this system, nasal airflow is measured indirectly by measuring the pressure differential across a small mesh window in the body plethysmograph. We have calibrated this measurement and developed software that automatically provides the correct values for all airflow rates. Also, we have developed software that automatically corrects for the phase shift caused by the plethysmograph structure. These refinements should provide more accurate values for nasal resistance.     

Dependence of pharyngeal resistance on genioglossal EMG activity, nasal resistance, and airflow.

We investigated the quantitative relationships among pharyngeal resistance (Rph), genioglossal electromyographic (EMGge) activity, nasal resistance (Rna), and airflow in 11 normal men aged 19-50 while they were awake. We made measurements with subjects seated with the head erect, seated with the head flexed forward approximately 40 degrees, and supine. Each subject wore a face mask connected to a pneumotachograph to measure airflow. After topical anesthesia of the nose, two catheters for measuring nasal and pharyngeal airway pressures were passed through one nostril: the nasal pressure catheter was positioned at the nasal choanae, and the pharyngeal pressure catheter was positioned just above the epiglottis. We measured EMGge activity with an intraoral surface electrode. The subjects breathed exclusively through the nose while inhaling room air or rebreathing CO2. We measured Rph, Rna, airflow, and EMGge activity at approximately 90-ms intervals throughout each inspiration. Rph was invariant as head position was changed. At any given head position, EMGge activity rose as airflow increased, and Rph remained constant. In contrast, Rna increased as airflow increased. Because Rph was constant, EMGge activity was not correlated with Rph, but EMGge was positively correlated with Rna and airflow. On the basis of the stability of Rph in the face of marked changes in collapsing forces, we conclude that the dynamic interplay of posture, head and jaw position, and upper airway muscle activity quite effectively maintains pharyngeal patency, and interactions among these factors are subtle and complex.     

Vagal control of larynx resistance to the air flow (author's transl)

Air flow larynx resistance changes have been recorded in dogs after electrical stimulation and lesion of the recurrent and vagus cervicalis nerves respectively. Experiments were carried out with glottis in situ and isolated. The effects of the administration of athropine i.v. (0.3 mg/kg) were also studied. Air flow larynx resistance decreased after secting the right recurrent nerves as well as after athropine administration. Electrical stimulation of the central end of the right vagus nerve produced a complex response characterized by an initial apnaea followed by a larynx resistance decrease. After a few seconds the response continued with glottis spasms followed by typical emetic movements. During the emetic movements larynx closed and opened throughout the respiratory cycle, the closing movement being simultaneous with the inspiratory position of the thorax and with minimal values of the intraabdominal pressure. Larynx resistance increased after uni- and bilateral sections of the vagus cervicalis and after the electrical stimulation of the peripheral end of the right vagus cervicalis. According to the present results, the possible existence of a controlling reflex of laryngeal sphincter motility, generated at the bronchopulmonary level, is postulated.     

Poststenotic flow disturbance in the dog aorta as measured with pulsed Doppler ultrasound

Blood flow velocity was measured in the dog aorta distal to mechanically induced constrictions of various degrees of severity employing an 8-MHz pulsed Doppler ultrasound velocimeter and a phase-lock loop frequency tracking method for extracting velocity from the Doppler quadrature signals. The data were analyzed to construct ensemble average velocity waveforms and random velocity disturbances. In any individual animal the effect of increasing the degree of stenosis beyond approximately 25 percent area reduction was to produce increasing levels of random velocity disturbance. However, variability among animals was such that the sensitivity of random behavior to the degree of stenosis was degraded to the point that it appears difficult to employ Doppler ultrasound measurements of random disturbances to discriminate among stenoses with area reductions less than approximately 75 percent. On the other hand, coherent vortex structures in velocity waveforms consistently occurred distal to mild constrictions (25-50 percent area reduction). Comparison of the phase-lock loop Doppler ultrasound data with simultaneous measurements using invasive hot-film anemometry, which possesses excellent frequency response, demonstrates that the ultrasound method can reliably detect those flow phenomena in such cases. Thus, the identification of coherent, rather than random, flow disturbances may offer improved diagnostic capability for noninvasively detecting arteriosclerotic plaques at relatively early stages of development.     

Activation of epileptic electrographic phenomena in the human EEG by nasal air flow.

The activating effect of deep oral breathing (with the nose closed) and nasal hyperventilation (with mouth closed) was examined in 62 patients with three different kinds of epileptic EEG abnormalities: unilateral localized temporal (fronto-temporal, occipito-temporal) abnormalities - group F, bilateral episodic theta-delta abnormalities - group TH, and bilaterally synchronous spike and wave abnormalities - group SW. Nasal hyperventilation was much more effective in group F and TH. Its effect was already significant 30-60 seconds after the start of deep breathing. In the group SW there were no statistically significant differences between the effects of nasal and oral hyperventilation. Unilateral nasal hyperventilation (the other nasal cavity being closed by tamponade) demonstrated a more pronounced activating effect on ipsilateral localized temporal EEG abnormalities. These effects of deep nasal breathing can hardly be explained by metabolic-vascular mechanisms, which probably are involved in the course of oral hyperventilation. On the other hand they are in agreement with animal experiments demonstrating that the mechanical stimulus of nasal air flow operates as a synchronizing impulse for certain rhinencephalic structures.     

Hydraulic resistance to radial water flow in growing hypocotyl of soybean measured by a new pressure-perfusion technique

Hydraulic resistances to water flow have been determined in the cortex of hypocotyls of growing seedlings of soybean (Glycine max L. Merr. cv. Wayne). Data at the cell level (hydraulic conductivity, Lp; half-time of water exchange, T _1/2; elastic modulus, ; diffusivity for the cell-to-cell pathway, D _c) were obtained by the pressure probe, diffusivities for the tissue (D _t) by sorption experiments and the hydraulic conductivity of the entire cortex (Lp_r) by a new pressure-perfusion technique. For cortical cells in the elongating and mature regions of the hypocotyls T _1/2=0.4–15.1 s, Lp=0.2·10^-5–10.0·10^-5 cm s^-1 bar^-1 and D _c=0.1·10^-6–5.5·10^-6 cm² s^-1. Sorption kinetics yielded a tissue diffusivity D _t=0.2·10^-6–0.8·10^-6 cm² s^-1. The sorption kinetics include both cell-wall and cell-to-cell pathways for water transport. By comparing D _c and D _t, it was concluded that during swelling or shrinking of the tissue and during growth a substantial amount of water moves from cell to cell. The pressure-perfusion technique imposed hydrostatic gradients across the cortex either by manipulating the hydrostatic pressure in the xylem of hypocotyl segments or by forcing water from outside into the xylem. In segments with intact cuticle, the hydraulic conductance of the radial path (Lp_r) was a function of the rate of water flow and also of flow direction. In segments without cuticle, Lp_r was large (Lp_r=2·10^-5–20·10^-5 cm s^-1 bar^-1) and exceeded the corticla cell Lp. The results of the pressure-perfusion experiments are not compatible with a cell-to-cell transport and can only the explained by a preferred apoplasmic water movement. A tentative explanation for the differences found in the different types of experiments is that during hydrostatic perfusion the apoplasmic path dominates because of the high hydraulic conductivity of the cell wall or a preferred water movement by film flow in the intercellular space system. For shrinking and swelling experiments and during growth, the films are small and the cell-to-cell path dominates. This could lead to larger gradients in water potential in the tissue than expected from Lp_r. It is suggested that the reason for the preference of the cell-to-cell path during swelling and growth is that the solute contribution to the driving force in the apoplast is small, and tensions normally present in the wall prevent sufficiently thick water films from forming. The solute contribution is not very effective because the reflection coefficient of the cell-wall material should be very small for small solutes. The results demonstrate that in plant tissues the relative magnitude of cell-wall versus cell-to-cell transport could dependent on the physical nature of the driving forces (hydrostatic, osmotic) involved.Abbreviations and symbols D _c diffusivity of the cell-to-cell pathway - D _t diffusivity of the tissue - radial flow rate per cm² of segment surface - Lp hydraulic conductivity of plasma-membrane - Lp_r radial hydraulic conductance of the cortex - T _1/2 half-time of water exchange between cell and surroundings - volumetric elastic modulus     

Effects of cold dry air nasal stimulation on airway mucosal blood flow in humans

Several studies have demonstrated that nasal challenges can induce reflex responses in the respiratory system. Some authors have described bronchoconstriction and modification of the pattern of breathing following nasal challenges by irritants and cold air. We propose to determine the effect of nasal stimulation with cold dry air on airway mucosal blood flow (Qaw) in the proximal tracheal bronchial tree of healthy humans. Nine healthy subjects participated in the study. Baseline measurement Qaw, nasal airway resistance (NAR) and airway caliber by specific airways conductance (SGaw) were followed by nasal challenge with cold dry air. Qaw, NAR and Sgaw were determined after the challenge. In those subjects in which a significant decline in Qaw was recorded the protocol was repeated after pretreatment with nasal anesthesia using topical lidocaine. Cold dry air challenge produced a significant decrease in mean Qaw for the nine subjects and this response was abolished by pretreatment with nasal anesthesia using topical lidocaine. There was no significant change in Sgaw and NAR after the challenge and topical lidocaine anesthesia. Our data indicates that nasal stimulation with cold dry air leads to a reduction in Qaw and that this effect may be mediated by a nasal reflex.