Rohrer's Equation Research Articles

Nasopharyngeal tubes in pediatric anesthesia: Is the flow-dependent pressure drop across the tube suitable for calculating oropharyngeal pressure?

BackgroundNasopharyngeal tubes are useful in pediatric anesthesia for insufflating oxygen and anesthetics. During nasopharyngeal tube‐anesthesia, gas insufflation provides some positive oropharyngeal pressure that differs from the proximal airway pressure owing to the flow‐dependent pressure drop across the nasopharyngeal tube (ΔPNPT).AimsThis study aimed to investigate whether ΔPNPT could be used for calculating oropharyngeal pressure during nasopharyngeal tube‐assisted anesthesia.MethodsIn a physical model of nasopharyngeal tube‐anesthesia, using Rohrer's equation, we calculated ΔPNPT for three nasopharyngeal tubes (3.5, 4.0, and 5.0 mm inner diameter) under oxygen and several sevoflurane in oxygen combinations in two ventilatory scenarios (continuous positive airway pressure and intermittent positive pressure ventilation). We then calculated oropharyngeal pressure as proximal airway pressure minus ΔPNPT. Calculated and measured oropharyngeal pressure couples of values were compared with the root mean square deviation to assess accuracy. We also investigated whether oropharyngeal pressure accuracy depends on the nasopharyngeal tube diameter, flow rate, gas composition, and leak size. Using ΔPNPT charts, we tested whether ΔPNPT calculation was feasible in clinical practice.ResultsWhen we tested small‐diameter nasopharyngeal tubes at high‐flow or high‐peak inspiratory pressure, proximal airway pressure measurements markedly overestimated oropharyngeal pressure. Comparing measured and calculated maximum and minimum oropharyngeal pressure couples yielded root mean square deviations less than 0.5 cmH2O regardless of ventilatory modality, nasopharyngeal tube diameter, flow rate, gas composition, and leak size.ConclusionDuring nasopharyngeal tube‐assisted anesthesia, proximal airway pressure readings on the anesthetic monitoring machine overestimate oropharyngeal pressure especially for smaller‐diameter nasopharyngeal tubes and higher flow, and to a lesser extent for large leaks. Given the importance of calculating oropharyngeal pressure in guiding nasopharyngeal tube ventilation in clinical practice, we propose an accurate calculation using Rohrer's equation method, or approximating oropharyngeal pressure from flow and pressure readings on the anesthetic machine using the ΔPNPT charts.

ROLE OF RESPIRATORY RATE IN THE TOLERABILITY OF PERSONAL RESPIRATORY PROTECTION EQUIPMENT

The factor limiting the tolerance of personal respiratory protection equipment should be considered the frequency of respiratory movements, which reflexively changes when additional respiratory resistance occurs. Unfortunately, there is almost no information in the available literature about changes in the tolerability of personal respiratory protection equipment at different rates of respiratory movements. The purpose of this work was to study the tolerability of personal respiratory protection equipment when changing the frequency of respiratory movements.The study was conducted on practically healthy persons of both sexes (78 people), aged from 20 to 36 years. To simulate the conditions for the use of personal respiratory protection equipment, inspiratory resistive respiratory loads of 20% of the maximum intraoral pressure during the Mueller test were used. The tolerance of personal respiratory protection equipment was assessed using the Borg visual analogue of dyspnea scale, which reflected the level of subjective discomfort that occurs when additional respiratory resistance is turned on. During the action of additional respiratory resistance, the persons were asked to hold the frequency of respiratory movements, which was set using a special setting.An increase in the rate of respiratory movements against the background of additional respiratory resistance leads to a significant deterioration in the objective and subjective indicators of the functional state of the persons; replacing the inhaled air with an oxygen-rich respiratory mixture with carbon dioxide absorption did not lead to a significant improvement in the functional state. A moderate decrease (up to 70% of the initial frequency of respiratory movements) in the rate of respiration leads to an improvement in the indicators of adaptive activity in conditions of additional respiratory resistance. A significant decrease (up to 35% of the initial frequency of respiratory movements) in the rate of respiration under conditions of additional respiratory resistance leads to a deterioration of objective and subjective indicators of the functional state of the subjects.An increase in peak respiratory flow rates caused by an increase in the rate of respiration, in accordance with the well – known Rohrer equation, significantly increases inelastic resistance and, as a result, respiratory needs. These needs can be met at some time due to a significant increase in the work of the respiratory muscles, but due to fatigue of the latter, psychoemotional tension increases quite quickly and the use of personal respiratory protection equipment is abandoned.

Double lumen endotracheal tube for percutaneous tracheostomy.

Percutaneous dilational tracheostomy is normally a bronchoscope-guided procedure. The insertion of a bronchoscope into an endotracheal tube (ETT) affects resistance, flow, and alveolar pressure. To improve airway management and ventilation during percutaneous tracheostomy, we developed a double lumen endotracheal tube (DLET). The aim of this in vitro study was to compare the linear constant of the Rohrer equation (K1), the nonlinear constant of the Rohrer equation (K2), the inspiratory and expiratory airway resistance, and ventilatory and airway pressures using the DLET with different standard sized ETTs. A trachea and lung model was used to compare the DLET to ETTs with 7, 7.5, and 8 mm inner diameters with and without a bronchoscope (4.5 mm external diameter), and 4 and 5 mm inner diameter ventilation tubes (F4, F5) of a translaryngeal tracheostomy. For each device, the pressure drop across the device and the Rohrer equation linear constant (K1) and nonlinear constant (K2) were calculated during a continuous flow of 10-90 L/min, the inspiratory and expiratory airway resistance values were calculated during volume controlled mechanical ventilation, and respiratory airway pressure values were calculated during volume and pressure controlled mechanical ventilation. DLET had lower K2, pressure drop, and inspiratory and expiratory airway resistance compared with conventional ETTs plus fiberoptic bronchoscope. Furthermore, during mechanical ventilation, DLET had a lower value of peak pressure, mean pressure, and intrinsic PEEP than the other ETTs plus fiberoptic bronchoscope. Use of the DLET during percutaneous dilational tracheostomy allows fiberoptic bronchoscopy without imposing excessive airway resistance. Reduced tube resistance during this procedure may confer additional safety in what is well known to be a hazardous procedure.

Endotracheal tube resistance and inertance in a model of mechanical ventilation of newborns and small infants—the impact of ventilator settings on tracheal pressure swings

Resistive properties of endotracheal tubes (ETTs) are particularly relevant in newborns and small infants who are generally ventilated through ETTs with a small inner diameter. The ventilation rate is also high and the inspiratory time (ti) is short. These conditions effectuate high airway flows with excessive flow acceleration, so airway resistance and inertance play an important role. We carried out a model study to investigate the impact of varying ETT size, lung compliance and ventilator settings, such as peak inspiratory pressure (PIP), positive end expiratory pressure (PEEP) and inspiratory time (ti) on the pressure–flow characteristics with respect to the resistive and inertive properties of the ETT. Pressure at the Y piece was compared to direct measurement of intratracheal pressure (Ptrach) at the tip of the ETT, and pressure drop (ΔPETT) was calculated. Applying published tube coefficients (Rohrer's constants and inertance), Ptrach was calculated from ventilator readings and compared to measured Ptrach using the root-mean-square error. The most relevant for ΔPETT was the ETT size, followed by (in descending order) PIP, compliance, ti and PEEP, with gas flow velocity being the principle in common for all these parameters. Depending on the ventilator settings ΔPETT exceeded 8 mbar in the smallest 2.0 mm ETT. Consideration of inertance as an additional effect in this setting yielded a better agreement of calculated versus measured Ptrach than Rohrer's constants alone. We speculate that exact tracheal pressure tracings calculated from ventilator readings by applying Rohrer's equation and the inertance determination to small size ETTs would be helpful. As an integral part of ventilator software this would (1) allow an estimate of work of breathing and implementation of an automatic tube compensation, and (2) be important for gentle ventilation in respiratory care, especially of small infants, since it enables the physician to estimate consequences of altered ventilator settings at the tracheal level.

A Pattern to Evaluate Airway Resistive Phenomenon Using Rohrer's Equation

The phenomenon of airway resistance to inflow is complex and has different behaviors as the fluid flows. The physiopathology of main respiratory diseases shows alterations in the resistive component. The complete description of the phenomenon requires more robust mathematical tools of the mechanics

Flow‐dependent resistance of nasal masks used for non‐invasive positive pressure ventilation

Endotracheal tube resistance is known to be flow-dependent and this understanding has improved the application of invasive ventilation. However, similar physiological studies on the interface between patients and non-invasive positive pressure ventilation (NPPV) have not been performed. Therefore, this study was aimed at investigating the resistance of nasal masks used for NPPV. The flow-dependent pressure drop of the small (S), medium-small (MS) and medium (M) Contour Nasal Mask (Respironics Inc., Murrysville, PA, USA) was measured with and without a connecting tube (length 18 cm, internal diameter 1.5 cm) in a laboratory study. The resistance was calculated by Rohrer's equation using the standard least-squares-fit technique. The present study explicitly differentiated between the resistance of the nasal mask alone when measured against atmosphere and the additional resistance caused by the nasal mask when airtightly fitted to a model head (interaction with the face). Higher flow rates resulted in a non-linearly increasing pressure drop across the interface. This flow-dependent resistance of the S/MS/M mask was comparably low when not interacting with the face, but increased when interacting with the face. This flow-dependent resistance of the mask was several-fold higher when adding the connection tube and tended to be higher during expiration. There is a non-linear flow-dependent pressure drop across the nasal mask which is low and independent of its size, but increases when interacting with the face. The connecting tube is the major determinant of the resistance originating from facial appliances used for NPPV.

Effects of PEEP on inspiratory resistance in mechanically ventilated COPD patients.

This study aimed to investigate the effect of increased lung volume with positive end-expiratory pressure (PEEP) on respiratory resistance in patients with chronic obstructive pulmonary disease (COPD). Ten patients with COPD were mechanically ventilated for acute respiratory failure. PEEP was set at 0, 5, 10 and 15 cm H2O. Using the rapid airway occlusion technique, the total inspiratory resistance of the respiratory system was partitioned into interrupter (Rint,rs) and additional effective (deltaRrs) resistances. At each level of PEEP, at constant inflation flow, the inflation volume (deltaV) was varied from 0.2-1 L, and, at constant deltaV, the inflation flow was varied from 0.2-1.2 L x s(-1). The changes in end-expiratory lung volume (deltaEELV) induced by PEEP were also measured. The difference between the EELV and the relaxation volume of the respiratory system (deltaFRC) increased significantly with PEEP of 10 and 15 cm H2O as compared to a PEEP of 0, the increase being associated with a significant reduction of Rint,rs. By contrast, deltaRrs was independent of deltaFRC. At constant deltaV, Rint,rs fitted Rohrer's equation (Rint,rs = K1 + K2 x flow). While K2 significantly declined with AFRC, K1 did not change. At all levels of PEEP, deltaRrs was not influenced by deltaFRC. With increasing lung volume induced by positive end-expiratory pressure, the inspiratory airway resistance decreased, whereas the viscoelastic behaviour of the respiratory system, as reflected by additional effective resistance, did not change.

Variations in airways impedance during respiratory cycle derived from combined measurements of input and transfer impedances.

Simultaneous measurement of input (Zin) and transfer impedances (Ztr) allows separation of airway and tissue properties at a single frequency, without making assumptions concerning the structure of the two compartments. This approach offers the possibility of studying the variation in airway impedance (Zaw) during the respiratory cycle. Zin and Ztr were measured at frequencies of 10, 20, 30 and 40 Hz in eight healthy subjects to study the variations in Zaw according to a modification of the Rohrer's equation: X=K1+K2(V'ao)-K3V, where V is volume and V'ao the flow at the airway opening. The results showed that Zaw could be modelled as a simple resistance-inertance pathway. Variations in airway resistance (Raw) with flow were greater during expiration than during inspiration with K2 values varying from 0.76-0.90 hPa x s2 x L(-2) during inspiration and 0.84-1.47 hPa x s2 x L(-2) during expiration, independently of frequency. Raw was negative volume dependent; it decreased more with increasing volume during inspiration than during expiration. Airways inertance calculated from the imaginary part of Zaw also underwent systematic variations during the respiratory cycle, but, in contrast to Raw, flow dependence was negative during both phases. In conclusion, the approach used in this study allows flow and volume dependencies of airways mechanical properties to be studied and can also provide indices of airway patency independently of flow, which is of great potential interest for studying variations in airway resistance during bronchomotor tests.

Flow resistances of disposable double-lumen, single-lumen, and univent tubes

Objective: To compare the airflow resistances of modern double-lumen, single-lumen, and Univent (Fuji Systems Corp; Tokyo, Japan) tubes. Design: A laboratory bench study. Setting: A university hospital laboratory. Measurements: Pressure differentials (Pd) were measured across study tubes at 10 L/min airflow (V̇) increments from 0 to 60 L/min in a tracheal model. Coefficients of resistance k 1 (linear) and k 2 (nonlinear) were calculated for each tube by the method of least squares using the Rohrer equation Pd/V = k 1 + k 2V. Data were assessed by analysis of variance (ANOVA) for the effects of tube design, circumference, and manufacturer on k 1 and k 2. Main Results: Calculated combined mean k 1 and k 2 were significantly lower for single-lumen tubes compared with double-lumen or Univent tubes. There were no significant differences for k 1 values between double-lumen or Univent tubes. The values for k 2 were significantly lower for double-lumen tubes compared with Univent tubes. The k 2 values were significantly lower for Rusch (Duluth, GA) or Sheridan (Argyle, NY) double-lumen tubes compared with Mallinckrodt (St Louis, MO) double-lumen tubes. This difference was because of the Y-connectors of the Mallinckrodt tubes. Conclusions: Flow resistances of modern disposable double-lumen tubes are lower than commonly perceived. In most clinical situations, there will be no decrease in flow resistance when a Rusch or Sheridan double-lumen tube is replaced by a single-lumen tube.

Airway and pulmonary tissue responses to capsaicin in guinea pigs assessed with the alveolar capsule technique.

We studied the effects of capsaicin on airway and lung tissue mechanics in anesthetized and tracheostomized guinea pigs that were mechanically ventilated at constant tidal volume (8 ml/kg) and breathing frequency (60 breaths/min). Dose-response curves to intravenously infused capsaicin (1, 10, and 100 micrograms/kg) were performed (five animals for each dose, one dose per animal). We measured airflow, volume (by integration of the flow signal), tracheal pressure, and alveolar pressure with an alveolar capsule. Capsaicin induced a dose-dependent increase in airway resistance, tissue resistance, and dynamic elastance. The relationship between airway pressure and flow was fitted by a quadratic (Rohrer) equation. Airflow became more turbulent after infusion of capsaicin. After infusion of 100 micrograms/kg capsaicin, airway pressure (at flow rates of 10 ml.s-1) increased from 3.03 +/- 0.40 (mean +/- SEM) to 9.58 +/- 1.88 cm H2O, whereas the pressure corresponding to viscoelastic properties of lung tissue increased from 0.92 +/- 0.14 to 8.58 +/- 1.12 cm H2O. We conclude that infusion of capsaicin results in mechanical effects in both airways and pulmonary tissue.

Use of the Blasius resistance formula to estimate the effective diameter of endotracheal tubes.

To early detect mucus deposition in endotracheal tubes (ETT), we propose using a geometric, flow-independent parameter, i.e., diameter of the ETT, based on a precise knowledge of ETT flow regime, instead of using the classic flow-dependent ETT resistance based on the empirical, nonlinear Rohrer equation. From the estimated slope of -0.24 derived from Moody diagrams characterizing the pressure-flow relationship in ETT of various inner diameters (D), we first assessed that the Blasius resistance formula slope of -0.25 could be applied to adult-size ETT, meaning that flow remains fully developed, turbulent, and hydraulically smooth (0.5 L/s less than or equal to V less than or equal to 1.4 L/s). Insertion into the ETT of a pressure catheter (external diameter: d) to stimulate in vivo measurements did not modify these results, provided the hydraulic diameter, D* = D - d, was substituted for D in the Blasius formula. The Blasius formula was then used to determine, from in vitro pressure and flow measurements in ETT before intubation and in ETT lined with dry mucus secretions, the effective diameter, shown here to be highly correlated to the actual diameter measured by volumetric water displacement. The effective ETT diameter was measured in eight patients at different stages after oral or nasal intubation. Compared with the actual ETT diameter measured before insertion, the effective diameter was slightly reduced (2.6 +/- 2.5%) during the first week of intubation and was strongly reduced (12.2 +/- 2.8%) during the second week.(ABSTRACT TRUNCATED AT 250 WORDS)

Nasal airflow characteristics in a normal sample

The present study aims to describe the characteristics of nasal airflow in terms of the relative contributions of laminar and turbulent flow to the total pressure drop across the nose. The sample comprised 20 dental students with no history of nasal airway obstruction. Rhinomanometric data were recorded by a Mercury NR6 rhinomanometer with a Rohrer programme by the anterior and posterior methods after decongestion. Rohrer equation coefficients were calculated for each respiratory cycle. Method errors ranged from 6.3 to 9.3 per cent of sample variances. At a threshold of 75 Pa, average unilateral NAR was about 300 Pa/l/s and average bilateral resistance about 250 Pa/l/s. Analysis of the Rohrer equation data showed average coefficients of laminar (k1) and turbulent (k2) flow of 113 and 807 in unilateral breathing, indicating a predominance of turbulent flow. In bilateral breathing a switching of airflow characteristics occurred, with k1 and k2 coefficients of 147 and 348 indicating a marked reduction in the turbulent component of flow. It is suggested that Rohrer equation coefficients might provide information about nasal airflow which are physiologically more meaningful than conventional resistance calculations based on a single point on the rhinomanometric pressure-flow curve.

Effect of serotonin on expiratory pulmonary resistance in cats

In five anesthetized paralyzed cats, mechanically ventilated with tidal volumes of 36-48 ml, the isovolume pressure-flow (IVPF) relationships of the lung were studied under control conditions and during serotonin-induced bronchoconstriction. At the end of a tidal inspiration, airway opening pressure was set between +3 and -15 cmH2O for single tidal expirations. After control measurements, animals were treated with progressively increasing doses of intravenous serotonin (10, 20, 50, and 100 micrograms.kg-1.min-1) and all measurements were repeated at each dose. No animal became flow limited during passive expiration against atmospheric pressure. Disregarding flow-limited segments, IVPF plots for three lung volumes showed that the resistive pressure-flow relationships were curvilinear under all conditions, thus fitting Rohrer's equation. Under control conditions and during the lowest dose of serotonin, the volume dependence of pulmonary resistance (RL) tended to balance its flow dependence so that during lung deflation against atmospheric pressure RL remained nearly constant. However, as bronchoconstriction became more pronounced, RL often increased disproportionately at the lower lung volumes. Changes in expiratory RL with serotonin relative to control values varied according to the flow rates used to make comparisons. The technique used to determine RL will partly determine the results obtained.

Flow and volume dependence of expiratory resistance in anesthetized cats

In five anesthetized paralyzed cats, mechanically ventilated with tidal volumes of 36-48 ml, the isovolume pressure-flow relationships of the lung and respiratory system were studied. The expiratory pressure was altered between 3 and -12 cmH2O for single tidal expirations. Isovolume pressure-flow plots for three lung volumes showed that the resistive pressure-flow relationships were curvilinear in all cases, fitting Rohrer's equation: P = K1V + K2V2, where P is the resistive pressure loss, K1 and K2 are Rohrer's coefficients, and V is flow. Values of K1 and K2 declined with lung inflation, consistent with the volume dependence of pulmonary (RL) and respiratory system resistances (Rrs). During lung deflation against atmospheric pressure, RL and Rrs tended to remain constant through most of expiration, resulting in a nearly linear volume-flow relationship. In the presence of a fixed respiratory system elastance, the shape of the volume-flow profile depended on the balance between the volume and the flow dependence of RL and Rrs. However, the flow dependence of RL and Rrs indicates that their measured values will be affected by all factors that modify expiratory flow, e.g., respiratory system elastance, equipment resistance, and the presence of respiratory muscle activity.

Characteristics of the upper airway pressure-flow relationship during sleep.

In examining the mechanical properties of the respiratory system during sleep in healthy humans, we observed that the inspiratory pressure-flow relationship of the upper airway was often flow limited and too curvilinear to be predicted by the Rohrer equation. The purposes of this study were 1) to describe a mathematical model that would better define the inspiratory pressure-flow relationship of the upper airway during sleep and 2) to identify the segment of airway responsible for the sleep-related flow limitation. We measured nasal and total supralaryngeal pressure and flow during wakefulness and stage 2 sleep in five healthy male subjects lying supine. A right rectangular hyperbolic equation, V = (alpha P)/(beta + P), where V is flow, P is pressure, alpha is an asymptote for peak flow, and beta is pressure at a flow of alpha/2, was used in its linear form, P/V = (beta/alpha) + (P/alpha). The goodness of fit of the new equation was compared with that for the linearized Rohrer equation P/V = K1 + K2V. During wakefulness the fit of the hyperbolic equation to the actual pressure-flow data was equivalent to or significantly better than that for the Rohrer equation. During sleep the fit of the hyperbolic equation was superior to that for the Rohrer equation. For the whole supralaryngeal airway during sleep, the correlation coefficient for the hyperbolic equation was 0.90 +/- 0.50, and for the Rohrer equation it was 0.49 +/- 0.25. The flow-limiting segment was located within the pharyngeal airway, not in the nose.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow and volume dependence of pulmonary mechanics in anesthetized cats.

The effects of inspiratory flow rate and inflation volume on pulmonary mechanics were investigated in six anesthetized-paralyzed cats ventilated by constant-flow inflation. Pulmonary mechanics were assessed using the technique of rapid airway occlusion during constant-flow inflation which allows measurement of the intrinsic pulmonary resistance (RLmin) and of the overall "pulmonary flow resistance" (RLmax), which includes the additional pulmonary pressure losses due to time constant inequalities within the lung and/or stress adaptation. We observed that, at fixed inflation volume, 1) RLmin fitted Rohrer's equation, 2) RLmax was higher at low than intermediate flows, and 3) RLmax-RLmin decreased progressively with increasing flow. At fixed flow, RLmax increased, whereas RLmin decreased with increasing volume. We conclude that during eupneic breathing in cats, the pulmonary flow resistance as conventionally measured includes a significant component reflecting stress adaptation.

Supraglottic airway resistance in normal subjects and patients with occlusive sleep apnea.

We assessed the flow-impeding properties of nose and pharynx combined in four normals and five patients with occlusive sleep apnea (OSA) while awake by measuring supraglottic pressure and airflow at the nose. We calculated two indices of impedance presented by the supraglottic airway: the second coefficient (K2) of Rohrer's equation and supraglottic resistance (Rsg) at 0.4 l/s. The influence of posture and nasal mucosal circulation was evaluated by measuring these indices in sitting and supine position before and after administration of a nasal decongestant. The effects of changes in posture were similar in both normals and patients: K2 and Rsg values were significantly larger in supine than in sitting position. The nasal decongestant significantly decreased both values in sitting and supine positions for normals and patients but did not eliminate the posturally induced changes. Patients had significantly greater K2 and Rsg values than normals in all conditions. These results indicate supraglottic airway narrowing in OSA patients. This narrowing probably results from structural encroachment on the pharyngeal airway.

Steady pressure-flow relationship of a model of the canine bronchial tree.

Static pressure differences (deltaP) across the entire length and portions of a latex reproduction of a canine bronchial tree were measured during steady inspiratory or expiratory flow (V). The reproduction consists of a 10-cm length of trachea through bronchi of about 2 mm in diameter. The airflow was simulated by a water flow with tracheal Renolds number (Re0) in the range from 1,500 to 10,000. Loss in total pressure (deltaPt) was computed by summing deltaPt and V were well described (r greater than 0.98) by a dimensionless Rohrer equation deltaPt/deltaPd0 = A + B Re0 applicable to gas flow, in which deltaPd0 is a Poiseuille pressure drop. For expiratory deltaPt, A was about twice that for inspiration, while the values for B were nearly equal. Differences in kinetic energy between sites of static pressure measurement are important in determining loss in total pressure. Rohrer's equation is a good approximation to the phenomenological laws of steady inspiratory and expiratory flow-pressure relations in the canine bronchial tree for the range of Reynolds number investigated.

Nasal airway inspiratory resistance.

The relationship between transnasal pressure and nasal flow is markedly curvilinear during tidal breathing in man, and there is poor agreement among the results of various methods used to define this characteristic with a single number. We used Rohrer's equation (P = K1 V + K2 V2), where P = pressure and V = flow, and calculated values for K1 and K2 from 474 nasal inspiratory pressure/flow curves obtained from 34 human subjects by a standard method of posterior rhinometry. Nasal airway inspiratory resistance at an air flow of 0.4 liter per sec (NAIR0.4) was also calculated. Rohrer's equation was found by regression analysis to fit each curve well (0.86 less than r less than 0.9999; mean, 0.983). There was a strong correlation between NAIR0.4 and K2: NAIR 0.4 = 0.91 K2 + 0.39 (r = 0.97). Nasal congestion induced in 7 normal subjects with histamine resulted in larger changes in K2 and NAIR0.4 than K1. Patients given an intranasal corticosteroid aerosol (beclomethasone dipropionate) in a double blind crossover trial showed symptomatic improvement in nasal congestion (P less than 0.01) and significant decreases in K2 (P less than 0.02) and NAIR 0.4 (P less than 0.05), but no change in K1 (P greater than 0.2).

Transition from Nasal to Mouth Breathing with Increasing Nasal Obstruction Estimated by Airflow Resistance Measurement

There have been numerous attempts to evaluate the relationships between the upper and lower airways. However, there are no available data indicating when the shift from nasal to oral breathing takes place as a subject's nasal obstruction increases. In this experiment twenty-four subjects, each with varying degrees of nasal obstruction, were examined. Their nasal and pulmonary resistances were measured for both nasal and oral breathing. Each airflow resistance was analyzed according to the Rohrer's equation. The examination results of those subjects who fell into the fourth degree classification of nasal obstruction showed transition from nasal to oral breathing. The pressure-flow curves of the nasal passages and the pleural surface during oral breathing had a same pattern. For the fourth degree cases, the nasal resistance was approximately onehalf of the total pulmonary resistance. In these circumstances the results from our study indicated that at the flow rate of 0.5 liter/sec the nose contributes about 53 % of the total pulmonary resistance.